Plain Carbon Steels

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PLAIN CARBON STEELS

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Ferrous Metals The Iron–Carbon System Cooling transformation for a

Steel with a Eutectoid CompositionCooling transformation for a Steel

with a Hypo-Eutectoid CompositionCooling transformation for a Steel

with a Hyper-Eutectoid CompositionCritical change pointsThe Effect of Carbon on the

properties of Plain Carbon Steels

Plain Carbon Steels

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FERROUS METALS

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Ferrous Metals Ferrous metals and alloys

are based upon the metallic element iron.

Comes from the Latin name of Iron, ferrum.

Iron is a soft, grey metal and it is rarely found in the pure state outside the laboratory.

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Table 4.1 Ferrous Metals

Name Group Carbon Content (%) Some UsesLow Carbon Steel

Medium Carbon Steel

High-carbon Steel

Grey cast iron

Plain Carbon Steel

Plain Carbon Steel

Plain Carbon Steel

Plain Carbon Steel

Cast iron

0.1-0.15

0.15-0.30.3.0.5

0.5-0.80.8-1.01.0-1.2

1.2-1.43.2-3.5

Sheet for pressing out such shapes as motor car body panels. Thin wire, rod, and drawn tubes

General purpose workshop bars, boiler, girders

Crankshaft forgings, axlesLeaf Springs, cold chiselsCoil springs, wood chisels

Files, drills, tap and die fine-edged tools (knives, etc.)

Machine castings

It shows the relationship between the amount of the carbon present and the resulting ferrous metals.

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The Iron-Carbon System

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THE CHANGE FROM FACE-CENTERED TO BODY CENTERED CRYSTALS RELEASES LATENT HEAT ENERGY MORE RAPIDLY THAT IT CAN BE DISSIPATED AND THE TEMPERATURE OF ROD MOMENTARILY RISES AND FOR A MOMENT, IT GLOWS

MORE BRIGHTLY.

RECALESCENCE

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4.2.1 Iron-carbon phase equilibrium diagram

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4.2.2 Effect of lattice change in volumea. Change in volume as crystal lattice rearranges them;

b. Method of demonstrating volume changes in temperature

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4.2.3 Iron-carbon phase equilibrium diagram (Steel Section)

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Three Important Phases

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FERRITE

This is a weak solution of carbon in a body-center cubic crystals of iron. It is a very

soft ductile and of relatively low strength.

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Austenite

This is a much concentrated solid solution of carbon in iron that ferrite. It is form

when carbon dissolves in face-center cubic crystals of iron in solid state.

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Cementite

An excess of carbon combines with iron to form iron carbide.

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Explanation of the Iron-phaseDiagram

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Eutectoid Composition

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THE POINT AT WHICH FERRITE AND CEMENTITE (IRON

CARBIDE) PRECIPITATE OUT FROM THE SOLID SOLUTION

AUSTENITE.

Eutectoid Point

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Cooling transformation for a steel with a eutectoid

composition

The transformation which occurs during the cooling of eutectoid

composition (0.83 percent carbon).

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Fig. 4.3.1 a 0.83% carbon steel

EUTECTOID TRANSFORMATION LAMELLAR PEARLITE

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Cooling transformation for a steel with a hypo-eutectoid

compositionDuring this transformation, the steel contains 0.5

percent carbon. Again, the steel will commence to solidify at temperature (T) and

dendrites of body-centered-cubic (BCC) crystals of x-phase composition will begin to

form.

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Fig. 4.4.1 An annealed 0.5% carbon steel

HYPO-EUTECTOID TRANSFORMATION (UPPER)

TYPICAL MICROSTRUCTURE(LOWER)

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Cooling transformation for a steel with a hyper-eutectoid

compositionThe transformation which occurs during the

cooling of a hyper-eutectoid steel of 1.2 percent carbon content. This time,

solidification commences at temperature (T) and is complete by the time the steel has

cooled to temperature.

