Small Amount Of Carbides Research Articles

Reactive Synthesis for Porous (Mo2/3Y1/3)2AlC Ceramics through Mo, Y, Al and Graphite Powders.

Through an activation reaction sintering method, porous (Mo2/3Y1/3)2AlC ceramics were prepared by Mo, Y, Al, and graphite powders as raw materials. The phase composition, microstructure, element distribution, and pore structure characteristics were comprehensively studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Archimedes method, and bubble point method. A detailed investigation was conducted on the influence of sintering temperature on the phase composition. Possible routes of phase transition and pore formation mechanisms during the sintering process were provided. The experimental results reveal that at 650-850 °C, transition metals react with aluminum, forming aluminum-containing intermetallics and a small amount of carbides. At 850-1250 °C, transition metals collaborate with graphite, producing transition metal carbides. Then, at 1250-1450 °C, these aluminum intermetallics interact with transition metal carbides and remaining unreacted Y, Al, and C, yielding the final product (Mo2/3Y1/3) 2AlC. Simultaneously, the pore structure alters correspondingly with the solid-phase reaction at different reaction temperatures.

Effect of Al addition on the microstructure and mechanical properties of IN718 alloy fabricated by laser deposition manufacturing

The IN718 alloys with different Al contents were fabricated by laser deposition manufacturing (LDM) technology. The microstructure and tensile properties of LDMed IN718 alloy with different Al contents before and after homogenization-solution-double aging (HSA) treatment were analyzed. The as-deposited samples show dendrite structure which develops with the addition of Al element. The microstructure of the as-deposited samples mainly consists of the γ matrix, Laves phases and a small amount of carbides. The HSA treatment improves the precipitation of γ″, γ′ and δ strengthening phases, and with the Al content increasing, the γ′ phase increases, but the γ″ phase decreases. With the increasing of Al content, the tensile strength of as-deposited samples increases, but the elongation decreases. For HSA-treated samples, the IN718+0.5Al alloy shows the highest tensile strength and elongation. The tensile fracture surfaces of LDMed IN718 alloys show dimpled surfaces, indicating the transgranular ductile failure mode.

Increased Hardness Value of Medium Manganese Steel Through Double Tempering, Hot Rolling, and Variation of Cooling Media

Research has been conducted to enhance the hardness value of medium manganese steel through a heat treatment. Initially, this process begins with austenization at a temperature of 900°C, followed by tempering at 650°C and double tempering at 600°C, with each stage lasting 30 minutes. Subsequently, each stage concludes with a hot rolling process, after which air or water cools the material. As a result of these processes, the hardness tests revealed an increase in the hardness of medium manganese steel, reaching up to 389.70 BHN with a tensile strength of 827 MPa, which was notably achieved through air cooling. This significant increase in hardness is attributed to the emergence of the martensite phase and the presence of a large number of carbides, which are more evenly distributed after the double-tempering process. Additionally, small amounts of carbides were observed in the austenite matrix. Upon examination of the SEM fractography results, it was revealed that the fracture was mixed, with a cleavage area slightly larger than the dimple area. This observation suggests that despite its high hardness value, the sample retains good toughness.

The influence of heat rate and austenitization temperature on microstructure and hardness of Hadfield steel

