The New Fe-Cr-Mo Ferritic Stainless Steels

Abstract

The new Fe-Cr-Mo ferritic stainless steels are reviewed with an emphasis on corrosion behavior. The properties of commercial steels are outlined showing how these alloys can be divided into general purpose (18Cr-2Mo), moderately severe service (26Cr-1Mo), and premium service (29Cr-4Mo) materials. The stress corrosion cracking (SCC), intergranular corrosion, pitting, crevice corrosion, and general corrosion of the Fe-Cr-Mo ferritic stainless steels in general is discussed. The influence of nickel on the corrosion resistance and toughness of ferritic stainless steels is considered.

Characterization of Gas Metal Arc Welding welds obtained with new high Cr–Mo ferritic stainless steel filler wires

“…At higher contents, Ti and Nb can however have a detrimental effect on material properties, so their maximum contents have to be limited [10][11][12]. During aging at high temperature, niobium can form various compounds like Laves phases or complex carbides that decrease ductility, toughness and high temperature strength [9].…”

“…The Mo content consequently has to be limited to about 2%. [10][11][19][20]. The welding of exhaust systems, generally using a Gas Metal Arc Welding (GMAW) process, can change the materials characteristics.…”

Effect of niobium on corrosion resistance to sulfuric acid of 430 ferritic stainless steel

“…One way to overcome this is to lower the C and N content 6,7 . Another alternative is to add a stabilizing element of C and N, such as Nb or Ti, which forms carbides and nitrites preferentially to those of Cr, avoiding thus its intergranular corrosion 2,6,[8][9][10][11][12] . This is the main purpose of adding niobium to this type of steels and the amount needed is about eight to eleven times the C plus N content 12 .…”

“…However, when these steels are cooled from the temperature range 900 °C -1150 °C, the high diffusion rate of C and N in these alloys determines a fast intergranular precipitation of chromium carbides and nitrides, turning them susceptible to intergranular corrosion [2][3][4][5][6] . One way to overcome this is to lower the C and N content 6,7 .…”

“…However, when these steels are cooled from the temperature range 900 °C -1150 °C, the high diffusion rate of C and N in these alloys determines a fast intergranular precipitation of chromium carbides and nitrides, turning them susceptible to intergranular corrosion [2][3][4][5][6] . One way to overcome this is to lower the C and N content 6,7 . Another alternative is to add a stabilizing element of C and N, such as Nb or Ti, which forms carbides and nitrites preferentially to those of Cr, avoiding thus its intergranular corrosion 2,6,[8][9][10][11][12] .…”