AISI 303 Flat Bars

AISI 303 hot rolled, annealed and pickled flat bar is an austenitic stainless steel flat rolled from steel to which sulphur has been added to a minimum of 0.15 percent. The sulphur forms manganese sulphide inclusions through the metal, and these break the chip as a cutter enters, so a block sawn from the flat mills, drills and taps faster than the same section in AISI 304, with short chips that leave the cutter clear. Chromium and nickel sit close to the AISI 304 levels, so the two flats look alike, but the inclusions are also where pitting starts. AISI 304 is the grade for a flat that must be welded or stand wet service. AISI 303 is the grade for a flat cut away in quantity where the service is mild and dry.

The flat is supplied annealed and pickled. The anneal softens the bar and returns the structure to austenite, which leaves it non-magnetic, and pickling strips the rolling scale and the chromium-poor skin under it, leaving a matte grey surface that takes machining directly. Heat treatment cannot harden the grade, and strength rises only by cold work, which a milled part does not receive. Welding is avoided, because the sulphur makes weld metal crack as it cools, and a section that has to be joined is usually ordered in AISI 304. Laxcon Steels rolls the flat to order in widths of 20 to 150 mm and thicknesses of 5 to 50 mm. Work commonly cut from it includes machined blocks and bodies, valve and pump parts, keys and gib strips, and sawn blanks for milled fittings.

Composition limits in weight percent are carbon 0.15 maximum, manganese 2.0 maximum, sulphur 0.15 minimum, phosphorus 0.2 maximum, silicon 1.0 maximum, chromium 17.0 to 19.0, nickel 8.0 to 10.0 and zirconium plus molybdenum 0.6 maximum.