Types of Stainless Steel

Austenitic Stainless Steel: As a non-magnetic alloy with high formability, austenitic stainless steel cannot be heat treated but can be used in cold work processes. It is corrosion-resistant, however, it is susceptible to cracking due to stress corrosion. It is widely used in the production of valves, bushings, shafts, bolts, nuts, brewing and filling equipment, and cryogenic tanks and vessels, aircraft fittings, etc. As a member of 200 or 300 series, austenitic stainless steels can be available in the following common grades in ascending order: 201, 202, 301, 302, 303, 304, 305, 308, 309, 310, 314, 316, 317, 321, 347, 348, and 384.

Ferritic Stainless Steel: Compared to austenitic stainless steels, this type of steels are magnetic and have lower corrosion resistance and ductility. However, ferritic stainless steel grades have a high resistance to cracking due to stress corrosion. It cannot be heat treated but can be used in cold work processes. It is widely used in the production of heat exchangers, furnace components, and automobile fasteners. As a member of 400 series, ferritic stainless steels can be available in the following common grades in ascending order: 405, 409, 430, 434, 436, 442, and 446.

Martensitic Stainless Steel: This type of steels is magnetic and available for heat treatment. Although their strength is higher, their corrosion resistance is lower than those of ferritic stainless steel. They are widely used in the production of pump shafts, valves, bolts, nuts, and screws, bushings, rivets, cutlery, jet engine components, aircraft fittings and accessories, mining machinery, coal chutes, gun barrels, and fire extinguisher tubes. As a member of 400 and 500 series, martensitic stainless steels can be available in the following common grades in ascending order: 410, 414, 416, 420, 431, and 440.

Precipitation Hardening Stainless Steel: This grade of steels can be heat treated, and their strengths are higher than those of austenitic stainless steels. Besides, they can preserve their strength also at high temperatures. This grade of steel is also known as PH Type stainless steel, and it is used in the production of defense and security equipment and structural components of aircraft. Precipitation hardening stainless steels can be available in the following common grades: 17-7 PH, PH 15-7 Mo, 17-4 PH, and 15-5 PH.

Duplex Stainless Steel: Since duplex stainless steels have a hybrid structure of austenitic and ferritic steels, they have excellent strength and resistance to stress corrosion cracking. Although they are easily heat-treated, they have lower cold formability. They are widely used in the production of chemical processing equipment, pressure tanks and vessels, and heat exchanger components. Duplex stainless steels can be available in the following common UNS grades: S32101, S32304, S32003, S31803, S32205, S32760, S32750, S32550, S32707, and S33207.

Stainless Steel Alloys

Stainless Steel 304: As the most widespread stainless steel alloy, Type 304 stainless steel is notable with its original surface finish. Its corrosion resistance and oxidation resistance are quite higher compared to carbon steels. Type 304 is a formable and weldable material, also, it can be reliably used under corrosive conditions. It is widely used in the production of transportation containers, railway and industrial equipment, hand tools, home appliances, cutlery, etc. 

Stainless Steel 305: Since Type 305 is the most formable stainless steel of all austenitic type, it is widely preferred in shell and barrel applications. As a versatile material, Type 305 can be used in both cold working and hot working processes. It can be hot worked using forging and heading methods. However, it is ideal for drawing, spinning, and blanking methods of the cold working process. Type 305 is a weldable material but it is not suitable for heat treatment. It is widely used in the production of drawn housings, kitchenware, tank covers, screws, fasteners, rivets, pens, and mechanical pencils.

Stainless Steel 309: With its resistance to high-temperature processes, Type 309 stainless steel can be reliably used at temperatures up to 1038 °C (1900 °F). It has a higher strength and corrosion resistance than those of Type 304. Type 309 is suitable for cold working processes, however, it cannot be heat treated. It has relatively high machinability and suitable for welding applications. Type 309 stainless steel is widely used in the production of furnace components, thermowells, oven linings, power boiler pipe supports and hangers, generators, brazing fixtures, anchor bolts, refractory supports, etc. and various equipment for paper mills and petroleum refineries.

