3C Carbide Research Articles

Temper-Resistance of Cr-W-Mo-V High Carbon Medium Alloy Steel and its Hardness Forecast

The temper-resistance temperature of Cr-W-Mo-V high carbon medium alloy steels is in a range at 200°C-300°C. Along with increasing C and alloy contents in particular Cr content of the steels, the temper-resistance is boost up gradually and maximal hardness arrives to 63-64HRC at temperature 200°C-250°C. When budget for quenching matrix composition and undissolved carbides, the actual quenching temperature TH is corresponding to the calculational temperature TC by phase-equilibrium thermodynamics as TH=TC + (1000°C－TC)/6.5, and roughly, the calculational temperature is less 20°C than actual temperature when quenching at 800°C-890°C. The carbides precipitation during tempering is agreement with phase equilibrium thermodynamic calculation incompletely, thereinto (Fe,Cr)3C carbide precipitation is leading at 200°C-250°C.The higher hardness at temper-resistance temperature is corresponding to tempering temperature of remnant austenitic decomposing acutely.The tempering hardness can be estimated on the basis of quenching hardness calculation. The quenching hardness value can be obtained from HC=α（1+β）/(0.00915α+0.00527), in which α is the square root of carbon content in the matrix and β is correction coefficient of solid solution strengthening.

Comparison of the microstructures in continuous-cooled and quench-tempered pre-hardened mould steels

The increased demand for plastic mould steels in pre-hardened condition has drawn the attention to this specific type of steel. As a result, more investigations are performed to understand microstructure and properties. In this work, the microstructures of two pre-hardened plastic mould steels, one quench-tempered (Uddeholm Impax HH) and the other continuously cooled (Uddeholm Nimax), are studied in delivery condition by means of different microscopy techniques and are linked to their production procedure. The results show that the quench-tempered material contains large amounts of M 3C carbides formed within the martensite plates as well as at the lath- and prior austenite grain boundaries. A few coarser Cr-rich M 7C 3 carbides have also been found. In comparison, the microstructure of the continuously cooled material consists of mainly bainite with much lower density and finer cementite particles. The hardness is with ∼40 HRC more or less constant over the cross section of both materials.

Study of the adsorption, electronic structure and bonding of C 2H 4 on the FeNi(1 1 1) surface

The adsorption of C 2H 4 on the FeNi(1 1 1) alloy surface has been studied by ASED-MO tight binding calculations. The C 2H 4 molecule presents its most stable geometry with the C C bond axis parallel to the surface along the [1, −1, 0] direction, bonded on top Fe atom and bonded along a Fe–Fe bridge site. As a consequence, the strength of the local Fe–Fe bond decreases between 37 and 62% of its original bulk value. This bond weakening is mainly due to the new C–Fe interactions however no Fe 3C carbide formation is evidenced on surface. The Fe–Ni and Ni–Ni superficial bonds are only slightly modified.

X-ray diffraction and Mössbauer spectrometry studies of the mechanically alloyed Fe–6P–1.7C powders

Nanostructured Fe–6P–1.7C powders were obtained by mechanical alloying in a planetary ball mill. Morphological, microstructural and structural changes during the milling process were followed by scanning electron microscopy, X-ray diffraction and 57Fe Mössbauer spectrometry. The crystallite size refinement to the nanometer scale (5–8) nm is accompanied by an increase in the internal strain. The nanocrystalline structure distortion is evidenced by the lattice parameter changes of the milling products. The hexagonal Fe 2P phosphide is formed within 6 h of milling, while the tetragonal Fe 3P and orthorhombic Fe 3C phases appear after 12 h of milling. A mixture of Fe 3P phosphide, Fe 3C carbide and α-Fe(C, P) solid solution is obtained on further milling time.

