論文
高Cr型肌焼鋼のA1変態点以下焼鈍における炭化物の均一分散化とその機構
2026 年 112 巻 4 号 p. 172-185
詳細
2026 年 112 巻 4 号 p. 172-185
In the JIS standard case-hardening steel, spheroidizing annealing can improve cold forgeability but inevitably results in uneven distribution of carbides (a mixture of lamellar carbides and spherical carbides, and uneven carbides distribution). This degrades cold forgeability and promotes grain coarsening during carburizing. To address this problem, new SA methods combined with suitable chemical compositions are required to achieve a uniform distribution of carbides in a hypoeutectoid steel.
This study found that an ideal structure with uniformly dispersed carbides can be obtained by using high-Cr case-hardening steel with ferrite - pearlite as the initial microstructure and holding it below the A1 temperature by precipitation of carbides in ferrite in addition to the dissolution of cementite in pearlite. Microstructure analysis and thermodynamic calculations revealed that in high-Cr compositions, the chemical potential of C in pearlite is significantly higher than in ferrite, which drives C diffusion from pearlite to ferrite, and precipitation of spherical carbides in ferrite. Furthermore, it was found that AlN particles in ferrite act as nucleation site of carbides, promoting precipitation of carbides in ferrite.
