Hot Stamping Steel Research Articles

Effect of Casting Roll Roughness on the Naturally Deposited Film and Its Related Heat Transfer During the Simulated Strip Casting of Hot-Stamping Steel

Effect of Casting Roll Roughness on the Naturally Deposited Film and Its Related Heat Transfer During the Simulated Strip Casting of Hot-Stamping Steel

Effect of V-Ti multi-microalloying on enhancing hydrogen embrittlement resistance in hot-stamping steel

Hydrogen embrittlement (HE) has become a significant concern that limits the usage of ultra-high strength hot-stamping steel. In this work, the utilization of a novel approach employing V-Ti multi-microalloying has yielded substantial improvements in the resistance of hot-stamping steel to HE. The experimental findings demonstrate that V-Ti multi-microalloying effectively restrained the coarsening of precipitates, leading to the generation of high-density nanosized (V, Ti) C complex precipitates. The first principle calculation results indicate that V-Ti multi-microalloying improved the hydrogen trapping capacity of (V, Ti) C compared with TiC. Additionally, this approach refined the prior austenite grain size, fortifying the material's resistance to hydrogen-induced cracking.

Tailored Casting and Hot Rolling Temperatures for the Preparation of Hot Stamping Steel Thin Strip

Tailored Casting and Hot Rolling Temperatures for the Preparation of Hot Stamping Steel Thin Strip

In-Situ Observation Combined with Numerical Simulation of the Solidification and Subsequent Cooling Process for Hot Stamping Steel

In-Situ Observation Combined with Numerical Simulation of the Solidification and Subsequent Cooling Process for Hot Stamping Steel

Analysis of the Oxidation Behavior and Formation of an Extremely Thin Oxide Layer with a Novel Hot-Stamped Steel

This study investigates enhancing the high-temperature oxidation resistance of hot-stamped steels by adding the Cr/Mn/Si elements to form an extremely thin oxide layer. Under low oxygen partial pressure conditions and high Cr content in the matrix, the oxide layer of a 38Cr3MnNbVMo hot-rolled plate containing the Mo element and high Si content was further thinned to 0.6 μm after cooling at 900 °C for 5 min. The structure of the ultra-thin oxide layer consists of Fe3O4, Mn oxides, FeCr2O4, Cr2O3, and Fe2SiO4 oxides. Compared to other antioxidant elements, under low oxygen partial pressure conditions, Si is more prone to oxidation, forming ultra-thin (22 nm) Fe2SiO4 oxides at the matrix interface. Combined with Cr2O3, FeCr2O4, and Mn oxides, it collectively inhibits the mutual diffusion of external O ions and matrix Fe ions. Furthermore, the addition of the Mo element improves the oxidation resistance. The synergistic effect of multiple powerful oxidation-resistant elements and oxide products effectively inhibits the growth of the iron oxide scale, enhancing the oxidation resistance of hot-rolled, hot-stamped steel.

Full-Process Numerical Simulation of Flow, Heat Transfer and Solidification for Hot Stamping Steel Manufactured via Thin Slab Continuous Casting Process

Full-Process Numerical Simulation of Flow, Heat Transfer and Solidification for Hot Stamping Steel Manufactured via Thin Slab Continuous Casting Process

Fracture behaviors of the 1500 MPa-grade anti-oxidation hot-stamped steel: Measurement, numerical simulation and experimental validation

Ultra-high strength hot-stamped steel has been increasingly and widely used for the improvement of the collision safety and lightweight level. The 1500 MPa-grade anti-oxidation hot-stamped steel (AHS-1500), as a newly developed hot-stamped steel, is promising in the automotive industry due to its advantages of anti-oxidation, high strength, high hardenability, and no coating. It is necessary to figure out its fracture failure behaviors and further predict the fracture risk for promoting the large-scale application. In this paper, the fracture behaviors of the AHS-1500 steel plate are investigated by experiments and simulation. The fracture tests are conducted under static and dynamic loads by considering various stress states, namely uniaxial tension, notched static tension, shear, punching, center-hole static tension, and VDA bending. The fracture failure behaviors are obtained. Moreover, an Swift+Hockett-Sherby combined hardening model is adopted to extrapolate the post-necking flow stress to obtain the stress-strain relation at large strains. A fracture failure model is further established based on the GISSMO fracture failure criterion to accurately describe the failure behaviors under various stress states. The nonlinear fracture failure strain and the necking instability strain are determined with the consideration of the influence of element size and strain rate. Finally, the three-point bending experiment of a cap beam part is conducted and simulated to verify the effectiveness of the proposed model. The simulated results match the experimental ones very well, with the absolute relative errors of only 1.4 % and 4.6 % for the peak force and peak displacement, respectively. This research is favourable for contributing to high-precision numerical analysis for the design of automotive structural components and providing technical support for large-scale promotion of the AHS-1500 steel.

