The metallurgical design of C125 grade for sour service has been carried out based on the knowledge of basic features governing toughness/KISSC in fully martensitic low-alloy steels which after tempering reach yield strength levels of 850 to 1000 MPa. In this work the effect of micro-alloying and heat treatment is analysed with respect to microstructure, precipitation evolution and SSC resistance in mildly sour environment. Results showed that in order to increase toughness and SSC resistance a suitable combination of V and Nb is required. Improvements were related to fine martensite packets and to high tempering temperatures required to achieve the desired strength, which promoted cementite spheroidizing.

Subject
Tubular goods, Materials, Carbides, Precipitation (solids), Composition, Tempering temperature, Microstructure, Precipitates, Steel, Sulfide stress cracking, Toughness, Yield strength, Martensite
Keywords:
Oil Country Tubular Goods (OCTG), C125, sour service, metallurgical design, toughness, NACE TM 0177-96 methods D and A
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2006
Association for Materials Protection and Performance (AMPP)
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