18:4:1高速度鋼の衝撃値

Abstract

The Charpy impact test of the high speed steel of the type 18:4:1 was carried out under the following conditions; (i)Tests at room temperature, using specimens quenched from 1200, 1250 and 1300°, all tempered at 100, 250, 400, 550, 650 and 750° for twenty-minutes. (ii) Tests at the higher temperatures of 100, 200, and 300°, using specimens quenched from the same temperatures as under (i), all tempered at 400, 550 and 650° for the same time. There are many literatures on the impact value of the high speed steel of the type 18:4:1 after quenched and tempered, but none of them has tried the impact test of these heat-treated steels at higher temperature to which the high speed tool steel might attain during the cutting operation. That was the main reason why the author came to execute these tests under the conditions (i) and (ii), attaching special importance to (ii), and gained the following results. (1) The curve gained here between the Charpy impact value and the tempering temperature is almost similar to Grossmann's result(1), and the specimen quenched from the lower temperature shows the higher impact value. To obtain the toughest high speed tool steel, it is advisable to quench it from 1200° and temper at 350_??_400°. Moreover, the steel treated at these temperatures also shows, at the testing temperature of 300°, higher impact value than any one treated at other temperature does. (2) The impact tests of specimens quenched from 1200, 1250 and 1300°C, all tempered. at 550°, show that the steel quenched from 1200° has the higher impact value at the testing temperature of 300° than at 200°, while it has almost the same value at either testing temperature when quenched from 1250°. Reversely, when quenched from 1300°, the impact value is higher at the testing temperature of 200° than at 300°. So if a tool steel suffers higher cutting temperature and then is required to be tougher, it should be quenched below the temperature of about 1250°