AISI 304 Channels

AISI 304 channel is hot rolled channel section in the general purpose austenitic stainless steel, the 18/8 combination of chromium and nickel with no deliberate molybdenum. Chromium gives the section its passive film, which holds in air, water and ordinary plant service, and nickel keeps the structure austenitic, so an annealed channel is non-magnetic and keeps its toughness in the cold. It is chosen over 316 where the service carries no chlorides, since the molybdenum 316 adds is paid for only against pitting in salt or brine. It is chosen over 304L where the frame is bolted or lightly welded, the lower carbon of 304L being bought for heavy welds left as welded. Laxcon Steels rolls the channel to order.

The channel is supplied annealed and pickled: the anneal heats the steel and cools it quickly so the chromium carbides return into solution, and the pickling strips the rolling scale. ASTM A276 sets the annealed minima at 515 MPa tensile strength and 205 MPa yield strength. Taper flange and parallel flange sections are both rolled, to the shape, dimension and mass tolerances of EN 10279. The grade takes strength only from cold work and work hardens under the tool, so drilling and sawing call for sharp edges and a steady feed. It welds readily, although slow cooling through about 450 to 850 C sensitises the weld zone, meaning chromium carbides form at the grain boundaries and open them to attack. Typical uses are equipment frames, walkway and platform supports, tank and vessel stiffeners, and machine guards.

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.