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The usual specifications for Cr-Mo-V steel castings fix modest levels of yield strength (350 to 450 MPa) in the hope of obtaining acceptable toughness. But this optimism sometimes leads to disappointment when only the components themselves are considered and not the attached parts. Tests carried out on Cr-Mo steel casings that have 100 000 h or more of service life show that, if toughness is sufficiently high in the as-received condition, and if certain precautions are taken into account at start-up, one may accept service embrittlement and even allow casings that reveal cracks caused by creep or thermal fatigue to remain in service. The aim of the work discussed in this paper has been to compare different grades of Cr-Mo steel distinguished in particular by chromium and nickel contents. Two subjects have been dealt with: the influence of the chemical composition on the optimal conditions of hardening and tempering and the preliminary study of age embrittlement (evaluated by the translation of Charpy V-notch and ductile fracture toughness transition curves).

Today with the rapid development of nuclear electricity generation on a large scale, there arises the problem of maintaining fossil fuel generating stations that have been in operation for some 100 000 h or more. Operators usually hope to prolong the service life of units where safety margins permit, with objectives attaining beyond 150 000 h. This is an extremely ambitious program that is thwarted by the very nature of the work demanded from this type of thermal generating station: namely fulfillment of the needs of daily and seasonal peak periods, which increase the number of severe thermal operating transients. This paper examines the question of metallurgical studies carried out by Alsthom-Atlantique on stator steel castings with a view to estimating their expectation of life potential. This work constitutes the second part of a study entitled “Quenching, Tempering, and Aging of Chromium-Molybdenum-Vanadium Cast Steels” in the Journal of Evaluation and Testing, Vol. 9, No. 2, March 1981.

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