STEEL. Classification of steel. Amount of carbon Amount of deoxidization Amount of alloys Depth of hardening. 15-Nov-17. R.D.

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1 STEEL Classification of steel Amount of carbon Amount of deoxidization Amount of alloys Depth of hardening 1

2 On the basis of carbon With increase in carbon following increases Hardness Fatigue resistance Hardenability Following decreases Ductility Malleability Toughness Machinability weldability Low carbon steel (upto 0.25%) Soft, ductile, malleable, tough, machinable, weldable, non hardenable Good for cold working processes Rolling into sheets for pressworking Good for fabrication work Can not be hardened by heat treatment 2

3 Applications of low carbon steel Wires Nails Screws Panels Rods Boiler plates and tubes Ship plates Crank shafts Connecting rods Buillding bars Grills Beams Angles Channels Medium carbon steel ( %) Intermediate properties that of low carbon steel-high carbon steel Medium hard, less ductile than low carbon steel Slightly difficult to machine, weld and harden Depth of hardening is low-shallow hardened Difficult to cold work hence hot worked 3

4 Applications of medium carbon steels Bolts Axles Lock washers Forging dies Springs Railway rails High carbon steel ( %) Hard Brittle Wear resistance Difficult to machine Difficult to weld Hot worked Applications Forging dies Punches Hammer heads Chiesels Vice jaw Drills Knives Bearings Cutters files 4

5 On the basis of alloying element and carbon Alloying elements such as Cu,Cr,Ni,Mn,V are added in steels to increase the desired properties. Low alloy steels- alloying content less than 10% High alloy steels- alloying content more than 10% Low carbon low alloy Low carbon high alloy High carbon low alloy High carbon high alloy On the basis of deoxidization Rimmed steel partially deoxidized, soft, easy to bend Killed steel fully deoxidized, high density, good strength 5

6 On the basis of hardening Non hardenable Shallow hardening Deep hardening What is pig iron Pigiron is the intermediate product of smelting iron ore. It is the molten iron from the blast furnace, which is a large and cylinder-shaped furnace charged with iron ore, coke, and limestone. Charcoal and anthracite have also been used as fuel. Pig iron has a very high carbon content, typically % which makes it very brittle and not useful directly as a material except for limited applications. It is used to make wrought iron, steel 6

7 What is wrought iron? Wrought iron is an iron alloy with a very low carbon (less than 0.08%) Corrosion resistance Used in pipe, nails, rivets available in plates, sheets, tubular forms Ship building, oil industries, architectural 7

8 Specification of steel IS:1762(Part 1)-1974 CODE FOR DESIGNATION OF STEELS Two methods of designation Steels designated on the basis of mechanical properties Steels designated on the basis of chemical composition Designation on basis of mechanical properties Symbol Fe or FeE for designation based on tensile strength or yield stress Figure indicating minimum tensile strength or yield stress in N/mm2 Chemical symbol for elements presence of which characterize the steel Symbol indicating special characteristics covering method of deoxidation, steel quality, degree of purity, weldability guarantee etc. 8

9 Symbol for method of deoxidation R Rimmed steel K Killed steel Symbol for Steel quality Inclusioins Degree of purity 9

10 Weldability Resistance to brittle fracture 10

11 Scarfing-Removing surface defects in billets and slabs by using an oxyacetylene torch or by chipping and grinding the steel. Pickling is a metalsurface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper, precious metals and aluminum alloys. A solution calledpickleliquor, which contains strong acids, is used to remove thesurfaceimpurities. 11

12 Examples FeE 270 Fe 410 K 12

13 Designation on basis of chemical Composition Unalloyed steels Example: 25C8 Unalloyed tool steel a) Figure indicating 100 times the average carbon percentage b) Symbol T for tool steel c) Figure indicating 10 times the average percentage of manganese Example: 75T5 13

14 Unalloyed free cutting steel a) Figure indicating 100 times carbon percentage b) Symbol C c) Figure indicating 10 times manganese percentage d) Symbol S, Se, Te or Pb depending on element present which makes it free cutting e) 100 times the percentage content of the element Example: 35C10S14K Alloyed steels a) Low alloy steels(total alloy < 10%) 1) figure indicating 100 times carbon percentage 2) Symbol of alloying elements each followed a figure indicating percentage content multiplied by a factor 1) Symbols indicating special characteristics Example : 40Ni8Cr8V2 14

