Research Of Quality Control Of Round Billet Of 42CrMo4 Steel For Wind Power Equipment

Due to the problems of low cleanliness,carbon segregation,and hardenability in the 42CrMo4 steel used in wind power of Beiman Special Steel Co.,Ltd.,this paper studies the quality control technology of continuous casting round billet starting with smelting and continuous casting process,which is have played an important role in promoting the quality of wind power used steel products of Beiman Special Steel Co.,Ltd.Firstly,the evolution of the cleanliness of 42CrMo4 steel during the smelting process is systematically evaluated through the tracer test and the analysis of oxygen and nitrogen.On this basis,the key technologies for the control of cleanliness of 42CrMo4 steel were proposed.(1)The average oxygen content of 42CrMo4 steel in the LF refining station is about 40ppm,which is reduced to 11～16ppm after aluminum deoxidization,the deoxidization rate is about 65%.The oxygen content in the vacuum refining steel by VD is further reduced first(deoxidization rate is 78%)and then slightly increased during continuous casting.The slag entrapment during the refining process of LF and VD is the main reason for the inclusion of large particles in the 42CrMo4 steel.The tundish refractory and the mold powder have almost no influence on the inclusions in the finished product.(2)On the basis of strictly setting the internal control components of the steel,the deoxidization process of 42CrMo4 steel is optimized,the deoxidization rate is increased to 85%,and the oxygen content is reduced to 6ppm.In order to effectively control the inclusions in the steel,the vacuum holding time of VD is 22～26min,which can be adjusted according to the control standards and process requirements of inclusions.Appropriately prolonging the vacuum time has significantly improved the control effect of DS inclusions.The effect of molten steel superheat,secondary cold water strength and electromagnetic stirring process on the solidification structure and typical defects of 42CrMo4 steel round billet is comprehensively studied through industrial tests.Based on this,the optimized technical measures are put forward and integrated application is carried out.(1)The effect of molten steel superheat and secondary cold water strength on segregation defect of continuous casting billet was analyzed.A reasonable molten steel superheat is 25℃～35℃,and the reasonable secondary cold water strength is 0.18L/kg.(2)The ratio of equiaxed crystal of 42CrMo4 steel casting billet is proportional to the electromagnetic stirring current and electromagnetic torque of the crystallizer,and inversely proportional to the electromagnetic stirring frequency of the crystallizer.In the case of low electromagnetic stirring intensity,the electromagnetic stirring at the end has a significant effect on increasing the ratio of equiaxed crystals.Adopting the stirring method with positive and negative intervals improves the equiaxed crystal ratio of 42CrMo4 steel.(3)After the continuous casting process technology was integrated and applied,the qualification rate of the segregation of the continuous casting round of the 42CrMo4 steel of Beiman Special Steel was greatly improved,and the qualified rate of the forged products after forging reached 100%.