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In this study, heavy rare-earth Y element was added to D2 cold work die steel to improve its carbide morphology and distribution, thereby increasing its impact resistance. A comprehensive study was conducted on the morphology and distribution of carbides in D2 steel in the as-cast, as-forged, and spheroidized annealing states. After the forging process, the degree of breakage of the network distribution of the as-forged M7C3 eutectic carbide morphology in the Y-containing D2 steel increased. As the Y content increased from 0 to 0.0210 wt%, the secondary dendrite spacing of the as-cast M7C3 eutectic carbides as well as the volume fraction and average size of carbide clusters decreased from 43 μm, 16.7%, and 29 μm–31.96 μm, 14.2%, and 23 μm, respectively. After the spheroidized annealing process, the addition of Y increased the M7C3 eutectic carbide spheroidization degree. Moreover, the number of the M7C3 secondary carbides increased from 50/25 to 71/25 μm2, and Y addition increased the number of dimples in the impact fracture and proportion of high-angle grain boundaries from 79.1% to 93.4%. Finally, the longitudinal impact toughness of D2 cold work die steel increased from 103.9 to 163.2 J.

Two chromium-rich carbide hard-faced plates, alloy—A and alloy—B, were subjected to a 3-body dry sand abrasion test. The difference was in the coating microstructure. Alloy-A contains globular chromium carbide (M7C3 type) in the austenite matrix, whereas alloy—B is composed of a banded structure with an alternate layer of carbide and austenite. Alloy B showed a superior abrasion resistance (nearly 40%) than alloy—A. A detailed microstructural investigation was made on the abraded surface. The higher abrasive wear resistance of alloy-B was attributed to the coating morphology, the composite-like microstructure resulted in an effective strain distribution among the austenite matrix and carbides. This postulate was supplemented by higher average misorientation, which was observed at sub-surface regions of the worn-out specimen, leading to form a strain-induced martensite. However, in alloy—A, the abraded surface contained abundant broken carbides. [ABSTRACT FROM AUTHOR]

In this study, the fatigue crack growth rate in four different tool steel microstructures (hot rolled, powdermetallurgically processed, as‐cast, and carbide‐free) is experimentally measured and correlated with hard phase size and spacing, as well as with the roughness of the fracture surface that is created by crack kinking. Numerical simulations of crack growth in carbide‐containing microstructures are conducted and investigated. The results indicate a favorable influence of carbides with a larger size and higher degree of roundness, as they create the largest mean free path between the individual carbides at the same hard phase volume content. This facilitates the formation of a plastic zone in the matrix, which dissipates crack energy and reduces the effective stress intensity. In addition, the effect of crack kinking is increased at larger carbide sizes. Concerning practical application, the results suggest that a high degree of deformation is favorable regarding the fatigue growth resistance of tool steels, and that the use of powder metallurgically (PM) grades with small carbides is discouraged, if the lifetime of a tool is mainly controlled by the crack growth rate and not crack initiation. Highlights: Carbide morphology exerts influence on the fatigue crack growth resistance of tool steels.The eigenerosion approach can simulate FCG in steels by visualizing mechanical fields.FCG resistance is enhanced by increasing the mean free matrix path between carbides.Larger carbide diameters further improve FCG resistance due to crack deflection. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement of a Ni-based superalloy, IN740H, was evaluated after gas-phase hydrogen pre-charging. Specimens with different grain sizes were prepared to induce different precipitation behavior under annealing treatment; the formation of needle-like MC carbide was found only in a specimen with a larger grain size and incoherent twin boundaries after annealing treatment at 1173 K. While other parameters including the grain size and annealing treatment turned out not to undermine the resistance to hydrogen embrittlement, the needle-like MC carbide was found to induce premature failure after hydrogen absorption.

Hydrogen embrittlement of a Ni-based superalloy, IN740H, was evaluated after gas-phase hydrogen pre-charging. Specimens with different grain sizes were prepared to induce different precipitation behavior under annealing treatment; the formation of needle-like MC carbide was found only in a specimen with a larger grain size and incoherent twin boundaries after annealing treatment at 1173 K. While other parameters including the grain size and annealing treatment turned out not to undermine the resistance to hydrogen embrittlement, the needle-like MC carbide was found to induce premature failure after hydrogen absorption. [ABSTRACT FROM AUTHOR]

