K-0519 ギガサイクル疲労特性に及ぼす介在物と組織の影響(S04-2 高強度鋼の超高サイクル疲労(1))(S04 金属材料の組織と疲労強度信頼性)

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Three SCM440 steels (heats B, C and D) were supplied for fatigue tests. Al_2O_3 inclusions of heats B and C were smaller than those of heat D. Heat B was ausformed and induction-tempered, whereas heats C and D were normally quenched and furnace-tempered. Fatigue limits at 10^8 cycles were 890 MPa for ausformed heat B, 840 MPa for quenched heat C and 750 MPa for quenched heat D. Fish-eye type fracture, which occurred in the quenched heats, disappeared in ausformed heat B. Origins of fish-eye type fracture were TiN inclusions in quenched heat C and Al_2O_3 inclusions in quenched heat D. Large and clear ODA, i.e. optically dark area, was observed on the fracture surface around the Al_2O_3 inclusion. On the other hand, ODA around the TiN inclusion was obscure and difficult to measure.
2001-08-22