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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Manufacturing Experience in an Advanced 9%CrMoCoVNbNB Alloy for Ultra-Supercritical Steam Turbine Rotor Forgings and Castings

[+] Author and Article Information
Ian Chilton

Alstom Power Ltd.,
Rugby CV21 2NH, UK

Pawel Jaworski

Alstom Power Sp. z.o.o.,
Elblag 82-300, Poland

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received July 13, 2012; final manuscript received November 22, 2012; published online May 20, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(6), 062101 (May 20, 2013) (8 pages) Paper No: GTP-12-1273; doi: 10.1115/1.4023606 History: Received July 13, 2012; Revised November 22, 2012

Advanced 9–12%Cr martensitic stainless steels to enable extension of steam turbine operating temperatures beyond 565 °C have been under development since the 1980s. Steam turbines with operating temperatures approaching 600 °C based on the first generation of these improved alloys, which exploited optimized levels of Mo, W, V, Nb, and N, entered service in the 1990s. Around the same time, a second generation of advanced alloys was developed incorporating additions of Co and B to further enhance creep strength. These alloys have recently been exploited to enable steam turbines with operating temperatures of up to 620 °C, and this new generation of steam turbines is now beginning to enter service. This paper describes the background to the development of these alloys and the experience gained in their application to the manufacture of high temperature rotor forgings and castings.

Copyright © 2013 by ASME
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Figures

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Fig. 1

Improvement in creep strength at 200,000 h for CB2 compared with boron-free steel

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Fig. 2

Creep strength as a function of Larson–Miller parameter for CB2 welds

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Fig. 3

Improvement in creep strength at 200,000 h for FB2 compared with boron-free steel

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Fig. 4

Creep strength of FB2-1%CrMoV steel dissimilar welds at 550 °C

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Fig. 5

Overall layout of typical 600/620 °C steam turbine (single HP turbine, single IP turbine, and double LP turbines)

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Fig. 6

Ultra-supercritical HP module design

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Fig. 7

Ultra-supercritical IP module design with inlet valves

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Fig. 8

Design of experimental casting and feeders

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Fig. 9

Microstructures in as-cast condition—grain boundaries decorated with films and colonies of fine lamellar carbides

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Fig. 10

Microstructures after austenitizing at 1095 °C and tempering at 735 °C—uniform tempered martensite

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Fig. 11

Collision of solidification zones creating areas vulnerable to cracking

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Fig. 12

Simulation of solidification to identify areas susceptible to shrinkage

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Fig. 13

Load and deformation velocity during upsetting with press limited to 50 MN

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Fig. 14

Temperature (a) and strain (b) distribution after the upsetting operation in Fig. 13

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Fig. 15

Load and deformation velocity during upsetting with press capacity over 100 MN

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Fig. 16

Temperature (a) and strain (b) distribution after the upsetting operation in Fig. 15

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