Eigenschaften von bei niedrigen Temperaturen angelassenen SAE-43xx-Stählen

Uniaxial tensile tests were performed on 4330, 4340 and 4350 steels in the as-quenched condition and after quenching and tempering at 150, 175 and 200°C for times of 10 minutes, 1 hour and 10 hours. Strength parameters decreased and ductility parameters increased continuously with increasing tempering. Mechanical properties are presented as a function of tempering conditions and steel carbon content, and hardness and ultimate strength changes are given as a function of Hollomon-Jaffe tempering parameters. All tempered specimens, except for some lightly tempered 4350 specimens, deformed plastically through necking instability and failed by ductile fracture. The stresses required for the ductile fracture, estimated from an analysis of the interfacial stresses at particles in the neck at fracture, showed no systematic variation with carbon content or tempering conditions despite significant variations in deformation and strain hardening. As-quenched specimens of the 4340 and 4350 steels, and some of the lightly tempered 4350 steels failed by brittle mechanisms. The deformation and fracture of the low-temperature-tempered 43xx steels are discussed in terms of the changes in fine structure caused as, during tempering, transition carbides increasingly replace dislocations with and without carbon atom segregation in the as-quenched martensite.