Dynamic Recrystallization Mechanisms of Nickel Niobium Alloys during Hot Working

This present work examines the influence of niobium in solid solution on the microstructural evolution of pure nickel at various deformation conditions. On this purpose, high-purity nickel and six model nickel-niobium alloys (Ni–0.01, 0.1, 1, 2, 5 and 10 wt. % Nb) were subjected to hot torsion test to large strains within the temperature range from 800 to 1000 °C at strain rates of 0.03, 0.1 and 0.3 s–1. Microstructural analyses were carried out using both optical and scanning electron microscopy-based electron back-scattered diffraction technique. The overall results showed the key role played by the Nb amount when coupled with various DRX mechanisms involved, i.e. DDRX, CDRX, and GDRX with respect to the prescribed deformation conditions, in reducing grain size and retarding DRX kinetics from which the microstructures of the examined materials such as Ni 2 and 10 wt. % Nb were seen evolving in different ways. In all these deformed materials, a transition from discontinuous dynamic recrystallization to continuous dynamic recrystallization was observed at low temperature and high strain rate whereas only discontinuous dynamic recrystallization occurred at high temperature.

Study on Deformation Behavior of Non–Hardenable Austenitic Stainless Steel (Grade X5CrNi18–10) by Hot Torsion Tests

The steel’s deformation resistance, in which high strain rates have an important influence on the mechanism of failure, might be obtained from a suitably instrumented torsion test. Determination of stainless steel deformability by hot torsion test is the only method that allows obtaining large deformations along the length of the test specimen, so it is mainly used to determine the characteristics at large plastic deformations. By this method, the hot deformability of stainless steel is determined by subjecting to hot torsion the cylindrical stainless steel specimens maintained at the deformation temperature in a tubular oven belonging to the Laboratory of Metal Rolling and Plastic Deformation, at the Faculty of Engineering – Hunedoara, University Politehnica Timişoara. For the experimental hot torsion tests, several stainless steel grades were used and included in a large series of studies destined to determining the deformation behavior of steel. Having in view the previous results obtained in the study of deformability characteristics of two stainless steels (hardenable martensitic stainless steel, grade X46Cr13 and non–hardenable ferritic stainless steel, grade X6Cr17), this paper includes the results of the hot torsion tests conducted to find the deformation behavior of the non–hardenable austenitic stainless steel (grade X5CrNi18–10). For analysis of laboratory hot torsion tests results the univariate and multivariate regression analysis was used, estimating the relationships among the hot–testing temperature, torque moment and number of torsions up to the breaking point of the specimens of austenitic stainless steel. Therefore, the optimum range of heating temperatures applied for deforming the studied steels results clearly from the deformability – temperature (plasticity – temperature and deformation resistance – temperature) diagrams. Correlations are useful because they can indicate a predictive relationship that can be exploited in the laboratory or industrial practice.

Application of Torsion Test for Determination of Rheological Properties of 5019 Aluminium Alloy

The paper presents the results of the study aimed at determination of plasticity of hard-deformed aluminium alloy grade 5019 in terms of parameters characteristic for the process of extrusion. The examinations were carried out in hot torsion test. Using the developed mathematical model of the analyzed alloy the mathematical modelling of torsion test was also performed.