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Fig. 4.3.1 An annealed 12% carbon steel

HYPER-EUTECTOID TRANSFORMATION

TYPICAL MICROSTRUCTURE

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Critical change points

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THE CHANGE POINTS ARE OFTEN REFERRED TO SIMPLISTICALLY, AS THE UPPER CRITICAL

TEMPERATURE (UCT) AND THE LOWER CRITICAL TEMPERATURE (LCT).

Critical change points

26Fig. 4.6 Critical change points for carbon steels

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The effect of carbon on the properties of plain carbon

steels

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Fig. 4.7 properties of plain carbon steelsThis shows the effect of the carbon content upon the

properties of plain carbon steels which have been cooled slowly enough to enable them to achieve phase

equilibrium.

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Plain carbon steels

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MANGANESE

This is an essential constituent element since it ensure the sound ingot in from blow holes. It combines with

any Sulfur present which would otherwise weaken the steel.

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Phosphorus

This is an impurity carried over form the iron ore. It forms

compound which made the steel brittle, and therefore, should removed as far as possible during the refinement process.

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Silicon

Its presence should be limited between 0.1 to 0.3 in the steels otherwise it can cause breakdown in cementite which would result in weakness. It has a little directly

effect upon the mechanical properties of plain carbon steels providing the amount present is limited to the percentage quoted above.

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Sulphur

This is an impurity carried over from fuel used in blast furnace to extract the iron from its ore. It tends to

combine with the iron to form iron sulphide which greatly weakens the steel.

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Table 4.8.1 some plain carbon steelsIt gives the composition, properties and typical applications of some general purpose of

plain carbon steels, together with reference to their British Standard specifications.

Types of Steels

British Standards Composition (%) Condition Properties Applications

C Mn Yp(Mpa)

UTS(Mpa)

Elong.(%)

Impact(J)

Hardness(HB)

Low- carbon steels

BS970.040

A10

0.1 0.4 Process annealed after cold rolling

- 300 28 - - Car body panels produced by drawing and pressing.

BS 15 0.2 - As rolled 240 450 25 - - General purpose mild steel. Welding quality, high tensile mild steel for building construction, etc.

BS 968 0.2 1.5 As rolled 350 525 20 - -Casting steel BS

1504/161B0.3 - Annealed after

casting to refine grain

265 500 18 20 150

General purpose, medium strength casting for machining.

Medium-carbon steel

BS970.080M40

0.4 0.8 Toughed by quenching from 850°C , temper at 600°C

500 700 20 55 200

Axles, crankshafts, etc., under moderate stress.

BS970.070M55

0.55 0.70 Harden by quenching from 825°C. Temper at 600°C

550 750 14 - - Gears and machine parts subject to wear.

- 0.70 0.35 Quench harden from 790/810°C. Temper at 150-300°C as appropriate.

- - - - 780

Hand chisels, cold sets, screwdrivers, blades, blacksmith’s tools, etc.

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BS 4659:BW18

1.00 0.35 Quench harden from 760/780 °C in water. Temper at 150-300°C as appropriate.

- - - - 800 Taps, screwing dies, wood drills, press tools, hand (fitting) tools, files, measuring and marking out in instruments, etc.

BS 4659: BW1C

1.20 0.35 Quench harden from 760/780 °C In water or oil. Temper at 150-300°C as appropriate.

- - - - 820 Fine edge tools, knives, files, surgical instruments.

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BS 970: part 1General inspection and general procedures and specific requirements for carbon, carbon manganese, alloys, and stainless steels.

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BS 970: part 2Requirement for steel for hot formed springs.

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BS 970: part 3Bright bars for general Engineering purposes.

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BS 970: part 4Valve steels

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Steel types (000-199) Carbon Manganese Steel (Number

shows Manganese content) (x100) (200-240) Free Cutting Steel, the 2nd and 3rd

digit represents the sulphur content (x100)(250-299) Silicon Manganese Steel(300-499) Stainless Steels and Steels resistance

to heat(500-999) Reserved for Alloy Steels

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Letter code A - The steel is supplied to a chemical

composition determined by chemical analysis of batch sample. H - The steel is supplied to a harden

ability specification. M – The steel is supplied to a mechanical

property specification. S – The material is a stainless steel.