Precipitation behavior and elemental distribution of MC carbides in high carbon and vanadium high-speed steel were analyzed through the thermodynamic calculations and experimental measurements. The results illustrated that the primary MC carbide always nucleated from the fine inclusions or particles as the heterogeneous nuclei and was followed by the occurrence of eutectic reaction (L→γ + MC). 2D lumpy (primary) and stripe-like (eutectic) MC carbides were mainly formed inside the grains, the former was mainly in hexahedral shape with four-leaf grass-shaped surface and few in complex polyhedral shape with short branches, while the latter was mainly in clustered coral-like morphologies. High cooling rate can effectively refine the size and reduce the quantity of primary MC, it can also promote the uniform precipitation of fine eutectic MC. The primary MC precipitated preferentially contained more N, C, V, and less Cr, Mo, W with a better uniformity of elemental distribution when compared with that in eutectic MC. For the latter, its composition (mainly V) changed obviously which was mainly affected by the carbide's quantity, distribution characteristic, and the actual solute concentration during the solidification process. Generally, the more quantity and much denser distribution of the eutectic MC branches, the less contents of C and V in the eutectic MC branches. Based on the 2D and 3D morphologies of MC carbides, the primary MC showed good symmetry and the eutectic MC showed an obvious directionality of its branch from grain interior to grain boundary. It provided an effective reference for further research on the growth mechanism of carbides. [ABSTRACT FROM AUTHOR]

Abstract A comparative high temperature wear study was conducted between two alloys: laser metal deposited vanadium-rich (V-rich) high speed steel (HSS) and spun cast carbide enhanced indefinite chilled double poured (CE-ICDP) iron. Laser Metal Deposition (LMD) of V-rich HSS alloy was performed by using a 4.0 kW Nd:YAG laser at three different laser scan speeds to investigate the effect thereof on the carbide size and morphology, phase constitution and mechanical properties (such as micro-hardness and wear resistance) of the laser metal deposits. A comprehensive microstructural characterization of these alloys revealed that the dendritic microstructure of the V-rich HSS alloy consisted of martensitic matrix and VC carbides. Increasing the laser processing speeds significantly changed the morphologies of VC carbides from square and round to angular and rod-like shapes. The micro-hardness of the V-rich HSS was improved from 760 HV to 835 HV by increasing the laser processing speed. During high temperature (500 °C) pin-on-disc wear tests, the V-rich HSS showed excellent wear resistance compared to CE-ICDP iron. It was found that V-rich HSS with square and round shape VC carbides (V-rich 10 mm/s) showed the most improved tribological performance with oxidative wear found to be the dominant wear mechanism at this temperature. Highlights • Increasing the processing speed changed the morphology of microstructural features of laser deposited HSS alloy. • Load bearing capability of VC carbides depends upon the size and shape of carbides. • Oxidative wear mechanism was found to be dominant at this temperature. [ABSTRACT FROM AUTHOR]

The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT.

In this paper, real-time cooling rate of Fe-Ti-C Metal Matrix Composites (MMCs) made by Direct Metal Deposition (DMD) are measured to monitor microstructure and carbide morphology. This research proves that carbide morphology developed by DMD of Fe–TiC composite coating on AISI 1020 carbon steel is highly affected by cooling rate and pre-heat. For this purpose, the DMD process is monitored by a thermal camera to obtain real-time values of the cooling rate resulted from a range of selected scan speeds. Two approaches are studied for the single-track depositions: (a) single speed and (b) dual speeds in which the scan speed changes during the deposition. The dual speed generates different preheat values during deposition and thus deviates the cooling rate. Consequently, the effect of cooling rate and preheat temperature are studied on carbide morphologies. Results show that scan speed plays the main role in the formation and distribution of TiC particles in the deposited layer by affecting the cooling rate and dilution (melt pool composition). Based on this research, it is possible to control the cooling rate in order to achieve specific carbide morphologies in the deposited layer. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) are used to characterize the deposited layers' microstructure. [ABSTRACT FROM AUTHOR]

The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT. [ABSTRACT FROM AUTHOR]

