Importance

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Abstract

The invention relates to a blank for a tool die, made of compound steel with a core of high speed steel and a surrounding ring of a different steel, said ring bringing about a prestress in the core. According to the invention, the prestress is due to the fact that the core consists of a high speed steel powder which has been compacted to full density, that the ring consists of a steel alloy, the residual austenite transformation to martensite and consequent volume increase of which is zero or considerably less than the residual austenite transformation to martensite of the high speed steel after the same heat treatment, and that the blank has been hardened and tempered to create in the core a compression stress as a result of the obstruction by the surrounding ring of the volume increase of the core. The invention relates also to a method for manufacturing such blanks. A high speed steel powder is filled into a thick-walled pipe, said pipe consisting of a steel different from high speed steel. The pipe is closed and subjected to hot isostatic compaction causing the high speed steel powder to become compacted to full density, forming a compact core in the pipe, so that a compound material is obtained. The pipe is cut into several discs or pieces of suitable lengths. The material is hardened and tempered, the high speed steel core during heat treatment undergoing a greater residual austenite transformation into martensite than the surrounding ring, a compression stress thus being created in the core.

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First Claim