Abstract
The microstructure and toughness of tungsten inert gas (TIG) backing weld parts in low-pressure steam turbine welded rotors contribute significantly to the total toughness of the weld metal. In this study, the microstructure evolution and toughness of TIG weld metal of 25Cr2Ni2MoV steel low-pressure steam turbine welded rotor under different post-weld heat treatment (PWHT) conditions are investigated. The fractography and microstructure of weld metal after PWHT are characterized by optical microscope, SEM, and TEM, respectively. The Charpy impact test is carried out to evaluate the toughness of the weld. The optical microscope and SEM results indicate that the as-welded sample is composed of granular bainite, acicular ferrite and blocky martensite/austenite (M-A) constituent. After PWHT at 580 °C, the blocky M-A decomposes into ferrite and carbides. Both the number and size of precipitated carbides increase with holding time. The impact test results show that the toughness decreases dramatically after PWHT and further decreases with holding time at 580 °C. The precipitated carbides are identified as M23C6 carbides by TEM, which leads to the dramatic decrease in the toughness of TIG weld metal of 25Cr2Ni2MoV steel.
Highlights
Steam turbines play an important role in modern power plants
As a result of concerns related to the environmental impact from pollutants and greenhouse gas, the power industry has had to improve thermal efficiency by developing ultra-supercritical (USC) combustion technology, which has led to elevated steam temperatures and continuously increasing demand being placed on their components’
The results showed that a large amount of stabilized martensite/austenite (M-A) islands appeared after the tempering treatment at 350 ◦ C, while the M-A islands decomposed into precipitated carbide distributing along the grain boundary, which is responsible for the tempering brittleness
Summary
Steam turbines play an important role in modern power plants. As a result of concerns related to the environmental impact from pollutants and greenhouse gas, the power industry has had to improve thermal efficiency by developing ultra-supercritical (USC) combustion technology, which has led to elevated steam temperatures and continuously increasing demand being placed on their components’performance [1]. Steam turbines play an important role in modern power plants. As a result of concerns related to the environmental impact from pollutants and greenhouse gas, the power industry has had to improve thermal efficiency by developing ultra-supercritical (USC) combustion technology, which has led to elevated steam temperatures and continuously increasing demand being placed on their components’. The material used to manufacture steam turbine rotors needs to have excellent performance, such as high ductility, deep hardenability, high strength, high fatigue strength and creep resistance [4,5,6]. NiCrMoV refractory steel has been proved to be a suitable material for meeting these requirements of steam turbine rotor materials [7,8,9]. It is difficult to manufacture high-quality steam turbine rotors by forging directly, because of their heavy section and large dimensions. Welded rotors have been widely used, with advantages including
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