The As-Cast condition of Hadfield alloy usually contains (Fe, Mn)3C carbides around the austenitic grains, which promote brittleness, making the steel impractical in industry. Heat treatment is normally applied to reduce carbide content, lower carbides, and improve toughness. However, a complete austenitic structure is not attainable during solution treatment. The dissolution temperature and dissolution time are critical to obtaining complete carbide content. Furthermore, heating must be done slowly, and the quenching speed must be fast enough. This study examines the effect of heat rate and austenitization temperatures in the solution treatment on the microstructure and hardness of Hadfield steel. The heat rate of 3, 6 and 10 oC/min is selected to determine whether there is a change in the microstructure of Hadfield steel. The four austenitization temperatures of 1000, 1100, 1150 and 1200 oC are used to ascertain carbide dissolution into the austenite matrix. Grain boundary, hardness, and phase transformation will confirm the microstructural change and hardness properties. The optical microscope shows carbide content is reduced as the austenitization temperature increases. The consequence of carbide dissolution affects the hardness. Its hardness decreases as temperature increase due to the loss of carbide. The as-Cast specimen has the highest hardness of 227.8 HV30, and the lowest hardness is 176.7 HV30 belongs to a specimen that is heated up to 1200 °C and quenched into water. Grain size is measured by the line intercept method, which shows its increase as temperatures increase. The result of grain measurement is as follows: As-Cast 224.6 mm, T 1000 °C 323.3 mm, T1100 °C 409.2 mm, T1150 °C 1014.4 mm, T1200 °C 881.6 mm. SEM-EDS confirms that the main phase is austenite, and a small amount of carbide is detected in the austenite matrix.

Microstructure and properties of 1300-MPa grade Nb microalloying DH steel

In this study, ultra-high-strength DH steels with different phase compositions were designed, their tensile strengths were greater than 1300 MPa, and the multiphase microstructures contained ferrite, martensite, retained austenite, and small amounts of carbides. The effects of different phase compositions on the mechanical properties and strain hardening behaviors of the ultra-high-strength DH steels were compared, and the mechanism of the retained austenite in the ultra-high-strength DH steels was comprehensively studied. The results show that with the increase in the volume fraction of martensite and retained austenite and decrease in the ferrite volume fraction, the yield strength and tensile strength increase, whereas, the elongation rate first increase and then decrease. The decrease in the soft-phase ferrite volume fraction and increase in the volume fraction of the hard martensite phase led to an increase in yield strength and tensile strength. Compared with tempered martensite, quenched martensite could improve the strength more significantly. The retained austenite transformed in the tensile process was the main cause of the change in elongation. The remarkable banded structure in the microstructure will cause a significant decrease in elongation after necking. The analysis of the strain hardening behavior show that the strain hardening rate decrease with the increase in the true strain. When the true strain was greater than 2%, the strain hardening rate of the steels followed the order: DH1 > DH2 > DH3; this trend was mainly influenced by the ferrite volume fraction. The strain hardening rate of DH2 was higher than those of DH1 and DH3 when the true strain was greater than 5.73%, which was mainly related to the more significant transformation-induced plasticity (TRIP) effect in the DH2. In addition to the retained austenite volume fraction, the carbon content in the retained austenite also had a significant effect on the TRIP effect. The high proportion of the hard-phase martensite, appropriate proportion of the soft-ductile-phase ferrite, and retained austenite contributed to the DH2 steel having the greatest tensile strength and elongation (13.17 GPa·%); moreover, the yield strength was 880 MPa, tensile strength was 1497 MPa, uniform elongation was 6.71%, total elongation was 8.8%, elongation after necking was 2.09%, and yield ratio was 0.59.

Dilatometric and Microstructural Study of Martensite Tempering in 4% Mn Steel.

This paper presents the results of martensite tempering resistance in 4% Mn steel. The material was quenched and tempered at 350 °C for 15, 30, and 60 min. The analysis of the quenching and tempering was carried out using dilatometric and microstructural approaches. The phase composition was assessed using X-ray diffraction. The Ms temperature and tempering progress were simulated using JMatPro software. The dilatometric analysis revealed a small decrease in the relative change in length (RCL) during tempering. This decrease was connected to the precipitation kinetics of cementite within the martensite laths. The microstructure investigation using a scanning electron microscope showed a very small amount of carbides, even for the longest tempering time. This showed the high tempering resistance of the martensite in medium-Mn steels. The hardness results showed an insignificant decrease in the hardness depending on the tempering time, which confirmed the high tempering resistance of martensite.

