The effect of high welding heat inputs in the range of 50–200 kJ/cm on the microstructural evolution,MX(M=Ti,Nb and V;X=N and C)precipitation and mechanical properties was investigated in the coarse-grained heat-affe...The effect of high welding heat inputs in the range of 50–200 kJ/cm on the microstructural evolution,MX(M=Ti,Nb and V;X=N and C)precipitation and mechanical properties was investigated in the coarse-grained heat-affected zone(CGHAZ)of a high-Nb(0.10 wt.%)structural steel.The results showed that the primary microconstituents varied from lath bainite(LB)to intragranular acicular ferrite(IAF)+intragranular polygonal ferrite(IPF),and the most content of IAF was acquired at 100 kJ/cm.Moreover,the submicron Ti-and Nb-rich MX precipitates not only pinned prior austenite grain boundaries but also facilitated IAF and IPF nucleation with the Kurdjumov–Sachs orientation relationship of[011]_(MX)//[111]_(Ferrite);the nanoscale V-rich MX precipitates hindered dislocation movement and followed the Baker–Nutting orientation relationship of[001]_(MX)//[001]_(Ferrite)with ferrite matrix,synergistically strengthening and toughening the CGHAZ.In addition,the−20℃impact absorbed energy firstly elevated from 93±5.2 J at 50 kJ/cm to 131±5.4 J at 100 kJ/cm and finally decreased to 59±3.0 J at 200 kJ/cm,being related to the IAF content,while the microhardness decreased from 312±26.1 to 269±12.9 HV0.1,because of the coarsened microstructure and the decreased content of LB and martensite.Compared to the CGHAZ properties with 0.05 wt.%Nb,a higher Nb content produced better low-temperature toughness,as more solid dissolved Nb atoms and precipitated Nb-rich MX particles in austenite limited prior austenite grain growth and promoted IAF formation.Furthermore,the welding process at 100 kJ/cm was most applicable for the high-Nb steel.展开更多
Microstructure and mechanical performances of the coarse grain heat-affected-zone （CGHAZ） for oil tank steel with different Ti content were investigated through Gleeble-3500, scanning electron microscopy, transmissi...Microstructure and mechanical performances of the coarse grain heat-affected-zone （CGHAZ） for oil tank steel with different Ti content were investigated through Gleeble-3500, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometer. The results show that the strength and low- temperature toughness of base material are significantly improved for the high titanium content steel, but the impact toughness of CGHAZ is seriously deteriorated after the high heat input welding and declined sharply with the heat input increasing, while the effects of heat input on impact toughness are very weak for the low titanium content steel, impact toughness of which is gradually larger than that of high titanium content steel with the welding heat input increasing because of the granular bainite increasing, TiN particle coarsening, and （Ti, Nb） N composition evolution during the high input welding for high titanium content steel.展开更多
The effect of Mo on nano-scaled particles,prior austenite grains and impact toughness of coarse-grained heat-affected zone(CGHAZ)in offshore engineering steels with Ca deoxidation was studied.The heat-affected zone(HA...The effect of Mo on nano-scaled particles,prior austenite grains and impact toughness of coarse-grained heat-affected zone(CGHAZ)in offshore engineering steels with Ca deoxidation was studied.The heat-affected zone(HAZ)toughness of Mo16 steel is obviously higher than that of Mo8 steel at all the heat inputs of 50,100,150 and 200 kJ/cm,with HAZ toughness of both steels decreased with increasing the welding heat input.When the Mo content is increased from 0.08 to 0.16%,the size of nano-scaled particles in HAZ is decreased from 18 to 15 nm,and their number density is increased from 0.7 to 0.9μm^(−2).Thus,the Zener pinning force is increased,and the prior austenite grain size(PAGS)is decreased,leading to the improved HAZ toughness.Microstructural characterizations show that the nano-scaled particles in both steels are Ti(C,N)with the solute elements of Nb and Mo.The calculated critical particle size of TiN is 10.2 and 8.4 nm in Mo8 and Mo16 steels at 1350℃,and the particles larger than the critical size are stable during the welding process.From the Zener pinning force calculation,Ti(C,N)particles play the more important role in the pinning effect on the prior austenite grain growth.Based on the regression analysis by the MATLAB results,the predicted values of PAGS at different heat inputs are well fitted with the experimental data.展开更多
