**1. Introduction**

As an important type of stainless steel, ferritic stainless steel has been a popular focus of research and application in recent years, not only because of its lack of nickel content but also because it is economical. Its cost is not affected by fluctuations in international nickel prices, and compared with austenitic stainless steel, ferritic stainless steel too has good thermal conductivity, low thermal expansion coefficient, good high temperature oxidation resistance, and good high temperature thermal fatigue resistance; thus, it has a wide range of applications in automotive exhaust systems [1–4]. However, with the constantly increasing requirements of automobile exhaust emission standards, automobile engine technology is continuously improving, and the exhaust gas temperature is continuously increasing. Better high temperature performance requirements are therefore imposed on the high temperature end material of the exhaust system [5–7].

Rare earth elements have a unique electronic layer structure and active chemical properties. In stainless steel, they can clean the steel, metamorphose inclusions, control solidification structure, and refine the grain [8–12], so they have received much attention from scholars these days. Some scholars have shown that the addition of rare earth elements in ferritic stainless steel can improve its corrosion resistance, mechanical properties, high temperature performance, and other service properties [13–16]. In order to study and improve the high temperature oxidation resistance, previously reported studies [17,18] show that adding Ce can increase densification of the oxidation film of ferritic stainless steel and improve its high temperature oxidation resistance. However, research data on the influence of rare earth elements on weld solidification crack sensitivity is still lacking. Automobile exhaust systems are generally applied as welded pipes, so the alloying effect on the weldability

of ferritic stainless steel needs to be investigated. Only with excellent weldability can the alloyed stainless steel be utilized commercially. In this study, the 441 type ferritic stainless steel is the research object. The effect of Ce on the weld solidification crack sensitivity of 441 ferritic stainless steel and its mechanism were studied using the Trans-varestraint test, and the theoretical support for solidification crack control of Ce-containing ferritic stainless steel is provided.