Effect of Different Quenching Methods on the Microstructure and Mechanical Properties of 30MnB5NbTi

The effects of different quenching methods on the microstructure and mechanical properties of 30MnB5NbTi hot stamping steel are investigated, and the quenched microstructure is characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The mechanical properties are evaluated by uniaxial tensile test. The results reveal that, in comparison to die quenching, oil quenching, or air cooling, water‐quenched samples (tempered after water quenching, die quenching and oil quenching) exhibit the highest ultimate tensile strength (UTS) and yield strength (YS), reaching 2052 and 1422 MPa, respectively. Various quenching methods enable multi‐level strength control for the same steel grade, achieving a strength control range of ≈1000 MPa. The microstructure of samples quenched by water, die, and oil is fully martensite, and martensite exhibited block and lath morphology. With the increase of cooling rate, martensite laths become finer and the prior austenite size decreased. The microstructure of air‐cooled samples is martensite, ferrite, and retained austenite. The strengthening mechanisms of different quenched samples are calculated. The results show that dislocation strengthening and precipitation strengthening are the two dominant strengthening mechanisms in 30MnB5NbTi hot stamping steel. Therefore, the properties of hot stamping steel can be improved by changing the cooling rate by designing physical dies.

Hydrogen diffusion and hydrogen embrittlement of a 1500 MPa hot-stamped steel 22MnB5 in different austenitizing conditions

We investigated the influence of hydrogen on a 1500 MPa hot-stamped steel 22MnB5 with different prior austenite grain size (PAGS, ranging from 14.0 μm to 22.2 μm), which were produced by precise control of the austenitizing temperature and time. All steel specimen exhibited a significant reduction of ductility (e.g., by 70%) and a small decrease in ultimate tensile strength (≤15%), measured using the linearly increasing stress test. The effect of PAGS on hydrogen embrittlement of the hot-stamped steel was not significant for these test conditions. Martensite with smaller PAGS exhibited a slightly lower hydrogen diffusion coefficient. Fracture for all steel variants after yielding occurred for hydrogen contents greater than those that actually occur during service.

Research on thermal efficiency and weld forming coefficient prediction of ultra-high strength steel welded joint under different energy inputs

As an ultra-high strength steel, Al–Si coated 22MnB5 hot stamping steel is widely used in the manufacturing of body-in-white structural parts. Compared with traditional welding technology, laser welding is widely used in the field of automobile body-in-white manufacturing due to its high energy density, small heat affected zone, and high weld quality. For ultra-high strength steel laser welded joints, the weld forming coefficient is an important index to reflect the welding quality. In order to investigate the influence of weld forming coefficient on the Al content and the thermal efficiency, laser welding experiments of ultra-high strength steel under different laser energy inputs are carried out. The melting of the base metal and coating under different laser energy inputs is also considered. Particle swarm optimization (PSO) algorithm is introduced into radial basis function (RBF) neural network model to optimize the central parameters as the RBF neural network model alone is not sufficient in predicting the outcomes. The results shows that if the laser power density is constant (7 × 105 W/cm2), when laser energy inputs are 400 J/cm to 1200 J/cm, the Al content in welded joints is 1.458%–1.886%, the melting efficiency of welded joints is 0.23–0.26, the energy conversion efficiency of welded joints is 0.45–0.46. When the laser energy inputs are lower than 522 J/cm, the Al content of the laser welded joint increases gradually. When the laser energy inputs are higher than 522 J/cm, the Al content of the laser welded joint decreases. The root mean square error(RMSE) of PSO-optimized RBF neural network testing sets prediction results is 0.1551, R-square (R2) is 0.771 and mean absolute percentage error (MAPE) is 2.758%. The prediction accuracy of the PSO-optimized RBF neural network model for the upper surface weld width, waist weld width, and lower surface weld width is 93.9%, 91.1%, and 92.2%.

