STP672: Structure-Property Relationships for Pearlite-Reduced Mo-Nb Steels Finish-Rolled Moderately Below Ar3

    Coldren, AP
    Staff metallurgist, research supervisor, and manager of High Strength Steel Development, Climax Molybdenum Company of Michigan, A Subsidiary of AMAX, Inc., Ann Arbor, Mich.

    Eldis, GT
    Staff metallurgist, research supervisor, and manager of High Strength Steel Development, Climax Molybdenum Company of Michigan, A Subsidiary of AMAX, Inc., Ann Arbor, Mich.

    Tither, G
    Staff metallurgist, research supervisor, and manager of High Strength Steel Development, Climax Molybdenum Company of Michigan, A Subsidiary of AMAX, Inc., Ann Arbor, Mich.

    Pages: 19    Published: Jan 1979


    Abstract

    A study of five laboratory steels was conducted to determine the relative effects of ferrite grain refinement, dislocation substructure, and niobium (carbon, nitrogen) [Nb(C,N)] precipitation strengthening on the as-rolled strength and toughness properties of 19-mm (0.75-in.) plates finish rolled in the two-phase region, moderately below the Ar3 temperature. The steels were molybdenum-niobium (Mo-Nb) pearlite-reduced steels having a nominal composition range of 0.08C, 1.4Mn, 0.1Si, 0.2/0.4Mo and 0/0.6Nb. The amount of ferrite formed prior to the last pass and the percent reduction imparted on the last pass were varied while the finishing temperature was held constant at 745°C (1375°F).

    It was found that the introduction of deformed ferrite into the structure brought two strengthening effects: dislocation substructure and, in the niobium-containing steels, strain-enhanced precipitation. The combined effect of these mechanisms reached a maximum in plates containing approximately 30 to 40 percent deformed ferrite that had experienced a 20 percent reduction on the final pass. The impact toughness was not impaired by this method of upgrading strength.

    Regarding grain refinement, the 0.2Mo-0.035Nb steel experienced increases in yield strength of up to 85 MPa (12.4 ksi) due to the additional grain refinement produced by rolling below the Ar3 temperature instead of finishing just above the Ar3. This type of strengthening was smaller in the 0.2Mo-0.06Nb steel and absent in the 0.4Mo-0.06Nb steel, because the initial grain sizes of these steels were finer, and lowering the finish-rolling temperature produced little or no further refinement.

    Keywords:

    steels, microstructure, pearlite-reduced steels, ferrite grain refinement, substructure, precipitation, controlled rolling, impact toughness


    Paper ID: STP36867S

    Committee/Subcommittee: E04.05

    DOI: 10.1520/STP36867S


    CrossRef ASTM International is a member of CrossRef.