Transactions of Materials and Heat Treatment

Title：Mechanism of delayed fracture for Apillar in hot stamping

Authors： Yu Haiyan Jiang Zhongwei

Unit： Tongji University COSMA Automotive (Shanghai) Co. Ltd.

KeyWords： ultra highstrength boron steel hot stamping delayed fracture Apillar dew point hydrogen embrittlement

ClassificationCode：U461

year,vol(issue):pagenumber：2017,42(3):40-43

Abstract：

For the delayed fracture of flanging after hot stamping of ultra high strength boron steel Apillar, experiments of thickness thinning rate, chemical composition, section hardness, residual stress and SEM observation were conducted, and the causes were discussed and the improvement measures were suggested. The results show that the crack surface is in dimple shape and the hydrogen embrittlement phenomenon occurs at the flanging fillet. Furthermore, the stress concentration at the flanging fillet during hot stamping leads to coating cracking,and it produces the delayed fracture of part because the gathered hydrogen atoms forming hydrogen molecules are easy to release from the coating gap after the part which is placed a period of time. Thus, the hydrogen embrittlement can be avoided by increasing dew point to deduce the introduction of hydrogen effectively.

Funds：

余海燕(1976-),女，博士，教授蒋忠伟(1981-)，男，硕士，中级工程师

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