Analysis of the Effects of Ti, Si, and Mo on the Resistance to Corrosion and Oxidation of Fe-18Cr Stainless Steels by Response Surface Methodology

We studied the corrosion and oxidation properties of Fe-18Cr-0.4Nb-(0.1 similar to 0.6)Ti-(1 similar to 3)Si-(0.5 similar to 2)Mo stainless steel. The resistance to general and pitting corrosion was evaluated and the results were analyzed by Response Surface Methodology (RSM) as a function of alloy composition. The effects of alloy composition and heat treatment on the oxidation resistance were also examined. Mo increased both general corrosion resistance and pitting corrosion resistance. Si improved the resistance of the alloys to pitting corrosion. Si was also beneficial for general corrosion resistance of the alloys containing Mo at more than 1 wt.%. However, Mo was detrimental when its content was lower. Effects of Ti on general corrosion properties appeared to be weak and a high concentration of Ti appeared to deteriorate pitting resistance. The thickness of the oxidation scale increased and adhesion of the scale worsened as the temperature increased from 800 degrees C to 900 degrees C. Weight gain of the alloys due to oxidation at 900 degrees C clearly showed that the resistance to oxidation is improved by annealing at 860 degrees C and an increase of Si content.