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The solid/liquid interface shapes and the solidified microstructures of the pseudo-binary eutectic γ-(Fe,Cr)3C were investigated under unidirectional solidification conditions. It has been observed that the microstructural forms of the eutectic structure are highly dependent on the morphology of the solid/liquid interface. During planar growth, the eutectic has a quasi-lamellar morphology. During cellular growth, the eutectic exhibits many oval cells or arrays, each of which displays three-dimensional growth anisotropy. Whilst growth parallel to the sample axis results mainly in a lamellar or split lamellar eutectic structure, lateral growth yields the characteristic ledeburitic structure. The ledeburite exhibits a rod-like regular eutectic morphology, with a volume fraction of the minor γ-phase from 20% to 35%, much smaller than its average value (47%) in the whole sample. Based on the structure observed, a growth pattern for the ledeburitic eutectic is proposed.

The precipitation of copper has been detected and studied in three of the main decomposition products of austenite: allotriomorphic grain-boundary cementite, pearlitic cementite, and Widmanstatten cementite plates. The investigation has been carried out on two high-alloy hypereutectoid steels containing copper contents of 1.0 and 2.5 wt pct. The main advantage of these high-alloy steels is that the parent austenite phase remains stable upon cooling to room temperature, thus preserving the parent phase and the parent/product interfaces in the microstructure for subsequent examination. Transmission electron microscopy (TEM) revealed that the copper precipitation occurs in proeutectoid allotriomorphic grain-boundary cementite in association with the transformation interface. The copper particles were dispersed in the form of rows (or sheets) within the allotriomorphs of cementite. Evidence for copper precipitate particles nucleated at structural features imaged at the growth interface was also obtained. Copper precipitation was found to occur in both the ferrite and cementite lamellae of pearlite, and again, examination of partially decomposed structures revealed copper particles nucleated at the austenite/pearlite transformation interface. In addition, copper particles were also observed at the ferrite/cementite interface of pearlite. Copper precipitation observed in Widmanstatten cementite plates revealed a precipitate-free midrib region in the plates and a higher concentration of copper particles toward the broad faces of the plate. Copper particles were also found located at coarse linear interface defects at the broad faces of the plate.

Pearlitic grey cast iron was surface melted using a 500 W CW CO2 laser at travel speeds 0.5–100 cm s−1. Detailed structural analysis of the laser modified layer was performed by optical and scanning electron microscopy (SEM), and microhardness depth profiles were measured. Temperature distribution was calculated from a three dimensional moving point source model, taking only the heat transfer into account. From the structural details observed in the austenitized zone some conclusions on the mechanism and kinetics of the pearlite austenite transformation at high heating rates were drawn. The melted zone consisted of primary austenite and ledeburite. At lower scanning speeds the structure was dendritic, at higher scanning speeds transition to dendritic-cellular structure was observed. From the secondary dendrite arm spacings the cooling rate during solidification was estimated as a function of the depth. Some discrepancies were found between our measurements and the literature data as well as predictions by the simple model neglecting convection in the melt.

The composition of pearlitic cementite in a 1 2 Cr 1 2 Mo 1 4 V steel has been extensively for long tempering times at a number of different temperatures. The chromium content of the cementite is found to increase steadily with time as the microstructure is tempered, at the expense of the iron content. Transformation of the cementite to alloy carbides occurs at long tempering times. The composition changes in the cementite have been modelled theoretically using numerical methods. There is excellent agreement between the predictions of the model and the experimental results. The dependence of composition on particle size has been studied and has been shown not to be significant because of the relatively large size and low chromium concentration of the pearlitic cementite. It is therefore possible to estimate an effective service temperature of components of 1 2 Cr 1 2 Mo 1 4 V steel in power plant for use in prediction of their remanent life.

Solidification behavior of high-nickel grain roll materials has been studied experimentally with a unidirectional solidification method. Two specimens were employed; A had the standard chemical composition, and B had the composition which promoted white iron solidification. Solidification structures were observed, and the amount of graphite was measured. The temperature difference between ledeburite (γ+Fe3C) and austenite-graphite (γ+G) eutectic fronts was measured, and there appeared to be a good correlation between this value and the amount of graphite. Then the positions of the two eutectic fronts and the temperature difference were discussed with regard to solidification parameters.The results obtained were as follows:(1) The critical cooling rate of transition from white to mottled iron in A is 0.12-0.15 K s–1, and for B, it is 0.050-0.067 K s–1.(2) The austenite-graphite eutectic front precedes the ledeburite eutectic front at a smaller growth rate, while the latter forms first at a larger growth rate in A. Ledeburite always forms first in B.(3) The sequences and temperature difference of both eutectic fronts agree with the results calculated using the Fe-C binary eutectic solidification model.

The spheroidization of cementite at subcritical and intercritical temperatures was studied quantitatively by evaluation of a shape factor for the cementite particles. It was found that the degree of spheroidization, as determined by the values of the shape factor, was markedly accelerated by treatments consisting in either (1) subcritical annealing after cold deformation or (2) intercritical annealing followed by subcritical annealing. Nevertheless, some differences were found among the microstructures resulting from the above treatments, which were related to the mechanisms of cementite formation in each of them. Also, the kinetics of austenitization during intercritical annealing was found to be accelerated by previous deformation, and the analysis of the formation of austenite at intercritical temperatures in terms of an Avrami equation was consistent with an "effective" saturation of ferrite-pearlite boundaries with austenite nuclei, followed by a planar mode of growth into the pearlite nodules.

Samples of a low alloy Cr-Ni-Mo mottled cast iron were melted using CW CO2 laser radiation. The laser treated layer presents severe defects, mainly cracks and pores. The amount of defects depends on the laser treatment technique, on the exact choice of operating parameters, as well as on the cast iron elaboration procedure. The best results were obtained using moderate power density, long interaction times, a moderate overlap between consecutive tracks and preheating the samples. The size of the graphite lamellae and the impurity content must be restricted to reduce the density of pores. The microstructure of the resolidified material depends also on the laser treating parameters. When the scanning speed is low, the solidification structure contains primary austenite dendrites in a ledeburitic matrix. During cooling, austenite transforms partially into martensite. An increase in the scanning speed leads to a decrease in the fraction of ledeburite and to a increase in the fraction of retained austenite. When the scanning speed exceeds a limit which depends on the power density, normal lamellar ledeburite disappears and a solidification structure consisting of long austenite dendrites with a interdendritic film of cementite forms. No martensite was detected in this case.

The mechanical and tribological properties of white cast irons are strongly dependent on whether they contain M7C3 or M3C carbides (M = Fe, Cr,etc.). In an effort to improve the wear resistance of such materials, the United States Bureau of Mines has studied the effects of adding 0.3 to 2.3 wt pct (throughout) Si to hypoeutectic irons containing approximately 8.5 pct Cr and 6.0 pct Ni. The eutectic carbides formed were identified by electron microprobe analysis, X-ray diffraction, and scanning electron (SEM) and optical microscopies. In addition, differential thermal analysis (DTA) was used to study the process of solidification. At Si contents of 0.3 and 1.2 pct, the eutectic carbides exhibited a duplex structure, consisting of cores of M7C3 surrounded by shells of M3C. Additionally, the microstructure contained ledeburite (M3C + γFe (austenite)). At the higher Si content of 1.6 pct, the eutectic carbides consisted entirely of M7C3, and some ledeburite remained. Last, when the Si content was raised to 2.3 pct, the eutectic carbides again consisted entirely of M7C3, but ledeburite was no longer formed. These observations can be explained in terms of the effects of Si and, to a lesser extent, of Ni on the shape of the liquidus surface of the metastable Fe-Cr-C phase diagram. The addition of Si reduces the roles played by the four-phase class IIp reactionL + M7C3 → M3C + γFe and the ledeburitic eutectic reactionL → M3C + γFe in the overall process of solidification.

Dissolution of spheroidal cementite in austenite at 910 °C has been studied by means of scanning and transmission electron microscopy. Three different morphologies of transformation have been observed. Most of the particles undergo a more or less homogeneous shrinkage. However, some of the particles transform to austenite by a Widmanstatten type of reaction, whereby austenitic plates form inside the cementite. It is also observed that some of the cementite transforms to M7C3 carbide and austenite by a eutectoid reaction. The results can be understood by considering the phase diagram and assuming that local equilibrium prevails at the phase interface during the reaction.

