Showing papers by "Kaneaki Tsuzaki published in 1994"

Formation mechanism of bainitic ferrite in an Fe-2 Pct Si-0.6 Pct C alloy

Abstract: The bainite transformation at 723 K in an Fe-2 pct Si-0.6 pct C alloy (mass pct) was investigated with transmission electron microscopy (TEM) and quantitative metallography to clarify the growth mechanism of the ferritic component of bainite. In early stages of transformation, the bainitic ferrite was carbide free. The laths of bainitic ferrite within a packet were parallel to one another and separated by carbon-enriched retained austenite. The average carbon concentration of the bainitic ferrite was estimated to be 0.19 mass pct at the lowest, indicating that the ferrite was highly supersaturated with respect to carbon. The laths did not thicken during the subsequent isothermal holding, although they were in contact with austenite of which the average carbon concentration was lower than the paraequilibrium value. In the later stage of transformation, large carbide plates formed in the austenite between the laths, resulting in the decrease in the carbon concentration of the austenite. Subsequently, the ferrite with a variant different from the initially formed ferrite in the packet was decomposed for the completion of transformation. The present results indicate that the bainitic ferrite develops by a displacive mechanism rather than a diffusional mechanism.

Effects of Rolling Reduction and Annealing Temperature on the Recrystallization Structure of Solidified Columnar Crystals in a 19% Cr Ferritic Stainless Steel

Abstract: The cold-roling and recrystallization behavior of solidified columnar crystals in a 19% Cr ferritic stainless steel has been investigated. As the rolling reduction increased, the recrystallization rate increased and the recrystallized grain size decreased. However, the (001) [110] initially-oriented columnar grains were hard to recrystallize without regard to rolling reduction so that the recrystallization structure was very inhomogeneous in grain size even in a heavily-rolled (90% rolled) specimen. The recrystallization rete of 70% rolled specimens increased as the annealing temperature increased. In particular, at the temperatures where carbides did not precipitate the recrystallization rapidly completed and a coarse-grained structure formed in a short time annealing because of rapid grain growth. As a result, in the Fe-19% Cr ferritic columnar crystals a favorable recrystallization structure with fine and uniform grain size cannot be obtained simply by increasing rolling reduction or by controlling annealing temperature.

Role of pre-straining of austenite in the improvement of shape memory effect in an Fe-33Mn-6Si alloy*

Abstract: The shape memory behavior of an Fe-33%Mn-6%Si alloy pre-strained at 573K (above Af) by various amounts up to 7% was examined. The shape memory effect was improved by pre-straining. However, it was hardly dependent on the amount of pre-strain and a small pre-strain of 1% was enough to improve the shape memory effect. The results were discussed from the viewpoint of the change in the strength of matrix and the flow stress in a shape change by applying the pre-strain. The importance of crystallographic reversibility in fee ↔ hcp martensitic transformations for the shape memory effect was also pointed out from the surface relief observation.