Stainless steel classification
发布时间：2019/4/12
Stainless steels can generally be categorized into 7 categories:
 
Ferritic Stainless Steels
  • Chromium is their major alloying element
  • Ductility and formability less than austenitic grades
  • Magnetic
  • Highly corrosion resistant, less durable than austenitic
  • Cannot be hardened by heat treatment
  • Contain between 10.5%-27% chromium and very little nickel
  • Common grades: part of the 400 series like 409, 410S, 430
Austenitic Stainless Steels
  • Comprise of 70% of total stainless steel production
  • Hardenable by cold working
  • Usually non-magnetic
  • High hardness and yield strength
  • Contain a maximum of 0.015% carbon, minimum of 16% chromium and sufficient nickel and/or manganese
  • Superaustenitic stainless steels (AL-6XN and 254 SMO)  have great resistance to chloride pitting and crevice corrosion
  • Common grades: 300 series like 304, 316, 320, 321, 347,309
Martensitic Stainless Steels
  • Highly machinable
  • Very strong and tough
  • Can be hardened by heat treatment
  • Magnetic
  • Contains chromium (12-14%), molybdenum (0.2-1%), nickel, (0 - < 2%), carbon (0.1 - < 1%)
  • Common grades: 410, 420, 440
Duplex Stainless Steels
  • Often divided into 3 sub classes
    • Lean Duplex
    • Standard Duplex
    • SuperDuplex
  • Mixed microstructure of austenite and ferrite about a 50/50 mix
  • Higher strength and better stress corrosion cracking resistance than most austenitic alloys
  • Greater toughness than ferritic alloys, especially at low temperatures
  • Good resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking
  • Common grades: 2205 and 2507
Precipitation-Hardening Martensitic Stainless Steels        
  • Designed to be formable in the solution annealed condition
  • Can be hardened by heat treatment
  • Contain chromium and nickel as major alloying elements
  • Corrosion resistance is usually better than that of straight chromium ferritics
  • Most common grade is 17-4PH
Superaustenitic Stainless Steels
  • Same structure as austenitic alloys
  • Enhanced levels of elements like chromium, nickel, molybdenum, copper and nitrogen
  • Superior strength and corrosion resistance
  • Common Grades: AL-6XN and 254 SMO
Superferritic
  • Structure and properties similar to ferritic alloys
  • Enhanced levels of chromium and molybdenum
  • Increased resistance to high temperatures and corrosive environments like seawater
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