Transformation-induced plasticity-aided steel was rolled at room temperature to different thickness reductions （0, 4%, 10%, 20%, 40%, and 60%）. The mechanical properties, microstructure and austenite fractions of th...Transformation-induced plasticity-aided steel was rolled at room temperature to different thickness reductions （0, 4%, 10%, 20%, 40%, and 60%）. The mechanical properties, microstructure and austenite fractions of the rolled samples were measured by tensile test, electron back scattered diffraction （EBSD） and X-ray diffraction （XRD） for each rolling. The deformation behavior was studied based on the analysis of the mechanical properties and microstructure of steel after tensile deformation, aiming at understanding the effects of cold rolling reduction on the decay behavior of the austenite and the change of mechanical properties of the TRIP steels. It was found that increasing rolling reduction increases the yield stress gradually but decreases the total elongation significantly. It is very interesting that after 10% rolling reduction the yield stress is about 1 000 MPa but still with 20% total elongation, which gives an excellent combination of yield strength and ductility. Based on the XRD results, it was revealed that in both rolling and tension the austenite volume fraction monotonically decayed with the increase of rolling strain, but the decaying rate is faster in tension than in rolling, which may be ascribed to the higher temperature in rolled specimens than in the tensioned ones during deformation. Experimental results and theoretical reasoning indicate that the decreasing trend of austenite volume fraction with strain can be formulated by a unique equation.展开更多
Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel was investigated. Thermomechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, in which t...Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel was investigated. Thermomechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, in which three different kinds of finish rolling temperatures were applied. The results show that polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. The finer ferrite grain size is produced through the deformation induced transformation during deformation rather than after deformation, which affects the mechanical properties of hot rolled TRIP steel. Mechanical properties increase with decreasing finish rolling temperature due to the stabilization of retained austenite. Ultimate tensile strength （UTS）, total elongation （TEL） and the product of ultimate tensile strength and total elongation （UTS×TEL） reaches optimal values （791 MPa, 36% and 28 476 MPa%, respectively） when the specimen was hot rolled for 50% reduction at finish rolling temperature of 700 ℃.展开更多
The microstructure characteristics with super fine ferrite grain size less than 5mm, appropriate retained austenite fraction around 5.0% and or removable abundant dislocations have been obtained by controlled rolling ...The microstructure characteristics with super fine ferrite grain size less than 5mm, appropriate retained austenite fraction around 5.0% and or removable abundant dislocations have been obtained by controlled rolling and cooling, which leads to well balance com- prehensive properties with high tensile strength of 510 and 615MPa, high elongation of 40% and 27%, low ratio of yield strength to tensile strength 0.83 and 0.80, as well as low ductile- brittle transition temperature less than -80 and -70℃ for advanced aluminum hot-rolled TRIP steel and silicon hot-rolled TRIP steel, respectively.展开更多
The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity （TRIP） steels. ...The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity （TRIP） steels. In the present study, low alloy C-Si-Mn TRIP steel was successfully fabricated by hot rolling process with a 4450 hot roiling mill. To maximize the volume fraction and stability of retained austenite of the steel, two different cooling methods （aircooling and ultra-fast cooling ＂AC-UFC＂ and ultrmfast cooling, air cooling and ultra-fast cooling ＂UFC-AC-UFC＂） were conducted. The effects of the cooling method on the microstructure of hot-rolled TRIP steel were investigated via optical microscope, transmission electron microscope and conversion electron Mossbauer spectroscope. The mechanical properties of the steel were also evaluated by conventional tensile test. The results indicated that ferrite and bainite in the microstructure were refined with the cooling method of UFC-AC-UFC. The morphology of retained austenite was also changed from small islands distributing in bainite district （obtained with AC-UFC） to granular shape locating at the triple junction of the ferrite grain boundaries （obtained with UFC-AC-UFC）. As a result, the TRIP steel with a content of retained austenite of 11. 52%, total elongation of 32% and product of tensile strength and total elongation of 27 552 MPa·% was obtained.展开更多
The effect of thermomechanical control processing（TMCP）on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation an...The effect of thermomechanical control processing（TMCP）on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation and transformation-induced plasticity behavior of retained austenite were analyzed.The results show that with multipass deformation,reduction per pass of more than critical deformation in austenite recrystallization region and total reduction of more than 58% in non-recrystallization region and high temperature section of two-phase region,austenite can be refined before γ→α transformation.It is beneficial to obtain refined ferrite grain in final microstructure.To obtain fine and uniform microstructure and excellent strength-ductility balance,a three-stage cooling process（laminar cooling-air cooling-ultra-fast cooling）after hot rolling was conducted.The ultimate tensile strength and elongation of the investigated steel can reach 663 MPa and 41%,respectively.展开更多
基金Sponsored by National Basic Research Program(973 Program) of China(2010CB630803)
文摘Transformation-induced plasticity-aided steel was rolled at room temperature to different thickness reductions （0, 4%, 10%, 20%, 40%, and 60%）. The mechanical properties, microstructure and austenite fractions of the rolled samples were measured by tensile test, electron back scattered diffraction （EBSD） and X-ray diffraction （XRD） for each rolling. The deformation behavior was studied based on the analysis of the mechanical properties and microstructure of steel after tensile deformation, aiming at understanding the effects of cold rolling reduction on the decay behavior of the austenite and the change of mechanical properties of the TRIP steels. It was found that increasing rolling reduction increases the yield stress gradually but decreases the total elongation significantly. It is very interesting that after 10% rolling reduction the yield stress is about 1 000 MPa but still with 20% total elongation, which gives an excellent combination of yield strength and ductility. Based on the XRD results, it was revealed that in both rolling and tension the austenite volume fraction monotonically decayed with the increase of rolling strain, but the decaying rate is faster in tension than in rolling, which may be ascribed to the higher temperature in rolled specimens than in the tensioned ones during deformation. Experimental results and theoretical reasoning indicate that the decreasing trend of austenite volume fraction with strain can be formulated by a unique equation.
