H13 Steel Acceptance and Heat Treat Criteria — 2005 • i

i • H13 Steel Acceptance and Heat Treat Criteria — 2005

Special Premium and Superior Quality Die H13 Steel and Heat Treatment Acceptance Criteria for Pressure Die Casting DiesNADCA #207-200X3 (Premium and Superior)

Contents Page

Abstract 1Statement of Purpose

1 I. Material Quality Requirements 2II. Material Quality Certification of Conformance 5III. Heat Treatment Quality Requirements 6IV. Heat Treatment Quality Testing Requirements 8V. Heat Treatment Quality Certification of Conformance

10 Acknowledgements 12Appendix 1: Guide to Sample Preparation Techniques 13 Appendix 2: Practical Guide to Steel and Heat

16Treatment Quality

Appendix 3: Welding Die Casting Die Materials 28by:

NADCA DIE MATERIALS COMMITTEE

ASTM Standards referred to in this document may be obtained from: ASTM Sales Department • 100 Barr Harbor Drive • West Conshohocken, PA 19428Phone: 610.832.9500

North America Die Casting Association9701 West Higgins Road Suite 880Rosemont, IL 60018-4733

Phone:

847.292.3600Fax:

847.292.3620E-mail: publications@diecasting.org

Copyright © 200x 3North American Die Casting AssociationWheeling Rosemont, Illinois 60018-4733

Printed in the United States of America

All rights reserved. No part of this book may be reproduced or utilized in any form or any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system without permission in writing from the publisher. Inquiries should be addressed to the North American Die Casting Association, 9701 West Higgins Road, Suite 880 Rosemont, Illinois, 60018-4733

Neither the North American Die Casting Association, nor the authors of this work:

• Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document;

• Assumes any liability with respect to the use of, or for damages resulting from the use of, any information, method, process or equipment described in this document.

ABSTRACTAn agreement has been reached with NADCA member firms that are major material suppliers and/or heat treaters of H13 die steel to the die casting industry. Acceptance criteria, restrictive specifications as noted, and a certification plan have been developed for both the Material Quality and the Heat Treatment Quality of Special Premium and Superior Quality Grade H13 die steels. By specifying die H13 steels produced to these specifications, improved levels of cleanliness, a reduction in micro and macro banding, and impact toughness capabilities are certified. These This steels will respond more uniformly and predictably to heat treatment, thus reducing the risk of excessive distortion and cracking during heat treatment and giving longer and more consistent die life.

When dealing with premium grade H13 neither the steel making process nor the forging practices are stipulated by this specification, provided that all quality requirements in this specification are met.

When dealing with superior grade H13 With the exception of Grade A (“Premium H13”) die steel, the steel making process shall include secondary refining, either ESR (electro-slag remelt) or VAR (vacuum arc remelt). However, small round stock less than 3” diameter may not be available by these remelt process. Regardless of the steel making process or the forging practices, material covered by this specification must meet all quality requirements in this specification.

The heat treatment quality requirements in this specification pertain to the vacuum hardening and high-pressure gas quenching process. While NADCA recognizes the viability of other heat treatment methods, the scope of the procedures within this specification are exclusively vacuum austenitizing and pressurized gas quenching.

STATEMENT OF PURPOSEThese acceptance criteria and specifications are not intended for all die casting applications. They apply where high volume production or critical performance is required. Die casters and tool builders should insist that certification of the Material Quality accompany each piece of Special Quality Premium or Superior H13 die steel purchased for use in die casting dies and that certification of the Heat Treatment Quality accompany each furnace load of Special Quality die H13 steel hardened in accordance with this protocol.

For certain applications requiring a higher level of Material Quality and Heat Treatment Quality, Superior Grade H13 is a variety of Special Quality die steels are listed in this specification as Grades B - H that are commercially available and should meet the appropriate specification requirements of NADCA #207-200 3 Superior.

For applications requiring a lesser level of Material Quality and/or Heat Treatment Quality, Grade A (“Premium H13”) die steel Premium Grade H13 is is available and should meet the appropriate specification requirements of NADCA # 207-200X 3 Premium.

It should be noted that die performance is a complex combination of many factors including die size & design, casting alloy, operational procedures, steel composition, austenitizing temperature, impact toughness and hardness. Other factors such as temper resistance, hot strength, and fatigue resistance also effect die performance and should be considered when specifying steel grade, heat treatment parameters. Final hardness should be selected based upon steel grade, size, and die design. Consult your steel supplier and/or heat treater for guidance.

NOTE: Every effort has been made to assure information contained in these procedures is correct. However, NADCA does not accept responsibility for damage, injury or costs incurred by using these procedures.

Check the suppliers’ instructions for specific directions on products used. Be sure to comply with all applicable safety codes and regulations.

I. Material Quality RequirementsA. Chemical composition (% by weight) of Critical

Alloying Elements & ImpuritiesSpecial Quality Both Premium and Superior grades of die H13 steel must conform to the Chemical Requirements of Table 1 ASTM A681 (latest revision) Section 6 with the following modifications, or emphasis.

PREMIUM GRADE A SUPERIOR ALL OTHER GRADESELEMENTS

MIN. MAX. MIN. MAX.

Carbon 0.37 * 0.42 * 0.37 0.42 Manganese

0.20 0.50 0.20 0.50

Phosphorus

— 0.025 *

— 0.015 ‡

Sulfur — 0.005 *

— 0.003 ‡

Silicon 0.80 1.20 0.80 1.20Chromium 5.00 * 5.50 * 5.00 5.50 Vanadium 0.80 1.20 0.80 1.20Molybdenum

1.20 * 1.75 * 1.20 1.75

* Modifications from ASTM A681 for premium quality

‡ Modifications from NADCA Premium Quality for Superior Quality

B. Hardness1. Both Premium and Superior Qualities: Annealed hardness of Special

Quality steel, as received, shall not exceed 235 HBW.

C. MicrocleanlinessThe permissible limits of microcleanliness (severity levels of non metallic inclusion content) shall be determined by ASTM E45, Method A (latest revision). Plate I-r should be used to obtain rating increments of 0.5. The maximum

allowable limits are as follows.

GRADE A PREMIUM

ALL OTHER GRADES SUPERIOR

INCLUSION TYPE

THIN HEAVY THIN HEAVY

A (sulfide) 1.0 0.5 0.5 ‡ 0.5B (aluminide) 1.5 1.0 1.5 1.0 C (silicate) 1.0 1.0 0.5 ‡ 0.5 ‡D (globular oxides)

2.0 1.0 1.5 ‡ 1.0

‡ Modifications from NADCA Premium Quality for Superior Quality

D. Ultrasonic quality (ASTMA-681 S1.1)Appropriate ultrasonic inspection techniques shall be performed to assure soundness. All blocks shall be free from internal defects such as stringers, oxides, porosity, bursts, heavy segregation, etc., as indicated by ultrasonic testing. Ultrasonic examination of the original steel stock shall be conducted in accordance with ASTM recommended practices A388 and E114 (latest revision). Acceptance criteria are as agreed upon between supplier and vendor.

