| Cryogenic treatment can increase material properties, but heat treatment and experimental parameters can have as great an impact. In this research, an AISI D2 tool steel was subjected to various austenitizing, tempering, and cryogenic treatments. Microstructure was assessed with optical and electron microscopy, and mechanical properties with tensile, impact, hardness, and wear tests. Cryogenic treatment after quenching increased hardness and wear resistance. This was attributed to transformation of some retained austenite to martensite and matrix strengthening by refinement of carbon atom clustering. Tempering at 250°C or higher following cryogenic treatment eroded mechanical property improvements, except for hardness. This was attributed to martensite and retained austenite weakening from carbide precipitation and coarsening. Holding at room temperature or tempering prior to cryogenic treatment stabilized retained austenite against transformation, reducing benefits. Methodology was developed for experimental procedures assessing effects of cryogenic treatment. A previously undescribed bainitic microstructure was found in specimens austenitized at 950°C. |
