Thermal diffusion chroming of complex shape steel parts using a thermoemission field

Abstract

Chemical-thermal treatment (CHT) technologies have been known and used since the 50s of the last century. CHT methods traditionally include carburizing, nitriding, diffusion metallization with zinc, chromium and other elements. CHT affects the chemical composition of the part surface, providing it with the required level of strength properties and corrosion resistance. The results of the authors' research show that the CHT technology and thermal diffusion chromium plating, in particular, can be significantly improved by activating the work of the internal thermionic field created by additives-emitters of electrons and oxygen anions in the saturating powder mixture. The correct choice of emitter additives allows not only to accelerate the diffusion of chromium, but also ensures such a technological prop-erty of the filling as good knockout of parts. The paper presents the results of thermal diffusion chromium plating of bushings with an inner diameter of 20 mm made of steel 40CrNiMo2 in saturating mixtures with serpentine and serpen-tine and coarse-grained ferro-tungsten powder as emitter additives. The efficiency of using such saturating mixtures is confirmed by the increased diffusion layer of chromium in the metal compared to chromium plating in traditional satu-rating mixtures by 60 and 130%, respectively, for a mixture with the addition of serpentine and a mixture with serpen-tine and ferrotungsten. The expediency of using mixtures of such compositions for chromium plating of complex-shaped parts is shown, and the use of coarse-grained ferrotungsten powder ensures its multiple use. The results of X-ray phase analysis of chromium-plated surfaces and measurements of their hardness are also presented