[Guangdong Province Stainless Steel Materials and Products Association], according to the news of Northeastern University, recently, State Key Laboratory of rolling technology and continuous rolling automation of Northeastern University, and professor Chen Liqing and others at the 2011 Collaborative Innovation Center for Iron and Steel Technology have launched a new study, to deeply explore the effects of element W and rare earth Ce on the high temperature oxidation resistance of new-type medium chromium ferrite stainless steel and its mechanism. They designed a series of type 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, and the formed oxide film is more uniform and dense, and has good adhesion, the number of defects at the oxide film/substrate interface is significantly reduced. Different addition amount of W has different effects on high temperature oxidation resistance; adding Ce or adding Ce and W at the same time can reduce the solid solution content of (Fe,Cr,Si)2(Nb,Mo) Laves phase at 1000-1050℃. The Laves phase precipitates in the grains or at the grain boundaries can effectively inhibit the diffusion of the reaction elements. In addition, the Laves phase precipitated at the oxide film/substrate interface, has an important influence on the growth behavior and the spalling mechanism of the oxide film, and a large amount of precipitation of the Laves phase causes peeling of the oxide film.

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. And ferritic stainless steel has suitable thermal conductivity and thermal expansion coefficient, which is suitable for applications in heat exchange and thermal cycling; These advantages make ferritic stainless steel become the best candidate material for the preparation of solid oxide fuel cell (SOFC) connectors and automotive exhaust manifolds. At present, the operating temperature of the traditional ferritic stainless steel used to manufacture automobile exhaust manifold is about 900℃, However, in order to meet environmental requirements, meet increasingly stringent vehicle exhaust emission standards, and consider the temperature rise after full combustion of gasoline, the local operating temperature of the vehicle exhaust manifold will reach 950–1050℃, or even as high as 1100℃. 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. In particular, 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-type high temperature resistant ferritic stainless steel.

It is reported that the results of the study were titled "High temperature oxidation behavior of ferritic stainless steel containing W and Ce" on July 17, 2018, published online in the internationally renowned journal "Corrosion Science" (5-year impact factor is 5.238). The first author of the article is Dr. Wei Liangliang, and Professor Chen Liqing, who is the author of the newsletter. The research work was funded by the National Natural Science Foundation Committee-China Baowu Iron and Steel Group Co., Ltd., a key project of the Steel Joint Research Fund (U1660205).