The Influence of Long-term Ageing on the Microstructure of Sanicro 25 Steel

Marek Sroka,Marek Kremzer,Adam Zieliński,Grzegorz Golański,D Bassir

doi:10.1051/matecconf/201925303004

Marek Sroka, Marek Kremzer + Show 3 more

Open Access

https://doi.org/10.1051/matecconf/201925303004

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Abstract

Sanicro 25 (22Cr25NiWCoCu) is a newly developed austenitic stainless steel used in the boiler pressure superheaters and reheaters with ultra-supercritical high-efficient parameters. The paper presents the results of microstructure testing and secondary phase separation processes after 20,000 h ageing at 700 and 750 °C. In the initial stage of ageing, the precipitation of numerous very small M23C6 chromium carbides and Laves phase were observed. The long-term ageing related to temperature revealed the existence of secondary phases: M23C6, MX, NbCrN, Laves phase and σ phase. The test results presented in the paper are part of the developed material characteristics to be used for predicting the service life of the material of components operated under creep conditions.

Highlights

IntroductionIn spite of the extensive promotion of renewable energy sources (solar, wind or water) for years and the expected increase in the share of nuclear technologies in the energy balance, in Europe and in the world power industry, the global energy sector is still mostly based on fossil fuels
In spite of the extensive promotion of renewable energy sources for years and the expected increase in the share of nuclear technologies in the energy balance, in Europe and in the world power industry, the global energy sector is still mostly based on fossil fuels.Despite the significant rise in prices of harmful gas emissions into the air, which is to curb the development of the conventional power generation, there are no signs that the proportion of sources of electricity generation could significantly change in the coming years [1,2,3]
The investigated steel is characterised by the austenitic matrix with the grain size of 7 according to the scale of models with annealing twins and numerous primary precipitates of varying size arranged in bands both within the grains and at the grain boundary

Summary

Introduction

In spite of the extensive promotion of renewable energy sources (solar, wind or water) for years and the expected increase in the share of nuclear technologies in the energy balance, in Europe and in the world power industry, the global energy sector is still mostly based on fossil fuels. One of the most modern currently used materials is Sanicro 25 (X7NiCrWCuCoNbNB25-23-3-33-2) steel, which was developed by AB Sandvick Material Technology. This steel is characterised by high nickel (24%), chromium (22%) and tungsten (3%) contents and the addition of elements such as niobium, cobalt and copper. It is primarily intended for components of boiler pressure superheaters and reheaters to be operated at up to 700 °C [8]. The high performance of Sanicro 25 steel justifies the increasingly higher demand for it and its more and more widespread use in ultra- supercritical and advanced ultra- supercritical power units [1, 9]

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Summary