Differences between the composition of surface and inner layers of fly ash particles

By studying samples from Czech power plants burning brown coal using X-ray photoelectron spectrometry (XPS) have demonstrated differences in the composition of the ashes in their surface and subsurface layers. The main components of the samples were compounds of aluminum, silicon and oxygen - aluminosilicates. Other elements included sulphur, fluorine and in some cases demonstrably calcium, sodium, magnesium, fluorine and iron. The largest part of the carbon compounds present is the so-called "adventitious carbon", contaminating carbon, i.e. hydrocarbons adsorbed on the surface from the atmosphere. Others come from technology including a small amount of carbides. Distribution of sulphur and iron compounds detected using a short time ion etching is in most cases following: sulphur compounds are concentrated on the surface of ash particles while iron compounds are typically concentrated inside. Differences in composition of surface layers were found to be significant as in the surface composition as in theirs depth profiles. Gas evolution was detected in an ash-water reaction test in which the analysis of the gas has shown that it is mainly about hydrogen and carbon dioxide. Another test with water showed the formation of an incrustation and documented the evolution of gases by the formation of bubbles. The released gases can form explosive mixtures with air, which must be taken into account when removing deposits with a water jet.

Microstructure gradient characteristics and mechanical properties of friction stir welded high strength QP980 steel

Friction stir welding (FSW) was carried out on 1.2 mm thick QP980 steel plate and W-Re stirring tool was used for FSW. This study focused on the microstructure gradient characteristics and mechanical properties of QP980 FSW joints. The FSW joints without defect could be obtained under welding parameter of 400 rev min−1–400 mm min−1. The martensite was the mainly microstructure in the stir zone (SZ) and the microhardness of the SZ was increased to about 480 HV. The martensite of the subcritical heat affected zone (SCHAZ) underwent tempering transformation and decomposition, small amount of carbides were precipitated from the martensite, so the microhardness of the SCHAZ was slightly decreased. The microstructure in the SZ had the highest dislocation density and the highest fraction of low angle boundaries. The tensile test results indicated that the joints were broken in the base metal (BM), which indicated that the FSW joints had excellent performance.

Preparation by Ball Milling–Thermal Decomposition Method and Characterization of Reduced Graphene Oxide Decorated with Ni Nanoparticles

Nickel acetate tetrahydrate [Ni(CH3COO)2·4H2O] was used as a precursor to prepare reduced graphene oxide decorated with Ni nanoparticles (Ni-rGO) by a ball milling–thermal decomposition method. Ni-rGO was characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction analysis, Fourier-transform infrared spectroscopy, and Raman spectrometry, and the adsorption energy between Ni atom and rGO was calculated based on first-principles calculations using density functional theory. The results showed that ball milling could be used to effectively restrain the agglomeration and reduce the size of rGO, and improve the adsorption energy between Ni particles and rGO. With increase of the milling time, the nucleation sites of Ni particles increased while the size of the Ni nanoparticles decreased. The thermal decomposition products of Ni(CH3COO)2·4H2O in Ar atmosphere were Ni with a very small amount of carbides. Ni-rGO was obtained by reduction of GO, ball milling, and thermal decomposition processes, and the combination between Ni atom and rGO was via chemisorption.

Effects of C and Mo on microstructures and mechanical properties of dual-phase high entropy alloys

A systematic study of the effects of interstitial element C and high melting point element Mo on the microstructural evolution and mechanical properties of dual-phase CoCrFeNiAl0.5 high entropy alloys (labeled as HEAs) is presented. In order to obtain a fine-grained microstructure, the HEAs were produced by powder metallurgy (P/M) method. Microstructures and mechanical properties were characterized using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA) and tensile tests. The results show that, with the addition of C and Mo, all the P/M HEAs exhibit a fine equiaxed microstructure. A small amount of carbides and σ phase are distributed evenly on the HEA matrix. The CoCrFeNiAl0.5 HEA containing 8 at. % of Mo and C shows combined high strength of 1280 MPa and reasonable ductility of 7.1%. The improvement of the tensile strength is caused by the solid solution strengthening, fine-grained strengthening and precipitation strengthening. The good ductility results from the fine-grained microstructure.

