The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by ...The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by employing different thermomechanical processes and then carefully characterized.Their relation to yield strength and impact toughness was analyzed.We conclude that the refinement of martensitic structures could lead to the significant increase of yield strength,which follows the Hall-Petch relation with the effect grain size defined by high angle boundaries(HABs).Impact toughness of UHSSS depends on the frequency and capability for retained austenite(RA)grains at both HABs and martensite lath boundaries to trap the propagating cracks via strain-induced transformation,in which the film-like RA grains at lath boundaries appear to make the greater contribution.展开更多
The coarse grain HAZ microstructure and property of X80 pipeline steel with different carbon content was investigated. The weld thermal simulation test was carried out on Gleeble 1500 thermal mechanical test machine. ...The coarse grain HAZ microstructure and property of X80 pipeline steel with different carbon content was investigated. The weld thermal simulation test was carried out on Gleeble 1500 thermal mechanical test machine. The Charpy tests were completed at --20 ℃ for evaluating the toughness of coarse grain heat affected zone （CGHAZ）. The microstructure was examined by optical microscope （OM） and transmission electron microscopy （TEM）, and the austenite constituent was quantified by X-ray diffraction. The results showed that the ultra-low carbon can improve the toughness of CGHAZ by suppressing the formation of carbide, decreasing the martensite austenite （M-A） constituent and increasing the residual austenite in the M A.展开更多
Ensuring the homogeneous and excellent mechanical properties of 2.25Cr-1Mo-0.25V ultra-thick steel plate is the key to the production of hydrogenation reactor equipment.Thus,it is required to understand the heterogene...Ensuring the homogeneous and excellent mechanical properties of 2.25Cr-1Mo-0.25V ultra-thick steel plate is the key to the production of hydrogenation reactor equipment.Thus,it is required to understand the heterogeneity of microstructures and properties of ultra-thick plate after heat treatment.In this work,the effect of post-weld heat treatment(PWHT)on the strength,plasticity,toughness and microstructures of the 193-mm-thick steel plate was investigated,and the formation mechanism of heterogeneity was elucidated.The PWHT decreased the room-and high-temperature yield strength(YS)and ultimate tensile strength(UTS)of the steel plate after normalizing and tempering(NT),while the room-and high-temperature YS and UTS decreased from the surface to the center of 193-mm-thick steel plate.It was attributed to the enhanced decomposition of martensite-austenite(M-A)constituents and coarsening of grains and precipitated carbides.展开更多
The stress corrosion crack （SCC） susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique （SSRT）, tensile with polarization and surface analysis technique. The curves o...The stress corrosion crack （SCC） susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique （SSRT）, tensile with polarization and surface analysis technique. The curves of tf^Cl/tf^W -strain rate are divided into three regions： stress-dominated region, SCC-dominated region, and corrosion-dominated region, so as the curves of εf^Cl/εf^W - strain rate and tm/tf-strain rate. The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution, which controls the corrosion process. The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution. Fracture appearances in different environments were analyzed by scanning electron microscopy （SEM）. SCC fracture appears as a mixture of intergranular and dimples, while it is totally dimples in the inert environment. The εf becomes the parameter to predict tf because the relationship between εf^Cl/εf^W and tf^Cl/tf^w is a straight line for AerMet 100.展开更多
To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performe...To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performed.With the increase in austenitizing temperature and time,the migration rate of austenite grain boundaries continuously increases with the dissolution of nano-carbides,and the formation of nano-oxides and twin martensite is also inhibited accordingly.The rapid growth in the size of prior austenite grains and martensite laths,as well as the decrease in the content of nano-oxides and twin martensite,led to a rapid decrease in the strength(yield strength and ultimate tensile strength)from HT2 to HTF specimens.The HT1 specimens(austenitizing at 830℃for 30 min,then oil quenching and tempering at 300℃for 120 min and finally air cooling)display excellent mechanical properties of yield strength of 1572 MPa,ultimate tensile strength of 1847 MPa,elongation of 9.84%,and fracture toughness of 106 MPa m^(1/2),which are counterparts to those of conventional DT300 steel forgings after heat treatment.展开更多
Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects ...Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.展开更多
Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The...Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The material is a new generation of fine grain and high purity SS400 steel that has the same ingredients as the traditional low carbon steel. The specimens are in two different states:welded and ultrasonic peening conditions. The corresponding fatigue testing data were analyzed according to the regulation of the statistical method for fatigue life of the welded joints established by International Institute of Welding(IIW). Welding residual stress was considered in two different ways: the constant stress ratio R=0.5 and the Ohta method. The nominal stress-number (σ-N)curves were corrected because of the different plate thickness compared to the standard and because there was no mismatch or angular deformation. The results indicated that: 1) Compared with the welded specimens, when the stress range was 200 MPa, the fatigue life of the SS400 steel specimens treated by ultrasonic peening is prolonged by over 58 times, and the fatigue strength FAT corresponding to 106 cycles is increased by about 66%; 2) As for the SS400 butt joint (single side welding double sides molding), after being treated by UPT, the nominal S-N curve (m=10) of FAT 100 MPa(R=0.5) should be used for fatigue design. The standard S-N curves of FAT 100 MPa(R=0.5, m=10) could be used for fatigue design of the SS400 steel butt joints treated by ultrasonic peening.展开更多
Submerged entry nozzle(SEN)clogging during continuous casting of Ti-stabilized ultra-pure ferritic stainless(Ti-UPFS)steels was systematically investigated via cross-sectional analysis and acid dissolution treatment.T...Submerged entry nozzle(SEN)clogging during continuous casting of Ti-stabilized ultra-pure ferritic stainless(Ti-UPFS)steels was systematically investigated via cross-sectional analysis and acid dissolution treatment.The SEN deposit profile was characterized as occurring in three major layers:(1)an eroded refractory layer;(2)an initial adhesive layer comprised an Al_(2)O_(3)-ZrO_(2) composite sub-layer and a dense Al_(2)O_(3)-based deposit sub-layer;and(3)a porous multiphase deposit layer mainly consisting of MgO·Al_(2)O_(3),CaO-Al_(2)O_(3),and CaO-TiOx.The MgO·Al_(2)O_(3)-rich inclusions did not adhere directly to the eroded refractory but were entrapped during the deposit growth.Results of inclusion characterization in the tundish revealed that the MgO·Al2O3-rich particles present in the tundish served as the primary source of clogging deposits.Furthermore,a novel cavity-induced adhesion model by circular approximation was established to explain the effects of complex inclusion characteristics and refractory material type on adhesion force.A high number of small MgO·Al_(2)O_(3) inclusions were expected to accelerate the buildup of clogging deposits.Improving the modification of MgO·Al_(2)O_(3)-rich inclusions in the size range of 2-4μm by Ca treatment was crucial to minimizing the risk of SEN clogging during the continuous casting of Ti-UPFS steels.展开更多
300 M ultra-high strength steel has been widely used in critical structural components for aviation and aerospace vehicles,owing to its high strength,excellent transverse plasticity,fracture toughness and fatigue resi...300 M ultra-high strength steel has been widely used in critical structural components for aviation and aerospace vehicles,owing to its high strength,excellent transverse plasticity,fracture toughness and fatigue resistance.Herein,low and high power selective laser melting(SLM)of 300 M steel and their microstructural evolution and mechanical properties have been reported.The results show that the optimal energy density range with the highest relative density for SLMed 300 M steel is between 60 and160 J/mm^3.Furthermore,molten pools for deposition exhibit a conduction mode with semi-elliptical shape at a lower laser power of 300~600 W but a keyhole mode with"U"shape at a higher laser power of 800~1900 W.The heterogeneous microstructure of as-built samples is cha racterized by a skin-core structure which is that tempered troostite with the coarse non-equiaxed grains in the molten pool is wrapped by tempered sorbite with the fine equiaxed grains in the heat-affected zone.The skin-core structure of SLMed 300 M steel has the characteristics of hard inside and soft outside.The average microhardness of samples varies from 385 to 341 HV when laser power increases from 300 to 1900 W.Interestingly,ultimate tensile strength(1156-1193 MPa)and yield tensile strength(1085-1145 MPa)of dense samples fabricated at diffe rent laser powers vary marginally.But,the elongation(6.8-9.1%)of SLMed 300 M steel is greatly affected by the laser power.展开更多
Baosteel has excelled in automotive steel sheets in the past three decades.It has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel prod...Baosteel has excelled in automotive steel sheets in the past three decades.It has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel products.Some milestones achieved by Baosteel automotive steel sheet were briefly reviewed.The current challenges in producing ultra-high strength steel(UHSS),especially hot-dip galvanized UHSS,were summarized.The most current advancements in UHSS and the corresponding hot-dip galvanizing processes were discussed.The galvanizability of Si-Mn-added QP steel and DP steel, Mn-added TWIP steel, and Al-added low-density steel has been improved by different techniques in Baosteel.展开更多
基金the support from the National Key Research and Development Program of China(2016YFB0300202 and 2016YFB0300102)the Fundamental Research Funds for the Central Universities(No.FRF-TP-18-002C2)。
文摘The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by employing different thermomechanical processes and then carefully characterized.Their relation to yield strength and impact toughness was analyzed.We conclude that the refinement of martensitic structures could lead to the significant increase of yield strength,which follows the Hall-Petch relation with the effect grain size defined by high angle boundaries(HABs).Impact toughness of UHSSS depends on the frequency and capability for retained austenite(RA)grains at both HABs and martensite lath boundaries to trap the propagating cracks via strain-induced transformation,in which the film-like RA grains at lath boundaries appear to make the greater contribution.
