Acta Metallurgica Sinica (English Letters) ›› 2019, Vol. 32 ›› Issue (3): 343-351.DOI: 10.1007/s40195-018-0832-3

Special Issue: 2019年钢铁材料专辑

• Orginal Article • Previous Articles     Next Articles

Fractional Cooling Strategy of the Hot-Stamping Process and Its Influence on Formability and Mechanical Properties of Ultra-High-Strength Steel Parts

Xian-Hong Han1, Cheng-Long Wang1, Si-Si Chen1,2, Jun Chen1()   

  1. 1 Department of Plasticity Technology, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, China
    2 SAIC General Motors Co., Ltd, Shanghai 201206, China
  • Received:2018-07-05 Revised:2018-08-15 Online:2019-03-10 Published:2019-02-22

Abstract:

The effects of forming temperature on the formability and product properties of hot-stamping boron steel B1500HS were investigated. Based on the fractional cooling strategy, boron steel sheets were heated to achieve full austenitization before they were removed from the furnace and cooled to the forming temperature using different cooling methods. Subsequently, they were simultaneously press-formed and quenched inside the tool until the martensitic transformation was finished. A series of thermal tensile tests were conducted to study the effects of forming temperatures on the stamping performance indices, including elongation, yield ratio, and hardening exponent. Then, the mechanical properties and microstructures of the hot-stamped products were characterized. Finally, an irregular part was formed using different fractional cooling strategies, while its formability and springback phenomena were discussed. The results show that using a fast-cooling method to reach 650 °C as the forming temperature optimizes the formability of the tested B1500HS boron steel. The best mechanical properties and smallest springback values were achieved using this optimal strategy.

Key words: Hot-stamping, Fractional cooling, Forming temperature, Formability