The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformati...The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformation behaviors of the steel,back propagation-artificial neural network(BP-ANN)with 16×8×8 hidden layer neurons was proposed.The predictability of the ANN model is evaluated according to the distribution of mean absolute error(MAE)and relative error.The relative error of 85%data for the BP-ANN model is among±5%while only 42.5%data predicted by the Arrhenius constitutive equation is in this range.Especially,at high strain rate and low temperature,the MAE of the ANN model is 2.49%,which has decreases for 18.78%,compared with conventional Arrhenius constitutive equation.展开更多
The time-temperature-transformation （TTT） curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on o precipitation was stu...The time-temperature-transformation （TTT） curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on o precipitation was studied by metallographic observation, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000℃, especially in the range of 800-900℃. The longer the aging time, the higher the amount of o precipi- tation. The area fxaction of various phases remains at a certain value upon the completion of ferrite deformation. The temperature of 850℃ is the most sensitive transaction temperature, the incubation time for the formation of o precipitation is less than 1 min, and aging for 20 min leads to the complete transformation of ferrite. The o phase is formed preferentially at the α/α/γjunction, and then grows along the α/α boundary in the matrix.展开更多
Microstructural changes during heating of highly alloyed Cr26Ni7 type super duplex stainless steel （SDSS2607） and its thermal deformation behavior were investigated. At different heating rates, the mechanism of phas...Microstructural changes during heating of highly alloyed Cr26Ni7 type super duplex stainless steel （SDSS2607） and its thermal deformation behavior were investigated. At different heating rates, the mechanism of phase transition from y phase to 6 phase and growth modes of ~ phase differed. Variations in microstructures for as- cast SDSS2607 during heat preservation at 1 220 ~C indicated two kinds of transformations from y phase to 6 phase. In-situ observations of microstructural changes during the tensile process at 1 050 showed a mutual coordination between y and 6 phases. When the true strain increased, the mutual coordination between 7 and 6 phases was damaged. Subsequently, cracks nucleated at the ＂y/g interface. With the increase in temperature, the strength of as- cast SDSS2607 decreased while its plasticity increased. Its thermoplasticity was poor, and the reduction in area of tensile specimens was less than 80%. When the deformation strain of hot compression increased, the stable deformation zone in the heat processing maps enlarged gradually. Moreover, the unstable deformation zones were extended.展开更多
The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impac...The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature.The experimental results indicate that the nose temperature of precipitation is 920℃ and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2min.Prolonging aging duration the amount ofσ-phase increases and a dual structure with σ and γ is obtained when aging for 120min.The precipitation ofσ-phase leads to severe deterioration in impact toughness （longitudinal/transverse direction） and corrosion resistance of SDSS.展开更多
Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the ...Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the microstructures that develop after folding and subsequent precipitation during heat treatment of UNS S32750 SDSS sheet samples.The microstructural and textural changes have been followed using SEM/EBSD techniques.Upon folding,both a texture and strain gradient form in the folded/bent region,subsequent heat treatment at 845℃results in the ferrite phase to transform to sigma,austenite and chi phases.Transformation was found to be accelerated by strain.Complete transformation of the ferrite phase occurred within half the annealing time required in the unstrained regions.The local mis-orientations in the ferrite and austenite phases reduced during annealing,however,the reduction in the austenite was not very high and a significant amount remained even after the longest annealing time.The texture components that developed during the folding process remained unchanged even after one hour annealing at 845℃.The implication of these findings could have a bearing on the formation of sigma phase during welding of SDSS that may have residual stresses introduced during final processing.展开更多
In this study, metallographic analysis and nanoindentation characterization were used to analyze the properties and microstructures of as-cast nitrogen alloyed 27Cr-7Ni-4Mo super duplex stainless steel （super-DSS）. ...In this study, metallographic analysis and nanoindentation characterization were used to analyze the properties and microstructures of as-cast nitrogen alloyed 27Cr-7Ni-4Mo super duplex stainless steel （super-DSS）. The as-cast microstructure of the super-DSS was characterized by its ferrite and island-like austenite phases. During the solution annealing process, the austenite volume percentage of the steel decreased gradually with increased annealing temperature. As a main element, the chromium content in the ferritic and austenitic phases elevated slightly at first then decreased with increased annealing temperature. The