Numerical Simulation of Induction Hardening of Torsion Bar
In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is to compare the experimental residual stress fields measured by X-ray diffraction with those predicted from finite element modeling of the whole induction surface hardening process. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the fatigue loading, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress distribution and optimize the process, especially for safety critical engineering components. Results of present study show that the improvement of fatigue performance is due to development of both hard microstructure and compressive residual stress at the surface layer of torsion bar during induction hardening.
Residual stresses in surface induction hardening of steels : Comparison between experiment and simulation
Deep induction hardening has been performed on two batches of smooth cylindrical specimens with a hardening depth respectively around 2 mm and 3 mm. The distributions of axial and circumferential residual stresses are analysed for the two specimen batches by X-ray diffraction technique. The radial normal stress field is estimated through the use of the well known Moore and Evans correction. Finally, the experimental residual stresses are compared with those obtained from a multiphysic finite element modelling of the whole induction treatment process, including electromagnetic, thermal, metallurgical and mechanical phenomena. The simulated residual stress field is in good agreement with X-ray analysis especially at depths lower than one-tenth the specimen diameter. At deeper depths, a correction of the experimental X-ray analysis has been done to obtain realistic values.
Isothermal bainitic transformation in low alloy steels: factors limiting prediction of the resulting material's properties
Abstract The present study identifies key material phenomena that limit the predactive capabilities of current approaches employed in modelling the properties of heat treated components. Focus is on aspects related to the isothermal austenite-to-bainite transformation in low alloy steels. Specifically, experimental data are presented on (i) the stress–strain response of austenate prior to transformation, (ii) the magnitude and progress of transformation plasticity and (iii) the effect of externally applied loads on the kinetics of the bainitic phase transformation. The data obtained demonstrate a substantial stress-induced as well as a strain-induced acceleration of the bainitic transformation, which has to be accounted for in modelling. Moreover, stress–strain response of the supercooled austenite was found to be drastically different from that estimated based on the behaviour of stable austenitic steels. The results also point out that transformation plasticity can contribute significantly to distortion...