The influences of impurity content, tensile strength, and grain size on in-service temper embrittlement of CrMoV steels

Journal Article · Wed Nov 01 04:00:00 EST 1989 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (USA)

DOI:https://doi.org/10.1007/BF02666669· OSTI ID:6816154

Cheruvu, N S; Seth, B B ^[1]

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1. Power Generation Operations Div., Westinghouse Electric Corp., Orlando, FL (US)

The influences of impurity levels, grain size, and tensile strength on in-service temper embrittlement of CrMoV steels have been investigated. The samples for this study were taken from steam turbine CrMoV rotors which had operated for 15 to 26 years. The effects of grain size and tensile strength on embrittlement susceptibility were separated by evaluating the embrittlement behavior of two rotor forgings made from the same ingot after an extended step-cooling treatment. Among the residual elements in the steels, only P produces a significant embrittlement. The variation of P and tensile strength has no effect on in-service temper embrittlement susceptibility, as measured by the shift in fracture appearance transition temperature (FATT). However, the prior austenite grain size plays a major role in service embrittlement. The fine grain steels with a grain size of ASTM No. 9 or higher are virtually immune to in-service embrittlement. In steels having duplex grain sizes, embrittlement susceptibility is controlled by the size of coarser grains. For a given steel chemistry, the coarse grain steel is more susceptible to in-service embrittlement, and a decrease in ASTM grain size number from 4 to 0/1 increases the shift in FATT by 61{degrees}C (10/10{degrees}F). It is demonstrated that long-term service embrittlement can be simulated, except in very coarse grain steels, by using the extended step-cooling treatment. The results of step-cooling studies show that the coarse grain rotor steels take longer time during service to reach a fully embrittled state than the fine grain rotor steels.

• OSTI ID: 6816154
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (USA), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (USA) Vol. 20A:11; ISSN MTTAB; ISSN 0360-2133
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
CHROMIUM-MOLYBDENUM STEELS
CRYSTAL STRUCTURE
EMBRITTLEMENT
FABRICATION
FORGING
GRAIN BOUNDARIES
IMPURITIES
KINETICS
MATERIALS WORKING
MECHANICAL PROPERTIES
MICROSTRUCTURE
PARTICLE SIZE
REACTION KINETICS
ROTORS
SIZE
TENSILE PROPERTIES
VANADIUM ALLOYS