MC-type Carbides Research Articles

Effect of welding thermal treatment on the microstructure and mechanical properties of nickel-based superalloy fabricated by selective laser melting

Strengthening the heat-affected zone in actual weld joint of Inconel 625 alloys was crucial for engineering applications in aerospace, petroleum, nuclear energy, and marine industries. In this study, Gleeble thermal simulations were employed to investigate the influence of welding heat on grain morphology, carbide evolution, and mechanical properties of Inconel 625 alloys manufactured by selective laser melting (SLM). Typical elongated columnar grains along the building direction and parallel columnar array with obvious layer boundaries along the scanning direction were observed in SLM-processed Inconel 625 alloys with hot isostatic processing treatment. After Gleeble thermal simulations, the prominent equiaxed grains appeared in the entire gauge region that was directly exposed to the simulated welding heat owing to the recrystallization process. Meanwhile, the size of equiaxed grains significantly increased with the increasing peak temperature. Particularly, only MC-type carbides were observed in the γ-Ni matrix before and after the thermal simulation owing to the fairly rapid heating (100 °C/s) and cooling (30 °C/s) process. Simulated welding heat produced a negative effect on the mechanical properties of the Inconel 625 alloys, especially for the peak temperature of 1350 °C. Then, the respective contributions of the four conventional strengthening mechanisms were successfully quantified for understanding the effect of the simulated peak temperature on the yield strength of the Inconel 625 alloys. Finally, the observations of microstructural evolution indicated that the cross-slip of dislocations was the dominant deformation mechanism to account for the large strain-hardening rate of the Inconel 625 alloys.

Improved Red Hardness and Toughness of Hot Work Die Steel through Tungsten Alloying

In order to elucidate the relationship between red hardness/toughness and tungsten content, strong carbide-forming element tungsten was added to a 5 wt.% Cr medium carbon steel (Cr5) in melting. After normalization and forging, the vacuum gas-quenched experimental steels were tempered at 560 and 600 °C for 10-40 h, respectively. Rockwell hardness and un-notched impact energy were evaluated. It was revealed that the precipitation phases play a critical role in the mechanical properties of the steels. The tungsten element effectively improved the red hardness of the steel by 6.3-15.8% when tempering at 600 °C for 10-40 h, while the corresponding impact toughness holds at the same level, about 250J, as Cr5 steel. Through observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), mesoscales carbides were found with a structure of (Fe, Cr, W, Mo, V)6C. It was deduced that tungsten element acts a positive role in inhibiting the coarseness of secondary M6C-type carbides and impeding the formation of M23C6 and M7C3, and thus enhances the thermal stability of Cr5W steel at elevated temperature. Furthermore, the tempering stability prediction model was constructed to predict the red hardness of tungsten-containing Cr5W steel.

Carbide precipitation and coarsening kinetics in low carbon and low alloy steel during quenching and subsequently tempering

As-quenched microstructure in a low carbon and low alloy steel has been examined by transmission electron microscopy and atom probe tomography. The coarsening kinetics of the cementite was investigated for the tempered steel. The results show that a number of nanosized auto-tempered transition‑iron-ε' carbide and cementite precipitate in the coarse lath martensite during quenching. The carbon concentrations of auto-tempered transition‑iron-carbide are typically around 10–15 at.%, lower than that for stoichiometric Fe2.4C or Fe2C transition ε carbide. Partitioning of Mn, Cr and Mo into the cementite occurs during tempering. The coarsening rate of the cementite is governed by volume diffusion of Mn, Cr and Mo, and Cr retards cementite coarsening more effectively than Mn and Mo. More stable M7C3 type carbide transforms from the cementite partially, and retains smaller size than the cementite during tempering with prolonged time.

Rupture behavior and fracture mode for Inconel 625–9% Cr steel dissimilar welded joints at high temperature

In the present study, the rupture behavior and fracture mode for the Inconel 625–9% Cr steel dissimilar welded joints are investigated. The results reveal that the relationship between the rupture time and stresses follows the formula: lg (t) = − 0.028 σ + 6.75, while the microhardness measurement shows that the specimens with applied stresses under 620 ℃ both fracture in the heat affected zone of 9% Cr steel (9Cr-HAZ). Therefore, the microstructure of the 9Cr-HAZ adjacent to the fracture is emphatically observed, and it is found that the tempered martensite is the typical microstructure in 9Cr-HAZ. Simultaneously, massive micro-voids can be detected in 9Cr-HAZ along the grain boundaries. In addition, the particles around the micro-voids are identified as Laves phases combining with M23C6-type carbides. Thus by consuming the solid solution strengthening elements, especially W and Cr, the precipitation of these second phase particles softens the matrix, which can cause the formation of micro-voids. Subsequently, the initiation and convergence of those dispersed voids eventually lead to the failure of the ruptured specimens.

Improved mechanical properties by nanosize tungsten-molybdenum carbides in tungsten containing hot work die steels

AISI H13 die steel with substitution of tungsten for vanadium (H13–W) was produced through vacuum induction melting and forging, followed by 1050°C-quenching and 600°C-tempering. Through 10–40 h of 600°C-tempering, H13–W exhibits superior red hardness as compared to H13 steel. The increments of hardness (4-6HRC) as well as yield strength were deducted to the precipitated M6C-type carbides with sizes ranging from 10 nm to 400 nm. Two classifications of carbides are identified. Type I of carbides has the nano size of 8–50 nm, and type II of undissolved primary carbides ((Fe1.34Mo1.62 Cr2.95W0.09)C) has the bigger size of 100–400 nm. The yield strength increments (Δσy) were modeled by a bivariate distribution of nano and undissolved precipitates. The calculated major strengthening effects from type I nano carbides in H13–W/H13 steels were close to the deduced values by Hall-Petch theory, they were 1053 MPa and 965.8 MPa, respectively. According to the calculation on equilibrium solubility of precipitations of MoC/Mo2C and WC/W2C, it was testified that MoC, Mo2C, WC and W2C were wholly dissolved into austenite at 1050 °C of quenching, followed by precipitating in large quantities in the form of nanosize carbides at 600oC-tempering.

Strength ranking for interfaces between a TiN hard coating and microstructural constituents of high speed steel determined by micromechanical testing

Knowledge about the adhesion of protective hard coatings on tool materials is of great importance to understand their failure mechanisms in metalworking. Until now, common techniques such as scratch and indentation tests are used to establish a qualitative ranking of a coating’s adhesion on various substrate materials. Nevertheless, there is a lack of quantitative measures to describe the strength of the interfaces between individual microstructural constituents of substrate-coating composites. The current work investigates the interfacial strength and thus the adhesion of TiN deposited as a hard coating on an MC-type carbide, an M6C-type carbide and on martensite being constituents of high speed steels. Tensile stresses were introduced at the interface between TiN and the individual microstructural constituents of a high speed steel via micromechanical testing of a novel MSC specimen within a scanning electron microscope. The tested MSC specimens were subsequently investigated in detail by scanning electron microscopy. Evaluation of the interface stress at fracture via finite element analysis yielded a ranking in interface strength and therefore coating adhesion in a sequence from high to low strength values from MC/TiN over M6C/TiN to martensite/TiN.

Influence of niobium microalloying on the thermal stability of medium-carbon carbide-free bainitic steel

This paper investigates the influence of niobium on the thermal stability of ultra-fine bainite microstructures and their mechanical properties by means of an isothermal transformation at 340 °C, followed by tempering in the range of 200–700 °C for two medium-carbon, carbide-free bainitic steels with and without 0.018 wt. % Nb. The results reveal that ultra-fine bainite microstructures, especially film-like retained austenite, is refined, and the average carbon content of retained austenite is also improved as a result of the addition of Nb element. Both of the bainitic steels in this paper exhibit good thermal stability at low temperatures (≤400 °C) and precipitation hardening arising from carbide precipitation following tempering at 500 °C. The precipitation strengthening compensates for the decrease in strength induced by the decrement in the dislocation density and coarsening of the bainitic ferrite plates during tempering process. M23C6- and MC-type carbides are precipitated in Nb-free and Nb steels, respectively, when the tempering temperature exceeds 400 °C. The further coarsening of the carbides and bainitic ferrite plates, and the decrement in the dislocation density in the latter, relate to the decrease in the mechanical properties for both of the tested bainitic steels following tempering at 500 and 600 °C. Compared to those in the bainitic steel without Nb, the larger size and superior thermal stability of MC-type carbides results in greater strength and elongation of the bainitic steel containing 0.018 wt. % of the Nb element, but does harm to its impact toughness after tempering at 700 °C.

Microstructural Evolution upon 10-wt% Mo Alloying and Laser Surface Melting of M2 High Speed Steels Hardfacings

The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10 wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite/austenite/martensite along with MC, M2C and M6C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbides from MC and rod like M2C to fibrous M2C and fishbone like M6C carbides. The LSM of Mo alloyed M2 HSS PTA deposits led to an overall decrease in the fraction of M6C carbides and fibrous M2C carbides accompanied by a decrease in hardness.

Performance of a Matrix Type High Speed Steel after Deep Cryogenic and Low Tempering Temperature

A matrix type high speed steel YXR3 designed for a combination of wear resistance and toughness is investigated for its mechanical properties after hardening by deep cryogenic treatment follow by tempering. The deep cryogenic quenching carried out at -200 °C for 36 hours and the single step tempering results in an obvious improvement in wear resistance while balancing the toughness, comparing with the conventional quenching followed by a double tempering treatment. The quantitative image analysis reveals little difference in the MC carbide size distribution between tempering at different temperatures. The synchrotron high energy XRD confirms the MC type carbide with some evolution in its orientation together with tempered martensite approaching the BCC structure at higher temperatures. In contrary to the conventional quenching and tempering, the lowest tempering temperature at 200 °C yields a moderate drop in hardness with increase in surface toughness proportionally while exhibiting exceptional wear resistance. Such thermal cycle can be recommended for the industry both for the practicality and improved tool life.

Evaluation of Microstructural Deterioration for a Directionally Solidified Ni-Based Superalloy by X-ray Computed Tomography

The evaluation of the microstructural deterioration was carried out by x-ray computed tomography for the first-stage blades, manufactured using a directionally solidified Ni-based superalloy (Ni-SA) retired from a land gas turbine, after service. The x-ray computed tomography was used to analyze the whole blade as well as, a segment of the top of blade with the purpose for obtaining results in a micrometer scale, which can be contrasted with the results of microstructural characterization. In order to evaluate the internal deterioration of the component, it was necessary to determine the in-service operation conditions of first-stage blades. Thus, the temperature distribution in the component during the start-up cycle was obtained, considering a transitory regime and using the conjugate heat transfer technique by means of Fluent ANSYS software. Besides, the mechanical stresses present in the component were calculated using finite element method implemented in ANSYS software. The main results of this work identified that the presence of cracking in the blade is associated with the occurrence of creep microcavities and coarsened particles of MC-type carbides, which showed debonding from the γ-matrix of the Ni-SA. The origin of the cracking was determined to occur in the cooling channels of the component.

Effects of forming temperature, soaking time and dwell time on the microstructure and mechanical properties of thixoformed nickel-based superalloy parts

Thixoforming has unique characteristics over the traditional casting and forging processes, but there is few research focusing on thixoforming of nickel-based superalloys. In this paper, nickel-based superalloy GH4037 parts were successfully formed by thixoforming with different parameters. The effects of forming temperature, soaking time and dwell time on the microstructure and mechanical properties of the formed parts were investigated. The results indicated that forming temperature and soaking time exerted a crucial role in microstructure evolution. With the increase of temperature and soaking time, the proportion of liquid phases in the microstructure increased. During thixoforming, liquid phases were squeezed from the middle region to the peripheral region, resulting in more liquid phases at the edge of the parts. MC-type carbides rich in Ti, V, W and Mo were observed in the liquid phases. When semi-solid billet was heated at 1380 °C for 30 min, the best mechanical properties including an ultimate tensile strength of 973 MPa, a yield strength of 634 MPa and an elongation of 45.6% were achieved. The dwell time had a slight effect on the microstructure and mechanical properties of the parts. The fracture surfaces of the tensile specimens exhibited mostly dimple surfaces and presented a transgranular ductile fracture mode.

