Kinetics and thermodynamic characteristics of the reduction-decarburization-carburization of an atomized cast iron powder in converted gas

Conclusions An investigation into the kinetics and thermodynamic calculations of the reduction-decarburization-carburization of an atomized cast iron powder in a converted gas stream (heating to 1000 or 1100°C), together with a comparison of these annealing processes with each other and with a self-reduction process (heating to 1000 °C), have shown the following. The highest rates of reduction and decarburization are attained simultaneously, but both maxima are displaced to an earlier stage by supplying a converted gas stream to the reactor (as opposed to self-reduction under the same temperature and time conditions) and to an even earlier stage by raising the temperature from 1000 to 1100°C (under the same conditions of supply of a converted gas stream to the reactor). In annealing with heating to 1000°C the realized percentage of the reducing power of the carbon contained in the powder and of the converted gas is twice as high as in annealing with heating to 1100°C. Self-reduction under the same temperature and time conditions is characterized by the highest percentage realization of thermodynamic reducing power, which is 1.5–2.2 times that in the annealing of the powder in a converted gas. After 20-to 30-min annealing in a converted gas the material is characterized by the lowest carbon content, and increasing the duration of annealing raises its carbon content to a level closer to that of the carbon potential of the surrounding gas phase. During annealing in a converted gas with heating to 1000°C the true carbon content of the sponge quite quickly approaches the carbon potential of the gas, whereas during annealing with rapid heating to 1100°C the process of secondary carburization of the sponge is strongly inhibited, probably as a result of densification both of the surface of the sponge itself and of the surface layers of the sintered powder particles forming the sponge. In annealing in a converted gas raising the temperature from 1000 to 1100°C is not beneficial from the point of view of intensity of reduction, but markedly decreases the intensity of undesirable carburization.Translated from Poroshkovaya Metallurgiya, No. 2(254), pp. 12–19, February, 1984.     

Reduction and decarburization during the annealing of atomized iron-carbon alloy powders

Conclusions General laws have been established governing the kinetics of the reduction and decarburization of an atomized cast iron powder during annealing in the gaseous products of the reaction between the oxygen and carbon in the powder and during subsequent annealing in a hydrogen stream. Reduction and decarburization rate curves have maxima, attained simultaneously; to the ascending branches of the kinetic curves there correspond time stages in which reduction and decarburization are not hindered by carbon diffusion toward the particle surfaces (as a result, at the cementite/oxide and austenite/oxide interfaces reactions predominate which are accompanied by CO evolution); to the descending branches of the kinetic curves there correspond stages during which the carbon concentration gradient in the metallic nuclei of particles decreases, as a result of which the reactions at the austenite/oxide interfaces become less, and those at the oxide/gas interfaces more, vigorous, the reactions accompanied by CO₂ evolution also increasing in intensity; after the material of the particles has been depleted of carbon, an equilibrium is attained in the process taking place in the FeO Fe stage, while the introduction of hydrogen into the reactor increases the rate of reduction, creating a second maximum on the kinetic curve.The reactions between the solid phases in the metallic nuclei of the particles and the oxygen in the scale on the surfaces of these particles have been found to play a dominant role.In the light of the adsorption-catalytic theory it may be concluded that the reduction-decarburization annealing of an atomized Fe-C alloy powder involves the following processes:Translated from Poroshkovaya Metallurgiya, No. 2(230), pp. 5–15, February, 1982.The authors wish to express their gratitute to V. F. Pekach and N. P. Kurganskii for the loan of the testing apparatus and assistance with its operation.     

Choice of oxygen-to-carbon ratio in an atomized cast iron powder in iron powder manufacture

Conclusions The supply to the reactor of a reducing gas for the reduction-decarburization of an atomized cast iron powder has no effect on the width of the range of permissible O/C ratios in the resultant powder. Industrial self-reduction in cases where no reducing atmospheres are available should be carried out, using an atomized jast iron powder with an O/C ratio of 1.4±0.25, in continuous annealing furnaces provided with lock chambers at their charging and discharging ends.Translated from Poroshkovaya Metallurgiya, No. 8(248), pp. 103–105, August, 1983.     

Mechanism of action of calcium and iron chlorides in the reduction annealing of an atomized raw material powder. I. Kinetics of reduction annealing of a raw material powder in the presence of calcium and iron chlorides

Translated from Poroshkovaya Metallurgiya, No. 5(317), pp. 7–12, May, 1989.     

Influence of impurities on the properties of powder metallurgy and cast iron-manganese alloys

Translated from Poroshkovaya Metallurgiya, No. 6(306), pp. 56–61, June, 1988.