Steel Metal Research Articles

Investigation Effect of 4-Aminophenol as a Corrosion Inhibitor for Mild Steel in Sulfuric Acid Medium

A high number of organic materials have been studied as inhibitors for corrosion in different conditions. In this paper, the effect of organic chemical (4-Aminophenol) as an inhibitor for mild steel metal corrosion was investigated in presence of sulfuric acid at different temperatures. The study was carried out using three known methods in testing corrosion process, methods of weight loss, thermometric, and polarization. The obtained results showed that when the inhibitor concentration increases, the corrosion rate decreases, and hence, the inhibition efficiency increases. Moreover, when the surface coverage at a temperature of 313 °C with organic inhibitor increases, the corrosion rate decreases as noticed in the weight loss method. For the thermometer method, the inhibitor was examined by temperature. The inhibition efficiency increases, as well as in the anodic and cathodic polarization method, where it is observed that the anodic and cathodic curves are present to measure the corrosion current and corrosion potential. As the higher the concentration of the inhibitor, the lower the current and the corrosion voltage. The reason for the effectiveness of this inhibitor is the presence of amine and phenol organic molecules in its composition, which can form a film on the metal surface and prevent corrosion from taking place.

Anomalous lubrication behavior of metal-polymer tribo-pairs

In the present study, we determined the coefficient of friction (COF) values of lubricated moving metal-fixed polymer and lubricated moving polymer-fixed metal tribo-pairs. The metal of stainless steel (304) and the polymer of polytetrafluoroethylene (PTFE) lubricated with poly-alpha-olefin (PAO6) base oil, 32# hydraulic oil (32#HO) or 15# aviation hydraulic oil (15#AHO) were tested on a standard ball-on-three plates (BTP) test machine. The tribo-pairs exhibited markedly different lubrication behaviors. For instance, the COF of a 304-PTFE tribo-pair (0.008) comprising a moving 304 ball and three fixed PTFE plates was approximately 3.5 times lower than that of a comparable PTFE-304 tribo-pair with the same lubricants under the same working conditions. The anomalous lubrication behavior was ascribed to the interfacial slip simulated by COMSOL Multiphysics software package to demonstrate the experimental results. The results indicated that interfacial slip is a key property of the materials used in the mechanical structures to decrease friction and wear, and increase the service life of tribo-pairs used in applications such as artificial joint replacements and pressure vessel seals.

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

An experimental investigation of screw-based material extrusion 3D printing of metallic parts

With the introduction of additive manufacturing (AM) methods, processes with the capability of 3D printing of metal materials were noticed. In general, AM processes with the ability to 3D print metals are more complex and costly in terms of equipment than processes that 3D print other materials (polymers and ceramics). Therefore, the use of 3D printing devices with less complexity and cost, such as extrusion-based 3D printers, for metal printing has attracted the attention of researchers. In this research, an extrusion-based 3D printer, equipped with a direct granule extruder system, was used for 3D printing of the feedstock of the metal powder injection molding (MPIM) process (with 93.7 % by weight of 440 C stainless steel metal powder). The optimal parameters of printing including linear speed (10 mm/s), temperature at the beginning (140 ℃) and end of the barrel (180 ℃), chamber's temperature (60 ℃), and nozzle diameter (0.5 mm) were determined experimentally. The debinding and sintering process was performed on 3D-printed samples. The samples are brittle after the sintering process, in such a way that the failure of the samples occurs by applying a small amount of force to them. According to the scanning electron microscope (SEM) micrograph of the fracture cross-section of the sintered samples, the number of cavities and defects in the samples was negligible and the presence of residual carbon can be seen in the sintered samples. According to the results of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDAX), the oxidation of iron and chromium elements as well as the presence of residual carbon (7.8 %), are the main factors for the incomplete sintering of the 3D printed samples.

