Plain Carbon Steels
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Transcript of 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
Tensile strength: 620-770 Mpa Brinell hardness: 179-229
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
Tensile strength: 690-850 Mpa Brinell hardness: 201-255
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
Tensile strength: 770-930 Mpa Brinell hardness: 223-277
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
Tensile strength: 850-1000 Mpa Brinell hardness: 248-302
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)