High Strength Steel 22MnB5 Research Articles

Effects of Secondary Cooling Segment Electromagnetic Stirring on Solidification Behavior and Composition Distribution in High-Strength Steel 22MnB5

Effects of Secondary Cooling Segment Electromagnetic Stirring on Solidification Behavior and Composition Distribution in High-Strength Steel 22MnB5

Thermomechanical analysis on the frictional contact behavior of a high-strength steel 22MnB5–die steel H13 tribopair at 800 °C by experiment and finite-element simulation

High-strength boron steels are widely used in manufacturing the auto bodies and parts of light-weight vehicles, but the high rates of surface scratches and die wear have consistently occurred during hot stamping for these steels. For an in-depth understanding of the tribological characteristics at this interface, the frictional contact behavior and thermomechanical mechanisms of boron steel 22MnB5 against die steel H13 at 800 °C were studied through experiments and finite-element simulations. The coefficient of friction and worn surface topography were investigated by pin-on-disk sliding tests. A three-dimensional thermomechanical finite-element model of a friction pair was established to explore the interfacial dynamic variations. Experimental and simulation results show that severe elastic–plastic deformation occurred on the worn surface of the boron steel, whereas an increase in the load decreased the coefficient of friction within a certain range because the growth rate of shear force was slower than that of the normal force. When the finite-element model was changed from the gradual loading stage to the initial sliding stage, the tangential friction force further increased the plastic deformation on the surface of boron steel. The scratches and furrows were mainly caused by the compression and shear from asperities of the rough surface, as confirmed by the high-frictional-stress regions concentrated on the peaks and flanks of asperities. During the high-temperature and high-pressure experiments, the plasticized and softened surface materials of the boron steel adhered to the die surface readily, resulting in peeling and delamination.

Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air

The high-strength boron steel 22MnB5 steel is widely used for automotive lightweight constructions. A novel approach is promising to tailor strength and ductility in the hardened condition using locally pre-tempered sheets for the hot stamping process. It results in the formation of locally soft spots where mechanical joining is subsequently intended. A slow pre-cooling of the later joining zones with cooling rates below a certain critical cooling rate for obtaining a decreased strength in these regions is required. A tubular air cooling system suited for this task is presented and tested in a process where the subsequent quenching of the overall sheet is realized by rapid cooling in a water bath. Varying the air pressure and cooling duration allows controlling the size of the softened local spot in a wide range and still obtaining a bainitic microstructure. Using two-stage cooling with point jet nozzles and a subsequent hot stamping process with water-cooled dies resulted in a main sheet hardness of about 470 HV5 and of 260 HV5 in the pre-cooled spots, respectively.

Research on the plastic fluidity of high-strength steel 22MnB5 based on the thermal-mechanical-fluid multi-filed coupling

The effects of technological parameters such as pre-deformation, strain rate, and final forming temperature on the formability of high-strength steel 22MnB5 were studied. Firstly, the finite element model of thermal-mechanical-fluid coupling was established by finite element simulation software ABAQUS. Secondly, the simulation and experiment of the pure hydraulic bulging with the forming temperature are 20, 100, 300, 500, and 700 °C and were carried out, respectively. Finally, by setting the technological parameters such as the cavity pressure loading rate (2, 4, 6, 8, and10 MPa/s) and final forming temperature T (20, 100, 300, 500, and 700 °C), the numerical simulation and the experiment of the coupling of the initial room temperature pre-deformation and high-temperature final forming were studied, and the optimal combination of process parameters was optimized by making the bulging height as the objective function at the end of the forming process. Keeping the cavity pressure loading rate is invariable; the bulging height difference between the two processes is 12.02, 20.43, 26.18, 33.20, and 39.39 mm, respectively, when the temperature is 300 °C. Keeping the final forming temperature is invariable; when the cavity pressure loading rate is 8 MPa/s and the temperature is 300 °C, the difference of the bulging height difference between the hot hydraulic bulging and room temperature hydraulic bulging is maximum, the largest value is 2.17 mm. Taking the bulging height as the criteria of material forming performance, the combination of the final forming temperature of 300 °C and the cavity pressure loading rate of 8 MPa/s is optimum. Finally, the whole coupling process is divided into three stages, and by using the form of structuring sectionalized constitutive equation, the influence law of the dual action of work hardening and softening on the deformation and fluidity of the material in the compound-forming process is analyzed from the perspective of the evolution law of microstructure.

