Intrinsic Factors that Trigger the Coaxing Effect in Binary Fe–C Ferritic Alloys with a Focus on Strain Aging

Fatigue Behavior in an Fe–N Binary Ferritic Steel: Similarity and Difference between Carbon and Nitrogen

“…In this study, we therefore focused on the fatigue damage evolution from crack initiation to mechanically or microstructurally small crack growth that covers 70% of fatigue life in steels. 9) In our previous studies 2,3,10,11) regarding Fe-C binary steels with supersaturated solute carbon, we clarified certain points in terms of fatigue crack initiation and small crack growth behavior. Therefore, we can interpret the fatigue behavior of an Fe-N alloy by comparison with that of the Fe-C alloys.…”

“…Commonly, the term "small crack" in fatigue phenomena is understood from different viewpoints, such as microstructurally small cracks, 5) mechanically small cracks, 6) physically small cracks, 7) and chemically small cracks. 8) According to the previous studies, 2,3) the kinetic effect of solute atoms effectively contributes to the regimes of fatigue crack initiation and mechanically or microstructurally small crack growth. In this study, we therefore focused on the fatigue damage evolution from crack initiation to mechanically or microstructurally small crack growth that covers 70% of fatigue life in steels.…”

“…1) In contrast, interstitial carbon enhanced transgranular fatigue crack resistance and improved the fatigue limit of steels. 2,3) The dramatic effects of interstitial atoms in steels are believed to be a key for enabling safe mechanical design and the development of next-generation fatigue-resistant materials.…”

“…3,11) (3) Crack coalescence was frequently observed at stress amplitudes higher than the fatigue limit, which can decrease fatigue life and strength. 2,3) (4) When the carbon content was increased from 0.006 to 0.017 mass%, the Fe-C alloy displayed a high level of coaxing effect due to suppression of intergranular fatigue crack initiation and propagation by strain age hardening at the crack tip. 2) Hence, this study was performed on a single-ferrite-phase Fe-N binary steel, to clarify the underlying effects of solute nitrogen on the fatigue properties and its correlation to small fatigue crack growth.…”

“…2,3) (4) When the carbon content was increased from 0.006 to 0.017 mass%, the Fe-C alloy displayed a high level of coaxing effect due to suppression of intergranular fatigue crack initiation and propagation by strain age hardening at the crack tip. 2) Hence, this study was performed on a single-ferrite-phase Fe-N binary steel, to clarify the underlying effects of solute nitrogen on the fatigue properties and its correlation to small fatigue crack growth. We compared the nitrogen effects with those of the solute carbon in an Fe-C binary system.…”