Papers by Keyword: Carbon Content

Abstract: The article considers the features of heat treatment of steels, includes quenching, phase transformations and their influence on the structure and properties of the material. The key parameters of heat treatment are described: heating temperature, holding time and cooling rate, as well as their role in forming the required mechanical characteristics of steel. Phase diagrams are considered, in particular for the "iron-carbon" system, and their significance for choosing processing modes. Additional friction-strain hardening (AFSH) of various steel grades (20, 45, U7, U12) after preliminary quenching and low-temperature tempering is studied. An analysis of microstructural changes and microhardness of surface layers after AFSH is carried out, which confirmed the effectiveness of additional hardening. It was found that steels with a higher carbon content, limited to 0.8 %, demonstrate a greater depth of the hardened layer and higher microhardness values, which determines their feasibility for use in conditions of increased wear. The results of the study emphasize the importance of choosing the optimal AFSH mode depending on the carbon content in the steel, which has a significant impact on the formation of the strength characteristics of the material.

Abstract: Materials consisting of a hard phase, usually WC, and a tough binder, traditionally Co, form the most successful class of composite materials, also known as Hard Metals (HM) or Cemented Carbides. Powder metallurgy routes are employed generally for the production of such [1]. The typical processing route of such materials involves mixing the components, kneading and consolidation. Alcohols, alkanes and alkenes are commonly used to limit any excessive heating and oxidation of powders during mixing the components. In this study, we report the results of milling in a more environmentally friendly aqueous milling media. The obtained results are presented comparatively with milling under a traditional media, such as isohexane and acetone. The characterization of the milled samples has been done from the structural, compositional and morphological point of view. Considering our previous results, an important aspect of the milled powder is the carbon content, which dictates the sintering behavior of such parts. The carbon balance investigation performed on a carbon analyzer has revealed no significant differences upon changing the milling media. This work emphasizes the influence of the milling media on the HM powder. HM powders with similar properties have been obtained both by traditional and aqueous milling. The comparative study has revealed that the substitution of the traditional milling media does not influence the carbon content in the HM powder.

Abstract: Spark erosion of WC-8Co carbide pieces in oil resulted in a powder consisting of nanostructured spherical microparticles formed by rapid crystallization of the melt. These particles consist of rounded WC grains with an average diameter of about 0.18 μm, surrounded by cobalt. The process productivity, specific energy consumption, microstructure, particle size distribution, chemical and phase compositions of the obtained powder are determined. It was found that as a result of oil pyrolysis, free carbon is formed (3.4 %), which makes this powder unsuitable for the production of carbide products from it. A technique has been developed and the process of controlled removal of excess carbon by annealing the obtained powder in a CO₂ atmosphere at a temperature of 1000 °C has been studied. As a result of annealing for 120 minutes, the carbon content decreases to the required value (5.6 %). Studies of the phase composition and microstructure showed that the obtained particles consist of elongated WC grains, the average diameter of which increased to 0.43 μm.

Abstract: The analysis of the results of steel de-oxidation with manganese and silicon during tapping from an arc furnace in the Ural Steel is carried out. It is shown that the absorption of manganese and silicon during de-oxidation varies widely: from 33.0 to 88.4% (average 68.8%) for manganese and from 25.9 to 79.8% (average 63.8%) for silicon. The main causes of high varies and low absorption of deoxidizing agents were established: low carbon content and high metal overheating before de-oxidation. A statistical analysis of St 37-3 steel de-oxidation data was performed with the aim of improving the efficiency of steel de-oxidation technology in a ladle. The regression equations are obtained, allowing to calculate the assimilation of deoxidizers and the consumption of ferroalloys, depending on the temperature and carbon content in the metal during tapping from the arc furnace.

Abstract: The target of processing bimaterial components by cost effective powder metallurgy is to combine unique properties from different parts of the component. Differential shrinkage rate and more often, radial mismatch which is more consistent in bilayer owing to sintering conditions (time, rate, temperature etc.) is known to compromise the interfacial bond strength and integrity of these components. Therefore, the aim of this study is to analyze the sintering compatibility and evaluate the mismatch strain in cemented tungsten carbide (WC-Fe-C) and steel (Fe-W-C) bilayer processed through powder metallurgy (PM) to combine the hardness and toughness properties applicable in machining industries for drilling tools. Through geometrical measurement, mismatch strain rate between layers at different sintering temperatures was calculated and a value as low as 13.7% was observed at the interfacial zone of MC–0.2 specimen sintered at 1280°C indicating a stronger bond between layers compared to those sintered at 1290°C and 1295°C where a huge mismatch was found increasing the tendency for delamination.

Abstract: SiC porous ceramics were prepared by oxidation-bonding technique using SiC powder as main material and carbon black as pore former. The phase composition, surface morphologies, bulk densities, porosities, mass and linear changes of the samples were also investigated. The physical-chemical properties have been analyzed. The results indicate that the oxidation reaction of SiC ceramics was accelerated with the increase of temperatures. It displays undamaged surface after 1400°C treatment, as well as fused surface after 1450°C treatment. The latter is attributed to violent oxidation reaction of SiC. As C contents increase, the porosities of the samples increase and the infiltration of O₂ into interior of SiC ceramics was facilitated. The internal network microstructure is controlled by O₂ infiltration and SiO₂ coating.

Abstract: To make steel exhibit attractive properties as high strength and good ductility, this paper presents a novel one step method for forming-Q&P integration—Hot Stamping-Dynamic Partitioning (HS-DP) process. The proposed HS-DP process is simulated with salt bath heat treatment. The effect of microstructure and mechanical properties in a low-carbon AHSS with different cooling rate of the new process is investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and tensile test methods. Microstructure of the steel subjected to HS-DP treatment is mainly composed of initial quenched martensite phase , final quenched martensite phase and retained austenite phase formed. The impact of retained austenite is also discussed, especially the influence of elongation caused by various retained austenite volume fraction and carbon-content. This experiment illustrates the promising application potential of the hot stamping-dynamic carbon partitioning process.

Abstract: Ti(C,N)-based cermets with three carbon contents are prepared by sintering in vacuum. The effects of carbon content on the microstructure, mechanical properties and wear resistance of Ti(C,N)-based cermets were investigated. The results show that the grains refine gradually and the hard phase core becomes smaller when the carbon contents increases. The mechanical properties closely relates to the carbon content. With the increase of carbon content, the furrows created by grains cutting are getting narrower and more intensive. When the carbon content reaches 0.8%, a large quantity of wear debris bonding blocks are attached on the wearing surface. In this condition, the Ti(C,N)-based cermets are of the minimum wear weight loss and the best comprehensive mechanical property.

Abstract: Ni-Cu-Zn ferrite powders were prepared by self-propagating high-temperature synthesis (SHS) using carbon powder with different mass fractions as fuel. The effects of carbon content in the raw materials on the phase composition, microstructure, density and magnetic property of the Ni-Cu-Zn powders were investigated by X-ray diffractometry(XRD), scanning electron microscope(SEM) and vibrating sample magnetometer(VSM), respectively. The results show that the use of carbon as a fuel brings no other impurities and improved the permeability. The single spinel phase powder was obtained when the precursor materials with a carbon powder of 5% in mass were used.

Abstract: Though the study of carbon content on the microstructure and properties of gray cast iron, mechanical properties test as well as metallographic observation, we could see that the mobility of molten iron is the best when carbon equivalent control at around 4.3%; Liquid iron tend to precipitate A or B type graphite and enhance the casting organization and property when carbon content was increased properly.