Study On "Gold Dust" Defect Of 430 Ferritic Stainless Steel

In this paper,the combination of numerical simulation and experimental analysis is used to study on 430 stainless steel "Gold Dust" defect.This paper includes the analysis of "Gold Dust" defect,the study on carbide precipitation behavior of 430 stainless steel at hot rolling,and the optimization measures to solve this problem.The main work and research results of this paper are as follows:(1)The macroscopic morphology and microscopic morphology of 430 stainless steel"Gold Dust" defect were analyzed,and it was found that the grain boundary carbides in hot-rolled sheets were related to the "Gold Dust" defect.The microstructure of the hot rolled sheet in which "Gold Dust' defect occurred was reduced by laboratory hot rolling experiments.The experimental hot-rolled sheet and the hot-rolled sheet of the steel mill were analyzed by metallography,scanning electron microscopy and electron probe.The carbides produced during the hot rolling stage are the key factors leading to "Gold Dust" defect(2)The phase transition mechanism of 430 and 410S stainless steel was studied by cyclic phase transition experiments.The experiment of cyclic phase transition was designed according to the phase diagram of 430 and 410S stainless steel,and the cyclic phase transition process was simulated by DICTRA using LE&PE model.In LE model simulation,the interface migration curve and the expansion curve exhibit the same characteristics when the temperature change rate(10,100,200?/min)is increased.and the interface migration simulation corresponds to the metallographic structure obtained by the cyclic phase transition experiment.It is indicated that the phase transition mechanism of 430 and 410S stainless steel is the LE model,the distribution of chromium may occur during the phase transition(3)The phase transition behavior of 430 and 410S stainless steel in the hot rolling temperature range was studied by continuous cooling experiments.The phase transition of 430 stainless steel in the continuous cooling process is PLE mode,below 800?,the segregation of chromium(2%)is left at the interface.The phase transition of 410S stainless steel during continuous cooling has two modes,which are PLE mode at 1200?900? and NPLE mode at 900?800?.Chromium distribution occurs at 1200?900?,and chromium segregation(0.5%)occurs at the interface below 800?.The microstructure analysis of the quenched sample obtained by continuous cooling,the chromium segregation at the phase interface generated during the continuous cooling process is an advantageous condition for the production of carbide.(4)A thermal simulation experiment was conducted to study the effect of the distribution of the cooling rate and the deformation of the hot rolling section on the formation of carbides after hot rolling.Controlling the cooling rate after deformation is 5,10,15,20,25,30?/s,and increasing the cooling rate after deformation can significantly reduce the generation of grain boundary carbides.By increasing the cooling rate(20?/s)between 1200?880? and distributing the deformation in the low temperature section,It can reduce the formation of grain boundary carbides under 5?/s cooling conditions.(5)Based on the work of thermal simulation,three groups were selected for hot rolling experiments.Three slabs of the same size were used to roll to the same thickness.Process scheme 1,air cooling to room temperaturea after hot rolling.Process scheme 2,quenching to room temperature after hot rolling.Process scheme 3,rapid cooling at 1200?900?,deformation at 900?880?,air cooling to room temperature after hot rolling.In process scheme 1,a large amount of carbides appearing in the grain boundary of the hot rolled sheet.In process scheme 2&3,a small amount of carbides appearing at the grain boundaries of the hot rolled sheet.