To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and microstructure evolution,deoxidized experiment ingots with different amounts of modified NPs were manufactured under diff...To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and microstructure evolution,deoxidized experiment ingots with different amounts of modified NPs were manufactured under different cooling conditions.Laser scanning confocal microscope(LSCM)was hereby used for in-situ observation of the phase transition and microstructural evolution during heat cycle process.The results revealed that the inclusion size was always smaller under water quenching than under air cooling,and the number of inclusions was greater under water quenching.After NP addition,the nucleant inclusions were identified as MgAl_(2)O_(4)spinel and irregular TiN inclusion from SEM-EDS measurement and equilibrium calculations using Factsage thermodynamic software.The higher cooling rate under water quenching resulted in less polygonal ferrite decrease and the formation of bainite in the steel.The LSCM experiments showed that ferrite side plates(FSP)always formed on the boundary prior to the formation of acicular ferrite(AF)on the intragranular inclusions,and the start transformation temperatures of FSP and AF phases both lowered after NP addition.The higher cooling rate and NP addition contributed to AF formation and increased the degree of interlocking of the AF phase.Finally,the relationship between the characteristics of inclusions and the kinetics of AF was investigated.展开更多
The reliability of steel welds becomes more critical issue with increasing steel strength,because brittle phases are more likely to form in the weld metals and heat-affected zone(HAZ) and thereby the toughness and duc...The reliability of steel welds becomes more critical issue with increasing steel strength,because brittle phases are more likely to form in the weld metals and heat-affected zone(HAZ) and thereby the toughness and ductility of the welds are degraded.Therefore,refinement of microstructure and minimization of the brittle phases are necessary to improve the reliability of the high-strength steel welds.In this presentation,microstructure formation that controls the toughness of weld metals and HAZ in high-strength low-alloy(HSLA) steel welds is reviewed and possible routes to the improvement of the weld microstructure and weld toughness are discussed.展开更多
The pipeline steel is usually produced by adding niobium and vanadium alloying elements.The titanium alloyed pipeline steel was studied in the paper to reduce the production cost and enhance the competitive ability of...The pipeline steel is usually produced by adding niobium and vanadium alloying elements.The titanium alloyed pipeline steel was studied in the paper to reduce the production cost and enhance the competitive ability of pipeline steel.The steel containing 0.070%Ti was refined in the laboratory vacuum refine furnace.The dynamic CCT curve of developed steel was conducted on Gleeble-1500 thermal simulator and multi-pass deformation tests of studied pipeline steel were performed to simulate the CSP hot-rolling technology.Corresponding microstructures were observed and the influences of such technology parameters as deformation strain,deformation temperature, cooling rate and finishing temperature etc.on microstructure were analyzed.The dynamic CCT curve was obtained.The test results showed that the volume fraction of acicular ferrite in the microstructure of Ti-microalloyed X70 pipeline steel increased obviously with the increase of cooling rate after thermo-mechanical deformation.However,the volume fraction of acicular ferrite varies scarcely after the cooling rate of 20℃/s.In order to obtain Ti-microalloyed X70 pipeline steel with excellent compound mechanical properties which has acicular ferrite as the main ideal microstructure,the cooling rate should be controlled to be 20℃/s or more.The higher of the finishing temperature,the more of the volume of acicular ferrite and the less of the volume of polygonal ferrite.The quite fine microstructure can be obtained by lowering the finish-cooling temperature.The results have shown that it is possible to produce the Ti-addition X70 pipeline steel from the point of view of microstructure.展开更多
The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles du...The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles during welding.The chaotically oriented IAF and refined PAGs inhibit crack initiation and propagation in the steel,resulting in high impact toughness.This work summarizes the com-bined effect of deoxidizers and alloying elements,with the aim to provide a new perspective for the research and practice related to im-proving the impact toughness of the heat affected zone(HAZ)during the high heat input welding.Ti complex deoxidation with other strong deoxidants,such as Mg,Ca,Zr,and rare earth metals(REMs),can improve the toughness of the heat-affected zone(HAZ)by re-fining PAGs or increasing IAF contents.However,it is difficult to identify the specific phase responsible for IAF nucleation because ef-fective inclusions formed by complex deoxidation are usually multiphase.Increasing alloying elements,such as C,Si,Al,Nb,or Cr,con-tents can impair HAZ toughness.A high C content typically increases the number of coarse carbides and decreases the potency of IAF formation.Si,Cr,or Al addition leads to the formation of undesirable microstructures.Nb reduces the high-temperature stability of the precipitates.Mo,V,and B can enhance HAZ toughness.Mo-containing precipitates present good thermal stability.VN or V(C,N)is ef-fective in promoting IAF nucleation due to its good coherent crystallographic relationship with ferrite.The formation of the B-depleted zone around the inclusion promotes IAF formation.The interactions between alloying elements are complex,and the effect of adding dif-ferent alloying elements remains to be evaluated.In the future,the interactions between various alloying elements and their effects on ox-ide metallurgy,as well as the calculation of the nucleation effects of effective inclusions using first principles calculations will become the focus of oxide metallurgy.展开更多
The correlation between microstructures and mechanical properties of a Nb-Ti microalloyed pipeline steel was investigated. The results revealed that with decreasing the finish rolling temperature and the cooling stop ...The correlation between microstructures and mechanical properties of a Nb-Ti microalloyed pipeline steel was investigated. The results revealed that with decreasing the finish rolling temperature and the cooling stop temperature,the matrix microstructure was changed from quasi-polygonal ferrite to acicular ferrite,as a result of improvement of both strength and low temperature toughness. By means of electron backscattered diffraction observation,an effective acicular ferrite packet contained several low angle boundaries or subboundaries plates which made important contributions to improvement of strength. It was found that many fine quasi-polygonal ferrite grains with high angle boundaries as the toughening structure were introduced into the acicular ferrite matrix to refine effective grain size and improve the toughness.展开更多
The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impe...The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impedance spec-troscopy test combining with optical micrographs,scanning electron microscopy,transmission electron microscopy and electron back-scattered diffraction.The results showed that,compared with room and high temperature,low temperature could influence the corrosion behavior of high-grade pipeline steel,which means that the corrosion potential and current density decreased and the corrosion resistance increased significantly.Moreover,double layer structures of the interface became thicker and more compact.Under low-temperature environment,acicular ferrite had the martensite/austenite constituents with less amount and smaller size,a higher density of low angle grain boundaries and smaller effective grain sizes compared with granular bainite,which demonstrated higher corrosion resistance.展开更多
The effect of inclusion-induced nucleation on hot-rolled steel base metal was evaluated in comparison with welding heataffected zone(HAZ).Microstructure and mechanical properties of hot-rolled low-carbon steel contain...The effect of inclusion-induced nucleation on hot-rolled steel base metal was evaluated in comparison with welding heataffected zone(HAZ).Microstructure and mechanical properties of hot-rolled low-carbon steel containing Ti–Ca oxide particles were studied.The results showed that inclusions in Ti–Ca deoxidized steel distributed dispersely and were effective for intragranular acicular ferrite nucleation.Under hot rolling and controlled cooling conditions,microstructure in steel base metal was significantly refined and mainly consisted of acicular ferrite and intragranular bainite,which exhibited higher strength and excellent toughness.The microstructural evolution behavior followed the process that acicular ferrite plates divided the austenite grain,intragranular bainite packets formed between interlocking acicular ferrite plates,and the remaining austenite decomposed into fine polygonal ferrite grains.The resultant complex microstructure improved the impact toughness significantly.By comparison,in HAZ microstructure,laminar grain boundary ferrite having similar crystallography orientation showed adverse effect on toughness.展开更多
Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of appli...Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of applications as it requires less production time and space with reduced energy consumption.Owing to its sub-rapid cooling rate during solidification and low reduction during hot rolling,DSC process exhibits a series of unique physical metallurgy characteristics.The process characteristics of DSC process and the microstructural evolution during the thermomechanical processing of low-carbon microalloyed steel are reviewed.The effects of hot rolling,cooling,coiling temperatures and microalloying elements on the microstructure and mechanical properties are then discussed.Finally,the future development orientations of DSC technology are suggested to fully utilize its unique features for the enhancement of its competitiveness and for the promotion of carbon neutrality of the steel industry.展开更多
In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm s...In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm separately.Meanwhile,the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal.Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy,which contributes to the generation of numerous fine and interlocking acicular ferrite.The acicular ferrite volume ratio of weld metal exceeds 60%.Moreover,the impact energy at-40℃ surpasses 115 J and the crack tip opening displacement value at-10℃ is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite,of which 85 kJ/cm is the best.The martensite-austenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite,without impairing the toughness.As the heat input increases,the content of acicular ferrite drops and then rises;the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.展开更多
基金The Chinese Scholarship Council(CSC)financially supported by the National Natural Science Foundation of China(Nos.51874024 and 51734003)the Fundamental Research Funds for the Central Universities(No.FRF-TP-18–009C1)
文摘To investigate the effect of surface-modified nanoparticles(NPs)on the inclusion refinement and microstructure evolution,deoxidized experiment ingots with different amounts of modified NPs were manufactured under different cooling conditions.Laser scanning confocal microscope(LSCM)was hereby used for in-situ observation of the phase transition and microstructural evolution during heat cycle process.The results revealed that the inclusion size was always smaller under water quenching than under air cooling,and the number of inclusions was greater under water quenching.After NP addition,the nucleant inclusions were identified as MgAl_(2)O_(4)spinel and irregular TiN inclusion from SEM-EDS measurement and equilibrium calculations using Factsage thermodynamic software.The higher cooling rate under water quenching resulted in less polygonal ferrite decrease and the formation of bainite in the steel.The LSCM experiments showed that ferrite side plates(FSP)always formed on the boundary prior to the formation of acicular ferrite(AF)on the intragranular inclusions,and the start transformation temperatures of FSP and AF phases both lowered after NP addition.The higher cooling rate and NP addition contributed to AF formation and increased the degree of interlocking of the AF phase.Finally,the relationship between the characteristics of inclusions and the kinetics of AF was investigated.
