Bainite self accomodating shear strains Free sex video chat recorded
Hence, when austenite transforms into grain boundary allotriomorphic ferrite, there is a uniform expansion, and vice-versa. Much more interesting deformations are associated with displacive transformations, where the shape change is in general described as an invariant-pane strain with a large shear component. For example, the freezing of water to ice is a reconstructive transformation where there is mass transport but no change in composition. Similarly, austenite in pure iron can transform into ferrite, either by a reconstructive mechanism involving diffusion, or by a martensitic mechanism. Edmonds) Materials Science and Technology 3 1987 441-449. Such a deformation leaves the plane of contact between the parent and product phases undistorted and unrotated. The strain energy associated with a constrained invariant-plane strain (IPS) is minimised when the product phase has a thin-plate shape. This is why Widmanstätten ferrite, bainite, acicular ferrite and martensite in steels grow in the form of plates. The familiar mechanisms of plastic deformation are slip, mechanical twinning and diffusion-induced creep. Christian) Theory of Transformations in Metals and Alloys, Part I, 2nd edition, Pergamon Press, Oxford, 1975. For very small plastic strains, the first two of these deformation modes are conservative - they preserve an atomic correspondence between the deformed and undeformed parts of the crystal so that the crystal contains a memory of its original shape. Alberry) Residual Stresses in Welded Constructions, Welding Institute, Cambridge 1977 Paper 2.
The purpose of the work presented here is to describe the relevance of these concepts to the welding of steels. Bhadeshia) Worked Examples in the Geometry of Crystals, Institute of Metals, London, 1987.
Cementite and -carbides are not included in the above classification, but it is believed that they grow by a displacive transformation mechanism at low temperatures.
Both kinds of reactions lead to changes in shape (Fig. The simplest of these occurs during reconstructive transformations in which the densities of the parent and product phases are different.
Little is known about the effect of stress on the development of microstructure in steel welds.
This paper contains an assessment of published data together with a description of the theory that is available for dealing with stress-affected transformations in steels.