Development of Niobium Alloyed Press Hardening Steel with Improved Properties for Crash Performance
Press hardening steel has become a much used material in car body manufacturing due to its excellent safety and lightweight potential.In some recent car models press hardening steel has reached already a weight share of more than 20% in the body structure while it is estimated that it could reach even around 40% in the future.However conventional press hardening steel based on the alloying concept 22MnB5 was designed originally not for automotive application.In spite of the high strength level, press hardening steel has generally low toughness due to the relatively high carbon content and its martensitic microstructure.Particularly important is the ductile-to-brittle transition temperature at low temperature, which might lead to unexpected failure in cold climate regions.Furthermore, hydrogen embrittlement is a major concem in press hardening steel as previous results indicated that only a few ppm of hydrogen could induce delayed cracking.Generally it is important that impact energy should be absorbed by the material to avoid unexpected disintegration of the structure.This material capability is usually characterized by the toughness.All these characteristics have not yet been systematically investigated in press hardening steel.Consequently, no attempts have been made to optimize conventional press hardening steel for obtaining better toughness, lower ductile-to-brittle transition temperature and reduced sensitivity to hydrogen induced cracking.A generally proven approach of improving the resistance against brittle failure in high strength steel is the refinement of microstructure, which can be efficiently achieved by Nb microalloying.This paper will introduce modified alloy designs for press hardening steel and explain fundamentally the metallurgical effects of Nb microalloying on the improvement of crack propagation resistance, bendability and delayed cracking behavior induced by hydrogen penetration in press hardening steel.The results reveal better toughness, improved bending behavior and increased resistance against hydrogen embrittlement.
martensitic steel toughness bendability hydrogen induced delayed cracking crash performance Nb microalloying
Jian Bian Wang Li Hardy Mohrbacher Lu Hongzhou Wang Wenjun
Niobium Tech Asia,068898 Singapore Baosteel Corporation,Shanghai 201900,China NiobelCon bvba,2970 Schilde,Belgium CITIC Metal Co.,Ltd,Beijing 100004,China
国际会议
2014 International Conference on Hot Stamping of UHSS(2014高强度钢热冲压成形国际会议)
重庆
英文
60-73
2014-08-21（万方平台首次上网日期，不代表论文的发表时间）