Heat Treatment Simulation Research Articles

Determination of Heat Transfer Coefficient by Inverse Analyzing for Selective Laser Melting (SLM) of AlSi10Mg

Heat treatment can improve performance and control quality in the additive manufacturing process. In the numerical simulation of heat treatment, the accuracy of the heat transfer coefficient will have a significant impact on the accuracy of the simulated temperature field. At present, The inverse analysis method is the most common and effective method to determine the heat transfer coefficient. Taking the actual temperature curve as the input condition, the heat transfer coefficient values of the heating, quenching, and air cooling components in the heat treatment process are successfully obtained. Based on the obtained heat transfer coefficient, a mathematical model of the heat transfer coefficient change with temperature during heat treatment is established. The heat transfer coefficient obtained by the inverse analysis method is then applied to the simulation of heat treatment, and more accurate simulation results are obtained. It is proven in this work that the inverse analysis method can improve the accuracy of the simulation model in the heat treatment process of AlSi10Mg.

Simulation of surface heat treatment with inclined laser beam

The beam inclination leads to a change in the laser spot size on the material surface. The higher the inclination, the larger the irradiated area and the lower the laser intensity. Moreover, if the material surface is outside of the beam focal plane, the intensity distribution profile becomes asymmetric. In this study, a heat source model, which calculates the intensity distribution on the workpiece surface as a function of beam parameters (beam waist, divergence half-angle) and process parameters (laser power, incidence angle, and distance to focal plane) was developed. The applicability of the heat source model was demonstrated by simulating 4 different laser hardening regimes. Once the heat efficiency coefficient had been calibrated the developed finite-element model allowed computation of temperatures while hardening with perpendicular laser beams as well as with inclined beams. The open-source software FEniCSx was used for the finite element computations. The mathematical formulation, required for performing temperature simulations with FEniCSx was briefly introduced.

Numerical simulation and Experimental Verification of Heat Treatment of ISO-CC8X Rivet Nut

In this paper, the method of finite element analysis is used to study and Simufact.forming software is used to simulate the cold forming process and heat treatment process of ISO-CC8X riveting nut. The changes of equivalent stress of the riveting nut after cold forming process and heat treatment process are obtained. Then, residual stress detection and metallographic experiments were carried out to verify the reliability of the numerical simulation. This method is of guiding significance to the design and optimization of heat treatment process of metal parts in practical production.

Design methodology of the Ni50Ti50 shape memory alloy beam actuator: Heat treatment, training and numerical simulation

Shape memory alloy (SMA) beam actuators are widely used in morphing structures, which leads to a surgent demand for a comprehensive design method. Previous methods have not considered the heat treatment and the evolution of actuation performance during training. In this study, an in-depth investigation was conducted into the Ni50Ti50 (at%) SMA beam actuator from the perspective of heat treatment, training, numerical simulation for developing a comprehensive and novel design methodology. The proper heat treatment conditions that result in the relatively high actuation performance for the Ni50Ti50 SMA beam were determined. The dependence of the thermomechanical behavior evolution on the training load was established. Moreover, a numerical analysis method for the SMA beam actuator based on a 3-D constitutive model with tension-compression asymmetry considered was detailed, followed by the calibration of material parameters. A forward design method for the SMA beam actuator was proposed with the shape and actuation performance evolution during training under various training loads fully considered in the design process. The proposed design method was applied for a design case and the accuracy of the design results demonstrated its feasibility.

Comprehensive unified model and simulation approach for microstructure evolution

The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials. There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches. This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution, emphasizing their advantages and disadvantages. Atomistic approaches, such as molecular dynamics, are restricted by the scale of the studied system because they are computationally expensive. Continuum mesoscale simulation approaches, such as phase field, cellular automata, and Monte Carlo, have inconsistent phenomenological equations, each of which only describes one aspect of microstructure evolution. To provide comprehensive insight into microstructure evolution, a unified model that is capable of equally evaluating the nucleation and growth processes is required. In this paper, a physics-based model is proposed that incorporates statistical mechanics, the energy conservation law, and the force equilibrium concept to include all aspects of microstructure evolution. A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments. Furthermore, the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed. The use of fundamental physical rules instead of phenomenological equations, together with the real spatial and temporal scales of the proposed model, facilitates the comparison of the simulation results with experimental results. To examine the accuracy of the proposed simulation approach, the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.

