Forged & Proof Machined Stainless Steel Bars

Above 120 mm a stainless bar is forged from an ingot or a bloom rather than rolled, and the forged surface carries scale, a decarburised skin and the small laps and folds of the hammer. Proof machining turns that skin off, usually 3 to 6 mm on diameter, so that the surface the customer receives has been seen and inspected in the bright and any defect that would otherwise appear halfway through a customer's machining programme is found at the works. The bar is then ultrasonically tested through a clean surface, which is the other reason the skin comes off.

The condition is chosen for the machining that follows: soft annealed or solution annealed for the austenitic grades, normalised or quenched and tempered for the martensitic and alloy grades. At 550 mm a metre of bar weighs 1.88 tonnes, so lengths are supplied cut to the customer's piece length rather than at the 6 metre maximum.

The hot rolled round bar covers 16 to 125 mm from the rolling mill; the forged and proof machined bar covers 120 to 550 mm from the press. The overlap at 120 to 125 mm is decided by the grade and the end use: a rolled bar is the lower-cost route, a forged bar has the higher reduction ratio that a large shaft or a pressure part with a through-thickness property requirement is specified on. The forging quality ingot is the starting stock for both this page and the customer's own forge.