2. 1 Teaching Innovation - Entrepreneurial - Global The Centre for Technology enabled Teaching & Learning, N Y S S, India DTEL DTEL (Department for Technology Enhanced Learning)

3. DEPARTMENT OF MECHANICAL ENGINEERING III-SEMESTER ENGINEERING METALLURGY 2 CHAPTER NO-4

4. CHAPTER 4:- SYLLABUSDTEL. Carbon & its Alloy 1 Classification of carbon steel 2 Alloy Steel 3 Effect of various element on steel 4 3 Stainless steel 5

5. CHAPTER-4 SPECIFIC OBJECTIVE / COURSE OUTCOMEDTEL Understand the classificaton steel. 1 Understand the effect of various alloying elementon steel. 2 4 The student will be able to:

6. DTEL 5 LECTURE 1:- Carbon & its alloy All of these steels are alloys of Fe and C – Plain carbon steels (less than 2% carbon and negligible amounts of other residual elements) Low Carbon (less than 0.25% carbon) Med Carbon (0.25% to 0.45%) High Carbon (0.45% to 2.0%) – Low Alloy Steel – High Alloy Steel – Stainless Steels– contain at least 10.5% Chromium

7. DTEL 6 LECTURE 1:-

8. DTEL 7 LECTURE 2:- CLASSIFICATION OF STEEL 1.Low Carbon (less than 0.25% carbon) Low strength, good formability If wear is a potential problem, can be carburized (diffusion hardening) Most stampings made from these steels AISI 1008, 1010, 1015, 1018, 1020, 1022, 1025 2. Med Carbon (0.25% to 0.6%) Have moderate to high strength with fairly good ductility Can be used in most machine elements AISI 1030, 1040, 1050, 1060 3.High Carbon (0.6% to 2.0%) Have high strength, lower elongation Can be quench hardened Used in applications where surface subject to abrasion – tools, knives, chisels, ag implements. AISI 1080, 1095

9. DTEL 8 LECTURE 3 :- ALLOY STEEL Other elements (besides carbon) can be added to iron to improve mechanical property, manufacturing, or environmental property. Example: sulfur, phosphorous, or lead can be added to improve machine ability. Again, elements added to steel can dissolve in iron (solid solution strengthening): – Increase strength, hardenability, toughness, creep, high temp resistance Generally want to use for screw machine parts or parts with high production rates! – Examples: 11xx, 12xx and 12Lxx.

10. DTEL 9 LECTURE 3:- Alloy steels grouped into low, med and high-alloy steels. – High-alloy steels would be the stainless steel groups. – Most alloy steels you’ll use fall under the category of low alloy.

11. DTEL 10 LECTURE 4:-TYPE OF ALLOY STEEL Alloy Steel > 1.65%Mn, > 0.60% Si, or >0.60% Cu Most common alloy elements : – Chromium, nickel, molybdenum, vanadium, tungsten, cobalt, boron, and copper. Low alloy: Added in small percents (<5%) – increase strength and hardenability High alloy: Added in large percents (>20%) – i.e. > 10.5% Cr = stainless steel where Cr improves corrosion resistance and stability at high or low temps

12. DTEL 11 LECTURE 5 :-EFFECT OF VARIOUS ALLOYING ELEMENT Manganese (Mn) combines with sulfur to prevent brittleness >1% – increases hardenability 11% to 14% – increases hardness – good ductility – high strain hardening capacity – excellent wear resistance Ideal for impact resisting tools

13. DTEL 12 LECTURE 5:- Sulfur (S) Imparts brittleness Improves machineability Okay if combined with Mn Some free-machining steels contain 0.08% to 0.15% S Examples of S alloys: – 11xx – sulfurized (free-cutting)

14. DTEL 13 LECTURE 5:- Chromium (Cr) Usually < 2% increase hardenability and strength Offers corrosion resistance by forming stable oxide surface typically used in combination with Ni and Mo – 30XX – Nickel (0.70%), chromium (0.70%) – 5xxx – chromium alloys – 6xxx – chromium-vanadium alloys – 41xxx – chromium-molybdenum alloys

15. DTEL 14 LECTURE 5:- Molybdenum (Mo) Usually < 0.3% increase hardenability and strength Mo-carbides help increase creep resistance at elevated temps –typical application is hot working tools Copper (Cu) 0.10% to 0.50% increase corrosion resistance Reduced surface quality and hot-working ability used in low carbon sheet steel and structural steels

16. DTEL 15 LECTURE 5:- Boron (B) for low carbon steels, can drastically increase hardenability improves machinablity and cold forming capacity Aluminum (Al) deoxidizer 0.95% to 1.30% produce Al-nitrides during nitriding

17. DTEL 16 LECTURE 6:- STAINLESS STEEL Stainless steels are another class of ferrous alloys, which have been made for and are used because of their excellent corrosion resistance. A true stainless steel has at least 12% Cr in the steel. This steel is exposed to oxygen, which forms a thin, stable Cr 2 O 3 coating on the surface, which is very corrosion resistant. The Cr 2 O 3 in the steel is very stable against attack by a number of chemicals and electrolytic corrosion actions. It is self healing if damaged. In general, there are four types of stainless steels based on their crystal structure and strengthening mechanisms. They are: Ferritic stainless steels Martensitic stainless steels Austenitic stainless steels Precipitation-hardened stainless steels

18. DTEL 17 LECTURE 7:- CLASSIFICATION OF STAINLESS STEEL The Austenitic Stainless Steel: austenite structure is retained in the room temperature by Ni (acts as substitutional atom): It has high corrosion resistance. Ferritic Stainless Steel: Less nickel content than austenitic stainless steel: Used for applications not requiring the high corrosion resistance of the austenitic stainless steels. Less expensive Martensitic Stainless steel: Excellent for applications for springs, and cutlery. Precipitation hardening stainless steel: increased resistance to dislocation motion, thereby increased strength, or hardness. Used for corrosion resistance structural members.

19. DTEL 18 LECTURE 8:- FERRITIC STAINLESS STEEL Ferritic Stainless Steels The effect of Cr on the iron-carbon phase diagram is to stabilize the ferritic phase. The ferritic or alpha phase (BCC) exists almost to room temperature. Cr is BCC and extends the alpha region and suppresses the gamma (FCC) region. At more than 12% Cr the gamma (FCC) phase does not form. The ferritic stainless steels are relatively inexpensive because they do not contain Nickel. Many Cr stainless steels contain up to 30% Cr and less than 0.12% C. They have good strength but only moderate ductility and formability because of the BCC form.

20. DTEL 19 LECTURE 8:-MARTENSETIC STAINLESS STEEL Martensitic Stainless Steels These stainless steels can be produced by using a heat treatment that austenitizes the sample (above ~750 o C), followed by quenching to Room Temperature to get Martensite. The Martensite can then be further strengthened by using tempering heat treatments. These steels are not as resistant to corrosion as other stainless steels but they have a higher strength. Applications include high-quality knives, ball-bearings and valves.

21. DTEL 20 LECTURE 8:- AUSTENITIC STAINLESS STEEL These steels are formed by adding Ni, which is a strong austenite stabilizing element. For example, 18% Cr and 8% Ni with 0.03% C will remain austenitic all the way to room temperature. Low or no carbide formation in these stainless steels means that they can have high ductility, easy formability, high corrosion resistance and moderate strength. Strength is obtained by solid solution strengthening and cold working. They do not have any phase transitions as they are cooled so they do not become brittle at low temperatures. High Ni and Cr content makes them expensive relative to other stainless steels. Small amounts of Ti or Nb form TiC or NbC, which aid strength by precipitation without reducing corrosion resistance.

22. DTEL References Books: 21 References Web: