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The application of laser surface melt hardening to nodular iron 400-12 causes the material to undergo microstructural changes. A newly created austenite-ledeburite microstructure with the presence of graphite nodules in the melted zone and a martensite-ferrite microstructure with graphite nodules in the hardened zone have been observed. Microscopy of the hardened zone was used to analyze the occurrence of martensite shells around the graphite nodules in ferrite matrix. The size of the shells was later supported by diffusion calculations. The qualitative effects of the changed microstructures were additionally verified by microhardness/depth measurements in the modified layer and microhardness measurements of characteristic microstructures around the graphite nodules in the hardened zone.

Wootz Damascus steel blades contain surface patterns produced by bands of cementite particles which are generated in situ as the blades are forged from small ingots. A process for making these blades has recently been developed which involves making ingots in a gasfired furnace followed by forging to blade shapes. This study presents a series of additional experiments which provide strong evidence that the mechanism responsible for the formation of the aligned cementite bands is similar to the mechanism that produces banded hypoeutectoid steels. That mechanism attributes the selective formation of ferrite bands to microsegregated alloying elements. The results of this study show that the cementite bands will form in ultraclean hypereutectoid steels (P and S levels

In order to modify the continuous network of eutectic cementite normally found in low alloy white cast irons into a dispersive distribution, strategies of controlling the morphology of eutectic cementite by additives are discussed. Qualitative arguments are presented and applied to the development of a complex modifier REAINTi. With the addition of this modifier to low carbon white cast irons nearly one fifth of the original eutectic cementite network can be modified into blocky particles in the plane of polish, and one third into isolated irregular ones. The experimental data shows that Ti(CN) may act as an effective nucleant or a grain refiner for eutectic cementite. The modification effects of rare earth elements are attributed to their abilities to purify the melt, promote divorced eutectic growth and refine the microstructure. Aluminium contributes to the modification by its purification effect.

Transformation induced plasticity (TRIP) effects associated with austenite dispersions in low alloy Fe-Mn-Sl steels can be enhanced by austenite stabilisation. Austenite which forms during conventional intercritical annealing does not possess the required stability in order to exhibit TRIP effects. In this work, thermodynamic calculations indicated that it is feasible to form austenite by a cementite to austenite conversion which occurs under paraequilibrium conditions, i.e with partition of carbon but with no partition of substitutional alloying elements. In this way the austenite inherits the manganese content of cementite and is chemically stabilised. A treatment consisting of a two-step annealing has been examined. In the first step, soft annealing, an Mn-enriched cementite dispersion in ferrite is formed. In the second step, intercritical annealing, austenite nucleates on the cementite particles, which are consumed to form austenite. It was experimentally determined that this austenite has been enriched in manganese and carbon and, therefore, is stabilised. The conversion reaction is followed by the conventional austenite nucleation at ferrite grain boundaries. This austenite is lean in manganese and is not stable. The net effect of the two-step annealing treatment is a significant austenite stabilisation relative to simple intercritical annealing, indicating a potential for enhanced TRIP effects in this class of steels.

Pure Fe-3.5 wt% C alloy was surface melted using a cw CO 2 laser and the microstructure of the laser tracks was investigated by scanning and transmission electron microscopy. Structure of the melted zones consisted of dendrites of partially transformed primary austenite and of very fine lamellar ledeburite. The secondary dendrite arm spacings were indicative of a cooling rate of ∼10 5 K s -1 , in good accord with calculations based on the model of a moving Gaussian beam. Using methods of quantitative metallography the volume fraction of dendrites within the melted zone and the volume fractions of the carbide and ferrite phases in the decomposed ledeburite were estimated. These data were combined with the results of a quantitative X-ray diffraction phase analysis (see Part II) and compared with the equilibrium phase diagram. It was found that the volume fraction of dendrites was near the equilibrium value while the volume content of cementite in the rapidly solidified structures was considerably higher than predicted from the equilibrium phase diagram.

When spheroidal graphite (SG) cast iron is overlaid with Stellite 1 cobalt-based superalloy by a plasma transferred arc melting process, a carbide-containing interfacial layer can exist between the substrate and the overlayer. Meanwhile, ledeburite can occur in the partially melted zone of the substrate. These microstructures may cause damage during application and thus are undesirable. In the present investigation, Stellite 1 alloy was overlaid on seven ferritic SG cast irons of various silicon content (2.0 to 3.9 mass%) and carbon content (1.5 to 3.8 mass%) under the same overlaying condition (current : 60 A ; voltage : 26 V). The purpose was to characterize the solidification structure with special emphasis on the interface region and the partially melted zone. The results indicate that the overlayer is hypereutectic. The carbide-containing interfacial layer can be eliminated by reducing the carbon content of the substrate. Both reducing the carbon content and increasing silicon content can reduce the amount of ledeburite formed in the partially melted zone. The formation of the ledeburite can be avoided if the silicon content is sufficiently large.