文摘The coarse grain HAZ microstructure and property of X80 pipeline steel with different carbon content was investigated. The weld thermal simulation test was carried out on Gleeble 1500 thermal mechanical test machine. The Charpy tests were completed at --20 ℃ for evaluating the toughness of coarse grain heat affected zone （CGHAZ）. The microstructure was examined by optical microscope （OM） and transmission electron microscopy （TEM）, and the austenite constituent was quantified by X-ray diffraction. The results showed that the ultra-low carbon can improve the toughness of CGHAZ by suppressing the formation of carbide, decreasing the martensite austenite （M-A） constituent and increasing the residual austenite in the M A.
基金supported by the National Natural Science Foundation of China-Outstanding Young Scholars(No.52325407)the National Natural Science Foundation of China(No.51904187)the Open Project of State Key Laboratory of Advanced Special Steel and Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(SKLASS 2022-06).
文摘Ensuring the homogeneous and excellent mechanical properties of 2.25Cr-1Mo-0.25V ultra-thick steel plate is the key to the production of hydrogenation reactor equipment.Thus,it is required to understand the heterogeneity of microstructures and properties of ultra-thick plate after heat treatment.In this work,the effect of post-weld heat treatment(PWHT)on the strength,plasticity,toughness and microstructures of the 193-mm-thick steel plate was investigated,and the formation mechanism of heterogeneity was elucidated.The PWHT decreased the room-and high-temperature yield strength(YS)and ultimate tensile strength(UTS)of the steel plate after normalizing and tempering(NT),while the room-and high-temperature YS and UTS decreased from the surface to the center of 193-mm-thick steel plate.It was attributed to the enhanced decomposition of martensite-austenite(M-A)constituents and coarsening of grains and precipitated carbides.
基金Project(51171011) supported by the National Natural Science Foundation of China
文摘The stress corrosion crack （SCC） susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique （SSRT）, tensile with polarization and surface analysis technique. The curves of tf^Cl/tf^W -strain rate are divided into three regions： stress-dominated region, SCC-dominated region, and corrosion-dominated region, so as the curves of εf^Cl/εf^W - strain rate and tm/tf-strain rate. The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution, which controls the corrosion process. The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution. Fracture appearances in different environments were analyzed by scanning electron microscopy （SEM）. SCC fracture appears as a mixture of intergranular and dimples, while it is totally dimples in the inert environment. The εf becomes the parameter to predict tf because the relationship between εf^Cl/εf^W and tf^Cl/tf^w is a straight line for AerMet 100.
基金funded by the Science and Technology Project of Guangdong Province (2020B090923001)Guangdong Basic and Applied Basic Research Foundation (2023A1515010384)The Fundamental Research Funds for the Central Universities (2023ZYGXZR005).
文摘To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performed.With the increase in austenitizing temperature and time,the migration rate of austenite grain boundaries continuously increases with the dissolution of nano-carbides,and the formation of nano-oxides and twin martensite is also inhibited accordingly.The rapid growth in the size of prior austenite grains and martensite laths,as well as the decrease in the content of nano-oxides and twin martensite,led to a rapid decrease in the strength(yield strength and ultimate tensile strength)from HT2 to HTF specimens.The HT1 specimens(austenitizing at 830℃for 30 min,then oil quenching and tempering at 300℃for 120 min and finally air cooling)display excellent mechanical properties of yield strength of 1572 MPa,ultimate tensile strength of 1847 MPa,elongation of 9.84%,and fracture toughness of 106 MPa m^(1/2),which are counterparts to those of conventional DT300 steel forgings after heat treatment.
基金the Key Research and Development Program of Hubei Province(2022BCA082 and 2022BCA077).
文摘Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.