Spatial Layout Assessment of Urban Mining Pilot Bases in China Based on Multi-Source Data Collaboration

Rapid urbanization in China has led to an exponential increase in the stocks of metals used in cities. Exploring their amount and growth patterns is an important way to forecast future metal demand and identify the potential for urban mining. Here, we use a combination of bottom-up and GIS tools to estimate the amount of in-use stocks and scrap metal of steel, copper, and aluminum in 366 regions of mainland China from 2010 to 2020. We then downscaled the 2020 metal scrap volume based on a multi-source dataset of socioeconomic factors. Finally, the accessibility of the urban mining pilot base (UMPB) was calculated using the two-step floating catchment area method (2SFCA), and the spatial layout assessment analysis of the UMPB was conducted under the supply–demand balance perspective. The results showed that the total in-use stocks of steel, copper, and aluminum increased from an initial 3186 million tons to 5216 million tons, with a corresponding trend of continued growth in the amount of metal scrap. The high value of scrap metal in 2020 is concentrated in the Beijing–Tianjin–Hebei urban agglomeration, the Yangtze River Delta region, and the Chengdu–Chongqing metropolitan area. The accessibility results show that the road network distance-based accessibility covered a smaller area than the Euclidean distance-based accessibility, but when the UMPB service radius was set to 300 km, the road network distance-based accessibility could also cover most of the eastern part of China. The spatial evaluation results of UMPB show that for service radii of 200 km and 300 km, low-supply and high-demand areas account for 6.32 percent and 5.89 percent, respectively.

Исследование влияния температурного режима пожара на эффективность вспучивающегося огнезащитного покрытия, предназначенного для огнезащиты стальных конструкций

Introduction. The usage of intumescent coating (hereinafter referred to as IC) is justified by the development of a fire protection project, taking into account the data on its fire protection efficiency, estimated under the influence of standard temperature conditions, the usage of which can lead to overestimating the fire resistance margin in the project or underestimating the thermal impact on the steel building structures with IC fire protection in conditions of a real fire. Aims and purposes. The purpose of the study is to evaluate the effect of fire temperature conditions on the effectiveness of IC. To achieve this goal, the following tasks were carried out: a temperature mode of fire in a building under different fire loads by the example of a warehouse building was estimated; experiments to estimate the influence of different heat fluxes, reduced thickness of metal and IC thickness on its effectiveness by the full factor experiment of the type 2 were conducted. Methods. To mathematically simulate real temperature fires, the Fire Dynamics Simulator (FDS) software package, which implements a field (differential) mathematical model, was used. To study the effect of the obtained fire temperature regimes on the effectiveness of IC, experiments were carried out according to the plan of a complete factor experiment type 2. The test specimens were carbon steel metal plates with dimensions of 100 × 100 mm with reduced thickness of 3 and 4.5 mm and painted with 0.25 and 0.5 mm organic-based single-component IC. A radiant heat flux panel with a radiant heat flux density of 10 to 50 kW/m2 was used to assess the effects of heat flux. Results and discussion. In the course of numerical experiments in the FDS software package, it was found that the thermal impact on steel building structures during a fire can differ significantly from the standard temperature regime, both upwards and downwards. The results of the experiment showed that the heating time of the test samples had the greatest influence of the actors under consideration (the value of the heat flux, the reduced thickness of the metal, the thickness of IC) had the value of the heat flux, as the largest absolute value of the regression equation was obtained. Conclusion. The assumption of possible underestimation of the thermal effect under “standard” temperature conditions on the fire resistance of steel building structures with IC fire protection was confirmed by the tests.

Effect of Al or Ti addition on the ferrite formation in ultra-low oxygen weld metal of low carbon steel

Effect of Al or Ti addition on the ferrite formation in ultra-low oxygen (about a few tens ppm) weld metal of low carbon steels were investigated. A bead-on-plate welding experiments were performed with a Tungsten Inert Gas (TIG) welding system. The double nozzle was attached to the welding torch used, Ar was passed along the outer nozzle and He is added along the inner nozzle. Optical micrographs showed that primary ferrite appeared along prior austenite grain boundaries and that as the temperature is decreased ferrite side plates were grew into grain interior. Their formation positions were approached to the welding end as the decreasing Al and increasing Ti content. This change in ferrite formation position attributed on the ferrite formation temperature, which was assumed to increase as the decreasing Al and increasing Ti content. Energy dispersive X-ray spectroscopy analysis of inclusions showed that Al and Ti were mainly associated with 0, it was obvious that the inclusions in the steels were Al- and Ti- oxide inclusions. Al-oxide inclusions were not favourable acicular ferrite nucleation sites and the inclusions contributing to acicular ferrite formation were Ti-oxide ones. The number density of acicular ferrite was small. This indicated that acicular ferrite formation was suppressed because the number density of inclusions was low under the ultra-low oxygen welding condition.

