AISI 304 Equal Angles

AISI 304 equal angle is a hot rolled stainless steel section with two legs of the same width, made from 20 x 20 x 3 mm up to 127 x 127 mm. Chromium at 18 to 20 percent and nickel at 8 to 10.5 percent hold the steel austenitic and build the passive film that keeps it from rusting in air, fresh water and most foodstuffs. Annealed 304 shapes meet minimums of 515 MPa tensile strength and 205 MPa yield strength under ASTM A276. The grade is taken instead of 304L where the angle is bolted or welded in light sections, since 304L gives up a little strength for the lower carbon that heavy welded work wants. It is taken instead of 316 where no chlorides are present, because the molybdenum in 316 answers salt and seawater.

The angle is supplied annealed and pickled: heated until the carbides return to solution, cooled quickly, then acid cleaned to take off the rolling scale. In that state it is non-magnetic and at its softest, and no heat treatment will harden it, so any further strength comes from cold work. It welds with the usual arc processes and needs no preheat; short passes and quick cooling keep chromium carbides from forming at the grain boundaries, a change called sensitisation that lowers corrosion resistance beside the weld. The steel hardens under a cutting edge, so machining asks for sharp tools and a steady feed. The section carries equipment frames in dairy and food plant, walkway and platform supports in chemical works, handrails and balustrades, and brackets and pipe supports in water treatment.

Composition limits in weight percent are carbon 0.08 maximum, manganese 2.0 maximum, sulphur 0.03 maximum, phosphorus 0.045 maximum, silicon 0.75 maximum, chromium 18.0 to 20.0, nickel 8.0 to 10.5 and nitrogen 0.1 maximum.