The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investi...The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO-Al2O3-Ti2O3-MnS inclusions with size around 2 μm are effective nucleation sites for IAF, whereas Al2O3-MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain （PAG） size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 μm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 μm. Therefore, the nucleation of IAF can hardly be observed.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
文摘The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO-Al2O3-Ti2O3-MnS inclusions with size around 2 μm are effective nucleation sites for IAF, whereas Al2O3-MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain （PAG） size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 μm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 μm. Therefore, the nucleation of IAF can hardly be observed.
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.
