Structural transformations in heat treatment of chrome-molybdenumvanadium tool steels

Abstract

1. During an isothermal hold of the supercooled austenite of types 65Kh6M1.5F3B and 65Kh6M3F3B chrome—molybdenum—vanadium steels in the area of subcritical temperatures (560–680°C) concentration microinhomogeneities or zones occur in it, which causes an increase in hardness and a reduction in specific electrical resistance of the martensite formed in further cooling. The substructure of the martensite does not depend upon the form of hardening. 2. The general character of the change in properties in tempering of hardened chrome—molybdenum—vanadium steels does not depend upon the preceding hardening cycle. However, after isothermal hardening the decrease in hardness in tempering at 300–400°C is less intense than after normal hardening. An increase in the isothermal hold time strenthens this effect. 3. The tempering temperature corresponding to the effect of secondary hardening does not depend upon the preceding hardening cycle while the increase in hardness is greatest after isothermal hardening. 4. The increased hardness of the steel after isothermal hardening and tempering at 530–540°C in comparison with the hardness after normal hardening and a similar temper is the martensite matrix. 5. Between the structural condition of chrome—molybdenum—vanadium steels after hardening and tempering, the hardness level, and tool life there is a correlation relationship. The life of certain forms of tools of 65Kh6M3F3B steel after isothermal hardening and tempering is under certain conditions close to the life of similar tools of R6M5 steel.