Alloy Steel

Definition: A steel to which one or more alloyingelements other than carbon have been deliberatelyadded (e.g. chromium, nickel, molybdenum) toachieve a particular physical property.

1. Nickel It increases the strength and toughness of the steel.

These steels contain 2 to 5% nickel and from 0.1 to0.5% carbon.

In this range, nickel contributes great strength andhardness with high elastic limit, good ductility andgood resistance to corrosion.

An alloy containing 25% nickel possesses maximumtoughness and offers the greatest resistance to rusting,corrosion and burning at high temperature.

Contd…

It has proved to be of advantage in the manufacture ofboiler tubes, valves for use with superheated steam,valves for I.C. engines and spark plugs for petrolengines.

A nickel steel alloy containing 36% of nickel is knownas invar. It has nearly zero coefficient of expansion. Soit is in great demand for measuring instruments andstandards of lengths for everyday use.

IES-1992Invar is used or measuring tapes primarily the to its

(a) Non-magnetic properties

(b) High nickel content

(c) Low coefficient of thermal expansion

(d) Hardenability

IES-2008Coefficient of Expansion is practically nil in a particular alloy. What is this alloy?

(a) Hadfield Manganese Steel

(b) Invar

(c) Vitallium

(d) Stellite

IES 2011Which one of the following is the major alloying elementin Invar?

(a) Aluminium

(b) Nickel

(c) Vanadium

(d) Copper

2. Chromium It is used in steels as an alloying element to combine

hardness with high strength and high elastic limit.

It also imparts corrosion-resisting properties to steel.

The most common chrome steels contains from 0.5 to2% chromium and 0.1 to 1.5% carbon.

The chrome steel is used for balls, rollers and races forbearings.

A nickel chrome steel containing 3.25% nickel, 1.5%chromium and 0.25% carbon is much used for armourplates. Chrome nickel steel is extensively used formotor car crankshafts, axles and gears requiring greatstrength and hardness.

3. Tungsten It prohibits grain growth, increases the depth of

hardening of quenched steel and confers the propertyof remaining hard even when heated to red colour.

It is usually used in conjunction with other elements.

Steel containing 3 to 18% tungsten and 0.2 to 1.5%carbon is used for cutting tools.

The principal uses of tungsten steels are for cuttingtools, dies, valves, taps and permanent magnets.

IES-2004For improving the strength of steel at elevated temperatures, which one of the following alloying element is used?

(a) Copper

(b) Tungsten

(c) Aluminium

(d) Zinc

4. Vanadium It aids in obtaining a fine grain structure in tool steel.

The addition of a very small amount of vanadium (lessthan 0.2%) produces a marked increase in tensilestrength and elastic limit in low and medium carbonsteels without a loss of ductility.

The chrome-vanadium steel containing about 0.5 to1.5% chromium, 0.15 to 0.3% vanadium and 0.13 to 1.1%carbon have extremely good tensile strength, elasticlimit, endurance limit and ductility.

These steels are frequently used for parts such assprings, shafts, gears, pins and many drop forged parts.

GATE-1997The alloying element mainly used to improve the endurance strength of steel materials is

(a) Nickel

(b) Vanadium

(c) Molybdenum

(d) Tungsten

IES-2000Addition of vanadium to steel results in improvement of

(a) Heat-treatability by quenching

(b) Hardenability

(c) Fatigue strength

(d) Resistance to oxidation at elevated temperature

5. Manganese It improves the strength of the steel in both the hot

rolled and heat treated condition.

The manganese alloy steels containing over 1.5%manganese with a carbon range of 0.40 to 0.55% areused extensively in gears, axles, shafts and other partswhere high strength combined with fair ductility isrequired.

The principal uses of manganese steel is in machineryparts subjected to severe wear. These steels are all castand ground to finish.

IESAlloy steel which is work hardenable and which is used to make the blades of bulldozers, bucket wheel excavators and other earth moving equipment contain iron, carbon and

(a) Chromium

(b) Silicon

(c) Manganese

(d) Magnesium.

6. Silicon The silicon steels behave like nickel steels.

These steels have a high elastic limit as compared toordinary carbon steel.

Silicon steels containing from 1 to 2% silicon and 0.1 to0.4% carbon and other alloying elements are used forelectrical machinery, valves in I.C. engines, springs andcorrosion resisting materials.

