Study on the Corrosion Resistance of Duplex Stainless Steel Welds

Research Project

Project/Area Number	60550523
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	溶接工学
Research Institution	Faculty of Engineering, Osaka University
Principal Investigator	NISHIMOTO Kazutoshi Faculty of Engineering, Osaka University, 工学部, 助教授 (60112017)
Co-Investigator(Kenkyū-buntansha)	NAKAO Yoshikuni Faculty of Engineering, Osaka university, 工学部, 教授 (20029086)
Project Period (FY)	1985 – 1986
Project Status	Completed (Fiscal Year 1986)
Budget Amount *help	¥2,000,000 (Direct Cost: ¥2,000,000) Fiscal Year 1986: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1985: ¥1,400,000 (Direct Cost: ¥1,400,000)
Keywords	Duplex structure / Stainless steel / Weld metal / Intergranular corrosion / Pitting / Segrigation / Carbide / Inclusion / Rapid healinf / 鋭敏化
Research Abstract	The influence of the microstructure on the pitting corrosion resistance of austenitic stainless steel weld metal was investigated using various types of commercial alloys. The eleven commercial stainless steels were welded and then tested for pitting corrosion resistance in ferric chloride solution. From pitting corrosion behaviour in ferric chloride solution,the commercial stainless steels can be categorized into three types,that is, Type <I> ( Type 304 ); the initiation sites for pits mainly concentrate on austenite/ferrite boundaries, Type <III> ( Type 316L and Alloy 170 ) ; most pits initiate in the austenite matrix and Type <II> ( Type 316 and 304N ) ; the intermidiate type of Type <I> and Type <III> . The SEM and TEM observations, and EDX analysis have revealed that the chromium carbides precipitated at ferrite/austenite boundaries are responsible for the intergranular type of pitting for steels of Type <I> and the oxide or sulphide inclusions in the austenitic matrix for the intergranular pitting for steels of Type <III> . In addition the decrease of chromium and molybdenum contents in the austenite matrix which solidified as the primary crystal seems to deteriorate the pitting corrosion resistance of this region for steels of Type <III> .