Effects of recrystallization annealing temperature on carbide precipitation, microstructure, and mechanical properties in Fe–18Mn–0.6C–1.5Al TWIP steel

The microstructure, dimple structure, and mechanical properties of a cold-rolled Fe–18Mn–0.6C–1.5Al TWIP steel were investigated as a function of annealing temperature. The recrystallization started at 600 °C and finished at 700 °C for the holding time of 10 min. The coarsening rate of recrystallized grains was increased over about 840 °C and Rockwell hardness was greatly decreased between 800 and 900 °C, which shows a good agreement with the equilibrium dissolution temperature of M 3C carbides. The reversion of the tensile strength occurred between 700 and 800 °C because of the carbide precipitation hardening. The precipitation-time-temperature diagram was generated by dilatometric tests, showing a nose temperature of 800 °C. The dimple size was decreased to 700 °C and then increased again with higher annealing temperature, having a strong proportional relationship with austenite grain size.

Abrasive wear study of white cast iron with different solidification rates

The abrasive wear resistance of white cast iron was studied. The iron was solidified using two solidification rates of 1.5 and 15 °C/s. Mass loss was evaluated with tests of the type pin on abrasive disc using alumina of different sizes. Two matrices were tested: one predominantly austenitic and the other predominantly martensitic, containing M 3C carbides. Samples with cooling rate of 15 °C/s showed higher hardness and more refined microstructure compared with those solidified at 1.5 °C/s. During the test, the movement of successive abrasives gave rise to the strain hardening of the austenite phase, leading to the attainment of similar levels of surface hardness, which explains why the wear rate showed no difference compared to the austenite samples with different solidification rates. For the austenitic matrix the wear rate seems to depend on the hardness of the worn surface and not on the hardness of the material without deformation. The austenitic samples showed cracking and fracture of M 3C carbides. For the predominantly martensitic matrix, the wear rate was higher at the solidification rate of 1.5 °C/s, for grain size of 66 and 93 μm. Higher abrasive sizes were found to produce greater penetration and strain hardening of austenitic matrices. However, martensitic iron produces more microcutting, increasing the wear rate of the material. The analysis of the worn surface by scanning electron microscopy indicated abrasive wear mechanisms such as: microcutting, microfatigue and microploughing. Yet, for the iron of austenitic matrix, the microploughing mechanism was more severe.

Load effect in abrasive wear mechanism of cast iron with graphite and cementite

In this study four irons were casted with different chromium and vanadium contents: 2.66% Cr, 5.01% Cr, 2.51% V and 5.19% V. Their microstructure is composed of: ledeburite, graphite and M 3C carbides (cementite). Pin-abrasion tests were carried out using fixed alumina abrasive grains at different loads: 1, 2, 4.6 and 10 N. The wear surface and the abrasive paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results reveal that the mass loss increased with the load increase, and the effect of the percentage of chromium on mass loss is inverted when the load is increased from 4.6 to 10 N; for 4.6 N the mass loss decreased when the chromium percentage was increased from 2.66% to 5.01%. Nevertheless, for 10 N the mass loss increased when the chromium percentage was increased. The worn surfaces of the materials tested at 1 N show microcutting caused by the abrasive tip that produces continuous microchips. The worn surfaces and the abrasive paper tested at 10 N show continuous microchips and brittle debris. The results show that high pressures produce a brittle wear mechanism and low pressures produce a more ductile wear micromechanism, for this, the applied pressure defines the dependence between the wear resistance and wear micromechanism.

Effect of the additions of carbide-forming elements on the microstructure and mechanical properties of steel shot

The effect of the additions of carbide-forming elements (vanadium, titanium, chromium, molybdenum) on the microstructure and mechanical properties of the steel shot produced by the atomization of an iron-carbon melt (0.8% C) by water at a low pressure (0.2 MPa) is studied. The introduction of alloying elements is shown to affect the sizes of the structural constituents that form during the solidification of shot particles and, hence, the mechanical properties (hardness, wear resistance) of the shot. The additions can decrease the grain size in the shot by a factor of 2.5–3. The formation of the MC (M is a carbide-forming element), VC, TiC, or M 2C (e.g., Mo2C) carbide increases the hardness of the shot material. Chromium and molybdenum form solid solutions with iron and complex (Fe, M)3C carbides.