Effects of Isothermal Aging on Microstructure Evolution, Hardness and Wear Properties of Wrought Co-Cr-Mo Alloy

In this work, effects of isothermal aging on phase transformation, microstructure evolution, hardness and wear resistance of the wrought Co-Cr-Mo alloy with low carbon content were investigated. Initially, temperature range of FCC to HCP phase transformation of the alloy was determined by a dilatometer test. Then, aging at the temperature of 850 °C for different holding times with subsequent water quenching was carried out. Metallography examination, x-ray diffraction analysis, microhardness test and wear test were performed for Co-Cr-Mo alloy specimens after the isothermal aging. It was found that the FCC to HCP phase transformation occurred in the temperature range between 700 and 970 °C. During the aging treatment, phase fraction of the HCP martensite increased with longer aging time. The FCC to HCP phase transformation was completed after 12 h, because very fine lamellae in different orientations thoroughly dispersed within FCC grains were observed. These lamella structures could be well correlated with formation of the HCP martensite. Small amounts of carbides were found at grain boundaries and grain intersections in the samples aged for 6 and 12 h. In addition, by longer aging time, the average grain size of the aged alloy became a little bit larger, while the hardness noticeably increased. For the examined Co-Cr-Mo alloy, higher amount of the emerged HCP martensitic phase led to the increased hardness value, but reduced friction coefficient and wear rate.

Effects of Microalloying on the Impact Toughness of Ultrahigh-Strength TRIP-Aided Martensitic Steels

The effects of the addition of Cr, Mo, and/or Ni on the Charpy impact toughness of a 0.2 pct C-1.5 pct Si-1.5 pct Mn-0.05 pct Nb transformation-induced plasticity (TRIP)-aided steel with a lath-martensite structure matrix (i.e., a TRIP-aided martensitic steel or TM steel) were investigated with the aim of using the steel in automotive applications. In addition, the relationship between the toughness of the various alloyed steels and their metallurgical characteristics was determined. When Cr, Cr-Mo, or Cr-Mo-Ni was added to the base steel, the TM steel exhibited a high upper-shelf Charpy impact absorbed value that ranged from 100 to 120 J/cm2 and a low ductile–brittle fracture appearance transition temperature that ranged from 123 K to 143 K (−150 °C to −130 °C), while also exhibiting a tensile strength of about 1.5 GPa. This impact toughness of the alloyed steels was far superior to that of conventional martensitic steel and was caused by the presence of (i) a softened wide lath-martensite matrix, which contained only a small amount of carbide and hence had a lower carbon concentration, (ii) a large amount of finely dispersed martensite-retained austenite complex phase, and (iii) a metastable retained austenite phase of 2 to 4 vol pct in the complex phase, which led to plastic relaxation via strain-induced transformation and played an important role in the suppression of the initiation and propagation of voids and/or cleavage cracks.

Evaluation of the quality of cladding deposited on continuous steel casting rolls

Abstract This paper presents the quality analysis of cladding layers deposited on continuous steel casting rolls made of 41CrMo4 (EN 10083-1-91). The effect of filler used on the tribological properties of claddings was analyzed. There was minimal mixing between the base material and interlayer observed in the process of hard surfacing. The microstructure of the interlayer and the coatings is martensite–ferrite. Dispersed carbides MC, M 7C3, and Cr23C6 were observed in the interlayer. Small amounts of carbides were also observed in the cover layer along with Cr2N and CrN, which was confirmed by energy dispersive X-ray analysis. The highest average hardness, 410 HV30, was measured in the cover layer at a distance of 1 mm from the surface. The lowest hardness was found in the base material, 239 to 243 HV30. The hardness of the interlayer metal is affected by mixing of cladding and cover layer metal. The cladding metal showed a martensite–ferrite structure and fine precipitates in the interlayer, and diffraction spectra of the carbides had the characteristics of MC, M 7C3, and Cr23C6 carbides. Lower abrasive wear has been reported in the reference material (a roll with a surface-hardened layer), which is in line with the contact surface hardness of test samples.