Effect of Microstructure and Texture on Mechanical Properties of Resistance Spot Welded High Strength Steel 22MnB5 and 5A06 Aluminium Alloy

The present study aims to investigate the effect of microstructure and texture on mechanical properties of resistance spot welding of high strength steel 22MnB5 and 5A06 aluminium alloy as a function of welding parameters. The pseudo-nugget zones (NZs) at the steel side have undergone full recrystallisation with a fine-grained ferrite structure containing a small amount of retained austenite and a high hardness of approximately 500 HV, which is a 35% increase in hardness compared to the base material (BM) with fine lath martensitic structure. The NZs at the Al side contain both a recrystallisation texture and shear texture. Higher tensile shear strength with increasing weld time could be linked to the random texture at the Al side. The highest tensile shear strength was achieved at an intermetallic layer thickness of 4 mm.

In situ observation on microstructure evolution of 22MnB5 in hot stamping process

High temperature confocal laser scanning microscopy (CLSM) was used to investigate the microstructure evolution of high-strength boron steel 22MnB5 during hot stamping. The experimental results show that it is complete austenitized at temperatures about 810 °C during the heating process. Most of the initial austenite grain size is small and locally coarse. At 920 °C to 1000 °C, the phenomenon of B remelted and solidified was observed which played a very good pinning role at the austenite grain boundary, preventing coarsening of austenite grains. The segregation of B and the addition of Mn result in a significant reduction in both the minimum boron reverse melt content and the final solidification temperature. In the continuous cooling stage, martensitic transformation occurs at the cooling rate of 60 °C/s, and the martensite start point is 400 °C and martensite finish point is 280 °C. A large number of bursts are concentrated from 380 °C to 330 °C. There are two main forms of martensitic transformation: first, martensite begins to appear at the coarse austenite grain boundary, and grows transgranularly. Second, the new martensite laths starts from the previously formed laths and grows at a certain angle into the austenite grains. The main factor in the increase of martensite in continuous cooling is the formation of variable temperature martensite rather than the growth of martensite laths. At the cooling rate of 20 °C/s, the bainite and ferrite transformation appeared and the conversion temperature of bainite was about 600 °C. The cooling speed has a great influence on the performance of the 22MnB5 hot stamping component. The room temperature microhardness at cooling rates of 5 °C/s, 20 °C/s, and 60 °C/s was 194 HV, 243 HV, and 430 HV, respectively. Therefore, ensuring sufficient cooling rate is a key condition for obtaining ultra-high strength hot stamping components.

Analysis of Al-Si Layer on Steel Sheet during Thermo Mechanical Processing Using Microscopic Methods

High strength steel 22MnB5 according to DIN EN 10083-3 belongs to the group of HF steels frequently used in the production of coachwork. Using the thermo mechanical pressing can be achieved that these steels have strength of about 1500 MPa. The surface of this steel is provided with a protective coating to protect it from oxidation. Galvanic ally, a Zn-based layer is used to provide cathodic protection. The Zn-based layer is limited by the temperature which is insufficient for TMP. Hot-dip galvanizing is also applied to an Al-based layer that does not serve as a cathodic protection but is used as an effective oxidation barrier. The quality of the Al-Si layer is important with regard to the resulting quality of the formed blank. The properties of the surface Al-Si layer affect not only the conditions for their application to the steel blank but also the external conditions which are determined by the conditions of the thermo-mechanical processing into the shape of the finished product. To assess the properties of this layer, microscopy methods, namely light and electron microscopy, were used. On the basis of analyzes, conclusions were drawn that should lead to securing the Al-Si layer with the required properties.

Parameter calibration for a shear modified GTN model and its application to forming limit prediction

Damage evolution is an unavoidable problem in the forming process of sheet metal, and an improper forming technology may cause ductile fracture of the final parts. The damage mechanics theory can give great insight to the failure mechanism and the numerical simulation using damage model can provide a new way to predict the fracture behaviour for sheet metal. The shear modified GTN model by Nahshon and Hutchinson with a piecewise interpolation function was applied, which can capture the damage evolution under both low and high stress triaxiality. Then, a method combined numerical simulation and optimization algorithm was adopted to calibrate the damage-related parameters. Furthermore, the shear modified model was used to predict the forming limit of a high strength steel 22MnB5.With the help of digital image correlation technique (DIC), both the strain field and forming limit curve obtained by the numerical simulation were compared with the experimental ones, and satisfactory results are obtained.

Mechanical properties of AlXFeY intermetallics in Al-base coatings on steel 22MnB5 and resulting wear mechanisms at press-hardening tool steel surfaces

Hard and brittle intermetallic AlXFeY phases formed in the Al-base coating applied on high-strength steel 22MnB5 promote strong wear of press-hardening tools during forming and quenching (approx. 800–100°C). In this study, bulk materials of the intermetallic phases Al13Fe4, Al5Fe2, Al2Fe, and AlFe were produced by remelting stoichiometric powder mixtures. These were then used for mechanical and wear investigations. We found that the dominating wear mechanisms on the tool steel surfaces are strongly influenced by the temperature and depend on the mechanical properties of the respective intermetallic phases. Phases of type Al13Fe4, Al5Fe2, and Al2Fe possess a high hardness of 850–1090HV0.5 and a low fracture toughness of 0.9–1.6MPa√m at room temperature, whereas the AlFe phase has a much lower hardness (520HV0.5) and a higher fracture toughness (26MPa√m ). The hardness of all phases decreases with increasing temperature. At high temperatures (500–800°C), the intermetallic phases lead mainly to adhesive wear of the tool steel surfaces. At lower temperatures, also abrasive wear occurs due to delamination of hard and brittle intermetallic particles. We found that abrasive wear of the tool steel surface could be decreased by adapting the phase composition in the Al-base coating.

