In this study, the influence of nanocrystalline structure on the plasma nitriding (PN) behavior of 17-4PH steel and corresponding corrosion mechanisms under different treatments were systematically investigated. The results showed that nanocrystalline structures introduced by ultrasonic surface rolling process (USRP) would affect the nitrides morphology, composition and distribution via accelerating element diffusion. The fabricated nanocrystalline structures could enhance the corrosion resistance of original and plasma-nitrided 17-4PH steel, which was attributed to its various microstructures. Homogeneous microstructures suppressed or alleviated the formation of micro-galvanic couple in USRP-treated 17-4PH steel and USRP-15 + PN specimen.

In this study, the decomposition of a martensite/austenite (M/A) microconstituent in bainitic steels was analyzed using differential scanning calorimetry (DSC) data in conjunction with Kissinger’s and Johnson–Mehl–Avrami–Kolmogorov (JMAK)’s formulas. In bainitic steel subjected to austempering heat treatment, the presence of an M/A microstructure adversely affects the mechanical properties. According to the kinetic equations derived, it is observed that after tempering the sample at 600 °C for 4000 s, the generation of each phase reaches its maximum. The SEM images taken before and after tempering reveal extensive decomposition of the M/A constituent in the microstructure. The proportion of the M/A microstructure decreased significantly from about 10% before tempering to less than 1% after. Additionally, the content of residual austenite also reduced nearly to zero. These observations are consistent with the predictions of the kinetic equations.

In this study, we have systematically investigated how both shot peening (SP) and re-shot peening (RSP) affect the surface integrity and fatigue performance of TC17 titanium alloy. Surface integrity involves a competitive mechanism with the coexistence of beneficial and detrimental factors, both of which collectively determine the fatigue performance. While compressive residual stress (CRS), dislocation multiplication, and work hardening serve as beneficial factors, surface roughness and surface damage act as the detrimental factors. The results reveal high-intensity SP produced a deeper work-hardened layer. However, it also caused larger surface roughness and more severe surface damage, yielding the relaxation of the surface CRS and poorer improvement of the fatigue performance than that achieved with medium-intensity peening. The RSP treatment demonstrated a superior balance of surface integrity factors by effectively reducing the degree of surface damage and elevating the magnitude of surface CRS. Thus, a 45.9-fold improvement in fatigue life was achieved relative to the base material (BM) specimen. Surface CRS was identified as the primary factor contributing to the enhanced fatigue performance.

The journal retracts the article titled “Kinetics of Martensite/Austenite Decomposition during Tempering of Ultrafine Nano-Bainitic Steels”