Investigation of carbon steel corrosion rate in different acidic environments

This study focused on evaluating the rate of carbon steel corrosion in one molarity of HNO3 H2SO4 and HCl in various acidic conditions. The twenty-day exposure of carbon steel specimens to acidic conditions was investigated and followed by the evaluation of corrosion penetration rate and mils per year. The results showed that the 1 M HNO3 solution was the most damaging to carbon steel due to its oxidizing character. Among the tested acidic media HNO3 was the most harmful followed by H2SO4 and HCl. Carbon steel metal's corrosion behaviour was affected by acid medium strength and exposure duration. Dissolving of carbon steel increased with increasing corrosive media severity and exposure time. Concept of passive behaviour in metals has been proposed as the primary reason for this effect. The corrosion penetration rate values for carbon steel used in the present investigation followed the order of HNO3 > H2SO4 > HCl when exposed to the three acidic environments. The maximum corrosion penetration rate values for carbon steel metal subjected to HCl H2SO4 and HNO3 were determined to be 0.008952 (2nd day) 0.03095 (1st day) and 0.039373 (1st day) respectively. In addition corrosion penetration rate values steadily dropped throughout the final days of immersion eventually becoming essentially constant in all acidic media. As a result of the greater impact of all the acidic media used in this investigation corrosion pitting occur on carbon steel consistently. By intensifying the acid medium these effects were exacerbated.

Exact shell solutions for conical springs. II. Radial cylindric curb

Actual manuscript examines the disk springs with constant material thickness. The kinematic hypothesis is used for modelling. Motivating feature is the possibility to calculate the disk springs of with free gliding edges and the edges with the constrained radial movement. Variation formulations are used for derivation. The developed equations are suitable for springs made of isotropic materials, as spring steel and light metal alloys. The advantage of the methodology is the derivation of closed form solutions with restrictions on radial movement of inner and outer edges. The developed formulas are recommended for industrial calculations of free and restricted Belleville washers.

Modeling fatigue life and hydrogen embrittlement of bcc steel with unified mechanics theory

The fatigue life estimation of metals operating in hydrogen-rich environments such as hydrogen pipelines, hydrogen-burning internal combustion engines, etc. is important. Studies in the past 40 years have shown that the diffusion of hydrogen into steel and other metals causes various chemical reactions, hydrogen-material interactions, and microstructural changes. That leads to hydrogen embrittlement (HE) and other types of hydrogen damage mechanisms including hydrogen environmentally assisted cracking (HEAC). Hydrogen embrittlement mechanisms, such as hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) can have synergetic effects in steel depending on the hydrogen concentration level. At concentrations above and below the critical hydrogen concentration, HEDE and HELP dominate the embrittlement process, respectively. Different HE mechanisms result in distinctly different fracture modes, both ductile and fully brittle. The ultrasonic vibration fatigue life of bcc steel with a ferrite-pearlite microstructure pre-charged with hydrogen at different concentrations is studied. Modeling is based on the unified mechanics theory (UMT), which does not need any empirical dissipation/degradation potential function or an empirical void evolution function. However, the UMT does require analytical derivation of the thermodynamic fundamental equation of the material, which is used to calculate the thermodynamic state index (TSI) of the material. The UMT is ab-initio unification of the second law of thermodynamics and the universal laws of motion of Newton [1]. Dissipation/degradation evolution is governed by Boltzmann's second law of thermodynamics entropy formulation. The original contribution of this paper is the derivation of the thermodynamic fundamental equation of pre-hydrogen embrittled bcc steel subjected to ultrasonic very high cycle fatigue and the numerical simulations of fatigue life estimation using the proposed novel model. The synergetic interaction of hydrogen embrittlement mechanisms in steel and other metallic materials, i.e., HELP and HEDE at different hydrogen concentrations (HELP + HEDE model) is also studied, reviewed, and applied. The synergetic effects between ultrasonic vibration fatigue life and synergistically active hydrogen embrittlement mechanisms in low carbon bcc steel (S355J2+N, equivalent to ASTM A656), according to the HELP + HEDE model for HE, is modeled for the first time using UMT and also thoroughly discussed.

