MATERIAL SCIENCE ASSIGNMENT

TOPIC : AIR HARDENING STEEL

NAME ( ROLL NO)

1.VISHAL GUGNANI (9)

2.VISHWAS UPPAL (2)

3.PRANJAL BAWEJA (5)

4.SUVIR BHATOTIA (15)

5.SAMKIT SHAH (32)

6.KUMAR SHUBHAM (17)

BRANCH

MBA Tech CS

Submitted to

Prof. PRAFULL BRAHME

DATE OF SUBMISSION :

12.12.2011

AIR HARDENING TOOL STEEL

INTRODUCTION ABOUT TOOL STEELS :

Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures (red-hardness). Tool steel is generally used in a heat-treated state.

With a carbon content between 0.7% and 1.5%, tool steels are manufactured under carefully controlled conditions to produce the required quality. The manganese content is often kept low to minimize the possibility of cracking during water quenching. However, proper heat treating of these steels is important for adequate performance, and there are many suppliers who provide tooling blanks intended for oil quenching.

TYPES:

1. Water hardening grades2. Oil hardening grade3. Air hardening grade4. D – grade5. Shock resisting grades6. High speed grades7. Hot working grade

Air hardening steel :

These tool steels are used on larger parts or parts that require minimal distortion during hardening. The use of air hardening helps reducing distortion as opposed to higher stress caused by quicker water quenching. More alloying elements are used in these steels, as compared to water-hardening grades. These alloys increase the steels' harden ability, and thus require a less severe quenching process. These steels are also less likely to crack and are often used to make knife blades.

The first air hardening grade tool steel was mushet steel, which was known as air-hardening steel at the time.

Modern air-hardening steels are characterized by low distortion during heat treatment because of their high-chromium content. They also harden in air because they have less alloyants than oil-hardening grades. Their machinability is good for tool steels and they have a balance of wear resistance and toughness (i.e. between the D- and shock-resistant grades).

Composition :

A-2 :

A common general purpose tool steel; it is the most commonly used variety of air-hardening steel. It is commonly used for blanking and forming punches, trimming dies, thread rolling dies, and injection molding dies.

AISI A2 Air Hardening Tool Steel

(Machine finish) T & B WITH SAW-CUT EDGES (Machine finish) FOUR SIDES PRECISION GROUND HOLLOW BAR DRILL ROD

DESCRIPTION

An air-hardening tool steel containing five percent chromium. Replaces the oil hardening ( 0 1 type) when safer hardening, less distortion and increased wear-resistance are required. Provides an intermediate grade between the oil hardening and the high carbon, high chromium (d 2) types.

ADVANTAGES

Low distortion in heat-treatment Good machinability High abrasion-resistance and hardness Good toughness for severe service Deep hardening properties in large sections

TYPICAL ANALYSIS

CARBON…..1.00 MOLYBDENUM…..1.10 MANGANESE…..0.60

VANADIUM…..0.25 CHROMIUM…..5.25

A-6 :

This grade of tool steel air-hardens at a relatively low temperature (approximately the same temperature as

oil-hardening grades) and is dimensionally stable. Therefore it is commonly used for dies, forming tools, and gauges that do not require extreme wear resistance but do need high stability.

AISI A6 Air Hardening Tool Steel

Rounds Moneysaving thins Machine finished flats FOUR SIDES

DESCRIPTION

An air-hardening tool steel with properties similar to A4 and A5 with lower hardness and higher toughness. Dimensional stability with high hardenability and good impact strength is characteristic of this grade.

ADVANTAGES

Low distortion in heat treatment High hardenability Good toughness Medium wear resistance Machinability-medium

TYPICAL ANALYSIS

CARBON …………………0.70 MANGANESE ………………...2.00

MOLYBDENUM ………...1.00 CHROMIUM …………………..1.00

Microstructure :

Applications :

A-2AISI A2 takes a place in the Uddeholm tool steel

range between AISI O1 and AISI D2, offering anexcellent combination of good wear resistance andtoughness. It may be regarded, therefore, as a“universal” cold work steel.For cutting operations the good toughness ofAISI A2 gives excellent resistance to chipping ofthe cutting edge. In many cases tools made fromthis steel have given better tooling economy thanhigh-carbon, high-chromium steels of the D3/W.-Nr. 2080 type. AISI A2 has much better machiningand grinding properties.

A-6 :

Typical applications for A6 tool steel are blanking dies, forming dies, trim dies, stamping dies, coining dies, notching dies, bending tools, rim rolls, punches, cams, thread roll dies, spindles, retaining rings, master hobs, precision tools, mandrels, compression molds, plastic molds requiring high hardness, ball screws, lead screws, general purpose tooling, etc.

Heat treatment :

A-2

HEAT TREATMENT

FORGING……………… 2000° to 2050° F, stop at 1700°F, cool slowly

NORMALIZING……… Do not normalize

ANNEALING…………. 1650° F, furnace cool, average Brinell 212

PREHEATING………… 1200° F, prior to hardening

HARDENING…………. 1775° F, air quench to 150°F

TEMPERING………….. 350° to 400° F, resulting hardness, Rockwell C 60-61

MACHINABILITY

Machines easily when properly annealed to 212 Brinell. Has a factor of 65 as compared with a one percent carbon tool steel which has a rating of 100.

TEMPERING RESULTS

The Rockwell C hardness obtained on specimens 1 in square when quenched in air from 1800° F, and quenched in oil from 1750° F and tempered at various temperatures are as follows:

  Hardness Rockwell C

Tempering Temperatures F

1800 F Air-Quench

1750 F Oil-Quench

None 64 65

300 62 62.50

400 60 61

500 56 57.50

600 56 56

700 56 56

800 56 56

900 56 56

1000 56 55

1100 50 50

1200 43 45

1300 34 34

These results may be used as a guide in tempering tools to desired hardness. However, since 1 in. specimens were used in this test, tools of heavy section or mass may be several points lower in Rockwell hardness for a given treatment.

A-6 :HEAT TREATMENT

FORGING ………………………………..1900°F to 2050°F

NORMALIZING ………………………...Do not normalize

ANNEALING ……………………………1350°F to 1375° F

ANNEALED HARDNESS ………………217-248 BHN

PREHEATING ……………………………1200°F – prior to hardening

HARDENING …………………………….1525° – 1600°F, air quench to 150°F

TEMPERING RESULTS

Quenched @ 1550°F.

Tempering Temperatures °F

Hardness Rockwell C

200 61.5

300 60.5

400 59.0

500 57.5

600 56.0

700 54.5

800 52.5

900 50.5

1000 48.5