Damascus steels are related to composites which combine the properties of diverse steel qualities. By forging steel plates with different compositions, in particular differences in the carbon content, a multilayered workpiece is manufactured. Forging of cast iron has not been common because of its low melting point and brittleness at lower temperatures. Wolfgang Scheiblechner, a blacksmith from Palfau in Austria, combined ductile cast iron and soft iron to a unique composite material, which was investigated by means of metallographic methods. The intersections of cast iron and iron are of high interest, where carbon diffusion from ductile cast iron (graphite 100 % C) to soft iron (0 % C) takes place. In this case, all the microstructures characteristic for cast irons, steels, and soft iron were present. The microstructures were additionally influenced by forging and quenching. The cast iron region was dominated by nodular graphite and bainite; ledeburite was observed occasionally. The soft iron regions showed coarse equiaxed ferrite and grain boundary cementite. In the transition areas, ferrite showed a wide variety of shapes, and the microstructure changed from hypereutectoid to hypoeutectoid steel. The various microstructures were characterized by light optical microscopy and confirmed by Vicker's microhardness measurements.

Laser processing of structure sensitive hypereutectic ductile iron, a cast alloy employed for dynamically loaded automative components, was experimentally investigated over a wide range of process parameters: from power (0.5-2.5 kW) and scan rate (7.5-25 mm s(-1)) leading to solid state transformation, all the way through to melting followed by rapid quenching. Superfine dendritic (at 10(5) degrees C s(-1)) or feathery (at 10(4) degrees C s(-1)) ledeburite of 0.2-0.25 mu m lamellar space, gamma-austenite and carbide in the laser melted and martensite in the transformed zone or heat-affected zone were observed, depending on the process parameters. Depth of geometric profiles of laser transformed or melt zone structures, parameters such as dendrile arm spacing, volume fraction of carbide and surface hardness bear a direct relationship with the energy intensity P/UDb2, (10-100 J mm(-3)). There is a minimum energy intensity threshold for solid state transformation hardening (0.2 J mm(-3)) and similarly for the initiation of superficial melting (9 J mm(-3)) and full melting (15 J mm(-3)) in the case of ductile iron. Simulation, modeling and thermal analysis of laser processing as a three-dimensional quasi-steady moving heat source problem by a finite difference method, considering temperature dependent energy absorptivity of the material to laser radiation, thermal and physical properties (kappa, rho, c(p)) and freezing under non-equilibrium conditions employing Scheil's equation to compute the proportion of the solid enabled determination of the thermal history of the laser treated zone. This includes assessment of the peak temperature attained at the surface, temperature gradients, the freezing time and rates as well as the geometric profile of the melted, transformed or heat-affected zone. Computed geometric profiles or depth are in close agreement with the experimental data, validating the numerical scheme.

Laser surface remelting has been utilized to improve the abrasion resistance of ductile irons by generating a rapidly solidified ultra-fine ledeburite surface layer. However, this significant improvement in abrasion resistance is at the complete expense of the excellent tribological and damping properties of the graphite phase which are equally as important as the abrasive wear properties in some service conditions. Therefore, it would be attractive if some fine graphite particles could be incorporated into the laser rapidly solidified ledeburite structure, fabricating a novel iron microstructure containing both the as-rapidly solidified eutectic cementite and the fine graphite particles. This iron-base alloy will, no doubt, have the combination of the excellent abrasive wear resistance of the rapidly solidified eutectic Fe{sub 3}C carbide or cementite, and the outstanding self-lubricating, heat conducting and damping properties of the graphite phase. Unfortunately, it is impossible to fabricate the novel material by rapid solidification processing alone, because following rapid solidification the melt solidifies according to the metastable Fe-Fe{sub 3}C system, no longer forming a graphite phase in the rapidly solidified iron structure. However, the laser melted structure of ductile iron is, from the thermodynamics point of view, highly unstable. This highly metastable nature of the structure maymore » provide the authors the opportunity to fabricate the above mentioned novel microstructure by partially graphitizing the cementite by appropriate subsequent thermal treatment. In the present paper, a laser melted ductile cast iron was heat treated by conventional heat treating method. The novel Fe-base alloy containing both the as-rapidly solidified eutectic cementite and the ultra-fine graphite was successfully fabricated as a consequence of the partial cementite-graphite phase transformation.« less

As-cast ductile cast iron with an as-machined shiny metal surface was remelted with a high-power (1 kW) pulsed Nd:YAG laser using both single- and multipass overlap melt tracks. Changes in the microstructure of the underlying laser melted track caused by the transient overlap heating during multipass overlap remelting process were studied. The rapidly solidified metastable ledeburite structure of the underlying laser melted track was found to be rapidly graphitized during overlap remelting. The graphitized zone consists of a fully graphitized zone containing extremely fine graphite nodules and a partially graphitized zone containing extremely fine graphite nodules and undissolved cementite. The overlap ratios of the melt tracks were shown to have no noticeable influence on either the graphitized microstructure and the size of the graphitization zones. This newly observed rapid graphitization phenomenon is preliminarily discussed in terms of the microstructural characteristics of the rapidly solidified ductile iron and the unique heating behavior of pulsed laser beam to material.

Considered the nature of changes in the morphology of carbides of the unalloyed high-carbon alloys type Damascus steel depending on the degree of supercooling of the melt, heat treatment and plastic deformation. It is shown that iron-carbon alloy with carbon content as in white cast iron at high degrees of supercooling can crystallize as a high-carbon steel. Considered three hypotheses for the formation of the eutectic carbides in pure iron-carbon alloys. The first hypothesis is based on the thermal process of dividing plates of secondary cementite or of ledeburite on isolated single grain. The second hypothesis is based on the deformation process of crushing of secondary cementite or of ledeburite into separate fragments (the traditional view on the formation of eutectic carbides). The third hypothesis is based on the transformation of metastable ledeburite in a stable phase of eutectic carbide prismatic morphology. Found that some types of wootz, which carbon content as in of white cast irons not is contain its structure of ledeburite. It is shown that the structure of consists entirely of the eutectic carbides prismatic morphology.

Bainite ordinarily refers to the ferrite-carbide aggregates that form in an intermediate temperature range overlapped by pearlite transformation and proeutectoid ferrite or cementite precipitation at higher temperatures and martensite transformation at lower temperatures. (More recently it has become acceptable to refer to carbide-free bainite when carbide formation is suppressed by alloying.) In the original 1939 paper on high carbon steels by Davenport and Bain, microstructure which corresponds to present ‘carbide-containing bainite’ was termed ‘troostite’ when formed just below pearlite transformation temperatures and ‘martensite-troostite’ when formed at lower temperatures just above the martensite transformation start temperature (M s ). However, it should be mentioned that complexity in morphology of the ferrite and cementite components subsequently led to a wide variety of microstructure definitions proposed by different researchers, sometimes in relation to transformation mechanisms. In this chapter, several kinds of definitions of the carbide-containing bainite structure are reviewed. Then characteristics of each of the ferrite and carbide (mainly cementite) components are described.

The influence of bainite morphology on the impact toughness behaviour of continuously cooled cementite-free low carbon bainitic steels has been examined. In these steels, bainitic microstructures formed mainly by lath-like upper bainite, consisting of thin and long parallel ferrite laths, were shown to exhibit higher impact toughness values than those with a granular bainite, consisting of equiaxed ferrite structure and discrete island of marteniste/austenite (M/A) constituent. Results suggest that the mechanism of brittle fracture of cementite-free bainitic steels involves nucleation of microcracks in M/A islands but is controlled by the bainite packet size, Spanish Ministry of Science and Innovation for financial support in the form of a PhD research grant (FPI grant under the project no. MAT2007-63873)

The precipitation of cementite under the influence of an externally applied stress, during the tempering of martensite in steels, is investigated using transmission electron microscopy. The stress appears to favour the development of particular crystallographic variants of cementite in any given plate of martensite. Hence, a Widmanstatten array of cementite particles in a normally tempered sample changes to an array consisting of just one variant in stress-tempered samples. The results are discussed in the context of the mechanism of carbide precipitation during the lower bainite reaction.

The influence of vanadium addition on the microstructure of high carbon steels has been investigated. A careful examination of the initial stages of austenite decomposi~ion has been made, using a r...

During laser surface rapid remelting of cast irons, the melt pool solidifies rapidly and metastably (i.e. according to the metastable Fe-Fe[sub 3]C system) producing an ultra-fine ledeburite hard surface which is much more abrasion resistant than the original substrate. Previous literature mainly focused on remelting various grey and ductile irons with high power CO[sub 2] lasers for improved wear resistance and other surface properties, and on studying the physical metallurgy of laser remelted surfaces. Unfortunately, the unstable nature and rapid tempering behavior of the rapidly solidified ledeburite were generally neglected, although some publications mentioned the tempering phenomenon during successive overlap remelting. In this paper, a laser remelted ductile case iron surface was tempered by rapid pulsed laser beam reprocessing. The rapidly solidified ductile iron was found to be rapidly graphitized, as a result, a layer of Fe-base alloy containing ultra-fine graphite particles was produced. The unusual rapid graphitization phenomenon was preliminarily discussed.

