18-4-1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 18-4-1 type high speed steel which were used for cutting tools and hot dies, 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 obtained were as follows:(1) The critical temperature and Ms point were lowered with the carbon content and the begining curve of the isothermal transformation was removed to right 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 0.65%. For obtaining the fully quenched hardness, the austenitizing time needed about 2 minutes for 10Φ×10mm specimen. The tempering hardness as the secondary hardening was raised with the carbon and the quenching temperature.(3) The quantity of retained austenite measured by the magnetic method increased with the carbon addition, but by the sub-zero treatment it decreased to a little amount. During the tempering, the decomposition of retained austenite was occurred at about 500°C rapidly and all amount of them was entirely decomposed between 575°C to 600°C tempering.(4) The toughness measured by the static bending test decreased with the carbon addition and the hot impact strength also decreased with the carbon content. The tensile strength, elongation and reduction area were hardly affected by the carbon content, but were affected by the tempering and testing temperature.