STP1042: Temper Embrittlement Susceptibility and Toughness of A 508 Class 3 Steel

    Tavassoli, A-A
    Manager of Scientific Studies and deputy head of a section, DMECN, IRDI, CEN-Saclay, Commissariat a l'Energie Atomique, Gif sur Yvette,

    Soulat, P
    Manager of Scientific Studies and deputy head of a section, DMECN, IRDI, CEN-Saclay, Commissariat a l'Energie Atomique, Gif sur Yvette,

    Pineau, A
    Professor, Centre d'Etudes de l'Ecole des Mines,

    Pages: 13    Published: Jan 1989


    Abstract

    A correlation has been established between the scatter in Charpy and fracture toughness results of an ASTM Specification for Quenched and Tempered Vacuum-Treated Carbon and Alloy Steel Forgings for Pressure Vessels (A 508-84a) Class 3 (UNS K12042) pressure vessel forging steel and the appearance of intergranular facets on the rupture surfaces of specimens tested at low temperatures. Extent of the intergranular rupture has been found to increase with prolonged aging at 500 to 550°C or following an embrittling treatment known as step cooling. Both intergranular rupture and the resultant increase in ductile to brittle transition temperature were reduced or eliminated by a de-embrittling treatment at temperatures ranging from 630 to 660°C, with optimum results obtained at 640°C. Auger analyses carried out on specimens exhibiting cleavage and intergranular rupture have shown segregation of carbon, molybdenum, sulfur, and, in particular, phosphorus at the grain boundaries.

    A statistical analysis based on a local rupture criterion is used to describe the probability of intergranular and cleavage failures. Based on the observations made, the main cause of scatter in low temperature results is concluded to be heterogeneous segregation of impurities in thick sections with a corresponding shift in ductile to brittle transition temperature. A slight increase in austenitization and de-embrittling temperatures is suggested in order to reduce segregation and improve toughness.

    Keywords:

    pressure vessel, forging, plate, pressurized water reactor (PWR), A508-Class 3, A533B, temper embrittlement, residual elements, segregation, cleavage, intergranular, Charpy, toughness, axisymmetric specimens, auger spectroscopy


    Paper ID: STP24573S

    Committee/Subcommittee: A01.11

    DOI: 10.1520/STP24573S


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