Papers by Keyword: Carbide

Abstract: Different types of carbide phases and regions of their precipitation in tempered martensite of austenitic steel have been investigated with orientation microscopy (EBSD) and electron microprobe analysis. The steel structure consisted of large grains of high-temperature ferrite (~ 15%), without visible mesostructured, and martensite packages with a great number of low-angle boundaries. High-angle boundary spectrum with the most prominent coincidence site lattice (CSL) boundaries, Σ3, Σ11, Σ25b, Σ33с Σ41с, is typical for martensite. This spectrum, resulted from austenite transformation by shear mechanism according to orientation relationships (OR), intermediate between Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). In the structure two types of carbide precipitates were observed: large MC [~ NbC] along the boundaries of former austenite grains, and dispersed M₂₃C₆ [~ (W,Mo)₂(Cr,Fe)₂₁C₆] predominantly along the boundaries in martensite packages. It has been shown that under martensite tempering M₂₃C₆ precipitation was mainly at high-angle intergranular boundaries. Carbide almost did not precipitate at low-angle and special CSL Σ3 boundaries. A few carbides were detected at special CSL boundaries, Σ11, Σ25b, Σ33с Σ41с.

Abstract: Nano size precipitate morphologies are very important for considering the precipitate hardening mechanism of HSLA steels. Systematic analysis of precipitates from nano scale to bulk scale were carried out using Nb bearing hot rolled steels through transmission electron microscopy (TEM) observations and chemical analysis of precipitates by solvent extraction. A small angle neutron scattering (SANS) experiment was also performed using a Hokkaido Univ. compact neutron source to understand average precipitate size. Results show that both changes in hardness and the amount of precipitates (under 20nm in size) have the same tendency. Precipitate is recognized as NbC plates, which have coherency with the steel matrix by Baker-Nutting orientation relationships. A row of precipitates, formed on the interface between austenite and ferrite during transformation, is also apparent. The SANS profile shows that small size precipitate formation is detected even though the amount of precipitation is small. In addition, the magnetic scattering component of the SANS profile has high sensitivity to NbC precipitates compared with that of the nucleus scattering component. By comparing precipitate data from comprehensive experiments, we consider the relationship between precipitate behavior and the hardening mechanism.

Abstract: Cutting performance of reaming alloy gray cast iron HT250 using carbide, cermet and CBN reamers was studied. Experiments were conducted under constant cutting parameters and cooling strategy. Tool life, hole diameter, spindle power, surface roughness and tool wear were analyzed. The hole diameter and spindle power would keep steady when reaming with carbide reamer after 400 holes to the tool life of 1050 holes. But holes diameter reduced and spindle power increased with the number of machined holes increasing during the whole tool life when using cermet or CBN reamer. The surface roughness Rz of the holes reamed by carbide reamer was within the tolerance, although it was worse than that reamed by cermet and CBN reamer. It can be summarized that the carbide was the most suitable material for reaming alloy gray cast iron because of the longest tool life, steady hole diameter and spindle power, qualified surface roughness. After machining, crater wear and clearance wear were produced on the cermet and CBN reamer, which were caused by abrasive wear. In addition, flaking and breakages appeared on the edge of cermet reamer, which were not found on CBN reamer. However, the clearance wear of carbide reamer was smaller than that of CBN reamer, and built up edge was found along the cutting edge.

Abstract: A heat resistant cast steel tube from an ammonia plant made of modified HP40 steel that failed after seven years of service was investigated for damage mechanism. The assessment of material degradation was carried out using optical microscopy, scanning electron microscopy (SEM) in combination with energy dispersive spectroscopy (EDS) analysis and mechanical tests. The main cause of failure appears to be overheating and localized corrosion along the network of intergranular carbides. Failed portion of the tube showed that the interdendritic eutectic carbides had coarsened, secondary carbides were precipitate and strongly coaresned within the austenitic regions. Witch decrease the mechanical strength and ductility of the service exposed tube compared with the as cast tube. Presence of unacceptable impurities like chlorine in the internal working gas destroy the protective oxide layer leading to penetration of corroding elements and degradation of service life of the tube.

