Complex Carbides Research Articles

Competition between formation of carbides and reversed austenite during tempering of a medium-manganese steel studied by thermodynamic-kinetic simulations and atom probe tomography

We investigated the thermodynamics and kinetics of carbide precipitation in a cold-rolled Fe-7Mn-0.1C-0.5Si medium manganese steel during low temperature tempering. The material was annealed up to 24 h at 450 °C in order to follow the kinetics of precipitation. Using thermodynamics and kinetics simulations, we predicted the growth of M23C6 carbides according to the local-equilibrium negligible partition (LENP) mode where carbide growth is controlled by the diffusion of carbon, while maintaining local chemical equilibrium at the interface. Atom-probe tomography (APT) measurements performed on samples annealed for 1, 6 and 24 h at 450 °C confirmed that LENP is indeed the mode of carbide growth and that Mn segregation is necessary for the nucleation. Additionally, we observed the heterogeneous nucleation of transition carbides with a carbon content between 6 and 8 at% at segregated dislocations and grain boundaries. We describe these carbides as a complex face-centered cubic transition carbide type (CFCC-TmC phase) obtained by the supersaturation of the FCC structure by carbon that will act as precursor to the more stable γ-M23C6 carbide that forms at the dislocations and grain boundaries. The results suggest that the addition of carbon does not directly favor the formation of austenite, since Mn is consumed by the formation of the carbides and the nucleation of austenite is thus retarded to later stages of tempering as every FCC nucleus in the initial stages of tempering is readily converted into a carbide nucleus. We propose the following sequence of transformation: (i) carbon and Mn co-segregation to dislocations and grain boundaries; (ii) formation of FCC transition carbides; (iii) growth controlled according to the LENP mode and (iv) austenite nucleation and growth.

Investigation of iron adsorption on composite transition metal carbides in steel by first-principles calculation

The nucleation potential of transition metal (TM) carbides formed in steel can be predicted by the behavior of iron adsorption on their surface. Therefore, Fe adsorption on the (001) surface of (A1-xmx)C (A = Nb, Ti, m = Mo, V) was investigated by the first-principles method to reveal the initialization of Fe nucleation. The Mulliken population and partial density of state (PDOS) were also calculated and analyzed in this work. The results show that Fe adsorption depends on the composition and configuration of the composite carbides. The adsorption energy (Wads) of Fe on most of (A1-xmx)C is larger than that of Fe on pure TiC or NbC. The maximum Wads is found for Fe on (Nb0.5Mo0.5)C complex carbide, indicating that this carbide has the high nucleation capacity at early stage. The Fe adsorption could be improved by the segregation of Cr and Mn atoms on the surfaces of (Nb0.5Mo0.5)C and (Ti0.5Mo0.5)C. The PDOS analysis of (Cr, Mn)-doped systems further explains the strong interactions between Fe and Cr or Mn atoms.

Microstructure and mechanical behavior of hot-work tool steels processed by Selective Laser Melting

The present study is aimed at identifying and testing high-strength alloys for tooling applications featuring suitable processability for laser-based additive manufacturing technologies. The microstructure and mechanical properties of the H11 hot-work tool steel and a leaner version of the same alloy (L-H11) processed by Selective Laser Melting were assessed as a function of specific microstructural conditions obtained by performing different heat treatments. Tempering was performed on quenched alloys or simply from as built material. The rapidly solidified microstructures revealed able to respond directly to precipitation hardening treatment without performing any prior solution annealing. The microstructure of the as-built alloys revealed characterized by α-Fe dendritic cells decorated at boundaries by C-rich γ-Fe regions. Air quenching was responsible for the transformation of the solidification cells into lath martensitic structures and for the formation of the M3C phase, which transformed into more complex carbide species on tempering. The hardness of quenched and tempered H11 steel is similar to that obtained by processing the alloy with conventional routes, and the final hardness gap between the two SLM processed H11 and L-H11 alloys treated according to optimal tempered condition was limited to 62 HV.