Crack generation, propagation mechanism and thermal property of Zn-coated hot stamping steel

Crack generation, propagation mechanism and thermal property of Zn-coated hot stamping steel

Mechanical Properties of Hot-Stamped Spherical Shell Q235 Steel after Exposure to Elevated Temperature

Mechanical Properties of Hot-Stamped Spherical Shell Q235 Steel after Exposure to Elevated Temperature

An integrated convolutional neural network-based surrogate model for crashworthiness performance prediction of hot-stamped vehicle panel components

During the structural design of vehicle components, Finite Element (FE) modelling has been extensively used for simulations of physical experiments. A typical design optimisation task requires iterative simulations to identify the optimum design, where FE simulations can be too time-consuming. Surrogate models have been developed to approximate complex simulations, which can reduce computational time and improve the efficiency of the design cycle. This paper presents a novel application of convolutional neural network (CNN) on rapid predictions of crashworthiness performance of vehicle panel components considering manufacturability. The dataset for training the model was generated based on the FE results of hot-stamped ultra-high strength steel (UHSS) B-pillar components. The formed components were analysed with a simplified lateral crash test to evaluate the deformation under impact. The trained model can instantly predict the deformation of the designed component with high accuracy compared to the FE results. Due to its high computational efficiency and precision, the surrogate model enables faster and more extensive design evaluations.

Microstructure and mechanical properties of adjustable-ring-mode laser welded and hot-stamped Al–Si coated boron steel joints

The microstructure and mechanical properties of adjustable-ring-mode (ARM) laser-welded, hot-stamped 22MnB5 steel joints were analyzed and compared with those of Al–Si coated 22MnB5. Al segregation into the fusion zone (FZ) was suppressed by a ring beam introduced via ring-beam-mode (RBM) and dual-beam-mode (DBM) laser welding. Dilution of the Al–Si coating in the FZ induced α-ferrite formation during hot stamping. After hot stamping, the α-ferrite fraction in the FZ decreased (from 23 vol% to 4.27 vol%) more than that in the center-beam-mode (CBM) welded joints owing to the ring beam. Electron backscattered diffraction analysis indicated the distribution of high-density and uniform geometrically necessary dislocations, which caused coordinated deformation in the martensite grains, in the RBM and DBM FZs. The average microhardness in the FZ in the tailor-welded blank (TWB) joints was ∼30–40 HV lower than that in the RBM and DBM welded base metal (480 HV) and that in the FZ of the CBM reduced to 295 HV because of the formation of a large amount of ductile α-ferrite. The tensile strength and elongation of the TWB joint in the CBM were ∼989 MPa and 1.1 %, respectively, which were significantly lower than those of the RBM (1245 MPa and 1.96 %, respectively) and DBM (1321 MPa and 2.12 %, respectively). Finally, the 22MnB5 steel sheets were subjected to ARM laser welding without removing the coating layer to evaluate the effect of the ring beam on Al segregation suppression in the FZ and mechanical properties of the TWB joints.

Hydrogen embrittlement studies of hot-stamped boron steel with different prior austenite grain sizes

Hydrogen embrittlement studies of hot-stamped boron steel with different prior austenite grain sizes

Evolution of the Microstructure and Mechanical Properties of As-Cast 22MnB5 Hot-Stamping Steel Processed by a Novel Sub-rapid Solidification Technique

Evolution of the Microstructure and Mechanical Properties of As-Cast 22MnB5 Hot-Stamping Steel Processed by a Novel Sub-rapid Solidification Technique

Studying the Effect of Cr and Si on the High-Temperature Oxidation-Resistance Mechanism of Hot Stamping Steel

The surface of hot stamping steel is severely oxidized during heating, holding, and transfer from the heating furnace to the stamping die in the production of traditional automotive parts. Coating-free hot stamping steel with Cr and Si elements exhibits excellent oxidation resistance during hot stamping without the protection of a surface coating. This paper investigates the oxidation behavior of three types of hot stamping steel at 800–1200 °C. The results show that although Cr-Si hot stamping steel performs excellently short-term (≤7.5 min) for oxidation resistance, its long-term (≥15 min) or high-temperature (≥1100 °C) oxidation resistance is much lower than that of the conventional hot stamping steel 22MnB5, affecting the production and surface quality control of the new coating-free Cr-Si hot stamping steel. By analyzing the oxidation kinetics and characterizing the structure of oxide layers in hot stamping steel, it was found that the structural change in the Cr and Si element enrichment layer between the oxide scale and the substrate varied in oxidation performance at different temperatures. When the oxidation temperature was below 1000 °C, the solid Cr and Si enrichment layer acted as a barrier to prevent the diffusion of Fe ions. When the oxidation temperature exceeded 1100 °C, the molten Cr and Si enrichment layer effectively adapted to the substrate and avoided blistering. Meanwhile, Fe2SiO4 penetrated the Fe oxide layer along the grain boundary and became a rapidly diffusing channel of Fe ions, contributing to a significant increase in the oxidation rate.

