Behavior of hydrogen in high-speed steels upon treatment in a glow discharge

Abstract

77wnnochenzical treatment in a glow discharge in hydrogen-containing gaseous media is used to harden highspeed tool steels. Such treatment is accompanied by saturation of the metal t)3, hydrogen, which leads to the appearance of hydrogen embrittlement. Transfer of hydrogen from the surface layers into the volume of the steel is accomplished by diffi¢sion fluxes. Accordingly, the investigation of diffusion processes occurring under thennochemical treatment conditions in a glow discharge is of both theoretical and practical interest.We have investigated the variation in hydrogen content and the diffusion of hydrogen upon treatment of steels R6M5 (cast), R6M5F3-MP and ROM2F3-MP (powder) in a glow discharge in a hydrogen-containing medium and (for comparison) in a hydrogen-free medium [I, 2] (see Table I).Nitriding of steels in a glow discharge (ion nitriding) in an ammonia atmosphere (procedure 1) was done on a stationary apparatus [3] at temperatures in the range 540-580°C, gas pressure of the medium (1.33-13.3). 102 Pa, interelectrode potential 400-100 V, and current density 0.5-2.0 mA/cm 2.Carbonitriding of steels in a hydrogen-free medium (procedure 2) was accomplished on a laboratory apparatus whose basic design we developed earlier in [4]. As the medium for carbonitriding, we used the dissociation products of ferrocyanides,* which reacted with the metal (the cathode) for a gas pressure of (1.33-13.3). 102 Pa, an interelectrode potential of 400-800 V, and a current of 1-50 mA/cm 2. In order to maintain a constant temperature for the samples and the saturating gas, and also a stable evaporation and dissociation rate, we used external heating of the reaction chamber. We investigated cylindrical samples of diameter 5 mm. Before thermochemical treatment in a glow discharge, the samples were subjected to standard (for the indicated steels) heat treatment: quenching from 1220°C and triple tempering at 560°C. Some of the samples were treated in a glow discharge in the as-supplied state.Analysis of the hydrogen content in the steels after treatment in a glow discharge according to procedures 1 or 2 was done by the method in [5] on a Leco RH-2 apparatus (at least three samples after each treatment procedure). The hydrogen content, determined by the indicated method, was averaged over the volume of the sample.The dependence of the average hydrogen concentration in a sample of cylindrical shape on the time for saturation from an external medium, in analogy with the data in [6], can be determined from the relation Kursk Polytechnic Institute.

Behavior of hydrogen in fracture and friction of metals and alloys

“…The absence of the autograph can be explained by the fact that free hydrogen absorbed by the structure of the metal in electrolytic hydrogen-charging or by the surface layer in friction passes into a bound state and is not liberated from the specimen at room temperature under atmospheric pressure or is liberated in a small amount and interacts with the photoemulsion in a molecular form after recombination without leaving traces on the photoemulsion of the plate. (It is known that hydrogen is removed from a specimen i 0 mm in diameter at temperatures below 200~ in over three weeks [7]. )…”

“…Figure 1 presents a comparatively even decrease in the density p of the material over the length of a specimen after a tensile test (by 0.01-0.36% in regions [2][3][4][5][6][7][8] and a jumpwise decrease by a factor of 4.8 -132 (by 1.72%) in the Ukhta Industrial Institute, Ukhta, Russia. fracture zone 9 [2], which is explained by an increase in the porosity of the material.…”