Microstructure and mechanical properties of HR3C austenitic steel after service

Abstract

Purpose: The purpose of the investigations was to determine changes in the microstructureand mechanical properties of HR3C creep resisting austenitic steel after service.Design/methodology/approach: The investigations were performed on test specimens takenfrom a part of the steam superheater tube. The range of the investigations included: microstructuralinvestigations - light and SEM microscope; analysis of precipitates - carbide isolates; investigationsof mechanical properties - hardness measurement, static tensile test, impact test.Findings: The precipitation processes at the grain boundaries lead to increase inintergranular corrosion of the HR3C steel resulting in loss of grains in the structure. Theimpact strength testing on test specimens with reduced width may result in overestimationof crack resistance of the material after service.Research limitations/implications: The comprehensive analysis of precipitationprocesses requires TEM examinations. Finding the correlation between the impact strengthdetermined on standard vs. non-standard test specimens with reduced width.Practical implications: The obtained results of investigations are used in industrialpractice for diagnosis of pressure parts of power boilers. Test procedures developed based oncomprehensive materials testing conducted under laboratory conditions are used in upgradingand design of pressure parts of steam boilers. The results of investigations are also the elementof database of the materials characteristics of steels and alloys as well as welded joints made ofthem working under creep conditions developed by the Institute for Ferrous Metallurgy.Originality/value: The results and analysis of the investigations of microstructure andmechanical properties of HR3C steel after service under actual boiler conditions are presented.