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Increasing the Efficiency of Metalform Tooling for Advanced High Strength Steels

By: Brett Krause and Tom Bell of Bohler Uddeholm Corporation


Introduction

• Information on Bohler Uddeholm• Newly developed tool steel and processing

– What makes it different

• Properties of the tool steel– Compared to current tool steel

• Current cold roll tooling case studies• Tool Steels for Blanking and Forming of AHSS

– What works best and why


Bohler Uddeholm

• World largest producer of Tool Steel– Austria, Sweden, Brazil

• Distribution in 37 countries• In North America

– 15 service locations– 400 employees– Downstream processing

• Value added: cutting, grinding, and machining


Introduction

• Trends– New steel making processes– Trim and Draw die tooling– Rolls for cold rolling of strip steel

• Suggested improvements for making steel more efficiently


What’s new

• New process for producing tool steel– Conventionally produced with addition of ESR– Spray form

• New alloys that offer superior performance to commonly used tool steels


Background and History of Dan Spray Process

• Process similar to Spray Forming or Thermal Spray techniques for hard surface coatings

• Positioned between conventional ingot metallurgy and P/M process metallurgy

• Developed in the mid 1970’s by researchers who formed Osprey Metals Company

• Many different types of alloys can be produced by this process such as Al and Si alloys, copper alloys and iron alloys


What is the Dan Spray Process?

• A metal stream is atomized• The atomized droplets are

collected by a substrate which allows a pre-form to be made in the form of tube and billets

• Eliminates HIP’ing• The pre-forms are ready for

further processing such as rolling or forging

Tundish

Spray chamber

Collector disc

Exhaust

Spray formed

billet

Melting furnace


Microstructure Comparison

Spray Form

10µm

P/M

3.5µm

Conventional

25µm


Spray Form Material for Roll Tooling

Grades C Si Mn Cr Mo V WLCV Spray Form 1.4 1.0 0.6 4.6 3.2 3.7

M1 0.8 0.4 0.3 3.8 8.7 1.4 1.8M2 0.8 0.3 0.3 4.1 5.0 2.0 6.1

8% Cr 1.1 0.9 0.4 8.3 2.1 0.5D2 1.55 0.25 0.35 11.8 0.8 0.95

Composition (wt%)


Spray Form - Property Comparison

Spray formed Metallurgy GradesSpray formed Metallurgy Grades

Conventional Metallurgy GradesConventional Metallurgy Grades

O1A2

D2

Increasing Wear Resistance

Incr

easi

n g c

h ipp

ing

resi

s ta n

c e

M2

S7

8% Cr

LCV Spray FormLCV Spray FormM1


Sendzimir Z- High Mill

Cold rolling

Case study – LCV Spray Form


Cold rolling - work roll at four high mill

COMPANY: Sandvik Materials Technology, Sweden.PRODUCT: Cold rolled high carbon, high chromium steel.ROLLING MILL: Four high cold roll mill - three in line, Initial cold rolling of hot rolled

strip to t = 0.9 – 3.8 mmROLL DIMENSION: Work roll, Ø271x1555 mm.COMMENT: The surface at the roll bearing position is significantly better for LCV Spray Form.

Phase 2 is to reduce regrinding depth to 0,10 mm for LCV Spray Form. Grinding with CBN is to be preferred.Phase 3 is to replace ROP 20 with LCV Spray Form in all three roll positions.Phase 4 is to improve performance further by increasing hardness of LCV Spray Form from 59 to 61 HRC - 63 HRC-.

RESULT:


ROP 20(H13 MOD.)

(0.7%C, 5.3%Cr, 1.1%Mo, 0.5%V)

LCV Spray Form – Phase1st Work Roll LCV Spray Form

2nd Work Roll ROP 203rd Work Roll ROP 20

Production Tonnage / Regrind 8 coils 28 coils

Failure Mechanism Abrasive Wear Abrasive Wear

Regrind Depth 0.3mm 0.3mm

Hardness 59 – 61 HRC 59 - 61 HRC


Cold rolling - work roll at four high mill

ROP 20(H13 mod.)

(0.7%C, 5 .3%Cr, 1 .1%Mo, 0 .5%V)

8%Cr steel LCV Spray Form

Produced tonnage/regrind 5 coils 7-8 coils 17-20 coilsFailure mechanism Abrasive wear Abrasive wear Abrasive wearRegrinding depth 0.15 mm 0.15 mm 0.05 mmHardness 59 - 61 HRC 59 - 61 HRC 59 - 61 HRC

COMPANY: Sandvik Materials Technology, Sweden.PRODUCT: Cold rolled high carbon, high chromium steel.ROLLING MILL: Four high cold roll mill. Intermediate mill,

T = 0.8 – 1.7 mm.ROLL DIMENSION: Work roll, Ø 160 x 1245/510 mm.COMMENT: The surface at the roll bearing position is significantly better

for LCV Spray Form.RESULT:



Calibration roll for manufacturing of welded stainless tube

COMPANY: AST, Sweden. PRODUCT: Stainless tube, Ø38 mm. WORK MATERIAL: 18/8 steel. TOOL DIMENSION: Calibration roll direct after annealing, which is

the most severe roll position from wear point of view, Ø 150 x 70 mm.

