Hot-Stamping of Boron Steel
Sabr, Ali (2020)
Sabr, Ali
2020
Master's Programme in Materials Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2020-12-15
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202012158841
https://urn.fi/URN:NBN:fi:tuni-202012158841
Tiivistelmä
Materials used in car body must fulfill several performance requirements during manufacturing and service life. Reducing car weight also reduces fuel consumption and causes lower gas emissions. One way to make that possible is to use hot-stamped boron steel components because the high strength of steel sheet thickness can be reduced without losing crashworthiness. The lower weight of the car body is as important with the electric car as it is with the combustion car because it enables a longer-lasting battery.
During hot stamping, steel suffers from high-temperature oxidation, and for that reason, coating became a vital solution to prevent high-temperature oxidation and provide corrosion protection during service life.
In this thesis, two different boron steel grades were tested, 22MnB5 galvannealed steel and 34MnB5 uncoated steel. 22MnB5 coated samples were hot-stamped at different stamping temperatures, starting from high temperature and gradually reducing stamping temperature in order to investigate the process's effect on final coating properties. An optical microscope was used to study and calculate the number and size of cracks in 22MnB5 resulted from friction force at different stamping temperatures. In the other material (34MnB5), two different compositions were investigated to evaluate the composition's effect on the final properties.
The results of coated 22MnB5 show a significant improvement in reducing the number and size of cracks when using lower stamping temperature. 34MnB5 exhibited a higher critical bending angle and lower tensile strength compared to commercial materials. Moreover, the material alloyed with higher Mo content shows more increase in the critical bending angle but decreased tensile strength.
During hot stamping, steel suffers from high-temperature oxidation, and for that reason, coating became a vital solution to prevent high-temperature oxidation and provide corrosion protection during service life.
In this thesis, two different boron steel grades were tested, 22MnB5 galvannealed steel and 34MnB5 uncoated steel. 22MnB5 coated samples were hot-stamped at different stamping temperatures, starting from high temperature and gradually reducing stamping temperature in order to investigate the process's effect on final coating properties. An optical microscope was used to study and calculate the number and size of cracks in 22MnB5 resulted from friction force at different stamping temperatures. In the other material (34MnB5), two different compositions were investigated to evaluate the composition's effect on the final properties.
The results of coated 22MnB5 show a significant improvement in reducing the number and size of cracks when using lower stamping temperature. 34MnB5 exhibited a higher critical bending angle and lower tensile strength compared to commercial materials. Moreover, the material alloyed with higher Mo content shows more increase in the critical bending angle but decreased tensile strength.