Effect of nitrogen addition on microstructure and erosion-corrosion behavior of stainless steel in acidic slurry

Effect of nitrogen content on the microstructure and erosion-corrosion (E-C) behavior of stainless steel (containing about 25% Cr, 5%-6% Ni, and 1%-2% Mo) was investigated by using optical microscope(OM), potentiodynamic polarization curve and immersion method, a self-made rotating disk apparatus and scanning electron microscopy (SEM) and so on. The results show that with the increase of nitrogen content from 0 (no adding) to 0.485 wt.%, the Cr(eq)/Ni(eq) ratio of the tested materials decreases from 4.14 to 1.23 and the ferrite volume percentage of the steel tested linearly decreases approximately from 90% to 10%. The effect of nitrogen content on polarization behavior of the studied steel was not significant. All the passive current densities (I(p)) and pure corrosion rates (V(c)) of the different N content specimens in the acidic solution (slurry containing 0.1 M H(2)SO(4)+0.06% Cl(-)+0.4% F(-), the simplified zinc hydrometallurgy slurry) are too low and nearly negligible. Whereas the pure erosion rates (V(e)) of the four scenarios of the steels tested (N content, wt.%: N1, no adding; N2, 0.143%; N3, 0.289%; N4, 0485%, respectively) are much higher than their V(c) values. The V(e) values of the tested steels are in the order of N4 > N1 > N3 > N2, at the same time, the total weight loss rates (V(t)) follow the order of N4 > N1 > N3 > N2, too. N2 steel consisting of approximately equal volume fractions of ferrite (alpha) and austenite (gamma) exhibits the most excellent E-C resistance and erosion resistance, while the stainless steels possessing the big difference between alpha phase and gamma phase, such as N1 steel nearly possessing single ferrite or N4 steel nearly possessing single austenite, show poorer E-C resistance and erosion resistance.