Structure-property relationships in thermo-mechanically processed Titanium - Molybdenum steels

A new Ti and Mo micro-alloyed hot rolled high strength steel was developed through thermo-mechanical controlled processing (TMCP). Microstructure and mechanical property of the above steel were investigated as a function of finish rolling temperature (FRT: 850°C and 750°C) followed by air cooling and water quenching. Microstructures of above steels processed at two FRTs were analysed by optical microscopy, scanning electron microscopy and precipitated particles were examined using transmission electron microscopy (TEM) coupled with energy- dispersive X-Ray spectroscopy (EDS). It is observed that air cooled sample processed at lowest FRT of 750°C reveals fine precipitates (10-20 nm) almost homogenously distributed throughout the ferrite phase. EDS results indicate presence of complex carbides precipitates of (TiMoV)C. These fine particles are significant for precipitation hardening. Air cooled steels exhibit 428 to 441 MPa yield strength and 643 to 683 MPa ultimate tensile strength along with 21 to 23% elongation, whereas higher yield strength of 931 to 1026 MPa and tensile strength of 1057 to 1154 MPa along with lower 9 to 11% elongation has been obtained after water quenching.

Surface properties tuning of welding electrode-deposited hardfacings by laser heat treatment

In this paper, several Cr-Mn-rich hardfacings have been open-arc deposited on S275JR carbon quality structural steel and further submitted to laser treatment at different powers. An overall increase with 34–98% in the average microhardness and wear resistance of the coatings has been obtained, due to the formation of martensite, silicides, as well as simple and complex carbides on the surface of the hardfacings, in comparison with the reference, not submitted to laser thermal treatment. Surface laser treatment of electrode-deposited hardfacings improves their chemical resistance under corrosive saline environments, as determined by the 43% lower amount of leached iron and respectively, 28% lower amount of manganese ions leached in a 10% wt. NaCl aqueous solution, comparing with the reference hardfacings. Laser heat treatment also promotes better compatibility of the hardfacings with water-based paints and oil-based paints and primers, through the relative increasing in the polar component of the surface energy (with up to 65%) which aids both water and filler spreading on the metallic surface.

Microstructural Studies of Cobalt Based Microwave Clad Developed on Martensitic Stainless Steel (AISI-420)

AISI-420 stainless steel is widely used to manufacture hydraulic and gas turbine components. The present work is concerned with microstructural studies of cobalt based clad developed through microwave energy in a microwave applicator. A domestic microwave oven was successfully used to develop clads at 2.45 GHz frequency. The developed clads were evaluated using optical metallography, scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction (XRD) to determine the microstructure, phases and elemental composition of developed surface. The microstructure study reveals that the developed clad shows good metallurgical bond between substrate without any interfacial cracks. XRD study confirms the presence of various complex metal carbides and intermetallics like Cr7C3, Cr3C2, M23C6, Cr2Ni3 which are formed during microwave heating. The average microhardness of the developed clad surface is 807 ± 96 HV, which is 132% higher than that of unclad surface (348 ± 7 HV).

Aspects Regarding Repetitive Maintenance Concept in Push Blades for Loading Equipment

Preventive repeated maintenance concept provides elaborating, developing and reconditioning, repeatedly, in economic efficient conditions, of the pushing blades that equip bulk loading machines, namely leveling them. Applying the solution implies developing and elaborating active areas in direct contact with processed materials by loading through welding. To this end the base material of the blades is chosen to comply with the addition material afferent to the selected process, for predetermined circle tries, approx. 5 in the present moment.Research conducted to validate the loading through welding technology had primary objectives to obtain material couples base/addition that have a high resistance to intense bending demands, under load, combined with a good abrasion usage resistance or high pressure. The chemical composition of the basic materials in the pushing blades, is afferent to high resistance steels, with a maximum of1.6%Mn, max. 1.5%Cr, max.2%Ni, max. 0.7%Mo and max. 0.005%B. The chemical composition of the deposited material, through welding, falls into steel prescription, type Fe-25%Cr-5%W-Nb-Ti-B, with metallographic structures that have a high content of complex carbides and hardness of minimum 60 HRC. Sclerometric tried and metallographic research of specific area of the deposited metal/base metal ensemble did not highlight any imperfections such as cracks or white sports in the thermal influenced areas.Research regarding exploitation behaviour, of basaltic aggregates in loading conditions or cereals, have shown a good resistance at wear.