Microstructural characterization of Hadfield austenitic manganese steel

distribution of the precipitate in the modified Hadfield austenitic manganese steels [12‐18]. However, the associated decarburization with the heat-treatment has not been reported. In the present investigation, an effective solution heat-treatment has been adopted to dissolve the (Fe, Mn)3C carbides in Hadfield austenitic manganese steel. The influence of the solution annealing heat-treatment on the microstructure, hardness values and abrasive wear resistance of Hadfield austenitic manganese steel have been also discussed. The synthesis of the steel was carried out in a high frequency air induction furnace. At first the blend of steel scrap (0.049%C, 0.43%Mn, 0.028%Si, 0.023%P, 0.013%S, 0.003%Al, 0.035%Cr and balance Fe, all in wt.%) and cast iron (4.5%C, 0.043%Mn, 1.05%Si, 0.175%P, 0.043%S and balance Fe, all in wt.%) was heated to 1,580 C and maintained at that temperature for 15 min followed by addition of calculated amount of electrolytic manganese (95% purity) to the melt. The melt was stirred continuously at this temperature for 10 min and finally cast in a metallic mould.

The formation of a tungsten containing surface layer in a carbon steel by compression plasma flow

Morphology, phase and elemental composition of a carbon steel surface layer after treatment by compression plasma flows containing a dispersed tungsten powder have been investigated in this work. The action of relatively short (∼ 120 μs) and intense (15–20 J/cm 2 per pulse) plasma pulses resulted in the formation of tungsten containing thin film consisting of clusters with the size of 100–200 nm. Besides, the film formation treatment with a few pulses allowed to alloy a surface steel layer with tungsten. This treatment also led to the formation of Fe 3W 3C and WC carbides in the surface layer.

Microstructure characteristics of Ni-based WC composite coatings by laser induction hybrid rapid cladding

To avoid low cladding rate and cracks of cladding layer, laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite coatings at the different laser scanning speed were investigated. For low laser scanning speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W 2C + Fe 3W 3C carbides, and bar-like (W, Cr, Ni) 23C 6 carbides were formed. With increasing laser scanning speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W 2C + FeW 3C + W 6C 2.54 carbides. With further increasing laser scanning speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W 2C + W 6C 2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.

An investigation of secondary carbides in the spray-formed high alloyed Vanadis 4 steel during tempering

The precipitation of secondary carbides in spray-formed high alloyed Vanadis 4 steel during tempering at 500, 550, and 700 °C has been characterized and the carbides identified in detail using transmission electron microscopy. It was observed that the very fine and dense nature of the secondary MC precipitates was responsible for the secondary hardening peak when tempered at 500 °C. When the tempering temperature was elevated to 550 °C, the hardness greatly decreased due to the precipitation of M 3C carbide. Overageing at 700 °C resulted in transformation of the fine secondary carbides to coarse M 7C 3, M 23C 6, and M 6C and a change in the matrix morphology from martensitic plates to recrystallized ferrite. The decomposition at this temperature initiates with the nucleation of fine M 7C 3 carbides preferentially at the martensite lath boundaries; prolonged 24 h tempering results in fully equiaxed, recrystallized ferrite and coarse precipitates.

Influence of secondary carbide precipitation and transformation on abrasion resistance of a 3Cr15Mo1V1.5 white iron

The relationship between the secondary carbide precipitation and transformation of the 3Cr15Mo1V1.5 white iron and abrasion resistance was investigated by using optical microscope (OM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the properties of secondary carbides precipitated at holding stage play an important role in the abrasion resistance. After certain holding time at 833 K subcritical treatment, the grainy (Fe, Cr) 23C 6 carbide precipitated and the fresh martensite transformed at the holding stage for 3Cr15Mo1V1.5 white iron improve the bulk hardness and abrasion resistance of the alloy. Prolonging holding time, MoC and (Cr, V) 2C precipitations cause the secondary hardening peak and the corresponding better abrasion resistance. Finally, granular (Fe, Cr) 23C 6 carbide in situ transforms into laminar M 3C carbide and the matrix structure transforms into pearlitic matrix. These changes weaken hardness and abrasion resistance of the alloy sharply.