The microstructures of the laser-hardened layer on gray cast iron were examined by optical microscopy, transmission electron microscopy and scanning electron microscopy. The wear test was done in a sliding wear device. The experimental results show that a structure with dendritic (M + A′) and interdendritically laminal transformed ledeburite (M + A′ + Fe3C) is formed in the melted layer and a structure with clusters of acicular martensite, retained austenite and graphite, i.e. (M + A′ + G), is formed in the solid transformed layer after laser melting processing. The martensite is a mixture of dislocation martensite and twin martensite. Dislocation pileups and twins are found to exist in the retained austenite. The strain-induced martensite transformation occurs in the retained austenite and the sequence of the transformation process during sliding wear is retained austenite (f.c.c.) → stacking fault (h.c.p.) → martensite (b.c.c.). The wear resistance of gray cast iron after laser melting processing is remarkably enhanced and the wear process consists of plastic deformation → initiation of microcracks → growth of microcracks → fracture (exfoliating metal chips) due to eliminating graphites (microcracks). The formation of transformed ledeburite and a large amount of retained austenite, the elimination of graphite flakes, and refinement of the microstructure are beneficial to the improvement in wear resistance after laser melting processing.

1. With accelerated heating up to the melting temperature during heat treatment for cast iron IChKh12M a composite structure is retained: a skeleton of primary ledeburite carbides included in a matrix of variable structure. 2. Use of accelerated austenitizing causes formation of a nonuniform solid solution of austenite in the cast iron matrix. Variation of the heating temperature and cooling rate makes it possible to change within wide limits the structure of the matrix and cast iron properties. An increase in heating temperature followed by slow cooling changes the cast iron matrix structure from pearlite-bainite to bainite-martensite. After quenching there is formation of a martensite-austenite structure. 3. Accelerated heating shifts the temperature of phase transitions for cast iron into a higher temperature region compared with furnace heating. On the basis of this an optimum heat treatment schedule was developed for cast iron IChKh12M which makes it possible to obtain high abrasive wear resistance. Heat treatment with heating for hardening in molten salts or electric heating is recommended for articles of cast iron IChKh12M which operate under abrasive wear conditions.

1. After electron beam treatment of the cast iron guides with an electron energy of E=1.5 MeV the structure of the surface layers consists of α- and γ-phases with a content in the latter of up to 1% C and also clusters ordered according to type Fe4C formed in the transition zone. In contrast to the original condition up to 10% austenite is observed in the transition zone of the iron. A ledeburite eutectic is formed in the surface and the transition zone to the base metal consists of fine crystalline martensite with areas of residual austenite, partially dissolved graphite inclusions, and ferrite grains. The fine crystalline martensite and the remaining ferrite grains are bordered with a troostite border. 2. Electron beam treatment with fusion of the surface of guides with gray iron with a ferrite matrix causes strengthening of them to a depth of up to 0.6 mm. 3. Production tests of the guides on the 250–2 mill in hot rolling of 8–10 mm wire in Western Siberia Metallurgical Combine showed an increase in their service life of 2 to 5.6 times.

The grain boundary cementite and Widmanstatten cementite consisted in a hypereutectoid steel have been considered to cause the brittle fracture. In this study, the effect of cobalt addition on the transformation behavior of the hypereutectoid steel has been examined in order to control the grain boundary cementite precipitation. It was found that in the case of hypereutectoid steels containing carbon content less than 1.3 wt%, the grain boundary cementite precipitation could be suppressed with the cobalt addition and patenting treatment.By suppression of grain boundary cementite, the hypereutectoid steel showed good drawability comparable with that of eutectoid steel and the increase of tensile strength comparing with eutectoid steel. The analysis using Embury-Fisher relation showed that the increase of workhardening rate was due to the refinement of lamellar spacing, which was confirmed by microstructural observation. Furthermore, it was found that refinement of lamellar spacing was attributed to increased carbon content in the case of fully pearlitic microstructure. The effect of cobalt addition on the transformation behavior was also discussed from CCT curves.

White cast iron powder rapidly quenched from the liquid condition with presence of the same phases and structural components differs markedly in structure from normally cast white iron.