ISRO-2015

Silicon steel is widely used in

(a) Cutting Tools

(b) Dies and Punches

(c) Electrical Industry

(d) Chemical Industry

7. Cobalt It gives red hardness by retention of hard carbides at

high temperatures.

It tends to decarburise steel during heat-treatment.

It increases hardness and strength and also residualmagnetism and coercive magnetic force in steel formagnets.

IES 2010Some high speed steels have cobalt (Co)added to them in amounts ranging from 2%to 15%, since this element improves the

(a)Cutting efficiency, especially at hightemperature

(b) Depth hardening ability of the HSS tool

(c) Red hardness of the HSS tool

(d) Grain structure of the HSS tool

8. Molybdenum A very small quantity (0.15 to 0.30%) of molybdenum

is generally used with chromium and manganese (0.5to 0.8%) to make molybdenum steel.

These steels possess extra tensile strength and are usedfor air-plane fuselage and automobile parts. It canreplace tungsten in high speed steels.

9. Boron Boron (not exceeding 0.003%) is a very powerful

hardenability agent, being from 250 to 750 times aseffective as nickel, 75 to 125 times as effective asmolybdenum, and about 100 times as powerful aschromium.

Only a few thousandths of a percent are sufficient toproduce the desired effect in low-carbon steels, but theresults diminish rapidly with increasing carbon content.

Since no carbide formation or ferrite strengthening isproduced, improved machinability and cold-formingcapability often result from the use of boron in place ofother hardenability additions.

It has no effect on tensile strength of steel.

IES-1992Small percentage of boron is added to steel to

(a) Increases hardenability

(b) Reduce machinability

(c) Increases wear resistance

(d) Increase endurance strength

10. sulphur It is an undesirable impurity in steel because its forms

iron sulphide, which can result in cracking.

However, in the presence of proper amount of Mn, it forms Mn S which improves the machinability of steels.

Its content may very from 0.06 - 0.30%.

11. Copper Copper has been known to resist atmospheric corrosion

for centuries, but only recently has it been used as anaddition to steel (in amounts from 0.10 to 0.50%) toprovide this property.

Low-carbon steel sheet and structural steels often containa copper addition to enhance corrosion resistance, butsurface quality and hot-working behavior tend todeteriorate somewhat.

Alloy Steel at a glanceDo-not form carbide: nickel, Silicon, Aluminium

Carbide forming order: Manganese, chromium, Tungsten, Molybdenum, vanadium, titanium, niobium.

(1) Manganese: Toughness & ductility

Machinability with sulphur

(2) Chromium: Corrosion resistance

Wear resistance , hardness

(3) Nickel: toughness

Contd…

(4) Tungsten, Molybdenum, Vanadium: hot hardness

Tungsten wear resistance,

Vanadium: endurance limit

Molybdenum creep property

(5) Si & Al deoxidizer, restrict grain growth

Si Magnetic permissibility

(6) Cobalt: hardenability

Impact strength

(7) Phosphorus: reduce strength to impact conductivity of copper

(8) Copper: Raises yield point

(9) Magnesium: because light weight it is used where weight is important.

Super alloy: Is for high temperature use [jet engine, gas turbine blade etc]

Ex: Hastelloy X

C – 0.1%

Mn – 1 %

Cr – 21.8%

Si – 1%

Ni – balance

Co – 2.5%

Mo – 9%

W – 0.6 %

Fe – 18.5%

IES 2011Match List –I with List –II and select the correct answer usingthe code given below the lists :

Codes

A B C D A B C D

(a) 1 2 3 4 (b) 4 3 2 1

(c) 1 3 2 4 (d) 4 2 3 1

List –I List –II

A. Copper 1. Corrosion

B. Nickel 2. Demagnetization

C. Manganese 3. Non Sparking

D. Vanadium 4. Deformation restriction

IES – 1996Which of the following pairs regarding the effect of alloying elements in steel are correctly matched?

