Primary Austenite Dendrites Research Articles

Effect of Dendrite Fraction on the M23C6 Precipitation Behavior and the Mechanical Properties of High Cr White Irons

High Cr white irons with various fractions of primary dendrite have been prepared through the modification of their chemical composition. Increasing C and Cr contents decreased the primary dendrite fraction. Eutectic solidification occurred with the phase fraction ratio of austenite: M7C3 = 2.76:1. The measured primary dendrite fractions were similar to the calculated results. ThermoCalc calculation successfully predicted fractions of M7C3, austenite, and M23C6. Conventional heat treatment at high temperature caused a destabilization of austenite, releasing it’s solute elements to form M23C6 carbide. Precipitation of M23C6 during destabilization preferentially occurred within primary (austenite) dendrite, however, the precipitation scarcely occurred within austenite in eutectic phase. Thus, M23C6 precipitation by destabilization was relatively easy in alloys with a high fraction of primary dendrite.

Application of the Hydraulic Diameter of Interdendritic Space for Calculating the Ultimate Tensile Strength of Gray Cast Iron

A comparative analysis of methods for estimating the gray cast iron ultimate tensile strength σu by the hydraulic diameter of interdendritic space DHydIP and the volume fraction of primary austenite dendrites fdc is performed. Almost the same accuracy of cast iron castings σu estimation according to both these parameters DHydIP and fdc of the primary microstructure is shown.

Effects of annealing treatment on microstructure and hardness in the 28 wt% Cr cast iron with Mo/W addition

In this study, the effects of annealing on the hardness and microstructure of 28 wt% Cr-2.6 wt% C iron with 1.4 wt% Mo/1 wt% W addition have been investigated. The as-cast samples were heated to 800℃ and held for 4 h followed by slow cooled with a cooling rate of 20℃h-1 to 500℃. Microstructures were characterized by X-ray diffractometry, optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Vickers macro-hardness and micro-hardness were measured. It was found that the as-cast microstructure in the hypoeutectic 28 wt% Cr iron without Mo or W addition consisted of primary austenite dendrite, eutectic M7C3 carbide and martensite. In the iron with 1.4 wt% Mo addition, multiple eutectic carbides of M7C3, M23C6 and M6C were observed. In contrast the addition of 1 wt% W changed the structure to hypereutectic containing primary M7C3, eutectic M7C3 and martensite. After the annealing heat treatment, ferrite +secondary carbides and some pearlite were present in the irons, due to decomposition of austenite during annealing. The macro-hardness in the as-cast condition of the iron without alloying and the irons with 1.4 wt% Mo/ 1 wt% W addition were 506, 529, and 576 HV30, respectively. Annealing heat treatment reduced the macro-hardness to about 390, 463, and 428 HV30, respectively.

Improvement of mechanical properties of iron castings via adjusting of solidification rate

The work is devoted to improvement of mechanical properties of iron castings via adjusting of the cooling rate without introduction of alloying additives. The new technological solution is suggested; it can be easily adapted to a casting technology. This solution is based on variation of the cooling rate of iron castings within structurally sensitive solidification intervals. For this purpose, the casting mould was initially cooled after pouring, then heated and cooled again. Cooling of the mould during the period of primary austenite crystal forming led to increase of dendrite crystallization rate and was executed using compressed air. Retarding of the cooling rate during the period of eutectic transformation was provided by the mould heating via burning of exothermic carbon-containing additives introduced in a facing layer of sand-clay moulding mix. Burning reaction is accompanied by heat extraction, what steeply retarded the cooling rate within the interval of eutectic transformation. Consequent acceleration of castings cooling within the interval of eutectoid transformation was achieved via repeated air blowing through a worked reaction layer. Adjusted cooling of iron castings allowed to provide the most favourable solidification conditions, taking into account strictly individual requirements for each structurally sensitive temperature intervals. It led to increase of a volumetric part of primary austenite dendrite crystals, to decrease of eutectic transformation overcooling degree, to forming of graphite eutectics and enlargement of dispersity of pearlite component in iron. Consequently, lowering of widespread iron castings rejects takes place, among them chilling, with simultaneous improvement of metal mechanical properties. As a result, the primary and real structures were varied, what had a positive effect on mechanical properties of casting metal. It is shown that use of solidification rate adjustment led to essential increase of metal tensile strength for the experimental casting.