15 Alloyed steels b) high alloy steels(total alloy >10%) 1)Symbol X followed by 100 times carbon percentage 2)Symbol of chemical elements followed by percentage rounded off to nearest integer value Example: X15Cr25Ni12 Alloyed steels c) alloyed tool steels The designation shall be as for low and high alloy steels except that the symbol T will be included in the beginning of the designation in low alloyed tool steels and XT instead of X in case of high alloy tool steels Example: XT75W18Cr4V1 d) Free cutting alloy steels(small chips) The designation shall be as for low and high alloy steels except that depending on the percentage of S,Se,Te, designation shall also consist of the chemical symbol of the element present followed by the figure indicating 100 times its content Example:X15Cr25Ni15S40 15

16 SAE-AISI Designation The SAE system uses a basic four-digit system to designate the chemical composition of carbon and alloy steels. SAE-AISI Designation The first digit (1), of this designation indicates a carbon steel; i.e., carbon steels comprise 1xxx groups in the SAE-AISI system and are subdivided into four categories due to the variance in certain fundamental properties among them. Thus the plain carbon steels are comprised within the 10xx series (containing 1.00% Mn maximum); resulfurized carbon steels within the 11xx series; resulfurized rephosphorized carbon steels within the 12xx series; non-resulfurized high-manganeze (up-to 1.65%) carbon steels which are produced for applications requiring good machinability are comprised within the 15xx series. 16

17 SAE-AISI Designation SAE designation 1xxx 2xxx 3xxx 4xxx 5xxx 6xxx 7xxx 8xxx 9xxx Type Carbon steels Nickel steels Nickel-chromium steels Molybdenum steels Chromium steels Chromium-vanadium steels Tungsten steels Nickel-chromium-molybdenum steels Silicon-manganese steels Carbon steels 10XX Plain carbon, Mn 1.00% max 11XX 12XX Resulfurized free machining Resulfurized/rephosphorized free machining 15XX Plain carbon, Mn % Manganese steels 13XX Mn 1.75% Nickel steels 23XX Ni 3.50% 25XX Ni 5.00% Nickel-chromium steels 31XX Ni 1.25%, Cr % 32XX Ni 1.75%, Cr 1.07% 33XX Ni 3.50%, Cr % 34XX Ni 3.00%, Cr 0.77% Molybdenum steels 40XX Mo % 44XX Mo % Chromium-molybdenum steels 41XX Cr %, Mo % Nickel-chromium-molybdenum steels 43XX Ni 1.82%, Cr %, Mo 0.25% 47XX Ni 1.05%, Cr 0.45%, Mo % Nickel-molybdenum steels 46XX Ni %, Mo % 48XX Ni 3.50%, Mo 0.25% 17

18 Chromium steels 50XX Cr % 51XX Cr % Chromium-vanadium steels 61XX Cr %, V % Tungsten-chromium steels 72XX W 1.75%, Cr 0.75% Nickel-chromium-molybdenum steels 81XX Ni 0.30%, Cr 0.40%, Mo 0.12% 86XX Ni 0.55%, Cr 0.50%, Mo 0.20% 87XX Ni 0.55%, Cr 0.50%, Mo 0.25% 88XX Ni 0.55%, Cr 0.50%, Mo 0.35% Silicon-manganese steels 92XX 0.65% Si %, Mn %, Cr 0- Nickel-chromium-molybdenum steels 93XX Ni 3.25%, Cr 1.20%, Mo 0.12% 94XX Ni 0.45%, Cr 0.40%, Mo 0.12% 97XX Ni 0.55%, Cr 0.20%, Mo 0.20% 98XX Ni 1.00%, Cr 0.80%, Mo 0.25% Alloy steels Why alloying is required? 18

19 Plain carbon steels are useful for Ordinary temperatures Atmosphere that are not highly corrosive Limited strength Low hardenability is a problem Alloy steel can be defined as one whose characteristic properties are due to some element other than carbon Manganese and silicon are deoxidizers reduce effect of oxygen and sulfur 19

20 Purpose of alloying Increase hardenability Improve mechanical properties at either high or low temperatures Increase wear resistance Increase corrosion resistance Improve toughness Influence of alloying elements on ironiron carbide diagram Change in critical temperature Change in eutectoid point position austenite stabilizer 20