Preliminary investigation of Cr-coated F82H: Evolution of microstructure and mechanical properties at the F82H/Cr interface during solid-state diffusion bonding above Ac1 temperature

Solid-state diffusion bonding was employed to join F82H steel and pure Cr metal under high vacuum at various temperatures above Ac1 in the range 1114 to 1323 K for 60 min, and at 1323 K for 120 min. After successful bonding at all temperatures, the F82H/Cr interface and interdiffusion zone were characterised using SEM-EDS, TEM and EBSD analysis, with respect to diffusion behaviour, chemical composition and microstructure. A thin interface layer formed on the Cr side of the joint, which decreased in thickness with decreasing bonding temperature, and was rich in M23C6 with mixed columnar and particulate nature. The depth of Cr diffusion into F82H decreased with decreasing bonding temperature. At temperatures ≥1231 K a layer of ferrite grains formed in the F82H region adjacent to the interface, due to the combined stabilising effect of enhanced Cr concentration and depleted C. At the lowest bonding temperature of 1114 K, a lath martensite microstructure was retained throughout the F82H due to a significantly lower extent of Cr and C diffusion. The diffusion coefficient of Cr in F82H was determined at all temperatures examined, and the activation energy of Cr diffusion in F82H >Ac1 was approximated as 225 KJ mol−1. Finally, hardness testing of the interface and interdiffusion zone suggests the F82H properties were retained after bonding at the lowest temperature of 1114 K, however at higher temperatures the newly formed ferrite region was softer. Further research is required to understand the impact of the hard M23C6-rich interface layer on mechanical properties of the joint, and whether microstructural change can be minimised, or even eliminated, below the Ac1 temperature.

Preliminary assessment of the possibility to use large-diameter pipes of Х52 steel for transportation of pure gaseous hydrogen under pressure

To assess resistance to hydrogen embrittlement caused by the presence of hydrogen in the transported product, and, accordingly, suitability of pipes for hydrogen transport, the base metal of large-diameter pipes of X52 strength class manufactured by JSC “ChelPipe” (part of the PJSC “TMK” group of companies) was studied. The work included the study of pure gaseous hydrogen effect under pressure up to 10 MPa on change in mechanical characteristics of the base metal of large-diameter pipes (LDP) during preliminary hydrogen charging for various time periods in a stationary autoclave under pressure, and during simultaneous loading with a slow strain rate (SSRT) under expected operating conditions. Results of the X52 LDP metal study show that there is no significant impact on the effect of gaseous hydrogen under pressure for up to 144 hours on mechanical characteristics of the base metal determined by static uniaxial tension (decrease in ductile characteristics does not exceed 9 %). During SSRT at a rate of not more than 1·10–6 s–1 in pure gaseous hydrogen environment under a pressure of 10 MPa, the change in strength and ductile characteristics does not exceed 13 % in comparison with reference tests in nitrogen environment under the same pressure. The results obtained allow us to consider that the base metal of low-alloy pipe steel with ferrite-perlite microstructure of X52 strength class is sufficiently resistant to hydrogen embrittlement. Final confirmation of the possibility to use LDP made from steel under study will be the results of further qualification tests, including the study of the weld metal and heat-affected zone properties.

Experimental and analytical study on local heat transfer distribution between smooth flat plate and free surface impinging jet from a circular straight pipe nozzle

The present study describes the heat transfer characteristics of free surface single-phase circular liquid jet impinging on a thin smooth flat surface subjected to uniform heat flux. The experimental setup is developed to measure the local temperature of a thin stainless steel metal foil using the infrared thermography technique. The effects of nozzle diameter (d = 2.5 to 10.8 mm), nozzle to plate spacing (z/d = 2 to 10), and Reynolds number (Re = 5000 to 24,000) on the local Nusselt number (Nu) distributions are studied. The local Nu is maximum in the stagnation region, and it decreases in the downstream flow following the stagnation region. The nozzle with a larger diameter shows maximum Nu compared to other nozzles. For a given z/d of 2 and a Reynolds number of 15,000, a maximum increment of 67% in local Nu is observed for a 10.8 mm nozzle in comparison to a 2.5 mm nozzle. The local Nu in the viscous boundary layer is found to be a function of the Reynolds number, Prandtl number, dimensionless r/d, and Weber number. The Nu increases with an increase in Reynolds number, however, the effect of the nozzle to plate spacing is negligible. The off-stagnation peak is observed for the 10.8 mm nozzle in the region of 0≤r/d≤0.7. The existing correlations reported in the literature are not able to capture the measured local Nusselt number distribution. Therefore, in the present study, an effort has been made to propose semi-empirical correlations for local Nu in the stagnation and viscous boundary layer region which will incorporate the diameter effect of the nozzle. The proposed correlations are able to predict the local Nusselt number distribution within the maximum deviation of 20%. The comparison between the free surface and submerged jet has been made which suggests that the local Nu for the submerged jet is higher compared to the free surface jet.

