Microstructure and mechanical tests of a weld on a TIG welded UNS S31803 duplex stainless steel pipe

Abstract

University of Stavanger was given a pipe consisting of two parts of the duplex stainless steel grade UNS S31803, which had been welded together using TIG welding. The thesis is about examining the weld that goes around the pipe. During the thesis both mechanical and microstructural tests were done. The specimens were machined at the university, the tensile test specimen by the workshop employees and the rest by the student. The mechanical tests were Charpy impact tests, tensile tests, and hardness tests, while the microstructure was studied using optical microscope, EBSD and EDS. The mechanical tests gave good results, where the values were similar to what one would expect of the base material. The microstructural findings showed some chromium nitrides and at least one carbide particle. There was 40 to 50% austenite in the entirety of the weld when looking over a large enough area. Near the root of the weld the microstructure was isotropic. Closer to the cap the ferrite grains were elongated in the same direction and bands of austenite rich areas crossed them.