The stress relaxation curves of Ultra-Low Carbon Bainitic(ULCB) steels with different Cu and B contents were measured by using Gleeble-1500 dynamic thermal-mechanical simulator. The results show that Cu and B added ca...The stress relaxation curves of Ultra-Low Carbon Bainitic(ULCB) steels with different Cu and B contents were measured by using Gleeble-1500 dynamic thermal-mechanical simulator. The results show that Cu and B added can accelerate the strain-induced precipitation reaction, and the effect of Cu and B is even more obvious with Cu and B combined addition or Cu content increased. The TEM analysis of precipitate engendered at the temperature of 850℃ C indicate that Nb(C,N) precipitate nucleates dominantly on the dislocation line, and grows with holding time extended while the precipitate particle size increases from 5 nm to 17 nm.展开更多
The microstructure and properties of stmulated heat affected zone (HAZ) of laser welded ULCB600 steel were investigate by applying the simulation technique with gleeble - 2000 dynamic thermal - me - chanical simulat...The microstructure and properties of stmulated heat affected zone (HAZ) of laser welded ULCB600 steel were investigate by applying the simulation technique with gleeble - 2000 dynamic thermal - me - chanical simulator.The influence of the preheat condition on the microstructure and properties of simu- lated HAZ of laser welded plate was also studied in order to evaluate the feasibility of reducing arisk that the ductility and toedness of HAZ may be poor by using preheat treatment.The results indicate that the grain size of laser - welded HAZ simulated is very small no matter if there is preheat, the toughness of simulated HAZ is therefore improved comparing to the base metal,and there is no obvious brittle - ductile transition in the range from - 80℃ to 20℃. The TEM analyses of sub -microstruc- ture also discover that microstructure constituent of both simulated HAZ is dominative lath martensite. However, the shaf of martensite is relatively coarse,and the dislocation density is relatively high for simulated HAZ with 200℃ preheat because of slower cooling rate. Combination of these tow factors is responsible for farer bardness and better toughness of simulated HAZ with preheat condition.展开更多
Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion ...Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 1250℃ for a certain holding period. A prestain of 20% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.展开更多
A creep technique was applied on a Gleeble-1500 thermal simulator for monitoring the aging precipitation in ultra-low carbon steels containing various coppers. The aging hardening curve was obtained by the hardness te...A creep technique was applied on a Gleeble-1500 thermal simulator for monitoring the aging precipitation in ultra-low carbon steels containing various coppers. The aging hardening curve was obtained by the hardness testing. With the aid of an optical microscope and TEM, the microstructure and the aging precipitates were detected. The results indicate that when the precipitation occurs during the creep a plateau will appear on the creep curve; the left-hand and right-hand endings of the plateau correspond to the precipitation start （Ps） and finish （Pf） times, respectively. The Pf obtained from the creep curve coincides with the peak hardness time （tp） at the aging hardening curve. A precipitation-time-temperature （PTT） diagram of the steel can be obtained.展开更多
超低碳贝氏体 (U L CB)钢采用极低的碳含量 ,充分利用 Mn、 Mo、Nb、Ni、Ti、B等元素的合金化作用 ,通过 U L CB组织获得了高的强韧性及优良的低温韧性 ;由于 U L CB钢碳含量极低 ,焊接性优良 ,焊接热影响区 (HAZ)韧性明显改善 ,裂纹敏...超低碳贝氏体 (U L CB)钢采用极低的碳含量 ,充分利用 Mn、 Mo、Nb、Ni、Ti、B等元素的合金化作用 ,通过 U L CB组织获得了高的强韧性及优良的低温韧性 ;由于 U L CB钢碳含量极低 ,焊接性优良 ,焊接热影响区 (HAZ)韧性明显改善 ,裂纹敏感性显著降低。UL CB钢焊接时 ,焊缝金属是焊接接头的薄弱环节 ,研制开发超低碳贝氏体焊接材料是实现 UL CB钢焊接的关键环节。展开更多
文摘The stress relaxation curves of Ultra-Low Carbon Bainitic(ULCB) steels with different Cu and B contents were measured by using Gleeble-1500 dynamic thermal-mechanical simulator. The results show that Cu and B added can accelerate the strain-induced precipitation reaction, and the effect of Cu and B is even more obvious with Cu and B combined addition or Cu content increased. The TEM analysis of precipitate engendered at the temperature of 850℃ C indicate that Nb(C,N) precipitate nucleates dominantly on the dislocation line, and grows with holding time extended while the precipitate particle size increases from 5 nm to 17 nm.
文摘The microstructure and properties of stmulated heat affected zone (HAZ) of laser welded ULCB600 steel were investigate by applying the simulation technique with gleeble - 2000 dynamic thermal - me - chanical simulator.The influence of the preheat condition on the microstructure and properties of simu- lated HAZ of laser welded plate was also studied in order to evaluate the feasibility of reducing arisk that the ductility and toedness of HAZ may be poor by using preheat treatment.The results indicate that the grain size of laser - welded HAZ simulated is very small no matter if there is preheat, the toughness of simulated HAZ is therefore improved comparing to the base metal,and there is no obvious brittle - ductile transition in the range from - 80℃ to 20℃. The TEM analyses of sub -microstruc- ture also discover that microstructure constituent of both simulated HAZ is dominative lath martensite. However, the shaf of martensite is relatively coarse,and the dislocation density is relatively high for simulated HAZ with 200℃ preheat because of slower cooling rate. Combination of these tow factors is responsible for farer bardness and better toughness of simulated HAZ with preheat condition.
文摘Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 1250℃ for a certain holding period. A prestain of 20% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.
基金financially supported by the National Natural Science Foundation of China (No. 50471089)
文摘A creep technique was applied on a Gleeble-1500 thermal simulator for monitoring the aging precipitation in ultra-low carbon steels containing various coppers. The aging hardening curve was obtained by the hardness testing. With the aid of an optical microscope and TEM, the microstructure and the aging precipitates were detected. The results indicate that when the precipitation occurs during the creep a plateau will appear on the creep curve; the left-hand and right-hand endings of the plateau correspond to the precipitation start （Ps） and finish （Pf） times, respectively. The Pf obtained from the creep curve coincides with the peak hardness time （tp） at the aging hardening curve. A precipitation-time-temperature （PTT） diagram of the steel can be obtained.
文摘超低碳贝氏体 (U L CB)钢采用极低的碳含量 ,充分利用 Mn、 Mo、Nb、Ni、Ti、B等元素的合金化作用 ,通过 U L CB组织获得了高的强韧性及优良的低温韧性 ;由于 U L CB钢碳含量极低 ,焊接性优良 ,焊接热影响区 (HAZ)韧性明显改善 ,裂纹敏感性显著降低。UL CB钢焊接时 ,焊缝金属是焊接接头的薄弱环节 ,研制开发超低碳贝氏体焊接材料是实现 UL CB钢焊接的关键环节。
