Seyed M. Ahl Sarmadi, M. Shamanian, H. Edris, M. Atapoor, A. Behjat, M. Mohtadi Bonab, J. Szpunar,
Volume 36, Issue 1 (6-2017)
Abstract
Super duplex stainless steel is a kind of duplex stainless steel that has pitting resistant equivalent number over than 40. Unified Numbering System (UNS) S32750 is a common super duplex stainless stee, that is mostly applied in oil and gas refinery industries, because of its proper corrosion-resistant properties . Therefore, joining of these steels by welding is very important, but the greatest problem in this regard is the corrosion and decrease in mechanical properties after welding.. In this research, UNS S32750has been joined by friction stir welding method. The tool being used in this research was a WC with 16mm shoulder diameter, 5 mm pin diameter, and 1.9 mm height. X-ray diffraction showed that harmful phases, such as sigma or chi have not been formed. Microstructure study indicated that grain size in the stir zone has decreased. Vickers Hardness Test Method has been applied on welded samples. Moderate microhardness of base metal was 285 Vickers but, the microhardness increased in the stir zone to 360 Vickers, because of decreasing the grain size. The cyclic polarization determined that potential and corrosion current of joint metal by friction stir welding method was similar to base metal. Also, it was revealed that ferrite percentage in the stir zone doesn't decrease very much because the friction stir welding heat input is very low and the colding rate is very high.
