Influence of Nb on the development of stainless steel long products

Usually niobium is added in ferritic stainless steels to avoid chromium carbides precipitation and then to improve corrosion resistance and to avoid embrittlement. This work shows that niobium can also be used in ferritic stainless steels long products to improve soft magnetic properties for actuators in the automotive industry or to improve the properties of a welding filler wire for the exhaust line of a car. The first example concerns stainless steels bars for the market of electromagnetic injection. Improving response-time of fuel injection valves is a great challenge for automotive industry in order to enhance car engine efficiency and to limit noxious gas emission. It is shown that low niobium stabilization makes recrystallization nucleation much faster and then prevents incomplete recrystallization. This leads to soft magnetic properties that make 17%CrNb ferritic stainless steels a very interesting solution for actuation. The second example concerns a new welding filler wire 430LNb for the exhaust line that combines corrosion resistance to salt attack, cyclic oxidation and thermal fatigue resistance of the weld. (AU) © TMS