EFFECT OF SILICON ON THF PROPERTIES OF SHOCK-RESISTING TOOL STEEL

Abstract

To investigate the influence of silicon on the properties of shock-resisting steel containing 0.5% carbon. 1.5% chromium, 2.2% tungsten and 0.2% vanadium, the authors measured the critical point, the Jominy hardenability, the as-quenched and the as-tempered hardenss, the length-change during tempering, the specific gravity, and the mechanical properties.
The results obtained are as follows:
(1) Critical point is raised with the silicon content, and a full hardness 57 to 61 Rockwell C is obtained by oil-quenching from 900-960°C.
(2) Hardenability is increased by addition of the silicon up to 0.78%, then decreased with more silicon addition. Steels containing 0.4% molybdenum posssess higher hardenability.
(3) The rate of softening with tempering temperature decreases in the steels between 200 and 350°C, and the magnitude of this decreases in softening rate is related to the silicon contents of the steels. In fact, the rate of softening becomes nil at about 300°C in the steels which contain 1% or more silicon.
(4) The quantity of the retained austenite measured by saturation permeameter increases slightly with the silicon content and quenching temperature. And the transformation of the retained austenite is retarded as the silicon content increases.
(5) From the results of dilatometer test, it was found that the temperature at which the third stage contraction can be detected is raised with the silicon content, and the temperature range over which the contraction occured is greater in lower silicon steel.
(6) The specific gravity of the 1% or more silicon steel does not decrease appreciably with 1-hour tempers at increasing tempering temperatures, between 200 and 350°C.
(7) Yield strength measured by tensil test and bend test is incresed. with the silicon, up to 0.8% and then slightly decreased with more silicon content. Hot hardness and tensile strength at 400°C increase with the silicon content.