Two kinds of low-carbon low-silicon TRIP (Transformation Induced Plasticity) steels containing vanadium are designed using ThermoCalc software in the light of both thermodynamics and kinetics.TRIP heat treatment proce...Two kinds of low-carbon low-silicon TRIP (Transformation Induced Plasticity) steels containing vanadium are designed using ThermoCalc software in the light of both thermodynamics and kinetics.TRIP heat treatment process of different steels is determined according to the calculation results respectively.Weld HAZ (Heat-Affected Zone) simulation tests indicate the weldability of TRIP steels is crucially sensitive to CE (carban equivelent) of the steel.However the impact toughness of CGHAZ (Coarse Grain Heat-Affected Zone) does not decrease drastically for TRIP steels microalloyed with Ti+V.The steel containing both of vanadium and titanium shows smaller grain size compared with that containing vanadium solely.This is because the precipitation of Ti/V carbonitride slows down the grain boundary motion speed and then retards the grain size coalescence in CGHAZ.展开更多
Effect of boron on microstructure and toughness of simulated CGHAZ of 790 MPa grade HSLA steel was studied.In the CGHAZ,boron improved the toughness of granular bainite(Bg),but deteriorated that of martensite.The maj...Effect of boron on microstructure and toughness of simulated CGHAZ of 790 MPa grade HSLA steel was studied.In the CGHAZ,boron improved the toughness of granular bainite(Bg),but deteriorated that of martensite.The major reason of boron improving toughness of Bg was to reduce the.quantity of M-A constituents.The reasons of martensitic brittleness in microstructure were discussed in detail.The experimental results proved that the order state of dislocations was an important factor of martensitic brittleness caused by boron, and the higher the order degree of dislocations was, the more brittle the martensite was.展开更多
In this study, the microstructure evolution and corrosion resistance in O. 5 M Na2CO3 - 1 M NaHCO3 solution of X80 high-deformability （ X8OHD ） pipeline steel coarse-grained heat-affected zone （CGHAZ） with several...In this study, the microstructure evolution and corrosion resistance in O. 5 M Na2CO3 - 1 M NaHCO3 solution of X80 high-deformability （ X8OHD ） pipeline steel coarse-grained heat-affected zone （CGHAZ） with several heat input levels were investigated. It is shown that the microstructure of CGHAZ changes from bainite ferrite to granular bainite as the heat input increasing. In addition, the corrosion resistance and the stability of passive film of base material are better than those of CGHAZ with several heat input levels. Too small or too big heat input is inadvisable and better corrosion resistance of CGHAZ is attained when heat input is 30 kJ/cm.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.52104333)the Natural Science Foundation of Inner Mongolia(Grant No.2024MS05029)+1 种基金the Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region(Grant No.NJYT24070)the Research Project of Carbon Peak and Carbon Neutrality in Universities of Inner Mongolia Autonomous Region(Grant No.STZX202316).
文摘The effect of high welding heat inputs in the range of 50–200 kJ/cm on the microstructural evolution,MX(M=Ti,Nb and V;X=N and C)precipitation and mechanical properties was investigated in the coarse-grained heat-affected zone(CGHAZ)of a high-Nb(0.10 wt.%)structural steel.The results showed that the primary microconstituents varied from lath bainite(LB)to intragranular acicular ferrite(IAF)+intragranular polygonal ferrite(IPF),and the most content of IAF was acquired at 100 kJ/cm.Moreover,the submicron Ti-and Nb-rich MX precipitates not only pinned prior austenite grain boundaries but also facilitated IAF and IPF nucleation with the Kurdjumov–Sachs orientation relationship of[011]_(MX)//[111]_(Ferrite);the nanoscale V-rich MX precipitates hindered dislocation movement and followed the Baker–Nutting orientation relationship of[001]_(MX)//[001]_(Ferrite)with ferrite matrix,synergistically strengthening and toughening the CGHAZ.In addition,the−20℃impact absorbed energy firstly elevated from 93±5.2 J at 50 kJ/cm to 131±5.4 J at 100 kJ/cm and finally decreased to 59±3.0 J at 200 kJ/cm,being related to the IAF content,while the microhardness decreased from 312±26.1 to 269±12.9 HV0.1,because of the coarsened microstructure and the decreased content of LB and martensite.Compared to the CGHAZ properties with 0.05 wt.%Nb,a higher Nb content produced better low-temperature toughness,as more solid dissolved Nb atoms and precipitated Nb-rich MX particles in austenite limited prior austenite grain growth and promoted IAF formation.Furthermore,the welding process at 100 kJ/cm was most applicable for the high-Nb steel.