E. Impact Capability TestingImpact capability testing pertains to all mill product forms with a thickness greater or equal to 2-1/2 inches. Specimen blanks shall be removed from the short transverse orientation corresponding to the center location of the parent block of steel (see Fig. 1 and 2). A minimum of one set of 5 impact specimens shall be tested per lot of material produced. A lot shall consist of all the product of a single ingot, which is forged or rolled via a common procedure to one size and annealed in a single furnace charge. Multiple starting ingots, variations in forging or rolling size or procedure, or variations in annealing furnace charge are defined as a multiple lots and shall require additional sets of tests.

Fig. 1. Schematic diagram illustrating the removal of capability Charpy V-notch specimens from the short transverse orientation corresponding to the center location of a parent block of steel that has a rectangular/square cross-section.

NOTE: The base of the notch shall be parallel to the longitudinal direction of the parent block or slab, See Charpy V-notch samples per ASTM A370, latest revision.

Fig. 2 Schematic diagram illustrating the removal of capability Charpy V-notch specimens from the transverse (radial) orientation corresponding to the center location of a parent bar of steel that has a circular cross-section.

NOTE: The base of the notch shall be parallel to the longitudinal direction of the parent

bar. See Charpy V-notch samples per ASTM A370, latest revision.

Individual specimens shall be machined oversize to be nominally 1/2” x 1/2” x 2-1/2”each. Specimens are to be hardened and tempered before machining to final dimensions. Specimens shall be heat treated, machined, and tested as follows (see Table 2 for designated autenitizing / tempering temperatures and final hardness):

1. Austenitize at 1885°F (1030°C) for 30 minutes;2. Oil quench. Oil temperature 120°F (50°C) maximum;3. Minimum double temper at a temperature of at least 1100°F (590°C)

for 2 hours minimum each temper to achieve a final hardness of 44/46 HRC;

4. Air cool to room temperature between each temper;5. Following the preceding laboratory hardening process, the samples

shall be machined to final size and finish ground. See Charpy full size test impact specimen per ASTM A370, Fig. 11a:

• adjacent sides shall be at 90 degrees ±10 minutes• cross section dimensions shall be ±0.100 mm (±0.004 in.)• length of specimen shall be 55 ±1 mm (2.165 ± 0.040 in.)• surface finish shall be 63 micro inch (1.6 micro meter) max.

on the 55 x 10 mm faces.

6. Five impact specimens shall be tested at room temperature on test machines that meet the calibration requirements of ASTM E23 or ISO 148/R442 (latest revision). The values of the highest and lowest specimens shall be discarded and the average of the remaining three results shall be computed. Testing shall yield the following specified values.

?7. Acceptance Criteria:

a) Premium Quality is 8 ft. lbs. (11 J) average with 6 ft. lbs. (8 J) single minimum value. b) Superior Quality is 10 ft. lbs. average (14 J) with 8 ft. lbs. (11 J) single minimum value.

see Table 2 for capability impact toughness acceptance criteria

NOTE: These impact toughness values apply only to impact specimens that are individually heat treated prior to final machining in accordance with the method prescribed above. Charpy impact specimens are to be notched after final machining. Ground notches are preferred and shall be used for referee purposes. EDM notches are not allowed.

F. Grain Size:Grain size shall be developed using the Direct Quench method per ASTM E112 by austenitizing at 1885°F (1030°C) for 30 minutes, quench at a moderate or rapid rate and temper at 1100°F minimum. Hardening should be in a protective

media or by using an appropriately oversize sample in a non-protective media. Grain size to be measured by using the ASTM comparative method and shall be predominately ASTM No. 7 or finer.

An alternative method to rate the grain size may be used. The Shepherd Fracture Grain Size shall be predominantly No. 7 or finer when made on a hardened (air cooled after heating for 30 minutes at 1885° F (1030° C), in a protective media or using an appropriately oversize sample in a non protective media) and untempered specimen taken from a representative sample.

G. Annealed Microstructure:The annealed microstructure of the as-received steel shall consist essentially of a ferritic matrix with a homogeneous distribution of spheriodized carbides when examined at 500X, after being polished and etched with 5% Nital. Acceptable microstructures for annealed die steels H13 steel are shown in the NADCA An-nealed Microstructure Reference Chart.

H: Banding Segregation:The annealed microstructure shall be free of excessive banding by conformance with the NADCA Banding Segregation Reference Chart for levels of microbanding or microchemical segregation. For sizes 4” and below, banding segregation shall not be cause for rejection unless excessive primary carbides are present.

II. Material Quality - Certification of Conformance:

Material that has been designated as NADCA Special Premium Quality or Superior Quality H13 die steel in accordance with this specification shall be accompanied by a Certificate of Conformance from the steel supplier that includes the following data and information:

A.

B.

C.

D.

NADCA Grade (A – H)

Supplier Heat Designation

Annealed Brinell Hardness

Chemical Analysis

E. Microcleanliness levels F. Confirmation that Ultrasonic

Inspection has been performed

G. Grain Size Number H. Annealed Microstructure

Rating NumberI. Microbanding Designation

LevelsJ. Impact capability test

results: shall include three individual results of specimens and average result, heat treatment and final hardness.

NOTE

The laboratory capability austenitizing temperature must be stated

III. Heat Treatment Quality Requirements

Vacuum Heat Treatment Process RequirementsThe most critical parameters in the heat treatment of Special Premium and Superior Quality H13 die steels are the austenitizing treatment and the quench rate from the austenitizing temperature. The quench rate must be controlled to provide optimum metallurgical properties while minimizing distortion and risk of cracking. A more detailed discussion of the heat treatment process is included in Appendix 2: Practical Guide to Steel and Heat Treatment Quality.

NOTE for SUPERIOR QUALITY: Except for Premium H13 Grade A, a test coupon must be attached to the workpiece prior to hardening. See Section IV-L for details.

NOTE: ALL Special Quality Die Steels can be certified as either “Class 1” or “Class 2” Heat Treatment Quality. Certification as Class 1 Heat Treatment Quality requires that a test coupon must be attached to the workpiece prior to hardening. See Section IV-L for details.

A. Equipment

Premium • Vacuum furnace with a minimum 2 bar backfill capability and a programmable

furnace controller linked to multiple load thermocouples. • Sufficient cooling capability to cool die surface from 1885° F (1030 °C) at a

minimum rate of 50°F/min. (28°C/min.). See Section III F. • Furnace must be capable of isothermal hold during quench based on input from

surface and core thermocouples where interrupted quench is required.Superior

• Vacuum furnace with high-pressure gas quenching capability and a programmable furnace controller linked to multiple load thermocouples.

• Sufficient backfill pressure and cooling capability to cool die surface from the designated austenitizing temperature 1885°F (1030°C) at a minimum rate of 50°F/min. (28°C/min.). See Section III F.

