Process for heat treatment of parts made from low and specified hardenability structural steel

Abstract

A size hardening heat treatment process for steel parts of a plate, cylindrical or spherical shape and using low or specified hardenability steel compositions which are through surface heated and very rapidly quenched to produce case hardening of the part. A set of graphs are provided which depict the relationship between the depth of hardening and the dimension of the part for each of a series of critical, i.e., ideal diameter values which allow producing a depth of hardening of a particular part by a proper selection of the DI value of the part. The DI values are calculated by a formula which allows a range of DI values to be created by varying the components of the steel as set out in the formula. The formula also insures a fine grain size to be created by the process to prevent cracking by the very rapid quenching required. A list of elements allowed in the steel but limited by a % mass set out for each component. A particular depth of hardening desired can be produced for a given part of a shape and dimension appearing in the graphs by composing the steel so that the DI is that critical which will produce the desired depth of hardening when the part is heated by through the surface heating and then very rapidly quenched.