Research on Hot Riveting Quenching Clinching of the High Strength Steel 22MnB5 and Aluminum Alloy 7075

Research on Hot Riveting Quenching Clinching of the High Strength Steel 22MnB5 and Aluminum Alloy 7075

Theoretical prediction of high strength steel 22MnB5 forming limit in high temperature based on M-K model

Abstract Hot stamping is an advanced manufacturing process in automobile manufacturing. Different from the traditional forming process in room temperature, the strain hardening, temperature, strain rate and microstructure of the material have great influence on the mechanics and failure behavior of the high strength steel. The traditional theoretical forming limit prediction method based on room temperature is not effective enough to predict the formability of parts under hot stamping condition. A forming limit prediction model for the high temperature forming process of 22MnB5 is obtained based on Norton-Hoff constitutive model, BBC 2005 yield criterion, and M-K model. The accuracy of the prediction model is verified by comparing with the experimental data in the literature. This model can be used as the forming limit prediction criterion for high strength steel in hot stamping process. The characteristics of forming limit curves under different conditions are obtained and the effect of yield criterion, temperature, and strain rate are summarized.

Microstructure, mechanical properties and failure mechanisms of resistance spot welding joints between ultra high strength steel 22MnB5 and galvanized steel HSLA350

Resistance spot welding of 22MnB5/HSLA350 and its weldability are investigated. From base material to the nugget, the microstructure of 22MnB5 side can be expressed as M/tempered M+ granular carbides/F+M/fine M/lath M, and on HSLA350 side, F+M/F+flocculent P+tempered M/F+flocculent P+M/F+M/lath M are observed. The heat-affected zone (HAZ) of 22MnB5 exhibits obvious softening region and strengthening region caused by the tempered M and quite fine M, respectively. The peak load of welded joints undergoes two stages of a dramatic increase and a subsequent decrease with increases in the welding current. The maximum value (13.82 kN) of peak load is achieved at a welding current of 8 kA. The failure modes involving interfacial failure (IF), pullout failure from the galvanized steel (PFG), pullout failure from boron steel and tearing of the galvanized steel (PFB-TG) and pullout failure from the boron steel (PFB) are discussed in detail.

Mechanical Properties of Al-Si Galvanic Coating and its Influence on Resistance Weldability of 22MnB5 Steel

Increase of quality and productivity in the same time are the most important in automotive industry. Use of high-strength steel 22MnB5 allows decrease of sheet metal thickness compared to standard steel. Commonly the steel 22MnB5 is welded with laser [1]. Use of this steel for spot resistance welding is not yet fully described. Steel 22MnB5 is coated with Al-Si galvanic coating for increasing high temperature oxidation resistance [2]. During hot stamping and subsequent heat treatment diffusion layer is created between coating and steel. The thickness of this layer is strongly dependent on temperature and time of heat process [3]. The paper deals with mechanical properties (chemical composition, indentation hardness) of this diffusion layer and Al-Si coating. Different thicknesses of diffusion layers were compared and its influence on weldability was described. Thin thicknesses have negligible effect on weldability, yet large thicknesses very negatively influence the weldability.

Fatigue strength of hybrid welded 22MnB5 overlap joints

Abstract In order to reduce the weight of automotive parts, lightweight materials like the press hardened AlSi coated high strength steel 22MnB5 is used. This steel enables a reduction of wall thicknesses and simultaneously ensures a high stiffness of the part, e. g., the B pillar. The usage of these steels requires suitable joining technologies. Therefore, a laser GMA hybrid welding process for fillet welds in overlap configuration was designed. This process provides high welding velocities and process tolerances against gaps and misalignments. In this case a single-mode fiber laser was used in order to reduce the thermal impact. Due to the fact that the laser focus spot has only a small diameter of 25 µm, a beam oscillation was used in order to distribute the laser energy over the melt pool width. This paper is focused on the cyclic load tests which were carried out and analyzed by the staircase method. The influences of laser power and oscillation width are dominating, whereas welding velocity and wire velocity have only a minor influence. By analyzing the failure location and crack propagation of specimens after the cyclic load test, the influence of the AlSi coating can be determined. Coating agglomerations at the fusion line of the melt pool are origins of crack initiation. This is attributed to the formation of brittle intermetallic phases.

