Corrosion behaviours of stainless steel parts formed by powder metallurgy process

This research investigated corrosion behaviours of AISI 304L and AISI 316L stainless steel specimens formed by powder metallurgy (P/M) process using accelerated electrochemical tests. Corrosion behaviours of the specimens were tested by potentiodynamic polarization measurements in 0.5M sulfuric acid, 0.5M sulfuric acid + 0.5M sodium chloride, 0.5M borate buffer, and 0.5M borate buffer + 0.5M sodium chloride, to simulate different corrosion behaviours caused by different environments. Corrosion behaviours of P/M specimens were compared with commercial stainless steel sheets of the same classifications. Corrosion potential and corrosion current density measurements showed that in the absence of Cl-, P/M specimens had similar corrosion behaviours, including comparable passivity, to stainless steel sheets in both acidic and neutral solutions. However, in acidic conditions with Cl-, all specimens showed signs of corrosion but the P/M specimens had much worse corrosion resistance and both P/M specimens never reached passivity. All specimens showed good passivity in neutral solution without Cl-, but in the presence of Cl-, only AISI 316 sheet specimen had no noticeable pitting. The P/M specimens were more susceptible to pitting corrosion and more severely damaged by corrosion than stainless steel sheets in all electrolytes, considering distribution of pits and pit depths. Pores in the P/M specimens were thought to be sites where pit grew, as a result of local acidification within the pores, bypassing pit initiation stage needed for pitting to occur on a normally passive surface. (C) 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference.