Alloy Steel: Low, medium and High alloy steel, Properties of Tool steel, Classification of Tool steel, Stainless Steel, Austenitic Stainless Steel, Ferritic stainless steel and Martensitic stainless steel ~ MECHTECH GURU

Alloy Steel: Low, medium and High alloy steel, Properties of Tool steel, Classification of Tool steel, Stainless Steel, Austenitic Stainless Steel, Ferritic stainless steel and Martensitic stainless steel

Alloy Steel

Steel is considered to be alloy steel when the maximum of the range given for the content of alloying element exceeds one or more of the following limits.

Mn-1.65%, Si-0.6%, Cu-0.6%

or in which a definite maximum quantity of any of the following elements is specified.

Al, B, Cr up to 3.99%, Cu, Mo, Ni,Ti, W, V or any other alloying element added to obtain a desired alloying effect.

Low and medium alloy steel

In low and medium alloy steel alloying element is not exceeding 10%.

High alloy steel

In high alloy steel, total alloying element is more than 10%.

For example: X10 Cr18 Ni9 S3

X- High alloy steel

10 %- 0.1 %C

Cr18 – 18 % Cr

Ni 9 – 9 % Ni

S 3 – Pickled condition

Tool Steel

Tool steel may be defined as special steel which are used to form, cut or otherwise change the shape of a material in to finished 0r semi-finished product.

Properties of Tool steel

i) Slight change of form during hardening.

ii) Little risk of cracking during hardening.

iii) Good toughness

iv) Good wear resistance

v) Very good machinability

vi) A definite cooling rate during hardening

vii) A definite hardening temperature

viii) Resistance to de-carburization

ix) Resistance to softening on heating

Classification of Tool steel

The Joint Industry Conference, U.S.A. has classified tool steel as follows:

Symbol                   Meaning

T                      W-High speed steel

M                     Mo-High speed steel

D                     High C, high Cr steel

A                      Air hardening steel

O                     Oil hardening steel

W                     Water hardening steel

H                      Hot work steel

S                      Shock resistance steel

Composition of Tool Steel

1) W-High speed steel

T1: C -0.7, Cr- 4, V- 1, W -18

T4: C -0.75, Cr- 4, V- 1, W- 18, Co- 5

T6: C- 0.8, Cr -4.5, V- 1.5, W- 20, Co- 12

2) Mo-High speed steel

M1: C- 0.8, Cr- 4, V- 1, W- 1.5, Mo- 8

M6: C- 0.8, Cr- 4, V- 1.5, W- 4, Mo- 5, Co- 12

3) High C, high Cr steel

D2: C -1.5, Cr- 12, Mo- 1

D5: C- 1.5, Cr- 12, Mo- 1, Co- 3

D7: C- 2.35, Cr- 12, V- 4, Mo- 1

4) Air hardening steel

A2: C- 1, Cr- 5, Mo- 1

A7: C- 2.25, Cr- 5.25, V- 4.75, W- 11, Mo- 1

A9: C- 0.5, Cr- 5, Ni- 1.5, V- 1, Mo- 1.4

5) Oil hardening steel

O1: C- 0.9, Mn- 1, Cr- 0.5, W- 0.5

O2: C- 1.45, Si- 1, Mo- 0.25

6) Water hardening steel

W2: C- 0.6/1.4, V- 0.25

W5: C- 1.1, Cr- 0.5

7) Hot work steel

H10: C- 0.4, Cr- 3.25, V- 0.4, Mo- 2.5

H12: C- 0.35, Cr- 5, V- 0.4, W- 1.5, Mo- 1.5

8) Shock resistance steel

S1: C- 0.5, Cr- 1.5, W- 2.5

S2: C- 0.5, Si- 1, Mo- 0.4

S5: C- 0.55, Mn- 0.8, Si- 2, Mo- 0.4

S7: C- 0.5, Cr- 3.25, Mo- 1.4

Stainless Steel

When 11.5% or more chromium is added to iron, a fine film of chromium oxide forms spontaneously on the surfaces. The film acts as a barrier to retard further oxidation, rust or corrosion. As this steel cannot be stained easily, it is called stainless steel. The stainless steel basing on their micro-structure can be grouped in to three metallurgical classes such as Austenitic stainless steel, Ferritic stainless steel & Martensite stainless steel.

Austenitic Stainless Steel

Properties of Austenitic Stainless Steel

1) They possess austenitic structure at room temperature.

2) They possess the highest corrosion resistance of all the stainless steels.

3) They possess greatest strength and scale resistance at high temperature.

4) They retain ductility at temperature approaching absolute zero.

5) They are non-magnetic.

Composition of Austenitic Stainless Steel

C- 0.03 to 0.25%, Mn- 2 to 10%, Si- 1 to 2%, Cr- 16 to 26%, Ni- 3.5 to 22% P & S Normal, Mo & Ti in some cases

Uses of Austenitic Stainless Steel

1) Aircraft industry (Engine parts)

2) Chemical processing (heat exchangers)

3) Food processing (Kettles, tanks)

4) Household items (cooking utensils)

5) Dairy industries (milk cans)

6) Transportation industry (Trailers & railways cars)

Ferritic stainless steel

Properties of Ferritic stainless steel

1) They posses a microstructure which is primarily ferritic.

2) They are magnetic & have good ductility

3) They do not work harden to any appreciable degree.

4) They are more corrosion resistant than martensitic steel.

5) They develop their maximum softness, ductility & corrosion resistance in the annealed condition.

Composition of Ferritic stainless steel

C- 0.08 to 0.20%, Si- 1%, Mn- 1 to 1.5%, Cr- 11 to 27%

Uses of Ferritic stainless steel

1) Lining for petrolium industry.

2) Heating elements for furnaces.

3) Interior decorative work.

4) Screws & fittings.

5) Oil burner parts.

Martensitic stainless steel

Properties of Martensitic stainless steel

1) They posses martensitic microstructure.

2) They are magnetic in all condition & possess the best thermal conductivity of the stainless types.

3) Hardness, ductility & ability to hold an edge are characteristics of martensitic steels.

4) They can be cold worked without difficulty, especially with low carbon content, can be machined satisfactorily.

5) They have good toughness.

6) They have good corrosion resistance to weather and to some chemicals.

7) They are easily hot worked.

Composition of Martensitic stainless steel

C- 0.15 to 1.2%, Si- 1%, Mn- 1%, Cr- 11.5 to 18%

Uses of Martensitic stainless steel

1) Pumps & valve parts

2) Rules & tapes

3) Turbine buckets

4) Surgical instruments, etc.

Alloy steel
Alloy steel

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