Machinability Improvement Through Heat Treatment In 8620 Low-Carbon Alloyed Steel

The effect of different heat treatments is evaluated on SAE 8620 low-carbon alloyed steel by means of drilling tests. Improving machinability through prior heat treatment in steels used for nitro-carburizing surface treatments is very important in the manufacturing of large series of parts, due to its impact in production costs. This is the case for the commonly used SAE 8620 grade, in its carburized and quenched and tempered state, for the production of gears, shafts and other transmission box components for the automobile industry. The machinability of the steel, determined by simple drilling tests (which are typical in industry labs), is a function of microstructure, which is determined by the state in which the steel is received and/or heat treatments prior to carburizing. This work shows that by employing some inter-critic annealing treatments, followed by sub-critic isothermal ones, the machinability of 8620 steel can be improved by ∼16% over the typical as-received cold drawn state.