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Stainless Steel Classifications

Stainless steels are commonly grouped into martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, duplex (ferritic-austenitic) stainless steels, and precipitation-hardening stainless steels.

Stainless steels are in general grouped into

  • martensitic stainless steels
  • ferritic stainless steels
  • austenitic stainless steels
  • duplex (ferritic-austenitic) stainless steels
  • precipitation-hardening stainless steels

Alloying metallic elements added during the making of the steel increase corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum.

Stainless steels are available in the form of

  • plate
  • sheet
  • strip
  • foil
  • bar
  • wire
  • pipes
  • tubes

Stainless steels are a iron-based alloy containing at between 10.5% to 30% Cr. Stainless steel achieve its stainless characteristic through the formation of an invisible and adherent chromium-rich oxide surface film.

Other alloying elements added to improve the characteristics of the stainless steel include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulphur, and selenium.

Carbon is normally in amounts from 0.03% to more than 1.0% in some martensitic grades.

Selection of stainless steels are in general based on

  • corrosion resistance
  • fabrication characteristics
  • availability
  • mechanical properties for specific temperature ranges
  • product cost

Since stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained, it is widely used in items such as automotive and food processing products, as well as medical and health equipment. The most common US grades of stainless steel are:

TYPE 304

The most commonly specified austenitic (chromium-nickel stainless class) stainless steel, accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316

Austenitic (chromium-nickel stainless class) stainless steel containing 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

TYPE 409

Ferritic (plain chromium stainless category) stainless steel suitable for high temperatures. This grade has the lowest chromium content of all stainless steels and thus is the least expensive.

TYPE 410

The most widely used martensitic (plain chromium stainless class with exceptional strength) stainless steel, featuring the high level of strength conferred by the martensitics. It is a low-cost, heat-treatable grade suitable for non-severe corrosion applications.

TYPE 430

The most widely used ferritic (plain chromium stainless category) stainless steel, offering general-purpose corrosion resistance, often in decorative applications.

Austenitic Stainless Steels
TypeEquivalent UNS
201 S20100
202 S20200
205 S20500
301 S30100
302 S30200
302B S30215
303 S30300
303Se S30323
304 S30400
304L S30403
302HQ S30430
304N S30451
305 S30500
308 S30800
309 S30900
309S S30908
310 S31000
310S S31008
314 S31400
316 S31600
316L S31603
316F S31620
316N S31651
317 S31700
317L S31703
317LMN S31726
321 S32100
330 NO8330
347 S34700
348 S34800
384 S38400
Ferritic Stainless Steels
TypeEquivalent UNS
405 S40500
409 S40900
429 S42900
430 S43000
430F S43020
430FSe S43023
434 S43400
436 S43600
442 S44200
446 S44600
Martensitic Stainless Steels
TypeEquivalent UNS
403 S40300
410 S41000
414 S41400
416 S41600
416Se S41623
420 S42000
420F S42020
422 S42200
431 S43100
440A S44002
440B S44003
440C S44004

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