Wyniki 1-1 spośród 1 dla zapytania: authorDesc:"Krzysztof Cieszyński"

Microstructural evolution of HR6W alloy during ageing at high temperature DOI:10.15199/28.2016.5.1


  The HR6W alloy (23Cr40Ni30Fe7WTiNb) is a candidate for boiler components of advanced ultra-supercricical (A-USC) conventional power plants. The influence of isothermal ageing at 700°C and 900°C for up to 110 hours on the microstructure of HR6W alloy was investigated in detail by advanced scanning and transmission electron microscopy methods. The results show that, beside primary MX carbonitrides, the M23C6 and Laves phase, Fe2W, were precipitated in the austenitic matrix. Their size and spatial distribution depend on ageing conditions. Microstructure changes influenced the hardness of the investigated alloy. Key words: HR6W, microstructure, scanning electron microscopy (SEM), transmission electron microscopy (TEM), steam power plant (SPP).1. INTRODUCTION The HR6W is Ni-Fe based alloy produced by Nippon Steel & Sumitomo Metal Corporation with a nominal composition of 23Cr40Ni30Fe7WTiNb designed for tubing, especially for superheaters and reheaters coils and for thick-walled elements of boilers. The HR6W alloy is the candidate for advanced ultra-supercritical (A-USC) boiler pressure elements owing to its superior creep and oxidation resistance at high temperature [1÷4]. The aim of the study was to examine a stability of the HR6W alloy microstructure during ageing at 700°C and 900°C affecting its mechanical properties during service in the power plant. The highest ageing temperature was chosen based on phase equilibrium diagrams and corresponds to operating temperature of 670°C for up to 200 000 hours service for HR6W alloy [5]. 2. MATERIAL AND EXPERIMENTAL DETAILS The chemical composition of the investigated HR6W alloy and standard requirements for HR6W alloy are presented in the Table 1. The alloy was delivered as the tube with outside diameter of 38 mm and wall thickness of 8.8 mm. The as-received alloy was solution treated at temperature range of 1190÷1250°C followed by fast cooling [6]; the exact parameters of heat treatment were[...]

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