RESULT:

LCV Spray Form D2Hardness 62 HRC 60 HRC

Produced hours/regrind 310 h 100 hFailure

mechanismMinor abrasive

wearAbrasive wear,

galling



Circular slitting knife

COMPANY: Sandvik Steel AB, Sweden.

PRODUCT: Valve band (for shock absorbers).

WORK MATERIAL: High carbon steel (20C), t = 0.6 mm, 1200 MPa.

TOOL DIMENSION: Circular slitting knife, Ø 210 x 7 mm.

RESULT: Sandvik has contacted their suppliers and asked them to make circular slitting knives in LCV Spray Form

M2 LCV Spray FormProducedcoils / regrind 10 – 11 coils 20 – 22 coils

Failuremechanism Abrasive wear Abrasive wear

Hardness 62 HRC 62 HRC



Work Material Testing Performed

0

10

20

30

40

50

60

200 400 600 800 1000 1200 1400

Form

abili

ty, A

80(%

) Mild Steel

HSLADP-steel

Trip-steel

Mart. steel

Bake Hardenable

IF

MPa58 87 116 145 174 203 KSI29

~125HB ~180HB ~22HRC ~33HRC ~38HRC ~44HRC

70 High Strength Stainless Steels

Grades of AHSS Tested


-3 000

0

3 000

6 000

9 000

12 000

15 000

0 0,005 0,01 0,015 0,02 0,025 0,03

Time,s

Forc

e,N

Chamfered punch

Flat punch with a PVD coating

Flat punch

This shock wave can be avoided by a chamfer ~30 % force reduction

by chamfered punch Punch Material P/M 4%V at 60 HRC

UHS Work Material – 1400 Mpa


Die ClearanceTool wear after 200 000 strokesTool steel: P/M 4%V at 60 HRC

11000 µm2

5675 µm2

9618 µm2

0

3 000

6 000

9 000

12 000

15 000

0 2 4 6 8 10 12 14 16

Die clearance, % of strip thickness

Punc

h w

ear

(µm

2 )UHS Work Material – 1400

Mpa


Surface Coatings

Tool material Hardness Coating Die clearanceP/M 4%V 60 HRC TiN 6%, 10%P/M 4%V 60 HRC TiC (CVD) 6%, 10%P/M 4%V 60 HRC TiCN 10%P/M 4%V 60 HRC TiAlN 10%

Results after 100 000 strokes

All four examples showed spalled surface coatings



Wear Mechanism –6% die clearance

0

10 000

20 000

30 000

40 000

50 000

0 50 000 100 000 150 000 200 000 250 000

Number of blanks made

( S7) - 58 HRC

(D2) - 58 HRC

P/M 4%V - 58 HRC

Punc

h w

ear

(µm

2 )



Wear Mechanism after 140 000 StrokesAISI S7 AISI D2 P/M 4%V

“Constant” abrasive wear



Tool Steels

8% Cr Tool Steel

D2

P/M 4% V

P/M 4% V Improved

Appearance after 50 000 strokes

AHS Work Material – 1200 Mpa; Production Environment test of Blanking

Punch

Example 3


Uncoated punch

PVD coated with TiAlN

Galling problems with uncoated tool

No galling with coating

Comparison after 200 000 strokes Surface Coating



Other feedback with using alternative tooling materials with AHSS

• Caldie Bar Stock: New die steel an alternative:– Easily Weldable – Flame and Thru-Hardenable– Inserted into cast steel / iron base

• Can be used for forming, blanking and trimming of Advanced High Strength (AHS) work materials.

• Carmo Granshots: Castable Tool Steel– Has the ability to be through hardened

• Smaller cross sections– Easily Weldable– Easily flame-hardenable– Trim and Draw dies


Conclusion

• For Cold Rolling Roltec offers superior wear resistance and surface finish for cold forming rolls.

• Vanadis 4 Extra and Caldie give an excellent combination of chipping resistance, compressive strength and wear resistance for blanking and forming of AHSS


Great Tooling Starts Here!

www.bucorp.com1-800-METAL-20

Thanks for your attentionThanks for your attention

Any Questions?Any Questions?



Great Designs in Steel is Sponsored by:•AK Steel Corporation•Dofasco Inc.

•Severstal North America Inc.•United States Steel Corporation

•Mittal Steel Company•Nucor Corporation

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