Production and properties of a superclean 2.5% Ni-CrMoV HP/LP rotor shaft. Final report
Technical Report
·
OSTI ID:10135581
- Japan Steel Works Ltd., Muroran, Hokkaido (Japan)
- Toshiba Corp., Yokohama (Japan)
- General Electric Co., Schenectady, NY (United States)
Based on the successful results of laboratory work by Bodnar and Hansen of BethForge and Jaffee of EPRI on an improved CrMoV rotor steel, a superclean 2.5%Ni-CrMoV trial high pressure-low pressure rotor shaft was produced by the Japan Steel Works, Ltd. (JSW). The shaft consisted of a 1270 mm diameter high pressure (HP) section and a 1750 mm diameter low pressure (LP) section. The chemistry and dimensions of the ingot were optimized based on a study at JSW with special attention being directed to the reduction of chemical segregation in the ingot. The steel was refined in a basic electric furnace and a ladle refining furnace, and then cast into a 90 metric ton ingot using the vacuum carbon deoxidation (VCD) process. After the preliminary heat treatment by double normalizing, the HP and LP portions were quenched differentially. The LP portion was water spray quenched from 935 C{degree} and the HP section was forced air cooled from 950{degree}C. The LP portion of the rotor shaft was tempered to two tensile strength levels of 860 MPa and 790 MPa by two stage tempering for evaluation. The FATT at the center of the LP and HP sections was approximately 22 C{degree} and 3 C{degree}, respectively, for a strength level of 790 MPa. Increasing the tensile strength of the LP section to 860 MPa increased the FATT to about 49 C{degree}. Creep rupture tests revealed that the creep rupture strength of the HP section was equivalent to the strength of a conventional CrMoV rotor steel. Generally, other characteristics such as fatigue properties and fracture toughness were equal to or exceeded those of the standard CrMoV turbine rotor steel levels. However, the notch rupture ductility was somewhat marginal and could interfere with the use of this alloy in steam turbine applications. The apparent cause of this difficulty was the removal of niobium from the original proposed chemistry because of concern about the potential adverse effects of chemical segregation.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (United States); Japan Steel Works Ltd., Muroran, Hokkaido (Japan); Toshiba Corp., Yokohama (Japan); General Electric Co., Schenectady, NY (United States)
- Sponsoring Organization:
- Electric Power Research Inst., Palo Alto, CA (United States)
- OSTI ID:
- 10135581
- Report Number(s):
- EPRI-TR--103689; ON: UN94008750
- Country of Publication:
- United States
- Language:
- English
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