Process Optimization for an Energy Efficient Heat Treatment of ADI*

Abstract Austempered ductile iron (ADI) materials show a good combination of mechanical properties, with high tensile strength levels (800-1600 MPa) and an elongation at fracture of up to 10 %. Due to its high fracture toughness as well as high fatigue resistance, ADI is a very attractive material group for applications under cyclic loads. However, the material properties are very sensitive to the applied process conditions during heat treatment. The basis for a substantial increase in the application of ADI materials in the industry requires the establishment of a predictable and robust process design. Here, an integrated process simulation of the heat treatment process coupled to required information about the as-cast quality of the component would aid in understanding process dependencies and defining a robust process window. For the austenitization step, the simulation can be used to determine the needed treatment times and temperatures. In the process simulation software MAGMA5, a new fast and efficient algorithm for heat exchange between thermally coupled diffusely radiating interfaces has been implemented and can be used for heat treatment simulation. The accuracy and computational performance of this new radiation model for the heat treatment of ADI is illustrated here for a real industrial suspension part. The steering knuckle is heated in a typical heat treatment box. Surface-to-surface radiation between the parts and with the surrounding furnace results in inhomogeneous temperature distributions. Integrated capabilities to perform virtual experiments and automatic optimization are used to determine optimal process conditions to meet both the quality requirements and the minimum required treatment time during austenitization. ▪

Temperature Regimes and Chemistry for Stabilizing Precipitation Hardening Phases in Al–Sc Alloys: Combined CALPHAD–Deep Machine Learning

Abstract In this work, CALPHAD-based calculations provided with data for various stable and metastable phases in 2XXX, 6XXX, and 7XXX classes of aluminum-based alloys. These data were scaled and then used to develop Deep Learning Artificial Neural Network (DLANN) models for all these phases as a function of composition and temperature. Code was written in the python programming language using TensorFlow/Keras libraries. DLANN models were used for determining the amount of various phases for new compositions and temperatures. The resulting data were further analyzed through the concept of Self-organizing Maps (SOM) and a few candidates were chosen for studying the precipitation kinetics of Al3Sc phase under the framework of CALPHAD approach. This work reports on heat-treatment simulation for one case of 6XXX alloy where the nucleation site was on dislocation, while a detailed study for other alloys is reported in a previously published work. Grain-growth simulations presented in this work are valid for single crystals only.

Transformation Plasticity in Carbonitrided PM-Steels: Quantification of Plasticity Effects in Dependence of the Part Density*

Abstract To optimize heat treatment processes of case hardened components, heat treatment simulations are used to predict surface layer conditions. Only a precise knowledge and modelling of the transformation processes allows a trustworthy prediction of the hardness and residual stresses in the surface zone. The transformation plasticity mechanism plays an essential role in the heat treatment process and its correct simulation has a significant influence on the resulting calculated residual stress profiles and component distortion. Without considering transformation plasticity, simulative residual stresses are significantly overestimated [1]. In this work, powder metallurgical components are pressed and sintered and subsequently carbonitrided for a dilatometric investigation to characterize the correlation between transformation plasticity effect and the density. The results show a dependence of the austenite-martensite volume change that led to a significant difference of 0.5 Vol-%. A model describing the martensite volume change with respect to density is proposed. This also affects the description of the transformation plasticity constants (K) between K = 5 – 6 × 10–5 MPa–1 in dependence of density. With currently available data, the effect of chemical composition and density cannot be separated and quantified and further studies are therefore necessary to allow such a refinement.