Corrosion behaviour of resistance-spot-welded high-Mn austenitic TWIP steel

ABSTRACT High-Mn twinning-induced plasticity (TWIP) steels have been proposed to meet higher passenger safety and crash-safe vehicle frame requirements demanded by the automotive industry. The corrosion behaviour of welded Fe–30Mn–5Al–0.5C–6Cr TWIP steel using the resistance-spot-welding (RSW) technique was studied. Welds showed a microstructure consisting of primary austenite dendrites and interdendritic δ-ferrite in both fusion zone (FZ) and base metal (BM), which is in agreement with an austenitic-ferritic (AF) solidification mode. The results reveal that the refinement of the microstructure in the weld region does not significantly affect the corrosion resistance of this region, having a low corrosion current density of the order of 1 μA cm–2. It was concluded that Cr-rich second phase particles along the austenite/δ-ferrite interface can lead to Cr-depleted zones, increasing pitting corrosion susceptibility. It was found that the minimum Cr content at the Cr-depleted zones is nearly independent of the δ-ferrite volume fraction.

Solidification, Macrostructure and Shrinkage Formation of Ductile and Compacted Irons

This manuscript summarizes recent investigation of the authors into the solidification and shrinkage defect formation of ductile and compacted graphite cast irons. The study makes use of the DAAS (direct austempering after solidification) technique, developed earlier by some of the authors, to reveal the solidification grains. In addition, color metallography is used to reveal the microsegregation pattern. The formation of shrinkage defects is related to both the solidification macrostructure and the microsegregation pattern. The examination of the macrostructure shows that large solidification grains, composed by dendritic austenite and graphite, characterize the solidification of compacted graphite irons of carbon equivalent values ranging from hypoeutectic to hypereutectic. Similar results are observed for ductile iron, but in this case, the hypereutectic irons display a finer macrostructure. The characteristics of the primary austenite dendrites are revealed by the microsegregation pattern, which is exposed by the color etching reagent. This pattern also clarifies the nature of the interaction between the growing austenite and the compact and spheroidal graphite particles. The microshrinkage cavities in both ductile and compacted graphite irons form at the interior of the austenite grains, where fluid feeding cannot compensate the contraction of the last-to-freeze portions of the melt. Schematics of the solidification of ductile and compacted irons are proposed, accounting for the experimental observations.

Examination of the Size and Morphology of Austenite Grains in Lamellar Graphite Cast Iron

There is a current discussion concerning the austenite grains of lamellar graphite irons and its growth at different carbon equivalent contents. The term “grain” is often employed to refer not only to the primary austenite, but also to the colonies or cells formed during the eutectic solidification. This investigation applies advanced experimental methods to study the solidification of lamellar graphite iron. A better understanding of the solidification process should lead to the design of better casting procedures. Samples of lamellar graphite iron were cast and directly austempered after solidification in order to reveal their solidification macrostructure. A typical ingot structure was found, with a narrow columnar-to-equiaxed transition. Electron backscatter diffraction technique was applied to confirm these macroscopic observations. Color etching was employed to determine the size of eutectic colonies at the columnar and equiaxed regions. The EBSD results confirm previous proposals, revealing that the solidification grains result from the growth of austenite dendrites. These grains include several eutectic colonies or cells inside, all these colonies or cells having the same crystalline orientation as the primary austenite dendrite. An analysis of the critical gradient for columnar-to-equiaxed transition could be developed. The size of the eutectic colonies at the columnar zone was found to be smaller than the size of the eutectic colonies at the equiaxed zone. Besides, the size of equiaxed grains strongly decreased with the increase in cooling rate, while no evident differences were obtained when the size of the columnar grains was measured.

