Study On Thermo-Mechanical Treatment Process And Mechanism Of B92SiQL Steel

B92SiQL steel is favored by prestressed galvanized steel wire because of its high strength and plasticity and good torsion resistance.The processing parameters have a great influence on the microstructure and phase transformation of B92SiQL steel.In this paper,the single-pass hot compression experiments of B92SiQL steel were carried out at deformation temperature of 750～1100℃ and strain rate of 0.1～20 s^-1.The dynamic and static continuous cooling transformation（CCT）experiments were carried out at deformation temperature of 800℃and 950℃ and cooling rate of 0.1～30℃/s.The hot deformation behavior of B92SiQL steel was analyzed,and two different constitutive models were constructed.The influence of hot deformation parameters on the deformation mechanism of B92SiQL steel was investigated.The optimal processing window of B92SiQL steel was obtained by combining the hot processing map.The effects of deformation temperature,cooling rate and deformation on the phase transformation of B92SiQL steel were studied.By studying the flow stress-strain curve after hot compression test,it is found that the stress value gradually increases with the decrease of deformation temperature and the increase of strain rate.The thermal activation energy（Q）of B92SiQL steel under peak stress is about 334.695 k J/mol by Arrhenius constitutive model.The linear correlation coefficient（R）between the predicted flow stress and the experimental value is about 0.99562,and the average absolute relative error（AARE）is about 4.0255%.By constructing the Zhou Jihua-Guan Kezhi model,the R value of the predicted flow stress and the experimental value is about 0.98227.The comparison results show that the strain compensated Arrhenius constitutive model is more suitable for the prediction of the flow stress of B92SiQL steel.The hot processing map of B92SiQL steel was constructed by dynamic material model（DMM）.It was found that the optimal deformation condition of B92SiQL steel with the highest power dissipation coefficient（η）and in the safe processing area was 1050～1100℃/0.1 s^-1.Through microstructure analysis,it is found that under the condition of deformation temperature of 900℃ and strain rate of 0.1 s^-1,there are elongated deformed grains in the microstructure.Under the hot deformation condition of 1100℃/0.1 s^-1,almost complete dynamic recrystallization（DRX）occurred in B92SiQL steel,and the grains were obviously coarsened.When the strain rate increased to 10 s^-1,the DRX grains did not have enough time to grow,and the size decreased significantly.According to the inflection point of the work hardening rate and the flow stress curve,the critical condition for DRX of B92SiQL steel was determined.The logarithm of critical stress and critical strain was linearly related to ln Z.According to the Avrami equation,the DRX dynamic model of B92SiQL steel was established.The prediction results were compared with the data of DRX volume fraction obtained by the stress-strain curve method.It was found that the model had high accuracy in predicting DRX volume fraction.The dynamic and static continuous cooling transformation（CCT）behaviors of B92SiQL steel under different deformation temperatures,cooling rates and deformation conditions were investigated.It was found that during the dynamic CCT process,when the deformation temperatures were 800℃ and 950℃,B92SiQL steel produced martensite at a cooling rate of 5℃/s.When the cooling rate was less than 5℃/s,the microstructure was lamellar pearlite,and the larger the cooling rate,the smaller the pearlite lamellar spacing.Combined with the CCT curve,it is found that when the deformation temperature is 800℃,the CCT curve shifts to the left and the time of phase transformation of B92SiQL steel is shortened.During the static CCT experiment,martensite was found in the microstructure of B92SiQL steel at a cooling rate of 3℃/s,indicating that deformation promotes the diffusion of C atoms and inhibits the generation of martensite.