Abstract
Hot stamping components with 1500 MPa ultra-high strength are obtained by press hardening during hot stamping, and the properties depend on the microstructures. It is very important that the microstructure evolution rule is found out during hot stamping process. To characterize the microstructure evolution during hot stamping, a method combining finite element and experiment is carried out. Samples were heated to 950°C and held for 300 second at a induction heating furnace, then taken out from the furnace and stayed in the air at different time (7 s, 11 s, 13 s, 22 s), respectively, finally the specimens were formed and quenched at a die. Microstructural observation as well as surface hardness profiling of formed specimens was performed. And the numerical simulation to predict the austenite transformation into ferrite, pearlite, bainite, and martensite and the volume fraction of each phase during the hot stamping process was made with ABAQUS software. The results show that the ferrite is observed when the specimen stays in the air for 22 s, and the temperature drops to 325°C when the dwell time increases from 7 s to 22 s. The results of numerical simulation and experimental results are in good agreement. So the method finite element can be used to guide the optimization of hot stamping process parameters.
Highlights
Even though a new generation advanced high strength steels with ultra-high strength and excellent formability are developed
The numerical simulation to predict the austenite transformation into ferrite, pearlite, bainite, and martensite and the volume fraction of each phase during the hot stamping process was made with ABAQUS software
The results of numerical simulation and experimental results are in good agreement
Summary
Even though a new generation advanced high strength steels with ultra-high strength and excellent formability are developed. The steel sheets are austenitized at temperatures between 900 ̊C and 950 ̊C and soaked for 4 to 8 minutes to obtain a homogenous austenitic microstructure. The steel sheets are formed and quenched in the cooled die, and complex geometries parts are obtained due to the high formability of the hot material. The austenitic microstructure transforms into a martensitic one. Et al [4] simulated the hot stamping process by a deformation dilatometer to investigate the phase transformations. Et al [5] developed a coupled 3D thermomechanical phase transformation finite element simulation of the hot stamping process. The effect of time to stay in the air of the austenitizing steel sheet on the phase transformations has rarely been investigated and unclear. The volume fraction of each phase during the hot stamping process was numerical simulated with ABAQUS software
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