Rolling mill for cold roll coils. cold rolling process. Tangsteel. Tangshan, China.

Project nominated for the Innovation of the Year Steelie Award 2022

Recently, the ratio of applying high-strength steel over 1GPa has been increased to reduce the car body’s weight and respond to fuel efficiency regulations.

In addition, it is necessary to maintain the stability of high-strength parts of the vehicle body to meet the strengthened crash requirement.

High-strength parts with hot stamping technology may experience brittleness due to bending and welding during a crash.

To overcome this issue, HYUNDAI Steel Company has developed a high-toughness 1.5 GPa hot stamping steel sheet that has fracture resistance, a world first.

In order to obtain the high-toughness hot stamping characteristics, many technologies, such as the homogenisation of the microstructure of the steel sheet, material cleanliness control and austenitic grain size refinement, were developed, and these technologies were commercialised through micro-alloy design and manufacturing processes.

Various evaluations have been conducted since 2021 to confirm the performance of high-toughness hot stamping 1.5GPa grade of car body parts, and the material toughness (VDA238-100 evaluation) was significantly improved by about 25%. It was confirmed that the spot welding strength increased by about 67%.

In addition, hydrogen embrittlement resistance was improved by about 36%. Based on these characteristics, it was confirmed that the displacement value was reduced by about 23% from the existing 142mm to 108mm in the free-drop tower test experiment.

To apply the high-toughness hot stamping 1.5GPa steel sheet, the company has been conducting advanced research with automobile customers since April 2022.

Hot stamping steel sheets having such high toughness may not only break an old belief that it can be easily broken in the event of a crash but also overcome the limitations of the material performance. It will show excellent performance for battery protection of eco-friendly
cars and secure passenger safety.

Furthermore, it is expected that HYUNDAI Steel Company will be able to develop customised materials and expand applied engineering through diversifying its hot stamping steel sheet portfolio.