K. V. Grigorovich

Electrodeposition and Physico-Mechanical Properties of Chromium Coatings Modified with Disperse Particles

Chromium electroplates from Cr(III)-baths modified with disperse phases of CeO2, Cr2O3, graphite, and ultradisperse diamond are studied. Mechanical properties of the composite coatings are investigated. The Cr2O3-particles present in the bath are found to cause the destruction of the coatings already during the plating. When modifying with CeO2-particles, good coatings with enhanced microhardness can be obtained at their concentration in the bath of no more than 15 g/l. The deposition rate in such cases exceeds that in the blank baths. The optimum range of the CeO2-particle concentration, allowing to obtain the maximal microhardness, is 5–8 g/l. The self-lubricating chromium-graphite composite coatings can be deposited at a graphite concentration in the bath of up to 4 g/l. The microhardness of the chromium coatings is most strongly affected by ultradisperse diamond particles that increase the microhardness by a factor of 1.4; they also decrease the coatings’ brittleness. When the ultradisperse diamond concentration in the solution is as high as 30 g/l, the diamond content in the composite coating reaches its limiting value of 12–14 vol % (or 6.4–7.2 wt %). The optimum ultradisperse diamond concentration was found to be 17 g/l in the baths and 10.5 vol % (or 5.6 wt %) in the composite coating. At these concentrations, the coatings with the maximum microhardness and lowest brittleness are obtained.

Effect of a pipe-steel killing technology on the composition and number of nonmetallic inclusions

Pipes made from steels 19G, 17GS, 17G1S, 10G2FBYu, 13G1S-U, and 20KT of various manufacturers and technologies are studied. Electron microprobe and fractional gas analyses are used to determine the main types and number of nonmetallic inclusions (NIs). The effect of a modification procedure on the oxidic cleanness of steel 20KT (produced at JSC “Volzhskii Pipe Works”) is studied. The use of a silicocalcium-filled wire is shown to increase the total contamination of the steel by nonmetallic, in particular, calcium aluminate and magnesium spinel inclusions, which are conditionally related to corrosion-active nonmetallic inclusions (CANIs). Fractional gas analysis is shown to allow the number of oxide inclusions of various types to be accurately determined in pipe steels. No correlation is found between the volume fraction of oxide inclusions determined by fractional gas analysis and the number of CANIs determined by a metallo-graphic method.

The structure of the chromium coatings modified by the dispersed particles

The microhardness and structure of composite chromium coatings modified by dispersed CeO2 and ultradispersed diamond (UDD), as well as the granulometric UDD distribution (both in the coatings and the bath) were investigated. The presence of the particles in the coatings reduced the number of microcracks and enhanced the microhardness. Passing from the chromium to the composite coatings makes the microhardness measured on the microsections and the specimen surface converge. Despite the uniform distribution of the particles in the coatings, nonuniform distribution of their sizes is satisfactorily described by a lognormal distribution function. A selective deposition of nano-size particles (with the most probable radius of UDD particles of 204 nm) was found out, although dynamic aggregates found in the solution have the most probable radius of 4530 nm. This is possibly associated with their disaggregation near the electrode and the inclusion of the finer particles into the coating.

Analysis of the complex deoxidation of carbon steel melts

The joint complex deoxidation of carbon steel melts is analyzed. A procedure is proposed to calculate the equilibrium oxygen concentration in a melt. Rail steel is used as an example to study the joint complex deoxidation of a melt by aluminum and silicon. Mullite (2Al2O3 · 3SiO2) and kyanite (Al2O3 · SiO2) are considered as the reaction products. Thermodynamic calculations demonstrate that the deoxidizing capacity of aluminum is increased in the presence of silicon in a melt. In this case, a substantial increase in the deoxidizing capacity in the concentration range 0.001–0.1 wt % Al is achieved when kyanite (Al2O3 · SiO2) forms in the reaction products. The results of laboratory and industrial experiments on complex deoxidation are shown to agree well with the calculated data. These results demonstrate that the proposed calculation procedure can be recommended to determine the equilibrium oxygen concentration in a melt in the presence of several deoxidizing elements.