• Furnace must be capable of isothermal hold during quench based on input from surface and core thermocouples where interrupted quench is required.

‡ Modifications from NADCA Premium Quality for Superior Quality

B. Furnace Loading• Pieces in the load shall be placed and distributed to allow for uniform heating

and quenching.• The geometry of the pieces must be considered to insure uniform heat

treatment and crack prevention.• The furnace must not be overloaded, so that the minimum quench rate can be

achieved.

C. Thermocouple Placement • A dedicated thermocouple hole for placement of the surface thermocouple (Ts) is

recommended. Hole should typically be 1/8” to 1/4” (3.175mm to 6.35mm) diameter, depending on thermocouple wire used and should be 0.625” ± 0.125” (15.87mm ± 3.175mm) deep.

• The surface thermocouple (Ts) hole should be located in the center of the largest area of the die in the backside and should be at least 1/4T x 1/4W or mid-radius from the nearest corner.

• The core thermocouple (Tc) should be placed as close to the center of mass as possible using existing coolant holes. In cases where core thermocouple placement is not possible, the furnace load shall be controlled from a load block that represents the maximum thickness of the die with a thermocouple at the center of mass.

• All thermocouple holes shall be packed with a fiber refractory material to prevent direct contact with quenchant.

• Thermocouple wires must be secured to prevent movement during quenching.• If multiple blocks are hardened in the same load, thermocouples should be

placed in the block with the largest cross section.

D. Preheating Practice• Load work into cold furnace and heat at a rate not to exceed 400°F/hour

(220°C/hour) as measured by Tc.• Heat to 1000°F to 1250°F (540°C to 675°C) furnace temperature and hold until

Ts-Tc<200°F (110°C).• Heat to 1550°F ± 50°F (845°C ± 10°C) and hold until Ts - Tc < 100°F (60°C).• Additional preheating steps may be used at the discretion of the heat treater or

toolmaker.

E. Austenitizing• Rapidly heat from final preheating temperature to the designated austenitizing

temperture (see Table 2) 1885°F ± 10°F (1030°C ± 5°C).• Soak time shall be 30 minutes after Ts - Tc< 25°F or 90 minutes maximum

afterTs = the designated austenitizing temperture 1885°F (1030°C) whichever occurs first.

F. Quenching• Quench as rapidly as possible to 300ºF (150ºC) as measured by the core

thermocouple, Tc. • Minimum quenching rate shall be: 50°F/minute (28°C/minute) between the

designated austenitizing temperture 1885°F and 1000°F (1030°C and 540°C), measured by Ts (in other words Ts shall reach 1000°F (590°C) in less than 18

minutes).

NOTE: This definition of how to measure the cooling rate is necessary to prevent discrepancies. In dies with ruling sections greater than about 12” (300mm), it may not be possible to achieve the recommended quench rate with all equipment.

• The quench may be interrupted when Ts is between 850° F and 750° F (455°C and 400°C).

NOTE: An interrupted quench is recommended when the difference between the surface (Ts) and core thermocouple (Tc), exceeds 200°F (90°C). If interrupted, rapid pressurized gas quenching must be resumed when either: 1.) Tc – Ts <= 200ºF (95ºC); 2.) Ts reaches 750ºF (400ºC); OR 3.) total interrupt time reaches 30 minutes maximum. Maintain pressurized gas quenching until Tc < 300ºF (150ºC).

• Continue rapid pressurized gas quenching when Tc - Ts<200°F (110°C) or 30 minutes maximum after Ts reaches interrupt temperature.

• Maintain pressurized gas quenching until Tc<300°F (150°C).• Die shall be cooled in still air until surface temperature Ts< = 120°F (50°C )

prior to tempering.• Die shall be immediately loaded for the first temper.

G. Tempering• A minimum of two tempering cycles are required before finishing operations.• Cool to ambient temperature between temper cycles.• Stress temper finished dies in air at 50°F (25°C) below highest tempering

temperature or1000°F (565°C) minimum. (This practice results in a minimum of three tempering cycles.)

• Tempering and stress temper cycles shall be held for one hour per inch of thickness based on the furnace thermocouple, two hours minimum.

H. Rehardening• If rehardening is required, the workpiece shall be reannealed at 1550°F–1600°F

(840°C - 870°C) for 1 hour per inch of thickness followed by slow cooling at less than 60°F (33°C)/hour to1100°F (540°C), then furnace cooled.

NOTE: Dies Must Not Be Rehardened Without Customer Approval.

IV. Heat Treatment Quality – Testing Requirements: REQUIRED FOR CLASS 1 & CLASS 2 HEAT

TREATMENT QUALITY CERTIFICATIONI. Hardness

• The recommended hardness range shall be within the range of 42 to 52 HRC. The lower end of the hardness range is recommended for dies where gross cracking is of concern whereas the high end of the range is recommended for

improved heat checking resistance.• Specific hardness range must be specified by the customer, stated as a 3-point

range; eg. 44-46 HRC.• Hardness testing shall be conducted following the latest revisions of ASTM E10,

ASTM E18, ASTM A956 or ASTM E384.• A minimum of five hardness readings is preferred (four corners and center face)

at positions agreed by customer.• Any deviation from the specified hardness range shall be referred to the

customer.

J. Furnace Chart Data• A copy of the furnace chart data produced from contact thermocouples in

accordance with III. C above and representing the actual load shall be available from the heat treater for 7 years minimum.

• The furnace chart data shall be presented in a legible manner documenting the thermal cycle experienced by the workpiece including preheating steps, austenitizing, and the quench from the hardening temperature to Tc<300°F (150°C).

• The minimum quenching rate, measured by Ts, shall be 50°F/minute (28°C/minute) between the designated austenitizing temperture 1885°F and 1000° F (1030°C and 540°C).

K. Hardened Microstructure

• The microstructure of a specimen representing the hardened detail shall be examined.

• The specimen shall be either 1) cut from a corner or edge of the hardened detail or 2) cut from a coupon that was attached flush to the detail throughout the hardening process. For Superior Quality see section IV L for test coupon details.

• The specimen shall be prepared in accordance with ASTM E3 and etched with a 5% Nital solution. (See Appendix 1.)

• The hardened microstructure of the specimen shall consist essentially of tempered martensite with some bainite.

• There shall be no evidence of pearlite, retained austenite, decarburization, carburization, or excessive intergranular precipitation.

• Unacceptable microstructures for hardened material are shown in NADCA Heat Treated Microstructure Reference Chart. (See inside back cover.)

REQUIRED FOR CLASS 1 HEAT TREATMENT QUALITY CERTIFICATION

L. Impact Toughness • A coupon approximately 2 ½” x 3 ½” x ½” thick shall be prepared from a

sample preferably from the same Grade/block of Special Quality die steel of known “annealed capability” impact toughness such that the 2 ½” dimension represents the thickness direction, the 3 ½” dimension represents width direction, and the ½” dimension represents the length direction of the parent material.

Surogate coupons are allowed and may be substituted.

