Electric-spark alloying of steel with tungsten-free hard metals

Conclusions A study was made of the ESA of steel with tungsten and tungsten-free TN type hard metals in different units and under different conditions, with and without anode dressing. It has been established that in alloying under finishing conditions the erosion of a dressed TN-20 alloy anode is greater than that of an undressed one; this is due to the formation of stable oxide films on the electrode surfaces. In contrast to this, in treatment under rough conditions the erosion of an undressed anode is greater because the oxide films cannot withstand the higher thermal stress generated during alloying. In ESA with tungsten alloys maximum erosion under both finishing and rough conditions is observed with undressed specimens. This is attributable to the formation of a defective zone promoting periodic brittle disintegration in the course of treatment. Removing the defective zone decreases the erosion of the material. The most favorable conditions for the formation of a reinforced layer are created in the alloying of a dressed cathode surface, and consequently it is best to perform ESA with a specific time of not more than 1 min/cm². Use of treatment conditions with large thermal loads increases the thickness and hardness of the reinforced layer. Reinforcement with TK type alloys sets up a stress which is greater on the specimen surface and extends to a greater depth than the stress generated in alloying with TN type hard metals. Electrodes made of the tungsten-free TN-20 hard metal can be used instead of tungsten alloy electrodes for the ESA of processes V and VI. The resultant reinforced layer is sufficiently thick and continuous.Translated from Poroshkovaya Metallurgiya, No. 11(239), pp. 64–69, November, 1982.     

Electric-spark alloying of steel with heterophase materials based on TiN and Al2O3

Conclusions A study was made of electric-spark alloying with alumina-containing titanium nitride composites sintered in argon and nitrogen. It was established that the most vavorable conditions of formation of a reinforced layer obtain in alloying with a TiN + 30 vol. % Al₂O₃ material sintered in argon. In alloying with TiN-Al₂O₃ composites, the conditions of formation of a reinforced layer deteriorate greatly when anodes sintered in nitrogen, rather than in argon, are used. In the ESA of steel with TiN-Al₂O₃ materials their erosion is less than that of the ZrN- Al₂O₃ composites investigated earlier, because the extent of brittle fracture accompanying the treatment is reduced. The erosion of TiN-Al₂O₃ materials is much less than that of pure TiN, as a result of which the coefficient of gransfer in ESA with TiN-Al₂O₃ anodes is four times higher. In view of this, alumina may be recommended as an effective addition to TiN-base electrode materials.Translated from Poroshkovaya Metallurgiya, No. 12(240), pp. 50–54, December, 1982.     

Electric-spark alloying of steel with hetrophase materials based on ZrN and Al2O3

Conclusions A study was made of the ESA of steel with electrodes made of ZrN-AlaO₃ composites with and without MO and W additions. Al₂O₃ contents in excess of 10 vol. % adversely affect the conditions of formation of a strengthened layer and increase the amount of brittle rupture erosion products by decreasing the thermal fatigue resistance of the electrode material. In ESA with composites sintered in argon the coefficient of transfer is 1.5–2 times higher and the total weight gain three times greater than in alloying with composites sintered in nitrogen. The ESA of steel with a Mo-containing ZrN-Al₂O₃ composite results in the formation of a strengthened layer which is more continuous and adheres more closely and more strongly to the basis material than a strengthened layer produced by ESA with a composite containing the same amount of W. ESA is accompanied by a redistribution of carbon in the surface layers of the cathode, resulting in the attainment of a maximum carbon concentration in the white layer, as well as by a comminution of the ferrite grain and a change in its shape.Translated from Poroshkovaya Metallurgiya, No. 4(208), pp. 51–56, April, 1980.     

Electric-spark alloying of steels with WC-Co hard metals

Conclusions A study was made of the electroerosion and cathode weight increase accompanying the ESA of steels with WC-Co hard metals and of some properties of resultant alloyed layers. In ESA the best results are obtained with VK20 alloy under soft conditions and with VK15 alloy under hard condition. The optimum alloying time is 5–10 min/cm² in process No. 2 and 3–5 min/cm² in process No. 5. Under these conditions ESA by the soft process (with VK20 alloy) ensures the formation of a hard (2200 kgf/mm²) white layer of the same thickness (40 m).Translated from Poroshkovaya Metallurgiya, No. 8(212), pp. 67–71, August, 1980.     

