Decomposition of supercooled austenite in steels of the 40Kh type

Conclusions In steels alloyed with strong carbide-forming elements (vanadium, niobium, and titanium) the rate of decomposition of supercooled austenite depends on the type and ratio of atoms of the carbide-forming elements bound in undissolved carbides and dissolved in the solid solution. This should be taken into account in selecting the optimal cooling rate for steels after austenitizing in order to obtain a given combination of mechanical properties.S. M. Kirov Ural Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 56–57, August, 1981.     

Intermediate temperature decomposition of supercooled high nitrogen austenite

Abstract

The mechanism of decomposition transformation of Fe–N the austenite system has been investigated. An improved process of austenitic nitriding, achieved by applying controlled nitrogen potential theory, allowed high nitrogen austenite samples with a uniform nitrogen concentration to be produced. The key point of this gas nitriding process is to keep the atmosphere at very low nitrogen potential. As a result, the nitride layer on the surface of the pure iron foil was reduced and pure iron ferrite was thoroughly nitrided, forming high N austenite (γ-Fe[N]) that is thermally stable at room temperature. The nitrogen concentration of this austenite was determined as 9·32 at.-%, which is almost the maximum value achievable in Fe–N austenite.     

Formation of austenite in steels

Conclusions On heating of steel austenite is formed in two stages: a) a diffusionless transformation, leading to the formation of low-carbon austenite; 2) subsequent saturation of the austenite with carbon [8]. In this case the austenite forms first in those places where, for whatever reason (the existence of an interface, differences in concentration, lattice defects), the free energy is larger, which facilitates the nucleation of austenite.Kharkov Highways' Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 2–5, September, 1968.