Abstract
The demand for heat-resistant steel has increased owing to its utility in numerous devices that must withstand high steam pressures and high temperatures, such as turbine rotors and blades in ultra-supercritical power plants. It is inevitable to join heat-resistance steel part by welding method, so it is important to maintain the toughness of the weld metals. In this study, the microstructure, low-temperature impact toughness, and fracture surface of as-welded and post-weld heat treatment (PWHT) of 2.25Cr-1Mo-0.25V weld metal were investigated. The microstructures of the as-welded and PWHT specimens are granular bainite and ferrite, respectively. This work revealed the relationship between effective microstructure nearby crack initiation origin and low temperature impact toughness for both the as-welded and PWHT specimens. The evolution of the microstructure and prior austenite was then investigated using confocal laser scanning microscopy (CLSM) to observe the formation of coarse ferrite grain structures. A suggestion for enhancing the low-temperature toughness was provided based on the effect of adjusting Mn content and forming acicular ferrite.
Highlights
The rapid development of modern, ultra-supercritical power plants has increased the demand for heat resistant steel in numerous devices that operate at high steam pressures and high temperatures such as turbine rotors, blades, and other rotating parts [1]
It was heated at 1420 °C with a rate of 10 °C/s and held for 240 s to accelerate the evolution of prior austenite and microstructure, the cooling rate of 10 °C/s was performed
The microstructure of the as-welded specimen is composed of bainitic ferrite, blocky
Summary
The rapid development of modern, ultra-supercritical power plants has increased the demand for heat resistant steel in numerous devices that operate at high steam pressures and high temperatures such as turbine rotors, blades, and other rotating parts [1]. Heat-resistant steel has a high temperature strength, creep strength, and corrosion resistance. Chromium (Cr) predominantly offers oxidation and corrosion resistance to the ferritic heat-resistant 2.25Cr-1Mo-0.25V steel. An increase in the Cr content can enhance the hardenability of heat resistant steel owing to its solid-solution strengthening effect [2,3]. Molybdenum (Mo) has long been used for heat resistance in order to enhance the creep strength. The Mo can effectively reduce the bainite transformation temperature and delay the grain boundary ferrite transformation, thereby promoting the formation of the bainite microstructure at a wide range of cooling rates [4]
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