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BEHAVIOUR OF A 1Cr‐1Mo‐0.25V STEEL AFTER LONG‐TERM EXPOSURE–I. CHARPY IMPACT TOUGHNESS AND CREEP PROPERTIES
Author(s) -
Moliniéa E.,
Piques R.,
Pineau A.
Publication year - 1991
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1111/j.1460-2695.1991.tb00681.x
Subject(s) - charpy impact test , materials science , creep , microstructure , metallurgy , embrittlement , ductility (earth science) , toughness , grain boundary , tempering , bainite , ferrite (magnet) , composite material , martensite
This paper deals with the effect of casting conditions and long‐term in‐service exposure on the Charpy‐V notch and creep properties of a 1Cr‐1Mo‐0.25V steel. The material is investigated under two conditions: (i) as‐cast in a thick part which produces a mixed ferrite‐bainite microstructure and (ii) as‐cast as a small ingot which produces a fully bainitic microstructure. The material from the thick part was taken from either the cold part (∽200°C) or the hot part (∽540°C) of a steam power casing which operated for about 150,000 h. A small shift in the ductile‐brittle transition temperature is shown after the long exposure time. This shift is related to segregation of phosphorus impurities along the grain boundaries as shown by Auger electron spectrometry. The bainitic microstructure exhibits a much better creep resistance compared to the thick part component material. Moreover, in the latter case, it is shown that long‐term in‐service exposure induces an increase in creep strain rate and a decrease in creep ductility at least for relatively short times to failure (≲1000 h). These variations in mechanical properties are briefly discussed in terms of microstructural changes. Scanning electron microscopy confirmed that grain boundary cavitation was responsible for decreasing the creep ductility at large times to failure (≳ 10,000 h).