Stainless Steel Technical Information

Basics of... Stainless Steel

Chromium is the key ingredient in the iron-alloy class known as Stainless Steel. The addition of more than 12% chromium, by weight, results in the formation of a non-corrosive oxide or "passive film," which serves as the protective barrier between the steel and the damage it can sustain from its environment. The passive film is what keeps the metal shiny, and can also re-form in the presence of oxygen if the metal is scratched or damaged. Because Stainless Steel is a family of alloys rather than a single metal, the inclusion of different elements yields varying properties: nickel is added for better corrosion resistance, ductility and weldability; molybdenum is added for resistance to pitting, carbon for higher strength and hardness, aluminum and silicon to improve oxidation resistance.

Basic Stainless Steel Groups

Austenitic (non heat treatable) - The grades of stainless steel are grouped by metallurgical type. The Austenitic grades, also known as the "300 series" are iron-nickel-chromium composites, non-magnetic in the annealed state (condition A) and non-heat treatable (they can be hardened by cold-working only). They are usually considered the most weldable of their category, and retain their austenitic atomic structure at all temperatures.

Martensitic (heat treatable) - The Martensitic grades are fully heat-treatable and magnetic, though not particularly corrosion-resistant, and they are extremely strong and highly machinable, containing significant amounts of carbon and chromium. Martensitic stainless steels are commonly used in bearings, cutlery and mildly corrosive chemical applications.

Type	Description	Drawing Stamping	Welding
Austenitic (non heat treatable)

303	Free machining version of type 304 stainless steel because of the addition of sulfur. Excellent for making heavier cuts in automatic machining operations	Fair	¹Very Good

304/304L	Most widely used stainless steel alloy. Low carbon content for increased weldability. 18-8 (18% chromium, 8% nickel) composition makes this alloy corrosion resistant and easy to form	Very Good	Very Good

316/316L	This alloy has a higher nickel and molybdenum content to give it increased corrosion resistance and resistance to pitting. Excellent for chemical processing applications.	Good	Very Good

321	Titanium stabilized, corrosion & oxidation resistant, used for primary parts fabrication	Good	Very Good

347	Columbium/tantalum stabilized, corrosion & oxidation resistant. Used in aircraft, automotive and chemical processing equipment	Good	Very Good

420 ESR	Electroslag remelted for cleanliness and uniformity. Made with carbon at .34/.42 for excellent hardenability up to 55 Rc. For applications requiring good wear properties and moderate corrosion resistance. Good Machinability. In the hardened ondition resists corrosion due to atmosphere, water, mild acids and alkalis and chemical off gassing from plastics. Used for plastic molds, die cast nozzles, gages, glass lens molds, EDM fixtures, jigs, scissors, cutlery, dental and surgical instruments, mechanical parts requiring moderate stainless properties. Welding requires special procedures.	Poor	Poor

Martensitic (heat treatable)

410	General purpose alloy with mild corrosion resistance. Heat treating this alloy creates an extremely hard surface	Fair	Fair

416	Similar to type 410 with greater machinability	Fair	²Poor

440C	Excellent abrasion and wear resistance, good in bearing and bushing applications. Corrosion resistant only if heat treated	Poor	Poor

15-5	Low temperature hardening that combines high strength and hardness with excellent corrosion resistance. It has good forgeability and good transverse mechanical properties	N/A	N/A

17-4	Low temperature hardening, minimum scaling or distortion, readily weldable, corrosion resistant	Very Good	Very Good

¹Fusion welding not recommended. ²Welding not recommended.

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