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Finite element (FE) analysis of the tensile test of TWB-HPF 22MnB5 steel was performed and compared with the experimental results. To improve the accuracy of the simulation, the damage theory of FLD and ductile damage theory were used in 2D and 3D simulations. The tensile strength of 22MnB5 steel was determined under various welding heat inputs for FE simulation. Crack propagation of the welded region indicated that the fracture was observed in the base metal under normal welding conditions. Also, the crack propagated along the HAZ region due to higher heat input of the welding, and lead fractures have been highlighted as a potential complication. [ABSTRACT FROM AUTHOR]

Within the context of reducing the environmental impact generated by the current generation, a constant challenge for the automotive industry is to produce vehicles with the lowest possible environmental impact. In this context, in order to reduce vehicle weight and, consequently, reduce fuel consumption and emissions of gases harmful to the environment, the automotive industries have been using advanced high-strength steels. These steels make it possible to reduce thickness without losing mechanical strength and, therefore, without compromising passenger safety. Among these steels, 22MnB5 steel stands out. Among the welding processes used to weld steel sheets, electrical resistance spot welding is the most widely used joining technique in the automotive industry. The main reasons for its wide application are that it is a process in which no material addition is required and it has a high processing speed and low processing costs. In this context, this study proposes a bibliometric and systematic review of electrical resistance spot welding of 22MnB5 steel. The main objective of this study was to identify current research trends and impacts, along with a comprehensive revision. The research was carried out using the Proknow-C method. A bibliographic portfolio of 50 articles was compiled. The bibliometric analysis revealed that articles related to this topic increased substantially between 2016 and 2023 compared to previous years. The systematic evaluation of the papers in the bibliographic portfolio made it possible to identify aspects such as the research problems addressed, the materials and methodologies used, the results evaluated, and the research gaps. It was found that most of the studies focused on the weldability and mechanical performance characteristics of similar two-plate joints with an average thickness of 1.5 mm and Al-Si coatings. Finally, this article provides a comprehensive overview of the research on electric resistance spot welding of 22MnB5 steel and can provide guidance for future studies to improve the process. [ABSTRACT FROM AUTHOR]

Residual stress plays an important role in the delayed cracking performance of the 22MnB5 hot roll bending pipe. In the present study, the residual stress distribution of the 22MnB5 hot roll bending pipes with different pipe thicknesses is compared. The results show that both the tensile and compressive residual stresses can be traced in the bending zone for the pipe with plate thickness around 1.5 mm. On the contrary, only tensile residual stress obtains in the residual stress measurement positions for the thicker one (~ 2.3 mm). In addition, the thicker 22MnB5 pipe exhibits poor delayed cracking behavior in the solution of 0.1 mol/L HCl for 300 h. Compared with thinner 22MnB5 pipe, high tensile residual stress occurs in the thicker one induced by phase transformation and deformation during the hot roll bending process, deteriorating its delayed cracking performance. [ABSTRACT FROM AUTHOR]

Finite element (FE) analysis of the tensile test of TWB-HPF 22MnB5 steel was performed and compared with the experimental results. To improve the accuracy of the simulation, the damage theory of FLD and ductile damage theory were used in 2D and 3D simulations. The tensile strength of 22MnB5 steel was determined under various welding heat inputs for FE simulation. Crack propagation of the welded region indicated that the fracture was observed in the base metal under normal welding conditions. Also, the crack propagated along the HAZ region due to higher heat input of the welding, and lead fractures have been highlighted as a potential complication.

The effects of austenitizing temperature and holding time on oxidative decarbonization behavior of bare 22MnB5 steel sheet were investigated by OM, SEM, XRD, XPS, and room temperature tensile measurement. The oxidation kinetic model of 22MnB5 steel was calculated and revealed that early oxidation was controlled by chemical reaction, and later oxidation was controlled by elemental diffusion, for oxide layer structure from inside to outside of SiO2 + Cr2O3, wustite (FeO + Fe3O4), Fe3O4, and Fe2O3. With the increase in heating temperature (890-950 °C) and holding time (5-15 min), both oxidation and decarburization layers of 22MnB5 steel increased continuously, leading to a decrease in tensile strength and increase in elongation, making an increase in product of strength and ductility of about 1-4 GPa%. Based on the oxidative decarbonization and mechanical properties, the optimal heat treatment of 22MnB5 steel is 920 °C for 5 min. [ABSTRACT FROM AUTHOR]

