Abstract: This invention relates to a blind fastener having a hollow sleeve with high surface hardness and sufficient elongation, and to a novel heat treatment method therefor. The method for the heat treatment of the blind fastener includes austempering. The austempering includes a step in which a hollow sleeve of cold-rolled low carbon steel with a carbon percentage of 0.08 to 0.13% is heated and maintained from 800° C. to 950° C. during carburization, and a subsequent step in which isothermal maintenance is performed from 320° C. to 500° C. The resulting carbon percentage (CP) value is from 0.3 to 0.5%. Even in the case of a low carbon steel blind fastener, the austempering can harden the surface of the sleeve and soften the inner portion other than the surface for suitable elongation in order to provide a blind fastener having a sleeve with high surface hardness and sufficient elongation.

Abstract: The present invention provides an improved structural assembly constructed of a plurality of structural members secured together. At least one of the plurality of structural members defines a first region characterized by comparatively high operational stress and a second region having a locally refined grain structure positioned such that the second region at least partially encompasses the first region to thereby enhance the strength, toughness and fatigue resistance of the at least one structural member in the first region. The present invention also provides a method for selectively improving the strength, toughness and fatigue resistance of a structural member in a region of high operational stress including the steps of casting the structural member in a pre-selected configuration. Regions of the structural member having comparatively high operational stress are identified. The structural member is secured to prevent movement.

Abstract: The present invention provides an improved structural assembly constructed of a plurality of structural members secured together. At least one of the plurality of structural members defines a first region characterized by comparatively high operational stress and a second region having a locally refined grain structure positioned such that the second region at least partially encompasses the first region to thereby enhance the strength, toughness and fatigue resistance of the at least one structural member in the first region. The present invention also provides a method for selectively improving the strength, toughness and fatigue resistance of a structural member in a region of high operational stress including the steps of casting the structural member in a pre-selected configuration. Regions of the structural member having comparatively high operational stress are identified. The structural member is secured to prevent movement.