Stainless Steel: A
Acid Pickling, Pickling
The removal, by immersion in a solution containing nitric and hydrofluoric acids, of the scale left after hot working or annealing. It leaves a matt grey finish.
Related terms: Passivation
A combination of two or more metals, or of metals and other elements. An alloy is formed by adding the 'alloying elements' to the 'parent' metal in the molten state. The parent metal usually accounts for more than 50% of the resultant mixture. Stainless Steel is an alloy of Iron plus Chromium (minimum 10.5%) with a small amount of Carbon plus various other elements (such as Nickely, Molybdenum, Titanium, Manganese) depending upon the grade.
A heat treatment cycle used to soften and restore ductility after cold working and to relieve internal stresses in a work piece.
The electrode in an electrochemical, or corrosion, cell from which a current flows into the cell. In corrosion processes material is dissolved at the anode.
Electrochemical corrosion protection, achieved by increasing the electrode potential of the steel.
Tubular products made by continuously welding formed strip that were not subject to a heat treatment such as annealing after welding.
A face centred cubic (FCC) phase found in all steels. In most carbon and low alloy steels it is present only above 760oC. In austenitic stainless steels their chemical composition stabilises austenite to room temperature and even cryogenic temperatures. Austenite is non-magnetic.
Austenitic Stainless Steel
Stainless Steels that contain a minimum of 18% Chromium and sufficient Nickel, or a combination of Nickel, Manganese and Nitrogen, to stabilise the face centred cubic (FCC) phase austenite down to cryogenic temperatures – This phase is normally present only above 760oC in most steels, These steels are, except in very particular circumstances, non-magnetic and have good ductility but relatively high work hardening rates. They have excellent corrosion resistance to most environments, although susceptible to stress corrosion cracking (SCC) above 60oC. Pitting and crevice corrosion can occur in chloride environments except with Type/Grade 316 where the Molybdenum content inhibits, but cannot always fully prevent, these problems. They cannot be hardened by heat treatment - The mechanical properties can only be increased by cold working.