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The authors of this scientific article conducted comprehensive studies aimed at identifying the influence of barium and cerium on the graphitization process and the structure of frictional gray cast iron. The purpose of this scientific article: to investigate the effect of barium and cerium, which are part of industrial foundry alloys used to modify iron-carbon alloys, on the morphology, distribution and dispersion of cementite and graphite. In the course of experimental studies, two industrial foundry alloys were used to modify cast iron. First foundry alloy: foundry alloy SiitMish-1 based on silicon and calcium. Second foundry alloy: foundry alloy TsISM; this foundry alloy is a powder alloy that contains silicon, calcium, barium, cerium. The authors of this article have established the optimal concentration of foundry alloys that provide the necessary degree of graphitization of cast iron without the formation of ledeburite. Such concentrations of foundry alloys make it possible to avoid the formation of ledeburite in the structure of cast iron and to limit the content of secondary cementite: the content of secondary cementite is optimal for gray friction cast irons, which have an austenitic structure of the metal base. The authors of this article found that the modification of cast iron with a foundry alloy TsISM, which contains barium and cerium, completely prevents the formation of graphite, which is located along the boundaries of dendrites. Graphite, which is located along the boundaries of dendrites, significantly reduces the frictional characteristics of cast iron. It was found that the modification of cast iron only with calcium does not allow avoiding the formation of graphite, which is located along the boundaries of dendrites.Modification of gray friction cast iron with a complex master alloy containing barium and cerium makes it possible to approximately three times reduce the length of graphite inclusions in comparison with cast iron modified with a silicon-calcium alloy.

The current research studied the effects of laser surface hardening treatment on the phase transformation and wear properties of gray cast irons heat treated by austempering or quench-tempering, respectively. Three austempering temperatures of 232 &deg, C, 288 &deg, C, and 343 &deg, C with a constant holding duration of 120 min and three tempering temperatures of 316 &deg, C, 399 &deg, C, and 482 &deg, C with a constant holding duration of 60 min were utilized to prepare austempered and quench-tempered gray cast iron specimens with equivalent macro-hardness values. A ball-on-flat reciprocating wear test configuration was used to investigate the wear resistance of austempered and quench-tempered gray cast iron specimens before and after applying laser surface-hardening treatment. The phase transformation, hardness, mass loss, and worn surfaces were evaluated. There were four zones in the matrix of the laser-hardened austempered gray cast iron. Zone 1 contained ledeburite without the presence of graphite flakes. Zone 2 contained martensite and had a high hardness, which was greater than 67 HRC. Zone 4 was the substrate containing the acicular ferrite and carbon-saturated austenite with a hardness of 41&ndash, 27 HRC. In Zone 3, the substrate was tempered by the low thermal radiation. For the laser-hardened quench-tempered gray cast iron specimens, three zones were observed beneath the laser-hardened surface. Zone 1 also contained ledeburite, and Zone 2 was full martensite. Zone 3 was the substrate containing the tempered martensite. The tempered martensite became coarse with increasing tempering temperature due to the decomposition of the as-quenched martensite and precipitation of cementite particles. In the wear tests, the gray cast iron specimens without heat treatment had the highest wear loss. The wear performance was improved by applying quench-tempering heat treatment and further enhanced by applying austempering heat treatment. Austempered gray cast iron specimens had lower mass loss than the quench-tempered gray cast iron specimens, which was attributed to the high fracture toughness of acicular ferrite and stable austenite. After utilizing the laser surface hardening treatment, both austempered and quench-tempered gray cast iron specimens had decreased wear loss due to the high surface protection provided by the ledeburitic and martensitic structures with high hardness. In the worn surfaces, it was found that cracks were the dominant wear mechanism. The results of this work have significant value in the future applications of gray cast iron engineering components and provide valuable references for future studies on laser-hardened gray cast iron.

The thermal conditions in the molten pool during the laser surface melting of ductile cast iron EN-GJS-700-2 were estimated by using infrared thermography and thermocouple measurements. The thermal data were then correlated with the microstructure of the melted zone. Additionally, the thermodynamic calculations of a Fe-C-Si alloy system were performed to predict the solidification path of the melted zone. It was found that increasing the cooling rate during solidification of the refined ledeburite eutectic but also suppressed the martensitic transformation. A continuous network of plate-like secondary cementite precipitates and nanometric spherical precipitates of tertiary cementite were observed in regions of primary and eutectic austenite. The solidification of the melted zone terminated with the Liquid &rarr, &gamma, Fe + Fe3C + Fe8Si2C reaction. The hardness of the melted zone was affected by both the fraction of the retained austenite and the morphology of the ledeburite eutectic.

Thermo-mechanical processing is performed to engineer the microstructure comprising of nano-spheroidized cementites in ultrafine-grained ferrite in high carbon steel to enhance strength-ductility relationship. Spheroidization is achieved through heavy warm rolling (4-passes of 30% reduction at 823 K and 873 K) followed by extended annealing (1 h and 2 h) at the respective deformation temperatures. The influence of annealing temperature and time on the evolution of carbide precipitates, the extent of spheroidization and ferrite softening is investigated employing scanning electron microscopy, electron back scatter diffraction and transmission electron microscopy techniques. A near-complete spheroidization is achieved following heavy warm rolling and subsequent annealing for 2 h at 873 K (WR873K-2H). Although ferrite grain size increases with time and temperature of annealing, it ceases to cross the ultrafine regime (470–750 nm) due to the pinning effect of the carbides that restricts the migration of ferrite grain boundaries. A simultaneous increase in strength and ductility is achieved following heavy warm rolling and subsequent annealing for 1 to 2 h at 873 K. Maximum elongation (~30%) is achieved in the WR873-2H specimen in contrast to ~20% elongation in as-received specimen. Such an increase in ductility is due to the near-complete spheroidization as revealed by the ductile mode of fracture in fractrographic analysis. Keywords: High carbon steel, Heavy warm deformation, Ultrafine grains, Spheroidized cementite, Tensile properties

The deformation behavior of cementite in drawn pearlitic steel and spheroidal cementite steel, which have hypereutectoid composition, was investigated by X-ray diffraction using synchrotron radiation. A detailed analysis of diffraction peak profiles reveals that the deformation behavior strongly depends on the shape of cementite in steel. The unit cell volume of the cementite in the drawn pearlitic steel compressively and elastically deforms by 1.5 to 2 pct of the initial volume at the early stage of drawing, whereas that in the drawn spheroidal cementite steel is compressed by 1 pct of the initial volume even at a large true strain. The cementite in the drawn pearlitic steel fragments into small pieces with increasing the true strain, and these pieces change to amorphous cementite. The dislocation densities of the cementite in the drawn pearlitic steel and in the drawn spheroidal cementite steel are estimated to be ~1013/m2 before drawing and ~1014/m2 after drawing. Although the large strain is induced in the cementite by drawing, the maximum strain energy in the cementite is too small to contribute to the dissolution of the cementite.

Recent years have been marked by considerable increase in the use of high-strength steel—especially martensitic and bainitic steel—for the manufacture of key industrial components and structures. The high strength depends on strain hardening of the steel. It is important to understand the strain hardening of steel of different structural classes with active plastic deformation, in order to ensure specified structural and phase states and mechanical properties. In the present work, by transmission electron-diffraction microscopy, the evolution of the structure, the phase composition, and the state of the defect substructure is compared for steel samples with martensite and bainite structure in active plastic deformation to failure. After austenitization at 950°C (1.5 h) and subsequent quenching in oil (for 38KhN3MFA steel) and cooling in air (for 30Kh2N2MFA steel), multiphase structure (α phase, γ phase, and cementite) based on packet martensite (38KhN3MFA steel) and lower bainite (30Kh2N2MFA steel) is formed. Quantitative results for the structural parameters of steel in plastic deformation permit analysis of the distribution of the carbon atoms in the structure of the deformed steel. The points of localization of carbon atoms in the martensite (quenched 38KhN3MFA steel) and bainite (air-cooled 30Kh2N2MFA steel) are identified. Deformation of the steel is found to be accompanied by the destruction of cementite particles. For quenched martensitic steel, the total quantity of carbon atoms in the solid solution based on α and γ iron is reduced, while their content at structural defects is increased. The redistribution of carbon atoms in the bainitic steel with increase in the strain involves the increase in the quantity of carbon atoms in the α iron, defects in the crystalline structure, and cementite at the intraphase boundaries; and the decrease in the content of carbon atoms in the cementite particles within the bainite plates and the γ iron.

It is detected that in some specimens of Damascus steel part of the excess cementite is of unusual origin, in contrast to excess phases of secondary cementite, ledeburite cementite, and primary cementite in ironcarbon alloys. It is revealed that a morphological feature of separate particles of cementite in Damascus steel includes anomalously large excess carbides in the form of irregular octahedral and prisms. It is shown that angular carbides form within the original metastable ledeburite colonies, and therefore they are called “eutectic.” It is established that unalloyed materials of the carbide class acquire Damascus properties steel properties during isothermal exposure on annealing, which leads to thermal separation of colonies of metastable ledeburite, to limitation of newly formed eutectic carbides, and to their subsequent coalescence. It is revealed that some sorts of Damascus steel, being within the field of white cast iron with respect to carbon content, do not contain broken ledeburite within their structure. It is shown that the pattern of carbide inhomogeneity entirely consists of eutectic of angular carbides of non-etching triangular-prismatic morphology.

Based on the chemical composition requirements and enhancing the utilization value of the products, this work put forward a direct preparation method for low Ni-Cr alloy cast iron from red mud and laterite nickel ore by high-temperature carbothermal reduction smelting and refining. X-ray fluorescence (XRF), optical emission spectrometer (OES), scanning electron microscopy (SEM) attached with energy dispersive spectroscopy (EDS) analysis, hardness and polarization tests were used in the characterization process. The results show that low Ni-Cr alloy cast irons contain 1.50–2.00 wt.% Ni and 0.70–0.80 wt.% Cr have been prepared as the mass ratios of red mud to laterite nickel ore vary from 80:20 to 70:30, in which the recovery were 93.70% for Fe and 99.83% for Ni, respectively. The alloy cast iron was consisted of ledeburite and cementite matrix with evenly distributed Ni and Cr elements and block and flake graphite precipitated phase. With the increasing of Ni and Cr contents, the hardness and corrosion resistance of the alloy cast irons improved. Keywords: Low Ni-Cr alloy cast iron, Red mud, Laterite nickel ore, Electric arc furnace

In recent years, application of high duration steels, first of all, martensitic and bainitic steels used in manufacturing of parts and structures of crucial function has increased significantly. It is possible to achieve a high duration state by means of effective deformation hardening of steels of various classes at rational use. Understanding of quantitative laws and mechanisms of deformation hardening of steels of different structural classes under active plastic deformation is necessary in terms of targeted formation of structure-phase states and mechanical properties of material. In this work, comparative analysis of structure evolution, phase composition and state of defective substructure of steel with martensitic and bainitic structures under active plastic deformation prior to fracture was performed using transmission electron diffraction microscopy. It was shown that after austenitization at temperature of 950 °C (1.5 hours) and subsequent quenching in oil of 38CrNi3MoV steel and normalization of 30Cr2Ni2MoV steel, a multiphase structure (α phase, γ phase, cementite) is formed, based on martensite of packet morphology (38CrNi3MoV steel) and lower bainite (30Cr2Ni2MoV steel). Obtained quantitative regularities of changes in parameters of steel structure in process of plastic deformation made it possible to carry out studies aimed at analyzing the distribution of carbon atoms in structure of deformed steel. Localization of carbon atoms in martensite structure (38CrNi3MoV hardened steel) and bainite (30Cr2Ni2MoV normalized steel) are revealed. It was established that steels deformation is accompanied by destruction of cementite particles. For hardened martensitic steel, with an increase in degree of deformation, the total number of carbon atoms located in solid solution based on α- and γ-iron decreases, and on structural defects – increases. Redistribution of carbon atoms in steel with bainitic structure with increase in deformation degree consists in growth of number carbon atoms located in α-iron, in defects of the crystal structure, and in intraphase boundaries cementite and its’ subsequent decrease in cementite particles within bainite plates and in γ-iron.

A model for estimating the upper to lower bainite transition has been developed for the iron–carbon–manganese–chromium–silicon alloy system by comparing the time required to decarburise a supersaturated bainitic ferrite platelet and that needed for the start of cementite precipitation in the ferrite. The problem is treated as a competition between the decarburisation time and the kinetics of cementite precipitation. Lower bainite is induced when the latter process is faster. The time for forming a volume fraction of 0.01 of the equilibrium amount of cementite is taken as the precipitation start time. The model was calibrated using experimental data from the iron–carbon system, and verified with the iron–carbon–manganese–molybdenum system and an experimental steel currently being developed for high-strength applications.

The growth of austenite from a mixture of ferrite and cementite in low-alloy steels can be classified into three temperature ranges above the eutectoid temperature. In the first range, the austenite growth and cementite dissolution are controlled by alloy element diffusion from the beginning. In the second, they are controlled by carbon diffusion and switch to alloy element diffusion control at a later stage. In the third, the cementite dissolution, if the ferrite matrix has transformed to austenite upon heating, is controlled by carbon diffusion until completion. The transition temperatures between these ranges are evaluated in a quaternary alloy containing Mn and Cr by Thermo-calc and DICTRA simulation, and are in essential agreement with earlier experimental results. The proposed simple approach of calculating the transition temperatures may facilitate our understanding of austenitization kinetics and the design of heat treatment, for example, homogenization and soaking, of high-carbon steels.

A Cr-Ni-Mo overlayer was deposited on the surface of compacted graphite iron (CGI) by the plasma transferred arc (PTA) alloying technique. The microstructure of Cr-Ni-Mo overlayer was characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and X-ray diffractometer (XRD). Results show that the cross-section consists of four regions: alloying zone (AZ), molten zone (MZ), heat affected zone (HAZ), and the substrate (SUB). The microstructure of AZ mainly consists of cellular γ-(Fe, Ni) solid solution, residual austenite and a network of eutectic Cr7C3 carbide while the MZ area has a typical feature of white cast iron (M3C-type cementite). The martensite/ledeburite double shells are observed in the HAZ. With decreasing the concentration of Cr-Ni-Mo alloys, the fracture mode changes from ductile in the AZ to brittle in the MZ. The maximum hardness of the AZ (450 HV0.2) is lower than that of the MZ (800 HV0.2). The eutectic M3C and M7C3 carbides increase the microhardness, while the austenite decreases that of the AZ.

International audience; The austenitization from a spheroidized microstructure during intercritical annealing was studied in a Fe-0.1C-3.5Mn alloy. The austenite grains preferentially nucleate and grow from intergranular cementite. The nucleation at intragranular cementite is significantly retarded or even suppressed. The DICTRA software, assuming local equilibrium conditions, was used to simulate the austenite growth kinetics at various temperatures and for analyzing the austenite growth mechanism. The results indicate that both the mode and the kinetics of austenite growth strongly depend on cementite composition. With sufficiently high cementite Mn content, the austenite growth is essentially composed of two stages, involving the partitioning growth controlled by Mn diffusion inside ferrite, followed by a stage controlled by Mn diffusion within austenite for final equilibration. The partitioning growth results in a homogeneous distribution of carbon within austenite, which is supported by NanoSIMS carbon mapping.

The influence of cementite precipitation and dissolution on the formation of the carbide-free, ultra-fine-grained, ferrite + austenite microstructure of medium manganese steel was analyzed. During heating to the intercritical temperature, cementite nucleates at low-angle lath martensite boundaries, austenite subsequently nucleates at ferrite/cementite boundaries, and the cementite is gradually replaced by the growing austenite grains. The intercritical austenite carbon is therefore due to cementite dissolution, rather than carbon partitioning between ferrite and austenite.

The effect of substitutional element aluminum (Al) on the cementite growth from austenite phase in Fe–C–Al alloy was simulated using ThermoCalc–Dictra software. The simulation is based on diffusional reactions of multi components in the system. The distribution of elements across the interface of cementite and austenite phases and cementite fraction as a function of time for different Al concentrations in Fe–C–Al system were evaluated. It has been found that the presence of Al retards the growth of cementite which attributes to the negligible solubility of Al in the cementite phase.

A medium Mn steel with the martensitic microstructure was rapidly heated at a high rate of 300 K/s to the intercritical temperature of 923 K (650 °C) and then isothermally hold for 5 minutes. Although cementite should dissolve above the Ae1 temperature due to the constraint of thermodynamics, it is surprising to find cementite particles after such intercritical annealing (IA), whose Mn contents and sizes are even up to 30 wt pct and 60 nm, respectively. Numerical simulations have been performed to reveal the mechanism responsible for this new observation. They indicate that a small nucleus of cementite in martensite could rapidly grow to the observed size before austenitization takes place during IA. Such a rapid growth is driven by the rapid partition of C from martensite into cementite. It is then concluded that the precipitation of cementite during the IA of martensitic Mn-alloyed steel appears inevitable no matter how high the heating rate is. Moreover, the growth kinetics of cementite depend on the composition and size of its neighboring martensitic phase, rather than those of cementite nucleus.

Three prototype metallurgical rolls were produced on the basis of G200CrNiMo4-3-3 material. The method applied for the microstructure forming was different for each roll: the roll marked WOT – as cast state (without a modification and heat treatment); the metallurgical roll marked WMT – during its casting the FeCaSi deoxidizing was applied and then modification by a complex inoculant and argoning; the metallurgical roll marked WNT – subjected to a heat treatment (incomplete normalizing).The mentioned above differences in the technology of making rolls caused changes in their microstructure.The cementite eutectic and pearlitic matrix occurred in each roll. The main differences in the microstructure of cast steel rolls concerned a morphology of precipitates of hypereutectoid cementite. In the WOT roll cementite was mainly in the Widmannstӓtten system. Precipitates of hypereutectoid cementite in the WMT roll occurred along grain boundaries of primary austenite. A large fraction of spheroidal hypereutectoid cementite, precipitated in the whole volume of the primary austenite grain, appeared in the WNT roll. The microstructure influenced the rolls hardness and was equal 260 ÷ 350 HBW.Tribological investigations indicated decreasing the abrasive wear resistance with increasing the hypereutectoid cementite fraction within the primary austenite grains.