Redistribution of alloying elements during tempering of a novel nanocrystalline steel consisting of a mixture of lower bainitic ferrite and carbon-enriched retained austenite has been analysed by atom probe tomography. Three physical processes, namely redistribution of substitutional solute across the austenite/bainitic ferrite interface before retained austenite decomposition, redistribution of solute across the lower bainite cementite/ferrite interface and the precipitation of transition carbides and cementite, have been observed. Results suggest that retained austenite decomposes during tempering before full equilibrium is reached at the interface. Moreover, cementite precipitates from supersaturated ferrite via a paraequilibrium transformation mechanism., The authors acknowledge financial support from European Coal and Steel Community (ECSC 7210-PR-345) and Spanish Ministerio de Ciencia y Tecnologı´a (Project-2006 6 0I 029). CGM would also like to thank Spanish Ministerio de Ciencia y Tecnologı´a for the financial support in the form of a Ramo´n y Cajal contract (Programa RyC 2004). Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by the Office of Basic Energy Sciences, Division of Scientific User Facilities, U.S. Department of Energy, under contract DE-AC05- 00OR22725 with UT-Battelle, LLC. The authors would also like to express their special gratitude to Prof. H.K.D.H. Bhadeshia for helpful discussions.

We studied the microstructure of the metallic inclusions in synthetic diamond crystals grown in FeNiC and FeCoC systems at a pressure of ≈ 5.5 GPa and a temperature of ≈ 1800 K. Scanning electron microscopy, X-ray diffraction, magnetic measurement and reflection optical microscopy have been used in the investigations. The metal inclusions in synthetic diamond crystals consist of ledeburite eutectic in a mixture with carbide.

Concepts of austenite stabilization in low carbon, low manganese steels via heterogeneous precipitation to produce compositional control of the austenite are discussed. A detailed thermodynamic analysis has been made of heterogeneous austenite formation in a microstructure consisting of tempered ferrite and dispersed manganese-rich cementite. A common basis has been defined for comparison of the energetics of two modes of austenite formation: (1) heterogeneous nucleation at a ferrite-cementite interface and subsequent growth into either ferrite or cementite and (2) heterogeneous precipitation on ferrite grain boundaries. A reduction in the manganese content of cementite below its equilibrium value was found to favor austenite nucleation at ferrite-cementite interfaces and the subsequent conversion of the cementite into austenite. Experimental verification of these results is also discussed.

A Damascus steel sword has been exhaustively examined to establish its chemistry, microstructure, properties, and something about its processing. The steel in this blade was a hypereutectoid, crucible-melted steel that was really quite clean. The principal inclusions were approximately 0.5 to 1.0 μm in diameter. The microstructure consisted of a pearlitic matrix with spheroidized primary cementite in a layered arrangement. The cementite layers were aligned with amazing regularity with individual layers containing several particles across their widths. The layered cementite distribution was compatible with the deformation of an original equiaxed cementite cellular array having a 400 μm diameter followed by an 85% reduction in thickness on forging. The final heat treatment resulted in a pearlitic matrix with a relatively fine pearlite spacing. The hardness and mechanical properties were measured and found to be those expected for a high carbon steel with a fine pearlitic microstructure.

1. The level of crack resistance of cast hypereutectoid steels is determined by the size of the inclusions of eutectic cementite which depends solely on the amount of carbon contained in the steel. Alloying with 0.86–1.72% Cr, 0.9–1.32% Ni and 0.16–0.3% Mo does not affect the amount of eutectic cementite, and has practically no effect on the level of crack resistance when the steel contains 0.90–1.00% C; it decreases somwhat when the carbon concentration increases to 1.80–1.90%. 2. Heat treatment (quenching in air from 920°C, tempering at 550°C) raises the level of crack resistance of chrome-molybdenum and chrome-nickel-molybdenum steels. The effect manifests itself the more strongly, the higher the degree of alloying of the steel with carbide forming elements is (with 0.9–1% C). 3. The optimal combination of hardness and dynamic crack resistance after heat treatment of specimens is attained in hypereutecoid alloy steels when the carbon content is slightly higher than the eutectoid concentration. This has to do with the complete dissolution of excess cementite and the formation of special globular carbides. The same combination of properties can be ensured in steels with higher carbon content by raising the degree of alloying of the steel with carbide forming elements.