Heat Treatment Consideration in Structural Simulations of Machine Elements: Analysis of a Starter Clutch Barrel

Consideration of heat treatment in simulations of structural components and its impact on predictions of behaviour during operation is analysed here. An automotive machine element with a complex geometry and dynamic load is analysed rather than a standard laboratory specimen under controlled conditions. The heat treatment analysis of a starter clutch barrel has been performed in DANTE followed by a structural analysis in ANSYS 2019 R3 during operation simulating a load cycle due to the start of an internal combustion engine. The heat treatment simulation consisted of carburisation, quenching and tempering. First, the carbon content and its distribution have been simulated. Next, the hardness of the starter clutch barrel and its distribution have been analysed with respect to the carbon distribution and hardness-dependent material properties of the AISI/SAE 4142 steel. Finally, the stress field after the heat treatment and during the operation of the starter clutch barrel has been thoroughly evaluated and compared to the simulation without the consideration of the heat treatment. Results of the simulation show that the heat treatment introduces favourable compressive stresses at the critical location of the starter clutch barrel and reduces the effective amplitude of the equivalent stress during the operation. Furthermore, the results of the simulation prove that heat treatment should be considered already during the early stages of the R & D process as it can have a decisive effect on the operational behaviour of the structural component. Moreover, a non-consideration of the heat treatment can lead into erroneous conclusions regarding the suitability of machine elements.

Simulation of Heat Treatment of Carburization and Nitrocementation of 16MnCr5 Steel

Simulation of Heat Treatment of Carburization and Nitrocementation of 16MnCr5 Steel

Experimental and Numerical Investigation of the Surface Layer Conditions after Carbonitriding of Powder Metallurgical Steels. Part 1: Diffusion in Components of Graded Porosity

Abstract Case hardening processes such as carbonitriding can be used to improve the performance of powder metallurgical structural components. Due to the amount of carbon and nitrogen introduced, it is possible to adjust the hardness and residual stress of the surface layer. Due to their porosity, powder metallurgical components show a significantly increased diffusivity and therefore increased demands on the process control. In order to be able to make a quantitative statement about the effects of diffusivity as a function of porosity, common densities of 6.9 g/cm3, 7.2 g/cm3and 7.35 g/cm3for PM-steel are examined in a total of ten process sequences. By means of simulative approaches, the resulting element depth profiles can be calculated and the surface layer condition can be predicted by a subsequent heat treatment simulation. In a two-part work, the mass transport during carbonitriding is investigated in the first part and the resulting surface layer conditions after heat treatment in the second part. By considering different process combinations and porosities, model approaches of volume and pore diffusion can be formulated and quantitative element depth profiles can be predicted and validated depending on the process parameters. ◼

Phase Field Simulation of AA6XXX Aluminium Alloys Heat Treatment

Heat treatment has a significant impact on the microstructure and the mechanical properties of Al-Mg-Si alloys. The present study presents a first Phase-Field modelling approach on the recrystallisation and grain growth mechanism during annealing. It focuses on the precipitate fraction, radius, and Mg-Si concentration in the matrix phase, which are used as input data for the calculation of the yield strength and hardness at the end of different ageing treatments. Annealing and artificial ageing simulations have been conducted on the MultiPhase-Field based MICRESS@ software, while the ThermoCalc@ software has been used to construct the pseudo-binary Al-Mg phase-diagrams and the atomic-mobility databases of MgxSiy precipitates. Recrystallisation simulation estimates the recrystallisation kinetics, the grain growth, and the interface mobility with the presence/absence of secondary particles, selecting as annealing temperature 400 °C and a microstructure previously subjected to cold rolling. The pinning force of secondary particles decelerates the overall recrystallisation time, causing a slight decrease in the final grain radius due to the reduction of interface mobility. The ageing simulation examines different ageing temperatures (180 and 200 °C) for two distinct ternary systems (Al-0.9Mg-0.6Si/Al-1.0Mg-1.1Si wt.%) considering the interface energy and the chemical free energy as the driving force for precipitation. The combination of Phase-Field and the Deschamps–Brechet model predicted the under-ageing condition for the 180 °C ageing treatment and the peak-ageing condition for the 200 °C ageing treatment.

