Optimization Of Continuous Casting Parameters And Controlment Of Central Segregation Of 42CrMo Slab

Central segregation and central porosity were easily generated in 42CrMo slab because of its high carbon content during continuous casting,which caused the microstructure and properties of product was not homogenous.The central segregation and central porosity of 42CrMo slab were decreased through optimizing of continuous casting parameters to increase equiaxed grain rate and employing the reasonable soft reduction,which was helpful for improving the internal quality of the slab.Firstly,Gleeble was used to measure the high temperature mechanical properties of 42CrMo slab.The effect of temperature on the strength and ductility of the slab was analyzed.The fracture surface of tensile specimens was observed by SEM.The microstructure of longitudinal section of specimens was observed by metallographic electron microscope to analyze fracture mechanism at different temperature.Then the effect of continuous casting parameters?superheat,casting speed and cooling intensity?on solidification structure of 42CrMo slab was simulated.The quantitative relationship between the continuous casting parameters and equiaxed crystal ratio was analyzed by simulating result.Finally,the influence of the continuous casting parameters on the soft reduction position and reduction amount was calculated.The quantitative relationship between them was also analyzed.According to high temperature mechanical properties test,it was seen that ductility of 42CrMo slab at 850?-1150? was high.The III brittle temperature zone was at 650?-825?.Therefore,the temperature of the slab during continuous casting was suggested to remain between 850?-1150?,and avoid below 850?.The fracture mechanism of plastic area at high temperature was mainly ductile fracture,the fracture mechanism at the III brittle temperature zone was mainly intergranular fracture.With the increase of superheat,casting speed and cooling intensity,the equiaxed crystal ratio of 42CrMo slab was decreased.The quantitative relation between them was,y = 99.69-0.18?4-2.14 AT2,y = 95.47+ 1.99W-1.23W² and y = 99.18?9.1SV-2.62V2 respectively.The influence of superheat on the equiaxed crystal ratio was most obvious,and the influence of casting speed was weak.The low superheat,weak secondary cooling intensity and low casting speed was suggested to increase the equiaxed crystal ratio,which was beneficial to improve the center segregation and central porosity of 42CrMo slab.The soft reduction position of the 42CrMo slab linearly increased with the increment of superheat and casting speed,L_fs0.5-=15.41 + 0.035?T,L_fs0.95 =17.37 + 0.03?T,L_fs0.5 =-3.598 + 20.11V,L_fs0.95 =-5.158 + 23.13V.The soft reduction position of the 42CrMo slab linearly decreased with the increment of secondary cooling intensity,L_fs0.5 =18.67-2.5W,L_fs0.95 =21.66-3.50W.The influence of casting speed on the reduction position was most obvious,and the influence of superheat was weak.According to the thickness of the shell and the critical strain of 42CrMo slab,the soft reduction amount was calculated.It was convenient to decide suitable soft reduction parameters under different continuous casting parameters according to the above quantitative formula.The low superheat,weak secondary cooling and low casting speed was chosen for continuous casting of 42CrMo slab based on the above research results.It was found that the quality of 42CrMo slab,especially central segregation and central porosity,was improved by comparing the slab before and after optimization soft reduction parameters.