Papers by Keyword: Multipass Deformation

Abstract: The multi-pass hot compression deformation behavior of the cast alloy with the composition of Mg-13Gd-4Y-2Zn-0.6Zr, was investigated, and the four-pass compression tests were conducted at the temperatures ranging from 350°C to 500°C and strain rate 0.01 s^-1. The experimental results showed that the alloys incurred different degrees of softening by multipass deformation. The microstructure evolution for the deformed alloy was investigated, the influence of the microstructure on the hardness properties of the alloy discussed. The tests reveal that dynamic recrystallization is not the main softening mechanism for this alloy; rather, kink deformation refines the grains to achieve the observed softening effect. The hardness test curve showed that the hardness increased gradually with an increasing number of deformation passes. The improvement of the main mechanical properties related to the strengthening by the grain refinement. In multipass deformation, the misorientation of the kink belt gradually increased,and refined the grains. On the other hand, the grain size of the eutectic phase at the grain boundary decreased with increase of deformation passes. In addition, the mechanical properties were improved by the distribution dispersion of tiny cuboidal particles and acicular-like phases in the matrix.

Abstract: Strain induced transformation (SIT) of austenite into ferrite has been frequently used as a powerful ferrite grain refinement mechanism. Ordinarily ferrite grain sizes of the order of 1-3μm are achieved via mechanical testing such as compression and torsion. Nonetheless, most of the work done so far employed continuous deformation in the range of 0.8 for compression experiments and in excess of this for torsion. SIT is a promising technique which may be used during actual hot rolling processing. However, in this case, not only deformations are applied with time interrupts between them but also the amount of total deformation allowable is relatively low, in order to attend to flatness and final gauges requirements. This work explores the consequences on SIT microstructure of deformation given in multiple passes as opposite to the usual continuous deformation presented in the literature. Multiple pass deformation at high temperature led to partial dynamic recrystallization and to a mixture of coarse and fine ferrite grains. Multiple pass deformation at the vicinity of Ar3 produced, on the hand, finer ferrite grains indicating that SIT took place. In this case, ferrite grains in the range of 1-3μm were produced and a much more homogeneous distribution of these grains was present.

Abstract: A new model of strain induced precipitation in niobium microalloyed austenite is proposed. This is based on the experimental observation of formation of microbands during hot deformation of iron – 30% nickel, which remains austenitic to room temperature. Precipitates are preferentially nucleated on nodes in the dislocation network in the microbands. This geometry enables features of earlier models to be simply explained, and facilitates extension of the model to multipass deformation. It is shown that the model captures all the essential features of previous experimental observations on microalloyed C – Mn steels. Currently, sensitivity analysis of the model and systematic experimental work are being undertaken to quantitatively validate the model.