Optimising nano-carbide precipitation in tool steels

It is well known that the wear resistance of tools can be improved using deep cold treatment to produce nucleation sites for the nano-sized carbides that form in the martensite during low temperature tempering following the extended treatment times. However, inconsistencies in the processing techniques used, particularly the soaking time at very low temperature and the steelʹs previous thermal history, have led to different conclusions as to the exact mechanisms involved. This paper reviews current thinking and attempts to explain the different results obtained in terms of the processing parameters and to elucidate the implications for the practical application of the technique to obtain optimum properties. An optimised process route using liquid nitrogen as the coolant is recommended and a possible technique to make further improvements in the process is suggested.