Stainless steel 1141 Grades of stainless steel

Stainless steel is the generic name given to corrosion and resistant steels with a minimum of 10.5% chromium, which oxidises to produce a surface patina that inhibits rusting. The stability of this thin passive layer increases as the chromium content increases, and is further enhanced by alloy additions of nickel and molybdenum.

The grades of stainless steel can be grouped into five basic groups:

• austenitic stainless steel — these are the most widely used types of stainless steels and are based on 17-18% chromium and 8-11% nickel alloys. They have high ductility and are readily weldable

• ferritic stainless steel — they contain 10.5-18% chromium, but less nickel than austenitic grades, and are less corrosion resistant

• duplex stainless steels — these steels are generally used where high stresses are to be resisted under severe corrosion conditions, and are often used for bars and pins. They typically contain 21-26% chromium, 4-8% nickel and 0.1-4.5% molybdenum

• martensitic stainless steels — these steels have a similar structure to ferritic stainless steels and are generally used for less corrosion resistant applications

• precipitation-hardened stainless steels — these steels are strengthened by heat treatment to very high temperatures and are used for heavy duty connections, such as the bolts.

Stainless steels are specified in BS EN 10088 and structural design is covered by supplementary rules given in Eurocode 3-1-4. The most widely used grades are standard austenitic grades 1.4301 (304) and 1.4401 (316), which are specified in BS EN 10088. The designation system refers to: 1 (steel), 43 or 44 (group of stainless steels), 01, etc. (individual grade identification).

The terms in brackets refer to the equivalent ASTM (American)

standard, where A304 and A316 are the common grades. The yield

strength is typically 200 to 220 N/mm (which is lower than for carbon steels), although the ultimate tensile strength is 500 to 700

N/mm (higher than for carbon steels). Duplex steels have 400 to

460 N/mm yield strength.

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