Electric-spark alloying (ESA) of steel with titanium carbide in its homogeneity range

Conclusions A correlation exists between changes in the parameters of the process of ESA of steel with titanium carbide in its homogeneity range and changes in the electronic structure of TiC_x. The erosion of titanium carbide, weight gain of the steel cathode, and proportion of fine-fraction particles in the erosion products of TiC grow with increasing degree of completeness of the carbon sublattice. This promotes growth of the alloyed layer, and is a result of a strengthening of the covalent component of the Ti-C bond, which predominates in the electronic energy spectrum of TiC_x. It has been found that the number of pearlitic colonies in the spark-heat-affected zone falls with decreasing distance from the alloyed surface, which is due to carbon impoverishment of this zone resulting from the carbon combining chemically with the titanium.Translated from Poroshkovaya Metallurgiya, No. 9(237), pp. 28–31, September, 1982.     

Electric-spark alloying of steels with chromium carbide base alloys

Conclusions It is shown that, of the Cr₃C₂-Fe cermets investigated, KKhZh-50 alloy is the best alloying electrode material. Alloying should be performed under soft conditions (E_pulse ^–2 J). The quality of the reinforced layer depends on the pulse energy and the base and electrode materials. The continuity of the layer increases and its surface roughness and thickness decrease with increasing pulse energy. Anode erosion and alloyed layer formation are affected by the secondary structure on the electron surface. For KKhZh-50 alloy its formation decreases anode erosion and the cathode weight gain, while for KKhNF-15 alloy, by contrast, it increases them. It is proposed that, to increase the corrosion resistance of such coatings (by about two orders), 65G steel should be alloyed in two stages, first with KKhZh-50 cermet and then with nickel.Translated from Poroshkovaya Metallurgiya, No, 4(304), pp. 1–6, April, 1988.     

Electric-spark alloying of structural alloys with a composite based on TiCN-AIN

The mass-transfer kinetics, the mechanism of formation, the tribotechnical characteristics, and the resistance to high-temperature oxidation of a coating formed on the hard alloy WC — 6% Co and on the titanium alloy VT6 by electric-spark alloying with electrode material based on TiCN — AIN with an Fe — Cr binder have been investigated. The phase distribution of the components in the coating was shown to be the same for both alloys. Electric-spark alloying of WC — Co and VT6 was found to reduce their wear by 33 and 60%, respectively. Moreover, the working temperature of the coated WC — Co alloy increased by 160 deg compared to the original surface. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 21–29, May–June, 2000.     

含钼耐候钢的腐蚀性能

通过显微组织观察、周浸加速腐蚀实验、锈层微观分析、锈层交流阻抗特征分析等方法,研究了合金元素钼含量对耐候钢腐蚀性能的影响.合金元素钼可以促进钢中贝氏体组织的形成,促使锈层更加致密,对钢基体具有更好的保护性,有利于提高钢的耐腐蚀性能.随着钢中钼含量的增加,实验钢锈层的腐蚀电位正移,自腐蚀电流密度减小,锈层的阳极溶解反应受到明显阻碍,锈层具有更好的保护性.     

Direct chromium alloying of steel using poor chromium-containing raw materials

Direct alloying of steel by chromium-containing briquettes with a cement binder is tested when they are added to a charge in a DSP-3M furnace under the conditions of the Mirgorod foundry from PAOArmaprom (Ukraine). The actual through extraction of chromium is more than 80 rel. %.     

Thermal conductivity of composite powder materials based on zirconium nitride,alumina, and molybdenum

Conclusions A study was made of the room- and high-temperature thermal conductivities of some composite materials. It is demonstrated that the temperature dependence of the thermal conductivity of a composite is not determined by a simple summation of the thermal conductivities of its components, being affected also by any reactions occurring between the components during sintering and leading to the formation of new phases or solid solutions. The composition dependence of the room- or high-temperature thermal conductivity of a composite system obeys the law of additivity in the absence of reaction between the components of the system, but deviates appreciably from it when the components do react with each other.Translated from Poroshkovaya etallurgiya, No. 5(221) pp. 58–62, May, 1981.     