1. Molybdenum: Forms abrasion resisting particles.

2. Phosphorus: Improves machinability in free cutting steels.

3. Cobalt: Contributes to red hardness by hardening ferrite.

4. Silicon Reduces oxidation resistance

Select the correct answer using the codes given below:

(a) 2, 3 and 4 (b) 1, 3 and 4

(c) 1, 2 and 4 (d) 1, 2 and 3

IES-1992Match the following:

List I (Alloying element in steel) List II (Effect)

A. Lead 1. Restricts grain growth

B. Aluminium 2. Raises yield point

C. Copper 3. Reduces strength to impact

D. Phosphorus 4. Free machining

Codes:A B C D A B C D

(a) 1 2 3 4 (b) 2 3 4 1

(c) 3 4 1 2 (d) 4 1 2 3

IAS-1995Assertion(A): In high speed steels, alloying elements tungsten, chromium and vanadium are added to make them suitable to work at higher speeds than tool steel or low alloy steels.Reason(R): Vanadium adds to the property of red hardness and tungsten and chromium add to high wear resistance.(a) Both A and R are individually true and R is the correct

explanation of A(b) Both A and R are individually true but R is not the

correct explanation of A (c) A is true but R is false(d) A is false but R is true

IAS-2002Watch List I (Alloying elements for tool steel) with List II (Improved mechanical property) and select the correct answer using the codes given below the ListsList I List II(Alloying elements for tool steel) (Improved

mechanical property)A. Carbon 1. HardnessB. Manganese 2. Hot HardnessC. Chromium 3. Lower Critical

TempD. Vanadium 4. Toughness

Codes:A B C D A B C D(a) 1 3 4 2 (b) 2 4 3 1 (c) 1 4 3 2 (d) 2 3 4 1

Stainless Steel They typical consists min.12% Cr along with other

alloying elements, thus highly corrosion resistantowing to presence of chromium oxide.

Three kinds - ferritic & hardenable Cr steels, austeniticand precipitation hardenable (martensitic, semi-austenitic) – based on presence of prominent micro-structural constituent.

Typical applications – cutlery, surgical knives, storagetanks, domestic items.

Ferritic steels are principally Fe-Cr-C alloys with 12-14%Cr. And small additions of Mo, V, Nb, Ni.

Contd…

Austenitic steels contain 18% Cr and 8% Ni plus minoralloying elements. Ni stabilizes the austenitic phaseassisted by C and N.

For, martensitic steels Ms is made to be above theroom temperature. These alloys are heat treatable.Major alloying elements are: Cr, Mn and Mo.

Ferritic and austenitic steels are hardened andstrengthened by cold work because they are not heattreatable.

Austenitic steels are non-magnetic as against ferriticand martensitic steels, which are magnetic.

Contd…

Austenitic stainless steels are non-magnetic and arehighly resistant to corrosion 304 alloy is 18-8 when 18%chromium & 8% nickel used costly material.

Austenitic stainless steels usually contain 18% Cr and8% Ni in addition to other minor alloying elements. Nistabilizes the austenitic phase assisted by C and N.Other alloying additions include Ti, Nb, Mo (preventweld decay), Mn and Cu (helps in stabilizingaustenite).

These steels are very tough and can be forged androlled but offer great difficulty in machining.

These steels cannot be hardened by quenching, in factthey are softened by rapid cooling from about 1000°C.

IES-2002The correct composition of austenitic stainless steel used for domestic utensils is

(a) 0.08% C, 18% Cr, .8% Ni, 2% Mn, 1% Si

(b) 0.08% C, 24% Cr, 12% Ni, 2% Mn, 1% Si

(c) 0.15% C, 12% Cr, 0.5% Ni, 1% Mn, 1% Si

(d) 0.30% C, 12% Cr, 0.4% Ni, 1% Mn, 1% Si

IES-2008Consider the following statements in respect of austenitic stainless steels:

1. Austenitic stainless steels are hardened and strengthened by cold working.

2. Austenitic stainless steels cannot be quenched and tempered.

Which of the statements given above is/are correct?

(a) 1 only (b) 2 only

(c) Both 1 and 2 (d) Neither 1 nor 2

IES-1997Assertion (A): Austenitic stainless steel contains 18% chromium and 8% nickel. Since it retains its austenitic structure at room temperature, it is called austenitic stainless steel.Reason (R): Chromium present in the steel improves its corrosion resistance by forming a thin film of chromium oxide on the surface.(a) Both A and R are individually true and R is the correct

explanation of A(b) Both A and R are individually true but R is not the

correct explanation of A (c) A is true but R is false(d) A is false but R is true

IES-2009Which one of the following elements is an austenitic stabilizer?

(a) Chromium

(b) Tungsten

(c) Nickel

(d) Molybdenum

IES-2009Which one of the following elements is a ferriticstabilizer?