It is studied the thermodynamic aspects of alloying effects during the treatment the low сhromium (3 − 5 % Cr) cast iron with Fe−Si−Mg inoculants. This effect is displayed at transformation of phase at cast iron structure. Instead ledeburite eutectic with cementite carbides Fe3C and (Fe, Cr) 3C the eutectic with carbide (Cr, Fe)7C3 is formed. Such carbide usually is formed at Chromium content no less 8 – 9 %. It is showed, what it caused the quasi-equilibrium state of cast iron during of it treatment with inoculants. On one side, the melt is the non equilibrium, because of into it presence the many microzones with higher content of Si and Mg. But on the other side the melt state at the microzones can to consider as quasi-equilibrium. In that microzones because of high carbon activity are created the conditions for carbide (Cr, Fe)7C3 forming. Such possibility it is confirmed by thermodynamic calculations. The application of the exposed effect is cause without the significantly expense to provide the substantial increasing of cast iron properties.

The model for austenite growth during α→γ transformation in steels is developed in order to provide modeling of the transformation kinetics with regard to the steel microstructure parameters and the processing condition. Two cases of austenite growth are considered, which can take place during intercritical annealing of low carbon steels. In the simplest case the one-dimension austenite growth is considered to start from the boundary between cementite and ferrite phases and to proceed into ferrite. Herewith, the rate-controlling stage of the growth process is the carbon diffusion from the cementite/austenite boundary to the austenite/ferrite boundary. In the second case the austenite growth is considered to start from the boundary between ferrite grain and pearlite region, and then proceeds into pearlite. Herewith, the carbon diffusion in austenite in immediate proximity to the transformation front controls the growth rate. Agreement of the models suggested with the experimental data is demonstrated.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The properties and fracture behavior of micro-alloyed and copper-bearing hot-rolled steels have been studied. It was found that copper precipitation occurred in both the ferritic and the cementite lamellae of the pearlite and thus seemed to have influenced the overall properties of the pearlite microstructure of the steels. A comparison of VC and e-Cu precipitation observed in the pearlite microstructure is presented. The effect of VC and copper precipitation on microcracking of the cementite lamellae of the pearlite is also discussed.

The aim of the paper is to discuss about the structural transformations at high-speed steel heating. Under the conditions of high-speed heating steel of posteutectoid composition realized by laser application and electron accelerator ledeburite formation that is the structure characteristic for pig iron has metallographically been revealed. Ledeburite formation in steels is conditioned by quick achievement of eutectic reaction temperature and keeping cementite areas in local fields at this temperature. It has been shown experimentally that ledeburite formation occurs at heating at the rate about 2500 degC/s in steel with windmannstet cementite structure.Using the method of mathematical simulation it has been shown that ledeburite structure theoretically cannot be obtained at heating steel with plate perlite structure thickness of which is 1-2 orders less than thickness of windmannstet cementite plates.

This paper deals with rapidly solidified binary Fe–C alloys containing 3.8 wt% and 4.3 wt% C. Their microstructure reveals that, as an effect of undercooling, the conventional eutectics have been suppressed and there is occurrence of the ferrite–cementite eutectic. Both phases are metastable: ferrite is supersaturated in C and cementite has a C deficiency. This is demonstrated by means of determination of phase fractions in metallographic sections and of lattice parameters via Rietveld refinement of X-ray diffraction patterns. A major consequence of non-stoichiometricity of cementite is the reduced value of the Curie temperature (up to 17 °C) with respect to that of the equilibrium compound. The maximum C deficiency in Fe3C1−x is estimated as x = 0.02. The free energy of defective cementite has been computed by means of the two sublattice model and compared with that of ferrite and austenite obtained from an assessed phase diagram. It is shown that the non-stoichiometric phase is close in energy to the equilibrium one for a composition range of several atomic per cent. It is suggested that this helps in explaining the mechanism of cementite dissolution by heavy deformation of ferrous alloys, and the ease of cementite nucleation in castings.

