Heat Treatment Simulation Research Articles

Process‐chain simulation for prediction of the distortion of case‐hardened gear blanks

AbstractIn this study, a process‐chain simulation model is presented for the prediction of distortion of low‐pressure gas carburised SAE 5120 (EN 20MnCr5) steel gear blanks. For this purpose, the evolution of the banded microstructure stemming from the continuous casting process was traced by computer simulations of subsequent shape rolling, forging and machining steps. Then, the simulated local orientation angles of the deformed banded microstructure are transferred to heat treatment simulation module as an input for the recently developed material model that exploits the “Anisotropic Transformation Strain (ATS)“ concept to reproduce the dishing behaviour which cannot be reproduced by former models. The results indicate that the suggested procedure provides quite good predictions of the dishing directions and dishing‐free cutting strategy, whereas; the dishing magnitude is predicted fairly reasonably considering large scatters in the experiments.

Effect of Heat Treatment on Fracture during Bending in AA6016 Aluminium Alloy Sheets

The bending properties of high strength precipitation-hardening AA6016-type Al alloy thin sheets in pre-aged T4P temper state were studied in this work. Microstructural features like grain boundary particles distribution and volume fraction of the matrix strengthening phases were considered as factors controlling the mechanical properties and the fracture of this grade. Remarkable decrease in ductility, accompanied by severe deterioration of bendability occurred when coarse precipitates were found into the grain boundaries. The in-situ fracture sequence investigations as well as the post-failure surfaces observations indicated that grain boundary ductile fracture mechanisms were involved in the propagation of the cracks during bending. Heat treatment simulations were carried out and the results showed that the precise control of the technological parameters during production of these sheets is the key factor responsible for obtaining an appropriate combination of strength and bendability. Only by providing both, homogeneous distribution of the matrix strengthening phases and a favourable grain boundary structure, the severe and often contradictory requirements for the functional properties of these alloys can be successfully satisfied.

Development and application of computer simulation code COSMAP on induction heat treatment process

Induction heating reduces energy consumption, contributes to the protection of the environment, and improves productivity. This paper describes the development and application of computer simulation of induction heat treatment considered with coupling of temperature field and magnetic field. In this paper, the developed simulation code COSMAP is introduced as a CAE software system for considering the design of induction heat treatment process. It covers all aspects of heat treatment simulation, from magnetic and electrical to thermal states, phase transformation, residual stresses including as well all metallurgical phenomena.

Computer modeling and validations of steel gear heat treatment processes using commercial software DANTE

The heat treatment process of a gear made of AISI 9310 carburized steel is modeled using the commercial heat treatment simulation software DANTE. Both carburization and quenching processes affect the residual stress distribution and distortion of heat-treated parts, which are important to service quality and fatigue life. DANTE/VCARB is used to design the boost/diffuse schedule of a vacuum carburization process. Oil quenching is modeled following the vacuum carburization process. Thermal gradient and phase transformation are two main sources of distortion and residual stresses in quenched parts. The relation of the carbon distribution, thermal gradient, and phase transformations during quenching is studied through the gear modeling example. Because of geometry, the residual stress distribution after quenching is non-uniform along the gear surface. In general, the root fillet has higher residual compression than either the root or tooth face locations after traditional oil quenching of carburized gears. The predicted residual stresses from the oil quenching model are imported into a single tooth fatigue bending model. The gear stresses under bending load indicate the possible cracking locations during the bending fatigue test. The importance of heat treatment residual stresses during gear design is pointed out, and it is commonly ignored in the gear design and manufacturing industry.

Using simulation for heat treatment process design: matching quenching process with steel grade and product geometry

The performance of steel parts is heavily dependent on the heat treatment process applied. The alloy content of the steel establishes the steel hardenability. The severity of the quenching establishes the local temperature history throughout the body of the part. In combination, the steel hardenability and the quenching process determine the final microstructure, mechanical properties, residual stress state and the performance of the part. The residual stress state, especially the surface stress state, is a significant factor in affecting fatigue life of the part. The steel hardenability and quenching practice can be adjusted to enhance residual surface compression and improve the fatigue life of a component. Computer simulation of the heat treatment process that includes calculation of the metallurgical phase transformations during the heating and cooling processes offers a method for scientifically designing the heat treatment process and selecting the steel alloy to optimise the performance of a particular product. In this paper, the DANTE heat treatment simulation software will be used to demonstrate this design methodology for a spur gear.