chromium partition coefficient in the steel varied by around 1.0. The contents of nickel, another main alloy element, also increased in the ferritic and austenitic phases with increased annealing temperature, as did the nickel partition coefficient in the steel, which tended to be close to 1.0. The nanoindentation characterization results indicate that the hardness of the austenite phase is slightly greater than that of the ferrite phase. They were similar to each other within a certain temperature range from 1 050 ℃ to 1 100℃. This temperature range was consistent with the temperature range in which the content ratio of the two phases was close to 1： 1. We found the Young＇ s modulus of the ferrite phase to be greater than that of the austenite phase. With increased annealing temperature, the Young＇ s modulus of the ferrite phase decreased while that of the austenite phase remained almost unchanged.展开更多
Super Duplex Stainless Steel has been studied for oil and gas industry applications since the 90 s, but their welding always is a technical issue. Then different methods were developed to meet all requirements present...Super Duplex Stainless Steel has been studied for oil and gas industry applications since the 90 s, but their welding always is a technical issue. Then different methods were developed to meet all requirements presents in ASME standards, where most of are applied for lower production, when compared to other materials such carbon steel. This study accomplished circumferential welding experiments in base material (BM)—UNS S32750 Super Duplex Stainless Steel with a thickness of 3.68 mm. Welding was performed using GMAW (Gas Metal Arc Welding) process with CMT (Cold Metal Transfer) control and the aid of a Motoman robot and a turntable device, which were used to ensure the accurate positioning of the torch and that the welding has been fully implemented in the 1 G position, respectively. This process achieves higher production in relation other welding process usually applied for this material class. The joints which presented adequate dimensional results were, then, subjected to tensile and hardness Vickers tests. To avoid the lack of penetration problem, the welding was performed using the CMT process combined with pulsed arc, thus, resulting in full penetration and improved surface finish. The results have shown that the CMT procedure, combined with pulsed arc, led to an adequate superficial finishing, mechanical properties and corrosion resistance in accomplishment with the requirements presented in applicable standards.展开更多
The characteristics of microstructure, mechanical property and corrosion behavior of Cr26Mo3.5 super stainless steel joints by pulse tungsten inert gas(P-TIG)welding and laser welding were investigated. The results in...The characteristics of microstructure, mechanical property and corrosion behavior of Cr26Mo3.5 super stainless steel joints by pulse tungsten inert gas(P-TIG)welding and laser welding were investigated. The results indicate that the widths of the center equiaxed grain zone(EGZ)and the columnar grain zone(CGZ)increase with the increase of heat input in both welding processes. The precipitates of Nb and Ti carbides and nitrides are formed in the weld metal(WM)and the heat affected zone(HAZ). The joints by laser welding show better tensile and corrosion resistance properties than those by P-TIG welding due to the heat concentration and lower heat input. The tensile strength and elongation increase with the decrease of heat input, and the fracture mode of the joints turns into ductile-brittle mixed fracture from ductile fracture when the welding method turns into P-TIG welding from laser welding. Moreover, the corrosion resistance of all joints declines slightly with the increase of heat input. Hence, laser welding is more suitable for welding Cr26Mo3.5 super stainless steel in engineering applications.展开更多
The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath marte...The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath martensite mixed with a small amount of retained austenite. With the raising quenching temperature, the original austenite grain size increases and the lath martensite gradually becomes thicker. The structures of the tempered steel are mixtures of tempered martensite and reversed austenite dispersed in the martensite matrix. The amount of reversed austenite is from 7.54% to 22. 49%. After different heat treatments, the tensile strength, the elongation and the HRC hardness of the steel are in the range of 813 1 070 MPa, 10.1%--21.2% and 21.33--32.37, respectively. The steel displays the best comprehensive mechanical properties after the sample is quenched at 1 050 ℃ followed by tempering at 650 ℃.展开更多
文摘The hot compression tests of 7Mo super austenitic stainless(SASS)were conducted to obtain flow curves at the temperature of 1000-1200℃and strain rate of 0.001 s^(-1)to 1 s^(-1).To predict the non-linear hot deformation behaviors of the steel,back propagation-artificial neural network(BP-ANN)with 16×8×8 hidden layer neurons was proposed.The predictability of the ANN model is evaluated according to the distribution of mean absolute error(MAE)and relative error.The relative error of 85%data for the BP-ANN model is among±5%while only 42.5%data predicted by the Arrhenius constitutive equation is in this range.Especially,at high strain rate and low temperature,the MAE of the ANN model is 2.49%,which has decreases for 18.78%,compared with conventional Arrhenius constitutive equation.
文摘The time-temperature-transformation （TTT） curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastor-digital thermal dilatometer, and the influence of isothermal aging on o precipitation was studied by metallographic observation, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000℃, especially in the range of 800-900℃. The longer the aging time, the higher the amount of o precipi- tation. The area fxaction of various phases remains at a certain value upon the completion of ferrite deformation. The temperature of 850℃ is the most sensitive transaction temperature, the incubation time for the formation of o precipitation is less than 1 min, and aging for 20 min leads to the complete transformation of ferrite. The o phase is formed preferentially at the α/α/γjunction, and then grows along the α/α boundary in the matrix.
基金sponsored by National key R & D program (No.2016YFB0300201)
文摘Microstructural changes during heating of highly alloyed Cr26Ni7 type super duplex stainless steel （SDSS2607） and its thermal deformation behavior were investigated. At different heating rates, the mechanism of phase transition from y phase to 6 phase and growth modes of ~ phase differed. Variations in microstructures for as- cast SDSS2607 during heat preservation at 1 220 ~C indicated two kinds of transformations from y phase to 6 phase. In-situ observations of microstructural changes during the tensile process at 1 050 showed a mutual coordination between y and 6 phases. When the true strain increased, the mutual coordination between 7 and 6 phases was damaged. Subsequently, cracks nucleated at the ＂y/g interface. With the increase in temperature, the strength of as- cast SDSS2607 decreased while its plasticity increased. Its thermoplasticity was poor, and the reduction in area of tensile specimens was less than 80%. When the deformation strain of hot compression increased, the stable deformation zone in the heat processing maps enlarged gradually. Moreover, the unstable deformation zones were extended.
基金Founded by the Special Project of Shaanxi Education Department(07JK309)Xi'an University of Architecture and Technology (JC0714)
文摘The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature.The experimental results indicate that the nose temperature of precipitation is 920℃ and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2min.Prolonging aging duration the amount ofσ-phase increases and a dual structure with σ and γ is obtained when aging for 120min.The precipitation ofσ-phase leads to severe deterioration in impact toughness （longitudinal/transverse direction） and corrosion resistance of SDSS.
文摘Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the microstructures that develop after folding and subsequent precipitation during heat treatment of UNS S32750 SDSS sheet samples.The microstructural and textural changes have been followed using SEM/EBSD techniques.Upon folding,both a texture and strain gradient form in the folded/bent region,subsequent heat treatment at 845℃results in the ferrite phase to transform to sigma,austenite and chi phases.Transformation was found to be accelerated by strain.Complete transformation of the ferrite phase occurred within half the annealing time required in the unstrained regions.The local mis-orientations in the ferrite and austenite phases reduced during annealing,however,the reduction in the austenite was not very high and a significant amount remained even after the longest annealing time.The texture components that developed during the folding process remained unchanged even after one hour annealing at 845℃.The implication of these findings could have a bearing on the formation of sigma phase during welding of SDSS that may have residual stresses introduced during final processing.
