Papers by Author: Liudmila M. Kaputkina

Abstract: Cast structure of ferric, austenitic and dual-phase high-nitrogen alloys and steels saturated with nitrogen at pressures of up to 3.2 MPa and solidified at cooling rates of 2 to 4•104 K/s has been investigated. Increasing the nitrogen concentration in the alloy and decreasing the cooling rate results in smaller nitrogen content in α and γ solutions and in larger content of crystallization nitrides.

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.

Abstract: Investigation into the effect of carbon and nitrogen contents of steels with an addition of chromium, nickel and manganese on their structure and properties after thermoplastic treatment has been carried out within the present study. For the physical modeling of thermoplastic treatment processes, a DIL 805A/D dilatometer with a deformation capability and a Gleeble 3800 simulator were used. The effect of carbon and nitrogen contents and the sum of these elements (C+N) on the hardening of the material during hot plastic working. The softening of the material depends on the C/N element ratio. The influence of the constituents under analysis on the dynamics of removal of cold work effects is different; C speeds up, while N slows down this process. The influence of the sum of the elements C and N depends on the type of nonmetallic phase precipitates. The structure and properties of such steels are determined by quenching and tempering cycles.

Abstract: Kinetics of deformation strengthening, polygonization and recrystallization processes have been studied, effects of alloying by nitrogen, combined carbon and nitrogen as well as by various other elements (Cr, Mo, Ni, Mn, V etc.) have been estimated for steels of different compositions and applications. Strain diagrams and structure state maps for the studied steels are presented. Strain diagram shape and attainable hot strength depend on the deformation conditions and basic alloying which determine strain hardening and diffusional processes of post-deformation softening. Alloying by nitrogen increases hot and cold strain hardening and retards recrystallization. Maximum strengthening obtained by cold deformation is accompanied by lowering of ductility and fracture toughness. Hence, it is applicable mainly to the austenitic steels. Nitrogen alloying enhances the austenite stability against g ® a transformation and consequently allows extending a composition range of steels which can be strengthened by cold deformation with large strains. The high-temperature thermomechanical treatment is more effective as a treatment improving a combination of mechanical properties. The schemes and regimes of thermomechanical strengthening treatments are proposed for low- and high- nitrogen containing steels of various structure classes.