Analysis of Quenching Crack Generation in Low Alloy Cast Steel by Using Heat Treatment Simulation

Analysis of Quenching Crack Generation in Low Alloy Cast Steel by Using Heat Treatment Simulation

Combined Butt Joint Welding and Post Weld Heat Treatment Simulation Using SYSWELD and ABAQUS

Due to increases in computational power, the finite-element (FE) method is now widely used to predict the thermal, material, and mechanical effects of welding. Welding simulations can provide important information about component distortions and residual stresses. This facilitates a reduction in lead-time and cost associated with the process planning. Moreover, welding is generally performed in combination with other manufacturing processes such as stress relief heat treatment. This article presents a simple method where welding and post weld heat treatment operations are combined using an uncoupled plasticity—creep model. Two FE codes, welding-function-specific SYSWELD and the general-purpose FE package, ABAQUS, were used to perform butt joint welding and post weld heat treatment simulations of two Inconel 718 plates. The predicted results obtained from the two FE codes, such as thermal histories, residual stresses, nodal displacements, and stress relaxation, are compared. Based on the results presented, some useful benchmarking comments on the use of the two FE codes for welding simulation are given.

Parameter identification for an Armstrong–Frederick hardening law for supercooled austenite of SAE 52100 steel

The mechanical properties of the supercooled austenite phase are sensitive parameters for the prediction of distortion of the components during heat treatments as the inelastic deformation occurs mostly on the soft austenite phase. Recent studies clarified that one of the overlooked issues related with the thermomechanical behavior of supercooled austenite during heat treatment and welding is its complicated cyclic hardening behavior (cf. Şimşir et al., Acta Materialia, 2010). Based on those concerns, this article presents an optimization method for determination of temperature-dependent parameters for an Armstrong–Frederick model with combined non-linear kinematic and isotropic hardening, which can potentially pull the quality of simulations through. The results indicate that the proposed approach yields satisfactory results for simulation of heat treatments and welding even with a small and imperfect experimental data pool.

3D modelling of a multi pass dissimilar tube welding and post weld heat treatment of nickel based alloy and chromium steel

A dissimilar tube welding is performed between the nickel based Alloy617 and creep resistant steel VM12 using the former as the weld material. SYSWELD welding software is used to model the thermal and mechanical analysis. A readily available thermal history is used to calibrate the heat source input for the thermal analysis to generate the adequate thermal cycle by fitting the welding velocity, heat intensity factor of the GOLDAK heat source and the length of molten zone. The transient temperature field is then incorporated as the input for the mechanical analysis to obtain the residual stresses in which the phase transformation of the materials during welding is taken into account. Subsequently, the weld materials are characterized by using the Norton’s creep law to determine the Norton parameters based on relaxation experiments. The residual stresses generated after the multi pass welding by SYSWELD is transferred into ABAQUS as the initial condition for the post weld heat treatment (PWHT) simulation. The simulations show that the residual stresses reduce in magnitude but still present even after PWHT.

Effects of Ferrite Content on the Tensile Strength and Impact Toughness of 2.25Cr-1Mo-0.25V Steels

In order to evaluate the effects of a pro-eutectoid ferrite content on the tensile strength and impact toughness of 2.25Cr-1Mo-0.25V steels, several samples with a different area fraction of ferrite in the range from 0 to 80% were prepared by a control of cooling rate from an austenitization heat treatment temperature of 930oC. The steels were then tempered at 690oC, followed by a heat treatment at 705oC as a simulation of postweld heat treatments. The results of microstructural observation indicated that the ferrite was uniformly distributed in the bainitic matrix. The results of tensile tests revealed that the tensile strength at room temperature and 450oC was slightly reduced with the ferrite content of up to 20%, but it was considerably reduced with the ferrite content of 80%. On the other hand, the results of impact tests at -60, -80 and -100oC indicated that the impact toughness was rapidly degraded with increasing ferrite content. These results attributed to the segregation of carbides in the bainitic matrix as a result of the formation of ferrite phase with low solubility of carbon. It is concluded that the ferrite content in the 2.25Cr-1Mo-0.25V steels could exert a sensitive inference on the impact toughness rather than on tensile properties.