In recent years, increasing automotive safety and energy efficiency has become a major concern in the automotive industry. Advanced high-strength steel (AHSS) was chosen for its weight reduction and high mechanical strength for the body in white (BIW). Specifically, it has been used in 22MnB5 steel press hardening type steel (PHS) with patchweld technology, which enables the production of reinforced and structural parts in a single stroke during the hot forming process. This study aimed to evaluate the resistance spot welding parameters for patchweld before hot stamping, considering the minimum and maximum residual stress, while ensuring a welding nugget diameter within the approved range. Microhardness and X-ray diffraction were used to analyze the welding zones for phase identification and residual stress measurements. After five weeks of elapsed time, the spot weld showed cracks that were not seen immediately after welding and were probably due to a high residual stress state.

22MnB5 hot forming steel is widely used in the automotive industry due to the increasing demand for lightweight vehicles. As surface oxidation and decarburization occur during hot stamping processes, an Al-Si coating is often precoated on surfaces. The coating tends to melt into the melt pool during the laser welding of the matrix and reduce the strength of the welded joint; therefore, it should be removed. The decoating process by sub-nanosecond and picosecond lasers and process parameter optimization were conducted in this paper. The corresponding analysis of the different decoating processes, the mechanical properties and the elemental distribution was carried out after laser welding and heat treatment. It was found that the Al element has an influence on the strength and elongation of the welded joint. The high-power picosecond laser has a better removal effect than the lower power sub-nanosecond laser. The best mechanical properties of the welded joint were obtained under the process conditions of 1064 nm center wavelength, 15 kW power, 100 kHz frequency, and 0.1 m/s speed. In addition, the content of the coating metal elements (mainly Al) melted into the welded joint is reduced with increasing coating removal width, which significantly improves the mechanical properties of the welded joints. Al in the coating rarely melts into the welding pool when the coating removal width is not less than 0.4 mm, and its mechanical properties can meet the automotive stamping requirements for the welded plate. [ABSTRACT FROM AUTHOR]

High-temperature oxidation resistance, hot formability, element distribution, and microstructure of Al-10% Si-(0.5–3.0%)Cu coating were investigated by means of glow discharge spectroscopy, optical microscope, scanning electron microscope, and energy-dispersive spectroscopy. Results show that the addition of Cu can increase high-temperature oxidation resistance above 950°C and improve hot formability so that no crack spreads into substrate steel as hot forming at 33.3% strain. Oxidation film structure is continual and compacting, and Si highly concentrates in the surface layer. The distribution of Cu has skin effect with peaking content 8.2% in the surface layer. After hot stamping, Al and Si diffuse into substrate steel, and Cu diffuses from inner to outer coating. Al–Si–Cu coating has smoother surface, straighter diffusion layer, and finer metal compound than Al–Si coating. Surface and diffusion layers are identified as aluminum oxide, Si-rich, and Cu phase and Al7SiFe2, Al3Fe, and CuAl3, respectively. Al-rich phase and the metal compound are composed of α-Al dissolving Fe, Si, and Cu and Al–Si matrix, Cu3Al, respectively.

Spheroidization is a common technique to improve the formability and machinability of material. Multiple combinations of deformation level and annealing time were employed to optimize the microstructure in 22MnB5 steel, aiming to achieve maximum spheroidization and keeping the process most economical. The critical annealing temperature for spheroidization was decided through differential scanning calorimetry measurement. Spheroidization was achieved by annealing of as-received and three different amounts of cold-rolled material, namely 10, 20, and 30% reduction in thickness. Annealing was done at 720 °C for four different times, 10, 20, 40, and 60 h, at all deformation levels. Convoluted multiple whole profile fitting technique of x-ray diffraction pattern was used to estimate the stored dislocation density in the material after different deformation levels. The microstructural investigation was performed using optical microscopy, scanning electron microscopy and EBSD techniques. The extent of spheroidization was measured through the average aspect ratio of cementite precipitate. Mechanical properties were measured through surface and core micro-hardness of initial and spheroidized samples. Microstructural characterization showed that deformation produced sub-grains and low angle grain boundaries, facilitating an easy path for diffusion of carbon. However, it was also found that a very high amount of pre-strain is also detrimental to the spheroidization process because it results in the formation of very long and sharp cementite lamella, which required more annealing time for spheroidization. The best processing parameter for spheroidization of 22MnB5 steel, considering the optimum spheroidization and minimum cost of the process, was found as 20% cold rolling reduction followed by 20 h annealing. [ABSTRACT FROM AUTHOR]

