Abstract The present invention relates to the heattreatment of steel. More particularly it relates to the heattreatment of all types of iron and steel which are capable of hardening on heating to the austenitising range and then quenching, without the need to introduce additional carbon during the heating step. For the sake of simplicity these types of iron and steel will be referred to hereinafter as ''''steel of the class which can be hardened by heating and quenching.'''' This class of materials comprises the plain carbon steels and cast steel of the medium- and high-carbon varieties and the alloy steels containing at least 0.25 percent by weight carbon. The present invention provides a method of heattreating steel of this class whereby the steel is provided with a surface layer that is resistant to scuffing and wear when subjected to friction under a heavy load and the underlying core is hardened so as to be resistant to indentation.
A method according to claim 1, wherein the said molten salt bath contains at least 10 percent by weight of alkali metal cyanate calculated as NaCNO.
Claim 2
Dependent Claim
29 words
A method according to claim 1, wherein the step of heating the steel into its austenitizing range is carried out by immersing the steel in a neutral salt bath.
Claim 3
Dependent Claim
40 words
A method according to claim 1, wherein the steel is a high-carbon steel and the step of heating the steel into its austenitizing range is carried out by immersing the steel in a molten salt bath containing alkali metal cyanide.
Claim 4
Dependent Claim
45 words
A method according to claim 1, Wherein the said molten salt bath held at a temperature in the range 700*-770* C. is restricted to the range 700*-750* C., the hot steel is immersed in this bath and is soaked therein for at least 5 minutes.