Stainless steel
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The document discusses stainless steel, its definition, history, properties, and various types including austenitic, martensitic, ferritic, duplex, and precipitation hardening stainless steels. It highlights that stainless steel is an alloy of iron with chromium that offers corrosion resistance, and outlines its applications in industries such as automotive, construction, medical, and food processing. It also notes that stainless steel can corrode under aggressive conditions, listing specific types of corrosion it may experience.
Stainless steel
- 1. Gateway Arch in St Louis – 304 series SS F-35 Joint Strike Fighter (JSF) Lightning II, built by Lockheed Martin – airframe 17-7 PH – 600 series SS
- 2. Definition of Stainless Steel History of Stainless steel Properties of Stainless steel Different types of Stainless steel Different grades of Stainless steel Application of Stainless steel
- 3. Stainless steel is an alloy of Iron with a minimum of 10.5% Chromium. Chromium produces a thin layer of oxide on the surface of the steel known as the 'passive layer'. This prevents any further corrosion of the surface. Increasing the amount of Chromium gives an increased resistance to corrosion. Stainless steel also contains varying amounts of Carbon, Silicon and Manganese. Other elements such as Nickel and Molybdenum may be added to impart other useful properties such as enhanced formability and increased corrosion resistance.
- 4. There is a widely held view that stainless steel was discovered in 1913 by Sheffield metallurgist Harry Brearley. He was experimenting with different types of steel for weapons and noticed that a 13% Chromium steel had not corroded after several months.
- 5. Electrical Resistivity • Electrical resistance is higher than that for plain-carbon steels Thermal Conductivity • Stainless Steel has lower thermal conductivity than Carbon steel
- 6. Coefficient of Thermal Expansion • Stainless steel is having greater coefficient of thermal expansion than plain-carbon steels High Strength • Exhibit high strength at room and elevated temperatures Melting Temperature Plain-carbon:1480-1540 °C Martensitic: 1400-1530 °C Ferritic: 1400-1530 °C Austenitic: 1370-1450 °C
- 7. Austenitic: This SS is having Austenitic structure (i.e. FCC) at room temp. They contain 16-25% chromium, and nitrogen. They are hardened only by cold working. Good toughness, formability, easily weldable, high corrosion resistance. Nonmagnetic except after excess cold working or welding due to martensitic formation. Can be successfully used from cryogenic temperatures to the red-hot temperatures of furnaces and jet engines. They are susceptible to SCC. App.: Automotive, Architecture, Food and beverage equip., Industrial equip.
- 8. Martensitic: They have a structure i.e. BCT. Due to addition of ‘C’ (0.15-1%), they can be hardened and strengthened by heat treatment. When steel is heated it transform from ferrite to austenite & on slow cooling it transforms back to ferrite. However, with fast cooling through quenching in water or in oil the carbon atoms become trapped in a somewhat distorted atomic matrix and structure becomes i.e. BCT. The main alloying element is ‘Cr’ i.e. 12-15% approx. App.: Steam turbine blades, valves body and seats, bolts and screws, springs, knives, surgical instruments, and chemical engg. equipments.
- 9. Ferritic: This SS is having Ferritic structure (i.e. BCC) at room temp. It containing 11.5-19% ‘Cr’ & C: 0.20max. They are having good corrosion resistance, magnetic and hardenable only by cold working. They are less expensive than Austenitic SS. Limitations: i) poor toughness at sub zero temp ii) Poor weldability due to embrittlement. App.: Automotive, building construction, Cladding, Urban furniture, commercial food equipment, industrial application
- 10. Duplex SS: This SS is having austenitic (50%) + ferritic (50%) microstructure. This SS is containing high Cr: 20.1-25.4%, Ni: 1.4-7%, Mo: 0.3-4% (e.g.2205; 2507). Combining many of the best features of both austenitic (i.e. application in cryogenic temp. to red-hot temp.) and ferritic types. It is magnetic, non-hardnable by heat treatment, has high TS than austenitic type, weldability similar to the austenitic stainless steel. App.: Heat exchangers, pressure vessels, Chemical-petrochemical ind., Oil-Gas ind., Nuclear Power plant
- 11. Precipitation hardening: This SS are not defined by their microstructure, but rather by strengthening mechanism (e.g.17-4pH (martensite) or 17-7pH (austenitic)). These grades may have austenitic, semi-austenitic or martensitic microstructures and can be hardened by aging at elevated temp. i.e. 480deg.C to 620deg.C. The strengthening effect is due the formation of intermetallic precipitates from elements such as copper or aluminum. Have the highest strength and to be used for specialized application where high strength together with good corrosion resistance is required. App.: Aerospace, defense, offshore oil & gas industries, missile components, motor shafts, valve stems, gears
- 13. Austenitic grades 302 General purpose 303 304EN 304ECu 308L 304 310 316 317LN High Sulphur Higher Ni Cu addition Higher Lower Cr & Ni Mo added More Mo & Cr + Calcium for cold for cold Cr & Ni C for increased for increased with reduced added heading heading for use better for high corrosion C for better for better application in welding corrosion temperature resistance corrosion machinability control resistance 303 Cu 304LN 304 HC 309L 304HS+Ca 316HS+Ca Cu & S for Lower C Higher Cu Higher For bright bar For bright bar enhanced content and for cold Cr & Ni with better with better drawability higher Ni headed nuts for welding machinability machinability and good for better and bolts machinability drawability 302 HQ 304L 316L Low C and Low C - better C reduced high Cu for corrosion for severely cold resistance. welding headed parts Wire drawing fabrication & forging. 321 316Ti Ti added Ti added to prevent to prevent carbide Carbide precipitation precipitation Ferritic grades Martensitic grades 430 410 General General purpose purpose 405 409 Ti 430L 430F 431 403 420 416 Low Cr; Al For improvedLow Carbon, S added Cr increased Special Increased S increased added to corrosion low Nitrogen for Ni added quality for C to for prevent resistance for fine wire improved for better turbines & improve improved hardening and drawing machinability corrosion highly mechanical machinability when cooled weldability resistance & stressed properties from elevated good mech. parts temperature properties 201 N & Mn partially replaces Ni
- 14. Although stainless steel is much more resistant to corrosion than ordinary carbon or alloy steels, in some circumstances it can corrode. It is 'stain-less' not 'stain-impossible'. In normal atmospheric or water based environments, stainless steel will not corrode. In more aggressive conditions, the basic types of stainless steel may corrode 1) Pitting corrosion 2) Crevice corrosion 3) General/Uniform corrosion 4) Stress corrosion cracking 5) Intergranular corrosion 6) Galvanic corrosion
- 15. Stainless steels of various kinds are used in thousands of applications. Some of the main applications are as follows: Domestic – cutlery, sinks, saucepans, washing machine drums, microwave oven liners, razor blades Architectural/Civil Engineering – cladding, handrails, door and window fittings, street furniture, structural sections, reinforcement bar, lighting columns, lintels, masonry supports Transport – exhaust systems, car trim/grilles, road tankers, ship containers, ships chemical tankers, refuse vehicles Chemical/Pharmaceutical – pressure vessels, process piping. Oil and Gas – platform accommodation, cable trays, subsea pipelines. Medical – Surgical instruments, surgical implants, MRI scanners. Food and Drink – Catering equipment, brewing, distilling, food processing. Water – Water and sewage treatment, water tubing, hot water tanks. General – springs, fasteners (bolts, nuts and washers), wire.