Cast iron 5 (i)

Classification of Cast ironCast iron are classified according to various criteria as below1) On the basis of furnace used in their manufacturing. i) Cupola Cast irons ii) Air furnace cast irons iii) Electric furnace cast irons iv) Duplex cast irons

2) On the basis of composition and purity. i) Low carbon, low silicon cast iron ii) High carbon, low sulphur cast iron iii) Nickel alloy cast iron

3) On the basis of microstructure and appearance i) white cast iron ii) Malleable cast iron iii) Grey cast iron iv) Nodular cast iron v) Mottled cast iron vi) Chilled cast iron vii)Alloy cast iron

White Cast iron

Composition of white Cast iron

MICROSTRUCTURE OF WHITE CAST IRON

CESSMEALLIABLIZING HEAT TREATMENT PROCESS

MICROSTRUCTURE OF MALLEABLE CAST IRON

PEALITIC-FERRITIC MEALIABLE CAST IRON

T.S. = 15 – 40 kg/mm2Hardness = 150-300 BHN. Ductility = less 1 %.

PROPERTIES OF GRAY CAST IRON

COMPOSITION OF GRAY CAST IRON

MICROSTRUCTURE OF GRAY CAST IRON

Types of graphite flakes in gray cast iron

i)Type A: - The most desirable flake pattern in gray cast iron in uniform distribution and random orientation of type A.

ii) Type B: - type b shows rosettes pattern & shorter length, get concentrated at the particular regions.

iii) Type C: - type C shows large and straight flakes with random orientation.

iv) Type D: - type d shows interdendritic segregation & randomly oriented over the microstructure.

v)Type E: - Graphite is randomly present over the microstructure in the form of nodules & length.

Hardness = 100-300 BHN.Ductility = 6-20 %T.S.= 38-80 kg/mm2

PROPERTIES OF NODULAR CAST IRON

microstructure OF NODULAR CAST IRON

microstructure OF mottled CAST IRON

Applications of nodular cast iron i) In agriculture – tractor and implement parts

ii) In automotive – crankshaft, piston and cylinder heads.

iii) Electrical fittings, switch boxes, motor frames, circuit breaker parts.

iv) In mining – hoist drums, drive pulley, flywheels, elevator buckets.

v) Steel mills- work rolls, furnace doors, table rolls and bearings.

vi) Tool and dies – wenches, levers, handles, chuck bodies, and dies for shaping non ferrous metals and alloys.

) FG 35 Si15

Average silicon percent x 10 = 1.5 x 10 =15Total carbon percent x 10 = 3.5 x 10 = 35Gray iron casting

a) Laminated materials b) particulate composite

c) Flake composite d) fiber composites

e)Fiber reinforced material f)filled composite

g) Laminar composites

h) dispersion strengthened composites

Purpose of alloyingi)To increase hardenibility.ii) To increase strength at ordinary temperatureiii) To improve high temperature propertiesiv) To increase wear resistancev) To increase toughness at any minimum hardnessvi) To increase resistance to oxidation and corrosionvii) They do not soften rapidly at high temperatures and retain high hardness for a long time.viii) More uniform properties throughout the cross section.

Effects of Alloying Elements

Solid solution StrengtheningCr, Ni, Al, Si.

Carbide formation V, Ti, Mo, W, Cr.

Formation of intermediate compoundsNi, Si, Al, W, V, Cr

Formation of Inclusions Si, Al, Mn, Cr, V.

Shifting of critical temperature Ni Mg

Effect on Hardenability

Other Effects •The corrosion and oxidation resistance may increase.

•Creep strength may get increase due to the presence and dispersion of fine carbide.

•Fatigue strength may also get increased.

Classification of Alloying Elements

Carbide forming elements e.g. Ti, V, W, Mo, Cr, Mn.

Graphitizing Elements- e.g. Si, Ni, Cu and Al.

Austenite Stabilizers- e.g. Ni, Mn, Cu, C, N etc.

Ferrite Stabilizerse.g. Cr, W, Mo, V, Si, Al etc.

Neutral Elements – Cobalt

1.Classification of Alloy Steels1) Free cutting steels: -Mg ,S and phosphorus

S and P are in 0.6 and 0.12% while Mg is 5 to 8 times the amount of sulphur. In high carbon steels lead is added in 0.35 % to increase machinability.

2) High strength low alloy steels: - C-0.07 % to 0.13 % with 0.5 Al.

3) Maraging steels :-

0.03 % C , Ni = 18-25 % ,Mo= 3-5 % ,Co= 3 to 8%, Ti=0.2 to 1.6 % and small amount Al. used for special application such as rocket, engine component and Pressure vessel.

4) Dual Phase steels: This steel shows high tensile strength and widely used for wheels, bumpers, disc, door panels etc. because of better formability.

5) Creep resisting steels: - Temperature resistance is increased by addition of W, Mo, V, Cr and Co.

