In this paper, both the numerical simulation and the experimental test are carried out to analyze the relationship between the direction and closure efficiency of voids during the forging process. The closing behaviors of through holes which are parallel and perpendicular to the pressure direction respectively are studied in comparison. Furthermore, the stress status and crash degree of internal voids with different axial ratio are examined to analysis the relationship between the closure efficiency and the axis direction. Finally, a method to determine the closure of voids by using stress curves is proposed.
Microstructure and mechanical properties of a new developed cold work die steel (SDC99) were investigated under solution treatment and comparison with Cr12MoV steel. The new developed high strength and high toughness cold work die steel has overcome the weakness of Cr12MoV which failed with tipping, fracture and collapse in services due to low toughness. The toughness achieves to 80J which is twice as Cr12MoV while the hardness is 62HRC.
In this study, based on the metallo-thermo-mechanical coupling theory, a FEM model of hot stamping including forming and quenching is built to investigate the cooling behavior and the microstructure evolution, and to predict the final mechanical properties of hot-stamped components. The results show that, after about 16s, the temperature of the entire component is lower than Mf of 22MnB5 boron steel and with a continuous uniform distribution. Most of austenite in component has transformed into martensite. To satisfy the required mechanical properties, the sufficient holding time of quenching in die is essential and it plays an important role in ensuring the required hardness. The predicted Rockwell hardness of component after hot stamping process is almost 512HV, which shows a good agreement with the experimental results. It implies that the metallo-thermo-mechanical numerical model established in this study is reasonable and reliable, which can provide a theoretical guidance for optimizing the hot stamping procedure.
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