Study On Reheating Temperature And Thermal Deformation Behavior Of Nb Microalloyed Reinforcement

500MPa grade high strength anti-seismic ribbed steel bars was a new economical and efficient building material. The bars had characteristics of big security reserves, good seismic property,high strength, good ductility et c, it was widely applied to high-level building structures in potential high-intensity earthquake district. In conventional process of produced hot rolled ribbed bar. Reheating temperature of slab and parameter of hot rolling’s control were the key of hot rolling stage. The former factor affected directly the prior-austenite and solution of the mirco-alloy elements, The later factor influenced recrystallized austenite size and load of rolling mill. Therefore, it is necessary to re-heating temperature and hot rolling process parameters for laboratory research, but also to lay the foundation for the actual production of niobium microalloyed high strength anti-seismic reinforcement.The tested steel was a kind of niobium microalloying (Nb=0.014%,0.027%,0.036%) anti-seismic ribbed steel in this paper. Effect of reheating temperature on austenization of the tested steel was studied by the application of heat-treatment experiment; next, the influence of deformation temperatures, strain rate and other process parameters on the test steel single pass and double pass hot deformation behavior and organization of tested steel are studied by using hot compression deformation simulation test; At the same time,effect of niobium content was analyzed.Reheating temperature on austenization of the tested steels showed that, In the range of reheating temperature from1150℃to1250℃, the austenite grain size of tested steels was increases with the increasing of temperature. For the three different niobium content tested steel, the optimal reheating temperature of0.014Nb steel was from1175℃to1200℃; the optimal reheating temperature of0.027Nb steel and0.036Nb steel were from1200℃to1225℃. In the range of niobium content from0.014to0.036%, the austenite grain size decreases with the increasing of niobium content under the same temperature. More than1200℃, austenite grain size of0.036Nb steel is not more than0.027Nb steel.Single-pass hot deformation behavior of0.027Nb steel indicate that, The deformation temperature from950℃to1100℃, and the strain rate from0.01to10s-1, as the deformation temperature increasing and strain rate reducing, The deformation resistance of tested steel decreased, the thermal deformation activity energy of0.027Nb tested steel is389.52kJ/mol, the relationship between Z parameters and flow stress as follows: In Z=5.4516ln[sinh(0.00852σ)]+33.41the hot deformation equation as follows: ε=1.200×1015[sinh(0.00852σ)]5.4516exp(-389520/RT)Double-pass hot deformation behavior of steel test results show that, The relationship between niobium content and recrystallize grain size is content with temperature. When deformation temperature was below1000℃, the function of grain refinement of niobium was not playing out the role. When the deformation temperature exceeds1025℃, the steel niobium content is higher, finer austenite grains, indicating niobium prevents austenite grain growth. Best deformation temperature of0.014Nb steel is980℃, best deformation temperature of0.027Nb and0.036Nb steel was1025℃.