The Precipitation Behavior and Mechanical Properties of Long Term Serviced HR3C/T92 Dissimilar Joint

Abstract

The dissimilar weld joint of HR3C steel and T92 steel is widely used in the ultra supercritical (USC) boiler due to the different service conditions of HR3C steel and T92 steel. It is important to study how serviced influenced the HR3C/T92 dissimilar joint. The HR3C/T92 dissimilar joint had already served 51020 h under 605 °C and 26.25 MPa. The microstructure and mechanical properties of the long term serviced HR3C/T92 dissimilar joint were tested by XRD, SEM, EPMA,TEM, the impact testing machine and the creep and stress rupture testing machine. The XRD results show that the weld is mainly γ-Fe, which is similar to the HR3C base metal, while the T92 base metal is mainly α-Fe. The SEM results indicate that serviced HR3C’s precipitation behavior is complicated, cause multiple precipitated phases precipitated during the service. Chain-liked M23C6precipitated along the grain boundary. M23C6phase cause the chromium depletion zone along the grain boundary. T92 base metal precipitated lots of carbide particles during the service. Those carbide particles are around 1 μm. The impact fracture of HR3C base metal is brittle fracture while the impact fracture of T92 base metal is ductile fracture. Moreover, the impact fracture of weld is mixed fracture. Chain-liked M23C6along the grain boundary is the main cause of the brittleness of serviced HR3C steel.The constant strain creep tests were proceeded under 650 °C, 700 °C and 750 °C. The high-temperature creep resistance of HR3C base metal is better than that of T92 base metal after service. The resistant to high-temperature creep of served joint is similar to that of serviced T92 base metal. With the increase of temperature, the creep resistance of the T92 base metal decreases the most. On the contrary, the creep resistance of the HR3C base metal shows the minimum reduction.