• The coupon shall be attached to each workpiece away from edges and corners such that a 2 ½”” x 3 ½” face of the coupon is in intimate contact with the workpiece. If tack welds are used, the welds should be placed along the 3 ½” dimension.

• The coupon shall accompany the workpiece through the preheating, austenitizing, quenching, and first temper of the hardening procedure.

• The coupon may be removed from the die after the first temper and separately tempered to 44/46 HRC.

• Test coupon must be tempered 44/46 HRC. • From the coupon, three 10mm x 10mm Charpy impact specimens shall be machined and notched and tested at room temperature in accordance with ASTM A370. The base of the V-notch shall be parallel to the longitudinal direction of the parent material. The samples shall be machined to final size and finish ground. See Charpy V-notch per ASTM A370 latest revision, Fig. 11a. Adjacent sides shall be at 90 degrees ±10 minutes

Cross section dimensions shall be ±0.100 mm (±0.004 in.) Length of specimen shall be 55 ±1 mm (2.165 ± 0.040 in.) Surface finish shall be 63 micro inch (1.6 micro meter) max. on the 55 x 10

mm faces. Ground notches are preferred; EDM notches are not allowed.

• Testing shall be conducted at room temperature on test machines that meet the calibration requirements of ASTM E23 or ISO 148/R442 (latest revision).

• Acceptance criteria: 8 ft-lbs (11 J) average with 6 ft-lbs. (8 J) single minimum value at 44/46 HRC. The three individual results and the average shall be reported.

NOTE: These toughness criteria are from specimens removed from a required test coupon of Special Superior Quality material that was attached to the workpiece during hardening and is meant to represent the properties of the workpiece itself.

V. Heat Treatment Quality - Certification of Conformance:

NADCA Special Premium and Superior Quality H13 die steel that has been hardened in accordance with this specification shall be accompanied by a Certificate of Conformance from the heat treater that includes the following data and information:

A. Heat Treat SourceB. Item IdentificationX. Heat Treatment Quality Class (1 or 2)X. NADCA Steel GradeC. Material Heat NumberD. Shipping WeightE. Specified HardnessF. Pre-Heat: Step 1 Temperature & TimeG. Pre-Heat: Step 2 Temperature & TimeH. Pre-Heat: Step 3 Temperature & TimeI. Hardening: Temperature & Soak TimeJ. Quench Rate K. Quench PressureL. Interrupt: Temperature & Hold TimeM. 1st Temper: Temperature, Soak Time, HardnessN. 2nd Temper: Temperature, Soak Time, HardnessO. 3rd Temper: Temperature, Soak Time, HardnessP. Final HardnessQ. *Hardened MicrostructureR. *ALL Special Die Steels except Premium H13 Grade A: Hardened Impact Toughness; shall include three individual results and average results.

* Test results can be provided by a heat treater or testing facility.

Example

HEAT TREATMENT QUALITYCertification of Conformance

Heat Treatment Quality ClassNADCA Steel Grade

Heat Treat Source:

Item Identification:

Material Ht. No.:

Material Brand:

Required Hardness:

Ship Wt. Ea.:

Ship Date:

Operation Temperature

Time

Furnace

Hardness

AnnealStress RelievePre-Heat: Step 1Pre-Heat: Step 2Pre-Heat: Step 3High HeatQuench RateQuench PressureInterrupt Temp.Temper: Draw 1Temper: Draw 2Temper: Draw 3Final Temp.Stress Temper

Final Hardness:

Hardened Microstructure:

Required for Class 1 Heat treatment superior quality: Test Coupons Attached: YES NO

Impact Toughness: 3 Individual Values-

ft.-lbs, ft.-lbs, ft.-lbs Average ft.-lbs

We certify that the above statements are true and correct and that all temperatures were obtained with standard and approved equipment.

Work or Shop Order No.:

Authorized Signature:

Date:

ACKNOWLEDGMENTS:

NADCA acknowledges the technical support and contributions of the following individuals and companies:

Die Materials Specification Task GroupChairman: Corwyn Berger Bodycote Materials Testing, Inc.

Jesse Adamson A. Finkl & Sons Co.Terry Bachmeier ThyssenKrupp Specialty Steels NAGuy Brada Bodycote Taussig, Inc.Carl J Dorsch Timken Latrobe SteelRudiger Ehrhardt ThyssenKrupp Specialty Steels EWKEdward Flynn GM PowertrainPatricia Miller Bohler Uddeholm NAEd Severson Crucible Materials Corp.

Die Materials Heat Treatment Task GroupChairman: John Fitzgerald FPM Heat Treating Vince Adkar ThyssenKrupp Heat Treatment NA Mark Baleja Century Sun Metal Treating Gene Hainault Therm-Tech of Waukasha Mark E. McCormick Paulo Products Co. Iqbal Shahid Bohler Uddeholm North America Craig Zimmerman Bodycote Thermal Processing

Cover pictures provided by Bohler Uddeholm and FPM Heat Treating. Appendix 1

Appendix 1: Guide to Sample Preparation Techniques

When taking samples for Impact Testing and Metallographic Examination, the location from which the test material is removed is important. Likewise, the direction and orientation of the test specimens can have a significant influence on the test results. Accordingly, it is imperative that samples be produced in strict accordance with the following guidelines.

Impact Capability Testing –As required by Section I.E., all mill product forms with a thickness greater or equal to 21⁄2 inches must be subjected to an Impact Capability test. A sample of test material, at least 21⁄2” x 31⁄2” x 1⁄2” is to be removed from the center location of the parent block of steel. The 21⁄2” dimension is to be parallel to the thickness dimension of the parent block; the 31⁄2” dimension is to be parallel to the width of the parent material; the 1⁄2” dimension represents the length direction of the parent material. See Figure 1a. Five Charpy V-notch (CVN) specimen blanks shall be removed from the short transverse orientation from the test material. See Figure 1b.

Figure 1a. and Figure 1b. Location & Orientation of Test Material and Charpy Impact Test Samples.

Individual CVN specimens shall be rough machined oversize to be nominally 1/2” x 1/2” x 2-1/2”each. The specimens are then to be hardened and tempered in accordance with the procedure listed in Section I.E. before machining to final dimensions. After final machining to 10mm x 10mm x 55mm per ASTM A370 Figure 11a, each specimen is to be notched in the Short Transverse (ST) orientation such that the base of the V-notch is parallel to the longitudinal direction of the parent material per Figure 1b above.

Impact Toughness; Required for Class 1 Heat Treatment Quality Certification-

Class 1 Heat Treatment Superior Quality material is required to have a special test coupon attached to the workpiece prior to hardening. See Section IV.L. The coupon is identical to the sample of test material used for Impact Capability testing described above. A coupon approximately 2 ½” x 3 ½” x ½” thick shall be prepared from a sample of Special Quality H13 die steel of known “annealed capability” impact toughness such that the 2 ½” dimension represents the thickness direction, the 3 ½” dimension represents width direction, and the ½” dimension represents the length direction of the parent material. The coupon shall be attached to the workpiece away from edges and corners such that a 2 ½” x 3 ½” face of the coupon is in intimate contact with the workpiece. See Figures 2a & 2b.