The analysis of the development of the microstructure of deep drawn automotive B pillar, as well as the analysis of deformation based on numerical simulation and experiment, was performed. The microstructure of steel sheet as well as Al-Si coating after various stages of B pillar production was investigated. It was found that the obtained microstructure of the B pillar was significantly different from that described in many studies as a proper one. The microstructure of the investigated material consisted of martensite, bainite, and a small amount of ferrite. Al-Si coating, despite its morphological changes, remained on the surface of B pillar and, in spite of this, did not fully eliminate oxidation and decarburization of B pillar material. The analysis of the state of strain allowed to evaluate the deformation safety of the process, as well as to verify the simulation results through measurements of sheet thickness variations.

The analysis of the development of the microstructure of deep drawn automotive B pillar, as well as the analysis of deformation based on numerical simulation and experiment, was performed. The microstructure of steel sheet as well as Al-Si coating after various stages of B pillar production was investigated. It was found that the obtained microstructure of the B pillar was significantly different from that described in many studies as a proper one. The microstructure of the investigated material consisted of martensite, bainite, and a small amount of ferrite. Al-Si coating, despite its morphological changes, remained on the surface of B pillar and, in spite of this, did not fully eliminate oxidation and decarburization of B pillar material. The analysis of the state of strain allowed to evaluate the deformation safety of the process, as well as to verify the simulation results through measurements of sheet thickness variations. [ABSTRACT FROM AUTHOR]

Abstract The temperature-dependent interfacial heat transfer coefficient (IHTC) is an essential thermo-physical parameter between the heat treatable 22MnB5 boron steel and spray medium to assess heat transfer intensity and the temperature distribution, which could consequently affect the microstructure and mechanical property distribution of the material after spray quenching. Numerous prediction approaches for IHTC in quenching process have been extensively developed, and it is essential to compare them to choose the most suitable method for spray quenching applications. In the present study, the temperature distribution and characteristic of boiling heat transfer on 22MnB5 hot steel blank in spray quenching are investigated. The temperature-dependent IHTC curve in spray quenching process is calculated by five different numerical algorithms, including the Heat Balance Method (HBM), the Revised Heat Balance Method (R-HBM), the Beck's non-linear Estimation Method (BEM), the Finite-element Inverse Optimization Method (FIOM) and the Finite-element Optimization Method (FOM), and calculation accuracy of the above methods are discussed in detail. Besides, the 'calculated' IHTCs are introduced into the CFD model as the boundary conditions to predict the internal temperature distribution of the blank, and further compared with the experimental temperature profiles. It is concluded that the BEM owns the best calculating accuracy and efficiency between solid-fluid interfaces in spray quenching, and the internal temperature distribution prediction with IHTCs based on the BEM has the highest anastomosis degree with the real temperature. Highlights • Five numerical inverse methods are compared to solve the IHTC of 22MnB5 steel in spray quenching process. • The characteristic of temperature-dependent IHTC of 22MnB5 during spray quenching process are investigated. • The calculating accuracy of two classified inverse methods is compared. • The calculating efficiency of two kinds of the IOM is compared for solving the transient IHTC. [ABSTRACT FROM AUTHOR]

In this study, a tailored die quenching experimental method using low closing pressures and an aluminum flat die was developed in order to evaluate the effects of the gap size on the cooling rate in the hot stamping process of a 22MnB5 steel grade. Initially, the necking behavior in hot stamping was investigated by deforming the specimens to different strain levels and subjecting them to quenching in order to assess this effect on the gap profile formed between the die surface and the sample. Next, a controlled gap was promoted in the central region of the aluminum cooler using aluminum spacers (simulating the gap) with different thickness (0.06/0.15/0.40/0.70mm). Then, its effects on the cooling rate and on the hardness after quenching were evaluated. The results showed that the cooling rate is very susceptible to gap size, that the ideal situation occurred when there was no gap, good heat transfer and higher average cooling rates of 120ºC/s were achieved, and that when the gap was wider than 0.20mm the average cooling rates were lower than 20ºC/s, consequently below the critical 22MnB5 steel cooling for quenching, which is 28ºC/s.

