| As the first generation of super austenitic stainless steel,904L has better corrosion resistance and comprehensive mechanical properties than conventional austenitic stainless steel,and is widely used in chemical industry,seawater treatment,sulfuric acid manufacturing and other industries.However,the higher alloy content leads to serious dendritic segregation and precipitation of 904L.At the same time,904L steel has poor Thermalplasticity due to its low thermal conductivity and high coefficient of linear expansion,which makes it easy to crack during hot working.The purpose of this work is to improve the cleanliness of 904L steel and reduce solidification segregation by adding rare earth Ce and electroslag remelting.The changes of O and S elements in steel before and after addition of Ce and electroslag remelting were studied by means of direct reading spectrometer,N/O analyzer,C and S analyzer.The variety,size and quantity of inclusions in VIM1#,VIM2#,ESR1#,and ESR2#steels were analyzed by means of Olympus metallographic microscope,scanning electron microscope and energy dispersive spectrometer.In order to reduce the dendritic segregation of 904L and improve the micro structure uniformity,the homogeneous annealing process of 904L was investigated.The element redistribution behavior in 904L solidification process was calculated by using Scheil-Gulliver model in Thermal-Calc software.The dendrite structure at the edge,R/2 and center of the ingot was observed by Olympus metallographic microscope and the secondary dendrite spacing was measured.Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)were used to analyze the composition of dendrite trunk and interdendrite,and the segregation coefficient was calculated.It is found that the segregation of Mo element in steel is the most serious.The diffusion coefficients of Mo at different temperatures were calculated by DICTRA module.By homogenization annealing experiment,the homogenization annealing schedule of 904L is 1200?×12 h or 1250?×8 h.The effect of rare earth Ce on the hot deformation behavior of 904L steel after homogenization annealing was investigated by single pass hot compression experiments.It is found that the addition of rare earth Ce increases the rheological stress and thermal deformation activation energy of 904L,and has the effect of strengthening grain boundaries and refining grains.The thermal deformation constitutive equation and hot working diagram of ESR1#,ESR2#steels were constructed.It was found that the addition of rare earth Ce increased the power dissipation factor,enlarged the machinable area and improved the Thermalplasticity of the materials to a certain extent.Finally,the optimum hot working interval of ESR2#is 1080?1140?,0.01?0.2s-1,and the optimum hot working interval of ESR2#is 1100??1150?,0.01?0.7s-1. |
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