After the completion of the hardening and tempering heat treatment (see Section IV.L.), three 10mm x 10mm x 55mm CVN specimens are to be finish machined from the test coupon per ASTM A370 Figure 11a, and notched in the ST orientation such that the base of the V-notch is parallel to the thickness direction of the test coupon (i.e. longitudinal direction of the parent material) per Figure 1b above.

Metallographic Examinations –A variety of Metallographic Examinations are required by this specification. For some of the required tests, if properly selected, a single specimen may be used for multiple requirements. The samples for Metallographic Examinations on Annealed Material should be taken from the test material cut for the Impact Capability testing. A single specimen can be used to evaluate the banding,

microcleanliness, and annealed structure. A separate specimen is required to evaluate the grain size of the material. This sample may be taken from a broken CVN specimen after completing the Impact Capability testing or may be taken from a specimen hardened in accordance with Section I.F. using the Direct Quench method per ASTM E112.

Samples for examination of annealed material must be taken such that the surface to be examined is parallel to the principal direction of deformation. Preferably, specimens should be taken from the near-center of the width and thickness of an end face of the block. See Figures 3a and 3b.

Fig 3a & 3b: Sketches showing location and orientation of metallographic specimens removed from block and round stock for determination of microcleanliness, banding, grain size, and microstructure of annealed material. The shaded faces in the figures are the faces which should be polished and etched for the metallographic examinations.

Specimens should be mounted, ground, and polished in accordance with standard metallographic procedures and ASTM E3. Examination for microcleanliness shall be conducted in the unetched condition in accordance with ASTM E45, Method A, Plate 1-r. Examination for Banding/Segregation and for rating the Annealed Microstructure shall be conducted in the etched condition. The specimens should be etched immediately after polishing by immersion in a 5% Nital solution for approximately 30 seconds to obtain a properly developed microstructure. The Banding/Segregation shall be evaluated and rated by metallographic examination at a magnification of 50X; the Annealed Microstructure shall be evaluated and rated at a magnification of 500X.

Grain Size determination shall be conducted on a properly prepared metallographic specimen of a laboratory quenched sample in the etched condition at a magnification of 100X. Due to the typically fine grain size, examination may be made at a higher magnification using the formula presented in ASTM E112 Comparison Method.

Samples for evaluation of the hardened microstructure shall be made on a specimen taken from commercially heat treated material and must include an as-hardened surface; i.e. not ground or otherwise machined after hardening. The sample should be taken from the hardened coupon used for Impact Toughness testing for Special Quality material or from a sample cut from a corner or edge of a hardened workpiece of Premium Quality material if no test sample was attached to the workpiece.

Specimens shall be mounted, ground, and polished in accordance with standard metallographic procedures. The specimens shall be etched by immersion in a 5% Nital solution for approximately 30 seconds to obtain a properly developed microstructure. See Figures 4a,b,c,d.

The microstructure shall be examined and rated at 500X. The hardened microstructure of the specimen shall consist essentially of martensite with some bainite. There shall be no evidence of pearlite, retained austenite, decarburization, carburization, or excessive intergranular precipitation.

Figure 4a,b,c,d. Microstructures of hardened Special Quality die steel Premium H13 showing the effects of sample preparation and etching techniques. Fig 4a: This image shows a die steel an H13 microstructure that has been properly ground, polished, and etched. Fig. 4b: This image shows polishing scratches, a pulled-out inclusion, surface dust particles and etch stains. All of these features are

polishing artifacts, and are not indicative of poor heat treatment. Fig 4c: This image shows the microstructure of the same specimen in Fig 4a, but in this case, the specimen has been overetched after polishing. The overetching masks critical details of the microstructure. The overetched condition can be the result of an incorrect acid concentration in the etchant, or an etching time that was too long. Fig 4d: This image shows the microstructure of the same specimen in Fig 4a, but in this case, the specimen has been underetched after polishing. The underetching makes critical details of the microstructure difficult or impossible to discern. The underetched condition can be the result of an oxidized specimen surface (too much time between polishing and etching), incorrect acid concentration in the etchant, or etchant that is too old.

Appendix 2: Practical Guide to Steel and Heat Treatment Quality

Introduction: Preparations, Instructions

Aim:This Appendix gives practical guidance for stress relieving, hardening and tempering processes applicable to hot work die steels H13 steel for use as die casting or squeeze casting tools, inserts, cores, etc. The main purpose is to provide optimum metallurgical properties while minimizing distortion and risk of cracking.

Written Instructions:It is strongly recommended that written instructions be given to the heat treater that itemize the requirements of the customer and take into account the requirements of the preceding specification. Such written instructions may include or exclude information given here. Where a difference occurs, the customer’s instructions shall take precedence.

Liaison:Close liaison between the customer and heat treater (over details such as required properties, permissible size change, etc.) will assist the heat treater in achieving the best results with the least risk.

Preparation For Heat Treatment:It is the tool maker’s responsibility to prepare the tool such that the risk of cracking, distortion and surface effects are minimized.

Examine material certification for statement of conformance to NADCA #207-200X 3

Supplier Grade Name & Heat Number

Confirmation of Ultrasonic Inspection

Annealed Hardness

Microcleanliness/Inclusion Content

Banding/Microsegregation Rating

Chemical Composition

Annealed Microstructure Rating

Impact Capability Test Results

Grain Size Number

Avoid stress risers – check for:

Sharp inside corners Deep tool & stamp marks Burrs

Weak, thin sections Very deep cavities

Ensure tool is not cracked before heat treatment:

Use dye penetrant, ultrasonic testing, magnetic particle

Notify heat treater if EDM is used prior to hardening

Ensure surfaces are free from dirt, rust, oxides, grease & cutting fluids

If die has been welded, mark the weld and notify the heat treater.

Steel grade

NADCA Grade H13, Premium, Superior)

Manufacturer & designation

Heat or batch number

Present Condition

Annealed after previous hardening

Hardened & tempered Stress relieved

Annealed

Surface Condition

Nitrided (specify type & depth)

Other surface treatment (type & depth)

Welded

Allowance for Distortion & Growth

Sufficient metal is left on tool (review stock allowance and critical dimensions w/ heat treater)

Identify critical dimension(s)

Final Hardness

Specify exact range (42-50 HRC for finished tools, higher values for smaller tools)

Specify location of test on tool

Review Records/Certification

Certification of compliance Furnace charts of temperature & times (see page 11)

Instrument calibration records

Test Results Requested

Hardness check Quench rate Impact test

Micro-examination of sample taken from die

Heat Treatment Guidelines

Instructions:• Heat treater must contact the customer if written

instruction differs from these recommended procedures• Furnace load size and placement must be appropriate to

assure conformance to recommended procedures• Must avoid change in surface composition e.g.

decarburization, oxidation, etc.• Maintain temperature controllers to AMS 2750 or latest

revisions.• Maintain instrument calibration records• Use thermocouples in the furnace load per procedure,

additional thermocouples may be used• Maintain accurate, traceable records of all technical

details such as temperatures, soak times, cooling rates and hardness

• Conditions must be controlled to limit surface effects such as decarburization, carburization or nitriding

• Hardening vacuum furnaces, with positive pressure capability of at least 2 bar on premium quality and 5 bar on superior quality.