6) High temperature alloys (Super alloys):-

They have high strength, hardness, wear resistance, creep resistance and oxidation resistance. They are iron base, Nickel base, cobalt base and refractor metals and alloys.

7) Low expansion steels: 36%Ni, 0.2%C, 0.5% Mn and balance iron.

8) Alloys for heating elements: -

Nicromes (nickel-chromium alloy)-temp.range is 11500C. 78.5%Ni,20%Cr and 1.5%Si.

Kanthal alloy (Iron +Chromium +aluminum).temp. range 13000C. 55%Fe,37.5%Cr,7.5% Al.

Platinum-14500C,

M,W-1750-25000C

Stainless steel shows following properties along with corrosion resistance

•High ductility.

•Good mechanical properties at low and high temperature.

•Good machinability.

•Good weldability.

•Excellent surface finish and appearance.

•Wide range of strength and hardness.

•Higher corrosion resistance.

•Oxidation and scaling resistance.

•Good creep resistance.

• Easy cold working property.

Classification of stainless steelsCr -12 to 18 % C-0.15 to 1.2 %.

They are hard and magnetic in character and used for springs, ball bearings, razors, pump shaft, paper machinery parts and surgical instruments etc.

1) Group A

2) Group BCr 13-27 % & C 0.08 -0.2 %.

Because of their fairly good formability, corrosion resistance and available at lower cost. They are widely used for vessels, furnace parts, heat exchanges heater, juice carrying pipes in sugar Industries.

3) Group C Cr+ Ni+ Mn= 24% in which Cr is 18

The corrosion resistance of the steel these steel is more than others and increase with increasing Ni and Cr amount. They are used for engines, food and chemical plants, tubular exchangers, wrist watches etc.

4) Precipitation Hardenable stainless steel Mo, Al or N in additions to Cr and Ni.

Used in aircraft and missile industries as materials for skins, nibs, bulkheads and other structural components.

Tools steels are used for shaping and cutting of metals. And classified as follows•Cold work tool steels•Hot work tool steels•High speed tool steels•Special purpose tools steels.

1) Cold work tool steels: - These steels are generally used for cold working of metals. They have good hardness and wear resistant at low temperature.Depending on the hardening characteristics they are classified as i) Water hardening steels (w-series) ii) Oil hardening steels.Iii) Air hardening steels.iv) High carbon high chromium steels.

i) Water Hardening Steels: -

C- 0.6 to 1.4%.Generally used for dies, hammers, chisels, and wood working tools.

ii) Oil Hardening Steels:

C - 1 %, Mn - 0.95 %, W - 0.5 %, Cr - 0.75 % V - 0.2 %.

These steels generally used for cutting tools and gauges.

iii) Air Hardening Steels: - Mn, Cr, Mo and W

Used for rolling and drawing dies.

iv) High Carbon High Chromium Steels: carbon above 2% and Cr – 12 % with W, Mo, V in small amount.

used in cutting tools, gauges, rolling and forming dies.

2) Hot Work Tools Steels: -

good strength, toughness, hardness and wear resistant at elevated temperature. Content of C is 0.35-0.65 % and classified according to principal alloying elements as below.

a) Chromium type: - These steels contain 3-7 % carbon with other alloying elements Mo, W, V. Because of their high ductility they are used for aluminum and magnesium dies, casting dies.

b) Tungsten tool steels: - These contains 9-18 % W and of 2-12 % Cr. They have excellent hardness and wear resistance. Used for extrusion dies for brass nickel and steel.

c) Molybdenum Tool Steels: - These steels contain 14-20 % Mo. Generally used where resistance is high temperature and toughness is required.

3) High Speed Tools Steel: - These steels maintain high hardness up to 550 o C and used for cutting of metals at high speeds. They also have high wear resistance and cutting ability. High speeds steels are of two types according principal alloying element.

a) Tungsten high speed tool steels: - these steels contains high amount of W and other elements as Cr, V & Co in smaller amount.

b) Molybdenum steels: - molybdenum steels are cheaper but cannot used widely because they subjected to oxidation and decarburization during heat treatment. These steels are used for drills taps, milling cutter, lathe tools and punches.

4) Special Purpose Tools Steels: -

Steels under these groups are as describe belowi) Shock resisting tool steels: -

It contain less than 0.5 % C.These steels shows less hardness and wear resistance and increase with addition of Mn, Cr, W, Mo, V and Si. Where Si, Mo increases strength, toughness and shock resisting properties while other elements increases hardness and wear resistant.ii) Low alloy steels: - Similar in characteristics to water hardening

tool steels. Generally used where high wear resistance and toughness are required.

iii) Carbon-tungsten tool steels: - It contains carbon less than 0.1 % with tungsten as alloying item. They have higher wear resistance.

iv) Mould steels: - these steels are used for plastic moulds. Ni and Cr added to increase its molding ability.