Research On Properties And Quality Control Of 65mn Hot Rolled Narrow Strip Steel

In recent years,with the narrow steel market saturation,the application of narrow steel is broadened,from the single pipe raw material to cold-rolled material,stamping pieces.The products are required of both low cost and differentiation.In this study,the phase transformation during continuous cooling,microstructure and properties for different cooling routes and products defects are investigated with 65Mn narrow strip steel.The main contents and results are as follows.(1)The characteristics continuous cooling transformation are studied for 65Mn steel.The static CCT curve was obtained and the critical transformation temperature is determined.The critical quenching rate is 40℃/s,which provides an important theoretical reference for the development of TMCP and heat treatment parameters.(2)The temperature and cooling rate of varied key position was measured in the 620 narrow strip workshop.The microstructure and properties were measured for different cooling method with varied storage way.The difference of the properties 1 under different cooling process is mainly determined by the content of ferrite and pearlite and the lamellar spacing of pearlite.The strength and hardness increases,and the elongation decreases with the increase of pearlite content and the decrease of the lamellar spacing.(3)The cooling process after finishing rolling is studied for 65Mn steel plate.The results show that the microstructure type has no effect on the microstructure of 1/4 steel after the final rolling,but the mechanical properties are improved.When the 1/2 water is used for ultra-fast cooling after finishing rolling,the microstructure is composed of pearlite and a small amount of retained austenite.Therefore,the mechanical properties of 65Mn steel sheet are improved under this condition.(4)The effects of cooling rate,coiling temperature and cooling rate on the microstructure and properties of 65Mn steel were studied.The results show that with the decrease of coiling temperature,the strength and hardness increased,the elongation decreased and the yield ratio increased.With the increase of cooling rate,the strength and hardness of the steel increased,and the elongation decreased.(5)The pearlite flatness of hot rolled strip is poor,the distribution of morphology is not uniform and the spacing of lamellar is different.The main microstructure is Soxhlet body,which contains two kinds of pearlite including flaky and granular,which leads to the uneven tensile strength and hardness of the 65Mn hot rolled narrow strip steel.