Stainless Steel info in 5 main categories.

There is Austenitic, Martensitic, Ferritic, Duplex and Precipitation hardening. find more steel info below.

200 Series Austenitic – Alloys: 201, 202, 203, 204 & 205 is a chromium-nickel-manganese alloy with high strength in the annealed. This series is non-magnetic, not heat treatable and has excellent formability for sever forming applications. It is used in structural applications and for the manufacture of washing machine tubs. Decreasing nickel content and increasing manganese results in weak corrosion resistance

300 Series Austenitic – Alloys: 301, 302, 303, 304, 305, 308, 309, 310, 314, 316, 317, 321, 330, 347, 384 is chromium-nickel alloy and its strength is developed by cold working. The series is non-magnetic, not heat treatable and has good formability. By adding molybdenum, the corrosion resistance is increased. It is used in food equipment, chemical equipment and architectural applications.

400 Series Ferritic – Alloys: 405, 409, 429, 430, 434, 436, 442, 446 is straight chromium alloy, magnetic but it is not heat treatable. This series is mainly used for automotive trim and cooking utensils. Ferritic stainless steels have a body–centered cubic crystal system and contain between 10.5% and 27% chromium with very little nickel, if any, but some types can contain lead.

400 Series Martensitic – Alloys: 403, 410, 414, 416, 420, 422, 431, 440 is straight chromium alloy, magnetic and can be hardened by heat treatment. It is used for fasteners, pump shafts and turbine blades. Martensitic stainless steel contains chromium (12–14%), molybdenum (0.2–1%), nickel (less than 2%), and carbon (about 0.1–1%)

Precipitation Hardening – Alloys: 13-8, 15-5, 15-7, 17-4, 17-7 is chromium-nickel, martensitic or austenitic. Develop strength by precipitation hardening reaction due to heat treatment. It is mainly used for valves, gears and petro-chemical equipment. The most common, 17–4PH, uses about 17% chromium and 4% nickel.

Duplex – Alloys: 329, 2205, 2304, 2507, 3RE60 is chromium-nickel-molybdenum. This series is more resistant to stress corrosion cracking than austenitic and it is also tougher than fully ferritic alloys. It is mainly used in pipelines or pressure shafting. Duplex grades are characterized into groups based on their alloy content and corrosion resistance, they are; Lean duplex, Standard duplex, Super duplex and Hyper duplex.

Interesting to know that there are over 150 grades of stainless steel, of which 15 are most commonly used. There are a number of systems for grading stainless and other steels, including UNS, DIN and US SAE steel grades. More steel info on this page.