Improvement and Analysis of Fatigue Strength for Mild Steel 20MnCrS5 during Carburizing and Quenching

Abstract

Distortion and fatigue are both important criteria for evaluating carburizing and quenching process. An optimized process was proposed to reduce distortion and improve fatigue strength simultaneously. Mild steel 20MnCrS5 were heat treated using standard condition and optimized condition respectively. The microstructure, hardness, residual stress, domain size, fatigue performance and crack growth rate with different conditions were studied. Due to carburization, the near surface of the materials have different microstructures with different carbon concentration. The carburized layer, subsurface layer and central layer were selected to prepare the fatigue specimens and to be evaluated. The strengthening effect was verified by comparing the fatigue limit and the crack growth rate. The strengthening mechanism was analyzed by comparing microstructure, retained austenite, residual stress and domain size. The results show that with the optimized condition the fatigue performance at different layers are improved while achieving higher surface hardness. The joint action of domain refinement, more compressive residual stress and less retained austenite results in the strengthening.

Verification of the Non-Axisymmetric Deformation Mechanism of Bearing Rings after Quenched in a Multi-Field Coupled Simulation

“…Based on the first law of thermodynamics, the conservation of energy, the increment of internal energy is equal to the sum of the heat energy transferred, the work done and the latent heat of phase transformation. The physical equation can be formulated [7][8][9][10] as:…”

“…σ i j , ε p ij are the stress and the plastic strain. ρ I , l I and ξ I are the density of I constituent, latent heat produced by I constituent, Coatings 2022, 12, 676 9 of 20 and the volume fraction of the I constituent, in that, the sum of the volume fractions of the I constituent (pearlite and bainite phases, martensite, and retained austenite) is 1 [7][8][9][10].…”

“…The → n is the direction vector of heat transfer. Consider the convective heat transfer boundary between the part and the quenching medium during quenching and list the boundary conditions as follows [7][8][9][10]:…”

“…Professor Inoue and Ju put forward the phase transition mechanics theory and developed heat-treatment simulation software (COSMAP) with a multi-field coupled function, according to the theory [5]. In recent years, COSMAP has been applied to solve many types of heat-treatment engineering problems [6][7][8][9][10][11]. Xusheng Li et al simulated a steel gear model based on the measured phase-change plasticity parameters and the metal-thermal-mechanical theory.…”