The Study of Hardness Evolution during the Tempering Process of 38MnB5Nb Ultra-High-Strength Hot Stamping Steel: Experimental Analysis and Constitutive Models

To elucidate the hardness evolution behaviors for 38MnB5Nb ultra-high-strength hot stamping steel, a series of tempering processes with varying tempering temperatures and times were carried out with a dilatometer. Meanwhile, the hardness of each sample was measured after dilatometer experiments. The results indicated that the tempering process parameters (including the tempering temperature and time) play an important role in the hardness of the studied steel. The hardness of 38MnB5Nb ultra-high-strength hot stamping steel at the quenched state is about 580 Hv, while it is 240 Hv for the quasi-annealed state. As the tempering time extends, the hardness is decreased sharply at the initial stage; then, the hardness is decreased in a quasi-linear trend with a slight slope; finally, the hardness almost keeps a constant value, which depends on the tempering temperature. In addition, the tempering process has a big effect on the mechanical properties of 38MnB5Nb ultra-high-strength hot stamping steel by increasing the product of the strength and elongation by about 40%.

The effect of heating rate and coating weight on the intermetallic growth of Al[sbnd]Si coated hot stamping steel

The effect of furnace heating rate on the intermetallic growth of AlSi coatings for 22MnB5 hot stamping steel was characterized and quantified for two different commercial coating weights, AS80 and AS150. Characterizing and quantifying the formation of the AlFe and Al-Fe-Si intermetallic layers is crucial to the optimization of the austenitization process, which continually strives to reduce furnace time while maintaining acceptable intermetallic development. Initial nominal heating rates up to the AlSi melting temperature (577 °C) varied from Low (7 °C/s) to Very High (23 °C/s) and then proceed to reduce which resulted in the nominal heating rates to vary from Low (1 °C/s) to Very High (7 °C/s) within a temperature range of 600 to 900 °C. The coating composition was similar at 600 °C for all the heating rate tests and suggests that there is potential to save furnace time by imposing high initial heating rates. SEM and EDS analysis was conducted on the coating at 50 °C intervals. The overall intermetallic transformation occurred significantly faster at the higher heating rates due to the accelerated diffusion of Fe into the coating. The intermetallic transformation also occurred faster for the thinner AS80 coating due to the shorter diffusion path of Fe. A simple empirical model was developed to predict the coating transformation percentage for any temperature and time from 600 °C. The formation of FeAl and Fe-Al-Si intermetallics was characterized. For each coating weight, the evolution of each intermetallic species was consistent for each heating rate, but at a delayed rate for each subsequently higher heating rate. Additionally, the tests conducted in this work showed that full austenitization of the base metal can be achieved during the heating phase (72 s for Very High heating rate).

Microstructural Control and Alloy Design for Improving the Resistance to Delayed Fracture of Ultrahigh-Strength Automotive Steel Sheets

The demand for higher-strength automotive steel sheets has increased significantly for lightweight and safe body concepts. However, the increment of the steel strength is often limited by the potential occurrence of delayed fracture. This paper discusses proper microstructure control and alloy design to improve the resistance against the delayed fracture of ultrahigh-strength automotive steel sheets in order to increase the usable upper limit of their strength and provides basic data serving as a practical guide for solving the problem of delayed fracture in ultrahigh-strength automotive steel sheets. It is confirmed that grain refinement, the appropriate dual-phase structure of martensite with ferrite or retained austenite, and surface decarburization, increase the resistance to delayed fracture. In terms of alloy design, the effects of Nb, Mo, and B on the delayed fracture resistance of hot-stamped steels have been investigated. The results suggest that there are other reasons for Nb to improve delayed fracture resistance in addition to grain refinement and the ability to trap hydrogen by its precipitates, as has been conventionally believed. Regarding Mo, it was clearly demonstrated that the segregation of this element at the grain boundary plays a main role in improving the delayed fracture resistance.