Research On Microstructure And Properties Of A New Corrosion Resistant Nickel-base Alloy Welding Joints

The microstructure and mechanical properties of welding joints of a new Ni base corrosion resistant alloy (there are two candidate components-X-1#and X-2#) were studied in this paper. It includes the same metal welding of the new alloy and the new alloy dissimilar metal welding with304austenitic stainless steel,625alloy, P91, P92martensitic steel respectively. The tensile properties and hardness of the welding joints were tested, and the microstructure were observed and analyzed with the metallographic microscope, scanning electron microscope. The main results are as follows:(1) No matter in the same metal welding or dissimilar metal welding joints, the microstructure from the substrate to the welding metal in fusion zone of X-1#and X-2#sides is good, there is no second phase or other compounds precipitation. However in the welding joints of dissimilar metals of the new alloys, some NbC and Laves phases are formed near the fusion zone of625alloy sides, and some ferrites which cause the rich in Cr and poor in Ni are formed near the fusion zone of304sides. What is more, some granular ferrites are formed near the fusion zone of P91and P92sides.(2) Both in the same metal welding or dissimilar metal welding joints, the thermal stability of X-1#and X-2#sides are good and the grains coarsening phenomenon is not apparent in the HAZ. However in the welding joints of dissimilar metals of new alloys, grains in625alloy,304austenitic stainless steel, P91and P92HAZ grow seriously, which reduces the Vickers-hardness values of welding joints.(3) Because of including W, Mo, Al and Ti in the alloy, X-2#alloy welding joint has better high-temperature strength and thermal stability than X-1#alloy. X-1#and X-2#welding coefficients are more than88%and the welding seams could be the weakest link.(4) The welding seams are the weakest link of X-1#/625and X-2#/625welding joints from room temperature to700℃tensile, and the coefficients of X-1#/625and X-2#/625welding joints are more than85%. The tensile tests of room temperature of X-1#/304and X-2#/304are plastic fracture, and the location of fracture is in the welding seam, while the tensile tests of500℃are brittle cleavage fracture, and the location of fracture is in the304matrix. The welding coefficient of X-1#/304is more than83.5%, and the welding coefficient of X-2#/304is more than92%. The welding coefficient of X-1#/P91, X-1#/P92, X-2#/P91and X-2#/P92welding joints in each temperature tensile experiment fluctuates greatly, and the lowest welding coefficient is61.98%in700℃tensile tests.