21 Effect of alloying elements on properties 1) Elements that do not form carbides in steel (e.g. Ni, Co, Al, Cu and N) 2) Elements that form stable carbides in steel (e.g. Cr, Mn, Mo, W, V, Ti, Zr, and Nb). Effect of alloying elements on properties Aluminum (Al): used as a grain refinement agent. It is also deoxidizing agent used in killed steels. Also increases nitridability (Used in nitriding steels). The added Aluminum reacts with Nitrogen in the molten steel to form Aluminum Nitride particles. These tiny particles precipitate along the boundaries of the Austenite as well as with in the Austenite grains. This restricts the growth of the grains. 21

22 Grain size measurement 22

23 Manganese (Mn) If more than 0.8% then only it is an alloy increases the strength, shock resistance, toughness, hardenability, weldability, hot formability. Reduces the tendency of red shortness In addition Mn is a strong austenite former by reducing the eutectoid temperature below to room temperature. Hadfield steel with 1% C and 12% Mn has strong deformation hardening ability allowing increase in strength in service (helmets,railway equipments, rock crushers jaws, shovel dippers, etc.) Comparison between strength and toughness 23

24 15-Nov-17 From Physical Metallurgy by Sidney H. Avner Ferritic- BCC not work hardenable Austenitic FCC work hardenable 24

25 Mn combines with sulfur and reduces amount of ferrous sulfide MnS remains solid at the rolling temperature of steel so reduces red shortness Fine grained manganese steel attain unusual toughness and strength Nickle(Ni) Lowers critical temperature and widens the temperature range for successful heat treatment Does not form carbide Reduces carbon percentage of pearlite, so higher percentage of pearlite compare to plain carbon steel(eutectoid point shifts left) Pearlite formed at lower temperatures- fine and tough compare to unalloyed steel Toughness is increased Increases corrosion resistance Gears, cams, crankshafts 25

26 Chromium (Cr) Less expensive than nickel Corrosion resistance Forms carbides Cr 7 C 3, (FeCr) 3 C having high hardness and wear resistance Improves high temperature properties High carbon-high chromium steels are having high hardness and wear resistance, used in making bearings, crushing machinery From Physical Metallurgy by Sidney H. Avner 26

27 Nickle-Chromium Combination imparts characteristic properties of each one Nickle -increase in ductility and toughness, chromium- increase in hardness and wear resistance Used for worm gears, piston pins, shafts, cams Molybdenum(Mo) Expensive Strong carbide former increases the hardenability, high temperature strength, decreases the risk for temper embrittelment. Temper embrittlement refers to the decrease in notch toughness of alloy steels when heated in, or cooled slowly through, a temperature range of 400 C to 600 C. Since the melting point of molybdenum carbide is very high, it provides high temperature strength which is very useful in some HSS (high speed steel) tools. Triple alloy nickel-chromium-molybdenum have the advantages of the nickel-chromium steels along with the high hardenability imparted by 27

28 Silicone(Si) increases strength, decreases oxide formation affinity. In addition Si has higher affinity to O than carbon therefore used as deoxidizing agent. Silicon increases strength and toughness Hadfield silicon steel with less than 0.01 percent carbon and 3 percent silicon has excellent magnetic properties for use in electrical machinery 9260 silicon-manganese steel offers unusual high strength and toughness which is used for springs and chisels and punches Vanadium (V) Most expensive Deoxidizer and carbide former Produces fine grain structure Tungsten (W) Strong carbide former Similar to molybdenum but 2 to 3 percent tungsten is equivalent to 1 percent molybdenum Expensive so generally not used Increases hardenability 28

29 Zirconium (Zr), Titanium (Ti), Niobium (Nb) and Tantalum (Ta) Strong carbide formers even better than Cr. Therefore commonly used in austenitic stainless steel to free the Cr and thus further increase the corrosion resistance. Their even small concentration can form small carbides at grain boundaries providing very fine grain size which is the reason to high strength and ductility of low alloy(hsla) steel, commonly used in automotive industry. Phosphorus (P) decreases the toughness, impact resistance, cold formability, weldability. increase the corrosion resistance. Sulfur (S) The excess sulfur forms the brittle FeS phase at the grain boundaries (hot brittleness). The solubility of S is higher than C therefore it restricts the formation of pearlite in the zones with higher S contents, leading a banded structure of pearlite and ferrite. This causes severe anisotropy in the mechanical properties of steel therefore S content is limited. However, 0.3% S may be added to free cuttingsteels to increase the chip formation thus themachinability. 29