文摘In this study, metallographic analysis and nanoindentation characterization were used to analyze the properties and microstructures of as-cast nitrogen alloyed 27Cr-7Ni-4Mo super duplex stainless steel （super-DSS）. The as-cast microstructure of the super-DSS was characterized by its ferrite and island-like austenite phases. During the solution annealing process, the austenite volume percentage of the steel decreased gradually with increased annealing temperature. As a main element, the chromium content in the ferritic and austenitic phases elevated slightly at first then decreased with increased annealing temperature. The chromium partition coefficient in the steel varied by around 1.0. The contents of nickel, another main alloy element, also increased in the ferritic and austenitic phases with increased annealing temperature, as did the nickel partition coefficient in the steel, which tended to be close to 1.0. The nanoindentation characterization results indicate that the hardness of the austenite phase is slightly greater than that of the ferrite phase. They were similar to each other within a certain temperature range from 1 050 ℃ to 1 100℃. This temperature range was consistent with the temperature range in which the content ratio of the two phases was close to 1： 1. We found the Young＇ s modulus of the ferrite phase to be greater than that of the austenite phase. With increased annealing temperature, the Young＇ s modulus of the ferrite phase decreased while that of the austenite phase remained almost unchanged.
文摘Super Duplex Stainless Steel has been studied for oil and gas industry applications since the 90 s, but their welding always is a technical issue. Then different methods were developed to meet all requirements presents in ASME standards, where most of are applied for lower production, when compared to other materials such carbon steel. This study accomplished circumferential welding experiments in base material (BM)—UNS S32750 Super Duplex Stainless Steel with a thickness of 3.68 mm. Welding was performed using GMAW (Gas Metal Arc Welding) process with CMT (Cold Metal Transfer) control and the aid of a Motoman robot and a turntable device, which were used to ensure the accurate positioning of the torch and that the welding has been fully implemented in the 1 G position, respectively. This process achieves higher production in relation other welding process usually applied for this material class. The joints which presented adequate dimensional results were, then, subjected to tensile and hardness Vickers tests. To avoid the lack of penetration problem, the welding was performed using the CMT process combined with pulsed arc, thus, resulting in full penetration and improved surface finish. The results have shown that the CMT procedure, combined with pulsed arc, led to an adequate superficial finishing, mechanical properties and corrosion resistance in accomplishment with the requirements presented in applicable standards.
基金Supported by the Research Institute,Baoshan Iron&Steel Co.,Ltd
文摘The characteristics of microstructure, mechanical property and corrosion behavior of Cr26Mo3.5 super stainless steel joints by pulse tungsten inert gas(P-TIG)welding and laser welding were investigated. The results indicate that the widths of the center equiaxed grain zone(EGZ)and the columnar grain zone(CGZ)increase with the increase of heat input in both welding processes. The precipitates of Nb and Ti carbides and nitrides are formed in the weld metal(WM)and the heat affected zone(HAZ). The joints by laser welding show better tensile and corrosion resistance properties than those by P-TIG welding due to the heat concentration and lower heat input. The tensile strength and elongation increase with the decrease of heat input, and the fracture mode of the joints turns into ductile-brittle mixed fracture from ductile fracture when the welding method turns into P-TIG welding from laser welding. Moreover, the corrosion resistance of all joints declines slightly with the increase of heat input. Hence, laser welding is more suitable for welding Cr26Mo3.5 super stainless steel in engineering applications.
文摘The microstructures and mechanical properties of Cr13 super martensitic stainless steel after different heat treatments were studied. The results show that the structures of the steel after quenching are of lath martensite mixed with a small amount of retained austenite. With the raising quenching temperature, the original austenite grain size increases and the lath martensite gradually becomes thicker. The structures of the tempered steel are mixtures of tempered martensite and reversed austenite dispersed in the martensite matrix. The amount of reversed austenite is from 7.54% to 22. 49%. After different heat treatments, the tensile strength, the elongation and the HRC hardness of the steel are in the range of 813 1 070 MPa, 10.1%--21.2% and 21.33--32.37, respectively. The steel displays the best comprehensive mechanical properties after the sample is quenched at 1 050 ℃ followed by tempering at 650 ℃.
