Abstract
The current research of the Q-P and Q-P-T process has been focused on controlling the heating temperature and holding time, or adding alloy elements into the steel to induce precipitation strengthening and improve the strength and plasticity of the steel. In this article, based on a quenching-partitioning-tempering (Q-P-T) process combined with a hot deformation technology, a deforming-quenching-partitioning-tempering (D-Q-P-T) process was applied to medium carbon steel. The effect of the heat treatment parameters on the microstructure and mechanical properties of experimental steel under deformation was studied. Through use of a scanning electron microscope (SEM), transmission electron microscopy (TEM) and tensile tests, the optimal heat treatment conditions for realizing high strength and plasticity that meet the safety requirements were obtained. The mechanism for the D-Q-P-T process to improve the strength and plasticity of experimental steel was discussed. A multiphase composite structure of lath martensite and retained austenite was obtained. Compared with the Q-P-T process, use of the D-Q-P-T process can increase the strength of steel by 57.77 MPa and the elongation by 5%. This study proposes a method to improve the strength and plasticity of steel.
Highlights
High-strength steel plays an important role in realizing lightweight automobiles with improved safety performance
In the D-quenching and partitioning (Q-P)-T experiment, a Gleeble-3800 thermal simulator was used to heat the samples to 950 °C for 5 min, followed by air cooling to 870 °C for 10 s; the samples were subject to a compression of 60% and quenching to 300 °C for 10 s, followed by tempering at 400 °C for 10 s, and, water quenching to room temperature
It can be seen from the figure that the grain size for the deforming-quenching process is large; for the deforming-quenching process, due to the deformation before the quenching process, with the influence of high temperature and large deformation, the sample shows dynamic recrystallization, which makes the grain refined and increases the dislocation density
Summary
High-strength steel plays an important role in realizing lightweight automobiles with improved safety performance. Research data show that the application of high-strength steel can reduce the thickness of 1.0–1.2 mm body panels to 0.7– 0.8 mm. Peng et al Chinese Journal of Mechanical Engineering (2021) 34:113 former elements (such as Nb, Mo and V) are added into Q-P-T steels to form fine stable carbides during the partitioning process so as to strengthen steels. Most of the research on the Q-P and Q-P-T process has been focused on controlling the heating temperature and holding time, or adding alloy elements into the steel to induce precipitation strengthening and improve the strength and plasticity of the steel. In addition to precipitation strengthening, fine grain strengthening is an important factor to improve the strength and plasticity of steel [26,27,28,29,30]. By introducing a deformation process before the Q-P-T process, the D-Q-P-T process was proposed to improve the comprehensive mechanical properties of steel
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