The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investi- gated through single pass compression experiment using a Gleeble 1500 thermomechanical simu...The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investi- gated through single pass compression experiment using a Gleeble 1500 thermomechanical simulator. By the regression of stress-sWain data obtained in the experiment, the deformation activation energy of DRX was identified, and the critical strain was calculated with the Po- liak-Jonas (P-J) method. Based on the analysis, the occurrence condition and kinetics of DRX were determined. The results show that as the Nb content increases from 0.08wt% to 0.095wt%, the activation energy of recrystallization raises from 365 to 395 kJ/mol. The critical swain of DRX can be determined more accurately by the P-J method, and the ratios of critical swain to peak sWain of XS0 and X100 pipeline steels are 0.51 and 0.49, respectively, which are similar to the results achieved by other researchers and calculated with empirical formulae.展开更多
The dynamic recrystallization (DRX) behavior of Nb-Ti microalloyed steels was investigated by isothermal single compression tests in the temperature range of 900-1 150 ℃ at constant strain rates of 0.1-5 s^-1. DRX ...The dynamic recrystallization (DRX) behavior of Nb-Ti microalloyed steels was investigated by isothermal single compression tests in the temperature range of 900-1 150 ℃ at constant strain rates of 0.1-5 s^-1. DRX was retarded effectively at low temperature due to the onset of dynamic precipitation of Nb and Ti carbonitrides, resulting in higher values of the peak strain. An expression was developed for the activation energy of deformation as a function of the contents of Nb and Ti in solution as well as other alloying elements. A new value of corrective factor was determined and applied to quantify the retardation produced by increase in the amount of Nb and Ti dissolved at the reheating temperature. The ratio of critical strain to peak strain decreases with increasing equivalent Nb content. In addition, the effects of Ti content and deformation conditions on DRX kinetics and steady state grain size were determined. Finally, the kinetics of dynamic precipitation was determined and effect of dynamic precipitation on the onset of DRX was clarified based on the comparison between precipitate pinning force and recrystallization driving force.展开更多
The recrystallization behavior of a low carbon high niobium microalloyed steel was investigated using continuous and interrupted hot compression tests. The results showed that the initiation of dynamic recrystallizati...The recrystallization behavior of a low carbon high niobium microalloyed steel was investigated using continuous and interrupted hot compression tests. The results showed that the initiation of dynamic recrystallization (DRX) could be detected from inflection in the plot of the strain hardening rate against stress regardless of the stress peak appearance. According to the Zener-Hollomon parameter equation, the activity energy of DRX (Qad) was ob tained and a new modified expression calculating Qdef was proposed in consideration of the chemical composition of experimental steel. Applying the 2% offset method, the static softening fraction was determined. The graphic representation of the softening fraction vs interruption time gave the information about the non-static reerystallization temperature (about 1 000℃ ) and the relationship of precipitation time temperature. Static recrystallization kinetics followed the Avrami's law at high deformation temperature, and different values of the exponent m were given to illustrate the effect of niobium element on static recrystallization at different deformation temperatures.展开更多
This work aims at the development of carbon steel AISI 1536 through the microalloying addition of boron. Three grades of this steel with different content of boron up to 0.0055% were melted in 100 kg induction furnace...This work aims at the development of carbon steel AISI 1536 through the microalloying addition of boron. Three grades of this steel with different content of boron up to 0.0055% were melted in 100 kg induction furnace. The pro- duced steels were hardened at 960°C for 30 min., followed by tempering at different temperatures and durations. All hardened steels have martensite phase as illustrated with microstructures and X-ray diffraction. Hardness of all tem- pered steel samples was measured to calculate the activation energies of carbon migration through martensite phase. The results indicated that the activation energies of carbon migration through martensite phase decreases with the in- crease of boron content due to its positive effect on the crystallinity of martensite phase. Also, the results showed that the addition of boron up to 0.0023% can improve the steel properties at the lowest temperature and tempered time.展开更多
Based on the Thermo-Calc thermodynamic software, the type of equilibrium precipitated carbides and their contents in high Mo Nb-microalloyed H13 steel (NMH13 steel) were calculated. The composition, morphology, and ...Based on the Thermo-Calc thermodynamic software, the type of equilibrium precipitated carbides and their contents in high Mo Nb-microalloyed H13 steel (NMH13 steel) were calculated. The composition, morphology, and distribution of carbides after spheroidal annealing of two forged experimental steels were comparatively examined by means of optical microscopy (OM), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). VC, M23 C6 and M6C are identified in H13 steel after spheroidizing annealing, while (V,Nb)C, M23C6 , M2C and M6C are observed in NMH13 steel. Moreover, it is found that the ad- dition of Nb significantly enhances the stability of MC phase and the high Mo content accelerates the precipitation of small rod-shape M2C phase in NMH13 steel. The amount of the fine carbides in NMH13 steel obviously increased with M2 C and M6 C precipitated from the ferrite phase, which is in accordance with the results of thermodynamic cal- culations.展开更多
在光学显微镜下,利用Leica Metal Work软件研究了一种强度级别为2100MPa的超高强度马氏体时效钢在850~1150℃的奥氏体晶粒长大规律。结果表明,实验钢奥氏体平均晶粒尺寸随加热温度升高和保温时间的延长而增大,其奥氏体平均晶粒尺寸与...在光学显微镜下,利用Leica Metal Work软件研究了一种强度级别为2100MPa的超高强度马氏体时效钢在850~1150℃的奥氏体晶粒长大规律。结果表明,实验钢奥氏体平均晶粒尺寸随加热温度升高和保温时间的延长而增大,其奥氏体平均晶粒尺寸与保温时间规律符合Beck方程,奥氏体化温度宜控制在800~950℃,其晶粒增长指数随温度的升高而减小,850~1150℃时实验钢奥氏体晶粒长大平均激活能为108.5 kJ/mol-1,并建立了实验钢在等温加热过程中的奥氏体晶粒长大方程。展开更多
文摘The dynamic recrystallization (DRX) behavior of high-grade X80/X100 pipeline steels with different Nb contents was investi- gated through single pass compression experiment using a Gleeble 1500 thermomechanical simulator. By the regression of stress-sWain data obtained in the experiment, the deformation activation energy of DRX was identified, and the critical strain was calculated with the Po- liak-Jonas (P-J) method. Based on the analysis, the occurrence condition and kinetics of DRX were determined. The results show that as the Nb content increases from 0.08wt% to 0.095wt%, the activation energy of recrystallization raises from 365 to 395 kJ/mol. The critical swain of DRX can be determined more accurately by the P-J method, and the ratios of critical swain to peak sWain of XS0 and X100 pipeline steels are 0.51 and 0.49, respectively, which are similar to the results achieved by other researchers and calculated with empirical formulae.