"Corrosivity extents of Ogogoro (locally brewed gin) to aluminum and steel metals and human health implications "

"Corrosivity extents of Ogogoro (locally brewed gin) to aluminum and steel metals and human health implications "

PENGARUH VARIASI METAL TRANSFER TERHADAP KARAKTERISTIK SAMBUNGAN LAS PADA PROSES PENGELASAN GMAW DENGAN PELINDUNG GAS ARGON

This study aims to determine the variation of metal transfer on tensile strength, impact, hardness distribution, macrostructure, microstructure and chemical composition of low carbon steel metal by GMAW welding method. The material used in this study was AISI 1018 low carbon steel. The material was welded using the GMAW method. Variation of globular arc, spray arc and short arc welding. The tests carried out included tensile testing, impact testing, hardness testing, macro-structural observations, micro-structural observations and chemical composition. The test phase to determine tensile strength refers to ASTM E8/E8M-09 with specimen dimensions of 100 mm long, 10 mm wide and 5 mm thick, while for impact testing refers to ASTM E23-07a with dimensions of 55 mm long, 10 mm wide and 10 mm thick. 10 mm with a notch depth of 5 mm and photographic observations of macro, micro and chemical composition. The test results show that the maximum tensile strength with the globular arc welding method is 526.3 MPa and the yield stress is 377.3 MPa, which is greater than that of the low carbon steel parent metal, which is 454 MPa. The impact toughness value of the globular arc welding method is 3.58 J/mm2. Results The microstructure of the weld metal undergoes structural changes in all welding methods. The test results for the chemical composition of the Fe content in low carbon steel materials by welding were 98.78% to 97.76%.

Experimental Study on Tin Slag Polymer Concrete Strengthening under Compression with Metallic Material Confinement.

Studies on the external strengthening of tin slag polymer concrete by fibre-reinforced plastic confinement have provided strength enhancement of tin slag polymer concrete up to 128% with carbon fibre-reinforced plastic confinement. However, the effect of metallic material confinement has yet to be studied. This article presents the experimental finding on tin slag polymer concrete strengthening through metallic material confinement under compressive loads. Machined mild steel metal tube has been employed to strengthen tin slag polymer concrete core in partial and fully confinement prior to compression testing. Through this study, compressive strength of tin slag polymer concrete short column has been enhanced with the metal tube confinement application from 59.19 MPa (unconfined) to 95.86 MPa (partial metal confinement) and 131.84 (full metal confinement) representing 61.95% and 122.74% of strength enhancement percentage. Material behaviour analysis through stress versus strain curves has revealed that the strain softening curve is modified by metal tube confinement before a fracture occurs on both partial and full metal confinement samples compared to the control sample (unconfined). In addition, the failure modes have indicated that the high ductility of metallic confinement material has effectively confined tin slag polymer concrete from sudden fracture where the metal tube in partial confinement indicates ductile expansion while the metal tube in full confinement has shown ductile crushing. In general, it was concluded that metallic material confinement on tin slag polymer concrete under compressive load has resulted in providing strength enhancement and modified the failure mode of tin slag polymer concrete. Finally, further research is recommended, especially by initiating numerical analysis to facilitate parametric studies on tin slag polymer concrete for structural material design.