文摘Contrast tests were carried out to study the fatigue performance of the butt joints treated by ultrasonic peening, aiming at the improvement of ultrasonic peening treatment(UPT) on welded joints of a new material. The material is a new generation of fine grain and high purity SS400 steel that has the same ingredients as the traditional low carbon steel. The specimens are in two different states:welded and ultrasonic peening conditions. The corresponding fatigue testing data were analyzed according to the regulation of the statistical method for fatigue life of the welded joints established by International Institute of Welding(IIW). Welding residual stress was considered in two different ways: the constant stress ratio R=0.5 and the Ohta method. The nominal stress-number (σ-N)curves were corrected because of the different plate thickness compared to the standard and because there was no mismatch or angular deformation. The results indicated that: 1) Compared with the welded specimens, when the stress range was 200 MPa, the fatigue life of the SS400 steel specimens treated by ultrasonic peening is prolonged by over 58 times, and the fatigue strength FAT corresponding to 106 cycles is increased by about 66%; 2) As for the SS400 butt joint (single side welding double sides molding), after being treated by UPT, the nominal S-N curve (m=10) of FAT 100 MPa(R=0.5) should be used for fatigue design. The standard S-N curves of FAT 100 MPa(R=0.5, m=10) could be used for fatigue design of the SS400 steel butt joints treated by ultrasonic peening.
基金the National Natural Science Foundation of China(51878263,U2001225,and 51638008)the National Key Research and Development Program of China(2018YFC0705400).
基金This work was financially supported by the National Natural Science Foundation of China(No.51574026).
文摘Submerged entry nozzle(SEN)clogging during continuous casting of Ti-stabilized ultra-pure ferritic stainless(Ti-UPFS)steels was systematically investigated via cross-sectional analysis and acid dissolution treatment.The SEN deposit profile was characterized as occurring in three major layers:(1)an eroded refractory layer;(2)an initial adhesive layer comprised an Al_(2)O_(3)-ZrO_(2) composite sub-layer and a dense Al_(2)O_(3)-based deposit sub-layer;and(3)a porous multiphase deposit layer mainly consisting of MgO·Al_(2)O_(3),CaO-Al_(2)O_(3),and CaO-TiOx.The MgO·Al_(2)O_(3)-rich inclusions did not adhere directly to the eroded refractory but were entrapped during the deposit growth.Results of inclusion characterization in the tundish revealed that the MgO·Al2O3-rich particles present in the tundish served as the primary source of clogging deposits.Furthermore,a novel cavity-induced adhesion model by circular approximation was established to explain the effects of complex inclusion characteristics and refractory material type on adhesion force.A high number of small MgO·Al_(2)O_(3) inclusions were expected to accelerate the buildup of clogging deposits.Improving the modification of MgO·Al_(2)O_(3)-rich inclusions in the size range of 2-4μm by Ca treatment was crucial to minimizing the risk of SEN clogging during the continuous casting of Ti-UPFS steels.
基金supported by the Pre-research Fund Project of Ministry of Equipment and Development of China though no.61409230301)the Fundamental Research Funds for the Central Universities through Program no.2019kfy XMPY005 and no.2019kfy XKJC042。
文摘300 M ultra-high strength steel has been widely used in critical structural components for aviation and aerospace vehicles,owing to its high strength,excellent transverse plasticity,fracture toughness and fatigue resistance.Herein,low and high power selective laser melting(SLM)of 300 M steel and their microstructural evolution and mechanical properties have been reported.The results show that the optimal energy density range with the highest relative density for SLMed 300 M steel is between 60 and160 J/mm^3.Furthermore,molten pools for deposition exhibit a conduction mode with semi-elliptical shape at a lower laser power of 300~600 W but a keyhole mode with"U"shape at a higher laser power of 800~1900 W.The heterogeneous microstructure of as-built samples is cha racterized by a skin-core structure which is that tempered troostite with the coarse non-equiaxed grains in the molten pool is wrapped by tempered sorbite with the fine equiaxed grains in the heat-affected zone.The skin-core structure of SLMed 300 M steel has the characteristics of hard inside and soft outside.The average microhardness of samples varies from 385 to 341 HV when laser power increases from 300 to 1900 W.Interestingly,ultimate tensile strength(1156-1193 MPa)and yield tensile strength(1085-1145 MPa)of dense samples fabricated at diffe rent laser powers vary marginally.But,the elongation(6.8-9.1%)of SLMed 300 M steel is greatly affected by the laser power.
文摘Baosteel has excelled in automotive steel sheets in the past three decades.It has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel products.Some milestones achieved by Baosteel automotive steel sheet were briefly reviewed.The current challenges in producing ultra-high strength steel(UHSS),especially hot-dip galvanized UHSS,were summarized.The most current advancements in UHSS and the corresponding hot-dip galvanizing processes were discussed.The galvanizability of Si-Mn-added QP steel and DP steel, Mn-added TWIP steel, and Al-added low-density steel has been improved by different techniques in Baosteel.
