반복인장-압축하중을 받는 이온질화 처리한 SM45C의 부식피로 파괴거동에 관한 연구

A study on the corrosion fatigue fracture behavior of ion-nitrided SM45C under alternating tension-compression loading

본 논문에서는 기계용 부품소재로 많이 사용되는 SM45C에 대하여 이온질화 처리시 N$_{2}$:H$_{2}$ 가스조성비 변화에 따른 효과가 반복인장-압축하중을 받는 부식피로파괴의 거동에 미치는 영향을 중점적으로 연구하였다.

This paper dealt with the effect of the ratios N2 to H2 gas on the corrosion fatigue failure behavior of ion-nitrided SM45C steel specimens. The specimens were water cooled after ion-nitriding at 500.deg. C for 3hrs in 5 Torr, 0.8N$_{2}$ and 0.5N$_{2}$ atmospheres. As the nitrogen concentration increases, the higher compressive residual stresses developed in the surface layer and the depth of nitrided layer increased, which in turn gave rise to increases in fatigue strength and corrosion fatigue life. In the region less than 1.5 * 10$^{5}$ cycles, fatigue failure initiated at the brittle nitrided case, whereas in the region higher than 1.5 * 10$^{5}$ cycles crack initiated from the non-metallic inclusions in the subsurface. The initiation of corrosion fatigue failure was mainly attributed to pitting of case hardened surface layer.