Simulación numérica del temple por inducción en aceros de baja aleación y análisis de la influencia de las tensiones residuales en el rolling contact

• DIRECTORS: Eneko Ukar (EHU) and Mario Cabello (Ikerlan).
• UNIVERSITY: UPV/EHU

ABSTRACT

The induction hardening process is a surface hardening technique that is increasingly used in industry due to the advantages it offers over other conventional heat treatments. It is typically used on critical components that are subjected to high loads and high pressure contacts, which require an elevated surface hardness. Although the industry's interest in this heat treatment in increasing, the definition of the most important process parameters is generally limited to the technicians' know-how and to previous experiences, increasing the associated costs and the time-to-market, since the design of the process is normally carried out by means of trial-and-error procedures.  The simulation of induction hardening is highly complex and computationally expensive because of the numerous interactions between physical fields. In the literature review, it has been observed that the application of induction hardening in complex industrial components is limited by the lack of numerical models capable of predicting the consequences of induction hardening. Numerical simulation is therefore key in the development of the induction hardening process and its effective implementation in modern industry. Furthermore, the study of the implications that induction hardening has on the in-service behavior of hardened components is a task to which engineers and scientists have devoted their attention in recent years, although it is not yet fully resolved.

In this doctoral thesis, the simulation of the induction hardening process is addressed in order to solve the limitations found in the existing literature. A numerical model to efficiently simulate the induction heating phase of ferromagnetic materials has been developed, which couples the electromagnetic and thermal fields through a semi-analytical model. This model has been experimentally validated on low alloy 42CrMo4 steel cylinders, obtaining more accurate and 80 % faster results than using other commercial software. Additionally, a coupled multiphysics model has been developed to simulate the second phase of the induction hardening process. This model couples thermal, mechanical and microstructural physics and has been experimentally validated in terms of prediction of microstructure, hardness and residual stress generation. The developed model, unlike other commercial software, allows to evaluate the impact of the various models used to describe different phenomena occurring during quenching. In this thesis, the impact of Transformation Induced Plasticity (TRIP) on the low alloy 42CrMo4 has been investigated, concluding that computational models should include this effect to improve residual stress predictions.  

Finally, the developed models have been combined with experimental techniques to investigate the influence of induction hardening residual stresses on rolling contact fatigue (RCF) behavior. In this study, a computational methodology has been developed to incorporate residual stresses in RCF life analyses and the influence of residual stresses has been studied numerically and experimentally using a modified three-ball-on-rod test. It has been observed that compressive residual stresses at the hardened case extend the life of the component and modify the depth at which the most critical damage occurs. For the numerical analysis, the Dang Van multiaxial criterion has been used and three critical shear stress quantities (Tresca, orthogonal shear and octahedral shear) have been compared in terms of life prediction and critical damage location. Numerical and experimental results indicate that the orthogonal shear quantity predicts more accurate results. 

The contributions made in this doctoral thesis are expected to reduce the current gap between the simplified models generally developed in the literature and the industrial cases of higher complexity, allowing empirical trial-and-error procedures to be considerably reduced and increasing the control over the resulting material characteristics obtained with the process. With this change in the paradigm, it is expected that, at an industrial level, greater economical, temporal and energetical efficiency can be achieved, also reducing the number of defectives.