Twin Grain Research Articles

Novel reconstruction approaches of austenitic annealing twin boundaries and grain boundaries of ultrafine grained prior austenite

Gaining access to the parent microstructural information is of great significance to explore transformation mechanism and mechanical properties. As a powerful route, existing automatic reconstruction techniques still have two unsolved issues for lath martensitic steels. The first one is to reconstruct annealing twin boundaries in prior austenite accurately, avoiding the distorted twin boundaries caused by orientation-shared variants on both sides. As for the second one, i.e., reconstruction of ultrafine grained prior austenite, no attempt has been succeeded, simply because the number of martensitic variants inside is insufficient for all current algorithms by now. In this paper, two novel approaches are proposed to overcome these difficulties respectively. For the first one, a three-step algorithm combined with parallel computing is developed to implement the basic reconstruction with much higher efficiency, then a physics-based method using phase field simulation is established to resolve the fake twinning morphology. The second one named as Bi-Adjacent-Block method aims at exploring morphologies (i.e., size and shape) of the ultrafine prior austenite grains (PAGs) but not intending to determine their orientations. To identify the PAG boundaries with higher accuracy, an approximate analytic determination of orientation relationship by using only two adjacent variants is developed for the first time.

HRPD and TEM Study of P/M 58Fe17Cr25Ni Austenitic Stainless Steel Synthesized by Spark Plasma Sintering

58Fe17Cr25Ni austenite stainless steel has been fabricated using metal powder through sintering with a spark plasma at temperatures of 900 and 950°C for 5 minutes. High purity Fe, Ni and Cr powders were used as materials for this steel. Before sintering, the powder was mixed in a milling equipment which was processed for 5 hours, then it is formed into a coin by pressing it under a load of 25 tons. High resolution powder neutron diffractometer was used for identifying the crystal structure in the 58Fe17Cr25Ni austenitic stainless steel. The sintering process at temperatures of 900C and 950°C generally forms microstructure having matrix of equiaxed austenite grains, with a crystal structure of face-centered cubic which included in the Fm3m space group. Some particles with high Cr content, a'-Cr, are distributed in all austenite grains. The austenite grains seen in the 58Fe17Cr25Niaustenitic stainless steel sintered at 900°C are twin grains. Dislocations, slip planes and bands are also existed in those grains. These defects are expected to decrease with increasing sintering temperatures up to 950° C. This change was followed by the appearance of air bubbles and sub-grains as the dominant sub-structures in the 58Fe17Cr25Ni austenitic stainless steel sintered at 950°C.

Improved hydrogen storage performance of Sm-Mg composites by adding nano-graphite

Sm5Mg41 + x wt% nano-graphite (NG) (x = 0, 2, 4, 8, 12) composites are synthesized via ball-milling. The influences of NG content on microstructure and hydrogen storage properties of the composites are researched systematically. The composites consist of Mg, Sm5Mg41, SmMg3, and NG. Nano scale Sm3H7 and MgH2 phases are observed after the hydrogen absorbing, and the newly formed Mg phase and the remaining Sm3H7 phase appear after hydrogen desorbing. NG is embedded in the surface of the composites in the form of nanosheets. Nanocrystalline Mg and some microscopic defects, including twin crystal, grain boundaries, and dislocations can be observed in the dehydrogenated sample. Such microscopic defects and nanocrystalline boundaries can reduce the total potential barrier needed to overcome during the hydrogen absorption/desorption reactions and thus the hydrogen storage kinetics of the alloy are improved. For the composites with x = 2, 4, 8 and 12, the activation energies of hydrogen desorption are 132.08, 128.06, 112.90, and 112.35 kJ/mol H2, respectively. The enthalpy changes for the hydrogen absorption are evaluated to be − 79.18, − 78.09, − 76.30, − 76.10 kJ/mol H2, indicating that the addition of NG had no obvious effect on the thermodynamic properties of the composites.

