Experimental investigation and finite-element modeling of the short-time induction quench-and-temper process of AISI 4140
Introduction
Induction hardening is a frequently used method to enhance the mechanical properties of parts such as gears and crankshafts. One goal of induction hardening is the introduction of compressive residual stresses that are beneficial to the fatigue limit of the material as stated by Withers (2007) in his comprehensive paper on the effect of residual stresses on fatigue.
Tempering is a common heat treatment after surface hardening. Tempering increases ductility and toughness of the very brittle martensitic surface, as it is e.g. stated in the book by Krauss (1989). The underlying metallurgical processes are mainly carbon redistribution and carbide precipitation as well as dislocation annihilation. An overview over the typical temperature ranges in which these processes occur is given by Speich and Leslie (1972). Usually, tempering is done as a conventional heating process in an oven with long tempering times and moderate heating rates. Advantages of rapid tempering using induction are short process times and a good reproducibility due to the induction heat treatment. Even more, studies of the mechanical properties of tempered samples report beneficial effects of rapid tempering. Furuhara et al. (2004) performed tempering experiments with heating rates up to 1000 C/s and stated an increase of the strength/ductility ratio with increasing heating rate for a given hardness after tempering. Recent investigations by Judge et al. (2018) revealed that the toughness of rapidly tempered steel samples is significantly higher as compared to conventionally tempered samples of the same hardness.
Due to volume changes during carbide precipitation and a decrease of the yield strength, tempering affects the residual stresses that are present after any hardening process. In spite of its importance for practical applications, the change of residual stresses in a surface hardened part during tempering for both rapid and conventional heating methods has not been investigated in much detail yet. Since the measurement of residual stresses is tedious, numerical simulations of the quench-and-temper (QT) process can help to gain understanding of the evolution of residual stresses.
Early simulation models of the conventional QT process were presented by Inoue et al. (1981) who included the volume changes due to phase transformations which were modeled by phenomenological Johnson–Mehl–Avrami–Kolmogrov-type (JMAK) equations to compute the residual stress evolution during tempering. Aubry (1998) developed a comparable tempering simulation model, also based on phase transformations modeled via JMAK equations, which included the effect of auto-tempering for the first time. They found this effect to be present in steels with high martensite start temperatures but it has shown little effect on the resulting residual stresses after tempering. Later, Wang (2006) studied the conventional tempering of carburized steels. The phase transformations during tempering were modeled using physically based nuclation and growth models. All these works on the QT process allowed the calculation of residual stresses after tempering, but only for conventional and thus relatively slow oven heat treatments. Zabett and Mohamadi Azghandi (2012) modeled the induction tempering of carbon steel including an electromagnetic heating model. This work was clearly focused on the heating simulation via induction, the only mechanical quantity that was calculated was the hardness after tempering. The recent study by Tong et al. (2018) reported results on the simulation of induction hardened and subsequently oven tempered specimen which allowed the calculation of phase transformations and residual stresses. The tempering times applied in this work were 2 h, thus it cannot be considered as short-time heat treatment.
As can be seen from the literature survey, no results on experiments and especially simulations of a short-time QT process are reported to this day. The present paper aims at filling this gap. It presents experimental results such as hardness and residual stresses of rapidly hardened and rapidly tempered specimen. A simulation of the complete QT process is presented and validated using the aforementioned experimental results. Special emphasis is put on the stability of residual stresses during the tempering process. For the first time the influence of the transformation induced plasticity during tempering (T-TRIP) due to the precipitation of carbides is addressed.
Section snippets
Samples
The mechanical properties of the material in the tempered state were determined using tensile tests with the sample geometry as shown in Fig. 1.
For the induction heating experiments, ring-shaped samples as shown in Fig. 2 were used.
All samples were manufactured from 90 mm bars of AISI 4140 (German grade 42CrMo4) steel with the chemical composition as given in Table 1. The chemical composition was measured using spark emission spectroscopy.
After machining, all samples were austenitized at 880 C
Measurement and modeling of mechanical properties
For the simulation of the tempering process, the mechanical properties are required including elastic modulus , yield strength and the hardening behavior. Generally, the mechanical properties during tempering depend on the current temperature as well as on the tempering state. Therefore, a model is sought that accounts for the temperature as well as the tempering state. To produce the necessary data to develop such a model, two series of tensile tests were performed. In the first series,
FE-model
The simulation model for the induction QT process is multiphysical including electromagnetic and thermal–metallurgical–mechanical submodels. The model is based on the commercial FE solvers ABAQUS/Standard and ABAQUS/Electromagnetic. The coupling between the electromagnetic and the thermal-metallurgical-mechanical simulation is done via Python scripts.
The main features of the models will be presented in the following.
Simulation and experiments of the induction QT process
In this section, the results from the induction QT experiments are discussed and compared to the results from the simulation model.
Hardening
Fig. 6 depicts the comparison of the simulated and measured temperature evolutions during hardening. The 3 phases of the process heating ( s), moving shower ( s) and quenching ( s) are clearly distinguishable.