The influence of solution temperature on the microstructure evolution and creep behavior of a new Ni–Co base superalloy for turbine discs, including the grain morphology, grain boundary character distribution (GBCD), and grain boundary (GB) carbide morphology, was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results showed that the creep fracture life first increased and then decreased with increasing solution temperature. The alloy solution treated at 1140 °C exhibited the best creep properties, with a creep life of 209 h. The enhanced creep performance of this alloy can be explained as follows: the volume fraction of GB carbides increased with increasing solution temperature, the diffuse fine granular carbides relieved stress concentration and strengthened GBs, the coarse primary γ′ phases rapidly dissolved, and the volume fraction of the fine and dispersed secondary and tertiary γʹ phases significantly increased. The narrower channels in the γ matrix increased the resistance to dislocation motion. The coherent Σ3 twin boundaries (TBs) with low interface energy hindered the dislocations and stacking faults intersecting the TBs on different slip planes. The relative frequency of Σ3 TBs increased to 53.6% when the solution temperature was increased to 1140 °C. The high proportion of Σ3 TBs played a key role in improving the creep resistance of the alloy. • Microstructure and creep behaviors were studied at different solution temperatures. • Creep life increased at first and thereafter decreased as solution temperature increased. • The continuous rod-like morphology of the M 23 C 6 carbide degraded the creep properties. • The improved creep properties were determined by the increase of Σ3 TBs and fine γ′. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of Fe–TiC metal matrix composite during metal deposition with laser and arc welding techniques is of technical and economic interest for hard surfacing of engineering components. Recent studies linked the resistance to abrasive wear with the size and morphology of TiC precipitates, which are strongly dependent on the deposition conditions and, more importantly, on the alloy chemistry. In this study, the effect of silicon and manganese on the TiC precipitates was explored and different processing conditions were assessed. The characterisation included optical and scanning electron microscopy, X-ray diffraction and microhardness testing. The results indicate that silicon and manganese can have a significant effect on TiC size and morphology. Therefore, the composition of the matrix alloy offers an effective pathway to modify the microstructure of in-situ precipitated Fe–TiC metal matrix composites. [Copyright &y& Elsevier]

It is well known that grain boundary cavitation at carbides is one of the detrimental damaging processes for the degradation of austenitic stainless steels that reduces the creep-fatigue life at high temperatures. In the case of the 316 and 304 austenitic stainless steels, it is found that grain boundary is considerably serrated with the modified heat treatments to the change of carbide morphology from triangular to planar shape. And it is found that the interfacial mismatch between the neighboring matrix and modified planar carbides has been reduced to have less incoherency than that between the neighboring matrix and triangular carbides, so that the creep-fatigue resistance has been remarkably increased. These results imply that the modified carbides, whose interface energy is lower, have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life. Therefore, it is suggested that the cavity nucleation factor is regarded as the material constant related with the carbide characteristics. [Copyright &y& Elsevier]

The crystal structures, morphologies, and compositions of carbides in a martensitic pipe steel of type X20CrMoV12.1 after long-term service at 550 °C have been carefully investigated using transmission electron microscopy (TEM) and dispersive x-ray spectrometry (EDS). Most of carbides are M23C6. The M23C6 particles in prior austenite grains and in martensite lath boundaries are extensively coarsened. Most of the finer carbides within the matrix are also identified as M23C6, and no other type of carbide was found except for some tiny plate-like V-rich carbides identified as MC. The V and O mass fractions in the M23C6 carbides have variable morphologies and locations, which might be due to their coarsening process. They are coarsening at different rates even after long-term exposure at elevated temperature. The formation of V-rich MC during the long-term service contributes to hardness maintenance and is good for microstructural stability. [ABSTRACT FROM AUTHOR]

Supersonic atmosphere plasma spraying (SAPS) can deposit Cr 3 C 2 -NiCr coatings in a very high efficiency to provide excellent anti-wear performance at high temperature. In the present work, the effect of post heat treatment on the microstructural evolution and the high-temperature wear performance (at 400 °C) of the Cr 3 C 2 -NiCr coatings was investigated. It is found that SAPS process facilitated the carbide dissolution/diffusion during particle flight while nano-sized carbides began to sufficiently precipitate from the supersaturated NiCr binder during post heat treatment. However, carbide decarburization could not be completely constrained and the volume fraction of carbide in the coating even thermally-treated at 750 °C was lower than that of original powders. The coating thermally-treated at 500 °C presented the highest hardness due to the precipitation strengthening of secondary carbides, which also induced the best wear-resistant property. Overall, the wear behavior of the coatings was correlated with the abrasive wear • SAPS process was effective in promoting carbide dissolution in the binder matrix. • Precipitation of secondary carbides during heat treatment improved coating hardness and high-temperature wear resistance. • Wear behavior of SAPS Cr 3 C 2 -NiCr coatings at 400 °C was featured of abrasive wear. [ABSTRACT FROM AUTHOR]

