The effects of direct quenching and tempering (DQ-T) process and conventional reheat quenching and tempering (RQ-T) processes on mechanical properties and microstructure of high strength steel were investigated. T...The effects of direct quenching and tempering (DQ-T) process and conventional reheat quenching and tempering (RQ-T) processes on mechanical properties and microstructure of high strength steel were investigated. The DQ process was found to enhance the hardenability of steel effectively. The tensile strength and yield strength of DQ specimen was 975 MPa and 925 MPa respectively, which were higher than those of RQ specimen's of 920 MPa and 871 MPa. In contrast, low temperature toughness (-40 ℃, AKV) of DQ-T specimen (124 J) was generally inferior to that of RQ-T specimen (156 J). The direct quenching temperature was one of the potential process parameters to determine strength/toughness balance of steel manufactured by DQ process. The experimental results showed that excellent strength/toughness balance was obtained when the specimens was quenched at temperature in the range of 850-910 ℃. The yield strength and impact energy (-40 ℃) of DQ steel decreased significantly with increasing of quenching temperature, although the tensile strength was nearly stable.展开更多
The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying elem...The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.展开更多
Intermetallic Ti-45Al-8Nb-(W,B,Y)(at.%)and Ti-46Al-5Nb alloys are directionally solidified at a constant growth rate of 30μm·s-1 using a Bridgman type apparatus.The quenched microstructures and lengths of differ...Intermetallic Ti-45Al-8Nb-(W,B,Y)(at.%)and Ti-46Al-5Nb alloys are directionally solidified at a constant growth rate of 30μm·s-1 using a Bridgman type apparatus.The quenched microstructures and lengths of different phase regions were observed and measured after various growing times of 0-30 min.Results show that the phase transformations in different phase regions are mainly depending on the high temperature microstructure and the supercooling degree during quenching process.After isothermal holding,the primary phase grows into the liquid phase,the dendrites change from equiaxed to columnar grains,and the length of the L+βphase region,L+β+αphase region and mushy zone varies,indicating that the entire directional solidification process can be described by a static equilibrium-nonequilibrium-dynamic equilibrium evolution process.In addition,the gap between the original growth interface and front interface shows that the actual crystal growth rate is not equal to the drawing velocity during directional solidification.展开更多
A wear-resistant steel was hot rolled at the same finish temperature, and subsequently treated with conventional reheat quenching and tempering process (RQ&T) and direct quenching and tempering process (DQ&T), r...A wear-resistant steel was hot rolled at the same finish temperature, and subsequently treated with conventional reheat quenching and tempering process (RQ&T) and direct quenching and tempering process (DQ&T), respectively. The effect of direct quenching on the microstructure and mechanical properties was investigated in detail by using optical microscope, transmission electron microscope and scanning electron microscope equipped with electron backscattered diffraction. The results showed that the microstructures of both the RQ and DQ specimens were complex constituents of lath martensite and lower bainite. Compared with the RQ specimen, the lower bainite content in DQ specimen was much higher. Furthermore, the bainite in the DQ specimen extended into and segmented the prior austenite grains, which can decrease martensite packet size. The proportion of high-angle boundary in the DQ specimen was higher than that in the RQ specimen, which may improve the impact toughness. The carbides in DQ&_T specimen were much finer and distributed even dispersively because direct quenching can retain substantive defects which may provide more nucleation sites for carbide precipitation in the tempering process. Besides, the mechanical properties of DQ and DQ&T specimens were superior than those subjected to RQ and RQ&T processes, respectively.展开更多
Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural ev...Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural evolution during hot rolling plays a major role in the properties of direct quenched and tempered products. The mathematical and physical modeling of hot forming processes is becoming a very important tool for design and development of required products as well as predicting the microstructure and the properties of the components. These models were mostly used to predict austenite grain size (AGS), dynamic, recta-dynamic and static recrystallization in the rods immediately after hot rolling and prior to DQ process. The hot compression tests were carried out on 42CrMo4 steel in the temperature range of 900-1 100 ℃ and the strain rate range of 0. 05-1 s^-1 in order to study the high tempera- ture softening behavior of the steel. For the exact prediction of flow stress, the effective stress-effective strain curves were obtained from experiments under various conditions. On the basis of experimental results, the dynamic recrystallization fraction (DRX), AGS, hot deformation and activation energy behavior were investigated. It was found that the calculated results were in good agreement with the experimental flow stress and microstructure of the steel for different conditions of hot deformation.展开更多
The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeli...The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeling. The flow field and heat transfer in quenching tank were simulated by computational fluid dynamics (CFD) method considering falling and moving of rods during process. Therefore, modeling of flow field was done by a fixed-mesh method for general moving objects equations, and then, energy equation was solved with a numerical approach so that effeet of boiling film heat flux was considered as a source term in energy equation for solid-liquid boundary. Simulated results were verified by comparing with published and experimental data and there was a good agreement between them. Also, the effects of external forced flow and film boiling were investigated on heat flux output, temperature distribution and heat transfer coefficient of rod. Also simulated results determined optimum quenching time for this process.展开更多
The influence of direct quenching (DQ) on microstructure and mechanical properties of 0.19C-1.7Si-1.0 Mn-0.05Nb steel was studied. The microstructure and mechanical properties of reheat quenched and tempered (RQ&T...The influence of direct quenching (DQ) on microstructure and mechanical properties of 0.19C-1.7Si-1.0 Mn-0.05Nb steel was studied. The microstructure and mechanical properties of reheat quenched and tempered (RQ&T) steel plate were compared with those of direct quenched and tempered (DQ&T) steel plates which were hot rolled at different finish rolling tem-peratures (1173 K and 1123 K), i.e., recrystallization-controlled-rolled direct-quenched (RCR&DQ) and controlled-rolled direct-quenched (CR&DQ), respectively. The strengths generally increased in the following order: RQ&T<RCR&DQ&T< CR&DQ&T. Strength differences between the CR&DQ&T and RQ&T conditions as high as 14% were observed at the tempered temperature of 573 K. The optical microscopy of the CR&DQ&T steel showed deformed grains elongated along the rolling direction, while complete equiaxed grains were visible in RQ&T and RCR&DQ&T steels. Transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) of the DQ steels showed smaller block width and higher density of dislocations. Inheritance of austenite deformation substructure by the martensite and differences in martensite block width were ruled out as major causes for the strength differences between DQ and RQ steels.展开更多
A high strength low alloy steel with low carbon equivalent was selected for simulating online direct quench- ing and coiling (DQ-C) process. The influence of stop quenching temperature on mechanical properties and m...A high strength low alloy steel with low carbon equivalent was selected for simulating online direct quench- ing and coiling (DQ-C) process. The influence of stop quenching temperature on mechanical properties and micro- structures was studied and compared with normal direct quenching and tempering (DQ-T) process. The study con- firmed that required mechanical properties were obtained for both the processes. Properties of the experimental steel with DQ-C process could reach the same level as that of DQ-T process in general. In the DQ-C process, strength de- creased with increase in stop quenching temperature. Martensite was obtained and experienced an aging process at stop quenching temperature below Mi. On fast cooling below Mi, martensite was partially transformed and carbon partitioning occurred during slow cooling. The reduction in solid solution carbon and increased amount of retained austenite led to lower strength compared with the DQ-T process. DQ-C process was more favorable for microalloy carbide precipitation. However, impact toughness under different cooling conditions was adequate because of low car- bon equivalent and refined microstructure.展开更多
基金Funded by the Scientific Research Foundation for Young Teachers (N090307004)the Fundamental Funds for the Central Universities of China (N100607002)
文摘The effects of direct quenching and tempering (DQ-T) process and conventional reheat quenching and tempering (RQ-T) processes on mechanical properties and microstructure of high strength steel were investigated. The DQ process was found to enhance the hardenability of steel effectively. The tensile strength and yield strength of DQ specimen was 975 MPa and 925 MPa respectively, which were higher than those of RQ specimen's of 920 MPa and 871 MPa. In contrast, low temperature toughness (-40 ℃, AKV) of DQ-T specimen (124 J) was generally inferior to that of RQ-T specimen (156 J). The direct quenching temperature was one of the potential process parameters to determine strength/toughness balance of steel manufactured by DQ process. The experimental results showed that excellent strength/toughness balance was obtained when the specimens was quenched at temperature in the range of 850-910 ℃. The yield strength and impact energy (-40 ℃) of DQ steel decreased significantly with increasing of quenching temperature, although the tensile strength was nearly stable.
