Research on Effect of Cooling Rate on Ti Microalloyed Q355B Yield Platform
In order to study the effect of cooling rate on the yield platform of Ti microalloyed Q355B,Q355B-Ti hot-rolled steel coils from a certain steel plant were selected.The tensile performance curves and metallographic structure were measured at 12 ℃/s,13 ℃/s,14 ℃/s,16 ℃/s,18 ℃/s,21 ℃/s,26 ℃/s,and 30 ℃/s cooling rates,respectively,while the final rolling temperature and coiling temperature remained unchanged.The results show that there is no obvious yield platform in the cooling rate range of 12～16 ℃/s,and a yield platform is generated in the 18～30 ℃/s range.The metallographic structure is bainite+ferrite.As the cooling rate increases,the morphology of the bainite structure changes from irregular feather like to regular polygonal,the grain size decreases,and the grain size increases from level 10 to level 11.Analysis suggests that the production of yield platform in Q355B-Ti hot-rolled steel coils requires a critical cooling rate of 18 ℃/s.Within the process design range,controlling the cooling rate can suppress or promote the production of yield platform.
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