Some aspects of diffusion in mixtures of tool steel powders and iron powders

Abstract

A fundamental study has been undertaken to determine enhancement of diffusion of alloying elements in mixed high speed steel–iron powder mixtures. Apparent diffusion coefficients were obtained by making simple diffusion couples. The data confirms that enhanced diffusion is observed and possible reasons for those observations are discussed.     

Volume changes accompanying the sintering of compacts from mixtures of titanium and iron powders

Conclusions The sintering of compacts from mixtures of titanium and iron powders at temperatures below the eutectic point is accompanied by their shrinkage, the sintering process being mainly determined by the particle size of the starting powders. During the sintering of compacts from mixtures of titanium and iron powders at temperatures exceeding the eutectic point the compacts grow in size, the extent of the growth depending on the particle size of the powders. This phenomenon may be attributed to the effect of heterodiffusion on sintering processes and to the crystallization pressure generated during the formation of intermetallic compounds.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 17–21, May, 1982.     

Filtering properties of highly porous materials prepared from iron powders with nonspherical particles

Conclusions We have shown that the method for preparing the initial powder has an effect on the permeability of the porous material.Other conditions being equal, the permeability is somewhat lower in specimens prepared from reduced powder than with fluidized and spherical powder. However, the possibility of using reduced powder to make components with a higher porosity and hence with a higher permeability makes use of this powder desirable.An increase in porosity of the material from 30 to 55% leads to an increase in permeability from 0.6 to 11.0 liter/min·cm² for a pressure drop of 0.3 kg/cm².A change in thickness of the specimen from 0.5 to 3 mm reduces the permeability by a factor of 2.5–6, and a change in the particle size from 60 to 110 increases the permeability by more than 1.3- to 1.6-fold.A comparison of filters with the same degree of purification, made from spherical and nonspherical powders, shows that they have approximately the same transmission capacity.The data obtained for the filtering capacity of a porous material as a function of the particle size of the powder, the wall thickness, and pressure drop can serve as a basis for selecting the characteristics of a material as a function of the actual design requirements.     

Diffusion and sintering activation in an alloy made of iron microparticle and nickel nanoparticle powders

Chemical-metallurgical method is used to fabricate a nickel nanopowder (“nanonickel”) and a powder made of iron microparticles clad by nanonickel. The diffusion coefficients in this iron-nickel system are 2–3 times lower and the activation energy of sintering is 2 times lower as compared to a nickel micropowder. The diffusion activation and shrinkage temperatures in this system differ by 200°C. Special features of the structure formation in the sintered powder materials are studied.     

Dissolution of carbon from alumina-carbon mixtures into liquid iron: Influence of carbonaceous materials

Due to their excellent thermal shock and wear resistance at high temperatures, alumina-carbon based refractories are used extensively in the steel industry. A clear understanding of factors affecting the dissolution of carbon from refractories is of crucial importance, as carbon depletion from the refractory can significantly deteriorate refractory performance and metal quality. Atomistic simulations on the alumina-graphite/liquid iron system have shown that nonwetting between alumina and liquid iron is an important factor inhibiting the penetration of liquid metal in the refractory matrix and limiting carbon dissolution. This study investigates the role played by the carbonaceous material in the dissolution of carbon from the refractory composite. Two carbonaceous materials, namely, petroleum coke and natural graphite, respectively, containing 0.35 and 5.26 pct ash, were used in this study. Substrates were prepared from mixtures of alumina and carbon over a wide concentration range. Using a sessile drop arrangement, carbon pickup by liquid iron from alumina-carbon mixtures was measured at 1550 °C and was compared with the carbon pickup from alumina-synthetic graphite mixtures. These studies were supplemented with wettability measurements and microscopic investigations on the interfacial region. For high alumina concentrations (>40 wt pct), carbon dissolution from refractory mixtures was found to be negligible for all carbonaceous materials under investigation. Significant differences however were observed at lower alumina concentrations. Carbon dissolution from alumina-petroleum coke mixtures was much lower than the corresponding dissolution from alumina synthetic graphite-mixtures and was attributed to poor wettability of petroleum coke with liquid iron, its structural disorder, and the presence of sulfur. Very high levels of carbon dissolution, however, were observed from alumina-natural graphite mixtures, with carbon pickup by liquid iron from mixtures with up to 30 wt pct alumina reaching saturation. A sharp reduction to near zero levels was observed in the 30 to 40 wt pct alumina range. Along with implications for commercial refractory applications, these results are discussed in terms of material characteristics, interactions between ash impurities and alumina, and formation of complexes in the interfacial region.