Atomic structures of iron-based single-crystalline nanowires crystallized inside multi-walled carbon nanotubes as revealed by analytical electron microscopy

Atomic structures of single-crystalline iron-based nanowires crystallized inside multi-walled carbon nanotubes during pyrolysis on silicon substrates with ferrocene as a precursor were analyzed using high-resolution analytical transmission electron microscopy and electron diffraction. Standard crystal lattices, namely body-centered cubic (bcc) α-Fe, face-centered cubic (fcc) γ-Fe and orthorhombic cementite Fe 3C, were all found to form inside the nanotubes. A fraction of α-Fe nanowires, thermodynamically favorable at room temperature, was found to be dominant. Both bcc and fcc nanowires display a wide variety of lattice planes being parallel to the nanotube walls, with none of the orientations being preferable. The minor fraction of the nanowires had unidentified long-period crystal lattices with doubled or tripled periodicities as compared to those found in the standard cubic iron phases. The crystal matching of these unusual structures to stable orthorhombic Fe 3C or less stable iron carbides, e.g., Fe 5C 2, Fe 7C 3, failed. The non-conventional phases were tentatively assigned to rarely seen silicon-doped octahedral iron carbides. Both long-period and standard cementite nanowires exhibited well-defined transient zones in the vicinity of nanowire–tube shell interfaces, where perfectly ordered carbide lattice fringes disappeared. The results suggest the non-existence of metastable equilibrium in the nanoscale Fe–C system between carbide and graphite phases during iron crystallization inside graphitic tubular channels.

Influence of secondary carbides precipitation and transformation on hardening behavior of a 15 Cr–1 Mo–1.5 V white iron

The influence of secondary carbides precipitation and transformation on hardening behavior of a 14 Cr–1 Mo–1.5 V white iron in sub-critical treatment was studied by using optical microscope (OM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that two hardening peaks appeared in the process of sub-critical treatment at 833 K, and the reasons for the two hardening peaks are different. In sub-critical heat treatment, Martensite transformation and (Fe,Cr) 23C 6 precipitation from austenite matrix, which harden the alloy, are responsible for the first hardening peak. MoC and (Cr,V) 2C precipitations and/or transformation from M 23C 6 causes the secondary hardening peak. Furthermore, the in situ transformation of (Fe,Cr) 23C 6 to M 3C carbide causes the formation of pearlite and an associated decrease of the bulk hardness.

TEM study on precipitation and transformation of secondary carbides in 16Cr–1Mo–1Cu white iron subjected to subcritical treatment

High chromium white irons solidify with a substantially austenitic matrix supersaturated with chromium and carbon. The subcritical heat treatment can destabilize the austenite by precipitating chromium-rich secondary carbides and other special carbides. In the as-cast condition the eutectic carbides are (Fe,Cr) 7C 3 and (Fe 4.3Cr 2.5Mo 0.1)C 3. The initial secondary carbide precipitated is (Fe,Cr) 23C 6 after heat-treating at 853 K for 10 h. There are MoC, Fe 2MoC and ɛ-carbide precipitating, and (Fe,Cr) 23C 6 transforms to M 3C after 16 h at 853 K. The ɛ-carbide and (Fe,Cr) 23C 6 accomplish transformation to M 3C and the matrix changes from martensitic to pearlitic after 22 h at 853 K. Thereby, in the subcritical heat treatment process, the initial secondary carbide precipitated is (Fe,Cr) 23C 6, followed by ɛ-carbide, MoC and Fe 2MoC. In addition, there are two in situ transformations from (Fe,Cr) 23C 6 and ɛ-carbide to M 3C carbides.

