The Effects of Fine Particle Peening on Surface Residual Stress of a TRIP-Aided Bainitic Ferrite Steel

Abstract

To apply a transformation-induced plasticity (TRIP)-aided steel consisting of bainitic ferrite structure matrix and metastable retained austenite of 10 vol% (TBF steel) to some precision gears, the effects of fine particle peening on the Vickers hardness and residual stress in a surface layer of the TBF steel were investigated. The peened surface layer showed much higher Vickers hardness and compressive residual stress than those of a quenched and tempered SNCM420 steel. The increased Vickers hardness was mainly caused by an increase in the strain-induced transformed martensite fraction. The compressive residual stress was increased by the increases in size and gravity of shot material and arc-height. The higher compressive residual stress was principally associated with (1) plastic strain due to severe plastic deformation and (2) expansion strain due to the strain-induced transformation of metastable retained austenite. Contribution of the (2) was approximately 30% of total residual stress.

Microstructure and Mechanical Properties of a TRIP-Aided Martensitic Steel

“…The term f is a constant, b is the Burgers vector, and r denotes the mean diameter of the second-phase particles. Because the microstructure of TM steel is composed of a soft matrix (wide lath-martensite) and a hard second phase (MA-like phase), high compressive internal stress, which results from a difference in flow stresses between the matrix and the second phase, takes place in the matrix [28]. Figure 9 shows a typical fracture in TM steel (Steel A) after stretch forming, stretch flanging, and bending tests.…”

“…In particular, fine particle peening can enhance the fatigue strength by increase in surface hardening and the compressive residual stress, with a small surface roughness, which resulted from strain-induced martensite transformation of retained austenite [28,37]. …”

Effects of Vacuum-Carburizing Conditions on Surface-Hardened Layer Properties of Transformation-Induced Plasticity-Aided Martensitic Steel

“…Natori et al [27] proposed that residual stress resulting from the strain-induced martensitic transformation (ΔσXα,t) can be calculated using Equation (3),…”

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

“…Many researchers found that shot peening considerably increases the fatigue strength of the conventional case-hardening martensitic steels [49][50][51][52][53][54][55][56][57][58][59]. Sugimoto et al [60][61][62] have reported that high fatigue strength and low notch-sensitivity for fatigue of the TM steel are achieved by fine-particle peening and/or vacuum carburization because of small surface roughness and the improved surface-hardened layer properties. In addition, 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].…”