Study On Phase Change Behavior And Rolling And Heat Treatment Of Q690 Engineering Machinery Steel

With the development of economic construction and infrastructure construction,the demand for high quality steel has been further increased.In order to get low-cost and high-performance steel,and phase transformation behavior and rolling and heat treatment process of related steels need to be systematically studied in order to provide reliable data for actual production.In this paper,several low carbon and high-strength steels were selected,and their phase transformation behavior and rolling and heat treatment processes were studied.The main contents and results are as follows:(1)The static and dynamic continuous cooling phase transition behaviors of the experimental steels with or without Mo containing were studied.For the experimental steel without Mo containing,the type of microstructure transformation is ferrite+pearlite+bainite?ferrite+bainite?bainite with the increasing of cooling rate.For the experimental steel Mo containing,the microstructure are bainite when the cooling rate is 0.1?20?/s.The microhardness increases gradually with the increasing of cooling rate,and the deformation increases the phase transformation start temperature of the experimental steel.(2)The isothermal phase transformation behaviors of the experimental steel under the condition of undeformation and deformation are studied.The results of thermal simulation experiment show that:For the experimental steel without Mo containing,the transformation of bainite increases with the decreasing of the holding temperature at undeformed condition holding for 500s,and the deformation promotes the bainitc transformation.The bainite transformation temperature is increased by deformation for the C-Mn steel isothermal holding for 500s.The amount of bainite increased,and the hardness value increased with the decreasing of holding temperature when the holding time is 15s.(3)The effects of final rolling temperature,final cooling temperature and off-line tempering temperature on the microstructures and properties of the experimental steel were studied.The results of hot rolling and tempering show that:With the decrease of final rolling temperature or final cooling temperature,the yield strength and tensile strength of the experimental steel increased.The better performance of the hot rolling steel is that the yield strength and tensile strength of the experimental steel are 839MPa and 1019MPa,respectively,and the impact energy at-20? is 202J;With the increase of tempering temperature,the strength of the experimental steel increases first and then decreases.The sample which tempering at 200? has the best mechanical property,and the heat input of the welding is up to 100kJ/cm.(4)The effects of off-line quenching temperature and tempering temperature on the microstructure and properties of the experimental steel were studied.The results of heat treatment experiment show that:With the increase of tempering temperature,the yield strength of the experimental steel increases first and then decreases,and its tensile strength decreases.When quenching temperature and tempering temperature are 850? and 200? respectively,the yield strength of the steel is 890MPa,and the tensile strength is 1062MPa,and the impact energy at-20? is 186J,so the mechanical property is good.