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

Abstract

The influence of tempering, prestraining, and retempering on the strength and toug .ness of martensitic and bainitic 4340 steel rods was investigated. The initial neat 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. Reduct .ons of area of 4 tc percent were effected by cold drawing through a die with and without backpull, followed by a retempering treatment. Ultimate ter.sile strengths approaching 385,000 psi for the martensitic stricture and 283,000 psi for the bainitic structure resulted with yield-tensile strength ratios approaching umity. 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 retempering temperature.

Enhanced Spring Steel’s Strength Using Strain Assisted Tempering

“…Still, yield and tensile strength remain very close if second tempering is carried out at low temperatures as was found for samples SAT 200–200, SAT 250–200, SAT 250–250 and SAT 250–300 ( Table 5 ). A similar effect was observed in [ 23 ]. A second tempering increased the difference between yield and tensile strength at a second tempering temperature above 300 °C.…”

Effect of Double-Step and Strain-Assisted Tempering on Properties of Medium-Carbon Steel

“…As a result, the nucleation and propagation of the fatigue crack are delayed, thus increasing the fatigue life [22]. In [23], the strength and toughness of martensitic and bainitic 4340 steel rods were investigated after strain-assisted tempering (SAT).…”