Raychem Limited

Roger F Iles

Peter L Brooks

Greville B Brook

The present invention relates to methods for modifying the temperatures at which metallic compositions capable of undergoing reversible transformation from the austenitic state to the martensitic state will undergo such transformation. According to the present invention, the transformation temperature of such metallic compositions may be raised by slowly heating a metallic composition which is in the martensitic state to a temperature above that at which transformation to the austenitic state normally occurs. Usually the slow heating is terminated and the composition cooled to a temperature below the temperature at which slow heating was terminated.

Heat-treating method

Some metallic compositions that undergo a reversible transformation between austenitic and martensitic states as a result of being heated or cooled through critical temperature ranges may lose a portion or all of the ability to revert from martensite to austenite. That loss can be inhibited by 'aging' the composition prior to its conversion to the martensitic state by holding it at a temperature at which it exists in the austenitic state. The time required to significantly inhibit loss of reversibility may vary as the nature of the composition changes. For a specific composition, the time required typically is shortened as the holding temperature is raised. The ability of a composition to respond to preconditioning methods by which its A.sub.s temperature can be elevated may also be improved by aging in the austenitic state prior to attempting preconditioning.

Austenitic aging of metallic compositions

Certain metallic compositions undergo a reversible transformation between an austenitic state and a martensitic state. The temperature at which these compositions begin to undergo the transition from martensite to austenite can be raised by deforming an article formed from the composition and maintaining it while in the deformed state at a temperature at which the composition would normally exist in the austenitic state.

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Foster City, CA, United States of America

Roger F Iles