The analysis of the fracture mechanism of thermal simulation CGHAZ of AHSS DP780: based on response surface method and quantum genetic algorithm

AHSS is widely used in the automobile industry due to its lightweight and high strength. However, the larger carbon equivalent results in poor weldability and causes a severe performance decrease in the performance of the CGHAZ. The thermal simulation was utilized to analyze the fracture mechanism of the CGHAZ of DP780 high-strength steel, and the microstructure and mechanical properties of the CGHAZ were studied by combining the response surface method (RSM) and the quantum genetic algorithm (QGA). Results showed that the predominant fracture type of CGHAZ was a brittle fracture. Meanwhile, the analysis combining energy dispersive spectrometer (EDS) and metallographic showed that the precipitation of carbides, the increase of the content of upper bainite (UB), and the coarse grains were the main reasons for brittle fracture. When the peak temperature, heating rate, and cooling rate were 1100 °C, 60 °C/min, and 1300 °C/min, respectively, the maximum impact energy of CGHAZ was 7.83 J. The results of optimization combining RSM and QGA showed that the impact energy of CGHAZ was increased by 0.7%, and the error between the results of verification and optimization was 1.93%. Therefore, it has positive significance for reducing the brittleness of CGHAZ by adopting lower heat input and slower cooling rate.