Abstract: The main purpose of processing of tough-to-machine materials is improving of cutting process of steels with different physicochemical properties and alloying by means of various chemical elements in combination with heat treatment. Producing of high quality surface layers depends on properties of material used to make details, that is why reasons of tough machining were identified: influence of chemical composition and resulting structure. The studies of grinding of tough-to-machine materials were undertaken by means of grinding wheels made from synthetic diamonds as they are most resistant and highly-productive. Based on the studies recommendations for using of characteristics of grinding wheels and tough-to machine steel grades.

Abstract: The application of hardening heat treatment process at high temperatures (1100-1170 °C) for high-chromium steels of martensitic-carbide class 95Kh18 and Kh12MFL has been studied. Metallic substrate consisted of high-carbon martensite and residual metastable austenite with some traces of carbide has been obtained. Experiments have shown the resulting structure gains high frictional hardening capacity upon the application of heat. Sufficient amount of cooling martensite can be traced in the analyzed steel after high-temperature quenching (cooling up to the temperature of-70°С). Being combined with residual metastable austenite, it provides the increase of abrasive wear resistance by 25% compared with high temperature annealing. The influence of tempering temperature on hardness and abrasive wear resistance of analyzed steels 95Kh18 and Kh12MFL has also been determined.

Abstract: The paper investigates the influence of alloying of high manganese steel with various materials on its wear resistance. It describes the results of differential scanning calorimetry and thermo-gravimetric analysis obtained in the process of thermal investigation of high manganese steel alloyed with different materials. The processes taking place in alloyed high manganese steel during heat treatment were considered. Besides, the paper shows the results of investigation of kinetics of oxidation of high manganese steels, temperatures of the start and completion of carbide decomposition and carbon burning; the comparative analysis of these processes was carried out. The research group determined the qualitative characteristics of the steel decarburization process depending on the implemented alloying scheme of high manganese steel. Scientific justification was given to the results obtained in the research work. The technological recommendations, which make it possible to calculate the optimum hardening temperature of high manganese steels, were given. General conclusions were made in the final part of the paper.

Abstract: This article studies the mechanism of work hardening of austenitic high manganese steel alloyed with chromium and vanadium. The steel was annealed at 650°C before austenitizing at 1100°C, and then was quenched with water. We have observed that after the heat treatment, the size of austenite grain was small (1,950μm² - level 6). The hardness of the steel was 223HB and the toughness was 115J/cm². After impact loading, there was no martensite but twinning and sliding in the microstructure of the steel. The nano austenite was found in the microstructure. The steel was also hardened by small austenite grain and the carbide particles were finely dispersed in the microstructure.

Abstract: Thispaper presents the results of the studies of the combined influence of properties of carbide substrate and composite coatings on tool wear resistance in machining of chromium-based heat-resistant alloys. It was established that the efficiency of carbide tools with coatings is determined by a combination of the properties of the carbide substrate and the coating itself. For carbides with relatively low strength and crack resistance, the efficiency of coatings appeared to be unsatisfactory because of brittle fracture of the substrate and thus intensive failure of coating. High heat resistance of cobalt-rhenium alloy is not realized during deposition of coating because of blocking of the most important property of heat-resistant Co/Re binder, i.e. the ability to hold carbide grains under significant deterioration of carbide matrix even at a high temperature in the cutting zone.The maximum efficiency of the coating in machining of chromium-based heat-resistant alloy is provided withcarbide tools made with a balanced ratio of hardness, heat resistance and strength.

Abstract: Effect of magnetic field strength on carbide precipitation behavior in W₆Mo₅Cr₄V₃ highspeed steel during medium temperature tempering was investigated. The applied magnetic field promoted the precipitation and refinement of M₆C and MC carbides at boundaries and in the grain interior, but maximum spheroidization occurred for those M₆C carbides precipitated at boundaries, the stronger the magnetic field strength, the stronger the spheroidization effect. The high magnetic field hinders the precipitation of M₂C type carbides, and the M₂C type carbides basically disappear when applying the magnetic field.