| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 98 === In this study, the effects of sodium sulfate and its concentration on the passivation and pitting corrosion behaviors of 420 martensitic stainless steel in NaCl solution were investigated. The commercial 420 type martenstiic stainless steel were tempering at 650oC with a previous solution annealing and oil quenched at 1050o C. By potentiodynamic polarization curve and potentiostatic estimation to compare the results obtained with the solution annealed / oil qunched 420 SS and tempered 420 SS with previous annealed / queched in 0.1 M NaCl with 0.0001 M~0.5 M Na2SO4 addition. The results showed the solution annealed / qunched one has better corrosion resistance. Furthermore, the pitting corrosion susceptibility of solution annealed / qunched 420 SS and annealed / qunched / tempered 420 SS were increased if the Na2SO4 addition was lower, in contrast, inhibition of pitting corrosion was observed if the Na2SO4 addition was high. The potentiodynamic polarizationcurves of annealed / qunched / tempered 420 SS appeared active-to-passive transition peaks in NaCl solution(＜ 1M) with or without Na2SO4 addition.
In this work, the 420 martensitic stainless steel with high clearance also investigated followed the same methodology as the previous stated. The results showed that the higher clearance one has better corrosion resistance than less clearance in the test environments.
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