Effects of Hot-Forging Process on Combination of Strength and Toughness in Ultra High-Strength TRIP-Aided Martensitic Steels

Recently developed ultra high-strength low alloy transformation-induced plasticity (TRIP)-aided steel with martensitic lath structure matrix or "TRIP-aided Martensitic steel; TM steel" possesses a high impact toughness. In this study, to apply the TM steel to some hot-forging parts, the effects of hot-forging on microstructure, retained austenite characteristics, tensile properties and toughness in the TM steels with chemical composition of 0.3-0.4%C, 1.5%Si, 1.5%Mn, 0.002%B, 0.02Ti, 0.05Nb (mass%) were investigated. The hot forging brought on an excellent combinations of tensile strength of 1500-2000 MPa or 0.2% offset proof stress of 1200-1560 MPa and Charpy impact absorbed value of 35-80 J/cm2 when partitioned at 250-350°C after quenching in oil. The combinations exceeded so much those of the conventional quench and tempering structural steels. From examinations of microstructure and retained austenite characteristics, it was found that the excellent combinations are mainly caused by (i) refined and uniform martensitic lath structure matrix with a small amount of carbide, (ii) increasing narrow martensite with high dislocation density and (iii) the increased stability of retained austenite, resulting from the FQP process.

Experiment Study on Micro-Hardness and Structure of NC Grinding Surface Layer of Spiral Bevel Gears

Through the analyses of experiment,mechanism of dislocation and coupling of grinding temperature and deformation field,many conclusions are gotten.Firstly,a tempering metamorphic layer of lower hardness is formed in hardening zones of grinding layer of spiral bevel gear. Secondly,the microstructure of grinding tooth surface is acicular martensite+residual austenite+ a small amount of carbides,and it’s outside to the inside presents the variation of "fine→coarser→finer".Thirdly, the critical condition of grinding burns is obtained,that is when grinding temperature is above 600°C,metamorphic layer depth is greater than 0.2mm or more. The formation characteristics of grinding cracks is also revealed. These provide a basis for the NC grinding quality control of spiral bevel gears.

Study on the softening in overlapping zone by laser-overlapping scanning surface hardening for carbon and alloyed steel

Softening in overlapping passes by laser-overlapped scanning surface hardening is a difficult problem of laser surface modification. Despite the advantage of laser quenching, softening in overlapping zone limits its practical application. In this paper, 45, 9Cr2Mo and W18Cr4V steel were hardened by laser-overlapping quenching. Softening occurred in all overlapping zones. The results of hardness testing indicated the softening width of 45 steel was the broadest and that of W18Cr4V steel was the narrowest. Different mixed microstructures composed the overlapping zone for three steels, i.e., tempered sorbite and a little tempered martensite in 45 steel, tempered martensite, tempered sorbite and a small amount of carbides in 9Cr2Mo steel, tempered martensite and a little carbide in W18Cr4V steel. The effect of activation energy of diffusion for carbon in steel and cooling rate on the decomposition of martensite have been investigated by developing a diffusion model based on the principle of carbon diffusion in martensite. The results indicated that action energy for diffusion of carbon in steel plays a main role in hindering decomposition of carbide and cooling rate has a limited action in reducing temper softening during laser-overlapping scanning.

Neutron diffraction analysis of martensite ageing in high-carbon FeCMnSi steel

Abstract A high-carbon metastable austenite phase was quenched in liquid nitrogen to obtain fresh athermal martensite. Different ageing treatments were performed in order to study the transformation of the martensite phase and the formation of carbides. Neutron diffraction experiments give detailed information on the transformations during the annealing treatment itself. The tetragonal athermal martensite transformed immediately, i.e. during the heating to the ageing temperature, to cubic martensite. Ageing at 400°C resulted in the decomposition of the austenite in ferrite and carbides and the formation of bainite. Those carbides could be determined as -carbides transforming in -carbides after extended annealing times. As was expected, ageing at 170°C resulted in the formation of a small amount of carbides while the austenite phase remained stable.

