800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding cond...800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.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
Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to researc...Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to research the weldability of the steel.The results show that the steel has lower cold cracking sensitivity,and preheating temperature of 100 ℃ can help completely eliminate cold cracks,generating good process weldability.The increase of preheating temperature can reduce the hardening degree of heat-affected zone.The strength of welding joint decreases and hardness reduces when heat inputs increase,and excellent mechanical properties can be obtained when low welding heat inputs are used.Fine lath bainites of different orientations combined with a few granular bainites that effectively split the original coarse austenite grains are the foundation of good properties.展开更多
Room temperature tensile tests were carried on the hot-rolled state ultra-low carbon and low alloy cabainite and martensite steels which were get by different finishing temperatures and different cooling methods.We us...Room temperature tensile tests were carried on the hot-rolled state ultra-low carbon and low alloy cabainite and martensite steels which were get by different finishing temperatures and different cooling methods.We used the Scanning Electron Microscopy (SEM),Electron Backscattered Diffraction (EBSD) and X-Ray Diffractometer (XRD) to identify the metallographic structure and analyse the precipitated phase.The inherent mechanism of high strength of ultra-low carbon and low alloy bainite and martensite steels was discussed,and the analysis indicated that the reinforcement of ultra-low carbon and low alloy bainite and martensite steels was mainly produced by the superposition of the dislocation strengthening,solution strengthening and grain refinement strengthening.展开更多
管道是石油天然气长距离输送最安全、经济的方式。过去40年,随着管道输量和效率需求的不断提升,以及钢铁冶金制造技术及相应装备的进步,管线钢的开发和应用取得了快速发展。针对这一特点,从应用需求驱动、合金成分设计、制造工艺与装备...管道是石油天然气长距离输送最安全、经济的方式。过去40年,随着管道输量和效率需求的不断提升,以及钢铁冶金制造技术及相应装备的进步,管线钢的开发和应用取得了快速发展。针对这一特点,从应用需求驱动、合金成分设计、制造工艺与装备、显微组织、力学性能等方面对管线钢的发展历程进行阐述,包括低碳微合金化且具有良好可焊性的化学成分设计优化,高纯净度冶金和控轧控冷(Thermomechanical Control Process,TMCP)技术发展,珠光体-铁素体、针状铁素体、铁素体-贝氏体双相或复相、超低碳贝氏体等管线钢显微组织特征变化,以及高强度、高韧性、高变形能力管线钢的研制。在总结管线钢历史沿革的基础上,针对超大输量、更复杂服役工况和输送介质、氢气、二氧化碳等新能源管道建设需求,结合钢铁行业技术发展前沿,探讨了未来管线钢的技术发展趋势与方向。展开更多
文摘800 MPa grade new ultra-low carbon bainitic （NULCB） steel is the recently developed new generation steel. The microstructure in the coarse-grained heat affected zone （CGHAZ） of NULCB steel under laser welding conditions was investigated by thermal simulation. The influence of the cooling time from 800℃ to 500℃.t8/5 （0.3-30 s）, on the microstructure of the CGHAZ was discussed. The experimental results indicate that the microstructnre of the CGHAZ is only the granular bainite which consists of bainitic ferrite （BF） lath and M-A constituent while t8/5 is 0.3-30 s. The M-A constituent consists of twinned martensite and residual austenite, and the change of the volume fraction of the residual austenite in the M-A constituent is very small when t8/5 is between 0.3 and 30 s. The morphology of the M-A constituent obviously changes with the variation of t8/5.As t8/5 increases, tile average width, gross and shape parameter of the M-A constituent increase, while the line density of the M-A constituent decreases.
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.
基金Item Sponsored by National Science and Technology Support Plan Project of China(2007BAE51B07)
文摘Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to research the weldability of the steel.The results show that the steel has lower cold cracking sensitivity,and preheating temperature of 100 ℃ can help completely eliminate cold cracks,generating good process weldability.The increase of preheating temperature can reduce the hardening degree of heat-affected zone.The strength of welding joint decreases and hardness reduces when heat inputs increase,and excellent mechanical properties can be obtained when low welding heat inputs are used.Fine lath bainites of different orientations combined with a few granular bainites that effectively split the original coarse austenite grains are the foundation of good properties.
文摘Room temperature tensile tests were carried on the hot-rolled state ultra-low carbon and low alloy cabainite and martensite steels which were get by different finishing temperatures and different cooling methods.We used the Scanning Electron Microscopy (SEM),Electron Backscattered Diffraction (EBSD) and X-Ray Diffractometer (XRD) to identify the metallographic structure and analyse the precipitated phase.The inherent mechanism of high strength of ultra-low carbon and low alloy bainite and martensite steels was discussed,and the analysis indicated that the reinforcement of ultra-low carbon and low alloy bainite and martensite steels was mainly produced by the superposition of the dislocation strengthening,solution strengthening and grain refinement strengthening.
文摘管道是石油天然气长距离输送最安全、经济的方式。过去40年,随着管道输量和效率需求的不断提升,以及钢铁冶金制造技术及相应装备的进步,管线钢的开发和应用取得了快速发展。针对这一特点,从应用需求驱动、合金成分设计、制造工艺与装备、显微组织、力学性能等方面对管线钢的发展历程进行阐述,包括低碳微合金化且具有良好可焊性的化学成分设计优化,高纯净度冶金和控轧控冷(Thermomechanical Control Process,TMCP)技术发展,珠光体-铁素体、针状铁素体、铁素体-贝氏体双相或复相、超低碳贝氏体等管线钢显微组织特征变化,以及高强度、高韧性、高变形能力管线钢的研制。在总结管线钢历史沿革的基础上,针对超大输量、更复杂服役工况和输送介质、氢气、二氧化碳等新能源管道建设需求,结合钢铁行业技术发展前沿,探讨了未来管线钢的技术发展趋势与方向。