Interaction of Chromium Carbide with Tungsten Oxide and the Effect of Synthesized Products on the Wear Resistance of Metal Matrix Composites Created

The interaction processes in the Cr7C3–WO3 system during high-temperature heating are considered. It is established that the resulting powder products are characterized by a multicomponent composition, in which chromium carbide and complex carbides of chromium and tungsten dominate. The properties and structure of these fine-grained powder compositions (master alloys) are studied. It is established that the microstructure of alloyed samples based on powdered iron with the addition of developed master alloys is characterized by high homogeneity and dispersion with fibrous, rod, and lamellar nanoscale carbide formations. The density, microhardness, hardness, and wear resistance of alloyed samples are determined. The effect of developed master alloys on the abrasion wear resistance of alloyed metal matrix composites is established.

Precipitation of Nano-Sized Carbides in a Ti-Mo Bearing Steel at a Low Transformation Temperature

While the role of Ti and Mo elements on precipitation strengthening in ferrite grains formed during austenite/ferrite transformation is very clear, some uncertainty still presents concerning influence of microalloying elements on bainite transformation. Therefore, the present study focuses on the precipitation behavior occurred in a Ti-Mo bearing steel during bainitic phase transformation under different heat treatment conditions, and the correlation of the precipitation behavior with hardness distribution. Through the present work, it is expected to achieve a better understanding of low-temperature precipitation behavior to assist metallurgists to find out the reason for maintaining a high hardness by longtime isothermal holding, which can provide insight to design a better quality steel product. Vickers hardness was measured from the 1C-2Ti-2Mo, 1C-2Ti-2Mo and 0.5C-1Ti-2Mo steels treated by isothermal holding at 550 oC for 5 to 60 min. The average Vickers hardness was in the range of 245 - 276, 290 - 335 and 220 - 245, respectively. Therefore, higher hardness can be obtained if the steel containing higher carbon and microalloying elements can form precipitations in the ferrite matrix. On the other hand, increasing Vickers hardness with isothermal holding times indicates a good thermal stability character of complex carbides. The excellent thermal stability can be attributed to the addition of Mo element, which can inhibit the growth of carbides during longtime isothermal holding. Furthermore, the addition of Mo in the steel can avoid annihilation of dislocations during longtime aging. By taking advantages of these two effects, high strength can be achieved for high-strength low-alloy steels containing Mo element. Transmission electron microscopy image showed nano-sized carbides nucleated at dislocations, instead of interfacial precipitations within ferrite grain matrix, because the interface precipitation morphology only occurred accompanying the austenite decomposition reaction. However, the bainitic phase transformation was of a displacive transformation character, thus the complex carbides could not form during the bainitic phase transformation due to a very fast transformation velocity.

Diode Laser Surface Alloying of Armor Steel with Tungsten Carbide

AbstractMetal matrix composite (MMC) surface layers reinforced by WC were fabricated on armor steel ARMOX 500T plates via a laser surface alloying process. The microstructure of the layers was assessed by scanning electron microscopy and X-ray diffraction.The surface layers having the WC fraction up to 71 vol% and an average hardness of 1300 HV were produced. The thickness of these layers was up to 650 μm. The addition of a titanium powder in the molten pool increased the wettability of WC particles by the liquid metal in the molten pool increasing the WC fraction. Additionally, the presence of titanium resulted in the precipitation of the (Ti,W)C phase, which significantly reduced the fraction of W-rich complex carbides and improved a structural integrity of the layers.