Surface as well as subsurface temperatures are in a good overall agreement during heating and quenching. The immediate rise of the measured
Influence of T-TRIP
To assess the influence of the tempering-TRIP effect caused by cabide precipitation during tempering, the simulation of tempering experiment 2 as discussed in Section 5.1 was repeated without accounting for T-TRIP. The resulting tangential residual stresses are plotted in Fig. 16. For direct comparison, the results from the simulation with T-TRIP (cf. Fig. 13a) are plotted as well. A striking difference can be seen from the plot. The tensile residual stresses at the surface without T-TRIP are
Conclusion
Short-time induction tempering experiments of induction hardened parts were performed that indicated that a severe change in the residual stresses after tempering occurs. With increasing maximum tempering temperature, the residual stresses are shifted into the tensile regime.
A comprehensive multiphysical FE-model for the simulation of short-time induction QT processes was developed and validated. The model consists of a coupled electromagnetic-thermal-mechanical-metallurgical simulation and was
Acknowledgement
This research was supported by the German Research Foundation (DFG) program with the grant number SCHU 1010/49-1.
References (43)
- et al.
Modelling of induction hardening in low alloy steels
Finite Elem. Anal. Des.
(2018) A review of the influence of grinding conditions on resulting residual stresses after induction surface hardening and grinding
J. Mater. Process. Technol.
(2001)- et al.
A dilatometric study on the influence of compressive stresses on the tempering of martensitic AISI 4140 steel – evidence of transformation induced plasticity during cementite precipitation
Mater. Sci. Eng. A
(2017) A general equation prescribing the extent of the austenite–martensite transformation in pure iron–carbon alloys and plain carbon steels
Acta Met.
(1959)Mathematical modelling of transformation plasticity in steels. II: Coupling with strain hardening phenomena
Int. J. Plast.
(1989)- et al.
Prediction of phase transformations during laser surface hardening of AISI 4140 including the effects of inhomogeneous austenite formation
Mater. Sci. Eng. A
(2006) - et al.
Influence of cyclic temperature changes on the microstructure of AISI 4140 after laser surface hardening
Acta Mater.
(2007) - et al.
Quantitative evaluation of effects of non-metallic inclusions on fatigue strength of high strength steels. I: Basic fatigue mechanism and evaluation of correlation between the fatigue fracture stress and the size and location of non-metallic inclusions
Int. J. Fatigue
(1989) - et al.
Separation of overlapping retained austenite decomposition and cementite precipitation reactions during tempering of martensitic steel by means of thermal analysis
Thermochim. Acta
(2011) - et al.
12.15 – Induction hardening: technology, process design, and computer modeling
Numerical simulation on induction heat treatment process of a shaft part: involving induction hardening and tempering
J. Mater. Process. Technol.
Simulation of induction tempering process of carbon steel using finite element method
Mater. Des.
A non-linear model for internal stress superplasticity
Acta Mater.
Beanspruchungsabh“angiges Umwandlungsverhalten und Umwandlungsplastizit”at niedrig legierter St“ahle mit unterschiedlich hohen Kohlenstoffgehalten
Simulation numérique par éléments finis en 3D du comportement thermomécanique au cours du traitement thermique d’aciers: application à la trempe de pièces forges ou couléss
Modeling of the temperature field, transformation behavior, hardness and mechanical response of low alloy steels during cooling from the austenite region
J. Heat Treat.
The tempering of iron-carbon martensite; dilatometric and calorimetric analysis
Metall. Trans. A
R“ontgenographische Untersuchung von Spannungszust”anden in Werkstoffen. Teil III. Fortsetzung von Matwiss. und Werkstofftechn. Heft 3/1995, S. 148-160 und Heft 4/1995, S. 199-216
Materialwiss. Werkstofftech.
Control of cementite precipitation in lath martensite by rapid heating and tempering
ISIJ Int.
Predicting the mechanical properties of a quenched and tempered steel thanks to a “tempering parameter”
Rev. Metall.
The deformation of metals under small stresses during phase transformations
Proc. R. Soc. A: Math. Phys. Eng. Sci.
Cited by (24)
Laminar plasma quenching-tempering: A rapid surface heat treatment technique for controllable modification of the rail steel
2023, Surface and Coatings TechnologyFailure analysis of ball screw in the progressive induction hardening and finishing machining
2023, Engineering Failure AnalysisLaser surface hardening: A simulative study of tempering mechanisms on hardness and residual stress
2023, Computational Materials ScienceA model for converting thermal analysis to volume fraction of high carbon bearing steels during low-temperature tempering
2023, Journal of Materials Science and TechnologyCitation Excerpt :Their multi-component precipitation modelling accurately predicted the volume fraction and stereological characteristics of precipitates quantitatively and shed light on the evolution of transition carbides into cementite. Recently, Tong et al. [13] and Kaiser et al. [14] studied the precipitation behavior of tempered carbides in 4140 steel during rapid heating considering the nucleation, growth and coarsening of carbides. However, no attempt was made to address the volume fraction of retained austenite as the precipitation modelling was inappropriate for retained austenite decomposition.
Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel
2022, European Journal of Mechanics, A/Solids