The Bauschinger effect in the supercooled austenite of SAE 52100 steel

During the heat treatment and the welding of steel components, the interactions between the thermal and phase transformation strains result in cyclic loading of the component, which often results in plastic deformation. Although this has long been a well-known fact, the cyclic hardening behavior of supercooled austenite was not investigated up to now. In this study, tension–compression tests were performed on the supercooled austenite of SAE 52100 ball bearing steel at several temperatures using Gleeble3500® thermomechanical testing machine. The results were compared with conventional hardening models used in heat treatment and welding simulation. The results indicate that the metastable austenite exhibits a complicated cyclic hardening behavior that can only be partially reproduced by commercial simulation software. In the outlook, it is concluded that more complicated cyclic hardening models should be implemented for better prediction of distortion and residual stresses after heat treatment or welding.

Analysis of decomposition processes of ausferrite in copper–nickel austempered ductile iron

Analysis of thermal decomposition processes of the ausferrite obtained during simulation of austempering heat treatment was performed on austempered ductile iron (ADI). The analysis method consisting in investigation of inverse phase transformations was applied. The material with specified phase composition and well-defined thermophysical properties, both resulting from the conducted heat treatment cycle, was heated under controlled conditions and the thermal effects—enthalpy change and volume change were recorded by means of differential scanning calorimetry (DSC) and differential dilatometry. The process of ausferrite decomposition in the range of 100–800 °C was discussed; the identification scheme and temperature sequence of phase transformations accompanying the ausferrite decomposition were established. The elaborated decomposition scheme allows selection of the ADI heat treatment and its optimization by means of the non-isothermal thermal analysis methods.

Laser surface hardening of martensitic stainless steel hollow parts

This paper deals with numerical simulation and experimental validation of laser heat treatment of an industrial axisymmetric hollow mechanical part by means of a strategy based on helical tracks. This component, made of AISI 420B martensitic stainless steel, features a low wall thickness and, according to this, it is not easily treatable by means of laser surface hardening. The work carried out was aimed at demonstrating that numerical simulation allows a drastic reduction of the experimental activity and that it makes possible to prove a very high sensitivity of the results to process parameters variation.

A new framework for simulation of heat treatments

In this study, a mathematical framework based on finite element method (FEM) capable of predicting temperature history, evolution of phases and internal stresses during thermal treatment of metals and alloys was developed. The model was integrated into the commercial FEA software MSC.Marc® by user subroutines. The accuracy of the model was verified by simulating the quenching of eccentrically drilled steel cylinders. Simulation results were justified via SEM observations and XRD residual stress measurements.

Post Welding Heat Treatment Simulation in Welded Stainless Steel Pipe and Comparison with Experiment

Due to the intense concentration of heat in the welding process, residual stresses are produced in the specimen. One of the most effective ways to relief welding stress is Post Welding Heat Treatment (PWHT). In this paper, finite element method is employed to model and analyze PWHT for two pass butt-welded SUS304 stainless steel pipe. In this simulation, firstly, the welding process has been modeled. Then the stress distribution of the specimen has been transferred to a second analysis for stress relaxation modeling. Norton law is used to investigate creep in stress relief process. Experimental tests are also carried out to verify the effectiveness of the proposed numerical models. The hole drilling method is used to measure the stress distribution in the specimen. The residual stress distribution data before and after PWHT are compared to investigate the effect of heat treatment on residual stress. Based on the modeling and experimental results, the tensile and compressive stresses distributions have been reduced. They are in a reasonable agreement with each other and prove the capability of the proposed modeling technique to simulate PWHT.