• Tempering/stress relieving: air, atmosphere or vacuum is allowed.

• Stress tempering/oxide treatment: air• Annealing: vacuum or atmosphere• Accurate temperature control is important.• Every tool shall be hardness tested and reported using

Rockwell C scale• A minimum of five hardness readings is preferred (four

corners and center) at positions agreed by customer.

• If decarburization, etc. is suspected, this may be checked by using Rockwell superficial or microhardness testing.

• A test coupon can be attached to the die prior to hardening to evaluate microstructure, toughness, etc. as requested by the customer. This is a mandatory requirement for Class1 Heat Treatment Quality certification Superior Quality H13.

NOTE: Dies Must Not Be Rehardened Without Customer Approval.

Stress Relieving After Rough MachiningThe stress relieving treatment may be performed to reduce the likelihood of distortion during subsequent machining or heat treatment.

Rough Machining• The rough machining operation can introduce high levels of residual stress

(heavy grinding may also produce a hardened skin due to the high temperatures generated).

• If not relieved, this stress may cause distortion during final machining or during the hardening operation.

• Leave sufficient stock on all surfaces at the rough machining stage to be removed using lighter cuts after the stress relieving operation - and before final hardening

Heating Temperatures and Soak• Charge into cool furnace (less than 500° F [260° C]). Heat to 1050°

F - 1250° F (560° C - 675°C) in a vacuum, electric or gas furnace.• Tools should be well supported and allow free circulation of the

heating medium so that they are heated uniformly.• Allow 20 min. per inch of section thickness for heating. Hold for a

minimum of 1/2 hour per inch of section thickness or a minimum of two hours, once the furnace reaches operating temperature.

• Where feasible, use a thermocouple in the center of the tool (e.g. in an ejector hole or waterline) to indicate when the center of the tool reaches temperature, then hold for 2 hours minimum.

CoolingSimple shapes: may be taken out and air cooled. Charge into cool furnace (less than 500° F [260° C]).Complex shapes: (e.g. where section thickness varies by more than 3 inches) should be furnace cooled to 800° F (430° C) maximum to reduce the cooling stress before air cooling.

In both cases, cool as uniformly as possible in still air away from drafts to prevent reintroduction of thermal stress.

Annealing

Annealing involves heating the tool slowly to a high temperature, then cooling slowly to develop the softest condition possible with this grade of steel. A tool which was incorrectly hardened or has softened in service may be annealed to reduce the risk of cracking and distorting during heating for hardening. The treatment may take over 24 hours. There is a risk of distortion, scaling and decarburization.

Heat: Slowly - Maximum rate of 400° F (220°C) per hour to a temperature of 1550°F – 1600°F. (840°C – 870°C).

Hold: Preferably until the center of die is up to temperature as indicated by a thermocouple in a hole in the die;

OR

For one hour per inch of thickness after furnace temperature stabilizes, two hours minimum.

Cool: Slowly - Maximum rate of 60°F (33°C) per hour to 1100° F (590°C) maximum. Then furnace cool.

Practical Details

Atmosphere Control Notes & PrecautionsAbove 1100° F (590°C) Vacuum 100 microns min.

Support well to prevent sagging. Separate work to aid uniform heating.

Below 1100°F (590°C) Air cool or vacuum backing pump or inert gas at 1 bar

May use thermocouple attached to the tool.

Endothermic gas mixture Nitrogen + hydrocarbon gas Nitrogen + hydrogen

Control atmosphere by dew point, CO2, or oxygen probe to carbon potential of 0.4%. Surface discoloration will occur.

InspectionHardness: 235 HBW maximum

Surface Layers: If little or no material is to be machined from the surface, check for decarb or carburization on a corner taken from the tool or on a sample of Special Quality die steel H13 included with the load.

Austenitizing: Heating For HardeningThree phases must be controlled: heating rate, hardening temperature and soaking time. All three will depend on the equipment used, the geometry and size of the tool and mechanical properties aimed for. The information below is in three parts. In the left column, the normal optimum aim values. In the center column is more detailed information, ranges and alternative variations. The right column gives technical details, precautions, etc.

Step Heating• Load work into cold furnace, and heat at a rate not to exceed

400°F/hr. (220°C/hr.)• Heat to 1000° F to 1250° F (540°C-675°C)• Hold until Ts-Tc < 200°F (110°C)• Heat to 1550° F ± 50°F (845°C ± 25°C )• Hold until Ts-Tc < 100°F ± (60°C) heat in “steps” holding• Alternative preheating steps may be used at the discretion of

heat treater or toolmaker. • Rapidly heat to a designated autenitizing temperature

1885°F ± 10°F (1030°C ± 5°C)• The outside of the tool heats up faster than the inside. This

creates stress due to thermal expansion and phase changes.

• Aim to reach austenitizing temperature with the outside and inside temperatures as close as possible.

• This can be achieved by heating slowly but it is more efficient to heat in “steps” holding temperature constant so that equalization can occur.

• Use the heating cycle which gives the least risk and is compatible the equipment available.

• The most sensitive temperatures are when the temperature reaches the “critical” temperature of 1560°F (850°C) and close to austenitizing temperature where grain growth can occur.

Austenitizing1925°F (1050°C)

1900°F (1040°C) High

Temperatures

• Better carbide solution

• Risk of grain

Choice of austenitizing temperature is a compromise

High temperatures give good carbide solution. The alloy absorbed gives resistance to tempering in service and a reduced rate

of heat checking.

growth

• More temperature resistance

• Less heat checking

• Lower impact toughness

1885°F (1030°C)

1875°F (1025°C) Normal

Range1850°F(1010°C)

1825°F (995°C) Low

Temperatures

• Less temper resistance

• More heat checking

• Higher impact toughness

• Less Distortion

Lower temperatures give less carbide and alloy solution, less resistance to softening and heat checking.

Soaking Times• With inserted thermocouples soak time shall be 30 minutes

after Ts-Tc < 25°F (15°C), or 90 minutes maximum after Ts=1885°F (1030°C), whichever occurs first.

Good heating practice means that soaking is more effective. Soaking is performed partly to equalize tool temperature but principally to dissolve carbides and increase effective alloy content of the matrix. This does not start until close to austenitizing temperatures. Too long a soak time increases the risk of sagging and can cause grain growth. A more common fault is too little soaking.

Austenitizing: Equipment, PrecautionsThe heating and cooling rates, load capacity, and uniformity should be established for individual equipment by instrumented tests before used on actual tools.

