Papers by Keyword: Decarburization

Abstract: In order to examine the decarburization behavior in the hot stamping (HS) method, the dependence of the microstructure evolution on the annealing temperature was experimentally studied using a Fe-0.21 mass% C-1.3 mass% Mn-0.2 mass% Si steel. The steel was isothermally annealed in the temperature range of T = 773-1173 K for various times of t = 100-12800 s in an ambient atmosphere. Here, the steel possesses the ferrite (α) + cementite (θ) two-phase microstructure at T = 773-923 K, the α + austenite (γ) two-phase microstructure at T = 1013-1073 K, and the γ single-phase microstructure at T = 1093-1173 K. During annealing at T = 1013-1073 K for t = 1600 s, however, the α layer with a uniform thickness is formed at the surface of the steel due to decarburization and gradually grows into the inside. Such formation of the a layer was not clearly observed at T 973 K and T 1093 K. Thus, the formation of the α layer hardly occurs under the HS annealing conditions. At T = 1033 K, the thickness of the α layer is mostly proportional to the square root of the annealing time. Such a relationship is called the parabolic relationship. Furthermore, the grain size of the α layer monotonically increases with increasing annealing time. Hence, the parabolic relationship guarantees that the growth of the α layer is controlled by volume diffusion.

Abstract: The growth of ferrite from alloyed austenite can take many forms: Widmanstätten ferrite and “plessites” in meteoric Fe-Ni-Co; ferrite layer growth under decarburization conditions; grain boundary precipitation and Widmanstätten ferrite and bainite in alloy steels. This contribution considers ways in which these different aspects of austenite decomposition can inform one another.

Abstract: In according to the DEFORM-3D software, we simulated the decarburization depth of the 60Si2CrVA spring steel in heat treatment, optimized the process parameters with the simulation results. The result of the research illustrated that the actual decarburization depth is consistent with the simulation result, which demonstrate DEFORM-3D has a practical guide for the process of heat treatment.

Abstract: In this study, the aluminizing of high silicon cast iron by hot-dipping in pure Al melt was performed and their high temperature oxidation behaviour was tested at 750 °C for virous exposure time. After high temperature oxidation tests, the microstructure analysis of all samples were investigated by means of metallographical examination, scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometer (EDS) and X-ray diffractometry (XRD).The results showed that the coating layers consisted of three layer, in the sequence of Al, Fe-Al and Si-rich layers from external topcoat to substrate. Nodules graphite had a blocking effect to retard the outward diffusion of Fe atoms and impeded the growth of Fe2Al5 in C-axis. Eventually, the cast iron substrate was oxidized directly by oxygen penetration via the greater cracks and pores to form Fe oxide nodules after 750 °C oxidation for 48h.

Abstract: The RH process is a secondary refining process that can simultaneously attain significant levels of removal of interstitial elements, such as carbon, nitrogen and hydrogen, from liquid steel. In the RH process, the decarburization rate plays a very important role in determining the productivity of the equipment. The kinetics of this reaction is controlled by mass transfer in the liquid phase. In the present work, a physical model of a RH degasser has been built and used in the study of the kinetics of decarburization. The effects of the gas flow rate and of the configurations of the nozzles used in the injection of the gas have been analyzed. The decarburization reaction of liquid steel was simulated using a reaction involving CO2 and caustic solutions. The concentration of CO2 in the solution was evaluated using pH measurements. Based on the experimental results, it was possible to estimate the reaction rate constant. A volumetric mass transfer coefficient was then calculated based on these rate constants and on the circulation rate of the liquid. The logarithm of the mass transfer coefficient showed a linear relationship with the logarithm of the gas flow rate. The slope of the line was found to vary according to the relevance of the reaction at the free surface in the vacuum chamber. A linear relationship between the volumetric mass transfer coefficient and the nozzle Reynolds number was also observed. The slopes of the lines changed according to the relative importance of the two reaction sites, gas-liquid interface in the upleg snorkel and in the vacuum. At higher Reynolds number, the reaction in the vacuum chamber tends to be more significant.

Abstract: One method for lining the inner surface of a steel cylinder with copper alloy is to pour molten copper alloy into a heated cylinder, which has been previously filled with borax anhydride. This process replaces the molten borax anhydride with molten copper alloy. After the cylinder is cooled, the embedded copper alloy is drilled along its center axis so that a prescribed thickness of the copper alloy may remain. However, when the cylinder is made of cast iron including high concentration of carbon, the copper alloy does not bond to the inner surface of the cylinder. To solve this problem, we investigated to utilize the decarburization phenomenon. Two methods were investigated. In one method, the cast iron cylinder filled with FeO powder is heated at a high temperature so that the carbon precipitates in the cast iron may get out through reaction with O2 formed by decomposition of FeO. In the other method, the cast iron cylinder is only heated in air. A decarburized layer is formed beneath an oxide layer. In both methods, the lining of cast iron with copper alloy was attained.

Abstract: Nanostructured WC-Co coatings have been manufactured by high velocity oxyfuel (HVOF) spraying using commercially available nanocomposite powders. The effect of feedstock powder characteristics on coating microstructure has been investigated. A significant loss of carbon occurred during HVOF spraying, which was much greater for a porous, irregular powder than for a dense, spherical powder. The decarburization promoted the formation of several additional phases in the coating, including W2C, W and CoxWxC. The microstructural differences in each coating arose from the different extent of feedstock powder melting because of initial powder morphology.