Microstructural characterisation of Fe–Cr–P–C powder mixture prepared by ball milling

In an attempt to prepare amorphous Fe 77Cr 4P 8C 11 alloy by mechanical alloying, powder mixtures of Fe, Cr, P and C (activated carbon) with a purity of 99.9% have been ball milled, under argon atmosphere for several periods up to 90 h, in a planetary ball mill (Fritsch P7). The structure and microstructure of the milled powders have been characterised, as a function of milling time, by X-ray diffraction and Mössbauer spectrometry. During the first stage of milling (up to 12 h), detailed analyses of the diffraction patterns and the Mössbauer spectra reveal a complete dissolution of the elemental powders and the formation of Fe x P (1 < x < 2), Fe 3P phosphides and Fe 3C carbide in addition to α-(Fe,Cr) phase. The amorphous like state is reached after 32 h of milling. Further milling leads to the appearance of new carbides such as (Fe,Cr) 7C 3 and ɛ′-Fe 2.2C with the phosphide (Fe,Cr) 3P type phase embedded in the amorphous matrix.

Inter-phase corrosion of chromium white cast irons in dynamic state

In the present paper, chromium white cast irons were prepared by the unidirectional solidification. The carbide sample was extracted for the corrosion and wear test. The inter-phase corrosion mechanism and the electrochemical behavior of chromium white cast irons in corrosion medium were discussed from the viewpoints of electrochemistry and erosion wear. The inter-phase corrosion rates between carbide and matrix were obtained for chromium white cast irons. It can be concluded from the investigation that the inter-phase corrosion rate of the alloy is more than half of the total corrosion rate in the medium. The electrochemical behavior of carbide is quite different from the test alloys and the matrixes, and the carbide always is in the self-passive state. The corrosion resistance of type M 7C 3 carbide is higher than that of type M 3C carbide. The free corrosive potential difference between carbide and matrix is the driving force of the inter-phase corrosion. In the present corrosive environment, the carbide is protected, but the matrix is corroded rapidly. Increasing the free corrosion potentials of the matrix can not only reduce the inter-phase corrosion rates, but also raise the corrosion resistance of chromium white cast irons greatly.

Structure and phase transformations of AISI M2 high-speed tool steel treated by PIII and subsequent compression plasma flows of nitrogen

The effect of ‘double’ treatment (plasma immersion ion implantation and subsequent compression plasma flows) on microstructure, element and phase composition, as well as on microhardness properties of AISI M2 high-speed tool steel has been studied. Such methods as Auger electron spectrometry (AES), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis and scanning electron microscopy (SEM) allowed us to obtain the data suggesting that under such treatment a martensite-austenite conversion and the formation of a deep (approx. 35 μm) three-layered structure take place. It has been established that transformations of near-surface regions are associated with the complete dissolution of the initial (Fe, Cr) 3(W, Mo) 3C carbide (≤5–10 μm) and the formation of γ N,M expanded austenite doped with atoms of nitrogen, carbon and alloying metals M=W, Mo, Cr.

Effect of carbide distribution on the fracture toughness in the transition temperature region of an SA 508 steel

An investigation was conducted into the effect of carbide distribution on fracture toughness in the ductile–brittle transition temperature region of an SA 508 steel used for nuclear reactor pressure vessels. Tensile properties and elastic–plastic cleavage fracture toughness were measured in the transition temperature region, and the fracture toughness data were interpreted by using a simple fracture model containing carbide size distribution. This modeling study indicated that the critical nearest-neighbor distance between coarse carbides was an important microstructural factor affecting elastic–plastic fracture toughness, since it satisfied a linear relationship with the critical distance between a crack tip to a cleavage initiation site. These findings suggested that reducing the total number of carbides, particularly the number of M 3C carbides larger than the critical size, and homogeneously distributing fine M 2C carbides, were useful ways to improve fracture toughness in the transition temperature region.