文摘The microstructures and mechanical properties of a series of direct-quenched steels containing,in weight percent,from 0.05 to 0.20 carbon,0.20 to 0.40 silicon,1.10 to 1.70 manganese and at least one microalloying element of vanadium,niobium,titanium and boron have been investigated.After controlled rolling,these steels were cooled in spray water to 400,300 and 200℃,respectively and then cooled in still air.Comparison of the Charpy V-notch impact toughness of direct-quenched steels without subsequent tempering was made with that of direct-quenched steels tempered at 600℃.It is found that an attractive combination of strength and toughness is achived by means of direct-quenching.There exists two types of microstructures in accordance with carbon equivalent.Lath martensitic microstructure is obtained for C>0.4%,granular bainitic microstructures for C.< 0.35%and mixtures of martensite and bainite for C,.in the range of 0.35— 0.40%.The effect of interrupted quenching temperature on microstructure is not significant for low C.steel,but interrupted quenching temperature has a strong effect on microstructure for high C,.steel.
基金the National Natural Science Foundation of China(Nos.:51671026,51831001,and 51921001)the Fundamental Research Funds for the Central Universities(No.FRF-GF-19-024B)。
文摘Intermetallic Ti-45Al-8Nb-(W,B,Y)(at.%)and Ti-46Al-5Nb alloys are directionally solidified at a constant growth rate of 30μm·s-1 using a Bridgman type apparatus.The quenched microstructures and lengths of different phase regions were observed and measured after various growing times of 0-30 min.Results show that the phase transformations in different phase regions are mainly depending on the high temperature microstructure and the supercooling degree during quenching process.After isothermal holding,the primary phase grows into the liquid phase,the dendrites change from equiaxed to columnar grains,and the length of the L+βphase region,L+β+αphase region and mushy zone varies,indicating that the entire directional solidification process can be described by a static equilibrium-nonequilibrium-dynamic equilibrium evolution process.In addition,the gap between the original growth interface and front interface shows that the actual crystal growth rate is not equal to the drawing velocity during directional solidification.
基金financially supported by the National Natural Science Foundation of China(Nos.51074052 and 51004035)
文摘A wear-resistant steel was hot rolled at the same finish temperature, and subsequently treated with conventional reheat quenching and tempering process (RQ&T) and direct quenching and tempering process (DQ&T), respectively. The effect of direct quenching on the microstructure and mechanical properties was investigated in detail by using optical microscope, transmission electron microscope and scanning electron microscope equipped with electron backscattered diffraction. The results showed that the microstructures of both the RQ and DQ specimens were complex constituents of lath martensite and lower bainite. Compared with the RQ specimen, the lower bainite content in DQ specimen was much higher. Furthermore, the bainite in the DQ specimen extended into and segmented the prior austenite grains, which can decrease martensite packet size. The proportion of high-angle boundary in the DQ specimen was higher than that in the RQ specimen, which may improve the impact toughness. The carbides in DQ&_T specimen were much finer and distributed even dispersively because direct quenching can retain substantive defects which may provide more nucleation sites for carbide precipitation in the tempering process. Besides, the mechanical properties of DQ and DQ&T specimens were superior than those subjected to RQ and RQ&T processes, respectively.
