Influence of Tempering, Prestraining, and Retempering on the Strength and Toughness of High-Strength 4340 Steel

摘要

The influence of tempering, prestraining, and retempering on the strength and toughness of martensitic and bainitic 4340 steel rods was investigated. The initial heat treatment consisted of a quench and temper to obtain martensite in one group and formation of bainite at 575 F followed by tempering in the second group. Reductions of area of 4 to 5 percent were effected by cold drawing through a die with and without backpull, followed by a retempering treatment. Ultimate tensile strengths approaching 385,000 psi for the martensitic structure and 283,000 psi for the bainitic structure resulted with yield-tensile strength ratios approaching unity. Notch tensile strength of the bainite was superior to that of martensite at comparable strength levels. The prestraining also caused a yield point drop and/or serrations in the flow curves. This was influenced by specimen test temperature and strain rate, tempering temperature, and retermpering temperature. (Author)