基金the National Natural Science Foundation of China(No.50334010)the Program of Education Branch of Liaoning Province of China(No.2006B075)
文摘Influence of hot rolling conditions on the mechanical properties of hot rolled TRIP steel was investigated. Thermomechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, in which three different kinds of finish rolling temperatures were applied. The results show that polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. The finer ferrite grain size is produced through the deformation induced transformation during deformation rather than after deformation, which affects the mechanical properties of hot rolled TRIP steel. Mechanical properties increase with decreasing finish rolling temperature due to the stabilization of retained austenite. Ultimate tensile strength （UTS）, total elongation （TEL） and the product of ultimate tensile strength and total elongation （UTS×TEL） reaches optimal values （791 MPa, 36% and 28 476 MPa%, respectively） when the specimen was hot rolled for 50% reduction at finish rolling temperature of 700 ℃.
文摘The microstructure characteristics with super fine ferrite grain size less than 5mm, appropriate retained austenite fraction around 5.0% and or removable abundant dislocations have been obtained by controlled rolling and cooling, which leads to well balance com- prehensive properties with high tensile strength of 510 and 615MPa, high elongation of 40% and 27%, low ratio of yield strength to tensile strength 0.83 and 0.80, as well as low ductile- brittle transition temperature less than -80 and -70℃ for advanced aluminum hot-rolled TRIP steel and silicon hot-rolled TRIP steel, respectively.
基金Key Projects in National Science and Technology Pillar Program During the Eleventh Five-Year Plan Period of China(2006BAE03A08)
文摘The controlled cooling technology following hot rolling process is a vital factor that affects the final micro- structure and mechanical properties of the hot-rolled transformation induced plasticity （TRIP） steels. In the present study, low alloy C-Si-Mn TRIP steel was successfully fabricated by hot rolling process with a 4450 hot roiling mill. To maximize the volume fraction and stability of retained austenite of the steel, two different cooling methods （aircooling and ultra-fast cooling ＂AC-UFC＂ and ultrmfast cooling, air cooling and ultra-fast cooling ＂UFC-AC-UFC＂） were conducted. The effects of the cooling method on the microstructure of hot-rolled TRIP steel were investigated via optical microscope, transmission electron microscope and conversion electron Mossbauer spectroscope. The mechanical properties of the steel were also evaluated by conventional tensile test. The results indicated that ferrite and bainite in the microstructure were refined with the cooling method of UFC-AC-UFC. The morphology of retained austenite was also changed from small islands distributing in bainite district （obtained with AC-UFC） to granular shape locating at the triple junction of the ferrite grain boundaries （obtained with UFC-AC-UFC）. As a result, the TRIP steel with a content of retained austenite of 11. 52%, total elongation of 32% and product of tensile strength and total elongation of 27 552 MPa·% was obtained.
基金Item Sponsored by National Fundamental Project of Science and Technology of China(ZZ0113A0101)
文摘The effect of thermomechanical control processing（TMCP）on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation and transformation-induced plasticity behavior of retained austenite were analyzed.The results show that with multipass deformation,reduction per pass of more than critical deformation in austenite recrystallization region and total reduction of more than 58% in non-recrystallization region and high temperature section of two-phase region,austenite can be refined before γ→α transformation.It is beneficial to obtain refined ferrite grain in final microstructure.To obtain fine and uniform microstructure and excellent strength-ductility balance,a three-stage cooling process（laminar cooling-air cooling-ultra-fast cooling）after hot rolling was conducted.The ultimate tensile strength and elongation of the investigated steel can reach 663 MPa and 41%,respectively.
