In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-r...In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 ℃ and austempering temperature is 400 ℃, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.展开更多
The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated ...The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated using dilatometry,scanning electron microscopy,transmission electron microscopy(TEM),and X-ray diffraction.The results show that the microstructures of CH steel with 0.3 wt.%Cr are ferrite,granular bainite,martensite,and retained austenite,while no ferrite is observed in the microstructure of CH steel with 1.0 wt.%Cr in the same process.Cr promotes the precipitation of(Nb,Ti)C in the high-temperature austenite region through theoretical calculations and TEM observations.Cr retards the bainite transformation and refines the grain size of CH steel.Furthermore,as isothermal holding temperature increases from 400 to 480℃,the bainite and retained austenite fractions of two CH steels decrease,while the martensite fraction increases in the steels after final quenching.Consequently,the strength has an increasing tendency and the total elongation has a decreasing tendency with increasing isothermal temperature.展开更多
To develop super-high strength TRIP steel for automobile application with good combination of strength and plasticity, an ultra high-strength TRIP steel 0.2 %C-2.0% Si-1.8% Mn was investigated at different intercritic...To develop super-high strength TRIP steel for automobile application with good combination of strength and plasticity, an ultra high-strength TRIP steel 0.2 %C-2.0% Si-1.8% Mn was investigated at different intercritical annealing temperatures and bainitic isothermal temperatures. Microstructures were observed by scanning electron mi- croscopy, transmission electron microscopy, electron backscatter diffraction, and X-ray diffraction, and mechanical properties were tested under a uniaxial tensile testing machine. It shows that the best comprehensive mechanical properties were obtained for the experimental steel particularly annealed at 820 ℃ and austempered at 410 ℃. Yield strength of the tested steel mainly depends on ferrite, while the high strength of the tested steel is related to mar- tensite which forms through blocky austenite transformation during cooling and subsequent tensile test attributed to the TRIP effect. Hence, it could be concluded that the grain size of the retained austenite and carbon content in re- tained austenite are the main reasons for high elongation of the tested steel.展开更多
The isothermal oxidation behavior of Fe-10 Al,Fe-15 Al,Fe-20 Al alloys with and without the addition of0.1 at% Y was studied at 800℃ under 1×105 Pa of flowing pure O2 for 24 h.The oxidation of three Fe-Al alloys...The isothermal oxidation behavior of Fe-10 Al,Fe-15 Al,Fe-20 Al alloys with and without the addition of0.1 at% Y was studied at 800℃ under 1×105 Pa of flowing pure O2 for 24 h.The oxidation of three Fe-Al alloys can be divided into transient state and steady state oxidation stages.The oxidation of each stage is approximately in accordance with the parabolic law.The addition of 0.1 at% Y changes the oxidation behavior obviously and leads to a significant increase of the weight gain of Fe-10 Al and Fe-15 Al.The scale grown on Fe-10 Al is much thicker and more complicated than that grown on Fe-20 Al,which is composed of an exclusive thin layer of Al2 O3 protective film.Due to the formation of a large number of nodules,the scales grown on Fe-15 AI cannot provide full protection for the alloy.Scale micro structure of the three Fe-Al-0.1 Y alloys is similar to their corresponding Fe-Al alloys.However,nodules with very small size still appear on the surface of Fe-20 Al-0.1 Y alloy.The critical Al concentration to form an exclusive Al2 O3 protective layer for Fe-Al binary alloy is on the borderline between 15 at%-20 at%.For Fe-Al-0.1 Y alloy,the presence of 20 at% Al is not enough to inhibit the growth of nodules.展开更多
The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type ...The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy（x=0–0.4） hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change.展开更多
基金supported by the National High Technology Research and Development Program (No. 2012AA03A508)the National Natural Science Foundation of China (No. 51271051)
文摘In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al-low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 ℃ and austempering temperature is 400 ℃, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.
基金The authors gratefully acknowledge the support from the Key Research and Development Plan of Shandong Province(No.2019TSLH0103)the New Energy Automobile Material Production and Application Demonstration Platform Project(No.TC180A6MR-1)Guangxi Innovation-Driven Development Special Fund Project(No.AA18242012).
文摘The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated using dilatometry,scanning electron microscopy,transmission electron microscopy(TEM),and X-ray diffraction.The results show that the microstructures of CH steel with 0.3 wt.%Cr are ferrite,granular bainite,martensite,and retained austenite,while no ferrite is observed in the microstructure of CH steel with 1.0 wt.%Cr in the same process.Cr promotes the precipitation of(Nb,Ti)C in the high-temperature austenite region through theoretical calculations and TEM observations.Cr retards the bainite transformation and refines the grain size of CH steel.Furthermore,as isothermal holding temperature increases from 400 to 480℃,the bainite and retained austenite fractions of two CH steels decrease,while the martensite fraction increases in the steels after final quenching.Consequently,the strength has an increasing tendency and the total elongation has a decreasing tendency with increasing isothermal temperature.
基金Item Sponsored by National Natural Science Foundation of China(51271035)
文摘To develop super-high strength TRIP steel for automobile application with good combination of strength and plasticity, an ultra high-strength TRIP steel 0.2 %C-2.0% Si-1.8% Mn was investigated at different intercritical annealing temperatures and bainitic isothermal temperatures. Microstructures were observed by scanning electron mi- croscopy, transmission electron microscopy, electron backscatter diffraction, and X-ray diffraction, and mechanical properties were tested under a uniaxial tensile testing machine. It shows that the best comprehensive mechanical properties were obtained for the experimental steel particularly annealed at 820 ℃ and austempered at 410 ℃. Yield strength of the tested steel mainly depends on ferrite, while the high strength of the tested steel is related to mar- tensite which forms through blocky austenite transformation during cooling and subsequent tensile test attributed to the TRIP effect. Hence, it could be concluded that the grain size of the retained austenite and carbon content in re- tained austenite are the main reasons for high elongation of the tested steel.
基金Project supported by the National Natural Science Foundation of China (51701054)the Science and Technology Research Program of Jiangxi Provincial Education Department of China (GJJ160770)。
文摘The isothermal oxidation behavior of Fe-10 Al,Fe-15 Al,Fe-20 Al alloys with and without the addition of0.1 at% Y was studied at 800℃ under 1×105 Pa of flowing pure O2 for 24 h.The oxidation of three Fe-Al alloys can be divided into transient state and steady state oxidation stages.The oxidation of each stage is approximately in accordance with the parabolic law.The addition of 0.1 at% Y changes the oxidation behavior obviously and leads to a significant increase of the weight gain of Fe-10 Al and Fe-15 Al.The scale grown on Fe-10 Al is much thicker and more complicated than that grown on Fe-20 Al,which is composed of an exclusive thin layer of Al2 O3 protective film.Due to the formation of a large number of nodules,the scales grown on Fe-15 AI cannot provide full protection for the alloy.Scale micro structure of the three Fe-Al-0.1 Y alloys is similar to their corresponding Fe-Al alloys.However,nodules with very small size still appear on the surface of Fe-20 Al-0.1 Y alloy.The critical Al concentration to form an exclusive Al2 O3 protective layer for Fe-Al binary alloy is on the borderline between 15 at%-20 at%.For Fe-Al-0.1 Y alloy,the presence of 20 at% Al is not enough to inhibit the growth of nodules.
基金Project supported by National Natural Science Foundation of China(51261001)
文摘The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy（x=0–0.4） hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change.
