DEVELOPMENT OF A HIGHLY WELDABLE AND CORROSION RESISTANT NICKEL-CHROMIUM FILLER METAL

摘要

This paper reports on a long term research effort to develop an improved filler metal for gas-tungsten-arc welding of Alloy 690. The goal of this work was to maintain the corrosion resistance of wrought Alloy 690 while eliminating ductility dip cracking (DDC) or other as-welded defects in prototypical welds. Results from weld mockups, weldability testing, microstructural and microchemical characterization, and computational modeling show that ductility dip cracking is a form of precipitation-induced-cracking and can be mitigated via alloying to control the type and extent of carbide formation. Additionally, these tests illustrate that in commercially available filler metals, alloying additions intended to provide DDC resistance (Nb, B, and Zr) are not effective and, in many cases, cause solidification cracking in addition to DDC. Based on these welding results, three candidate alloys of 24 wt.%, 27 wt.%, and 30 wt.% chromium were further evaluated for their mechanical properties, phase stability, and resistance to environmentally assisted cracking (EAC). Results to date show weldability, mechanical properties, and phase stability comparable to EN82, but significantly improved resistance to EAC. These findings are used to define an alloy designated EN52i, that offers a desirable combination of weldability and corrosion resistance.