Microstructure evolution and grain refinement mechanism of rapidly solidified single-phase copper based alloys

• The maximum undercoolings were achieved respectively by using the deep undercooling technology. • The recalescence behavior and microstructure refinement were systematically studied. • The relationship between solute composition and solidification process was established. • High-angle grain boundaries and twin boundaries exist in the microstructure at high undercooling. The Cu65Ni35, Cu60Ni40 and Cu55Ni45 alloys were undercooled by fluxing method, and the rapid solidification structure with different undercoolings were also obtained. At the same time, the interface migration process during rapid solidification was photographed by high-speed photography, and the relationship between the morphological characteristics of solidification front and undercooling was analyzed. The microstructures of the three alloys were observed by metallographic microscope, and the microstructure characteristics and evolution law were systematically studied. It was found that two grain refinement events occurred in the low undercooling range and high undercooling range, respectively. The EBSD test of grain refined microstructures showed that the microstructure in the low undercooling range has a high proportion of low-angle grain boundaries and high strength textures. However, there were a large proportion of high-angle grain boundaries and a high proportion of twin grain boundaries and more randomly oriented grains in the microstructure in the high undercooling range. The TEM test of the Cu55Ni45 alloy with the maximum undercooling of 284 K showed that there were high-density dislocation networks and stacking faults in the grains. Finally, the evolution relationship between microstructure hardness and undercooling was systematically studied. It was found that the microhardness of the three alloys decreased sharply near the critical undercooling. Combined with EBSD, TEM and microhardness analysis, it was confirmed that the grain refinement under low undercooling was caused by dendrite remelting, while the grain refinement under high undercooling was caused by stress-induced recrystallization.

Significantly lowered coefficient of friction in copper alloy with a gradient nanograined-nanotwinned surface layer

Heterogeneous gradient nanostructure has been evidenced to significantly reduce the coefficient of friction and wear loss. However, the tribological performance and underlying microscopic mechanisms of gradient nanograined metals containing stable nanotwins with superior strength-ductility synergy are still unclear. In this work, an ultra-precision machining technique named single point diamond turning was developed to fabricate a stable gradient nanograined-nanotwinned layer on Cu-4.5%Al alloy (in which stacking fault energy was tailored through alloying of Al). The reciprocal dry-sliding tests under loads of 10 N and 35 N at room temperature were conducted on gradient nanograined-nanotwinned specimen and five Cu counterparts (uniformly refined grain sizes, nanotwins, and gradient nanograins). The gradient nanograined-nanotwinned specimen exhibits the unprecedented low steady-state coefficient of frictions (0.18–0.24), demonstrating further improvement in comparison with the gradient nanograined Cu (0.31–0.35). Moreover, scanning electron microscope, white light interferometer, and high-resolution transmission electron microscope observations were mainly employed to evaluate the microstructural evolutions of worn surfaces and subsurface layers. It reveals that the worn subsurface of stable gradient nanograined-nanotwinned specimen consists of grain refinement, slightly grain coarsening and dynamic recrystallization, and deformation layers along the depth direction, showing further effectively suppressed grain coarsening process relative to the gradient nanograined Cu. Accordingly, a twin boundary migration plus grain rotation-mediated grain coalescing process in the worn subsurface is elucidated to be responsible for such mechanical-structural stability of the gradient nanotwinned structure towards the superior tribological properties.

Influence of the loading rate of force on the formation of deformation twins in martensitic stainless steel under repetitive loading–unloading process

The effect of loading rate of force in repetitive high stress loading/unloading (RHSL) treatment on the formation of deformation twins in a martensite stainless steel was studied by SEM-EBSD and TEM. It is found that RHSL successfully generates a large number of twins at room temperature with low strain rate and small plastic deformation. The number fraction and area fraction of twin grains are monotonously increased with the loading rate. RHSL provide a continuously driving force that promotes the abundant generation of twins. Higher loading rate favors the more nucleation of stacking faults and twins and their intersections of multi-orientation.