Comparison of the microstructure and mechanical properties of FeCrNiBSi alloy fabricated by laser metal deposition in nitrogen and air

Laser metal deposition (LMD) as a promising on-line maintenance technology can effectively reduce the maintenance cost of energy and mining machinery. However, the process of LMD for on-line maintenance is faced with two difficulties: insufficient inert gas and oxidation of materials. To overcome the difficulties, this work proposed to use nitrogen which is easily isolated from air and an FeCrNiBSi alloy powder having good oxidation resistance as the powder delivery gas and the feedstock material for repairing AISI 5140 by LMD, respectively. The microstructure and mechanical properties of the FeCrNiBSi coatings deposited on AISI 5140 substrates by LMD in nitrogen and air were compared. Both coatings had a hypoeutectic microstructure composed of a primary austenite dendrite within a eutectic structure consisting of a (Cr,Fe)2B phase and an austenite phase. The coating fabricated in air possessed lower yield stress, ultimate tensile stress and microhardness, higher total elongation than the coating fabricated in nitrogen due to the eutectic volume fraction in the former was lower. The composition and microstructure of the coating fabricated in air varied monotonously from the substrate/coating interface to 300 μm. By contrast, a continuous eutectic lamella was formed at the interface of the coating fabricated in nitrogen, which hindered the diffusion of elements, caused a sudden change in composition, and was detrimental to the mechanical properties. Therefore, for repairing AISI 5140, the FeCrNiBSi powder was deposited onto AISI 5140 by LMD in air, and the yield stress and ultimate tensile stress were slightly higher than those of the AISI 5140, indicating that AISI 5140 could be repaired with FeCrNiBSi by LMD in air. In addition, the microstructural characteristics that less eutectic in overlapping zone of the laser deposited coatings and its influence on the mechanical properties were discussed.

Precipitation behavior of boron-carbide hard phase comprising a new high-boron high-speed steel

The solidification process and the precipitation behavior of the boron-carbide hard phase comprising a new high-boron high-speed steel were investigated through the combination of phase balance calculations (by Thermo-Calc software) and experimental tests. The results revealed that a primary austenite precipitation reaction (L → γ), ternary eutectic reaction (L → γ + M2 (B, C) + M2C), and secondary boron carbide precipitation reaction (γ → M (B, C) and γ → M3 (B, C)) occurred during the solidification process of the steel. These reactions occurred at characteristic temperatures of 1350 °C, 1220 °C, 1100 °C, and 1000 °C, respectively. The precipitation reaction of primary austenite yielded a primary austenite dendrite and a eutectic structure distributed along the grain boundary. The ternary eutectic reaction products were austenite, M2 (B, C) and M2C, which were distributed in the grain boundaries in a manner consistent with interdependence and mixed growth. Similarly, the secondary M3 (B, C) boron carbide, converted from the (Fe, Cr)3C carbide, was precipitated from the austenite matrix. The solidification process consisted of four stages: diffusion of alloying elements, aggregation of alloying elements at grain boundaries, nucleation of M3 (B, C) phases and growth of M3 (B, C) phases. This new high-boron high-speed steel can be widely used in rolls and other fields where wear resistance is required.

Characterization of eutectic borides formed during solidification of borated stainless steel 304B4

AISI 304B4 stainless steel (SS) containing 1.3 wt.% boron was cracking extensively during fabrication of neutron shields for Prototype Fast Breeder Reactor (PFBR). However, earlier study on 304B4 steel showed good resistance to weld solidification cracking due to eutectic backfilling in the cracks during welding. In order to understand the backfilling mechanism in this steel, microstructural characterization was performed on 304B4 SS in solution-annealed and re-melted and solidified conditions. In solution-annealed condition, microstructure of 304B4 SS consists of austenite matrix with random distribution of blocky Cr2B-type borides. On contrary, as-solidified microstructure reveals the primary austenite dendrites and interdendritic eutectic of (Fe,Cr)2B-type borides of varying morphologies. In addition to (Fe,Cr)2B, spheroidal non-equilibrium Fe23(CB)6-type borides were also found inside the austenite dendrites. The eutectic liquid rich in boron and Fe, which has low solidus temperature, contributes significantly to backfilling of hot cracks formed during welding. This was confirmed through characterization of eutectic borides in the as-solidified structure which shows Fe-rich (Fe,Cr)2B and Fe23(CB)6 types of borides. Finally, reasons behind severe liquation cracking of 304B4 SS observed during fabrication of neutron shield has been explained based on Scheil’s solidification simulations.

EBSD Analysis of the Primary Austenite Grains in Lamellar Graphite Cast Iron

This work investigates the size and morphology of the primary austenite grains present in lamellar graphite cast iron. Samples of lamellar graphite iron were cast and austempered during the post-solidification cooling stage in order to preserve part of the original austenite at room temperature. Electron backscatter diffraction technique was applied to reveal the regions of different crystalline orientation of the austenite. The eutectic colonies and the last-to-freeze areas were also examined by color etching of the same regions previously analyzed by electron backscatter diffraction. The results reveal that the solidification units of lamellar graphite iron are formed by austenite grains that include several eutectic colonies inside, all of which have the same crystalline orientation as the primary austenite grain. For all the samples studied, it can be confirmed that there are no eutectic colonies with a different crystalline orientation than that of the primary austenite dendrites.