It is shown that the excess carbide phase in Wootz is of an unusual nature origin that differs from the excess phase of secondary cementite, ledeburite and primary cementite in iron-carbon alloys. It is revealed that the morphological features of excess cementite in Wootz lie in the abnormal size of excess carbides having the shape of irregular prisms. It is discovered that the faceted angular carbides are formed within the original of metastable ledeburite, so they are called “eutectic carbides”. It was found that angular eutectic carbides in the Wootz formed during long isothermal soaking at the annealing and subsequent deformation of ledeburite structures. It is revealed that carbon takes up 2.25% in Wootz (in the region of white cast iron), while none in its structure of crushed ledeburite. It is shown that the pattern of carbide heterogeneity consists entirely of angular eutectic carbides having an irregular trigonal-prismatic morphology. It is shown that Wootz (Damascus steel) is non-alloy tool steel of ledeburite class, similar with structural characteristics of die steel of ledeburite class and high-speed steel, differing from them only in the nature of excess carbide phase.

The nature of change in the amount and morphology of iron dendrites and excess phases in relation to the degree of high-carbon alloy melt supercooling is considered. It is revealed that in pure iron-carbon alloys by changing the degree of melt supercooling it is possible to obtain steel with a carbon content as in white cast iron, or white cast iron with a carbon content as in steel. It is shown that before forging Damascus steel the structure is ideal with a pearlite matrix, without secondary free cementite, and with excess ledeburite phase. Features of ferrite and ledeburite shape change with thermomechanical treatment (forging) are studied. It is detected that during deformation heating for forging there is ledeburite recrystallization into a more stable phase of eutectic carbide. Limits are determined for transformation of pure high-carbon alloys in carbide class steel of the Damascus type.

The addition of a third element to hypereutectoid Fe-C alloys may cause inclusions of a minor constituent in the precipitate of cementite from austenite even if the initial austenite is supersatura ...

Obtaining of layered excess cementite distribution in hypereutectoid steel by deformation in the intercritical temperature range is considered. The initial state prior to deformation is cast steel and heat treated cast steel. It has been revealed that in the cast state excess cementite can be represented in the form of plates in a volume of austenite grains, in the form of network along austenite grain boundaries, in the form of liquation-induced aggregates (tangles) in the interaxial intervals of austenite dendrites. Typically a cast structure contains all of these morphologies. Sometimes excess cementite can be represented as primary cementite in nonequilibrium ledeburite. It has been found that a reliable method to obtain the layered structure without the presence of coarse particles of cementite is deformation in the intercritical temperature range of hypereutectoid carbon steel with an initial Widmanstatten morphology of excess carbide phase.

In this chapter, first, classification of the cast irons based on the Fe–C binary diagram is carried out. White cast irons are those that follow the metastable Fe–C diagram and give eutectics with ledeburite and cementite. Grey cast irons are those that follow the stable Fe–C diagram and give eutectics with graphite and austenite. In this first chapter, additions (graphitizing elements, inoculants, carbonigenous agents and silicon) used to facilitate either the metastable or the stable solidifications are also described.

Atom probe tomography was performed to study cementite dissolution as a function of the strain state of pearlite colonies with respect to the applied external strain in severely drawn pearlite steels. We prove that the migration of carbon from cementite into ferrite in the colonies increases under iso-stress conditions relative to that under iso-strain conditions at strains above 1.26. Our findings indicate that the strain state is an important microstructural component that controls the carbon redistribution in steel wires. We propose that the carbon–dislocation interaction is likely to be more prevalent under iso-stress conditions than in the iso-strain state.

© 2015 Acta Materialia Inc. The role of C and Mn during the growth of pearlite under non-steady state conditions is analyzed by comparing phase compositions of austenite, ferrite and cementite (γ+α+θ) through the use of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and atom probe tomography (APT) measurements across the austenite/pearlite interface. A local Mn enrichment and C depletion at the austenite/pearlite interface has been measured, which causes a change in the transformation driving force with time during divergent pearlite growth., Authors acknowledge financial support to MINECO and FEDER in the form of ENE2009-13766-C04-01 and MAT2013-47460-C5-2-P projects.

Cementite dissolution kinetics in austenite was investigated in a hypereutectoid steel alloy during continuous heating. The quantitative change in cementite volume fraction as a function of thermal history was determined from dilation curves by using the martensite start temperature to calculate prior austenite carbon content. Two characteristics of the cementite dissolution kinetics were found: (1) the cementite dissolution rate increased with time regardless of heating rate due to the increased surface area of cementite particles, and (2) the rate of cementite dissolution was strongly affected by heating rate. An empirical equation combining the effects of cementite volume change and heating rate is proposed to describe cementite dissolution kinetics. A continuous heating transformation diagram for hypereutectoid steels was obtained and compared with the DICTRA simulations and metallographic analyses.

