STP1042

    The Influence of Residual Copper in Annealed and Postweld Heat Treated 2-1/4Cr-1Mo Steel

    Published: Jan 1989


      Format Pages Price  
    PDF (716K) 29 $25   ADD TO CART
    Complete Source PDF (6.4M) 29 $70   ADD TO CART


    Abstract

    Vacuum arc remelted (VAR) and electroslag remelted (ESR) 2-1/4Cr-1Mo tube-sheet forgings were produced for the steam generators of the now terminated Clinch River breeder reactor project. The forgings were produced to American Society of Mechanical Engineers (ASME) SA336 Grade F22a, and test metal in the annealed and simulated postweld heat treated (PWHT) condition had to meet the minimum yield strength requirement of 207 MPa. All of the VAR forgings passed the yield strength requirement, while all of the ESR forgings marginally failed the yield strength requirement. The main difference between the two steels was the lower copper content of the ESR forgings (for example, 0.046 versus 0.13%). The yield strength increment in the annealed condition was accounted for by solid-solution strengthening due to copper, whereas in the PWHT condition, precipitation strengthening due to ϵ-copper accounted for the difference. This additional strengthening increment would have been sufficient to ensure that all of the ESR forgings met the minimum yield strength requirement. Both strengthening increments were confirmed with laboratory-produced and heat treated 2-1/4Cr-1Mo steels with copper levels of 0, 0.16, and 0.32%, and were found to be compatible with the most recent iron-copper phase equilibria. Yield strength was also found to increase by increasing the cooling rate from the PWHT. This strengthening increment is attributed to solid-solution strengthening due to carbon, nitrogen, molybdenum, and chromium, and precipitation strengthening due to (M2X) carbides. The data presented in this paper provide an example of residual copper affecting the mechanical properties of a 2-1/4Cr-1Mo steel. Furthermore, much of the data base used to establish the mechanical property capabilities of 2-1/4Cr-1Mo steel was developed using steels that had relatively high copper levels (or were not analyzed for copper), and were air-cooled from the PWHT, thus producing a data base of yield strength values that are higher than can be achieved under the constraints of the specification.

    Keywords:

    2-1/4Cr-1Mo steel, residual copper, full annealing, iron-copper phase diagram, postweld heat treatment, precipitation strengthening, solid-solution strengthening, carbide strengthening, steam generator, tubesheet forgings


    Author Information:

    Bodnar, RL
    Senior research engineer and research fellow, Bethlehem Steel Corporation, Bethlehem, PA

    Bramfitt, BL
    Senior research engineer and research fellow, Bethlehem Steel Corporation, Bethlehem, PA

    Cappellini, RF
    Director of technology and new product development, Bethlehem Steel Corporation, Bethlehem, PA


    Paper ID: STP24580S

    Committee/Subcommittee: A01.22

    DOI: 10.1520/STP24580S


    CrossRef ASTM International is a member of CrossRef.