Full process chain simulation of the (wire-based) laser metal deposition process towards fatigue life prediction

As virtual manufacturing in additive manufacturing (AM) becomes more mature, the benefits of using this technology increases. Virtual manufacturing simulations often capture only one step in the AM process chain decoupled from the subsequent steps. However, all steps in the process chain influence the final product in their own way. Therefore, this study focusses on the development of a virtual manufacturing framework to perform sequential process simulations of the complete process chain for AM parts. This framework can ultimately be used to obtain insights on the effect of additional processes or process variations on the final product. In this study, the framework is used to obtain insights on the effect of residual stress due to the laser metal deposition (LMD) process on the fatigue life of the final part. To this end, a calibration and validation of a part-scale LMD process simulation is performed to obtain deformations and residual stresses. This is followed by a heat treatment simulation to determine the effect of post heat treatment on the deformation and residual stresses of the final part. By combining the residual stress field with fatigue loads, the effect of different process steps on the fatigue life is investigated.

Setup of a numerical model for Post Welding Heat Treatment simulation of steel joints

A 3D numerical model aimed at predicting the deformations of a S355 steel T-joint in both as-welded and post-welding heat treated conditions was developed. Experimental tests were carried out with the objective to collect data necessary to the heat source calibration and model validation in terms of microstructure and joint distortions. All metallurgical phenomena were taken into account such as specific volume change and transformation plasticity induced by solid-state phase transformations. A viscoplasticity model for stress relief processing implemented in Sysweld finite elements code was used. Numerical results showed a satisfactory agreement with experimental ones. Further investigations will be necessary to consider also the validation of residual stress relief effects.

Investigation on residual stress induced by multiple EDM discharges

The thermal removal mechanism of electrical discharge machining (EDM) process leads to modifications of the rim zone. One of these modifications is tensile residual stress. This tensile stress reduces the mechanical load that can be tolerated in the final part application. Hence, it is important to know the resulting residual stress depending on the induced thermal loading by EDM. In this work, the residual stress is simulated based on the resulting temperature field generated by the EDM discharges. The predictions are based on a solution of the heat conduction equations taking into account the material removal, where the heat flux into the work piece is calibrated by measurement data. The tensile residual stress is then determined by using a reduced order model for the temperature boundary condition in the heat treatment simulation software SysWeld®. In the first step, a single discharge is investigated, subsequently the methods are applied to predict the tensile stress for multiple discharges. The simulation results are compared to the residual stress measured in specimen for single and multiple discharge experiments using X-ray diffraction.

Heat treatment simulation of Ti-6Al-4V parts produced by selective laser melting

Abstract The present work focuses on the simulation of the heat treatment applied after printing of Ti-6Al-4V parts. The numerical tool aims at predicting the influence of heat treatment conditions (e.g. holding time, temperature) on the residual stress field and the distortions for SLM produced parts. The numerical model relies on a thermo-viscoplastic constitutive model. To determine the corresponding material parameters, different creep tests have been performed at temperatures ranging from 723 K to 1173 K. According to the results, the stationary creep strain rate is independent of the hydrostatic pressure, which indicates that the high temperature behavior is not impacted by the initial porosity. Also, the material parameters are observed to change significantly from 873 K, which is due to the progressive transformation of the initial martensitic α ′ microstructure into the α + β lamellar microstructure. To validate the proposed approach, some numerical simulations have been performed for two different parts, for which distortions have been measured. The numerical and experimental distortions have then been compared to each other. For both parts, the agreement between experimental and numerical data is correct.