Laser beam welding of magnesium to coated high-strength steel 22MnB5

Magnesium alloy AZ31 was laser-welded to AlSi10Fe3-coated high-strength steel 22MnB5. The surface of the 22MnB5 steel sheet was treated by sandblasting before welding. Laser welding of magnesium with steel was found to be a welding-brazing process, due to the large difference in the melting temperatures of steel and magnesium. The liquid magnesium was wetted on the solid steel surface, which thus was a brazing process on the steel side. AZ61 magnesium welding filler was used to improve adhesion of the liquid magnesium to the steel surface. Furthermore, the suitability of using a flux was determined. Welded steel/magnesium joints with a high tensile strength of 2680–3090 N (178–213 MPa) were produced using a flux and inductive preheating of the conditioned steel surface. Under tensile loading, the welded joints did not fail at the steel/magnesium interface, but in the AZ61 magnesium welding filler. Metallurgical bonding at the magnesium/steel interface was attributed to the formation of a thin Al-Fe-rich layer, which is due to the alloyed aluminum (6 mass%) in the magnesium welding filler.

Laser beam welding of aluminum to Al-base coated high-strength steel 22MnB5

The microstructure of aluminum—Al-coated steel laser beam welding joints was analyzed with respect to the welding energy. Quantitative and qualitative analysis of the welding microstructure were used to measure the weld width as well as the thickness of the resulting intermetallic layer at the 22MnB5/aluminum interface in relation to the welding parameters. Weldability of Al-coated steel could be improved by removing brittle coating particles and oxides on the steel surface by sandblasting. Adhesion of aluminum filler material to the 22MnB5 steel sheet could be enhanced by inductive preheating of the steel surface during laser welding. This produced welded 22MnB5/aluminum joints that exhibited a linear mechanical resistance of 220MPa and which failed away from the brittle intermetallic layer on the aluminum side under a tensile load. The shear strength of the intermetallic layer on the 22MnB5/aluminum interface was evaluated to 74±21MPa.

Corrosion Behavior Study of 22MnB5 Steel and its Weld Using Electrochemical Method

Corrosion behaviors of ultra high strength steel 22MnB5 and its weld were studied based on electrochemical method in the present work. Electrochemical measurements such as Tafel polarization curve and electrochemical impedance spectroscopy were performed to investigate the corrosion mechanisms of 22MnB5 steel and its weld. The testing results indicated the weld metal possessed less corrosion resistance than the base metal, and the main reason for this phenomenon is the microstructure variation of the weld metal.

The Basic Research and Application on Hot Forming of High Strength Steel

Taking the high-strength steel 22MnB5 as the research object, starting from the phase transformation and the performance of the sheet at high temperature, the impact of various process parameters on the part was studied, pressing the stringers with hot forming technology simultaneously. Using metallurgical microscope, hardness tester and universal tensile testing machine, the microstructure and mechanical properties of the parts were analysed. The result show that, under the selected process parameters, the microstructure of the workpiece is desired lath martensite, the hardness is above 450HV, the tensile strength is above 1450MPa, which meet the production requirements.

Experimental Study on Hot Bending of Ultra High Strength Steel 22Mnb5 and its Lightweight Application

Experimental Study on Hot Bending of Ultra High Strength Steel 22Mnb5 and its Lightweight Application

Modeling and FE Simulation of Quenchable High Strength Steels Sheet Metal Hot Forming Process

High strength steel (HSS) sheet metal hot forming process is investigated by means of numerical simulations. With regard to a reliable numerical process design, the knowledge of the thermal and thermo-mechanical properties is essential. In this article, tensile tests are performed to examine the flow stress of the material HSS 22MnB5 at different strains, strain rates, and temperatures. Constitutive model based on phenomenological approach is developed to describe the thermo-mechanical properties of the material 22MnB5 by fitting the experimental data. A 2D coupled thermo-mechanical finite element (FE) model is developed to simulate the HSS sheet metal hot forming process for U-channel part. The ABAQUS/explicit model is used conduct the hot forming stage simulations, and ABAQUS/implicit model is used for accurately predicting the springback which happens at the end of hot forming stage. Material modeling and FE numerical simulations are carried out to investigate the effect of the processing parameters on the hot forming process. The processing parameters have significant influence on the microstructure of U-channel part. The springback after hot forming stage is the main factor impairing the shape precision of hot-formed part. The mechanism of springback is advanced and verified through numerical simulations and tensile loading-unloading tests. Creep strain is found in the tensile loading-unloading test under isothermal condition and has a distinct effect on springback. According to the numerical and experimental results, it can be concluded that springback is mainly caused by different cooling rats and the nonhomogengeous shrink of material during hot forming process, the creep strain is the main factor influencing the amount of the springback.