Stainless Steel 310:  This grade of stainless steel is suitable for use in extreme temperatures as it can maintain its corrosion resistance and its strength at temperatures up to 1150°C (2100°F). Moreover, it can be reliably used at cryogenic temperatures as low as -270°C (-450°F). Its corrosion resistance is higher than that of Type 309. It is suitable for welding and cold working applications, however, heat treatment cannot be applied to it. It is widely used in the production of parts and components for high-temperature applications such as heat exchangers, furnaces, oil burners, combustion tubes and chambers, radiant tubes, and kilns.

Stainless Steel 314: It is almost same with Stainless Steel 310, but it includes more silicon to cope with increased heat. Type 314 is widely used in the production of heat exchangers, oil burners, furnaces, combustion tubes and chambers, flare tips, annealing covers, firebox sheets, fluidized bed coal combustors, welding rods, filler wires, coal gasifier components, radiant tubes, kilns and tube hangers.

Stainless Steel 317: It is widely used under highly corrosive conditions. Type 317 stainless steel, which is a weldable and easy-to-machine material, can be used in cold and hot working applications, however, it is not suitable for heat treatment. Type 317 is widely used in the production of generators, boilers, condenser tubes, heat exchangers, absorption towers, pressure tanks and vessels, stack liners, pipes, fittings, and valves.

Stainless Steel 321: This grade of stainless steel is suitable for use in extreme temperatures up to 815°C (1500°F). It has a good creep and rupture resistance, and excellent resistance to scaling and vibration fatigue. Type 321 stainless steel is widely used in the production of exhaust systems of the airplanes, various components of jet engines, cabin heaters, pressure tanks and vessels, boiler shells, flexible couplings, expansion joints, wire clothing, etc.

Stainless Steel 347: Although it shows similar characteristics to Type 321, its intergranular corrosion resistance is higher. Type 347 stainless steel is widely used in the production of exhaust systems of airplanes, various components of jet engines, cabin heaters, chemical processing equipment, pressure tanks and vessels, boiler shells, flexible couplings, expansion joints, wire clothing, etc.

Stainless Steel 348: Although it is almost identical to Type 347, it has more cobalt content in its composition. Type 348 stainless steel is widely used in the production of exhaust systems of airplanes, various components of jet engines, cabin heaters, chemical processing equipment, pressure tanks and vessels, boiler shells, flexible couplings, expansion joints, wire clothing, etc.

Stainless Steel 405: This grade of stainless steel has high weldability, formability, and machinability. However, the parts that are welded cannot be annealed. Type 348 stainless steel is widely used in the production of annealing boxes, quenching racks, steam nozzles, etc.

Stainless Steel 409: It can maintain its superior corrosion resistance in operations at high temperatures. This grade of steel has high weldability and machinability, and it is reliably used in cold and hot working processes. However, it is not suitable for heat treatment. Type 409 stainless steel is widely used in the production of agricultural machinery, automotive exhaust systems (pipes and mufflers), catalytic converters, car thermostats, supports and hangers for structural components, and shipping containers.

Stainless Steel 410: The minimum chromium content of 11.5% provides this alloy with superior corrosion resistance against several chemicals and acids. This grade of stainless steel has high weldability and machinability, and it is reliably used in cold and hot working processes. Type 410 stainless steel is widely used in the production of nuts and bolts, screws, press plates, pipes, valves, cutlery, medical instruments, oil refinery equipment, etc.

Stainless Steel 414: Although it is almost identical to Type 410, it has more nickel content in its composition; thus, it has improved corrosion resistance. Type 414 stainless steel is widely used in the production of nuts and bolts, screws, press plates, pipes, valves, cutlery, medical instruments, oil refinery equipment, etc.

Stainless Steel 430: This grade of stainless steel has high formability, and it shows superior acid resistance and stress corrosion cracking resistance. Type 430 stainless steel is widely used in the production of home appliances, kitchen utensils, cutlery, screws and fasteners, car trims, etc.

Stainless Steel 431: The corrosion resistance of Type 431 of stainless steel is the highest among all martensitic stainless steels that can be hardened. This grade of stainless steel is suitable for hot or cold working processes and can be hardened up to 40 HRC. Type 431 stainless steel is widely used in the production of valves, pipes, nuts and bolts, propeller shafts, various components of airplanes, marine equipment, etc.

