AISI 316 Threaded Bars

AISI 316 threaded bar is fully threaded austenitic rod in the molybdenum-bearing grade, threaded from M6 to M45 (1/4 to 1-3/4 inch) in lengths to 6 metres. Molybdenum, added to the chromium and nickel of AISI 304, raises resistance to pitting, the localised attack chlorides start at a surface, so 316 is specified for fastenings in salt air, splash zones, brine and process water where 304 pits at the thread roots. It is chosen over 316L where the bar is bolted rather than welded, the lower carbon of 316L being bought against sensitisation, the carbide precipitation that opens grain boundaries beside a heavy weld. Laxcon Steels rolls and threads the bar to order.

The bar is supplied solution annealed, the condition that takes chromium carbides back into solution and leaves the steel softest and most corrosion resistant; it cannot be hardened by heat treatment and gains strength only from cold work. Threads are rolled rather than cut, so metal is displaced into the form and the grain follows the thread. ISO 3506-1 sets the classes A4-50 annealed, A4-70 cold worked and A4-80 high strength cold worked, the number being the minimum tensile strength in tens of megapascals; ASTM A193 grade B8M covers the same steel as bolting, Class 1 solution treated and Class 2 solution treated and strain hardened. Typical uses are anchor and hanger rods in coastal plant, tie rods and studs on chemical equipment, fixings in water and effluent treatment, and marine handrail fastenings.

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 16.0 to 18.0, nickel 10.0 to 14.0, molybdenum 2.0 to 3.0 and nitrogen 0.1 maximum.