Why high-alloy material shearing machine blades need to be tempered multiple times: High-alloy blades that are quenched at high temperatures need to be tempered multiple times. 

For example, medium-thick plate shears made of H13 (4Cr5MoSiV1) steel require more than two tempers. This is because these high-temperature quenched high-alloy steel blades contain more retained austenite after quenching. The purpose of multiple tempering is to allow the retained austenite to transform into martensite during tempering cooling, and the martensite formed from retained austenite then transforms into tempered martensite. 

If a single long tempering is used, it is difficult to achieve the above structural transformations, resulting in insufficient tempering. This will lead to inconspicuous secondary hardening, poor dimensional stability of the workpiece, higher brittleness, and lower service life. 

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