• AISI H13-TiC composite coatings were fabricated using a pulsed Nd: YAG laser. • Dissolution of TiC particles in the melt pool resulted in MC carbides precipitation. • Alteration in pulse laser variables changed the concentration of dissolved Ti and C. • Higher effective peak power density led to an increase in the Fe/Ti weight ratio. • Decreasing Fe/Ti weight ratio encouraged the formation of dendritic morphology. In this study, composite coatings were fabricated by preplacing a TiC layer on H13 tool steel and surface melting with a pulsed Nd: YAG laser. Since the morphology of hard phase particles is one of the determinants of the wear properties of composite coatings, the role of process variables on the shape and size of carbide precipitates was investigated. The transverse cross-section of the laser-scanned samples was studied by an optical microscope to evaluate the geometrical changes of alloyed areas. Scanning electron microscopy and X-ray energy dispersive spectroscopy were used to probe the microstructure and chemical composition of the coating layers. X-ray diffraction was used to identify the phases. The results showed that by the partial or total dissolution of TiC particles in the melt pool, TiC-type MC carbides precipitated as the primary phase. Alterations in pulse laser variables changed the geometry of the alloyed region and hence the concentration of dissolved Ti and C elements in the composite coating. Investigation of the effect of the laser variables in the form of "effective peak power density" (EPPD) revealed that increasing the EPPD led to an increase in the Fe/Ti weight ratio in the composite. As the Fe/Ti weight ratio increased, the shape of the MC precipitates changed gradually, from fully developed dendrites to petal, and polyhedral morphology. [ABSTRACT FROM AUTHOR]

The influence of carbide morphology on the deformation and fracture mechanisms of as-received and complete spheroidization 14Cr1MoR steel was investigated using an in situ scanning electron microscope (SEM) under tension testing. During spheroidization damage, the carbide morphology changed from the original lamellar cementite present in pearlite to granular M23C6 carbide, which was concentrated along the ferrite grain boundaries. The yield strength and tensile strength of 14Cr1MoR steel decreased with the increasing degree of spheroidization damage. In situ SEM observations revealed that the deformation and crack initiation started from the ferrite matrix in both as-received and completely spheroidization-damaged 14Cr1MoR steel samples. However, the extension of slip bands and crack propagation behavior of both samples were different during the in situ tensile process, which could be ascribed to the difference in carbide morphology. In the as-received 14Cr1MoR steel sample, hard and brittle lamellar pearlite resulted in high-strength ferrite/ pearlite boundaries, which inhibited the movement of slip bands. With further deformation, the concentration of stress at the crack tip resulted in the emergence and propagation of cracks along the ferrite/pearlite boundaries. In the case of the completely spheroidized 14Cr1MoR steel sample, slip bands bypassed the grain boundary carbide and continuously expanded into the neighboring ferrite grain. In addition, micro-voids and fractures of grain boundary carbides were observed due to the large stress concentration at the front of crack tip. Then, the micro-voids connected with the main crack to complete the crack propagation behavior. The morphological changes of carbides deteriorated the mechanical properties and altered the fracture behavior of 14Cr1MoR steel. It is worth noting that the fracture surface morphology of 14Cr1MoR steel changed from a combination of lamellar fracture and dimpled morphology to a completely dimples-dominated morphology after spheroidization. [ABSTRACT FROM AUTHOR]

A billet of hypoeutectic high-chromium white iron (19% Cr, 2.5% C) was spray formed using Gas-to-Metal Ratios (GMR) of 0.9, 1.0, and 1.1. Microstructural studies and dry sand rubber wheel abrasion tests were carried out, on the one hand, to compare between the spray formed and conventionally cast material and, on the other hand, to investigate the relationship between gas-to-metal-ratio, eutectic carbide morphology and abrasion resistance. The spray formed material was characterized by a considerably finer carbide morphology (max. ˜30 μm) than the conventionally cast material (max. 100-200 μm). The coarser carbide morphology is believed to be responsible for the superior abrasion resistance of the conventionally cast material. Although the carbide morphology of the spray formed material was only moderately influenced by the changes in the gas-to-metal-ratio, there was a clear improvement in the abrasion resistance with decreasing gas-to-metal-ratio. The improvement correlated with a decrease in the fraction of very fine (<1.5 μm) carbides, rather than with an increase in the mean carbide size. [ABSTRACT FROM AUTHOR]