Microstructure and Stress Corrosion Cracking Behavior of the Weld Metal in Alloy 52-A508 Dissimilar Welds

Abstract

In the nuclear power industry, dissimilar metal welding is widely used for joining low alloy steel to austenite stainless steel components with nickel-base filler metals. In this study, attention was paid to the weld metal in multi-pass Alloy 52-A508 dissimilar welds. An approximately 2 mm wide transition zone was observed that consisted of a martensitic layer (10$20 um) along the weld interface and the austenite phase region with varying degrees of dilution. After post-weld heat treatment, the microstructures near the weld interface consisted of martensite, carbides and Type II boundaries. The presence of Type II boundaries significantly reduced the resistance to stress corrosion cracking (SCC) and formed intergranular cracking under simulated reactor coolant conditions. Constant extension rate tensile (CERT) tests were performed on the notched tensile specimens in 300 C water at two extension rates, 3 Â 10 À4 and 1 Â 10 À6 mm/s. A fast CERT test can be regarded to have no contribution of corrosion, and its results can be used as standards for comparison. In the slow CERT tests, the ductility losses of round-bar specimens with a circumferential notch at various regions in the weld metal were ranked accordingly. The relative susceptibility to SCC in terms of the ductility loss in increasing order of severity was as follows: the undiluted weld metal, the transition zone and the weld interface. SEM fractographic observations were consistent with the SCC results, i.e., an increased ductility loss or SCC susceptibility was associated with more brittle fractures.

Evaluation of microstructure and texture across the welded interface of super duplex stainless steel and high strength low alloy steel

“…In general, the width of this carbon-depleted region may become noteworthy when the clad metal is heated to high temperatures for long times, for example during post weld heat treatment [21].…”

TEM Microstructure and Chemical Composition of Transition Zone Between Steel Tube and An Inconel 625 Weld Overlay Coating Produced by CMT Method

“…The width of the transition zone where martensite was formed amounted to 2-3 μm in the case of overlaying alloy 625, and 35-39 μm in the case of 309L steel. The presence of about 20 μm wide martensitic area in weld overlays made of Alloy 52 deposited by the GTAW method was documented by Chung by means of scanning electron microscopy [21]. Apart from this, investigations of the transition zone of weld overlays made of Inconel 82 were carried out by Chen [22].…”

Optimization of Laser Keyhole Welding Strategies of Dissimilar Metals by FEM Simulation

“…The selection of combination of materials has been performed taking also into account real industrial applications: joining of ferritic or martensitic to austenitic stainless steels and ferritic to martensitic steels are very common in nuclear power generation industry, [4,6,7,[40][41][42] in the chemical, petrochemical, and oil and gas industries, [4,6,7] especially in heat exchangers [43] and hydraulic valves, [20,21] and in the automotive industry [44] ; joining of nickel-based alloys to alloy steels is commonly used in turbocompressor rotors [45] and in power plant and electrical applications. [42] B. FEM Simulation of Laser Keyhole Welding For the simulation of laser keyhole welding, the FEM commercial software SYSWELDÒ has been employed.…”