Decarburization Control of H13 Steel Under Varying Process Pressures During Austenitization

Decarburization during austenitization degrades the surface integrity and mechanical performance of tool steels, yet the quantitative influence of process pressure remains unclear. In this study, the effect of process pressure on the decarburization behavior of H13 tool steel was investigated. Specimens were austenitized at 920-1020 °C for 60 min under pressures ranging from 0.01 to 760 Torr. Carbon concentration profiles were measured by electron probe microanalysis, and hardness degradation and mass loss were evaluated. A one-dimensional diffusion model with a Robin boundary condition was applied to describe the coupled effects of carbon diffusion and surface reaction. High-vacuum conditions suppressed decarburization, whereas increasing pressure accelerated carbon loss, leading to deeper decarburized layers and pronounced hardness reduction. The model reproduced the experimental results and revealed a pressure-dependent transition in the dominant decarburization mechanism.