Martensitic Transition and Superelasticity of Ordered Heat Treatment Ni-Mn-Ga-Fe Microwires

The preparation of Ni-Mn-Ga and Ni-Mn-Ga-Fe master alloy ingots and microwires was completed by high vacuum electric furnace melt melting furnace and melt drawing liquid forming equipment, and the lattice dislocations and defects formed inside the microwires during the preparation process were corrected by stepwise ordered heat treatment. The micro-structure and phase structure were characterized using a SEM field emission scanning electron microscopy and an XRD diffractometer combined with an EDS energy spectrum analyzer; the martensitic phase transformation process of the microwires was analyzed using a DSC differential scanning calorimeter; and the superelasticity of the microwires was tested by a Q800 dynamic mechanical analyzer. The results indicate that Fe doping can refine the grain, transform the phase structure from parent phase to single 7M martensite, reduce the number of martensitic variants, and increase the mobility of the twin grain boundary interface. The MT phase transition temperature (MS) is substantially increased in the martensite transition (MT) process by the increase of the number of free electrons in its lattice. During the superelasticity (SE) test, both microwires displayed superior recover-ability of SE curves, and the Fe doping curves showed similar characteristics of “linear superelasticity”, showing higher critical stress values and complete SE in the experiment. The critical stress satisfies the Clausius-Clapeyron equation and exhibits higher temperature sensitivity than Ni-Mn-Ga microwires.

Synergistic optimization of electrical-thermal properties of dual vacancy Bi1−x-yPbyCu1−xSeO by improving mobility and reducing lattice thermal conductivity

We fabricate Bi1−x-yPbyCu1−xSeO (x = 0, 0.03, 0.06, y = 0, 0.10) samples via 4 min-microwave synthesis combined with 5 min-spark plasma sintering. The phase composition, microstructure, valence, and electrical and thermal transport properties of the samples are investigated at 298–873 K. Pb doping provides impurity carriers and increases the concentration to 0.9–3.0 × 1020 cm-³ . Bi and Cu vacancy could provide a carrier transport channel to reduce carrier scattering probability, leading to improved mobility. Twin crystals, stacking faults, and grain boundary segregation are observed in Bi0.87Pb0.10Cu0.97SeO on scanning transmission electron microscopy. Bi and Cu vacancy increase the sample point defects in Pb-doped or undoped samples which results in a decrease in lattice thermal conductivity. The lattice thermal conductivity of Bi0.87Pb0.10Cu0.97SeO is decreased to an extremely low value of 0.13 Wm−1 K−1 and a maximum ZT value of 1.09 is achieved at 873 K.

Development of a new, fully automated system for electron backscatter diffraction (EBSD)-based large volume three-dimensional microstructure mapping using serial sectioning by mechanical polishing, and its application to the analysis of special boundaries in 316L stainless steel.

We report the development of a fully automatic large-volume 3D electron backscatter diffraction (EBSD) system (ELAVO 3D), consisting of a scanning electron microscope (ZEISS crossbeam XB 1540) with a dedicated sample holder, an adapted polishing automaton (Saphir X-change, QATM), a collaborative robotic arm (Universal Robots UR5), and several in-house built devices. The whole system is orchestrated by an in-house designed software, which is also able to track the process and report errors. Except for the case of error, the system runs without any user interference. For the measurement of removal thickness, the samples are featured with markers put on the perpendicular lateral surface, cut by plasma focused ion beam (PFIB) milling. The individual effects of both 1μm diamond suspension and oxide polishing suspension polishing were studied in detail. Coherent twin grain boundaries (GBs) were used as an internal standard to check the removal rates measured by the side markers. The two methods for Z-spacing measurements disagreed by about 10%, and the inaccurate calibration of the PFIB system was found to be the most probable reason for this discrepancy. The angular accuracy of the system was determined to be ∼2.5°, which can be significantly improved with more accurate Z-spacing measurements. When reconstructed grain boundary meshes are sufficiently smoothed, an angular resolution of ±4° is achieved. In a 3D EBSD dataset of a size of 587 × 476 × 72μm3, we focused on the investigation of coincidence site lattice ∑9 GBs. While bearing predominantly a pure tilt character, ∑9 GBs can be categorized into three groups based on correlative 3D morphologies and crystallography.

