Numerical and experimental investigation on the residual stresses generated by scanning induction hardening

Induction hardening is widely used in the industry as a surface heat treatment that improves the surface and the subsurface hardness of components greatly. The hardened case, which usually is a few mm, highly impacts the surface and structural integrity of the component. In this work, we simulate the scanning induction hardening process by means of finite element modeling. The computed hardness, microstructure, and residual stress profile are compared with experimentally measured data using several surface and subsurface characterization techniques. A very good agreement is found between the simulated and experimentally measured residual stresses, which were characterized by the incremental hole drilling technique

Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel

The usage of induction hardening in the industry has increased in the last years due to its efficiency and repeatability. Induction hardening produces a hard martensitic layer on the specimen surface, which is accompanied by the generation of compressive residual stresses in the hardened case and tensile stresses in the untreated core. Residual stresses generated by induction hardening greatly impact on fatigue performance, as they act as crack growth retardants. In this work, a multiphysical coupled finite element model is developed to simulate induction hardening and compute the final residual stress state of the specimens along the microstructural transformations and hardness evolution. The impact of the transformation induced plasticity strain in the stress-state of the specimen during the process is also studied. The experimental validation shows that considering the transformation induced plasticity in induction hardening simulations improves the residual stress predictions, concluding that this effect should be included to achieve good residual stress predictions, especially in the subsurface region

Predicting the induction hardened case in 42CrMo4 cylinders

Induction hardening has the potential to produce favorable surface integrity that can improve fatigue performance and extend the lifetime of a component. The localized superficial heating provided by induction is the main advantage of this process, as it allows the core to remain intact and, therefore, ductile, while the surface is hardened. Achieving favorable characteristics in the hardened case is of great importance, as this process is usually applied to load bearing and wear-susceptible metallic components. The simulation of the hardening process by induction heating is a complex and challenging task at which many efforts have been directed in the last years. Due to the numerous interactions of the many physics that take part in the process (electromagnetic, thermal, microstructural and mechanical), a highly coupled finite element model is required for its numerical simulation. In this work, a semi-analytical induction heating model is used to compute the induction hardening process, predicting the size and shape of the hardened layer and the distribution of the hardness. Using the semi-analytical model allows the computational time to be much faster compared to a fully coupled model using a commercial software, where the time consumption for the presented 2D case is reduced by 20 %. Experimental validation is presented for cylindrical 42CrMo4 billets heated by a short solenoidal inductor, which shows good agreement with the predicted results, reaching an average error of 3.2 % in temperature estimations

Fatigue Assessment of Selective Laser Melted Ti-6Al-4V: Influence of Speed Manufacturing and Porosity

Additive Manufacturing represents a promising technology as an alternative to the conventional manufacturing process, with rapid and economic product development, as well as a significant weight reduction and a freeform design. Although the mechanical properties of additively manufactured metals, such as the Ti-6Al-4V alloy, are well-established, a complete understanding of the fatigue performance is still a pending aspiration due to its inherent stochastic complexity and the influence of several manufacturing factors. This paper presents a study of the influence of speed manufacturing and porosity in the fatigue behaviour of a Ti-6Al-4V alloy. To this aim, a numerical simulation of the expected porosity at different laser velocities is performed, together with a simulation of the residual stresses. These numerical results are compared with experimental measurements of residual stresses and a qualitative analysis of the porosities. Then, fatigue strength is experimentally obtained for two different laser speeds and fitted by a probabilistic model. As a result, the probabilistic S–N fields for different laser velocities are found to be similar, with scatter bands nearly coincident, drawing the conclusion that this effect is negligible in comparison with other concurrent ones, such as roughness or surface defects from manufacturing conditions, promoting crack initiation and premature fatigue failure

Influence of induction hardening residual stresses on rolling contact fatigue lifetime

Rolling contact fatigue is a unique mode of fatigue that components under cyclic contact loading experience. In this work, the impact of induction hardening residual stresses in rolling contact fatigue lifetime is investigated experimentally and numerically using the Dang Van multiaxial criterion. Various residual stress fields from induction hardening are simulated using the finite element method and are mapped into a classical monocontact finite element model. The impact of induction hardened residual stresses on the lifetime of a component has been investigated, and the importance of incorporating the residual stress profile into fatigue life assessments is affirmed

A semi-analytical coupled simulation approach for induction heating

The numerical simulation of the induction heating process can be computationally expensive, especially if ferromagnetic materials are studied. There are several analytical models that describe the electromagnetic phenomena. However, these are very limited by the geometry of the coil and the workpiece. Thus, the usual method for computing more complex systems is to use the finite element method to solve the set of equations in the multiphysical system, but this easily becomes very time consuming. This paper deals with the problem of solving a coupled electromagnetic - thermal problem with higher computational efficiency. For this purpose, a semi-analytical modeling strategy is proposed, that is based on an initial finite element computation, followed by the use of analytical electromagnetic equations to solve the coupled electromagnetic-thermal problem. The usage of the simplified model is restricted to simple geometrical features such as flat or curved surfaces with great curvature to skin depth ratio. Numerical and experimental validation of the model show an average error between 0.9% and 4.1% in the prediction of the temperature evolution, reaching a greater accuracy than other analyzed commercial softwares. A 3D case of a double-row large size ball bearing is also presented, fully validating the proposed approach in terms of computational time and accuracy for complex industrial cases