Effect of Heat Treatments on the Mechanical Properties of DIN 50Cr3 Spring Steel

Abstract: This experimental study was conducted to investigate the optimum combination of properties between ductility and toughness from one hand and strength and hardness from the other hand of a commercial grade of light duty spring steel DIN 50Cr3 having a chemical composition of (0.25 % C, 0.8%Cr , 0.79%Mn , 0.2% Si).A heat treatment process by quenching in both oil or water followed by tempering cycles at different temperatures for various tempering times was adopted. The proper austenitization temperature was found to be 870 C. The structure after quenching reveals the formation of martensite with limited amount of retained austenite. Tempering was performed at different temperatures from 250 to 550 C for prolonged times ranging from 1hr up to 3 hr.It was found that oil quenching provides sensibly higher elastic properties than water quenching particularly in the low tempering temperature range. More ever, by increasing the tempering temperature and time ultimate tensile strength, hardness were gradually decreased while ductility remarkably improved. The resultant microstructure after tempering was characterized by a tempered martensitic structure with simple and complex dispersed carbides. Optimum elastic properties were delivered out of this steel after tempering at 450 C for 1hr.

Microstructure and wear resistance of Fe-Cr13-C-Nb hardfacing alloy with Ti addition

In order to achieve the maximum benefit from the carbide-forming elements Ti and Nb, it is very important to have a better understanding of the strengthening mechanism of the two carbide-forming elements in the hardfacing alloy.The Fe-Cr13-C-Nb hardfacing alloy with and without Ti addition were deposited respectively on carbon steel substrates by shielded metal arc welding. The carbide-forming elements in the two hardfacing alloys were S1-0.158Nb and S2-0.156Nb+0.263Ti(wt.%). Optical microscope (OM), scanning electron microscope (SEM) and energy-dispersive spectrometer(EDS) were used to investigate the effect of titanium addition on the microstructure of the hardfacing alloy. The impact experiment was conducted using the Charpy impact testing machine. The wear resistance was tested through a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied.The results show that, the carbide precipitation of the Fe-Cr13-C-Nb hardfacing alloy was determined by Ti addition. Ti has greater affinity than Nb for carbon to form TiC, and the prior TiC precipitates act as nucleation sites for NbC to promote precipitation of complex carbides in the hardfacing alloy. The microstructure of the Fe-Cr13-C-Nb hardfacing alloy with titanium addition exhibited hard carbides dispersion in a tough martensite matrix, where the hard carbides provide the resistance to abrasion. So the Fe-Cr13-C-Nb hardfacing alloy with titanium addition showed a better wear resistance, and the wear mechanism was mainly interrupted plastic grooves with minimum depth and desquamation of carbides.

Evolution of mechanical properties and microstructure of differently cryogenically treated hot die steel AISI–H13

AbstractThis paper investigates the influence of different cryogenic treatments vis-à-vis conventional vacuum heat treatment on the evolution of static mechanical properties and microstructure of hot die steel grade AISI–H13. Deep cryogenic treatment was performed under two different temperatures (−154 °C and −184 °C) and varying soak duration of 6, 21, and 36 h. The resultant mechanical properties were characterized in order to understand the influence of cryogenic treatment vis-à-vis vacuum heat treatment and tempering on the hardness, toughness and the tensile strength. The results showed that samples cryogenically treated at −154°C for a soak duration of 6 h and tempered at 620°C for 2 h had 3.1% higher hardness, samples cryogenically treated at −184 °C for a soak duration of 6 h and tempered at 620 °C for 2 h showed 69 % higher percentage elongation, 36% higher toughness (Charpy V–notch) and showed 12.8% reduction in tensile strength in comparison to conventionally treated samples. X-ray diffraction and field emission scanning electron microscopy techniques were utilized for confirmation of various phases and complex carbides, morphology of microstructure and morphology of fractured surfaces, respectively.

