Study on Bending Beam Delayed Cracking of Ultra High-strength DP Steel for Automotive Use

Automobile lightweight project can effectively reduce energy consumption and exhaust emission, but it will reduce automobile safety. Therefore, using a large number of high-strength or ultra-high-strength steels in automobiles is an effective way to give consideration to both lightweight and safety. Delayed cracking is a symptom-free cracking phenomenon, which is extremely destructive. It is necessary to evaluate the delayed cracking performance of ultra-high strength steel before it is used. In this paper, the delayed cracking properties of three ultra-high strength dual-phase steels DP780, DP980 and DP1180 for automobile are studied by bending beam delayed cracking test. The experimental results show that the delayed cracking resistance of DP780, DP980 and DP1180 steel becomes worse in turn, and DP1180 steel has the worst delayed cracking resistance. In addition, the content and morphology of martensite will affect the delayed cracking performance. The morphology of martensite in the tested steel is lathy, and the higher the martensite content, the worse the delayed cracking resistance of the steel.