The Effect Of Niobium Carbonitride On Austenite Static Recrystallization

V, Nb and Ti are traditional microalloyed elements. The carbon amount in microalloyed steel became lower and lower in order to meet the need of well weldability. In order to compensate the lack of strength caused by low carbon, strengthening of microalloyed element has become more and more important. Nb can prevent recrystallization drastically and rise the non-recrystallization temperature. Much more deformation is allowed in the extended non-recrystallization zone, which reinforce the grain refinement effect of deformation. What's more, fine niobium carbonitride particles can strengthen the steel by precipitation. Two kinds of low-carbon Nb bearing steels(14# and 12#) were involved in this paper.Isothermal compression deformation was carried on 1150℃, 1100℃, 1050℃, 1000℃, 975℃, 950℃, 900℃and 850℃respectively. The effect of niobium carbonitride on austenite static recrystallization had been studied by recrystallization kinetics curve and electronic transmitted microscope analysis on second particleThe study results showed that there was a plain in the recrystallization kinetics curve when the samples of 14# steel were compressed isothermally on 900℃. There were plains in the recrystallization kinetics curves when the samples of 12# steel were compressed isothermally on 1000℃, 975℃and 950℃. After the plains retained for a certain time, the recrystalliztion proceeded with higher speed. The activation energy of recrystallization kinetics curve with plain was higher than that of recrystallization kinetics curve without plain, which demonstrated that recrystallization with plain on the kinetics curve had been prevented drastically. The microstructure gained after deformation and air cooling of the two kinds steels were granular bainite and pearlite with little sorbite respectively. There were more grains retaining orientation of deformed austenite in the structure with low recrystallization rate than in the structure with high recystallization rate.The electronic transmitted microscope analysis on second particle showed that a great scale of second particles precipitated within the grain, on the grain boundary and in the dislocation with cubic, rectangular and sphere pattern. The size of the spots on the recrystallization kinetics curve plain, which was 10~30nm was much smaller than that of the spots beyond the recrystallization kinetics curve plain, which was 100~200nm. The particles with small size prevent the recrystallization and the particles with big size have nothing to do with the recrystallization. The conclusion drawn from above was that the prevented recrystallization actually resulted from the pinning force caused by the second particles that precipitated on the grain boundary during the isothermal compression. When the particles became coarse, the...