30 STAINLESS STEEL Highly resistant to corrosion Chromium is predominant alloying element Minimum 11% of chromium Nickel and Molybdenum 30

31 From Physical Metallurgy by Sidney H. Avner Classification of stainless steel Austenitic stainless steel Martensitic stainless steel Ferritic stainless steel 31

32 Austenitic Stainless Steel 200 Series austenitic chromium-nickel-manganese alloys. Type 201 is hardenable through cold working; Type 202 is a general purpose stainless steel. 300 Series The most widely used austenite steel is the 304, also known as 18/8 for its composition of 18% chromium and 8% nickel. 304 may be referred to as A2 stainless (not to be confused with A2 grade steel, also named Tool steel, a steel). A typical composition of 18% chromium and 10% nickel, commonly known as 18/10 stainless, is often used in cutlery and high-quality cookware. Applications of austenitic stainless steel construction structures piping water treatment applications High quality cookware 32

33 Ferritic Stainless Steel Good mechanical properties compare to austenitic Less corrosion resistance Less Ni% Less expensive Magnetic Applications Household applications Automotive applications Martensitic stainless steel Martensite Martensite, named after the German metallurgist Adolf Martens ( ), most commonly refers to a very hard form of steel quenching diffusion less phase transformation It can be hardened by heat treatment. Martensitic stainless steel contains chromium (12 14%), molybdenum (0.2 1%), nickel (less than 2%), and carbon (about 0.1 1%) (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic 33

34 BCC FCC % empty space Largest interstitial sphere Max. % Solulibility of iron 0.36X10-8 cm3 0.52X10-8 cm

35 Applications of martensitic stainless steel cutting utensils surgical and dental instruments ball bearings steam and gas turbines 35

36 Tool Steel Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and their resistance to deformation at elevated temperatures (red-hardness). classification According to the quenching media used Water cooled Oil cooled Air cooled According to the application Hot working steel Cold working steel High speed steel According to the alloy content Carbon tool steel Low alloy tool steel High alloy tool steel 36

37 Selection of tool steels Expected productivity Ease of fabrication Cost Toughness Wear resistance Red hardness carbide formation helps W, Cr and Mo Machinability Cutting- single edge, multiple edge high hardness, heat and wear resistance Shearing punch and blanking dies high wear resistance, toughness Forming high toughness, high strength, high red hardness 37

38 Water hardening tool steels(w grade) Plain carbon tool steels Less expensive than the alloy tool steels Water quenched Hard martensitic structure Less heat resistance Applications limited to low speeds and light cuts on soft materials Shock resisting tool steels(s grade) Low carbon 0.45 to 0.65 Silicon, chromium, tungsten, molybdenum Si strengthens ferrite, chromium and molybdenum increases hardenability Tungsten red hardness Oil hardened Hardness below RC60 Forming tools, punches, shear blades 38

39 Cold work tool steel (O,A,D) Majority of tool applications Oil hardening- low alloy Small amount of Manganese, chromium, tungsten Less distortion compare to water quench fair machinability Good wear resistance, fair toughness Good red hardness Blanking, forming etc. Hot work tool steels(h grade) Chromium, molybdenum, tungsten min 5% Hot work chromium base Min 3.25 % Cr Red hardness Low carbon for good toughness RC40 to RC55 Deep hardenable-air hardened Less distortion Hot die work 39

40 Hot work tungsten base 9% W, 2 to 10% Cr High temperature softening resistance More brittle Air hardened Mandrels, extrusion dies Hot work molybdenum base 8% Mo Same properties as tungsten base More resistance to heat cracking Lower cost compare to tungsten base 40

41 High speed tool steels(t,m) High amount of alloys Tungsten, chromium, vanadium, molybdenum Carbon content 0.70% to 1.5% Excellent red hardness, fair toughness resistance Molybdenum base-tungsten base Cutting tools, drills, broaches etc. 41