18-4-2型高速度鋼の性質におよぼすCの影響について

Abstract

To investigate the influence of the carbon on the properties of 18-4-2 type high speed steel which were used for forming or finishing cutting tool, the authors measured the critical temperature, Ms point, quenched and tempered hardness, retained austenite, dimensional change, toughness and mechanical properties at high temperature.The results obtaned were as follows:(1) The critical temperature and Ms point were lowered with the carbon addition and the beginninig curve of the isothermal transformation was moved to long time side with the carbon addition.(2) The quenched hardness was raised with the austenitizing temperature in the lower carbon content and was lowered as the carbon increased to more than 0.76%. For obtaining the fully quenched hardness, the austenitizing time needed about 1 or 2 minutes for 16 φ×10mm specimen. The tempering hardness as the secondary hardening was raised with the carbon addition and with the quenching temperature elevated.(3) The quantity of retained austenite measured by the magnetic method increased with the carbon addition. During the tempering, decomposition of the retained austenite was occurred at about 500°C rapidly and all amount of them was entirely decomposed between 575°C to 600°C(4) The toughness measured by the static bending test decreased with the carbon addition and the impact strength at elevated temperature also decreased with the carbon addition. The tensile strength, elongation and reduction of area at elevated temperature were hardly affected by the carbon addition, but were affected by the tempering and testing temperature.