基金supported by the Fundamental Research Funds for the National Science and Technology Support Program(No.2011BAE25B01)
文摘Microstructure and mechanical performances of the coarse grain heat-affected-zone （CGHAZ） for oil tank steel with different Ti content were investigated through Gleeble-3500, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometer. The results show that the strength and low- temperature toughness of base material are significantly improved for the high titanium content steel, but the impact toughness of CGHAZ is seriously deteriorated after the high heat input welding and declined sharply with the heat input increasing, while the effects of heat input on impact toughness are very weak for the low titanium content steel, impact toughness of which is gradually larger than that of high titanium content steel with the welding heat input increasing because of the granular bainite increasing, TiN particle coarsening, and （Ti, Nb） N composition evolution during the high input welding for high titanium content steel.
基金supported by the National Natural Science Foundation of China(U1960202).
文摘The effect of Mo on nano-scaled particles,prior austenite grains and impact toughness of coarse-grained heat-affected zone(CGHAZ)in offshore engineering steels with Ca deoxidation was studied.The heat-affected zone(HAZ)toughness of Mo16 steel is obviously higher than that of Mo8 steel at all the heat inputs of 50,100,150 and 200 kJ/cm,with HAZ toughness of both steels decreased with increasing the welding heat input.When the Mo content is increased from 0.08 to 0.16%,the size of nano-scaled particles in HAZ is decreased from 18 to 15 nm,and their number density is increased from 0.7 to 0.9μm^(−2).Thus,the Zener pinning force is increased,and the prior austenite grain size(PAGS)is decreased,leading to the improved HAZ toughness.Microstructural characterizations show that the nano-scaled particles in both steels are Ti(C,N)with the solute elements of Nb and Mo.The calculated critical particle size of TiN is 10.2 and 8.4 nm in Mo8 and Mo16 steels at 1350℃,and the particles larger than the critical size are stable during the welding process.From the Zener pinning force calculation,Ti(C,N)particles play the more important role in the pinning effect on the prior austenite grain growth.Based on the regression analysis by the MATLAB results,the predicted values of PAGS at different heat inputs are well fitted with the experimental data.
基金financially supported by VANITECNSFC(No.50971137.)
文摘Two kinds of low-carbon low-silicon TRIP (Transformation Induced Plasticity) steels containing vanadium are designed using ThermoCalc software in the light of both thermodynamics and kinetics.TRIP heat treatment process of different steels is determined according to the calculation results respectively.Weld HAZ (Heat-Affected Zone) simulation tests indicate the weldability of TRIP steels is crucially sensitive to CE (carban equivelent) of the steel.However the impact toughness of CGHAZ (Coarse Grain Heat-Affected Zone) does not decrease drastically for TRIP steels microalloyed with Ti+V.The steel containing both of vanadium and titanium shows smaller grain size compared with that containing vanadium solely.This is because the precipitation of Ti/V carbonitride slows down the grain boundary motion speed and then retards the grain size coalescence in CGHAZ.
文摘Effect of boron on microstructure and toughness of simulated CGHAZ of 790 MPa grade HSLA steel was studied.In the CGHAZ,boron improved the toughness of granular bainite(Bg),but deteriorated that of martensite.The major reason of boron improving toughness of Bg was to reduce the.quantity of M-A constituents.The reasons of martensitic brittleness in microstructure were discussed in detail.The experimental results proved that the order state of dislocations was an important factor of martensitic brittleness caused by boron, and the higher the order degree of dislocations was, the more brittle the martensite was.
基金This work was supported by The National Natural Science Foundation of China （No. 51271099）.
文摘In this study, the microstructure evolution and corrosion resistance in O. 5 M Na2CO3 - 1 M NaHCO3 solution of X80 high-deformability （ X8OHD ） pipeline steel coarse-grained heat-affected zone （CGHAZ） with several heat input levels were investigated. It is shown that the microstructure of CGHAZ changes from bainite ferrite to granular bainite as the heat input increasing. In addition, the corrosion resistance and the stability of passive film of base material are better than those of CGHAZ with several heat input levels. Too small or too big heat input is inadvisable and better corrosion resistance of CGHAZ is attained when heat input is 30 kJ/cm.
