High temperature plastic deformation of CuZn30 brass was investigated in the temperature range between 650 • C and 850 • C. Torsion tests were performed for experimental plan according to test array 5 × 4, i.e. five temperatures 650, 700, 750, 800, 850 • C and four speeds of torsion shear strain rate 0.5, 2.5, 12.5, and 25 s −1. Mathematical model has been developed to predict high-temperature shear stress behaviour of CuZn30 brass. Explicit equation, which is a function of peak stress, temperature and shear strain rate, was used in the mathematical model. There are four constants in the equation; one of those is the activation energy which for CuZn30 brass reaches the value Q = 180.3 kJ mol −1. Measured and calculated values of shear stress are shown in graphs in dependence on the value of deformation, where the temperature of deformation and the speed of deformation are the parameters for the particular curves. The predicted results are in accordance with the experimental curves stress-deformation that can be used to model the behaviour of hot extrusion pressing of CuZn30 brass.

No abstract

No abstract

The aim of this paper was to analyze the high temperature embrittlement of TiNb IF steel using plastometric torsion tests. High temperature embrittlement in the temperature range 600 -1200°C is a problem mainly connected with additions of microalloying elements to steel and also with inhomogeneous and coarse-grained microstructure formed during continuous casting. Reduction of high temperature ductility can lead to cracks in the slab. These surface cracks can easily become oxidised, and then they do not fuse during forming operations. A significant decrease in hot ductility of the analyzed steel occurred in the stable austenite just above the temperature of 1100°C, where the number of rotations to failure (N f ) in the sample was lowest, at 28.4. The cavities ratio was 1.9%, which occurred mainly below the fracture line. At the bottom of the dimple transcrystalline ductile failure (DTDF), complex particles based on Al, Ti, Mn, S, N were observed. In this temperature range the embrittlement is mainly attributed to fine precipitation of sulfides, oxides, particulates based on microalloys as well as segregation of impurities on the austenite grain boundaries.

The aim of this work was to observe the relationship between hot ductility and morphology, distribution and size of particles in TiNb IF steel after hot torsion testing at the critical temperatures of deformation with low as well as maximum values of plasticity. Transmission electron microscopy showed that the particles at all temperatures of deformation with minimum number of turns to failure e.g. 1132°C (33.72 rev.), 946°C (6.24 rev.), 637°C (5.54 rev.) as well as with maximum value of plasticity at 844°C (1726 rev.) were of globular, cuboid or elliptical shape. EDX analysis revealed that there were different types of particles such as carbides, sulfides, and carbonitrides of Ti and Nb, Al and Si oxides, Mn sulfides, and phosphides. Quantitative evaluation of particle size in the carbon extracted replicas showed 20% of total number of particles with size 2r = 30-39 nm and an average linear dimension = 42 nm at the deformation temperature of 1132°C. There were 28% of the particles with size 2r = 20-29nm and = 41nm at the temperature of 946°C while at the temperature of 637°C there were 29% of particles with size 2r = 20-29 and 26% with size 2r=10-19 nm and = 41 nm. In the case of maximum plasticity (1726 rev.) at 844°C, the presence of large particles was confirmed with = 105 nm size and 9% distribution in three size categories of 20-29, 30-39, 90-99 nm.