GB1415394A - Process for producing chromium and chromium oxide electrocoated tin-free steel - Google Patents

Abstract

1415394 Electro-depositing chromium and chromium oxide PENNWALT CORP 5 Feb 1973 [3 March 1972] 5652/73 Heading C7B Cr and Cr oxide coated tin-free steel strip is produced by annealing a cold rolled steel strip, e.g. wound into a tight coil at 1150 to 1250 F for 7 to 10 hours, then electro-depositing thereon Cr and forming thereover a Cr oxide layer, e.g. in a solution of CrO 3 containing NaOH and Na2 Si F 6 ; the strip being rinsed with an aqueous medium containing (e.g. 100-2500 ppm of) a reagent, which reacts with carbonaceous deposits on the strip at the annealing temperature to form a volatile product, between cold rolling and annealing. The reagent may be colloidal S or a S-containing compound which reacts to form CS 2 , e.g. alkali or alkaline earth metal or ammonium (bi)sulphate, (bi)sulphite, thiocyanate, dithionate, thiosulphate, (poly)sulphide, or an organic (di)sulphide, thioether, sulphoxide, sulphone, sulphate ester, sulphonate or (diethyl)thiourea; or it may be an O-containing compound which reacts to form CO, e.g. alkali or alkaline earth metal oxide, hydroxide or salt decomposing to oxide at the annealing temperature, such as nitrite, borate, bicarbonate, permanganate or Ti oxalate. Prior to cold rolling, the steel (e.g. slab) may be hot rolled, pickled in dilute H 2 SO 4 or HCl and rinsed; after cold rolling, the strip may be cleaned in hot aqueous alkaline solution, rinsed and scrubbed, prior to rinsing with the aqueous reagent. After annealing, the strip may be temper or cold rolled, again cleaned, pickled in dilute H 2 SO 4 and rinsed.