The subject of investigations constituted the G200CrNiMo4-3-3 cast steel applied for metallurgical rolls. This is the material, which microstructure can be modified by the heat treatment. The presented hereby work concerns the initial state (as cast condition) of the investigated cast steel. This cast steel constitutes the initial material for the heat treatment. The morphology of carbide precipitates, including the cementite precipitated on grain boundaries of the primary austenite, hypereutectoid cementite precipitated in the Widmannstӓtten system and lederburitic cementite, were characterised in the study. The results of investigations of mechanical and fractographic properties of the G200CrNiMo4-3-3 cast steel, were also presented. Among others, the values of fracture work in the impact test, fracture toughness (KIc) and wear resistance were given. The crack pathway together with the hypereutectoid cementite fraction role in its development, was presented. The obtained investigation results, presented in the hereby paper, will constitute the comparison base for the assessment of the heat treatment influence on the microstructure and properties of the tested G200CrNiMo4-3-3 cast steel.

This chapter describes the phases and the association of the phases that produce the well-known traditional microstructures of carbon steels, namely the morphologies of ferrite, cementite, pearlite, bainite, and martensite as produced as a function of cooling from temperatures at which austenite is stable. Recent alloying and processing approaches, as described in later chapters of this volume, produce the unique modifications of these phases and microstructures that comprise the automotive steels described in this volume.

Temperature dependence of the absorbed impact energy in fully pearlitic steels was investigated. Two-step brittle-to-ductile transitions were observed. The value of the activation energy associated with the first transition is comparable to that of low carbon ferritic steels, indicating that the first transition is the brittle-to-ductile transition of ferrite phase in pearlitic steels. It suggests that the first transition is controlled by the dislocation glide in ferrite. The value of the activation energy associated with the second transition is higher than that of the first transition. Micrographs of fracture surfaces and side surfaces after fracture tests suggest that the activation energy associated with the second transition should relate to the deformability of cementite in pearlite, that is, the second transition is controlled by the dislocation activity in cementite of pearlite.

Nanostructural evolution of cementite lamellae in pearlitic steel wires subjected to cold drawing remains elusive, making it difficult to understand the origin of remarkable ductility in cementite. Using high-resolution transmission electron microscopy (HRTEM), the mechanisms underlying the inelastic deformation of cementite in pearlitic steel wires were examined and elucidated. Deformation of cementite in drawing should be included in two mechanisms: (1) Dislocation mechanism: deformation in low strain pearlite should rely on the movement of dislocation. Flat-crystal cementite was broken up into several different orientation cementite particles. (2) Grain rotation mechanism: the deformation mechanism should be by the rotation of cementite particles. Cementite still keeps lamellar shape, but it was divided into a multilayer structure: central nano-crystal and outermost amorphous cementite.

Effect of Mn, Si and Cr on spheroidization of cementite in Fe-1mass%C steel has been investigated over a range of austenitizing temperatures. In Fe-1C steel, a fully spheroidized structure is obtained but some large cementite particles are formed. The addition of 1.5 mass% Si or Cr accelerates spheroidization of cementite. An addition of Cr remarkably refine the cementite particle size, but the influence of Si addition on the cementite particle size is not remarkable. A fully spheroidized structure fails to develop in steel with the addition of 1.5% Mn under the condition used in present study. Some lamellar cementite still exist in the 1.5Mn steel. The pearlite-promoting effect of Mn is possibly attributed to the inhomogeneous distribution of cementite particles during the intercritical austenitization.

The ladle treatment technique for molten Hadfield steel was utilized by using four groups of CaSi inoculants and Mg metal in order to exclude the most hard-control conventional heat treatment process. The effect of ladle treatment on the morphology of Cementite networks, hardness, impact strength, and wear abrasion resistance were investigated. The SEM indicates that cementite is dispersed throughout the austenite matrix in a new eutectic. This eutectic grows on heterogeneous nuclei either SiO2 or MgS. Impact strength of modified as cast Hadfield steel exceeds the as heat-treated steel. The wear abrasion resistance of modified steel is 350% in excess of the conventional Hadfield steel.

Two hypereutectic cast irons (5.01 pct Cr and 5.19 pct V) were cast and the polished surfaces of test pieces were deep-etched and analyzed via scanning electron microscopy. The results show that graphite lamellae intersect the cementite and a thin austenite film nucleates and grows on the cementite plates. For both compositions, graphite and cementite can coexist as equilibrium phases, with the former always nucleating and growing first. The eutectic carbides grow from the austenite dendrites in a direction perpendicular to the primary plates.

Nanostructured bainite is extremely resistant to severe tempering making it difficult to reduce its hardness sufficiently to allow certain processing before heat treatment into its final state. An attempt is therefore made to introduce the divorced pearlite reaction that relies on the presence of pro-eutectoid cementite in the austenite in order to produce a microstructure containing spheroidal cementite particles simply by continuous cooling from the two phase austenite and cementite field. It is demonstrated that dramatically reduced hardness values can be achieved using this method.

