GB740352A - Improvements relating to alloy steels and to chromised articles made therefrom - Google Patents

Abstract

An alloy steel, suitable for high temperature applications such as boiler or superheater tubes or steam pipes, has the following composition:- .C.0.03-0.2.per cent, .V.0.05-0.4.per cent, .Mo.0.1 -1.0.per cent, .Mn.0.3 -1.0.per cent, .Ti.0.05-0.5.per cent, .Fe, and the usual impurities, the.. .remainder... The steel may also contain Si 0.04-0.5 per cent, Al used as a deoxidizer to the ladle in amounts up to 3 lbs./tons of steel and B up to 0.005 per cent. Articles made of the steel may be given a chromizing treatment. A treatment described consists in packing articles in a gas-tight retort surrounded with a mixture of pieces of ferro-chromium and sillimanite impregnated with chromous chloride. A stream of hydrogen is passed through the retort to remove oxygen and the retort is heated in a gas-fired furnace. Hydrogen chloride gas is introduced into the retort for 15 minutes when a temperature of 1080 DEG C. is reached. The temperature is maintained for 8 hours, then the retort is cooled and the articles removed. The chromized article may then be coated with aluminium or aluminium paint and heat treated, e.g. by heating to at least 1050 DEG C. and air cooling or oil or water quenching The cooling may be at a rate controlled to precipitate carbon as carbides in finely dispersed form, further heating to a temperature below the austenitic change point to produce complex carbides containing Ti and cooling at a rate to produce further precipitation of carbides. The Provisional Specification describes also alloys in which the range of proportions of the constituents are C 0.08-0.3 per cent, V 0.05-0.35 per cent, Mo 0.1-1.0 per cent, Mn 0.3-1.0 per cent with Ti from 1 to 4 times the quantity of C.