1 METALLURGY I (RM-1420) Dosen: Fahmi Mubarok, ST., MSc. Metallurgy Laboratory Mechanical Engineering ITS- Surabaya 2008 Crystal Structures of Iron Fe – Fe 3 C Phase Diagram Steels Cast Iron http://www.its.ac.id/personal/material.php?id=fahmi LECTURE X LECTURE X Fahmi Mubarok X Æ 2 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Review (Concept of solubility) ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. (a) The three forms of water – gas, liquid, and solid – are each a phase. (b) Water and alcohol have unlimited solubility. (c) Salt and water have limited solubility. (d) Oil and water have virtually no solubility. Illustration of phases and solubility: 2 Fahmi Mubarok X Æ 3 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Crystal Structures of iron Crystal Structures of iron Fahmi Mubarok X Æ 4 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Fe Fe - - Fe Fe 3 3 C C Phase Phase Diagram Diagram 3 Fahmi Mubarok X Æ 5 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Fe-Fe 3 C Phase Diagram •Region – Pure Iron < 0.008% wt C – Steel 0.008 < % wt C < 2.14 – Cast Isron 2.14 < %wt C < 6.70 • Phases: – α-Ferrite (α) – Austenite (γ) – δ-Ferrite (δ) – Cemenite (Fe 3 C) • Critical temperature: Fahmi Mubarok X Æ 6 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Four Solid Phases • α-Ferrite (α) – Solid solution of a carbon in α-Iron – BCC structure – Carbon only slightly soluble in matrix • Maximum solubility of 0.022 % wt C at 727 o C to about 0.008 wt% C in room temperature • Austenite (γ) – Solid solution of a carbon in δ-Iron – FCC structure Æ can accomodate more carbon than ferrite • Maximum solubility of 2.14 % wt C at 1147 o C, then decreased to 0.8 wt% C at 727 o C. • The difference in C solid solubility between γ and α is the basis of hardening in many steel. 4 Fahmi Mubarok X Æ 7 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Four Solid Phases • δ-Ferrite (δ) – Solid solution of a carbon in δ-Iron – BCC structure – NO technological importance cause only stable at high temperature. • Maximum solubility of ferrite being 0.09 % wt C at 1493 o C • Cementite (Fe 3 C) – Intermetallic Fe-C compound –Fe 3 C : 6.7 wt% C + 93.3 wt% Fe – Forms when solubility limit of carbon in α-ferrite is exceeded below 727 o C – Orthorombic crystal structure : very hard and brittle. Fahmi Mubarok X Æ 8 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Three Invariant Reactions Three Invariant Reactions 5 Fahmi Mubarok X Æ 9 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Eutectoid steel (Pearlitic steel) • Microstructure: pearlite - Lamellar eutectoid product alternates plates of α + Fe3C - Two phases grow simultaneously • Lever rule Fahmi Mubarok X Æ 10 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Formation of Pearlite 6 Fahmi Mubarok X Æ 11 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Hypoeutectoid steel Fahmi Mubarok X Æ 12 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Hypoeutectoid steel ->Lever Rule 3 αt(total ferrite) Fe C (Cementite) 6.70 0.38 6.70 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 4 Example: Calculating composition of steel with 0.38 wt%C T = 730 o C T=25 o C 4. 3. The fraction of eutectoid ferrite thus are: αe α αt 0.95 0.52 0.43% WWW = − =− = 7 Fahmi Mubarok X Æ 13 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Hypoeutectoid steel composition (0.38 wt% C) Fahmi Mubarok X Æ 14 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Hypereutectoid steel 8 Fahmi Mubarok X Æ 15 Metallurgy 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 cementite b. The fraction of total ferrite and cementite phases c. The fraction of eutectoid cementite Fahmi Mubarok X Æ 16 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Hypereutectoid steel composition (1.4 wt% C) 9 Fahmi Mubarok X Æ 17 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Plain Carbon Steels 1. Satisfactory where strength and other requirement are not too severe 2. Used successfully at room temperatures and in atmospheres that are not highly corrosive 3. 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 throughout 3. 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 temperature 5. Poor impact resistance at low temperatures 6. Poor corrosion resistance for many engineering environments 7. Oxidezed readily at elevated temperatures Fahmi Mubarok X Æ 18 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Elements in Plain Carbon Steels 1. 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 SiO 2 or silicate inclusions 10 Fahmi Mubarok X Æ 19 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Alloying Steels Plain Carbon Steels Plain-carbon steels properties are not always adequate for all engineering applications of steel Alloy Steels 1. Alloy steels have been developed which, although they cost more, are more economical for many uses 2. In some applications, alloy steels are the only materials that are able to meet engineering requirements 3. The principal element that are added to make alloy steels are nickel, chromium, molybdenum, manganese, silicon, and vanadium 4. Other elements sometimes added are cobalt, cooper, and lead Fahmi Mubarok X Æ 20 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Effect of carbon content [...]... White Cast Iron Fahmi Mubarok • High compressive strength and excellent wear resistance but extremely brittle and difficult to machine • Used where: – resistance to wear is most important – The service does not require ductility • White cast iron Malleable cast iron (malleabilization) • Mechanical properties: – – – – Hardness brinell Tensile strength Compressive strength Modulus of elasticity Metallurgy... solid solution ! Intermetallic compound ! Invariant point ! Isomorphous ! Lever rule Metallurgy Lab Mech Eng Dept ITS Surabaya X 27 METALLURGY I (RM-1420) MINGGU XI-XIII NON EQUILIBRIUM TRANSFORMATION Dosen: Fahmi Mubarok, ST., MSc -Isothermal transformation diagram - Coling tranformation diagram - Formation of martensite Metallurgy Laboratory Mechanical Engineering ITS- Surabaya 2008 14 . 1 METALLURGY I (RM-1420) Dosen: Fahmi Mubarok, ST., MSc. Metallurgy Laboratory Mechanical Engineering ITS- Surabaya 2008 Crystal. C) 9 Fahmi Mubarok X Æ 17 Metallurgy Lab. Mech. Eng. Dept. ITS Surabaya Plain Carbon Steels 1. Satisfactory where strength and other requirement are not too severe 2. Used successfully at room. brittle and difficult to machine • Used where: – resistance to wear is most important – The service does not require ductility • White cast iron Æ Malleable cast iron (malleabilization) • Mechanical