Structure Formation and Strengthening of Hot Deformed Nitrogen-Containing Steels

Abstract

The structural and phase transformations and the strengthening of nitrogen-containing steels resulting from alloying and thermomechanical treatment have been investigated using X-ray diffraction analysis, optical microscopy, hardness measurements and tensile testing. For the modeling of thermomechanical treatment processes, a DIL 805A/D dilatometer with a deformation capability and a Gleeble 3800 simulator were used. Rational nitrogen or nitrogen plus carbon concentrations are determined by basic composition of an alloy. They are limited by the processes of precipitation of excess phases during crystallization and their dissolution during heating stage of the thermal or thermomechanical treatment. Combined alloying by carbon and nitrogen leads to significant complication of phase and structural transformations in steels, including hot deformation that manifests itself in changes of strain-stress diagram parameters. Effectiveness of increasing of a hot deformation resistance under alloying by nitrogen and carbon depends on a basic composition of steel, C/N ratio and temperature-strain rate deformation conditions.