Similarities and differences in heat treatment simulation of aluminium alloys and steels

AbstractAluminium alloys are nowadays applied in light weight constructions of many areas, e.g. transportation. Several manufacturing technologies are used in production chains of aluminium components. For improvements in strength heat treatments are carried out with aluminium alloys (precipitation hardening) as well as with steels (martensitic hardening). Besides the intended microstructures and properties, dimension and shape changes as well as residual stresses of the components are heat treatment results. Simulation tools based on the finite element method help to predict heat treatment results without extensive tests. Among other inputs one necessary pre‐requisite is a detailed database for the material. This database must contain the fundamental material parameters like heat conductivity, specific heat capacity, density, thermal expansion coefficient, modulus of elasticity, Poisson´s ratio and strain hardening, all of them depending on phases and temperature. Further, models for phase transformations and precipitation processes must be implemented. For steels heat treatment simulations of complex components are already possible. Some heat treatment parameters and material parameters of steels and aluminium alloys differ significantly. Aluminium alloys usually exhibit lower solution annealing temperatures, higher cooling rates, higher heat conductivity, higher thermal expansion coefficient, lower modulus of elasticity and lower strength. Further, the material database is partially missing for aluminium alloys, especially precipitation models. Exemplarily heat treatment simulations focused on the material parameters of aluminium alloys will be presented and similarities as well as differences compared to steels will be discussed.

In‐process measurement system based on laser triangulation during heat treatment

AbstractThis paper presents the calibration and the use of a laser triangulation system for non‐contact measurements of workpiece geometry changes during heat treatment. The system was developed within the scope of the Collaborative Research Centre SFB570 of the Deutsche Forschungsgemeinschaft to provide geometrical information obtained in hot environments (temperatures up to 900 °C) for the verification of heat treatment simulations. Due to its in‐process‐measurement capability, this system also enables the closed‐loop control of distortion compensation. It will be applied in a furnace specially designed for heating steel rings symmetrically or asymmetrically.The developed calibration routine, which includes the application of gauge rings with different diameters, is described and the obtained uncertainties are discussed. Measurement results of an austenitic cylindrical ring are compared with reference dilatometry data to validate the calibration routine.

Latent heat of martensitic transformation in a medium-carbon low-alloy steel

The latent heat of non-equilibrium martensitic transformation in AISI 4340 steel was obtained from experiments to measure the heat transfer coefficient and numerical calculations—using the inverse method based on the finite-difference method—of heat transfer and martensitic transformation kinetics. The average and maximum increases in surface temperature of a cylindrical specimen during oil quenching due to the temperature-dependent latent heat were 43 and 83 °C, respectively, indicating the importance of martensite latent heat for accurate heat treatment simulation.

簡便なデータベース作成法を用いた構造用鋼の熱処理シミュレーションの開発

Heat treatment is one of the important manufacturing processes that determine the quality of metallic products. However, the heat treatment processes are usually based on artisan skills and experiences on the manufacturing floor, and therefore, it sometimes is costly and time-consuming to design the processes. There is room to refine the design of processes by simulation techniques. Here we describe a way to streamline the processes of heat treatment using a simulation technique. We developed a method for estimating the hardness of heat-treated steels. To predict the steel hardness after heat treatment, it is necessary to develop a heat transfer analysis procedure and to set up a database of required steels. First we built a heat treatment simulation program using the finite difference method. Then, to simulate the hardness after the heat treatment, we built a database using the Jominy test and the tempering parameter. Some examples of simulated results on heat-history and hardness of carbon steel cylinders during water-quenching and tempering are presented, and the validity of the program is evaluated by comparing the calculated values with the experimental values. The calculated hardness agreed well with the experimental values.

Explanation of the origin of quench distortion and residual stress in specimens using computer simulation

Measurements of distortion and internal residual stresses after quenching in specimens (e.g., cylinders, disks, rings) have been performed for many years. As a result, patterns of distortion and stress distribution have been identified in the typical shapes, steels and cooling conditions. These experimental data were examined by pioneers of the heat treatment simulation for verifying their computer programs in the 1970s and 1980s. However, early researchers did not fully explain the mechanism of distortion and residual stress generation based on their simulated results. A way to explain the generation mechanism using simulated results, especially distributions of all types of strains, has been recently developed and successfully applied to some experimental works by the authors of this paper. Its concept is described briefly, and its applications for some specimens are summarised.