M <sub>7</sub>C <sub>3</sub>: The Story of a Misunderstood Carbide

Since the discovery of the M7C3-type carbide in 1935, it has been the subject of many experimental and theoretical studies. Initially, the structure was thought of as being either trigonal or hexagonal, while later publications indicated that the structure was more likely to be orthorhombic. Even today, 8 decades after its discovery, many publications claim that M7C3 carbides are either hexagonal or orthorombic “beyond doubt”, while others, acknowledge the lack of agreement in the literature and try to resolve it using first principles calculations which rely on the atomic positions in the previously suggested structures. To date, no hard evidence was presented to support either claim in an indisputable manner. Using EBSD (electron backscattered diffraction), TEM (transmission electron microscopy) diffractions and high-resolution STEM (scanning transmission electron microscopy) imaging gathered from 8 zone-axis of the (Cr,Fe)7C3 phase formed in the as-cast AlCrFe2Ni2 high entropy alloy, we were able to determine that only the hexagonal structure is a viable option. Furthermore, we demonstrate the co-existence of two variants of the newly revealed atomic structure which we believe were mistakenly identified as stacking faults in previous studies.

Evaluation of Liquation Cracking Behavior and Susceptibility in Heat-Affected Zone of CM247LC Superalloy Welds for Turbine Blade Application

In this study, the weldability of the as-cast CM247LC superalloy for turbine blade applications was metallurgically evaluated in terms of its hot cracking behavior and susceptibility. For this purpose, a real blade was manufactured using a directional solidification casting process, and gas tungsten arc welding was performed at the tip and cavity of the upper blade. Hot cracking was confirmed in the heat-affected zone (HAZ) of gas tungsten arc welds, and the cracks were characterized as liquation cracks, since a cobble or dropletshaped crack surface consistent with a liquid film was clearly confirmed. Microstructural analysis of the cracking surface and thermodynamic calculations helped elucidate the metallurgical mechanisms of the liquation cracking. In other words, the cracking was attributed to liquation of the γ-γ’ eutectic colony and the constitutional liquation of the MC-type carbides: these phases existed in the as-cast microstructure. In particular, it was calculated that liquation of the γ-γ’ eutectic colony during welding occurs at least at 1488 K and that constitutional liquation of MC-type carbides begins at 1411 K, while the equilibrium solidus temperature of the CM247LC alloy is 1530 K. Finally, the liquation cracking susceptibility was quantitatively evaluated through a spot-Varestraint test, and it was confirmed for the first time that the higher susceptibility of as-cast samples can be suppressed by employing a pre-weld heat treatment such as solution treatment.

Carbon-alloyed Fe35Mn10Cr20Ni35 high entropy alloy synthesized by mechanical alloying plus spark plasma sintering

A non-equiatomic (Fe35Mn10Cr20Ni35)98.8C1.2 high entropy alloy (HEA) was synthesized by mechanical alloying plus spark plasma sintering. Microstructure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The mechanical behaviors were measured by Vickers hardness, nano-indentation and compression tests. After 75 h’ mechanical alloying, (Fe35Mn10Cr20Ni35)98.8C1.2 HEA powder with simple FCC structure was prepared. M7C3-type carbide particles with a size of about 100–200 nm are observed to precipitate from FCC-matrix during spark plasma sintering process. In (Fe35Mn10Cr20Ni35)98.8C1.2 HEA synthesized by mechanical alloying plus spark plasma sintering routine, the density of dislocations is much higher than that in Fe35Mn10Cr20Ni35 HEA prepared by arc-melting method, and the grain size is much smaller. Combined effects of dislocation hardening, fine grain strengthening and precipitation hardening of second phase particles make (Fe35Mn10Cr20Ni35)98.8C1.2 HEA possess much higher compression yield strength than Fe35Mn10Cr20Ni35 HEA prepared by arc-melting routine (1200 MPa–180 MPa), especially the former two effects. The formation of dislocation cells and twins during plastic deformation is thought to support to the high plasticity of (Fe35Mn10Cr20Ni35)98.8C1.2 HEA in our study.