Pin-on-disc wear and friction of hypereutectic ductile iron, the type employed for automotive components, was investigated at sliding speeds of 5 and 7.5 m $s^{-1}$, before and after laser surface treatment by $CO_2$ continuous- wave and Nd-YAG pulsed lasers. A significant increase in transition load and wear resistance upon laser treatment has been attributed to the ultrafine microstructure and high hardness; laser-melted ledeburite was superior to martensite by transformation hardening. Wear rate at a specific contact pressure and sliding speed bears a log-linear relationship with the harmonic mean of tensile and fatigue stress of ductile irons. The role of lubrication by graphite during mild wear and plastic deformation in severe wear of pearlitic ductile iron, and its enhanced resistance to plastic flow on laser melting, have been confirmed. The coefficient of friction of a ductile iron pin sliding on a steel disc before and after laser melting has been determined and compared with that of white iron of identical composition and structure obtained by conventional chilling.

Carbon fibers and textiles based on them are being used increasingly to reinforce composites. In this article we report the results of inetallographic research on the surface layers formed by passing an electric current through a hardened steel part and a fabric or felt made of a carbon-fiber material on its surface.

After laser surface remelting of nodular iron 400-12 a modified layer consisting of remelted and hardened layers has been observed. Microscopy of the hardened layer was used to analyse the occurrence of martensite shells and/or ledeburite shells around the graphite nodules in the ferrite matrix. The size of the shells was subsequently supported by diffusion calculations.

The transformation interfaces of pearlite, allotriomorphic cementite, M[sub 23]C[sub 6], and Widmanstaetten cementite plates in high-Mn high-C alloy steels have been studied by TEM. Linear striations in the interface have been analyzed and related to intersections with stacking faults in the parent austenite phase. Emphasis is given to the pearlite interface where it is found that the striations at the interface increased as a result of thermomechanical treatment of the austenite prior to isothermal transformation, consistent with an increased density of planar defects. The effect of heat treatment, and Si alloying additions, are also considered. Both conventional and in situ TEM of the pearlite interface showed that the linear defects stretched across both ferrite and cementite phases at the pearlite interface, apparently without any deviation or change in image contrast. The results are compared with similar ones made of the static [gamma]/[alpha] interphase boundaries in duplex stainless steel. The effect of prior deformation structure in the parent austenite on the growth and interface structure of Widmanstaetten cementite plates has also been considered.

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.

The most technologically advanced material for valve seats of internal-combustion engines are the phosphorus-alloyed cast irons strengthened by a reinforcing phase consisting of the phosphide eutectic and cementite, the ratio between which depends on the Cr to P ratio, the technology of the modification, and the cooling rate of the castings. The optimum structure of the cast iron for valve seats, which produces a combination of good machinability and high wear resistance is the troostomartensitic or troostosorbitic matrix with a network of the FE5-type phosphide eutectic (with cementite lamellae), and clusters of graphite combined with fine- and medium-size flakes with less than 5% of the structurally free graphite. The optimum combination of wear resistance, machinability, and strength of the valve seats is attained at the ratio Cr/P=3–4 and modification by 0.5–0.8% ferrosilicon. The wear of the phosphorous-containing cast iron with a troostomartensitic or troostosorbitic matrix is determined by the amount of the cementite in the ledeburite and, when its content is small or it is absent, by the type of the phosphide eutectic. A phosphorus-containing cast iron of the type of 360S3KhGMD has been suggested which has gone into production. It has the composition: 3.5–3.8% C, 2.5–3.0% Si, 0.7–1.0% Mn, 0.9–1.2% Cr, 0.9–1.2% Mo, 0.3–0.6% P, 0.7–1.2% Cu, and up to 0.1% S.

The e ects of the thermal cycles on the microstructures and properties of ductile iron modi ed by electrolytic plasma treatment were investigated. Microstructure changes occurring in the modi ed surface were characterized with scanning electron microscopy, X-ray di ractometry techniques. Martensitic structure evolved in the heat a ected zone and ledeburite structure was produced in the molten zone of the ductile iron. Microhardness of the treated specimens improved considerably as compared to the original sample. X-ray di raction clearly revealed the formation of a martensite phases in the modi ed zone.

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.