拡散付着型Mo系合金鋼粉の焼結冷間鍛造および真空浸炭窒化熱処理による疲労強度および耐摩耗性の向上

抄録

This study aims to obtain the superior mechanical properties of Mo diffusion-bonded alloyed steel by the optimum combination of processes: primary-sintering (PS), cold-forging (CF), heat treatment (HT) and shotblast. In our previous research, it was found that the fracture of sintering connections, namely, micro-cracks occurred on the surface layer of high-density specimens in addition to the work hardening on materials, which decreased both the impact energy and the bending strength. Also, since the optimum heat treatment leads the diffusion bonding of the pressurized cracks in the surface layer, the microstructure could be reformed. In this study, it was found that the 0.4 mass%Mo-steel powder had both the highest densification and deformability among the powders of 0.4, 1, 2 and 4 mass%Mo without precipitation of the unneeded ternary molybdenum carbide Fe₃Mo₃C. Also, when sintered specimens were cold-forged, the impact waveform of those showed clearly effects of both the work hardening and the damage of the microstructure. Finally, both the superior fatigue strength and the wear resistance were implemented with the proper processes to 0.4 mass%Mo sintered steel such as a second sintering, vacuum carbonitriding heat treatment and shotblast. Obtained properties were equal to or more than those of wrought steel SCr420H.