Stainless Steel

Grade

Stainless steel is a corrosion resistant steel alloy with a minimum of 10.5% chromium. There are different grades and surface finishes of stainless steel produced to accommodate the environment in which the material will be implemented. Unlike carbon steel, stainless steel does not rust when exposed to air and moisture due to the sufficient amount of chromium present. The chromium creates an invisible passive film of chromium oxide that will not let oxygen attack the surface and prevents rusting of the iron base.

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

• 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

Popular Stainless Steel Grades Available at ARUPUSU BUNKA GINKO :