Intercritical annealing（IA） at various temperatures followed by quenching and partitioning（IAQP） treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-l.87Mn（wt%） sheet steel.Optimized microstructure and enha...Intercritical annealing（IA） at various temperatures followed by quenching and partitioning（IAQP） treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-l.87Mn（wt%） sheet steel.Optimized microstructure and enhanced mechanical properties were achieved through appropriate adjustment of IA temperatures.The steel which was annealed at1,033 K for 600 s,then quenched to 573 K and partitioned at 693 K for 20 min,designated as 1033 QP steel,exhibits maximum 16.3 vol% retained austenite（RA） with good mechanical properties（ultimate tensile strength 886 MPa and total elongation 27%）.It was found that the thermal and mechanical stabilities of RA are mainly influenced by the combined effect of its average carbon content and amount of adjacent martensite.Furthermore,the transformation-induced plasticity effect increased the peak n-values observed at the second stage of the work hardening of IAQP steels.展开更多
Pre-quenching prior to intercritical annealing quenching and partitioning(Q-P)process was proposed to enhance the volume fraction of retained austenite and the mechanical properties of a low-carbon Si Mn steel.The int...Pre-quenching prior to intercritical annealing quenching and partitioning(Q-P)process was proposed to enhance the volume fraction of retained austenite and the mechanical properties of a low-carbon Si Mn steel.The intercritical austenite exhibited a lath morphology due to the martensitic microstructure maintained prior to intercritical annealing.Consequently,the alloy element enrichment of intercritical austenite,in which the alloy element was aggregated at the austenitic boundaries and further diffused inside,improved the stability of intercritical austenite and decreased the M_(s) of it.As a result,the fraction of retained austenite in steel was increased,which improved the mechanical properties of the experimental Q-P steel.展开更多
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financially supported by the National Natural Science Foundation of China (No. 51174251)the National Basic Research Program of China (No. 2010CB630803)
文摘Intercritical annealing（IA） at various temperatures followed by quenching and partitioning（IAQP） treatments was conducted on a cold-rolled Fe-0.2C-1.42Si-l.87Mn（wt%） sheet steel.Optimized microstructure and enhanced mechanical properties were achieved through appropriate adjustment of IA temperatures.The steel which was annealed at1,033 K for 600 s,then quenched to 573 K and partitioned at 693 K for 20 min,designated as 1033 QP steel,exhibits maximum 16.3 vol% retained austenite（RA） with good mechanical properties（ultimate tensile strength 886 MPa and total elongation 27%）.It was found that the thermal and mechanical stabilities of RA are mainly influenced by the combined effect of its average carbon content and amount of adjacent martensite.Furthermore,the transformation-induced plasticity effect increased the peak n-values observed at the second stage of the work hardening of IAQP steels.
文摘Pre-quenching prior to intercritical annealing quenching and partitioning(Q-P)process was proposed to enhance the volume fraction of retained austenite and the mechanical properties of a low-carbon Si Mn steel.The intercritical austenite exhibited a lath morphology due to the martensitic microstructure maintained prior to intercritical annealing.Consequently,the alloy element enrichment of intercritical austenite,in which the alloy element was aggregated at the austenitic boundaries and further diffused inside,improved the stability of intercritical austenite and decreased the M_(s) of it.As a result,the fraction of retained austenite in steel was increased,which improved the mechanical properties of the experimental Q-P steel.
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%.