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Table 4.8.2 application of the six symbol code

• First three codes are the steel type• The fourth code is the letter code.

• The last two codes are the carbon content

BS 970 specification Description

070M26 Plain carbon steel with composition of 0.26 % carbon and 0.70% manganese. The

letter 'M' indicates that the steel has to meet a prescribed mechanical property

specification

150M36 As above except that the composition for this steel is 0.36% carbon, 1.5% manganese.

220M07 A low-carbon free-cutting steel with a composition of 0.07% carbon and 0.20%

sulphur. Again the letter 'M' indicates that the steel has to meet a prescribed

mechanical property specification.

070A20 Low-carbon steel with a composition of 0.20% carbon 1 and 0.70% manganese. The

letter 'A' indicates that the steel has to meet a prescribed chemical composition

specification.

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Table 4.8.3 carbon and carbon-manganese steels (derived from BS 970)

SteelHeat treatment condition symbol

P

Tensile strength: 550-700 Mpa Brinell hardness: 152-201

LRS Re A I Rp0.2

070M20 19 355 20 41 340

070M26 29 355 20 41 325

080M30 63 340 18 34 310

080M36 - - - - -

080M40 - - - - -

080M46 - - - - -

080M50 - - - - -

070M55 100 355 18 28 325

120M19 150 340 18 27 310

150M19 - - - - -

120M98 - - - - -

150M28 - - - - -

120M36 - - - - -

150M36 - - - - -

216M28 63 355 20 34 325

212M36 100 340 20 34 310

225M36 - - - - -

216M36 100 340 20 34 310

212M44 - - - - -

225M44 - - - - -

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Q


LRS Re A I Rp0.2

- - - - -

13 415 16 34 400

19 415 16 34 400

29 400 16 34 370

63 385 16 34 355

100 370 16 - 340

- - - - -

- - - - -

29 450 16 47 415

63 430 16 54 400

100 415 16 41 385

150 400 16 47 370

100 415 18 41 385

150 400 18 47 370

19 430 18 41 415

63 400 17 47 370

63 400 18 34 370

63 400 17 34 370

100 400 18 34 370

- - - - -

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R


LRS Re A I Rp0.2

- - - - -

- - - - -

- - - - -

13 465 16 34 450

19 465 16 34 450

29 450 16 - 415

63 430 14 - 400

100 415 14 - 385

19 510 16 34 495

29 510 16 41 480

29 510 16 34 480

63 480 16 41 450

29 510 16 34 480

63 480 16 41 450

- - - - -

13 495 16 54 480

29 480 16 34 450

29 480 16 34 450

63 465 16 34 430

100 450 16 34 415

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S


LRS Re A I Rp0.2

- - - - -

- - - - -

- - - - -

- - - - -

- - - - -

13 525 14 - 510

29 495 14 - 465

63 480 14 - 450

- - - - -

- - - - -

- - - - -

13 510 16 34 555

19 570 14 34 555

23 555 14 41 525

- - - - -

- - - - -

- - - -

- - - - -

13 540 14 27 525

29 525 14 27 495

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T


LRS Re A I Rp0.2

- - - - -

- - - - -

- - - - -

- - - - -

- - - - -

- - - - -

13 570 12 - 555

19 570 12 - 555

- - - - -

- - - - -

- - - - -

- - - - -

- - - - -

13 635 12 34 620

- - - - -

- - - -

- - - - -

- - - -

- - - - -

13 600 12 27 585

Note: LRS = Limiting ruling section, A =

Elongation (%), Rp0.2 = 0.2% proof stress

(Mpa), Re = Yield stress (Mpa), I = Izod impact

Value (J)

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Plain Carbon Steels