Additional thermocouples attached to the work will assist control, reduce risk and increase efficiency.

Vacuum Furnaces

Characteristics Precautions

• Good support – work is not moved during whole heating and quenching cycle.

• Heating is by convection and radiation.

• Furnace has low thermal mass. Work is charged into cold furnace, heating is rapid and must be controlled.

• Good control over oxidation and decarburization is typical

• Loading pattern is important. Do not charge very large parts along with very small.

• Must control load size to assure that the minimum quench rate can be achieved.

• Use thermocouples attached to tools, (Ts and Tc) to measure actual tool temperature.

• Vacuum of 50 to 100 microns with leak rate below 5 microns per hr. Very low pressure may cause loss of alloys from surface.

• Austenitizing temperatures usually chosen towards top of recommended range.

Equipment Class 1 Special Quality Die Steels Premium —

• Vacuum furnace with a minimum 2 bar backfill capability and a programmable furnace controller linked to multiple load thermocouples.

• Sufficient cooling capability to cool die surface from 1885° F (1030 °C) at a minimum rate of50°F/min. (28°C/min.).

• Furnace must be capable of isothermal hold during quench based on input from surface and core thermocouples where interrupted quench is required.

Class 2 Special Quality Die Steels Superior —• ‡ Vacuum furnace with a minimum 5 bar backfill capability and a

programmable furnace controller linked to multiple load thermocouples.• Sufficient cooling capability to cool die surface from 1885°F (1030°C) at a

minimum rate of 50°F/min. (28°C/min.).• Furnace must be capable of isothermal hold during quench based on input from

surface and core thermocouples where interrupted quench is required.‡ Modifications from NADCA Premium Quality for Superior Quality

Quenching: Practical TechniquesH13 has high hardenability so that pressurized gas quenching is satisfactory if properly controlled. A minimum quench rate of 50°F (28°C) per minute is recommended.

Practical quenching techniques are described below but the heat treater must take into account equipment capability as well as size and geometry of the tool.

EQUIPMENT: DETAILS: TECHNICAL INFORMATION:

Vacuum Furnaces

Single Step-

Minimum 2 bar (pre-mium quality) or 5 bar (superior quality) backfill capability with a programmable controller linked to multiple load thermocouples.

Sufficient cooling capability to cool die surface (Ts) from 1885°F (1030°C) to 1000°F (540°C) at a rate of 50°F (28°C) per minute.

Ts should reach 1000°F (540°C) in less than 18 minutes.

Pressure gas quench until coreTc < 300°F (150°C) – air cool until die surface Ts less than 120°F (50°C). Temper immediately.

Quench rate is not solely a function of quench pressure (2 bar, 5 bar etc.).

Quench rate depends on block size, gas quenchant, velocity and pressure, heat exchanger efficiency and the furnace load.In dies with ruling size greater than 12” (300mm), it may not be possible to achieve the recommended quench rate with all equipment.

Quenching: Toughness, Isothermal Quenching

Selection of a quenching rate is a “trade off”; faster quench rates give better metallurgical structure, but increase distortion and the risk of cracking.

Isothermal or step quenching techniques can be used to optimize metallurgical properties while reducing distortion and the risk of cracking.

Quenching Rate vs. StructureFour quenching rates are shown: 1-fastest...4-slowest1. Structure martensite. Ideal structure; quench rate is too fast

to be practical.2. Structure martensite plus grain boundary carbides.

Achievable with small tools.3. Structure is martensite plus bainite plus grain boundary

carbides. Practical structure for medium to large tools. Curve shown is slowest recommended and is achievable by pressurized gas quench.

4. Structure contains pearlite which reduces toughness and heat checking resistance even though tempered hardness maybe correct.

Effect On ToughnessEffect of cooling rate versus toughness is shown for quench rates 2, 3 and 4 above. Faster quench rates result in increased toughness.

The cooling rate is a function of the size of the tool and the quenching power of the equipment used. This relationship should be established before the heat treatment begins.

Causes of DistortionThe surface cools faster than the core.

Above the martensite transformation temperature, the surface and corners contract faster than the core, causing stresses which lead to distortion of large blocks.

At lower temperatures, the surface transforms to martensite or bainite and expands. The core is above the transformation temperature and is still contracting. Stresses develop between these regions which may distort or crack the tool.

The greater the temperature difference between the surface and the core the greater the risk.

Isothermal Treatments The initial cooling rate must be fast enough to minimize grain boundary precipitation and to suppress the formation of pearlite.

Once below 1000° F (540° C), pearlite will not be produced. The tool may be held at a constant temperature between 750°F - 850° F (400°C - 455°C) to allow the surface and core to equalize before quenching further. Although the surface still cools faster, the temperature difference is reduced so the stress is reduced.

Prolonged isothermal holds should be avoided to minimize the formation of bainite.

Tempering - PracticalDirectly after quenching, H13 is hard, brittle and highly stressed. It is vulnerable to cracking spontaneously and must be tempered while still warm.

Further tempering will reduce the stress level and hardness but increase toughness and resistance to cracking in service.

The final hardness level chosen depends on the application and is normally in the range of 42-50 Rockwell C.

This is achieved by careful control of temperature and time of tempering. A minimum of two tempers is required to give dimensional stability and the correct metallurgical structure.

Hardness is not a good indicator of how a tool will perform. Tool life is more dependent on the metallurgical structure of the steel.

Preparation:Cool to surface temperature ≤ 120°F (50°C)Select final hardness range and plan tempering schedule.

Do not allow tool to cool below 90°F (33°C). Keep it away from drafts, avoid rapid cooling.Use data in Tempering – Technical section to help plan the schedule. Use steel manufacturer’s data if available.

First Temper — MandatoryPlace tool in furnace at 800°F (425°C)maximum.Hold at 1050°F (565°C) minimum for two hours after core reaches setpoint. Allow 60 min. per in. of thickness to reach heat.Air cool to ambient temperature.

Furnaces may be vacuum, electric or gas, with temperature control to give accuracy and unifor-mity of ± 10° F (±5°C) maximum.Some surface discoloration will occur but decar-burization or other metallurgical damage is not caused at these low temperatures.The tool is now safe to cool to room temperature and the hardness should be measured.

Second Temper — MandatoryPlace in furnace at 800°F (425°C) maximum.Hold for specified time - two hours minimum, Minimum temperature 1025°F (550°C).Air cool to Ambient temperature.

From the hardness value, determine which tem-pering curve to use. See next page.Select the temperature and time to give the required hardness. Aim low; tempering can be repeated to reduce hardness, but if the tool is softened too low it may have to be rehardened.Check hardness in specified position.

Third Temper (If necessary)Hardness still too high: Adjust tempering parameters and retemper.Hardness correct: Tool can be finished and stress tempered.Note: May be combined with surface treatments-oxiding, nitriding, nitrocarburizing, etc.

A third temper may be required to “fine tune” the hardness level.Even if hardness is correct, a stress temper after finishing has the following advantages:• It leaves an oxide coating to reduce soldering.• Elevated temperature surface treatments can be used as the stress temper.