Simulation and experimental study of induction heat treatment of titanium disks

During induction heat treatment (IHT) of titanium disks, the influence of the main electrotechnological parameters, in particular the inductor current, on the temperature of their surfaces was established at an exposure within t = 5 min. In the course of numerical simulation, i.e. when solving the self-consistent boundary value problem of electrodynamics and thermal conductivity for the "inductor – titanium disk" system, the influence of the inductor current in the range 2.7–4.5 kA on the average exposure temperature of the titanium disk was determined, which varied from 800–850°C to the melting temperature (about 1670°C) and above. In order to confirm numerical calculations, experimental studies on IHT in the same temperature range were performed. In addition to the inductor current IIND varying in the range from 2.7 to 4.5 kA, the influence of the corresponding value of the electric power PE in the range from 0.21 to 0.95 kW on the exposure temperature during IHT was considered. Changes in the surface morphology of the titanium disks were studied over a wide temperature range. The initial oxide coating was retained on the surfaces of the samples processed at a minimum exposure temperature of T = 800–850°C. A thick scale of titanium dioxide was also preserved on the surfaces of semi-molten titanium disks. In the IHT exposure range at temperatures from 1000–1050°C to 1500–1550°C, the scale was spontaneously separated from the surfaces of titanium disks; however, a high-strength oxide sublayer was formed under it.

High-Frequency Heat Treatment of AISI 1045 Specimens and Current Calculations of the Induction Heating Coil Using Metal Phase Transformation Simulations

AISI 1045 specimen was compared through a high-frequency heat treatment simulation and experiment considering metal phase transformation. Hardening zone predictions were confirmed through cooling and metal phase transformation simulations after obtaining the results from electromagnetic heat transfer simulations. The cooling process was modeled by applying the cooling coefficient of the cooling water in the same way as the actual heat-treatment process. To obtain the current flowing through the coil during high-frequency induction heating, the voltage was measured and applied using the resistance–inductance–capacitance circuit calculation method. Experimental and simulated results of the heating temperature and curing depth of an AISI 1045 specimen with a carbon content of 0.45% were compared; the comparison indicated good agreement between the two. Using the simulation results, we established a method for obtaining the current flowing through the induction coil for predicting the extent and depth of the hardening zone during high-frequency induction heat treatment.

Physical simulation and dilatometric study of double-step heat treatment of medium-Mn steel

The work addresses physical simulation and dilatometric study of one-step and double-step heat treatments of medium-Mn steel designed for automotive sheets. The conventional one-step isothermal bainitic transformation was applied as the reference heat treatment. The newly implemented heat treatment consisted of isothermal holding in a bainitic region followed by additional holding of the material at reduced temperature also in the bainitic range. This step was added to refine the microstructure, which led to the stabilization of the retained austenite. Calculations of equilibrium state and non-equilibrium cooling and simulations of the developed thermal cycles were performed using the thermodynamic JMatPro software. The physical simulations of the heat treatment were performed in the dilatometer. The obtained samples were subjected to microscopic observations using light and SEM microscopy. One- and two-step heat treatments allowed to obtain bainitic structures with high contents of retained austenite. Lowering the temperature of one-step isothermal holding resulted in the bainite refinement and adjacent retained austenite. The increased Mn content in steel increased its susceptibility to form coalesced bainite resulting in the partial formation of thicker plates despite a decrease in a process temperature.

Experimental and simulation of C45 steel bar heat treatment with the GTAW method application

The motivation of the paper is an attempt to indicate the relationship between the selected Gas Tungsten Arc Welding (GTAW) technology and the parameters of the boundary conditions for the simulation of the heat treatment process of elements made of medium-carbon steel. The authors of the paper prepared and described a series of numerical simulations and experimental studies concerning this problem. Simulations often use previously-developed analytical equations to describe the relationships between process parameters. The results obtained for the input data for determining the heat source power (voltage) from the analytical equation and experimental measurements were compared. Several cases of the size of the areas of direct influence of the GTAW arc (various radius of a simulation heat source) were analysed. All computations were performed in the author’s software based on Finite Element Method (FEM) solving the heat transfer equation with the convection term. In this paper, the GTAW heating parameters (boundary condition) for a current intensity equal 30 A were identified. With the assumed arc efficiency coefficient, the arc voltage set on the device and the measured value of the arc current, the optimum radius of the heat source was determined. The identification of parameters was confirmed by the convergence of the results of numerical simulation in three-dimensional space (3D) with the results of the experiment. Unfortunately, the applied methodology did not give good results for current equal to 50A.