| Due to the rising prices of nickel-containing austenitic stainless steels and the scarcity of nickel resources,it is imperitive to developt high-formity,corrosion-resistant,and wrinkle-resistant low-carbon nitrogen ultra-pure ferritic stainless steels for the sustainable development of stainless steel production.Addition of stabilizing elements is the general method for the development of high-performance Fe-Cr ferritic stainless steels which are widely used in home appliances,automotive exhaust system,and building decoration.Based on this,the Fe-17%Cr ultra-pure ferritic stainless steel based on titanium-stabilized 430 ferritic stainless steel was chosen in this paper.The microstructure of Fe-17%Cr ultrapure ferritic stainless steel after cold rolling and melTiNg was studied.Morphology,mechanical properties and electrochemical corrosion properties were also investigated.The formation mechanism of white defect stripes on the surface of Fe-17%Cr ultrapure ferritic stainless steel cold-rolled plates was investigated by means of metallographic microscope(OM)and scanning electron microscope(SEM).The results show Ti and N tend to segregate to the solid/liquid interface during solidification of Fe-17% Cr ultrapure ferritic stainless steel since the equilibrium distribution coefficients of Ti and N solutes in the Fe-Cr melt are both less than unity.At the final stage of solidification,a large amount of TiN particles are formed at the grain boundaries.During the subsequent rolling process,some TiN particles enriched at the grain boundaries are elongated and deformed and others are crushed,which results in the occurence of the white strpes.Combined XRD and compositional analysis(EDS),it was found that there are two kinds of TiN in the present stainless steel,one is single TiN,and the other is composite TiN with an oxide as heterogeneous nucleus.Thermodynamic calculation under equilibrium solidification conditions was carried out first.Calculations using the equilibrium method show that TiN can only precipitate when the solid fraction reaches 0.2.However,TiN was observed on the surface of the water-cooled samples during with high cooling rate,which indicats that TiN can precipitate at the initial stage of solidification when the cooling rate is sufficiently high.Therefore,it is necessary to consider the influence of thermodynamics and kinetics(solidification rate)simultaneously.The non-equilibrium solidification model which relates the composition and growth rate at the solid/liquid interface during solidification was developed to explore the effect mechanism of the coolong rates on the TiN precipitation behavior under non-equilibrium conditions.It was found that the calculated results using this model are in agreement with the experimental results.By comparing the tensile properties of titanium-stabilized Fe-17%Cr ultra-pure ferritic stainless steel and titanium-yttrium-stabilized Fe-17%Cr ultra-pure ferritic stainless steel cold-rolled plates,the effect of the the stabilizing elements Ti and Nb on the strength and elongation was explored(give the conclusion here).By comparing the electrochemical corrosion performances of the center and surface samples of the as-cast Fe-17% Cr ultrapure ferritic stainless steel,the corrosion properties of as-cast microstructures with different TiN characteristics were explored(give the conclusion here). |
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