Effect of pre-annealing heat treatment on destabilization behavior of 28 wt. % Cr-2.6 wt. % C high-chromium cast iron

In the present work, the effects of pre-annealing heat treatment on microstructure and hardness in destabilized 28 wt. % Cr-2.6 wt. % C high-chromium irons have been investigated by X-ray diffraction, light microscopy, and scanning electron microscopy. As-cast specimens were annealed at 800°C for 4 h, and then furnace cooled. Destabilization after annealing was carried out at 1000°C for 2 and 4 h, followed by forced air-cooling to room temperature. Vickers macro-hardness was measured on specimens from each condition. The results revealed that the as-cast microstructure consisted of primary austenite dendrites with an interdendritic eutectic structure of M7C3 carbide and eutectic austenite. The eutectic austenite had partially transformed to martensite during cooling in the mold. During annealing at 800°C, austenite converted to carbides + ferrite and some pearlite. The hardness decreased from 507 to 425 HV30. Destabilization led to precipitation of secondary carbides and transformation of dendritic and eutectic austenite to martensite with some retained austenite. After destabilization, the macro-hardness increased from 736 HV30 in the iron without prior annealing up to 843 HV30 in the iron with annealing plus destabilization. For maximum hardness, prior annealing reduced the destabilization time from 4 to 2 h.

Microstructure and Tempering Behaviour of 28Cr-2.5C-1W Cast Irons

In this work, the effects of 1 wt.% tungsten addition and variation in tempering times on the microstructure and hardness of nominal 28 wt.%Cr high chromium irons were investigated. As-cast samples were destabilised at 1050 °C for 4 hours and then hardened by air cooling. Tempering after destabilisation was carried out at 450 °C for 2, 4 and 6 hours followed by air cooling. X-ray diffractometry, light microscopy and scanning electron microscopy were used to characterize the microstructures of the irons. The results show that the as-cast microstructure of the iron without W addition consisted of primary austenite dendrites with eutectic M7C3 and eutectic austenite partially transformed to martensite. The iron with 1 wt.%W addition contained primary M7C3 and eutectic M7C3 in an austenite matrix. Destabilisation treatment of the austenite matrix in both irons allowed precipitation of secondary carbides and transformation to martensite during air cooling. Phase transformation of eutectic M7C3 was also found in the iron with W addition. The formation of primary M7C3 in the 1 wt.%W iron increased the as-cast macro-hardness from 500 (no W) to 576 HV30. Destabilisation increased the macro-hardness up to 736 (no W) and 780 HV30 (1 wt.%W) since secondary carbide precipitation allowed austenite to transform to essentially martensitic matrices. At longer tempering times, the macro-hardness further increased up to about 820 HV30.

Effect of Destabilisation and Tempering Heat Treatments on Hardness and Corrosion Behavior of 28 wt.%Cr Cast Irons with Mo Addition

The effects of destabilisation and tempering heat treatments on hardness and corrosion behavior in 28 wt.%Cr-2.6 wt.%C cast irons with up to 6 wt.%Mo addition were studied. The irons were destabilised at 1025 °C for 4 h and air cooled. Tempering was carried out at 450 °C for 4 h. Phase identification and microstructure were investigated by X-ray diffraction (XRD), light microscope (LM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Vickers macro-hardness was measured. A potentiodynamic technique was used to indicate aqueous corrosion resistance. The results revealed that the as-cast microstructure of 28 wt.%Cr iron consisted of primary austenite dendrites with eutectic M7C3 carbides. In the irons with 6 wt.%Mo addition, eutectic carbides including M7C3, M23C6 and M6C were found. After destabilisation, the microstructure contained secondary carbide precipitates within an essentially martensitic matrix. Vickers macro-hardness of the as-cast and destabilised irons increased from 500 HV30 and 736 HV30 in the 28 wt.%Cr iron up to 570 HV30 and 870 HV30 in the iron with 6 wt.%Mo addition. Tempering slightly increased the macro-hardness. The as-cast 28 wt.%Cr iron had the lowest values for critical current density and passive current density. The destabilised + tempered treatment gave the lowest corrosion resistance.

