Quenching and partitioning (Q&P) heat treatments with different annealing temperatures and fixed initial quenching tem-peratures were applied to cold-rolled low-carbon steel with the initial microstructure of ferr...Quenching and partitioning (Q&P) heat treatments with different annealing temperatures and fixed initial quenching tem-peratures were applied to cold-rolled low-carbon steel with the initial microstructure of ferrite and pearlite, aiming to gain the same amount of austenite (preset value) before the partitioning stage. The chemical compositions of the material have been specially designed, containing 1.6 wt.% silicon and 0.8 wt.% aluminum to avoid the precipitation of carbides. The micro-structure evolution of the investigated steel was characterized using a dilatometer, an optical microscope, a scanning electron microscope (SEM), an X-ray diffractometer, an electron backscattered diffraction and transmission electron microscope. Consequently, the microstructure of all samples looks quite similar. At the same time, according to SEM micrographs and dilatometer data, there are competitive reactions in Q&P process, such as the precipitation of carbides, the transformation of bainite and the formation of secondary martensite. Thus, the measured austenite is less than the preset values. Mechanical properties of the material were detected by uniaxial tensile tests. The results indicate that the ultimate tensile strength of the four groups of samples is similar, but the total elongation has a significant downward tendency with the increase in annealing temperatures. After annealing at 840 ℃, the steel possesses great ultimate tensile strength of about 1200 MPa and optimum total elongation of about 20.37% with favorable products of strength and elongation of about 24.35 GPa%.展开更多
基金This research was supported by the National Key Research and Development Program of China(No.2017YFB0304801).
文摘Quenching and partitioning (Q&P) heat treatments with different annealing temperatures and fixed initial quenching tem-peratures were applied to cold-rolled low-carbon steel with the initial microstructure of ferrite and pearlite, aiming to gain the same amount of austenite (preset value) before the partitioning stage. The chemical compositions of the material have been specially designed, containing 1.6 wt.% silicon and 0.8 wt.% aluminum to avoid the precipitation of carbides. The micro-structure evolution of the investigated steel was characterized using a dilatometer, an optical microscope, a scanning electron microscope (SEM), an X-ray diffractometer, an electron backscattered diffraction and transmission electron microscope. Consequently, the microstructure of all samples looks quite similar. At the same time, according to SEM micrographs and dilatometer data, there are competitive reactions in Q&P process, such as the precipitation of carbides, the transformation of bainite and the formation of secondary martensite. Thus, the measured austenite is less than the preset values. Mechanical properties of the material were detected by uniaxial tensile tests. The results indicate that the ultimate tensile strength of the four groups of samples is similar, but the total elongation has a significant downward tendency with the increase in annealing temperatures. After annealing at 840 ℃, the steel possesses great ultimate tensile strength of about 1200 MPa and optimum total elongation of about 20.37% with favorable products of strength and elongation of about 24.35 GPa%.
