Papers by Keyword: Carbide

Abstract: The carbide distribution and retained austenite effects in cold work tool steels on their wear behavior are studied using different quenching, tempering and cryogenic processes. Treated specimens were characterized using optical and scanning electron microscopy, hardness measurements, X-ray diffraction as well as wear tests in a block-on-roller method without lubrication. Beside primary carbides being large and non-uniformly distributed in the D2-B specimen, the weight losses of the D2-B specimen (62.4 HRC) quenched and tempered at 200°C was highest among all tested specimens due to substantial retained austenite in the tempered martensite matrix. With the aid of small and uniform dispersed carbides, the DC53 steel specimen (61.3 HRC) showed less weight loss and exhibited the best wear resistance. The weight loss from cryogenically treated specimens was lower than that of non-cryogenically treated one.

Abstract: Laser cladding is an adequate technique to fabricate Metal Matrix Composite (MMC) layers because of its focused high energy which allows the partial melting of hard ceramic reinforces particles like carbides. Thus, the wettability and gradual transition between metal and particle can be improved. However, metastable or new intermetallic phases can be formed during laser processing due to severe thermal cycle imposed to the clad with unknown properties in some cases. In this work our experience on microstructural analysis of Ti-MMC coatings acquired during the last five years is summarized. Special attention is paid on carbide dilution and secondary carbides formation mechanisms when TiC, SiC, Cr₃C₂, WC and B₄C are mixed with titanium alloys.

Abstract: The properties and precipitation rules of secondary phases generated during isothermal aging of duplex stainless steels and factors affecting the precipitates were reviewed in this article. These secondary phases include carbides(M23C6,M7C3), nitrides(Cr2N,CrN) and intermetallic phases(σ-phase, χ-phase, Fe3Cr3Mo2Si2, R-phase, π-phase, α′-phase). With the right understanding about the phases, the aim is the suitable heat-treating processes would be chose to avoid the unfavorable influences of secondary phases.

Abstract: The structural characteristics of electric melt, as-cast grey irons were studied in critical solidification conditions, such as very low sulphur content (< 0.025%) and a low (%Mn) x (%S) control parameter (< 0.015) with low Al residual (< 0.002%), without resulphurising or preconditioning. The efficiency of Ce-Ca-Al-FeSi alloy was tested at lower addition rates (0.15-0.25wt.%), as traditionally high inoculant addition rates have been employed in low sulphur grey cast irons. Ce bearing ferrosilicon with similar Ca and Al levels appears to be more efficient than a commercial Ba-Ca-Al-FeSi inoculant, especially at low addition rates (< 0.2wt.%) for the key structure parameters: fewer carbides and less undercooled graphite with small eutectic cells at a higher count.

Abstract: Ca, Ba and Ca-Ba bearing FeSi alloys were compared for their effectiveness in chill (carbide) control, using iron chemistries with critical element levels [< 0.035%S, (%Mn) x (%S) < 0.02, <0.003%Al]. Relative clear and total chill measurements were employed, for chill wedges with different cooling modulii (CM = 0.11 – 0.35 cm). Previous experiments illustrated that the eutectic undercooling of this type of base iron is excessively high, demonstrating a relatively high need for inoculation. Under these conditions, Ca inoculation had a significant effect compared to Ba inoculation, while a Ca-Ba combination improved most of the solidification parameters. The results also illustrate the importance of residual Al and confirm its key role in graphite nucleation in grey irons. The content of the active elements (Al, Ca, Ba) in FeSi based alloys appears to be more important if they inoculate low sulphur irons, more so than increasing the addition rate of an unsuitable inoculant composition.

Abstract: The transformation of the solidification microstructure and the phase changes in AISI M2 grade high-speed steel modified with powder addition of TiB₂ have been studied focusing on the effect of austenitising temperatures. In order to investigate kinetics of both the microstructure and phase transformations in eutectic carbides, primarily M₂C carbide decomposition, upon heat treatments with respect to diffusion processes, different techniques of electron scanning microscopy, X-ray diffraction analysis and energy dispersive X-ray spectrometry have been used.

Abstract: The present work deals with the evolution of mechanical properties and structure of low-carbon Fe-1,12Mn-0,08V-0,07Ti-0,1C (wt.%) steel after severe plastic deformation (SPD) and high-temperature annealing. Steel in initial ferritic-pearlitic state was deformed by equal channel angular pressing (ECAP) at T=200°C and high pressure torsion (HPT) at room temperature. The evolution of ultrafine grained structure and its thermal stability were investigated after annealing at 400-700°C for 1 hour. The results shown that SPD leads to formation of structure with an average size of (sub-) grain of 260 nm after ECAP and 90 nm after HPT. Ultrafine grained structures produced by SPD reveal a high thermal stability up to 500°C after ECAP and 400°C after HPT. At higher annealing temperatures a growth of structural elements and a decrease in microhardness were observed.

Abstract: Microstructural design of a new generation of 9%Cr steels for fossil power plants is considered. It was shown that microstructural stability of 9%Cr steels impairs their creep resistance. Two types of restoration processes can occur in the heat resistance steels under creep conditions: (i) normal grain growth and (ii) dynamic recovery. The first process associates with the migration of high-angle boundaries (HAGB) of blocks of tempered martensite lath structure (TMLS). However, their migration is negligible even during creep deformation. Boundaries of packets and prior austenite boundaries (PAB) are effectively pinned by precipitations of M₂₃C₆ and Laves phase Fe₂(W,N). The second process consists of transformation of lath boundaries to subboundaries and their subsequent migration (subgrain coarsening) under creep. Under aging the migration of low-angle boundaries (LAGB) is retarded by uniformly distributed nanoscale M(C,N) dispersoids and particles of M₂₃C₆ precipitated on these boundaries under tempering. Under creep the dissolution of M₂₃C₆ carbides located along LAGBs and coagulation of uniformly distributed M(C,N) carbonitrides facilitates LAGB migration. It was shown that the normal grain growth is not important for deterioration of creep strength. Conversion of the lath boundaries into subgrain boundaries strongly decreases creep rate. In contrast, continuous subgrain coarsening is the main process restricting the ability of the 9%Cr steel for long-range service under creep conditions. Tertiary creep is attained due to the occurrence of subgrain coarsening.

Abstract: The article is dedicated to the experiments and tests on the phenomena of precipitation and dissolution of alloy iron carbides in vacuum carburization processes. Special attention has been paid to the possibility of using artificial neural networks to predict the speed of the processes examined. In the section below, we are presenting the precipitation phenomena taking place in vacuum carburization processes and the experiments that were conducted. Moreover, a qualitative and metallographic analysis of carbide phenomena was described together with the method of numerical modelling and predicting the processes with the use of artificial neural networks.

Abstract: The article is dedicated to the experiments and tests on the phenomena of precipitation and dissolution of alloy iron carbides in vacuum carburization processes. This researches was done in order to evaluate to the possibility of using artificial neural networks to predict the speed of the processes examined (it is described in the part II). In the section below, we are presenting the precipitation phenomena taking place in vacuum carburization processes and the experiments that were conducted.