Development of High Performance Cast Iron with Combination of Improved Mechanical and Thermal Properties Through Mo Addition

High performance cast iron with a combination of improved mechanical properties and thermal conductivity is developed through Mo addition in gray cast iron. The primary austenite dendrite as well as the eutectic cell can be refined by Mo addition. Decrease of the amount and length of graphite flakes as well as Mo solid-solution strengthening leads to high ultimate tensile strength, while the uniform distribution of graphite flakes is responsible for the improved thermal conductivity.

On the Primary Solidification of Compacted Graphite Iron: Microstructure Evolution during Isothermal Coarsening

It is widely accepted that in most commercial hypoeutectic alloys, both static mechanical properties and feeding characteristics during solidification, are extremely linked to the coarseness of the primary phase. It is therefore of critical importance to provide tools to control and predict the coarsening process of the dendritic phase present in hypoeutectic melts. The characterization of the primary phase, a product of the primary solidification, has traditionally been neglected when compared to the eutectic solidification characterization in cast iron investigations. This work presents the morphological evolution of the primary austenite present in a hypoeutectic compacted graphite cast iron (CGI) under isothermal conditions. To that purpose, a base spheroidal graphite cast iron (SGI) material with high Mg content is re-melted in a controlled atmosphere and reversed into a CGI melt by controlling the Mg fading. An experimental isothermal profile is applied to the solidification process of the experimental alloy to promote an isothermal coarsening process of the primary austenite dendrite network during solid and liquid coexistence. Through interrupted solidification experiments, the primary austenite is preserved and observed at room temperature. By application of stereological relations, the primary phase and its isothermal coarsening process are characterized as a function of the coarsening time applied. The microstructural evolution observed in the primary austenite in CGI and the measured morphological parameters show a similar trend to that observed for lamellar graphite cast iron (LGI) in previous investigations. The modulus of the primary austenite, Mγ, and the nearest distance between the centre of gravity of neighbouring austenite particles, Dγ, followed a linear relation with the cube root of coarsening time.

MICROSEGREGATION OF SILICON IN CAST IRON

The literature presents contradictory data on the microsegregation of silicon in cast iron. Authors of the previous works have investigated silicon microsegregation in dendritic cell consisting both of primary austenite and eutectic austenite that grows on the primary austenite dendrites. Since the silicon content in austenite affects the temperature and completeness of the phase transitions during cooling and heat treatment, the absence of data on silicon microsegregation do not allow to predict the microstructure of cast iron in the as-cast condition and after heat treatment. The silicon microsegregation in gray cast iron with composition Fe + 3.11 % С + 1.6 % Si + 0.4 % M n by the energy dispersive X-ray spectroscopy and calculation of the nonequilibrium solidification in the Thermo-Calc software were investigated. The silicon microsegregation in the primary austenite is not observed. The silicon content in the primary austenite was ≈2 % that is higher than silicon content in the eutectic austenite ≈1.5 %. Due to the calculations results the microsegregation of silicon in primary austenite are negligible. By calculation the non-equilibrium solidification of ternary alloys Fe – Si – C [Fe + 1.5 % Si + X % C], at X = 1.5; 2.8; 3.7 it was shown that the only primary austenite solidified at 1.5 % С and microsegregation of silicon are positive (Si content in the center of the dendritic cells is lower than on its boundaries). For the alloy with 2.8 % С, the microsegregation of Si in the primary austenite is also positive, however the silicon content in the eutectic austenite, growing on the primary austenite during the austenite-graphite eutectic formation, will be lower and the “rim effect” (maximum Si content at the boundary between primary and eutectic austenite) should appears. At the 3.7 % of C in alloys the primary dendrites amount should be limited, so the major part of the dendritic cell should consist of the eutectic austenite, the Si content in which should be decreasing during the solidification. In this case the so-called negative microsegregation should occur.