文摘The reliability of steel welds becomes more critical issue with increasing steel strength,because brittle phases are more likely to form in the weld metals and heat-affected zone(HAZ) and thereby the toughness and ductility of the welds are degraded.Therefore,refinement of microstructure and minimization of the brittle phases are necessary to improve the reliability of the high-strength steel welds.In this presentation,microstructure formation that controls the toughness of weld metals and HAZ in high-strength low-alloy(HSLA) steel welds is reviewed and possible routes to the improvement of the weld microstructure and weld toughness are discussed.
文摘The pipeline steel is usually produced by adding niobium and vanadium alloying elements.The titanium alloyed pipeline steel was studied in the paper to reduce the production cost and enhance the competitive ability of pipeline steel.The steel containing 0.070%Ti was refined in the laboratory vacuum refine furnace.The dynamic CCT curve of developed steel was conducted on Gleeble-1500 thermal simulator and multi-pass deformation tests of studied pipeline steel were performed to simulate the CSP hot-rolling technology.Corresponding microstructures were observed and the influences of such technology parameters as deformation strain,deformation temperature, cooling rate and finishing temperature etc.on microstructure were analyzed.The dynamic CCT curve was obtained.The test results showed that the volume fraction of acicular ferrite in the microstructure of Ti-microalloyed X70 pipeline steel increased obviously with the increase of cooling rate after thermo-mechanical deformation.However,the volume fraction of acicular ferrite varies scarcely after the cooling rate of 20℃/s.In order to obtain Ti-microalloyed X70 pipeline steel with excellent compound mechanical properties which has acicular ferrite as the main ideal microstructure,the cooling rate should be controlled to be 20℃/s or more.The higher of the finishing temperature,the more of the volume of acicular ferrite and the less of the volume of polygonal ferrite.The quite fine microstructure can be obtained by lowering the finish-cooling temperature.The results have shown that it is possible to produce the Ti-addition X70 pipeline steel from the point of view of microstructure.
基金supported by the National Natural Science Foundation of China(No.U1960202).
文摘The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles during welding.The chaotically oriented IAF and refined PAGs inhibit crack initiation and propagation in the steel,resulting in high impact toughness.This work summarizes the com-bined effect of deoxidizers and alloying elements,with the aim to provide a new perspective for the research and practice related to im-proving the impact toughness of the heat affected zone(HAZ)during the high heat input welding.Ti complex deoxidation with other strong deoxidants,such as Mg,Ca,Zr,and rare earth metals(REMs),can improve the toughness of the heat-affected zone(HAZ)by re-fining PAGs or increasing IAF contents.However,it is difficult to identify the specific phase responsible for IAF nucleation because ef-fective inclusions formed by complex deoxidation are usually multiphase.Increasing alloying elements,such as C,Si,Al,Nb,or Cr,con-tents can impair HAZ toughness.A high C content typically increases the number of coarse carbides and decreases the potency of IAF formation.Si,Cr,or Al addition leads to the formation of undesirable microstructures.Nb reduces the high-temperature stability of the precipitates.Mo,V,and B can enhance HAZ toughness.Mo-containing precipitates present good thermal stability.VN or V(C,N)is ef-fective in promoting IAF nucleation due to its good coherent crystallographic relationship with ferrite.The formation of the B-depleted zone around the inclusion promotes IAF formation.The interactions between alloying elements are complex,and the effect of adding dif-ferent alloying elements remains to be evaluated.In the future,the interactions between various alloying elements and their effects on ox-ide metallurgy,as well as the calculation of the nucleation effects of effective inclusions using first principles calculations will become the focus of oxide metallurgy.