(a) Nickel

(b) Manganese

(c) Copper

(d) Chromium

IES-2004Match List I (Name of alloy) with List II (Major alloying elements) and select the correct answer using the codes given below the Lists:List I List IIA. Invar 1. ManganeseB. Hadfield steel 2. ChromiumC. Stellite 3. NickelD. Stainless steel 4. Tungsten

5. MolybdenumCodes:A B C D A B C D

(a) 5 1 4 2 (b) 3 2 5 1(c) 5 2 4 1 (d) 3 1 5 2

IES-2005Match List I (Alloying Element) with List II (Effect on Steel) and select the correct answer using the code given below the Lists:

List I List II

A. Vanadium 1. Increases endurance strength

B. Molybdenum 2. Improves creep properties

C. Silicon 3. Increases hardness

D. Chromium 4. Increases resistance to high temperature oxidation

Codes:A B C D A B C D

(a) 2 1 3 4 (b) 1 3 2 4

(c) 2 1 4 3 (d) 1 2 3 4

IESMatch List-I (Alloying element in steel) with List-II (Property conferred on steel by the element) and select the correct answer using the codes given below the lists:List-I List-IIA. Nickel 1. Corrosion resistanceB. Chromium 2. Magnetic permeabilityC. Tungsten 3. Heat resistanceD. Silicon 4. Hardenability

Codes:A B C D A B C D(a) 4 1 3 2 (b) 4 1 2 3(c) 1 4 3 2 (d) 1 4 2 3

IES-2008Which of the following elements given below determine(s) the maximum attainable hardness in steel?

1. Chromium 2. Manganese

3. Carbon 4. Molybdenum

elect the correct answer using the code given below:

a) 1 only (b) 1 and 2

(c) 3 only (d) 2 and 4

IES 2010Consider the following statements:

Alloying elements are added to

1. Improve hardness and toughness.

2. Corrosion and oxidation resistance improvement.

3. Improve machinability and hardenability.

4. Increase weight and volume.

Which of the above statements are correct?

(a) 1, 2 and 3 only (b) 2, 3 and 4 only

(c) 1, 2 and 4 only (d) 1, 2, 3 and 4

DESIGNATION OF STEEL, (INDIAN STANDARD)

Two systems of notation are recommended by IS :

(a) Based on ultimate tensile strength.

(b) Based on chemical composition.

(a) Based on Ultimate Tensile Strength: This isapplicable to carbon and low alloy steels.

The symbol consists of the letter St followed by thenumber representing the ultimate tensile strength inkgf/mm2 , for example, St 32. The new coding consistsof the letter Fe followed by the number representingthe ultimate tensile strength in N/mm2 , for example,Fe 410.

Contd…

(b) Based on Chemical Composition: This type ofdesignation is preferred if subsequent heat treatmentis carried out.

1. Plain Carbon Steels: These are designated by letterC followed by a number representing the averagepercentage carbon content, for example, C 14 - carbonsteel with 0.14%, C.

Its new designation is 14 C4. Here, the first figureindicates 100 times the average of Carbon content,then letter C, and the last figure indicates 10 times theaverage percentage of Mn content rounded off to thenext integer.

Contd…

2. Alloy Steels: Here the letter C is omitted and thenumbers representing the carbon content are followed bychemical symbols for one or more of the predominantalloying elements followed by numbers indicating theiraverage contents, for example, 15 Cr 65 - chromium steelwith 0.15°%,C and 0.65% Cr.

20 Cr 18 Ni 2 - Nickel - chromium steel with 0.2% C, 18%Cr and 2% Ni.

The coding of the alloy steels is given below :- The averagealloy content upto 1 per cent, Alloy index number will be : -Average alloy content upto two decimal places, underlinedby a bar. For average alloy content one per cent and above,alloy index number will be : rounded to the nearest wholenumber upto 0.5 rounded down and above rounded up.

IES-2001The alloy steel designated as 40 Cr18 Ni 2 by Bureau of Indian Standards contains

(a) 0.4% C, 18% Cr and 2% Ni

(b) 4.0% C, 1.8% Cr and 0.2% Ni

(c) 0.4% C, 1.8% Cr and 2% Ni

(d) 0.4% C, 1.8% Cr and 0.2% Ni

IES-199618/8 stainless steel contains

(a) 18% stainless, 8% chromium.

(b) 18% chromium, 8% nickel.

(c) 18% tungsten, 8% nickel.

(d) 18% tungsten, 8% chromium.

The End