Microstructural features, mechanical properties and high temperature failures of ferritic to ferritic dissimilar welds

Abstract

Dissimilar metal welds (DMWs) between ferritic steel grades are found extensively in the construction of thermal power plants. The potential combinations and approaches for joining dissimilar ferritic steels are nearly limitless. For DMWs, the difference in alloy composition (specifically chromium and carbide-forming elements) provides the main driving force for carbon diffusion during welding, post-weld heat treatment and long-term service at elevated temperatures. Since the high temperature creep strength of local, carbon-denuded zones can be dramatically reduced from that of the parent or filler material, the service performance of ferritic DMWs can be severely reduced. This article reviews experimental observations on microstructural evolution in dissimilar ferritic welds, activities to describe the observed phenomena by modelling and simulation and discusses the performance of these welds at high temperature. Lastly, a well-engineered approach to the design of ferritic DMWs is discussed in the context of thermal power plants which are subject to damage by creep.

Experimental investigations on P22/P91 dissimilar shielded metal arc welds for power plant applications

“…This coarsening of HAZ is mainly due to migration of carbon from the base metal to the weld fusion zone. 5–7 Weld metal microstructure is composed of cast dendrites fully upper bainite structure (Figure 5(c)). The interface of the P91 base and the P22 matched filler weld is a mismatch region due to the significant difference in chromium concentration, which leads to a Cr-gradient across the weld boundary.…”

“…The tensile strength obtained in the case of electrodes C2 was higher than the P22 base and closer to the base metal P91, which is in agreement with the results proposed in previous literature. 7,25 The mechanical properties of the welds depend upon its microstructure of the weld and chemical composition. Materials used in high-temperature applications require good ductility and tensile properties.…”

“…Qualification testing of weldments is an essential consideration for the selection of welding procedures, filler materials, and PWHT ranges. 7,8 The components used in power plants may require welding of the cracks that can develop during fabrication, storage, and transportation stages, or during their service life. In dissimilar welding, the essential requirement of weld metal is to possess the same mechanical properties as the parent metal, so the selection of welding consumable plays a vital role in enhancing the quality and other properties of the weld compared to the base metal.…”

The Effects of Electrochemical Hydrogen Charging on Room-Temperature Tensile Properties of T92/TP316H Dissimilar Weldments in Quenched-and-Tempered and Thermally-Aged Conditions

“…In several last decades, demands for higher efficiency and lower environmental pollution in electricity generation, have led to the development of so-called "ultra-supercritical" (USC) power plant boiler technology using as a working medium supercritically heated and pressurized steam with temperature of 620 • C and pressure of 25 MPa and above [1][2][3]. Specific constructional components with variable properties and design conditions often require the applications of dissimilar metals joints [4][5][6]. In the maximally thermally-loaded steam circuits of the USC boiler equipment, dissimilar weldments between tempered martensitic and austenitic heat resistant steels are being frequently employed, e.g., within superheater and reheater sections.…”

In-situ Observation of Martensite Decomposition in HAZ of Cr-Mo Steel Weldment

“…This could cause a concern during welding and post weld heat treatment (PWHT) in which soft zone and hard zone could occur at the weld interface in Heat Affected Zone (HAZ) and weld metal, respectively. Many researchers studied microstructures of the soft zone [4][5][6][7][8][9][10][11][12] as well as performed mechanical characterization in dissimilar metal weldments [4,[8][9][10][11][12][13][14][15][16]. In as-welded condition, martensite structure was found in heataffected zone (HAZ).…”