Stainless Steel 434: Although it is almost identical to Type 430, it has more molybdenum content in its composition; thus, it has improved heat and corrosion resistance. As a formable and weldable alloy, it has also high machinability. Type 434 stainless steel is widely used in the production of car trims and moldings, combustion chambers of furnaces, gas burners, ventilation hoods, gutters, dishwashers, bases of steam irons, cutlery, etc.

Stainless Steel 436: Although it is almost identical to Type 434, it has more molybdenum and titanium content in its composition; thus, it has improved resistance to pitting corrosion. Type 436 stainless steel is widely used in the production of combustion chambers of furnaces, gas burners, ventilation hoods, gutters, dishwashers, bases of steam irons, cutlery, etc.

Stainless Steel 442: The high level of chromium content provides this alloy with superior corrosion resistance. Although it is prominent with its high heat resistance, it is not suitable for heat treatment, and its machinability is quite low. Type 442 stainless steel is widely used in the production of components for combustion chambers of furnaces, zinc die casting machines, nitrogen fixation equipment, storage tanks for nitric acid, decoration trims, etc.

Stainless Steel 446: With its superior hot corrosion and oxidation resistance, it can be reliably used in applications with high operating temperatures. As a weldable alloy, Type 446 stainless steel has high machinability, however, it is not suitable for heat treatment. Also, cold working processes are quite difficult with this alloy. Type 446 stainless steel is widely used in the production of boiler baffles, thermocouple protectors, neutral salt baths, waste heat recovery boilers, X-ray tubes, oil burners, waste incinerators, etc.

Stainless Steel UNS S31803: Although its corrosion resistance is quite high, it is not suitable for operating temperatures over 260°C (500°F). As a weldable alloy, this grade of steel can be easily machined, and it is suitable for both cold formation and hot formation. It is the most common of all duplex steels. UNS S31803 grade stainless steel is widely used in the production of valves, chokes, manifolds, pumps, flanges, bolts and nuts, connectors, screws and fasteners, screw conveyors, augers, generators, instrumentation tubes, press rolls, etc.

Stainless Steel UNS S32003: This duplex steel, which is enhanced with the addition of nitrogen, has an improved strength. This grade of stainless steel can be easily machined and has high formability. UNS S32003 grade steels are widely used in the oil and gas applications at subsea fields.

Stainless Steel UNS S32101: This grade of duplex steel has higher strength and better corrosion resistance than Type 304 stainless steels. UNS S32101 grade stainless steel is widely used in the chemical processes, biodiesel production plants and biodiesel tanks, white-liquor storage tanks, washers, bridges, floodgates, desalination system components, and wastewater treatment plants.

Stainless Steel UNS S32304: Although it is almost identical to Type 304 and Type 316 stainless steels, its high yield strength is higher than that theirs. This grade of stainless steel is weldable and can be easily machined. Besides, it is suitable for both cold and hot working processes. UNS S32304 grade stainless steel is an ideal material for storage tanks, pressure tanks/vessels, etc.

Stainless Steel UNS S32205: Although it is almost identical to UNS S31803 grade stainless steel, it has more nitrogen in its composition; thus, it has improved corrosion resistance. UNS S32205 grade stainless steel is widely used in the production of pipes, valves, chokes, manifolds, pumps, flanges, bolts and nuts, connectors, screws and fasteners, couplings, screw conveyors, power generators, equipment for oil and gas industry, instrumentation tubes, press rolls, etc.

Stainless Steel UNS S32760: This grade of super duplex stainless steel is weldable and has high machinability. The strength and corrosion resistance of UNS S32760 are significantly higher than those UNS S32205. This grade of stainless steel is widely used in the production of mining tools and equipment, marine equipment, pharmaceutical products, etc.

Stainless Steel UNS S32550: This grade of super duplex stainless steel is prominent with its excellent strength and high corrosion resistance. It is widely used in the production of pumps, valve bodies, shafts, marine equipment, etc.

Stainless Steel UNS S32707: This grade of hyper duplex stainless steel is weldable and is widely used in high chloride environments. The corrosion resistance and strength of UNS S32707 are higher than those of UNS S32750. It is widely used in the production of marine equipment, petroleum equipment, heat exchangers, etc.

Stainless Steel UNS S33207: This grade of hyper duplex stainless steel is prominent with its excellent stress corrosion cracking resistance and superior mechanical strength. UNS S33207 is widely used in the production of oil and gas exploration tools and equipment.