Multiscale characterization of the 3D network structure of metal carbides in a Ni superalloy by synchrotron X-ray microtomography and ptychography

Synchrotron X-ray microtomography and ptychography were used to characterize the 3D network structure, morphology and distribution of metal carbides in an as-cast IN713LC Ni superalloy. MC typed carbides were found to distribute mainly on the grain boundary between the matrix γ and γ' phase. The differences in solidification cooling rate had a minor influence on the volume fraction of the MC type carbides, but significantly affected the carbide size, distribution and network morphology. Depending on the local composition of the remaining liquid phase and geometric constraints, the carbides can form either spherical or strip or network morphologies. The research demonstrated clearly the advantage and technical potential of using the two complementary tomography techniques synergistically to characterize non-destructively complex multiple-phase structures in three dimensional space with a spatial resolution of ~30 nm.

A Study of Microstructure and Mechanical Properties for the Autogenous Single-Pass Butt Weldment of a Ferritic/Martensitic Steel Using Gas Tungsten Arc Welding

A 12% Cr ferritic/martensitic steel, HT-9, has been used as a primary core material for nuclear reactors. The microstructure and mechanical properties of gas tungsten arc butt welded joints of HT-9 in as-welded, and as-tempered conditions have been explored. In as-welded condition, the fusion zone (FZ) contained a fresh martensite matrix with delta (δ)-ferrite. The δ-ferrite was rich in Cr and depleted in C compared with the matrix. The heat-affected zone (HAZ) could be divided into three areas as the distance from the fusion line increased: δ-ferrite/martensite duplex zone, fully recrystallized zone, and partly recrystallized zone. Prior austenitic grains did not coarsen in the δ-ferrite/martensite duplex zone due to the newly nucleated δ-ferrite grains and incompletely ferritizing (δ-ferrite) during the welding thermal cycle. The weldment microhardness distributed heterogeneously with values above 600 HV1.0 in the HAZ and FZ and 250 HV1.0 in the base metal (BM). Solute C in the matrix, induced by the dissolution of carbide during the welding process, dominated the microhardness variation. Low toughness was observed in the FZ with a quasi-cleavage fracture tested from − 80 to 20 °C. The tensile fracture occurred in the relatively soft BM tested from 20 to 600 °C. In as-tempered condition (760 °C for 1 h), M23C6-type carbides precipitated within the martensitic laths, the lath boundaries, and the δ-ferrite/martensite interfaces. Moreover, V, Cr, Mo-rich nitrides with very small size also precipitated in the δ-ferrite/martensite interface. The tempering treatment improved the homogenous distribution of weldment hardness significantly. Tensile fracture still occurred in the BM of the weldment specimens tested from 20 to 600 °C. The impact toughness improved significantly, but the ductile–brittle transaction temperature was − 12 °C which was higher than that of the normalized and tempered (N&T) BM. δ-ferrite was considered to be one of the major factors aggravating the impact toughness in the FZ.

Sintering Preparation of 15 wt% Cr Cast Iron as well as Its Mechanical Properties and Impact Abrasive Wear

15 wt% Cr sintered High Chromium Cast Iron (HCCI) with full density was successfully prepared by Super-solidus Liquid Phase Sintering (SPLS) technique, with water atomized 15 wt% Cr high chromium cast iron powder as initial materials. Its densification behavior and microstructure evolution in SPLS process and mechanical properties were investigated systematically. Additionally, the impact abrasive wear resistance under different impact energies were also analyzed and compared with another sintered HCCI with 20 wt% Cr. The results indicated that sintering temperature has a strong influence on the sintered alloy’s density, hardness, impact toughness and bending strength. The M7C3 type (M is Cr and Fe) carbides were obviously coarsened as temperature increased and their rod-shaped branches were fully developed at the same time, thereby resulting in carbide network formation in the matrix. The reasonable sintering temperature range was 1195–1205 °C, and the optimum mechanical properties had the hardness of 63.9 HRC, bending strength of 2112.65 MPa and impact toughness of 7.92 J/cm2. What is more important impact abrasive wear test results indicated 15 wt% Cr sintered HCCI’s wear resistance could be comparable to 20 wt% Cr sintered HCCI under impact energy 1~3 J/cm2, and it is more cost effective.

