Abstract
In order to meet the needs of the automotive industry, it is necessary to produce “tailored” parts. The U-shaped die equipped with a high-speed airflow device was designed to conduct the hot stamping experiments. The microstructure, micro-hardness, tensile properties, and fracture behavior of the parts were analyzed. The experimental results showed that the quenched phase of the hardened section was mainly martensite, and the micro-hardness and tensile strength could reach 445 HV and 1454 MPa, respectively. The fracture mechanism was brittle fracture. For the toughness section, as the tool temperature increased from 300 to 600 °C, both micro-hardness and tensile strength decreased. Meanwhile, the area fractions of bainite and ferrite increased, and the area fraction of martensite reduced. The fracture behavior was plastic fracture.
Highlights
Hot stamping parts of high-strength steel can realize the lightweight of automobiles [1]
The formation of abundant martensite was because of the higher cooling rate, which was the result of low die temperature
The formation of bainite and ferrite was due to the longer transfer time and the left shift of the continuous cooling transformation (CCT), which was caused by the plastic deformation [6]
Summary
Hot stamping parts of high-strength steel can realize the lightweight of automobiles [1]. It is necessary to produce parts with tailored mechanical properties to meet the needs of the automotive industry. Common methods of producing tailored parts can be classified into four categories. Laser welding technology is used to produce tailored parts. Múnera et al [3] developed components using tailor welded blanks composed of both hot forming steel and steel which is not so hardened. Mori et al [4] carried out hot stamping experiments using bypass resistance heating and have obtained parts with a strength distribution. Wang et al [5] performed experiments with different annealing processes and obtained tailored parts. Locally reducing the cooling rate of blanks provides an effective way to produce tailored parts. The operation is simple and the parts have good formability and high forming accuracy
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