Influence of cryogenic treatment on microstructure and mechanical properties of high strength AISI D2 tool steel

摘要

Cryogenic treatment, known as treating materials at sub-zero temperatures, has been added to conventional heat treatment cycle of high alloyed steels where martensitic transformation is incomplete after quenching to room temperature. Incomplete martensitic transformation occurs due to the effect of high content of alloying elements on pushing down martensite start and finish temperatures to very low values, specifically, on tool steels.ududIn spite of obtaining significant improvements in mechanical and wear properties after cryogenic treatment, there is no cohesive picture about what exactly modifies the microstructure of tool steels during cryogenic treatment and therefore divergent opinions on the influence of process parameters are still reported. For example, the suggested time length for cryogenic treatment starts from few seconds to several days indicating the lack of understanding about micromechanisms responsible for microstructural evolution while holding at cryogenic temperatures.ududIn this regard, the main objective of this project is to develop a better understanding on the fundamental micromechanisms operating during cryogenic treatment. To attain this objective, the following milestones are pursued.ud- To study the conventional cryogenic treatment and finding challenges.ud- To identify and characterize the optimum starting microstructure before cryogenic treatment.ud- To determine the important processing parameters those control the evolution of microstructure and hardness.ud- To investigate the interaction between carbide precipitation and martensitic transformation in the AISI D2 steel.ud- To propose an optimal cryogenic treatment for AISI D2 steel.