Hydrogen trapping by M_4C_3 carbide in tempered carbon-vanadium-molybdenum martensitic steels, and modeling of M_4C_3 precipitation during tempering

摘要

Hydrogen-trapping behavior in carbon-vanadium-molybdenum martensitic steels was studied. Steels in which M_4C_3 precipitates show hydrogen-trapping ability, and the dominant factors of trapping capacity are the average size, number density and chemical composition of M_4C_3. The model which can predict these parameters was developed. In this model, the precipitation and Ostwald ripening behavior of M_4C_3 (plate-shaped) particles during the tempering of carbon-vanadium-molybdenum martensitic steel has been characterized and modeled, taking account of local equilibrium, the capillarity effect, and simultaneous cementite enrichment and dissolution. M_4C_3 particles are represented as parabolic cylinders of revolution, with the tip radius chosen to yield the maximum lengthening rate. Transmission electron microscopy has been used to validate the theory; measurements of the average length, number density and chemical composition of M_4C_3 particles shows good agreement with experimental observations.