文摘Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural evolution during hot rolling plays a major role in the properties of direct quenched and tempered products. The mathematical and physical modeling of hot forming processes is becoming a very important tool for design and development of required products as well as predicting the microstructure and the properties of the components. These models were mostly used to predict austenite grain size (AGS), dynamic, recta-dynamic and static recrystallization in the rods immediately after hot rolling and prior to DQ process. The hot compression tests were carried out on 42CrMo4 steel in the temperature range of 900-1 100 ℃ and the strain rate range of 0. 05-1 s^-1 in order to study the high tempera- ture softening behavior of the steel. For the exact prediction of flow stress, the effective stress-effective strain curves were obtained from experiments under various conditions. On the basis of experimental results, the dynamic recrystallization fraction (DRX), AGS, hot deformation and activation energy behavior were investigated. It was found that the calculated results were in good agreement with the experimental flow stress and microstructure of the steel for different conditions of hot deformation.
文摘The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeling. The flow field and heat transfer in quenching tank were simulated by computational fluid dynamics (CFD) method considering falling and moving of rods during process. Therefore, modeling of flow field was done by a fixed-mesh method for general moving objects equations, and then, energy equation was solved with a numerical approach so that effeet of boiling film heat flux was considered as a source term in energy equation for solid-liquid boundary. Simulated results were verified by comparing with published and experimental data and there was a good agreement between them. Also, the effects of external forced flow and film boiling were investigated on heat flux output, temperature distribution and heat transfer coefficient of rod. Also simulated results determined optimum quenching time for this process.
文摘The influence of direct quenching (DQ) on microstructure and mechanical properties of 0.19C-1.7Si-1.0 Mn-0.05Nb steel was studied. The microstructure and mechanical properties of reheat quenched and tempered (RQ&T) steel plate were compared with those of direct quenched and tempered (DQ&T) steel plates which were hot rolled at different finish rolling tem-peratures (1173 K and 1123 K), i.e., recrystallization-controlled-rolled direct-quenched (RCR&DQ) and controlled-rolled direct-quenched (CR&DQ), respectively. The strengths generally increased in the following order: RQ&T<RCR&DQ&T< CR&DQ&T. Strength differences between the CR&DQ&T and RQ&T conditions as high as 14% were observed at the tempered temperature of 573 K. The optical microscopy of the CR&DQ&T steel showed deformed grains elongated along the rolling direction, while complete equiaxed grains were visible in RQ&T and RCR&DQ&T steels. Transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) of the DQ steels showed smaller block width and higher density of dislocations. Inheritance of austenite deformation substructure by the martensite and differences in martensite block width were ruled out as major causes for the strength differences between DQ and RQ steels.
基金Item Sponsored by National Natural Science Foundation of China(51234002)
文摘A high strength low alloy steel with low carbon equivalent was selected for simulating online direct quench- ing and coiling (DQ-C) process. The influence of stop quenching temperature on mechanical properties and micro- structures was studied and compared with normal direct quenching and tempering (DQ-T) process. The study con- firmed that required mechanical properties were obtained for both the processes. Properties of the experimental steel with DQ-C process could reach the same level as that of DQ-T process in general. In the DQ-C process, strength de- creased with increase in stop quenching temperature. Martensite was obtained and experienced an aging process at stop quenching temperature below Mi. On fast cooling below Mi, martensite was partially transformed and carbon partitioning occurred during slow cooling. The reduction in solid solution carbon and increased amount of retained austenite led to lower strength compared with the DQ-T process. DQ-C process was more favorable for microalloy carbide precipitation. However, impact toughness under different cooling conditions was adequate because of low car- bon equivalent and refined microstructure.
文摘研究了轧后在线淬火+离线回火(DQ-T)对12MnNiVR容器钢显微组织及力学性能的影响.结果表明,在线淬火至300℃获得的组织以条状贝氏体为主,淬火至30℃的组织为马氏体加贝氏体.经离线回火,原始带状下贝氏体为回火索氏体替代,同时析出大量微小FexC粒子.在630~710℃区间,随着回火温度的升高,屈服强度和硬度急速降低,而低温韧性明显提升.回火时间增加,强度下降,韧性增强.在最佳DQ-T工艺条件下:容器钢的ReH为660MPa,Rm为700MPa,A为19.4%,Akv(-20℃)为104 J.