Tempering: TechnicalTempering relieves internal quenching stresses and changes the metallurgical structure. A secondary hardness peak occurs at around 950° F (510° C) caused by elimination of retained austenite and formation of complex carbides. At higher temperatures, hardness drops and toughness increases.

The shape and position of the tempering curve is affected by composition, hardening temperature, soak time and quench rate. Longer soak times are preferred over higher tempering temperatures to promote better hardness uniformity.

Selection of Final HardnessFinal hardness is at the die caster’s discretion and should be selected based upon steel grade, size, and die design. Do not temper below 1000° F (540° C). Lower hardness is specified for larger tools to give better toughness.

High hardness (up to 52 HRC): Increased wear resistance and better resistance to heat checking.

Low hardness (42 HRC): Greater resistance to gross cracking, but less resistance to heat checking.

Tempering CurvesCurves shown are typical. Use steel manufacturer’s information when available.

Response to tempering can vary with the steel composition and the hardening schedule. Choose the curve which most closely fits the hardness obtained after the first temper.

Example: As quenched, the tool was 56 HRC. After first (1000° F [540°C]) temper, hardness dropped to 54 HRC. The center curve should be used. To achieve 46 HRC, the second temper should be 1080° F (580° C).

Master Tempering ParameterThe Master Tempering Parameter is a useful way of judging the effect of time (although

temperature is the major factor). Time of tempering also affects the process. The Master Tempering Parameter permits one to calculate the effect.

For example, to achieve 46 HRC, a small tool may be tempered at 1080° F (580°C) for four hours.

A large tool may have to soaked for 24 hours to attain uniformity. In this case, the temperature must be reduced to 1025° F (550° C).

In both cases, the Master Tempering Parameter is 31727 and the final hardness

is 46 HRC.

This graph gives the tempering parameter. This value may be used to calculate many combinations of time and temperature.

Stress Tempering of Hardened ToolsThis is a low temperature treatment that will not soften the body of a hardened and tempered tool but imparts useful benefits e.g.:It will reduce stress levels and temper rehardened layers in tools which have been welded or electrical discharge machined (EDM).

On tools welded with maraging, stainless steel, or other welding rods, always follow the welding rod manufacturer’s recommendations. If the welding was done using maraging rod, stress tempering can age harden the welds to approximately that of the die. Used at regular intervals on production tools, stress relieving will reduce the rate of heat checking and increase die life.

Use On • Electrical discharge machined tools (EDM) • Tools welded with H13 rods • Tools welded with maraging, stainless or other welding rods • Tools taken out of service

Heating Temperature

Holding (Soak)

Close temperature control is essential. Use vacuum, electric or gas furnace.

Cooling Simple shapes: Take out and cool in still air.

Complex shapes: e.g. where section thickness varies by more than 3”(75mm) Furnace cool to 800°F (430°C) maximum, to reduce cooling stress, take out and air cool.

Cleaning In both cases, cool as uniformly as possible in still air away from drafts to prevent re-introduction of thermal stresses. Do not remove the oxide layer since this will help prevent soldering in service.

Appendix 3: Welding Die Casting Die Materials

Introduction Die casting dies are welded for two primary reasons. The first is corrections or changes to dies before they go into service. The second is for repair.

Welding of die casting dies involves risks such as cracking. The following general guidelines and information are designed to help reduced potential defects. Note: A welded die will never be as good as an unwelded one and a decrease in life expectancy may occur.

The Weld Zone

Heat Affected Zone The weld area will be composed primarily of weld rod material. The structure will consist of as-cast, quenched, and un-tempered material. The heat affected zone will be composed of base material exposed to high heat from the welding process. This zone will typically be softer than the base material.

Die Preparation for Welding1. Remove Cracks: Remove all cracks completely by grinding or

machining. The groove shape should be in a “U” configuration. Avoid shapes with sharp corners such as “V” shapes.

2. Clean Die: Clean the die by removing oxide, dirt’ and discolorations. Dry material thoroughly.

3. Examine Die: Examine the die for residual cracks using crack detection techniques such as die penetrant, or magnetic particle inspec tion. If cracks are found, follow step 1. above. Clean die after penetrant or magnetic particle inspection.

Welding Procedure

1. Weld Materials: Weld materials should be chosen based on the material being welded, the amount of weld required, and the desired properties of the weld. When in doubt, contact the material supplier for details.

2. Preheat Die Block: Pre-heat die blocks to the recommended temperature for that particular grade. Rules of thumb: Annealed material: 1000°F Hardened material: 75% of the tempering temperature maintain heat during welding.

3. Deposit Weld Bead: Deposit weld bead using equipment designed to produce good clean welds.

Avoid welding with un-shielded electrodes

Maintain pre-heat temperatures during welding

4. Examine Weld:

5. Post-heat Die Block: Check the weld for undercuts or imperfections. Allow the finished weld to cool slowly. Quenching the tool or allowing the tool to sit un-tempered for a long period of time may cause cracking.

Annealed dies: Re-anneal completely or temper at appropriate tempering temperature.

Hardened dies: Temper at 25 degrees F below the previous tempering temperature for two hours minimum.

Pre-heat GuidelinesPre-heating before welding will minimize the risk of cracking a die during welding. Pre-heating allows the base material and weld to cool slowly from the welding temperature, minimizing thermal shock.

Pre-heat temperatures for specific materials can be obtained from the material supplier or from the weld material supplier.

A good rule of thumb for pre-heating hardened materials is to use a temperature roughly equal to 75% of the tempering temperature used during heat treatment of the tool.

Post-heat GuidelinesWelded tools should be post-heat treated by either fully annealing or tempering the entire weld zone. The postheat treatment relieves stresses caused from the microstructural and thermal changes that happen during the welding process.

The post-heat treatment should be done immediately following the welding process to minimize the risk of stresses cracking the die.

NOTE: These processes are necessary to insure a quality weld. They should not be considered optional.

Charpy full size test impact specimen per ASTM A370, Fig. 11a.

Charpy full size test impact specimen per ASTM A370, Fig. 11a.

Figure 1b

Figure 1a

One or more metallograpic specimens for rating the annealed microstructure, microcleanliness, and microbanding on a longitdiual, short-transverse face.

Figure 2b

Figure 2a

Fig. 2a- Photo showing test coupon attached to the surface of an insert in preparation for hardening.

Fig. 2b- Sketch showing location and orientation of CVN and microstructure specimens to be removed from test coupon after hardening.

Figure 3a

Figure 3b

Figure 4c

Figure 4d

Figure 4a

Figure 4b

To welding rod manufacturer’s recommendations.

50°F below highest tempering temperature (if known) OR

1000°F (540°C)

Welding rod manufacturer’s instructions. (if available)

Soak 1/2 hr. per inch of maximum section with a minimum of two hours, after furnace reaches temperature.

ORUntil center of tool reaches specified temperature, by a thermocouple in the center of the tool.