Third-generation advanced automotive medium-Mn steel, which can replace 22MnB5 steel, was newly developed to improve the lightweight and crashworthiness of automobile. Studies on the formability and simulation method of medium-Mn steel have just been initiated. In this study, finite element simulation models of square-cup deep drawing were established based on various material property experiments and validated by experiments. The effects of blank holder force (BHF), fillet radii of tools (die and punch) on the maximum drawing depth (MDD), thickness distribution of the formed products, and the microstructure before and after forming were investigated and compared with those on 22MnB5 steel. Results show that the MDD of the two steels decreased with increased BHF but increased with the fillet radius of punch; however, the fillet radius of die showed no significant effect on the MDD for both steels. Compared with hot-formed 22MnB5 steel, the martensitic transformation of the hot-formed medium-Mn steel is rarely influenced by the process parameters; thus, it holds the complete, fine-grained, and uniform martensitic microstructure. Moreover, the medium-Mn has better formability, lower initial blank temperature, and smaller impact of BHF and fillet radius of tools on the hot-formed product. Thus, a theoretical basis for the replacement of 22MnB5 steel by medium-Mn steel in hot forming process is provided. [ABSTRACT FROM AUTHOR]

In this study a new experimental method using low closing pressure and a flat aluminum die was developed in order to investigate the hot stamping process of a 22MnB5 steel grade. Initially, an experimental set up was developed and validated. Next, experiments were carried out to evaluate the behavior of this steel when subjected to quenching, using this experimental set up and different cooling conditions such as water, oil and air. Results were assessed by cooling curves, as well as by mechanical tests and metallographic analyzes. Cooling rates close to 110oC/s, hardness up to 480HV and ultimate tensile strength up to 1600 MPa were achieved, which are considered acceptable values for this steel in normal conditions of hot stamping [ABSTRACT FROM AUTHOR]

Although in the past complicated and often considered ‘exotic’ process, hot stamping of steel is now widely used in the automotive industry and for some safety components it becomes obligatory. The hot stamped parts are used in regions where very high strength is required. But for some applications also ductility needs to be incorporated in parts to guide the absorption of energy under crash loading, for other the material thickness has to be reduced smoothly due to lightweight. This will be achieved by tailoring the material properties within the component. This new generation of hot formed parts is already standard in the market, but still difficult in the engineering. And the next one is already in start position – aluminum warm forming is planned as a substitution of the heavier steels for structural parts, but newly also for outer panels, where they have to fulfil all requirements on visible parts. Light, strong, accurate, high quality and warm formed to improve the formability of the material. This paper describes successful engineering methods in virtual hot stamping process with tailored properties and of warm and hot formed aluminum parts. [ABSTRACT FROM AUTHOR]

The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles. However, sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed. Thus, an investigation is conducted to experimentally quantify such influence for a commonly used steel (the 22MnB5 steel) based on the hot and cold forming processes. For each process, a number of samples are used to conduct a uniaxial tensile test to simulate the forming process. After that, some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage. Finally, a microstructure test is conducted to analyze the microdefects of the remaining samples. Based on the results of the first two tests, the effect of material damage on the service performance of 22MnB5 steel is analyzed. It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance, such as the failure strain, the ultimate stress, the capacity of energy absorption and the ratio of residual strain. The reductions are generally lower and non-linear in the former process but higher and linear in the latter process. Additionally, it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes. The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5. [ABSTRACT FROM AUTHOR]

