Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength...Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitationoccurred during the isothermal relaxation stage after deformed in the non-recrystallizationtemperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles,(Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles riseswith the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in thelattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in theprecipitates increases with the relaxation time. The results were compared with the refinementeffect of microstructures caused by relaxation-precipitation controlling transformation (RPC)processing.展开更多
The ageing behavior of an Nb-bearing microalloyed steel at 525℃ was investigated by thermo-simulation test, hardness measurements and transmission electron microscopy (TEM). Prior to ageing, the steel was deformed in...The ageing behavior of an Nb-bearing microalloyed steel at 525℃ was investigated by thermo-simulation test, hardness measurements and transmission electron microscopy (TEM). Prior to ageing, the steel was deformed in austenite zone followed by a long relaxation. Experimental results indicate that the hardness decreases gradually in the initial stage until ageing for 120 min, and then increases continuously until 1200 min. The coarsened precipitates (>10 nm) formed in deformed austenite remain nearly unchanged in size, even after ageing for long time, while the further precipitates, which nucleate in a phase, contribute to the increasing of hardness. By comparison, the undeformed samples in austenite subjected to the same ageing process display a very similar hardness change trend to that of over-relaxation ones and have higher hardness values at each corresponding period.展开更多
The evolution of the microstructures and hardness of a bainitic plate steelduring tempering at 650 deg C has been investigated. The steel was manufactured by RFC(relaxation-precipitation controlling phase transformati...The evolution of the microstructures and hardness of a bainitic plate steelduring tempering at 650 deg C has been investigated. The steel was manufactured by RFC(relaxation-precipitation controlling phase transformation) technique. A part of the plate wasreheated to 930 deg C and held for 1 h before quenched into water (RQ). No obvious change wasdetected by means of optical microscopy in the RFC steel tempering for 0.5 h, while dislocationcells were formed inside the bainite laths, accompanied by an obvious drop of hardness. The bainitelaths started to coalesce in some regions, but the sample hardness kept nearly constant duringtempering from 1 to 7 h. With further tempering, polygonal ferrite was formed in local regions whilethe hardness decreased dramatically. The RQ samples softened faster during tempering and finallytransformed into the polygonal ferrite completely. These results indicate that the thermo-stabilityof fine non-equilibrium microstructures is tightly related to their history.展开更多
基金This work was financially supported by the national key basic research and development program of China (No.G1998061507).
文摘Thermal simulation test, TEM (Transmission Electron Microscope) and nanobeamEDS (Energy Dispersed x-ray Spectrum) techniques were used to investigate the precipitation behaviorof Nb, Ti, Mo etc. in HSLA (High Strength Low Alloy) steel. The strain induced precipitationoccurred during the isothermal relaxation stage after deformed in the non-recrystallizationtemperature region. After 30% predeformation at 850 and 900℃, there are two kinds of particles,(Ti,Nb)(C,N) and a few Nb(C,N), to precipitate during holding. The content of Nb in particles riseswith the relaxation time increasing. During the final holding stage, some Nb and Ti atoms in thelattice sites of the precipitates would be replaced by Mo atoms, and the Mo content in theprecipitates increases with the relaxation time. The results were compared with the refinementeffect of microstructures caused by relaxation-precipitation controlling transformation (RPC)processing.
基金The work was financially supported by the National High-Tech Research and Development Program of China (No.2003AA001020).
文摘The ageing behavior of an Nb-bearing microalloyed steel at 525℃ was investigated by thermo-simulation test, hardness measurements and transmission electron microscopy (TEM). Prior to ageing, the steel was deformed in austenite zone followed by a long relaxation. Experimental results indicate that the hardness decreases gradually in the initial stage until ageing for 120 min, and then increases continuously until 1200 min. The coarsened precipitates (>10 nm) formed in deformed austenite remain nearly unchanged in size, even after ageing for long time, while the further precipitates, which nucleate in a phase, contribute to the increasing of hardness. By comparison, the undeformed samples in austenite subjected to the same ageing process display a very similar hardness change trend to that of over-relaxation ones and have higher hardness values at each corresponding period.
基金The work was financially supported by the National Key Basic Research and Development Program of China (No.G1998061507) and CITIC-CBMM (No.2002RMJS-KY002)
文摘The evolution of the microstructures and hardness of a bainitic plate steelduring tempering at 650 deg C has been investigated. The steel was manufactured by RFC(relaxation-precipitation controlling phase transformation) technique. A part of the plate wasreheated to 930 deg C and held for 1 h before quenched into water (RQ). No obvious change wasdetected by means of optical microscopy in the RFC steel tempering for 0.5 h, while dislocationcells were formed inside the bainite laths, accompanied by an obvious drop of hardness. The bainitelaths started to coalesce in some regions, but the sample hardness kept nearly constant duringtempering from 1 to 7 h. With further tempering, polygonal ferrite was formed in local regions whilethe hardness decreased dramatically. The RQ samples softened faster during tempering and finallytransformed into the polygonal ferrite completely. These results indicate that the thermo-stabilityof fine non-equilibrium microstructures is tightly related to their history.
