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alternates plates of α + Fe3C- Two phases grow simultaneously
• Lever rule
Fahmi Mubarok
X 10Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Formation of Pearlite
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Fahmi Mubarok
X 11Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypoeutectoid steel
Fahmi Mubarok
X 12Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypoeutectoid steel ->Lever Rule
3
αt(total ferrite)
Fe C (Cementite)
6.70 0.386.70 0.022
= 0.95%1 0.95 0.05%
W
W
−=
−
= − =
(proeutectoid ferrite)
γ(that will form pearlite)
0.76 0.38(0.76 0.022)
0.52%1 0.52 0.48%
W
W
α−
=−
== − =
1
2
3
4Example: Calculating composition of steel with 0.38 wt%CT = 730oC T=25oC4.3.
The fraction of eutectoid ferritethus are:
αe ααt 0.95 0.52
0.43%
W W W= −
= −=
7
Fahmi Mubarok
X 13Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypoeutectoid steel composition (0.38 wt% C)
Fahmi Mubarok
X 14Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypereutectoid steel
8
Fahmi Mubarok
X 15Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypereutectoid steel -> lever rule
Exercise 10a. Determine the following composition of 1.4 wt%C at a temperature near eutectoid line :
a. The fraction of pealite and proeutectoid cementiteb. The fraction of total ferrite and cementite phasesc. The fraction of eutectoid cementite
Fahmi Mubarok
X 16Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Hypereutectoid steel composition (1.4 wt% C)
9
Fahmi Mubarok
X 17Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Plain Carbon Steels
1. Satisfactory where strength and other requirement are not too severe2. Used successfully at room temperatures and in atmospheres that are not highly
corrosive3. Can be produced in a great range of strengths at a relatively low cost
Limitation
1. Cannot be strengthened beyond about 100.000 psi without significant loss in toughness (impact resistance) and ductility
2. Large section cannot be made with a martensitic structure throughout3. Rapid quench rates are necessary for full hardening in medium-carbon plain carbon
steels to produce a martensitic structure. This rapid quenching leads to shape distortion and cracking of heat-treated steel
4. Show a marked softening with increasing tempering temperature5. Poor impact resistance at low temperatures6. Poor corrosion resistance for many engineering environments7. Oxidezed readily at elevated temperatures
Fahmi Mubarok
X 18Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Elements in Plain Carbon Steels1. Sulfur (<0.05 %)
• Sulfur combines with iron to form iron sulfide (FeS), which usually occurs as a grain boundary precipitation
• FeS is hard and has a low melting point, it can cause cracking during hot working of steel (hot-short)
2. Manganese (0.03 % -1.0 %)• The fuction of manganese in counteracting the negative effects of sulfur• Manganese combines with the sulfur persent in the steels to produce manganese
sulfide (MnS), thus no FeS will form.3. Phosphorus (< 0.04 %)
• This small quantity tends to dissolve in ferrite, increasing the strength and hardness slightly
• In large quantities, phosphorus reduces ductility, thereby increasing the tendency of the steel to crack when cold worked (cold-short)
4. Silicon (from 0.05%-0.30%)• Silicon dissolves in ferrite, increasing the strength of the steel without greatly
decreasing the ductility• Silicon is used as a deoxidizer, and forms SiO2 or silicate inclusions
10
Fahmi Mubarok
X 19Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya
Alloying Steels
Plain Carbon SteelsPlain-carbon steels properties are not always adequate for all engineering
applications of steel
Alloy Steels1. Alloy steels have been developed which, although they cost more, are
more economical for many uses2. In some applications, alloy steels are the only materials that are able to
meet engineering requirements3. The principal element that are added to make alloy steels are nickel,
chromium, molybdenum, manganese, silicon, and vanadium4. Other elements sometimes added are cobalt, cooper, and lead