Effect of Complex Carbide Precipitates on the Structure and Mechanical Properties of Cold-Rolled Ultra-Low Carbon Steels During Bell-Furnace Annealing

Features of the formation and evolution of nanosize carbonitride precipitates and their effect on the microstructure and mechanical properties of cold-rolled product of medium-carbon steels microalloyed (stabilizing) with titanium of an industrial melt with a different carbon content are studied. It is established that precipitates have a complex (Ti,Nb)C composition, there is almost no nitrogen within them, although Nb is present in spite of its low (impurity) content in the steel. Precipitate size increases with an increase in temperature, annealing duration, and carbon content in steel. It is shown that during annealing in bell furnaces the structure and properties of rolled product are determined by the action of three main factors: occurrence of primary and selective recrystallization, with a direct and indirect (by delaying recrystallization) effect of nanosize carbide precipitates, and also the degree of reduction during skin rolling. During annealing of test steel cold-rolled product in bell furnaces, it is possible to achieve a unique set of mechanical properties that are difficult to combine: a prescribed low value of yield and ultimate strength ratio (0.60–0.75) with relative reduction of area of 30%, which is important for manufacturing complex shape components by efficient forging methods and deep drawing. Optimum values of annealing and skin rolling parameters providing preparation of these mechanical properties are determined.

A Study on the Aging Behavior of Al6061 Composites Reinforced with Y2O3 and TiC

The reinforcement particles play important roles in determining microstructural development and properties of Al6061 composites. In the present work, the aging behavior of Al6061 reinforced with Y2O3 and TiC particles produced via mechanical alloying are investigated. The results indicate that the peak-aged Al6061 alloy without reinforcement demonstrates the highest hardness, which corresponds to the formation of the Mg–Si precipitates. However, precipitation formation is not observed in the case of the Al6061 composites, which can be attributed to the fact that the Mg–Si clusters and GP zones are inhibited by the presence of the reinforcement particles. The solute elements segregate in the complex oxides or carbides and contribute to only a slight increase in hardness.

Effect of carbon impurity in irradiated mixed uranium–plutonium nitride on the phase composition upon β−-decay of fission products

As shown by thermodynamic modeling, accumulation of fission products in the course of irradiation of mixed uranium–plutonium nitride containing 0.25 wt % C impurity leads to the formation of a multicomponent carbonitride solid solution containing U, Pu, Am, Np, Zr, Y, lanthanides, and also separate carbide (UMoC2, U2RuC2, URu3C0,7, BaC2, SrC2) and nitride (U2N3) phases and intermetallic compounds U(Ru, Rh, Pd)3. The β−-decay of metallic radionuclides in separate carbide phases of spent nuclear fuel leads to changes in their chemical compositions. The transformation kinetics of separate dicarbide (89SrC2 → 89YC2, 90SrC2 → 90YC2 → 90ZrC + C, 140BaC2 → 140LaC2 → 140CeC2) and complex carbide (U99MoC2 → UC2 + 99Tc) phases was calculated.

Simulation of quenching process of steels creating complex carbides

The scientific research, presented in this paper, deals with numerical modelling of the quenching process of conventional carbon steels. The developed numerical model simulates the quenching process of the hypereutectoid steels whose microstructure contains complex carbides. Those include the high-alloyed hyper-eutectoid steels intended for example for bearings, or high speed steel products. The calculation software SYSWELD, based on the finite element method, was used. The results of numerical modelling were compared with actual properties of quenched samples made of the hyper-eutectoid bearing steel. The microstructure was studied and hardness was measured in order to verify the numerical model's accuracy. The presented results indicate the absence of carbidic phase in the simulation calculations. This implies relatively large deviations in the simulated hardness results compared toh reality. Those deviations must be considered in the case of simulating the microstructure and hardness of bearing steels using the SYSWELD software.

Осаждение покрытий из металлического стекла электроискровой обработкой в среде гранул состава Fe39Ni8Cr7W7Mo7Co2C16B14

The article is devoted to the deposition of FeNiCrWMoCoCB coatings on the basis of metallic glasses on a steel 35 substrate by an electrospark treatment in a medium of granules of pure metals and alloys used as electrode materials. X-ray diffraction studies have shown the predominance of the amorphous phase in the coating composition. It is shown that its fraction increases with an increase in the run-in time of the granules mixture used up to 300 min. According to the X-ray data, during annealing, the amorphous phase persists up to the temperature of 600°C and then crystallizes into the phase of a complex iron-based carbide (Cr,Fe,W,Mo)23Fe12(W,Mo)2C12 . The corrosion properties, microhardness and wear resistance of the coatings obtained are studied. Polarization tests in a 3.5 % aqueous NaCl solution showed an increase in the corrosion potential of the coatings with an increase in the run-in time of the granules used. A completely metallic glass coating showed a lower corrosion current and a higher polarization resistance as compared to steel 35. The study of oxidation kinetics has shown that the use of the FeNiCrWMoCoCB coating on steel 35 increases the resistance of its surface to high-temperature gas corrosion by 16 times in 100 hours of testing at a temperature of 700°C. The microhardness of the deposited layers was about 8 GPa that is 4 times higher than that of non-coated steel 35. The wear resistance of the deposited FeNiCrWMoCoCB coatings to dry sliding friction relative to P6M5 steel showed that its wear for 30 km of the test was almost 2 times lower than that of steel 35. The proposed approach opens the possibility for a one-stage synthesis of metallic glasses in the form of coatings in an automatic mode from individual crystalline components.

Development of Ni-WC composite clad using microwave energy

Cladding of suitably designed materials on functional surface which are subjected to sever tribological loading can lead to increase in components life. Development of clad includes several techniques such as thermal spraying, High velocity oxy fuel and laser cladding. However cladding done through the above listed process pertain certain defects like cracks, distortion, poor adhesion strength etc.In the present work a new process method has been developed to clad Ni (matrix)-80 wt.%WC (reinforcement)-20 wt.% powder on poor wear resisting material through microwave irradiation of frequency 2.45GHz. The characterization of developed clad is done using X-ray diffraction (XRD), Field emission electron microscope (FE-SEM), Back scattered electron image and Vickers micro hardness. XRD pattern of developed composite clad showed presence of compounds like NiSi, NiW, and W2C phase. The wear resistant complex carbide phase have been seen in the structure of the clad transverse section showed good metallurgical bonding between the substrate and the developed clad.

Electrods type Fe-25%Cr-4%W-V-Ti-La for hard surfacing

Performing the active surfaces subjected to abrasive wear by hard surfacing is difficult to made because the missing of adequate materials. This fact imposed the elaboration and implementation into industrial production of a new generation of materials with adequate properties. In order to assure the wear protection of the surfaces in contact with materials to be processed, these surfaces must be characterized by high hardness and toughness. Elaboration of the product recipe for the electrodes type Fe-25%Cr-4%W-V-Ti-La was made by comparison between the data mentioned in the speciality literature and the experimental results obtained by SIMPLEX method for wear resistance. Improving the depositions toughness was obtained by microalloying with lanthanides, but structures finishing was made by addition of V and Ti. In the slagging process, the electrodes basicity was min. 3.2 BB units, and metallic powders were been elected in such a way as the electrodes to be in the grade of max. 5cm3 /100g deposited metal. The deposited metal using the electrodes fabricated in the above mentioned conditions has a fine grained martensitic structure, having a high content of complex carbides of Cr, V and Ti, and the hardness of min. 60 HRC.