Plasma coatings of mechanically doped Co-C-Mo and Co-C powders

X-ray structure analysis and metallography are applied for investigations into the phase composition and structure of powdered model alloys Co-9.2% C and Co-1% Mo-9.2% C after various treatments (mechanical doping, thermal treatment, sintering) and plasma coatings produced from these powders. It is demonstrated that carbides CoxCy are formed within mechanical doping and plasma spraying, which are absent in the equilibrium state diagram. High microhardness of plasma coatings (up to 8.3 GPa) is associated with formation of carbides and amorphous phase. Carbon losses at stages of plasma spraying of coatings are determined.

Simulation of the sulfide phase formation in a KhN60VT alloy

The conditions of the existence of sulfide phases in Fe–Ni–S alloys and four-component Fe–50 wt % Ni–0.001 wt % S–R (R is an alloying or impurity element from the TCFE7 database) systems are studied using the Thermo-Calc software package and the TCFE7 database. The modification of nickel superalloys by calcium or magnesium is shown to increase their ductility due to partial desulfurization, the suppression of the formation of harmful sulfide phases, and the uniform formation of strong sulfides in the entire temperature range of metal solidification. The manufacturability of superalloys can decrease at a too high calcium or magnesium content because of the formation of intermetallics with a low melting temperature along grain boundaries.

Evaporation of reaction-zone components in the low-temperature plasma treatment of chromium-bearing melts

The evaporation of iron, Fe–Cr, Fe–Ni, and Fe–Cr–Ni melts at the plasma spot in treatment by low-temperature argon plasma is studied. Experiments with different masses of metal and with variation in arc power of the plasmatron are conducted so as to determine the conditions corresponding to stable surface temperature of the metal. The results show that, for experiments in which the plasma flux completely exposes the surface of the metal droplet, arc power no less than 2.0 kW is optimal; the mass of the metal should be 5‒10 g. The evaporation process is studied as function of the melt composition, and the evaporation rates are determined. Of the alloys considered, Fe–Cr–Ni melt is characterized by the highest evaporation rate in the neutral atmosphere of a laboratory plasma furnace. The surface temperature of the melt is determined indirectly, on the basis of the evaporation rate. The surface temperature of the plasma-treated melt is found to vary in the range 1950–2100 K with variation in arc power from 1.6 to 2.4 kW.

Determination of free nitrogen in carbon steels by inert gas fusion method

The possibility to use hot extraction (thermal extraction in a carrier-gas flow) for fractional analysis of nitrogen in carbon steels is shown for cord and reinforcing-bar steels. A rapid procedure is developed for an analysis of free nitrogen in carbon steels. The validity of the analytical procedure is confirmed by high-temperature hydrogen extraction. The data obtained by the two methods correlate well with each other. A sample preparation procedure is developed for the determination of the content of dissolved nitrogen.

Application of high-temperature extraction in a carrier gas for a quantitative determination of TiN in rail steel

The possibility of application of high-temperature extraction in a carrier gas to determine the content of nitrogen from titanium nitride inclusions in rail steel specimens of industrial melts and model alloys is considered. The temperatures of the onset of the dissociation of basic nitrides in rail steel are calculated under the conditions of a carbon-saturated melt. The nitrogen content in titanium nitrides in rail steel is calculated under the equilibrium conditions in the system. The experimental and calculated data on the characteristic temperatures of TiN dissociation and the nitrogen content in TiN are compared. A satisfactory convergence of the calculated and experimental data is obtained. The possibility of application of high-temperature extraction in a graphite crucible in a carrier gas flow for fractional analysis of nitrides in steel is shown.

STUDY OF THE KINETICS OF CARBON OXIDATION BY ARGON-OXYGEN PLASMA IN CHROMIUM-CONTAINING MELTS

The article describes the investigation of treatment processes of such alloys as Fe – Cr and Fe – Cr – Ni by oxygen-containing plasma. The laboratory unit, which is a plasma furnace with a tungsten cathode and a water-cooled copper anode, can simulate processes that occur in the contact area of plasma arc and melt surface. It was also developed a mathematical model describing the processes occurring in the interaction between plasma torch and surface of the molten metal. According to the results of the experiments the authors have determined the kinetic parameters of decarburization process of high-chromium melts by argon-oxygen plasma. The results allow to conclude that treatment of high-chromium melts by plasma which contents less than 15–17 % of oxygen provides a high degree of decarburization with low chromium haze. The comparison of model calculations and experimental data has shown good reproducibility.