• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.5
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• pp.25-30
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• 2010

The authors have studied on the corrosion resistance of the hot stamped steel sheets for the application to automotive parts. Recently automotive companies have focused on the hot stamped parts to meet the light weighting needs and the safe reason. Because of the cost reduction of the hot stamped parts, automotive companies increase the usage of the coated steel sheets, especially Al-Si coated steel sheets. The coated layer of Al-Si coated steel sheets contains up to 50% of Fe, which was diffused from the steel sheet, after hot stamping. The hot stamped steel sheet was not phosphated due to the oxidation layer of the coating, however, the result of the water resistance test is similar to that of the conventional GA steel sheets. The pitting depth and the weight reduction of the coated layer of hot stamped steel sheets are less than those of GA steel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.89-94
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• 2015

This study was conducted to compare the laser weldability of boron steel and hot-stamped steel. In general, boron steel is used in the hot-stamping process. Hot-stamping is a method for simultaneously forming and cooling boron steel in a press die after heating it to the austenitizing temperature. Hot-stamped steel has a strength of 1500 MPa or more. Thus, in this study, the laser weldability of boron steel and thet of hot-stamped steel were investigated and compared. A continuous wave disk laser was used to produce butt and lap joints. In the butt welding, the critical cooling speed at which full penetration was obtained in the hot-stamped steel was lower than that of boron steel. In the lap welding, the joint widths were similar regardless of the welding speed when full penetration was obtained.

• Laser Solutions
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• v.15 no.1
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• pp.1-5
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• 2012

Recently ultra high strength steels(UHSS) has been widely applied to the structural or safety components in the automotive industry. Specially, hot stamping boron steel 22MnB5 has shown the crash-resistant characteristics when applying to bumpers and pillars. Lap joint Laser welding of the hot stamped and die quenched sheets of Boron steel was carried out using 3kW Nd/YAG laser. The appropriate Lap joint laser welding conditions were founded separately for four lap joint combinations. The lower sheest is a hot stamped sheet in common and the upper sheet is selected among the hot stamped steel and high strength steels such as SPCC, 370MPa, and 590MPa grade high strength steels. Cross bead sections and local hardening and softening were observed as well as tensile-shear test results.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.7-12
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• 2008

A hot stamping technology of vehicle door impact beam made of thin sheet steel has been developed, with the aim of ensuring occupant safety in a side collision. This technology has been implemented to increase the strength of vehicle body parts and to reduce not only the weight of door impact beam but also the number of work processes. Mechanical tests were performed to obtain material properties of hot-stamped specimen and those were used as input data in stamping and structural simulation for optimal design of door impact beam. Strength of hot-stamped door impact beam increased to the value 102% higher than that of conventional pipe-shaped door impact beam and structural simulation showed that hot-stamped door impact beam achieved 28% weight reduction.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.39.2-39.2
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• 2010

Recently, hot stamping process has been paid attention greatly by automobile makers in accordance with the fuel efficiency and environmental issues as well as crash safety issue. The hot-stamped parts, however, demand extreme mechanical properties such as tensile strength of over 1470 MPa or equivalently Vickers hardness of around 450. In this work, to meet the demand efficiently, a method to predict mechanical property of hot-stamped parts based on numerical phase transformation scheme has been proposed associated with the thermo-mechanical coupled finite element analysis. This work deals with various phase transformation equations and validates them to select appropriate model for 0.2C-0.1Si-1.4Mn-0.5Cr-0.01Mo-0.002B steel sheet. The authors show that an efficient method saving time and cost to develop hot-stamped automobile parts ensuring suitable mechanical properties such as Vickers hardness and strength.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.540-547
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• 2011

Recent years have seen advent of hot stamped parts made from laser-welded blanks of boron steels for structures requiring high crash energy absorption. However, the presence of Al-Si coating interfered with satisfactory mechanical characterizations after laser butt welding. In this study, laser ablation technology was considered in order to facilitate adequate mechanical characterization of the final hot-stamped panels.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1373-1377
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• 2014

Hot-stamping is a method of obtaining ultrahigh-strength steel by simultaneously forming and cooling boron steel in a press die after it has been heated at $900^{\circ}C$ or above. After heat treatment, boron steel has a strength of 1500 MPa or more. This material ensures a high level of quality because it overcomes the spring-back phenomenon, which is a problem associated with high-strength steel materials, and the degree of dimensional precision is improved by 90 or more because of the good formability compared with existing types of steel. In this study, the welding characteristics were identified through the butt and lap welding of hot-stamped steel using a disk laser. Full penetration was obtained at a faster speed with butt welding compared to lap welding, and a white band was observed in every specimen.

• Transactions of Materials Processing
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• v.21 no.3
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• pp.186-194
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• 2012

Hot stamping is a forming method that offers various advantages such as superior mechanical properties, good formability, and very small springback. However, relatively large-sized parts, such as front pillars, exhibit poor formability when hot stamped due to the limited material flow and thickness reduction imparted by the process. This reduction in thickness can also lead to cracks. One of the reasons is the relatively high friction between the sheet and the die. In this study, in order to obtain the optimal conditions for hot stamping of front pillars, various process parameters were studied and analyzed using the sheet forming software, J-STAMP. The effects of various parameters such as the die structure, blank shape, blank holding force, punch speed, clearance(upper and lower dies) and distance block were analyzed and compared.

• Corrosion Science and Technology
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• v.23 no.3
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• pp.221-227
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• 2024

During hot stamping of hot-dip zinc-coated steel sheets such as hot-dip galvanized steel sheets and hot-dip galvannealed steel sheets, an oxide mainly composed of ZnO is formed on the sheet surface. However, excessive formation of ZnO can lead to a decrease in the amount of metal Zn in the coating layer, decreasing the corrosion resistance of hot-stamped members. Therefore, it is important to suppress excessive formation of ZnO. While the formation of Al oxides and Mn oxides along with ZnO layer during the hot stamping of hot-dip zinc-coated steel sheets can affect ZnO formation, crystal structures of such oxides have not been elucidated clearly. Thus, this study aimed to analyze structures of oxides formed during hot stamping of hot-dip galvannealed steel sheets using transmission electron microscopy. Results indicated the formation of an oxide layer comprising ZnAl₂O₄ at the interface between ZnO and the coating layer with Mn₃O₄ at the outermost of an oxide layer.

• Transactions of Materials Processing
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• v.23 no.6
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• pp.357-362
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• 2014

The purpose of the current study is to predict the hardness distribution in steel products after hot stamping using a quench factor analysis(QFA) coupled with FE-simulations. QFA is a method to predict properties such as hardness and tensile strength based on time-temperature-property(TTP) curves and can determine properties based on the temperature histories. The constants($K_1{\sim}K_5$) of QFA were determined using hardness data obtained after various cooling rates. In the current study, a rear side member was selected for evaluation and FE-simulations were performed to obtain the temperature histories during hot stamping. The predicted temperature data were imported into the QFA to calculate the hardness distribution of the hot stamped parts. A hot stamping experiment of the rear side member was conducted to verify the predicted hardness. The simulation results show good agreement with the experimental measurements.