Abstract
Surface-hardened layer characteristics and fatigue strength properties of transformation-induced plasticity-aided martensitic steels subjected to heat-treatment or vacuum carburization followed by fine-particle peening are revealed for automotive applications specially for powertrain parts. The as-heat-treated steels without the case-hardening process possess excellent impact toughness and fatigue strength. When the steels are subjected to fine-particle peening after heat-treatment, the fatigue limits of smooth and notched specimens increase considerably, accompanied with low notch sensitivity. Vacuum carburization and subsequent fine-particle peening increases further the fatigue strength of the steels, except notch fatigue limit. The increased fatigue limits are principally associated with high Vickers hardness and compressive residual stress just below the surface, resulting from the severe plastic deformation and the strain-induced martensitic transformation of metastable retained austenite, as well as low surface roughness and fatigue crack initiation depth.
Highlights
Sugimoto et al [60,61,62] have reported that high fatigue strength and low notch-sensitivity for fatigue of the TRIP-aided martensitic (TM) steel are achieved by fine-particle peening and/or vacuum carburization because of small surface roughness and the improved surface-hardened layer properties
They showed that further increase in fatigue limit of the steels is achieved by using of multi process of vacuum carburization and fine-particle peening which increases the hardness and residual stress in the surface hardened layer [63,64,65]
This surface-hardened layer which are enhanced by the strain-induced martensite transformation of review paper is based on our researches referring to the fatigue strength of TM steels because no metastable retained austenite and severe plastic deformations, as well as the surface roughness and researcher could identify and address potential issues
Summary
Four types of transformation-induced plasticity (TRIP)-aided steels with different matrix structures and different chemical compositions, namely “TRIP-aided bainitic ferrite (TBF) steel” [1,2,3,4,5,6,7,8,9,10],. 0.2%C–1.5%Si–1.5%Mn–1.0%Cr–(0–0.2)%Mo steels subjected to layer heat-treatment correlated with the Vickers hardness and the residual stressTM in the surface-hardened which are or vacuum-carburization followed by fine-particle peening are explained. The fatigue enhanced by the strain-induced martensite transformation of metastable retained austenite and strength properties are mainly correlated with the Vickers hardness and the residual stress in the severe plastic deformations, as well as the surface roughness and fatigue crack initiation depth This surface-hardened layer which are enhanced by the strain-induced martensite transformation of review paper is based on our researches referring to the fatigue strength of TM steels because no metastable retained austenite and severe plastic deformations, as well as the surface roughness and researcher could identify and address potential issues.
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