The Effect of Molybdenum on Precipitation Behaviour in Austenite of Strip-Cast Steels Containing Niobium

Two low-C steels microalloyed with niobium (Nb) were fabricated by simulated strip casting, one with molybdenum (Mo) and the other without Mo. Both steels were heat treated to simulate coiling at 900 °C to investigate the effect of Mo on the precipitation behaviour in austenite in low-C strip-cast Nb steels. The mechanical properties results show that during the isothermal holding at 900 °C the hardness of both steels increases and reaches a peak after 3000 s and then decreased after 10,000 s. Additionally, the hardness of the Mo-containing steel is higher than that of the Mo-free steel in all heat-treated conditions. Thermo-Calc predictions suggest that MC-type carbides exist in equilibrium at 900 °C, which are confirmed by transmission electron microscopy (TEM). TEM examination shows that precipitates are formed after 1000 s of isothermal holding in both steels and the size of the particles is refined by the addition of Mo. Energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) reveal that the carbides are enriched in Nb and N. The presence of Mo is also observed in the particles in the Nb-Mo steel during isothermal holding at 900 °C. The concentration of Mo in the precipitates decreases with increasing particle size and isothermal holding time. The precipitates in the Nb-Mo steel provide significant strengthening increments of up to 140 MPa, higher than that in the Nb steel, ~96 MPa. A thermodynamic rationale is given, which explains that the enrichment of Mo in the precipitates reduces the interfacial energy between precipitates and matrix. This is likely to lower the energy barrier for their nucleation and also reduce the coarsening rate, thus leading to finer precipitates during isothermal holding at 900 °C.

The Interface Microstructures and Mechanical Properties of Laser Additive Repaired Inconel 625 Alloy.

The microstructure and micro-mechanics around the repaired interface, and the tensile properties of laser additive repaired (LARed) Inconel 625 alloy were investigated. The results showed that the microstructure around the repaired interface was divided into three zones: the substrate zone (SZ), the heat-affected zone (HAZ), and the repaired zone (RZ). The microstructure of the SZ had a typical equiaxed crystal structure, displaying simultaneously precipitated block-shaped MC-type carbides (NbC, TiC), with bimodal sizes of approximately 10 μm and 0.5 μm and an irregularly shaped flocculent Laves phase. Recrystallization occurred in the HAZ, and led to significant grain growth; a portion of the second phase dissolved in the original grain boundaries. In the RZ, there was a columnar crystal structure, and the size increased with increasing deposition thickness. Moreover, the microstructure between the layer interface and layer interior was quite different, presenting an overlapping transition zone (OTZ), in which the dendritic structure coarsened and more Laves phase were precipitated, compared to in the layer interior. The hardness and tensile properties of the LARed samples were equivalent to those of the wrought substrate, which indicates that laser additive repairing (LAR) is a reliable repair solution for damaged and mis-machined components comprising Inconel 625 alloy.

Effect of withdrawal rate on precipitation characteristics of MC-type carbides in a nickel-based directionally solidified superalloy with high Re content

The precipitation characteristics of MC-type carbides during directional solidification of a rhenium-containing nickel-based superalloy were investigated at different withdrawal rates ranging from 50 to 200 μm/s. The results indicate that the carbides are located in the interdendrite, which includes the intergranular and intragranular regions. With increasing in withdrawal rates, the area of intergranular region decreases and the area of intragranular region increases. At lower withdrawal rate of 50 μm/s, the carbides are mainly located on the grain boundaries. However, an increase in the withdrawal rate promotes carbide from the intergranular region to the intragranular region, this is attributed to a rise in the withdrawal rate, which decreases the area of intergranular region and increases the area of intragranular region. When the withdrawal rates increase from 50 to 200 μm/s, the total number of carbides in the intergranular and intragranular regions increases. The morphologies of the carbides in the intergranular region are mostly blocky, sheet-like, rod-like and coarse Chinese script-shaped after a deeply-etched treatment, whereas the carbides in the intragranular region are primarily sheet-like, rod-like, and fine Chinese script-shaped. Further, it is suggested that rhenium is not the forming element of MC-type carbide in the superalloy with rhenium.