| 摘要 |
The invention relates to apparatus and accompanying methods for use therein for forming a material (504), which has high strength and good workability, by rapidly deforming a suitable base metal (501) having a banded structure, such as illustratively a previously cold worked plain low carbon steel alloy, in order to generate a high rate of change in its internal energy which depresses the transformation temperatures of the base metal and thereby induces an allotropic phase transformation to occur therein. This rapid deformation can be produced through rolling, extrusion or forging and causes an extremely high heating rate to occur at each surface of the base metal. Prior to being deformed, the base metal is maintained at a fairly low temperature, e.g. at or near room temperature. The tooling, preferably rolls, that is used to provide the deformation is maintained at a modestly elevated temperature. Subsequent rapid deformation of the base metal causes an extremely high heating rate to occur at each surface thereof which, in turn, depresses the upper and lower on heating transformation temperatures at surface regions of the base metal and thereby causes the banded structure of the metal situated in these surface regions to transform into equiaxed grains. If the heating rate is insufficient to raise the temperature of the core of the base metal, which contains banded grains, to a level that causes metal in the core to transform, then the core will retain its banded cold worked structure. Consequently, the transformed surface regions (510, 510') will possess an equiaxed grain structure which provides increased ductility; while the core (511) of the material retains its banded (deformed) grain structure which provides high strength. Hence, the surfaces (512, 512') of the material become soft and ductile while the core possesses considerably higher amounts of hardness, yield and tensile strength than either surface. This material advantageously exhibits both good workability and relatively high strength. Alternatively, if the deformation rate is increased, such as by using small diameter rolls, in order to increase the bulk heating rate of the base metal and the appropriate thickness of the base metal has been chosen, then the entire base metal transforms into equiaxed grains. In this case, the resulting material (404) possesses a ductility and hence workability similar to that of a fully annealed structure.
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