1Department of Sakai, Industrial Research Institute, Osaka Prefecture, Sakai
The author has carried out torsion impact tests for a carbon tool steel to study the toughness of highly hardened tool steels that are usually hard and poor in ductility in the service condition. According to these tests, it was shown that the curve of relations between the impact value and the tempering temperature has a high peak near 200°C and a deep dip near 250°C in the tempering at temperatures lower than 300°C. In order to more comprehensively investigate these phnomena, static torsion tests were performed and the results were compared with those of the previous torsion impact tests.
As a result, it has been clarified that (1) the tempering temperature producing a peak of the impact value slightly elevates with increase of the austenitizing temperature, (2) that the changes in the impact value are mainly influenced by the change of plastic deformation work defined by dividing the area under torque-twist angle curve, and (3) the toughness of hardened tool steel is significantly affected not only by the tempering temperature but by the tempering time.
Thus it has been decided that the static torsion test as well as the impact torsion test is very effective as a toughness testing method for hardened tool steel in which strength is more essential than ductility.
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