Simulation of hot stamping process needs reliable material data, especially at high temperatures where plastic deformation takes place in austenitic microstructure. In the current study, high-temperature non-isothermal compression tests (NICT) at different ranges of temperature, strain and strain rate as well as constitutive modeling of the flow curves were carried out. The Johnson-Cook and the Nemat-Nasser phenomenological models for isothermal deformation conditions were revised and applied to fit the flow curves during high-temperature NICT. It was shown that the models can satisfactorily predict the material flow stress at the mentioned conditions. Furthermore, the models were employed in order to describe the work-hardening behavior of the material. The results indicated that the fitted work-hardening rate can successfully follow the experimental data during deformation till no strain-induced phase transformation is initiated. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical joining of dissimilar materials is a key technology in the automotive industry as it enables the realization of car bodies that incorporate multiple materials. However, it remains difficult to join materials such as aluminum alloy to high-strength/low-ductility materials such as advanced high-strength steel, hot-pressed steel, and carbon fiber reinforced plastic by using joining methods that are based on forming technology. The purpose of this study is to develop a new joining process, called “hole clinching,” for these material combinations. In the hole-clinching process, the ductile material is positioned uppermost and the brittle material—into which a hole is formed—is positioned below that. The upper sheet is indented into a die cavity through the hole in the lower sheet and spread so that the two sheets interlock geometrically. In this study, hole-clinching tools were designed based on the geometrical relationship between the forming volume and the joint strength. Finite element analysis and practical experiments were performed to verify the practicality of the hole-clinching process. The cross-sections of the hole-clinched joints formed in our experiments were in good agreement with the results of the finite element analysis. Then, a single-lap shear test was performed to evaluate the joint strength. The hole-clinched joints, regardless of the material combinations, provided a joint strength in excess of the desired 2.5kN. These results point to the applicability of the hole-clinching process to the joining of dissimilar materials. [Copyright &y& Elsevier]

Highlights: [•] We evaluated the fatigue behaviour of press hardened 22MnB5 steel. [•] The effect of shearing on fatigue performance is evaluated. [•] Results are compared with cold forming UHSS grades. [•] The applicability of 22MnB5 to fatigue resistant components is addressed. [•] Fracture mechanics can be used to rationalize the fatigue behaviour. [Copyright &y& Elsevier]

Hot forming of ultra high strength steel (UHSS) sheet metal grade 22MnB5 boron for channel components using water cooling is studied on a laboratory scale. After hot forming, the different microstructures such as martensite, bainite, and pearlite in formed component are produced, which are closely related with mechanical properties of formed component. The effect of forming start temperature and the contact state between blank and die on the microstructure evolution is investigated. In addition, the effect of processing parameters, such as forming start temperature and blank holder force (BHF), on the final quality of component, i.e., springback, that happens after hot forming of UHSS is investigated. It can be concluded that the forming start temperature has a significant effect on the final mechanical properties of formed components. The effect of forming start temperature on springback is examined in detail under a wide range of operating conditions. The higher the BHF and the forming start temperature, the lower is the springback after hot forming. Furthermore, thermo-mechanically coupled finite element analysis model encompassing heating of sheet blank, forming and quenching are developed for hot forming process. The stress distributions on sheet blank under different conditions during hot forming are compared to gain a fundamental understanding of the mechanism of springback. Comparisons show that numerical simulation results have good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The chemical and phase composition of the coating and the coating/substrate interface of an Al-Si-coated 22MnB5 hot stamped steel was investigated by means of SEM-EDS, XRD, micro-XRD and electron diffraction. Moreover, the surface profile was analyzed by XPS and roughness measurements. The XPS measurements showed that the thickness of the Si and Al oxide layers increased from 14 to 76 nm after die-quenching, and that the surface roughness increased as well as a result of volume changes caused by phase transformations. In addition to the FeAl(Si) and Fe2Al5 phases and the interdiffusion layer forming complex structures in the coating, electron diffraction confirmed the presence of an Fe2Al5 phase, and also revealed very thin layers of Fe3(Al,Si)C, Fe2(Al,Si)5 and Al-bearing rod-shaped particles in the immediate vicinity of the steel interface. Moreover, the scattered nonuniform layer of the Fe2Al8Si phase was identified in the outermost layer of the coating. Despite numerous studies devoted to researching the phase composition of the Al-Si coating applied to hot stamped steel, electron diffraction revealed very thin layers and particles on the coating/substrate interface and outermost layer, which have not been analyzed in detail. [ABSTRACT FROM AUTHOR]