A thermodynamic analysis of the formation of zirconium nitride from zirconium tetrachloride

Conclusions On the basis of a thermodynamic calculation of the heterogeneous system zirconium-nitrogen-hydrogen-chlorine the feasibility is demonstrated of obtaining zirconium nitride in the condensed state, with a virtually complete transformation of the metal into the nitride and a comparatively low expenditure of energy (about 80,000 kJ/kg), at temperatures of 2000–2400°K, a pressure of 1 bar, and a 50-fold dilution of the stoichiometric composition to a ZrNClH ratio of 1504200. Use of ammonia instead of nitrogen at the same ratio of the elements increases the amount of energy expended to 106,000 kJ/kg.Translated from Poroshkovaya Metallurgiya, No. 12 (156), pp. 1–3, December, 1975.     

Resource-saving direct alloying of steel

The development of the alloying and modification of steel by oxides, including natural materials, is very promising. Potential materials include barium–strontium carbonate ores, nickel concentrates, and vanadium converter slag, which may be used to produce steel with improved properties, without the expensive process of producing ferroalloys and intermediate alloys. Considerable research is required to improve steel-making processes. Thermodynamic modeling may be used for that purpose. In the present work, thermodynamic modeling is used for elementary systems involved in the extraction of barium, strontium, vanadium, and nickel from their oxides by means of different reducing agents. The results indicate that microalloying and modification of steel by inexpensive materials is possible; and permit the determination of the type of reducing agent and the optimal quantities employed. The Terra software used in thermodynamic modeling permits the determination of the equilibrium composition of the multicomponent heterogeneous system for high-temperature conditions, on the basis of the maximum-entropy principle. The reducing agents considered are carbon, silicon, and aluminum. The influence of the temperature and reducing-agent consumption on the reduction processes is investigated. The results regarding the reduction of barium and strontium show that silicon or aluminum is the best reducing agent when barium-bearing oxide materials are employed. The optimal reducing-agent consumption corresponding to maximum reduction of the barium and strontium is determined. The possibility of reducing nickel by carbon is confirmed. It is found that vanadium may be reduced by silicon or carbon or a complex process in which carbon is the predominant reducing agent. The results permit the development of a resource-saving technology based on oxides for the alloying, microalloying, and modification of Fe–C systems.     

Mechanical alloying of brittle materials

Mechanical alloying by high energy ball milling has been observed in systems with nominally brittle components. The phases formed by mechanical alloying of brittle components include solid solutions (Si + Ge → SiGe solid solution), intermetallic compounds (Mn + Bi → MnBi), and amorphous alloys (NiZr₂ + Ni₁₁Zr₉ → amorphous Ni₅₀Zr₅₀). A key feature of possible mechanisms for mechanical alloying of brittle components is the temperature of the powders during milling. Experiments and a computer model of the kinetics of mechanical alloying were carried out in order to esti-mate the temperature effect. Temperature rises in typical powder alloys during milling in a SPEX mill were estimated to be ≤350 K using the kinetic parameters determined from the computer model. The tempering response of fresh martensite in an Fe-1.2 wt pct C alloy during milling was consistent with the maximum results of the computer model, yielding temperatures in the pow-ders of ≤575 Ki.e., ΔT ≤ 300 K). Thermal activation was required for mechanical alloying of Si and Ge powder. No alloying occurred when the milling vial was cooled by liquid nitrogen. The pos-sible mechanisms responsible for material transfer during mechanical alloying of brittle components are considered.     

Effectiveness of alloying thermostable steel with vanadium and nitrogen

Compared to alloying with molybdenum, dispersional vanadium-nitride hardening more effectively increases the thermal stability and thermal fatigue strength of structural and special steel and also reduces the susceptibility to thermal and reversible tempering embrittlement.