Recently, the State Key Laboratory of Rolling and Automation of Northeastern University and Professor Chen Liqing from the 2011 Collaborative Innovation Center for Steel Common Technology have conducted a new study to deeply explore the effect of elements W and rare-earth Ce on high temperature antioxidant behavior of the new medium chrome ferritic stainless steel and its mechanism. They designed a series of 444 ferritic stainless steels with different W and Ce contents, and studied the oxidation resistance at high temperature. The micro-analytical methods were used to characterize the oxidation products and precipitates at the interface/matrix. The study found that adding rare-earth element Ce or adding a certain amount of W at the same time can significantly reduce the oxidation reaction rate of ferritic stainless steel at high temperature; the formed oxide film is more uniform and dense, and has good adhesion in the oxide film; and the number of defects at the interface of the substrate is significantly reduced. Different W additions have different effects on high temperature oxidation resistance; adding Ce or adding Ce and W simultaneously can reduce the solid solution of (Fe, Cr, Si)2(Nb, Mo) Laves phase at 1000-1050oC; the Laves phase precipitates in the grains or at the grain boundaries can effectively inhibit the diffusion of the reaction elements. In addition, Laves precipitated at the oxide film/substrate interface has an important influence on the growth behavior and spalling mechanism of the oxide film, and a large amount of precipitation of the Laves phase causes the oxide film to peel off.
Ferritic stainless steel is favored by researchers and the industry because of its good formability, excellent stress corrosion resistance, high temperature oxidation resistance and low cost. Ferritic stainless steel has suitable thermal conductivity and thermal expansion coefficient, and is suitable for applications in heat exchange and thermal cycling. These advantages make ferritic stainless steel the best candidate for the preparation of solid oxide fuel cell (SOFC) connectors and automotive exhaust manifolds. Traditional ferritic stainless steel currently used to manufacture automotive exhaust manifolds has an operating temperature of about 900oC, but in order to meet environmental requirements and meet increasingly stringent automotive exhaust emission standards, and considering the temperature rise of gasoline after full combustion, the local operating temperature of the automotive exhaust gas manifold will reach 950–1050oC, even up to 1100oC. In order to adapt to the use of the hot end of the new generation of automobile exhaust system in such a high temperature environment, it is necessary to further understand the high temperature service and degradation behavior of the new ferritic stainless steel on the basis of understanding the alloying mechanism for alloy design. It has been shown that the thermo-mechanical fatigue properties of ferritic stainless steel can be improved by adding alloying element W, but the effect of W on the high temperature oxidation resistance of ferritic stainless steel is less studied. In addition, the addition of rare-earth elements is also expected to improve the high temperature oxidation resistance and hot corrosion resistance of ferritic stainless steel materials. However, to date, the proper addition amount of alloying elements and its mechanism of action are still unclear, especially the synergistic effect of high melting point alloying element W and rare-earth Ce on the high temperature oxidation resistance of ferritic stainless steel needs further exploration. A deep understanding of the high temperature oxidation resistance behavior and mechanism of multi-alloyed high temperature resistant ferritic stainless steel will play an important role in the design and application of new high temperature resistant ferritic stainless steel.
The results of the study were published online on July 17, 2018 under the title "High temperature oxidation behavior of ferritic stainless steel containing W and Ce" on the internationally renowned journal "Corrosion Science" (5-year impact factor is 5.238). The first author of the article is Ph.D. student Wei Liangliang and Professor Chen Liqing is the corresponding author. The research work was funded as a key project in the Joint Research Fund between National Natural Science Foundation of China - China Baowu Iron and Steel Group Co. (U1660205).
Full text link (https://doi.org/10.1016/j.corsci.2018.07.017).