An Overview of Fatigue Strength of Case-Hardening TRIP-Aided Martensitic Steels

Abstract

Surface-hardened layer characteristics and fatigue strength properties of transformationinduced 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.

Kinetics of Austenite Phase Transformations in Newly-Developed 0.17C-2Mn-1Si-0.2Mo Forging Steel with Ti and V Microadditions

“…The factors determining the presence of this phase lead to its stabilization thanks to the appropriate concentration of C, multi-stage heat treatment, and Si added to the steel, which contributes to a significant delay in the precipitation of cementite in bainitic ferrite [ 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Pioneering works in this area have been carried out for over twelve years, mainly in Japanese and German units [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. However, the optimal parameters of hot working and cooling profiles to achieve the above-mentioned mechanical, technological, and operational properties have not been developed so far.…”

Low and Medium Carbon Advanced High-Strength Forging Steels for Automotive Applications

“…To further enhance the wear resistance and fatigue strength of the AFSs, a surface layer shell hardened up to 60 HRC is needed [48,79]. Many engineers also want to know such mechanical properties of case-hardened AFSs.…”

“…A small quantity of metastable retained austenite and the decreased carbide fraction may make a contribution to the impact toughness. [78,79]. L c : Quasi-cleavage length affected by the MA phase located on prior austenitic, packet, and block boundaries.…”

Low and Medium Carbon Advanced High-Strength Forging Steels for Automotive Applications

“…To further enhance the wear resistance and fatigue strength of the AFSs, a surface layer shell hardened up to 60 HRC is needed [47,81]. Many engineers also want to know such the mechanical properties of case-hardened AFSs.…”