Phase precipitation and corrosion properties of copper-bearing ferritic stainless steels by annealing process

The effects of different annealing processes on the phase precipitation behavior and corrosion properties of copper-bearing 430 ferritic stainless steel were systematically investigated.The shape,quantity and distribution of copper-rich precipitates by different annealing processes were characterized by scanning electron microscopy,transmission electron microscopy,backscatter electron and backscatter diffraction.The pitting resistance behavior in simulated physiological saline envi-ronments(0.9 wt.%NaCl)was investigated using electrochemical workstation and X-ray photoelectron spectroscopy.The results showed that the copper-rich phase prepared by repeated rolling and annealing gradually changed from long needle-like to short thick rod-like and granular,whose distribution tended to be uniform and diffusive,and the number of copper-rich phases increased.After solution/antibacterial annealing process,the size and density of the copper-rich phase increase,resulting in a discontinuity of the passivation film on the stainless steel,which reduces the pitting resistance to some extent.The refinement mechanism revealed that pre-deformation brings about a modification in both precipitation mechanism and growth kinetics of epsilon copper.

Influence of refining process and utilization of different slags on inclusions, titanium yield and total oxygen content of Ti-stabilized 321 stainless steel

Ti-stabilized 321 stainless steel was prepared using an electric arc furnace, argon oxygen decarburization (AOD) furnace, ladle furnace (LF), and continuous casting processes. In addition, the effect of refining process and utilization of different slags on the evolution of inclusions, titanium yield, and oxygen content was systematically investigated by experimental and thermodynamic analysis. The results reveal that the total oxygen content (TO) and inclusion density decreased during the refining process. The spherical CaO–SiO2–Al2O3–MgO inclusions existed in the 321 stainless steel after the AOD process. Moreover, prior to the Ti addition, the spherical CaO–Al2O3–MgO–SiO2 inclusions were observed during LF refining pro-cess. However, Ti addition resulted in multilayer CaO–Al2O3–MgO–TiOx inclusions. Two different samples were prepared by conventional CaO–Al2O3-based slag (Heat-1) and -TiO2-rich CaO–Al2O3-based slag (Heat-2). The statistical analysis revealed that the density of inclusions and the -TiOx content in CaO–Al2O3–MgO–TiOx inclusions found in Heat-2 sample are much lower than those in the Heat-1 sample. Furthermore, the TO content and Ti yield during the LF refining process were controlled by using -TiO2-rich calcium aluminate synthetic slag. These results were consistent with the ion–molecule coexist-ence theory and FactSage?7.2 software calculations. When -TiO2-rich CaO–Al2O3-based slag was used, the -TiO2 activity of the slag increased, and the equilibrium oxygen content significantly decreased from the AOD to LF processes. Therefore, the higher -TiO2 activity of slag and lower equilibrium oxygen content suppressed the undesirable reactions between Ti and O.

Effect of Cu on Surface Microcrack of Austenitic Stainless Cold Rolled Coil

In order to find out the cause of surface microcrack on 304 austenitic stainless cold rolled coils which is produced in a steel plant of China, lots of studies have been carried out. The results indicated that the copper guide of steekle mill used in hot rolling process contacts directly with the hot rolled coil, so parts of copper melt and glued to the surface of the stainless steel plates due to a higher temperature of stainless steel plates than the copper melting temperature, which leads to deterioration of austenitic grain boundaries. Shear stress produced in the process of repeatrolling on finishing mill induces the surface microcracks and promotes it. After changing the copper guide to the cast steel one, such kinds of surface microcracks have never appeared.