High-temperature friction and wear characteristics of hardened ultra-high-strength boron steel

The usage of ultra-high-strength boron steel (UHSS) in automotive industry has increased rapidly in the recent past. Forming of UHSS components is performed at elevated temperatures, which also offers the possibility of hardening through quenching directly after forming. However, the influence of hardening on friction and wear during relative sliding between the tool and the workpiece is unclear. Therefore, the friction and wear characteristics at elevated temperatures of hardened and unhardened UHSS and tool steel pairs are investigated in this study. The results show that both friction and wear at all the investigated temperatures are affected by hardening of the UHSS. For uncoated UHSS, the hardening resulted in lower friction and the tool wear increased at low temperatures, but was not affected at elevated temperatures. This was attributed to the higher hardness after hardening combined with the presence of an oxide scale on the UHSS after heating and quenching. For Al-Si-coated UHSS, the hardening reduced friction and tool steel wear at elevated temperatures, and also reduced the wear of the Al-Si-coated high-strength steel at low temperature mainly owing to the formation of an intermetallic layer on the Al-Si-coated UHSS surface after exposure to elevated temperatures.