基金the National Natural Science Foundation of China(No.50474086,50334010)the Program for New Century Excellent Talents in Universities(No.NCET-04-0278)of the Ministry of Education
文摘The dynamic recrystallization (DRX) behavior of Nb-Ti microalloyed steels was investigated by isothermal single compression tests in the temperature range of 900-1 150 ℃ at constant strain rates of 0.1-5 s^-1. DRX was retarded effectively at low temperature due to the onset of dynamic precipitation of Nb and Ti carbonitrides, resulting in higher values of the peak strain. An expression was developed for the activation energy of deformation as a function of the contents of Nb and Ti in solution as well as other alloying elements. A new value of corrective factor was determined and applied to quantify the retardation produced by increase in the amount of Nb and Ti dissolved at the reheating temperature. The ratio of critical strain to peak strain decreases with increasing equivalent Nb content. In addition, the effects of Ti content and deformation conditions on DRX kinetics and steady state grain size were determined. Finally, the kinetics of dynamic precipitation was determined and effect of dynamic precipitation on the onset of DRX was clarified based on the comparison between precipitate pinning force and recrystallization driving force.
基金Item Sponsored by National Natural Science Foundation of China(51074052)Fundamental Research Funds for Central Universities of China(N100607001)
文摘The recrystallization behavior of a low carbon high niobium microalloyed steel was investigated using continuous and interrupted hot compression tests. The results showed that the initiation of dynamic recrystallization (DRX) could be detected from inflection in the plot of the strain hardening rate against stress regardless of the stress peak appearance. According to the Zener-Hollomon parameter equation, the activity energy of DRX (Qad) was ob tained and a new modified expression calculating Qdef was proposed in consideration of the chemical composition of experimental steel. Applying the 2% offset method, the static softening fraction was determined. The graphic representation of the softening fraction vs interruption time gave the information about the non-static reerystallization temperature (about 1 000℃ ) and the relationship of precipitation time temperature. Static recrystallization kinetics followed the Avrami's law at high deformation temperature, and different values of the exponent m were given to illustrate the effect of niobium element on static recrystallization at different deformation temperatures.
文摘This work aims at the development of carbon steel AISI 1536 through the microalloying addition of boron. Three grades of this steel with different content of boron up to 0.0055% were melted in 100 kg induction furnace. The pro- duced steels were hardened at 960°C for 30 min., followed by tempering at different temperatures and durations. All hardened steels have martensite phase as illustrated with microstructures and X-ray diffraction. Hardness of all tem- pered steel samples was measured to calculate the activation energies of carbon migration through martensite phase. The results indicated that the activation energies of carbon migration through martensite phase decreases with the in- crease of boron content due to its positive effect on the crystallinity of martensite phase. Also, the results showed that the addition of boron up to 0.0023% can improve the steel properties at the lowest temperature and tempered time.
基金Item Sponsored by National High Technology Research and Development Program of China(2013AA031601)
文摘Based on the Thermo-Calc thermodynamic software, the type of equilibrium precipitated carbides and their contents in high Mo Nb-microalloyed H13 steel (NMH13 steel) were calculated. The composition, morphology, and distribution of carbides after spheroidal annealing of two forged experimental steels were comparatively examined by means of optical microscopy (OM), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). VC, M23 C6 and M6C are identified in H13 steel after spheroidizing annealing, while (V,Nb)C, M23C6 , M2C and M6C are observed in NMH13 steel. Moreover, it is found that the ad- dition of Nb significantly enhances the stability of MC phase and the high Mo content accelerates the precipitation of small rod-shape M2C phase in NMH13 steel. The amount of the fine carbides in NMH13 steel obviously increased with M2 C and M6 C precipitated from the ferrite phase, which is in accordance with the results of thermodynamic cal- culations.
文摘在光学显微镜下,利用Leica Metal Work软件研究了一种强度级别为2100MPa的超高强度马氏体时效钢在850~1150℃的奥氏体晶粒长大规律。结果表明,实验钢奥氏体平均晶粒尺寸随加热温度升高和保温时间的延长而增大,其奥氏体平均晶粒尺寸与保温时间规律符合Beck方程,奥氏体化温度宜控制在800~950℃,其晶粒增长指数随温度的升高而减小,850~1150℃时实验钢奥氏体晶粒长大平均激活能为108.5 kJ/mol-1,并建立了实验钢在等温加热过程中的奥氏体晶粒长大方程。