Kinetics on transformation of inclusions in low carbon martensitic stainless steel during heat treatment process
Inclusions have a significant impact on the mechanical properties and corrosion resistance of low-carbon martensitic stainless steel.Existing investigations mainly focuses on the control of inclusions in the molten steel of low-carbon martensitic stainless steel,while there is little studies on the transformation of inclusions during the heat treatment process.Through laboratory heat treatment experiments and kinetic calculation,the transformation law of inclusions in the heating process of low carbon martensitic stainless steel was revealed.It is shown that the main composition of inclusions before the heat treatment is 24％Al2O3-9％MgO-41％CaO-26％SiO2.After heat treat-ment,the content of Al2 O3 increases,content of CaO and SiO2 decrease,and the content of MgO fluctuats.With the increase of temperature from 900 ℃ to 1 200 ℃,the size,area fraction and number density of the inclusions in steel are fluctuated due to the chemical reaction between the inclusions and the steel matrix.With the increase of heating temperature,the diffusion coefficient of elements in the low carbon martensitic stainless steel increase,which is conducive to the chemical reaction between steel matrix and inclusions,resulting in the increase of the transformation rate of inclusions.A kinetic model of inclusion evolution during the heating of low carbon martensitic stainless steel is established,considering the diffusion of elements and the chemical reactions at the boundary layer.The model is used to calculate the variation of the composition of inclusions over time during the heat treatment process,which can be used to predict effects of various parameters on inclusion composition during the heat treat-ment process.
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