Improved superclean NiCrMoV rotor steel
- Bethlehem Steel Corp., PA (USA). Homer Research Lab.
Due to its excellent creep rupture properties and relative economy, silicon-deoxidized, tempered bainitic 1%CrMoV steel is currently used extensively for high-temperature steam turbine rotor forgings operating at temperatures up to 565{degree}C. However, there is considerable impetus to improve the toughness of this steel while maintaining its current level of creep rupture strength and vice versa. The toughness of 1%CrMoV steel is improved by lowering the bainite start (B{sub s}) temperature in a superclean' base composition which is essentially free of Mn, Si, P, S, Sb, As and Sn. The B{sub s} temperature can be lowered through the addition of alloying elements (i.e. C, Ni, Cr and Mo). Through suitable alloy additions, the 50% FATT of this grade was lowered from approximately 100{degree}C to below room temperature. This improved toughness provides the opportunity to eliminate the special precautionary procedures currently used in the startup and shutdown of steam turbines. In general, the creep rupture strengths of these new superclean' steels equal or exceed that of the standard 1%CrMoV steel. In addition, the superclean' steels have not been found to be susceptible to temper embrittlement, and have similar room temperature fatigue crack propagation characteristics and elevated tensile properties to the standard 1%CrMoV steel. The most promising steels in terms of a balance between creep rupture and toughness properties contain 2.5% Ni and 0.03%/0.04% Nb (for austenite grain refinement and enhanced tempering resistance), i.e. 2.5NiCrMoVNb steel. These new steels may also find application in combination high-temperature -- low-temperature rotors and gas turbine rotors. 106 refs., 34 figs., 10 tabs.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (USA); Bethlehem Steel Corp., PA (USA). Homer Research Lab.
- Sponsoring Organization:
- EPRI
- OSTI ID:
- 6830412
- Report Number(s):
- EPRI-ER-6887
- Country of Publication:
- United States
- Language:
- English
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IMPACT STRENGTH
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