When cast irons containing ledeburitic cementite are heated, the peripheral regions of the inclusions are decarburized as a result of the diffusion of carbon to the surrounding metal, and the chemical composition of the carbide M3C deviates from stoichiometric. This is manifested by the formation of microrelief on the surface of the inclusion of ledeburitic cementite, in which the layered structure within a single monocrystal of cementite has practically a single preferred direction. The development of microrelief and the formation of baikovite have much in common.

Investigation into the behavior characteristics of particle phases in laser cladding WC-TiC-TaC/Co based ceramic-metal composite coating suggested that TiC particles had exhibited a continuous increase in amount from the bottom to the top of clad layer, and partial TiC particles gathered and became large. Partial WC and TaC particles exhibited smashing phenomenon (heat damage), and the degree of heat damage of both WC and TaC particles was much more serious than that of TiC particles. Experimental results also showed that there existed obviously a surrounding structure (Ti, W, Ta) C at edge of carbonitride phase TiC in clad coating. In addition, ledeburite with shape of fish-bone was generated in the toppest region of clad coating, coarser eutectic microstructures was generated in boding zone of clad coating in the liquid state solidifying process, and both of these microstructures contained W, Ti, Ta etc. elements.

Cold-drawn pcarlitic steel wires have the highest strength of all steel products.It is a promising way to enhance the mechanical properties by increasing the carbon content.However,the proeutectoid cementite forms easily due to the hypereutectoid composition and deteriorates the mechanical and processing properties of steel wires.It is important for hypereutectoid steel wire drawing to achieve a fine and fully pearlitic microstructure without proeutectoid cementite.The austenitization and following continuous cooling process were simulated in the dilatometer for a hypereutectoid steel. The microstructure was observed with OM and SEM.The transformation temperature,prior-austenite grain size,pearlitic interlamellar spacing and proeutectoid cementite thickness were determined by dilatometric curves or OM/SEM images.The austenite grain size increases rapidly with a higher temperature and almost keeps invariant with a longer austenitization time.Faster cooling rate,higher austenitization temperature or longer austenitization time decrease the starting and finishing temperature of phase transformation,widen the temperature range,refine the pearlitic interlamellar spacing and suppress the proeutectoid cementite precipitation(reduce the thickness or make it discontinuous). However,it is easy to form martensite which is bad for the homogeneity of pearlitic microstructure by increasing the cooling rate or austenitization temperature simply.A fine pearlite in a pseudoeutectoid microstructure is achieved by extending the austenitization time to 60 min and controlling the austenitization temperature and cooling rate.Discontinuous proeutectoid cementite is observed in the samples with the higher austenitization temperature.Higher austenitization temperature and longer time are helpful to weaken the carbon concentration gradient.The homogeneous carbon distribution restrains carbon diffusion for cementite nucleation during the proeutectoid cementite precipitation and pearlite transformation,which decreases the transformation temperature.Compare to pearlite transformation, the proeutectoid cementite precipitation is affected more strongly by the carbon diffusion due to a longer diffusion distance.Therefore,the precipitation amount of proeutectoid cementite is reduced if the carbon diffusion is restrained.The amount of grain corner and grain edge reduce more dramatically than that of grain boundary if austenite grain size increases.The proeutectoid cementite only nucleates in grain corner and grain edge.The pearlite nucleation can form in grain boundary.Therefore,the larger austenite grains result in the sharp reduction in the sites for nucleation of proeutectoid cementite. Then,the amount of proeutectoid cementite are reduced and the morphology becomes discontinuous.

Ductile iron in as-machined surface was remelted by a high power pulsed Nd:YAG laser. Processing efficiency, microstructure and hardness of the laser remelted layers were investigated as a function of processing parameters. Microstructural changes after successive multi-pass overlap remelting were studied. It is demonstrated that the processing results were sensitive to pulse frequency, pulse power density and spot diameter, while surface conditions have only minor influence. Depending on processing conditions, two types of microstructures in the laser remelted zone were observed. An extremely fine dendrite-free lamellar eutectic structure occurred in the surface layer of the melted track. In the lower part of the remelted track, a plate-like ledeburite interspersed by small amount of primary austenitic dendrite was present. In overlapping tracks, the previous rapidly solidified ledeburite was ultra-rapidly graphitized by the heat input from the successive remelting track. The thickness of the graphitization zone and the graphitized microstructure were closely related to the processing conditions. The phenomenon of the rapid graphitization has not been reported so far and is discussed as a consequence of the cycling temperature fluctuations during pulsed laser heating. The results were finally compared with those obtained with a CO2 laser using cw- radiation.

