Microstructure Stability of Alloy 740H and its Effect on Material Properties

Abstract

Alloy 740H was developed specifically for boiler tube and steam transfer pipe for the Advanced-Ultrasupercritical steam boiler application. The composition was formulated to provide creep strength, weldability and oxidation and coal ash corrosion resistance. It is the first nickel-base age-hardened alloy to be approved under Section 1 of the ASME Boiler and Pressure Vessel Code. Although a significant amount of microstructure and creep data was submitted to support the code case, it was largely collected on tube and light plate, much of this from pilot-scale material. The data package did not cover other product forms, sizes, hot working methods and weld joint configurations that may be required to construct a power plant. These include large diameter pipe, bends, fittings, heavy section welds, dissimilar metal welds, etc. that have complex thermal cycles and composition gradients. An ongoing effort is underway to characterize the microstructure and properties of alloy 740H under a range of manufacturing processes and to project these results through the potential life cycle of a plant. This paper describes the current status of this work. Paper published with permission.

Determination of Location-Specific Solidification Cracking Susceptibility for a Mixed Dissimilar Alloy Processed by Wire-Arc Additive Manufacturing

“…Conventionally used ferritic-martensitic steels, such as P91 steel, can be employed only up to 650°C [1]. Hence, Ni-based superalloys, such as Inconel 740H (referred as 740H hereafter), were designed with high Co (~20 wt.%) and Cr (~24 wt.%) content to achieve superior creep properties up to 850°C [2]. However, 740H is expensive compared to the traditional P91 steels due to the high content of alloying elements.…”

Determination of Location-Specific Solidification Cracking Susceptibility for a Mixed Dissimilar Alloy Processed by Wire-Arc Additive Manufacturing

“…Conventionally used ferritic-martensitic steels, such as P91 steel, can only be employed up to 650 • C [1]. Hence, Ni-based superalloys, such as Inconel 740H (referred as 740H hereafter), were designed with high Co (~20 wt.%) and Cr (~24 wt.%) content to achieve superior creep properties up to 850 • C [2]. However, 740H is expensive compared to the traditional P91 steels due to the high content of alloying elements.…”