The effect of Ta substitution for Nb on the microstructure and wear resistance of an Fe-Cr-C hardfacing alloy

The effect of Ta substitution for Nb on the microstructure and wear resistance of an Fe-Cr-C hardfacing alloy deposited with gas tungsten arc welding (GTAW) process was investigated. Results showed that the microstructure of the base composition was a hypoeutectic one consisting of primary austenite dendrites and eutectic constituents of γ+M7C3. Addition of Nb did not change the hypoeutectic nature of the microstructure. However, coarse semi-cuboidal NbC was formed in the microstructure. Moreover, compared with the base composition, higher eutectic content and finer austenite dendrites were observed as a result of Nb addition. Ta substitution for Nb has changed the microstructure from hypoeutectic to hypereutectic containing primary hexagonal M7C3 carbides in an eutectic matrix along with coarse semi-cuboidal TaC particles. Hardness test results revealed that the hardness value increased by the addition of Nb or Ta. Maximum hardness value was obtained from Ta-containing coating. Reciprocating wear test results were directly related to the hardness of the hardfacing alloys. Hence, Ta-containing coating exhibited a superior wear resistance mainly due to the formation of primary hexagonal M7C3 carbides and coarse TaC precipitates. As well, Scanning Electron Microscopy (SEM) of the worn surfaces revealed evidences of abrasive and delamination wear mechanisms.

Structure and Properties of Cast Iron DESIGNATED for Working Layer of Rolls

<p class="1Body">The formation of the structure and properties of cast irons designated for the working layer during solidification and subsequent tempering of Indefinite Chill Double Poured Centrifugal Casting Rolls (ICDP) has been studied.</p><p class="1Body">Graphitization of cast irons designated for the working layer of rolls occurs under isothermal conditions at high temperatures, which vary over the cross section and resulted from casting the roll core. At subsequent slow cooling, secondary carbides precipitate and austenite partially transforms into martensite; the resulting end structure consists of martensite and austenite metallic base (primary austenite dendrites) with 11.4 per cent of retained austenite, 26 per cent of eutectic and secondary carbides, and 2.6 per cent of flake graphite.<em> </em></p><p class="1Body">The amount of retained austenite in the metallic base of the cast structure of cast iron designated for the working layer, heated to 430 °C, decreases<strong> </strong>from 11.4 per cent to 3.2 per cent due to the partial transformation into bainite. The martensite tetragonality decreases due to the carbide precipitation; the existing excess phases grow and the new ones are formed; the total volume fraction of the carbide phase increases to 29.8 per cent and graphite to 3.7 per cent.</p>

On the stable eutectic solidification of iron–carbon–silicon alloys

Extensive effort was expanded to elucidate the growth and morphology of the stable eutectic grains during early solidification of continuous cooled Fe–C–Si alloys. To this purpose, quenching experiments at successive stages during solidification have been carried out on five cast irons with various magnesium and titanium levels designed to produce graphite morphologies ranging from lamellar to mixed compacted–spheroidal.The graphite shape factors were measured on the metallographic samples, and their evolution as a function of the chemical composition and the solid fraction was analyzed. Extensive scanning electron microscopy was carried on to evaluate the change in graphite shape during early solidification, to establish the fraction of solid at which the transition from spheroidal-to-compacted-to-lamellar graphite occurs, and to outline the early morphology of the eutectic grains. It was confirmed that solidification of Mg containing irons started with the development of spheroidal graphite even at Mg levels as low as 0.013 mass%. Then, as solidification proceeds, when some spheroids developed one or more tails (tadpole graphite), the spheroidal-to-compacted graphite transition occurs.The new findings were then integrated in previous knowledge to produce an understanding of the eutectic solidification of these materials. It was concluded that in hypoeutectic lamellar graphite iron austenite/graphite eutectic grains can nucleate at the austenite/liquid interface or in the bulk of the liquid, depending on the sulfur content and on the cooling rate. When graphite nucleation occurs on the primary austenite, several eutectic grains can nucleate and grow on the same dendrite. The primary austenite continues growing as eutectic austenite and therefore the two have the same crystallographic orientation. Thus, a final austenite grain may include several eutectic grains. In eutectic irons the eutectic grains nucleate and grow mostly in the liquid. The eutectic austenite has different crystallographic orientation than the primary one.The solidification of the austenite/spheroidal graphite eutectic is divorced, with graphite spheroids growing on primary austenite dendrites. The eutectic austenite grows on the primary austenite and has the same crystallographic orientation. The result is large austenite (primary and eutectic) dendrites that incorporate numerous graphite spheroids. A eutectic grain cannot be defined.