This paper describes an automatic system for segmentation and quantification of the microstructures of white cast iron. Mathematical morphology algorithms are used to segment the microstructures in the input images, which are later identified and quantified by an artificial neuronal network (ANN). A new computational system was developed because ordinary software could not segment the microstructures of this cast iron correctly, which is composed of cementite, pearlite and ledeburite. For validation purpose, 30 samples were analysed. The microstructures of the material in analysis were adequately segmented and quantified, which did not happen when we used ordinary commercial software. Therefore, the proposed system offers researchers, engineers, specialists and others, a valuable and competent tool for automatic and efficient microstructural analysis from images.

This work presents the examples of structural reasons for failure of the necks of cast iron rolls. The most common reason for damage of metallurgical roll necks is a presence of shrinkage porosity in their volume. Moreover, a high fraction of ledeburitic cementite can lead to the formation of a continuous net of eutectic carbides, which facilitate cracking. Even very thin net of secondary carbides, formed on the boundaries of former grain of austenite, can significantly facilitate propagation of the crack. Continuous net of ledeburitic cementite, in the case of its precipitation in a form of bands and existence of hardened areas in the alloy matrix can lead to roll neck fracture relatively easy. The use of flake graphite cast iron for metallurgical rolls increases a risk of the fracture of roll neck.

Two quenched plain-carbon steels containing 0.5% and 0.8% C have been subjected to tempering in the temperature range 100–700°C. The changes in structure and properties have been investigated by optical and transmission electron microscopy and hardness measurements. The 0.5% C martensite is lath type with strings of retained austenite decorating the lath boundaries, while the martensite in 0.8% C steel is mainly plate type with scattered austenite islands locked between the plates. On tempering the 0.5% C steel softens continuously because of the decomposition of the martensite into cementite and ferrite even at temperatures as low as 150°C. In contrast, the 0.8% C steel exhibits a definite hardening stage at 100°C, caused by precipitation of ordered particles about 300 nm in size. This is followed by precipitation of η- and e-carbides at 200°C and cementite at higher temperatures. Recovery in both steels started at 600°C and was complete by 700°C. This results in equiaxed ferrite grains with intergranular cementite beads.

1. The retained austenite in quenched steel R9M4K8 has a smaller lattice constant, which increases during tempering. This is evidently due to elastic compression of the austenite lattice during the martensitic transformation and the subsequent reduction of elastic deformation of austenite during tempering resulting from stress relaxation. 2. No stable cementite is observed in quenched steel R9M4K8. It appears after tempering for 1 h at 350–600°. This may indicate a substantial change in the properties of carbides of the cementite type formed in the presence of high-carbon martensite and austenite in the elastically compressed condition. The higher strength and toughness of quenched steel R9M4K8 in comparison with other high-speed steels are evidently due to the absence of cementite. 3. Intermetallic phases of the Laves type are observed in the steel in all structural conditions. 4. Special carbides of the MC (VC) and M2C (Mo2C) types are precipitated during tempering of steel R9M4K8. Highly dispersed M6C carbides are observed after tempering at temperatures above 650°, and thus M6C is a weakening phase. 5. After the optimal heat treatment (quenching from 1220°, austenite grain size grade 10–11, triple tempering at 560° for 1 h), ensuring the maximum hardness, strength, and toughness of steel R9M4K8, the structure consists of highly alloyed (∼7.3% alloying elements) twin-dislocation martensite, excess carbides (not dissloved during quenching) of the M6C and MC types, intermetallic phase of the Laves type (∼8.7%), and dispersed special carbides of the MC and M2C types with a size of order 50 A and M3C in the form of platelets with a length of 1000–5000 A and thickness 100–700 A (∼5.0% in all).

