Surface treatments usually are used to modify the appearance and properties of stainless steel surfaces. Simultaneously, the corrosion resistance of the stainless steel surface being related intrinsically to the spontaneous formation of a passive layer also will be affected. In this respect, the influence of different surface treatments on the corrosion resistance of Type 304 (UNS S30400) stainless steel to pitting corrosion has been evaluated by means of potentiostatic electrochemical noise measurements and surface characterization. Typical industrial treatments including mechanical grinding, glass blasting, and pickling were taken into account. Additionally, special consideration was put on the effect of aging conditions of the passive layer after surface treatments, in particular on the relative humidity. Benefits and limitations of the different applied surface treatments concerning protectiveness of the stainless steel surface were determined and discussed.
Nickel-free, nitrogen alloyed austenitic stainless-steels, with about 19 wt.-% Mn and 0,8 wt. % N, are an interesting alternative to classic CrNi austenitic stainless steels due to their superior mechanical properties (Rm > 900 MPa, A5 > 50 %, Av > 350 J) in the solution annealed condition. The formation of chromium-rich nitrides during suboptimal heat treatment, processing or application leads to an inhomogeneous distribution of alloying elements in the microstructure, which reduces the corrosion resistance. Consequently, an accurate knowledge of the sensitization behavior is indispensable for the use of nickel-free, high-nitrogen austenitic stainless steels. The relationship between artificial aging, phase formation and corrosion resistance was investigated on the alloys X8CrMnN18-19 (1.3815) and X8CrMnMoN18-19-2 (1.4456), both alloyed with 0,8 wt.-% Nitrogen, in the present work. The microstructural evolution was studied by LM and SEM while the corrosion resistance was characterized with the electrochemical potentiodynamic reactivation (EPR) and the KorroPad indicator-test. Both alloys showed increased corrosion susceptibility within critical aging parameters. Finally, a sensitization diagram was described successfully for both alloys showing the positive effect of molybdenum.