Effect Of Rare Earth On Inclusions In Copper-bearing Ferritic Stainless Steels

The copper-bearing ferritic stainless steels with significant antibacterial properties, great corrosion resistance and outstanding economic values are widely used in food industry, food service industry, home furnishing, etc. However, the nonmetallic inclusions formed during the process of smelting exert negative effects on their performances badly. With the development of smelting clean steel technology, it has been shown that the effects of rare earth (RE), which has the effects of purifying molten steel, modifying inclusion and micro-alloying are more clear and stable in clean steels. Therefore, in this paper, RE was added into the copper-bearing ferritic stainless steel, and the effect of RE on the nonmetallic inclusions were investigated. Theoretical directions for improving comprehensive performance of the steel would be provided by the results.The precipitation behavior of inclusions during solidification process of liquid steel was calculated and analyzed firstly by the FactSage software. Then the tested ferritic stainless steel was prepared by the smelting, forge work and rolling. Effects of RE on the quantity, size, distribution, morphology and type of nonmetallic inclusions were investigated by metalloscope as well as SEM. Finally, the effect of RE on the impact toughness and strength of Copper-bearing Ferritic Stainless steels were studied by impact tests and tension tests.The results under the conditions of this experiment are obtained as follows:(1) Most of the nonmetallic inclusions which present irregular bulk or chain distribute isolatedly with less quantity and large size in copper-bearing ferritic stainless steel without RE. However, the nonmetallic inclusions refined become spherical or ellipsoidal with large quantity and distribute fairly uniformly in the matrix when RE is added into steel.(2) The nonmetallic inclusions in copper-bearing ferritic stainless steel without RE are mainly Al2O3, MnS and aluminosilicate. With the increment of RE addition amount, MnS transform to rare earth oxysulfide while Al2O3transform to rare earth aluminate and rare earth oxides gradually.(3) MnS transform to rare earth oxysulfides and Al2O3transform to rare earth oxides completely when the RE addition amount is0.016wt.%and0.064wt.%respectively.(4) Trace amount of RE can improve the impact toughness, tensile and yield strength of the copper-bearing ferritic stainless steel. When RE addition amount is0.016wt.%, the impact toughness, tensile and yield strength of the copper-bearing ferritic stainless steel reach maxima, which were58.7%、4.5%、12.5%respectively more than that of ferritic stainless steel without RE.