Mechanism study on solid‐state reduction in the Fe2O3–NiO–Cr2O3–C system using thermal analyses

In order to clarify the interactions among metal oxides during reduction of pickling sludge, the reduction mechanism of the metal oxide mixture, Fe2O3–NiO–Cr2O3, which simulates the composition of these metal oxides in pickling sludge, was studied using graphite as a reductant, by means of thermal analysis techniques. X‐ray diffraction analysis was used for characterization of reduction products. In addition to the reduction test on the metal oxide mixture mentioned above, for comparison, separate tests on the reduction of Fe2O3, NiO and Cr2O3 were also conducted. The results demonstrate that through formation of a transitional compound ‘FeCr2O4’, Fe2O3 promotes the complete reduction of Cr2O3 at a temperature lower than that required for reducing pure Cr2O3. On the other hand, Cr2O3 hinders the reduction of Fe2O3 at lower temperatures. The whole reduction process may be classified as five distinguishable reduction stages in which possible reactions were proposed to represent the reduction mechanism. The reduced metals in the final product exist primarily in the form of solid solutions, such as ‘Cr–Fe–Ni’, which mainly containing ‘(Fe,Ni)’ and ‘(Fe,Cr)’, and small amounts of carbides, such as (Cr,Fe)7C3 and/or Cr7C3.

Influence of tungsten carbide particle size and distribution on the wear resistance of laser clad WC/Ni coatings

Thick composite coatings of carbides (e.g. WC) in a metal matrix are ideal for components subject to heavy abrasive wear. An emerging deposition technique for such wear resistant cemented carbide coatings is laser cladding. This technique has, contrary to surface welding and spraying methods, the potential to coat very locally and on highly complex components. Adhesion and damage resistance is also improved by laser cladding. In this paper the influence of carbide particle size and distribution on the wear resistance of laser clad coatings is discussed. A nickel based matrix reinforced with WC/W 2C carbides is deposited by a CO 2 laser on low carbon steel substrates. Different coatings are made with three different particle sizes of the carbides and volume fractions ranging from 0 up to 50%. Three different wear modes are evaluated. First, ball-on-disc tests with an Al 2O 3 ball have been performed. The ball cratering test with 4 μm SiC abrasive is used to assess mild abrasive wear. Finally, the resistance against severe two body abrasion is tested in a pin-on-disc test. A clear dependency of the wear resistance on the carbide concentration is found, which is more pronounced for the coatings with the finest WC/W 2C carbides. The magnitude of the decrease in wear however is highly dependent on the wear mode. In two body abrasion and in the sliding wear, a small amount of carbides is sufficient to improve the wear resistance drastically. Other coating characteristics such as microstructure, hardness and internal stress are assessed.

Precipitation Behavior on Carbon Steel Modified by Double Glow Plasma Surface Alloying with W and Mo

Many brittle precipitates appeared in the alloyed layers which were formed in surface modified carbon steel by DGPSA (Double Glow Plasma Surface Alloying) with W and Mo because of the slow cooling rate in the alloying furnace. As a result, the mechanical properties of these alloys were significantly degraded by precipitation of the brittle phase. Phase analysis of the electro-extracted precipitates by X-ray diffraction (XRD) revealed that they were mainly composed of the μ-phase and a small amount of carbide, M6C . In the present study, their microstructures were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). It was concluded that the chemical components, temperature and time were the main thermodynamic factors influencing their deposition. The isothermal transformation (IT) diagram of the precipitates showed that there were two transforming climaxes. Based on the IT diagram, a technique was developed to depress the precipitate deposition.