In this paper the total driving force for the decomposition of retained austenite and martensite are calculated together with the nucleation and growth characteristics of cementite in the two phases. The results demonstrate that the driving force for the decomposition of martensite is an order of magnitude less than that of austenite. However, the driving force for cementite precipitation in martensite is two orders of magnitude greater than in austenite with a much shorter incubation period. On short term tempering cementite precipitates from martensite whereas on longer term tempering decomposition of retained austenite occurs because of the increase in driving force which is enhanced by the contraction of the martensite on decomposition. It is argued that the precipitation of cementite from the austenite results in tempered martensite embrittlement, a mechanism dependent upon the two related decomposition processes. The segregation of trace impurities or the precipitation of cementite at the gr...

The plastic-flow behavior of ferrite + pearlite, pearlite + cementite, and austenite + cementite mixtures in plain carbon steels has been examined over the temperature range 500 to 1050 °C, strain-rate range 6 x l0−6 to 2 x l0−2 s−1, and carbon range 0.005C to 1.89C. Up to the eutectoid temperature the strength of the ferrite + pearlite mixture more than doubles as the carbon content increases from 0.005C to 0.7C, so that whereas in low-carbon steels the ferrite is weaker than the higher temperature austenite phase, in eutectoid steels the fully pearlitic structure is stronger than the fully austenitic structure. Manganese and silicon strengthen ferrite more effectively than they do austenite. A 0.17 pct phosphorus addition strengthens the ferrite + pearlite mixture across the range of microstructures from fully ferritic to fully pearlitic. Beyond the eutectoid composition, the amount of proeutectoid cementite does not significantly affect the strength of the pearlite, but above the eutectoid temperature it appreciably strengthens the austenite and cementite mixture at the strain rate of 2 X 10-2 s-1.

The surface of nodular cast iron was first coated with tungsten carbide powder, then melted by concentrated solar energy to form an alloyed layer on its surface. By scanning a high energy focal point over the surface, a predominantly alloyed surface was created after rapid solidification. The surface of the alloyed layer was quite flat, with a microstructure of very fine ledeburite. This alloyed layer possessed a very high hardness and high tempering resistance, and had greatly improved wear resistance compared to untreated nodular cast iron. In addition, excellent adhesive wear resistance is displayed by the alloyed material.

The microstructural changes produced by plasma arc local-melting method in the fusion region or deposited metal, fusion boundary region and heat-affected zone (HAZ) of flake graphite cast iron were investigated. Cylindrical base metal specimens were locally melted at fixed time intervals under a stationary plasma torch using argon plasma gas and Ar + 10% H2 shielding gas. The welds were produced autogenously and with filler metals. The cooling rate in the fusion region was recorded. Evaluation of the fusion boundary area included metallurgical analysis, microhardness and electron probe microanalysis. In the absence of filler metal, the structure of fusion region where completely melted was ledeburite. In the centre of the fusion region the structure appears to be that of hypoeutectic white cast iron, and in the fusion boundary of this region the structure appears to be fined ledeburite. In the fusion boundary region where supercooled phenomena can occur, fine martensite precipitates appear along the fusion line for small heat input and secondary graphite is seen for large heat input. The HAZ is composed of white martensitic, dark martensitic and martensitic-fine pearlitic layers for small heat input, and of finely laminated pearlitic and finely laminated pearlitic-ferritic layers for large heat input. Using filler metal, the structure of the deposited metal is found to be that of a nickel austenitic matrix precipitating tiny graphite nodules or slim graphite for nickel and Ni-Fe filler metals, but to be a pearlitic matrix for iron filler metal. In the fusion boundary region, nickel-martensite, eutectic or slim graphite and fine nickel-martensite are precipitated from the nickel system filler metal, and the columnar structure of ferrite and pearlite is obtained from iron filler metal. The HAZ is composed of thin ledeburitic, martensitic, martensitic-fine pearlitic and finely laminated pearlitic layers for the nickel filler metal, of ledeburitic and finely laminated pearlitic layers for the Ni-Fe filler metal, and of thick ledeburitic, eutectic graphite-crystallized and finely laminated pearlitic layers for iron filler metal. The hardness of the ledeburitic layer and the nickel-martensitic portion is very high where the liquid existed. The diffusion of nickel from the deposited metal into the HAZ can occur at least until the fused base metal of HAZ.