GB849313A - A metallurgical process for treating steel - Google Patents

Abstract

A process for treating steel which strain hardens and hardens by some mode of precipitation when worked at a temperature between 350 DEG F. and the lowest critical temperature for the steel composition comprises rolling or advancing the steel through a die to effect reduction in cross-section while the steel is at a temperature within the above range and then heat treating the steel subsquent to the elevated temperature reduction step. In an example a hot-rolled, pickled and limed bar, rod, wire or tube of non-austenitic steel having a pearlitic structure in a matrix of free ferrite is extruded or drawn through a die whilst at a temperature within the range of 450 DEG to 850 DEG F. and then heated to the austenitizing temperature (1500 DEG F.), for one hour, quenched in oil and tempered. In another example the heat treatment consists in heating the steel above the transformation range (1500 DEG -1600 DEG F.), followed by a partial quench to a temperature within the range of 200 DEG F. to the lower critical temperature of the steel. In another example the heat treatment after the reduction step consists in martempering the steel by heating to a temperature above its transformation temperature and quenching the steel in a bath maintained at a temperature slightly below the Ms range until transformation to martensite is complete and then cooling the steel to room temperature. In a further example the steel is austempered by heating above its transformation range (1500 DEG -1600 DEG F.), and quenching at a temperature slightly above the Ms range and at a rate to extract heat from the steel to avoid passage through the austenite range and then cooling. In another example the steel is subjected to diffusion transfer after the reduction step by either carburizing, nitriding, cyaniding, chromizing or carbonitriding followed by cooling to room temperature. Specifications 761,150 and 761,151 are referred to.