基金Item Sponsored by National Natural Science Foundation of China (51074052)Fundamental Research Funds for Central Universities of China (N100607001)
文摘The correlation between microstructures and mechanical properties of a Nb-Ti microalloyed pipeline steel was investigated. The results revealed that with decreasing the finish rolling temperature and the cooling stop temperature,the matrix microstructure was changed from quasi-polygonal ferrite to acicular ferrite,as a result of improvement of both strength and low temperature toughness. By means of electron backscattered diffraction observation,an effective acicular ferrite packet contained several low angle boundaries or subboundaries plates which made important contributions to improvement of strength. It was found that many fine quasi-polygonal ferrite grains with high angle boundaries as the toughening structure were introduced into the acicular ferrite matrix to refine effective grain size and improve the toughness.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFB0304900)the National Natural Science Foundation of China(Grant No.51911530129).
文摘The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impedance spec-troscopy test combining with optical micrographs,scanning electron microscopy,transmission electron microscopy and electron back-scattered diffraction.The results showed that,compared with room and high temperature,low temperature could influence the corrosion behavior of high-grade pipeline steel,which means that the corrosion potential and current density decreased and the corrosion resistance increased significantly.Moreover,double layer structures of the interface became thicker and more compact.Under low-temperature environment,acicular ferrite had the martensite/austenite constituents with less amount and smaller size,a higher density of low angle grain boundaries and smaller effective grain sizes compared with granular bainite,which demonstrated higher corrosion resistance.
基金This work was supported by the National Natural Science Foundation of China(U1860201 and 51904070)China Postdoctoral Science Foundation(2018M631804)the Fundamental Research Funds for the Central Universities(N170703005).
文摘The effect of inclusion-induced nucleation on hot-rolled steel base metal was evaluated in comparison with welding heataffected zone(HAZ).Microstructure and mechanical properties of hot-rolled low-carbon steel containing Ti–Ca oxide particles were studied.The results showed that inclusions in Ti–Ca deoxidized steel distributed dispersely and were effective for intragranular acicular ferrite nucleation.Under hot rolling and controlled cooling conditions,microstructure in steel base metal was significantly refined and mainly consisted of acicular ferrite and intragranular bainite,which exhibited higher strength and excellent toughness.The microstructural evolution behavior followed the process that acicular ferrite plates divided the austenite grain,intragranular bainite packets formed between interlocking acicular ferrite plates,and the remaining austenite decomposed into fine polygonal ferrite grains.The resultant complex microstructure improved the impact toughness significantly.By comparison,in HAZ microstructure,laminar grain boundary ferrite having similar crystallography orientation showed adverse effect on toughness.
文摘Direct strip casting(DSC)is one of the cutting-edge technologies for the steel industry in the twenty-first century.Under the background of carbon peak and carbon neutrality,DSC technology has a bright future of applications as it requires less production time and space with reduced energy consumption.Owing to its sub-rapid cooling rate during solidification and low reduction during hot rolling,DSC process exhibits a series of unique physical metallurgy characteristics.The process characteristics of DSC process and the microstructural evolution during the thermomechanical processing of low-carbon microalloyed steel are reviewed.The effects of hot rolling,cooling,coiling temperatures and microalloying elements on the microstructure and mechanical properties are then discussed.Finally,the future development orientations of DSC technology are suggested to fully utilize its unique features for the enhancement of its competitiveness and for the promotion of carbon neutrality of the steel industry.
基金the Major Science and Technology Innovation Project of Shandong Province(No.2019JZZY020239)。
文摘In order to study the latest designed large heat input welding material of marine engineering extra-thick plate,EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85,100 and 115 kJ/cm separately.Meanwhile,the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal.Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy,which contributes to the generation of numerous fine and interlocking acicular ferrite.The acicular ferrite volume ratio of weld metal exceeds 60%.Moreover,the impact energy at-40℃ surpasses 115 J and the crack tip opening displacement value at-10℃ is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite,of which 85 kJ/cm is the best.The martensite-austenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite,without impairing the toughness.As the heat input increases,the content of acicular ferrite drops and then rises;the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.