Ferritic stainless steels constitute approximately one-half of the AISI type 400 series stainless steels. These steels contain 10% to 30% Cr along with other alloying elements, notably Mo. Ferritic stainless steels are noted for their excellent stress corrosion cracking resistance and good resistance to pitting and crevice corrosion in chloride environments. They are cheaper alternative to austenitic stainless steels. However, the heat of welding leads to grain coarsening in the heat-affected zone and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferrite phase without any intermediate phase transformation. It is therefore recommended that these alloys are welded with a low heat input and at high welding speeds. While these alloys have useful properties in the wrought condition, welding is known to reduce toughness, ductility, and corrosion resistance because of grain coarsening and formation of martensite. Welding these commercial grades usually requires preheat and post weld heat treatment. For these reasons, the application of this group alloys is limited Recently, ferritic stainless steels are finding greater importance in structural applications including fabrication of rail wagons. However, the only shortcoming of ferrtic stainless steels is the poor notch toughness due to coarse grains in the weld fusion zone. Hence, the present work has been carried out to choose the best filler metal to weld AISI 409M grade ferritic stainless steel by studying the effect of three different filler metals: austenitic stainless steel (ASS), ferritic stainless steel (FSS) and duplex stainless steel (DSS) on tensile and impact properties of welded joints.
(1) Of the three filler metals used, the joint fabricated by DSS filler metal showing 9% and 7% higher tensile strength compared to the joints fabricated by ASS and FSS filler metals, respectively.
(2) Of the three filler metals used, the joint fabricated by ASS filler metal showing 75% and 25% higher impact toughness compared to the joints fabricated by FSS and DSS filler metals, respectively.