AISI 304 Threaded Bars

AISI 304 threaded bar is bar rolled in the general purpose austenitic stainless steel and threaded along its whole length, M6 to M45, or 1/4 to 1-3/4 inch, in lengths to 6 metres. The chromium forms the passive oxide film that keeps the thread from rusting in air, water and food service, and the nickel holds the austenitic structure. The grade carries no deliberate molybdenum, so where the fixing sits in seawater, de-icing salt or a chloride process stream, 316 threaded bar in class A4 resists pitting better and is the usual step up. Where a long welded assembly cannot be annealed afterwards, the lower carbon of 304L is chosen instead. For dry, damp and mild outdoor fixing work 304 covers the duty. Laxcon Steels rolls the thread to order.

The bar is supplied solution annealed, heated and cooled fast so the chromium carbides return into solution, which leaves it soft, ductile and non-magnetic. It cannot be hardened by heat treatment and takes strength only from cold work, and rolling the thread is itself cold work, so a rolled thread is stronger than a cut one and can read slightly magnetic. ISO 3506-1 sets class A2-70 at 700 MPa tensile strength and 450 MPa proof strength, and the annealed class A2-50 at 500 MPa and 210 MPa. ASTM A193 grade B8 Class 1 is carbide solution treated at 515 MPa tensile and 205 MPa yield. Typical uses are pipe hangers and building services supports, tie and anchor rods, frames in dairy and food plant, and studs cut to length.

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.