Eutectoid steel with the ultrafine or fine-grained ferrite (α)+cementite (θ) particles structure was formed by hot deformation of undercooled austenite at 0.1 s−1 or 5 s−1 at 650 °C using a Gleeble 1500 hot simulator and subsequent annealing. The microstructural evolution of fine (α+θ) structure was investigated by means of a scanning electronic microscope, electron backscattered diffraction and transmission electron microscope, and the mechanical properties of fine (α+θ) steel were analyzed in comparison with that of ultrafine (α+θ) steel. The results show that only dynamic transformation of undercooled austenite into proeutectoid ferrite occurs during hot deformation at 650 °C at 5 s−1. During water quenching, lamellar pearlite with small colony sizes is formed and the average size of pearlite colonies decreases with increasing the strain. By subsequent annealing at 650 °C for 30 min, the spheroidization of lamellar pearlite takes place, resulting in the formation of fine (α+θ) structure consisting of ferrite matrix with the average size of about 4.9 μm and fine cementite particles mainly within ferrite grains. In comparison with ultrafine (α+θ) steel consisting of ferrite matrix with the average size of about 1.8 μm and relatively large cementite particles mostly located at grain boundaries, the yield strength, tensile strength, uniform elongation, total elongation and work-hardening capability of fine (α+θ) steel improve markedly.

Pearlite spheroidisation of 100CrMn6 steel was investigated. This process is well known and studied during conventional soft annealing. Presented paper describes cementite lamellae fragmentation during accelerated carbide spheroidisation. Mechanism of cementite lamellae fragmentation during conventional soft annealing depends on carbon and iron diffusion in ferrite-cementite system. On the other hand, accelerated carbide spheroidisation relies on partial pearlite austenitization and backward austenite decomposition. Aim of presented experiments was to examine shape evolution of cementite particles during transition from lamellar to globular form. Pearlite spheroidisation is normally quantified by image analysis of 2D metallographic section. Conventional metallographic observation was used for globular-lamellar particle ratio estimation. However, whole lamellae observation is necessary for spheroidisation process revelation. Ferrite matrix deep etching and cementite separation was performed to study morphological aspects of acceolerated carbide spheroidisation.

The surface of nodular cast iron (NCI) with a ferrite substrate was rapidly remelted and solidified by plasma transferred arc (PTA) to induce a chilled structure with high hardness and favorable wear resistance. The effect of scanning speed on the microstructure, microhardness distribution, and wear properties of PTA-remelted specimens was systematically investigated. Microstructural characterization indicated that the PTA remelting treatment could dissolve most graphite nodules and that the crystallized primary austenite dendrites were transformed into cementite, martensite, an interdendritic network of ledeburite eutectic, and certain residual austenite during rapid solidification. The dimensions of the remelted zone and its dendrites increase with decreased scanning speed. The microhardness of the remelted zone varied in the range of 650 HV0.2 to 820 HV0.2, which is approximately 2.3–3.1 times higher than the hardness of the substrate. The wear resistance of NCI was also significantly improved after the PTA remelting treatment.

Brittle pro-eutectoid cementite that forms along prior-austenite in hypereutectoid steels is deleterious to mechanical properties. The optimum process parameters which suppress the formation of pro-eutectoid cementite in hypereutectoid steels with carbon content in the range of 0.8%–1.3% in mass fraction, were investigated. Pro-eutectoid cementite formation is effectively hindered by increasing the deformation temperature and decreasing the amount of strain. Transformation at lower temperatures close to the nose of the cooling-transformation diagram also reduces the tendency of the formation of pro-eutectoid cementite. Control of prior-austenite grain size and grain boundary conditions is important. Due to larger number of nucleation sites, finer prior-austenite grain size results in the acceleration of transformation to pro-eutectoid cementite. However, large prior-austenite and straight boundaries lead to less nucleation sites of pro-eutectoid cementite. The cooling rate and carbon content should be reduced as much as possible. The transformation temperature below 660 °C and the strain of 0.5 at deformation temperature of 850 °C are suggested.

Surface layers containing ~ 1.57–2.55% (wt) carbon were produced by atmospheric electron-beam cladding of low carbon steel plates with an iron–graphite powder mixture. The main process parameter determining the thickness, structure, and mechanical properties of the hardened layer was the electron-beam current. As the beam current was increased from 20 to 26 mA, the thickness of the cladding layers increased from 1.2 to 2.6 mm and the hardness decreased from 5.7 to 4.5 GPa. In friction tests against fixed abrasive particles, the wear-resistance of the cladding layers was close to the wear resistance of pack-carburized specimens. In electron-beam cladding of steel plates 10 mm thick with the powder mixture with electron-beam scanning over the plate surface, the cooling rate of the surface layer was less than the critical value, which made it impossible to obtain a martensitic structure. The main structural components in the cladding layers were ledeburite, secondary Widmanstatten cementite, and pearlite. To produce a high-carbon martensitic structure directly during cladding by enhancing the heat transfer to the colder volume of the workpiece, it is necessary to increase the thickness and mass of the workpiece or reduce the thickness of the hardened layer. Saturation with carbon and quenching of the cladding layer can be performed successively using the same electron accelerator.