Parameter Optimization of Gas Metal Arc Welding Process for Welding Dissimilar Steels

Welding is a method of joining similar and dissimilar metals through the use of coalescence. GMAW is a semi-mechanized, fully-mechanized, or automatic process that is widely used in fabrication. GMAW is expected to evolve further to allow for better arc control, bead contour control, deposition control, and higher productivity. The goal of this study is to enhance welding process variables for dissimilar steel metal joints made of duplex stainless steel (DSS) to ASTM/UNS S32205 and erosional steel CORTEN-A to ASTM A242. Such a dissimilar metal joint finds use in the transportation sector, particularly in the construction of rail cars. The square butt joint between two 2 mm-thick sheets was investigated using the gas metal arc welding (GMAW) process with CO₂ as the shielding gas and flux-cored wire of grade 309L as the filler material. The L₉ Taguchi array was used to optimize the tensile strength of the resulting weld joint, which was the desired quality characteristic. GMAW process parameters such as voltage, wire feed rate, and welding speed are optimized at three levels. Using ANOVA, the effects of each factor have been studied. It was found that the ideal set of parameters exists and that the voltage is the most crucial factor. A confirmation test was performed to validate the results, and it was accompanied by a figure and tables.

Gas Metal Arc Welding Process Variables Enhancement for Welding Significantly different Steels

The goal of this study is to enhance welding process variables for dissimilar steel metal joints made of duplex stainless steel (DSS) to ASTM/UNS S32205 and erosional steel CORTEN-A to ASTM A242. Such a dissimilar metal joint finds use in the transportation sector, particularly in the construction of rail cars. The square butt joint between two 2mm thick sheets was investigated using the gas metal arc welding (GMAW) process with CO2 as the shielding gas and flux cored wire of grade 309L as the filler material. The L9 Taguchi array was used to optimize the tensile strength of the resulting weld joint, which was the desired quality characteristic. GMAW process parameters such as voltage, wire feed rate, and welding speed are optimized at three levels. Using ANOVA, the effects of each factor have been studied. It was found that the ideal set of parameters exists, and that the voltage is the most crucial factor. A confirmation test was performed to validate the results, and it was accompanied by a figure and tables.

Crashworthiness analysis of a composite guardrail under impact loading

Road safety barriers prevent cars from deviating from the roads. Guardrails as common roadside safety barriers protect cars from dangers alongside the roads, such as steep slopes and trees, and redirect traffic from road hazards. Conventional guardrails are generally made of metal or concrete. Although steel guardrails absorb a high amount of crash energy by deformation, these types of guardrails have short lifecycles of less than 15 years. Due to their unique properties, composite materials are potential candidates to use as guardrails. The present study considers the three types of guardrails (steel, composite, and fiber metal laminate (FML)), and the crash model is developed according to standards. LS-DYNA software is employed to simulate and conduct the crash test In the first stage, impact simulation is performed on a carbon/epoxy composite plate. In the next step, impact simulation is performed on a metal fiber multilayer (FML) plate with carbon fiber and aluminum metal. Then, the crash test on the steel guardrail is completely simulated. These three stages are performed to verify the proposed model. In the next stage, the crash test for a carbon/epoxy composite guardrail is simulated, and the effect of different parameters is investigated. Finally, a crash test on the FML guardrail with carbon fibers and steel metal is simulated. Two FML samples with [CE/Steel/CE] layups are considered. The absorbed energy, specific energy, and acceleration severity index (ASI) for all different guardrails are obtained and compared to determine the optimum guardrail regarding energy absorption, mass, and ASI parameters. Results reveal that sample FML-B guardrail is the best of the three guardrail types, with the highest specific energy absorption and lower ASI parameter.

Microstructure evolution and its effect on the stress rupture behavior of 9%Cr-CrMoV dissimilar welded joint

Taking the economic factor into account, 9 %Cr martensite heat-resistant steel is chosen to be joined with CrMoV steel by welding technique to utilize their potential at different temperatures. In the present study, the dependence of rupture time on the applied stress was determined and in accordance with the equation of lg(tr) = 7.224–0.014σ. All the stress rupture specimens were ruptured in the base metal of CrMoV steel (CrMoV-BM), indicating the high welding quality and the slight effect carbon migration on the stress rupture properties. The microstructure characterization revealed that the M23C6, M7C3 and MX type carbides were identified in the CrMoV-BM in the original state. These carbides were the typical precipitates existed in the heat resistant steel. Partially coarsened carbides and Mo-rich M6C phase were detected during the stress rupture test. The micro-voids tended to be initiated in the regions near these partially coarsened carbides and Mo-rich M6C ones along the grain boundaries. Subsequently, the macro-cracks formed via the micro-void convergence and eventually caused the fracture of the ruptured specimens.