Reverse transformation at 725–800°C × 0–35 s from a ferrite/pearlite to austenite was investigated in spring steel 60Si2MnA with various pearlite fineness obtained by isothermal transformation. Then, its influence on the structure inheritance in the spring steel during heat treatment process was discussed. The results indicated that various pearlite fineness influences clearly start temperature of the reverse transformation. Austenite preferentially nucleates at the ferrite/cementite interface within pearlite, the neighboring pearlite colony boundary and the proeutectoid ferrite/pearlite boundary during the reverse transformation process. And the angle between pearlite lamellae and austenite growth direction has an important influence on austenite growth rate. Besides, the ferrite/pearlitic structure has structure inheritance phenomenon, because various hot-rolled microstructure affect the austenite nucleation and growth during heat treatment process.

Purpose. The development of heat treatment modes of white cast irons for structure changes in their eutectic constituent, namely in disturbing the monolithic structure of ledeburite colonies cementite structure and eutectic net continuity. Also the mentioned heat treatment modes are targeted to the eutectic net shift for the most suitable position from the point of plastic deforming. Methodology. The hypoeutectic white cast irons with 2.92…3.35 % carbon content and additionally alloyed by 3.18 % vanadium have been used as the research materials. The mentioned alloys have been pre-heat treated and hot twist tested. Findings . The research results showed that the carbide net breaking by plastic deforming leads to cast irons mechanical properties increasing but has difficulties in implementation due to the white cast irons low plasticity. The influence of different pre-heat treatment modes on structure and plasticity of white hypoeutectic cast irons have been investigated. They include the isotherm soaking under the different temperatures as well as multiply soakings and thermo-cycling. The influence of eutectic level, as well as pre heat treatment modes on different composition white cast irons hot plasticity have been investigated. Originality . It was determined that the heat treatment, which leads to double α→γ recrystallization under 860 – 950 °С and reperlitization under 720-680 °С results in significant increase of plasticity, as well as in un-alloyed and alloyed by vanadium white cast irons. It takes place due to carbide matrix phase separation in ledeburite colonies by new phase boundaries forming especially due to carbide transformations under vanadium alloying. Practical value . The implementation of pre-heat treatment with phase recrystallization resulted in hypoeutectic white cast irons plasticity increasing. The obtained level of cast iron plasticity corresponds to the one of carbide class steels, which ensures the successful deformation by forging and rolling.

The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion - the intergranular one - occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels.

The paper brings the results of directional solidification of Fe-Fe3C eutectic alloy. The Bridgman method with vertical thermal gradient in conducted research was applied. Two values of rate was used for sample movement testing. One sample after solidification, was immediately taken of the cooler. The distribution of thermal gradient in the alloy was determined. The value of thermal gradient in liquid at the solidification front was determined. On the samples, where cementite eutectic was oriented, interphase spacing λ̅ was measured. The results of the dependence between parameters v and λ̅ were presented. The research with application of optical microscope and computer programme to image analysis NIS-Elements was used.

The effects of alloying elements on the kinetics of austenitization from pearlite structure were studied by computer simulation in Fe–C–M ternary alloys, where M is Mn, Cr, Si or Ni, assuming local equilibrium conditions at all transformation interfaces. A thin austenite film was assumed to nucleate at ferrite/cementite interfaces and grow in one dimension. The existence of a partition to no-partition transition temperature (PNTT) was rationalized. Above the PNTT, the growth rate of austenite is governed by the difference in carbon activity between austenite/cementite and ferrite/austenite interfaces; a substitutional element influences the reaction rate by affecting carbon activity. Below the PNTT, redistribution of M is necessary. The PNTT increases with the concentration of all alloy elements except Ni, which has a large segregation tendency in austenite from both ferrite and cementite, as well as repulsive interaction with carbon. The amount of overheating at PNTT from Ae1 increases in the order Si (∼...

The detailed mechanism of divorced pearlite in bearing steels began to be actively discussed more recently. The survey of divorced pearlite in higher Mn bearing steel was carried out through scanning electronic microscope following isothermal transformation heat treatment. The results show that while divorced transformation taking place in the higher Mn bearing steel just slightly below A1, the cementite could be produced in such way as growing on the base of pre-existing cementite particles in austenite, or emerge either in globular particles or in short rod directly from the austenite. Under isothermal transformation, the carbon atoms in austenite prefer to precipitate on the original boundary of the austenite. The enough small size of the cementite particles remained in the austenite is helpful for getting spheroidal cementite particles structure through divorced eutectoid transformation.