Influence of Powder Plasticity on Bonding Strength of Cold-Sprayed Copper Coating

When cold spraying is performed at a velocity equivalent to or greater than a specific material-dependent critical velocity, powders suffer intensive plastic deformation and localized heating of interacting surfaces. The thermomechanical reaction of the sprayed powder upon impacting the substrate material triggers thermally dependent metallurgical bonding and/or mechanical interlocking mechanisms. In this study, three Cu feedstocks, fabricated through electrolysis (EP), gas-assisted water atomization (WA), and inert gas atomization (GA), were characterized and annealed before cold spraying. The electron back-scattered diffraction technique was used to analyze the grain structure and plastic microstrain within the powders and coatings. The plastic microstrains that originally existed in the Cu powders were released after 30 min of annealing at 500 °C. The influence of plastic deformation behavior (associated with the grain structure and plastic microstrain of powder feedstocks) on the bonding strength of the cold-sprayed Cu coatings on AA6061 aluminum alloy substrates was examined. The results indicate that EP powder with an asymmetric dendrite morphology was not conducive to the intensive plastic deformation that may cause recrystallized twin grains to form after cold spraying. Furthermore, the homogeneous microstructure of the spherical Cu feedstocks, which may be induced by strain release as recrystallized twin grains and low-angle boundary grain growth through annealing, caused the cold-sprayed Cu coating to have high ductility and low hardness. The findings reveal the low strain hardening and residual stress in the cold-sprayed coating—characteristics regarded as providing key advantages for the bonding strength of the coating.

Effect of twin grain boundary on material thermal expansion

Based on first-principles phonon calculations within the framework of quasiharmonic approximation, we study the effect of twin grain boundary (TGB) on the thermal expansion of insulating materials. We select diamond-structure solids (C, Si, and Ge) and rutile $({\mathrm{SnO}}_{2})$ as representatives of the covalent and ionic bonding materials that are important systems commonly accompanied with TGB. We found distinct effects of TGB on thermal expansion in two types of materials. For diamond-structure solids, the thermal expansion of (111)-oriented twinning structure varies subtly from that of pristine material within the temperature range studied, which is primarily induced by the modification of vibrational phonon mode by the TGB effect. Distinctly, the thermal expansion of $\mathrm{SnO}_{2}$ twinnings increase substantially by comparison with the pristine case and depend strongly on the twin orientation. The (101) twinning shows much larger thermal expansion than the (301) twinning. Further analysis indicates the physical mechanism can be mainly attributed to the effect of rotational degree of freedom of the $\mathrm{SnO}_{6}$ octahedron motif and the stress induced by TGB. Our work reveals the physical mechanism underlying the distinct effect of TGB on thermal expansion caused by different chemical bonding, and meanwhile provides an insightful understanding of the relationship between specific structural features and thermal expansion in solid-phase materials.

Formation of contact and multiple cyclic cassiterite twins in SnO2-based ceramics co-doped with cobalt and niobium oxides.

Contact and multiple cyclic twins of cassiterite commonly form in SnO2-based ceramics when SnO2 is sintered with small additions of cobalt and niobium oxides (dual doping). In this work, it is shown that the formation of twins is a two-stage process that starts with epitaxial growth of SnO2 on CoNb2O6 and Co4Nb2O9 seeds (twin nucleation stage) and continues with the fast growth of (101) twin contacts (twin growth stage). Both secondary phases form below the temperature of enhanced densification and SnO2 grain growth; CoNb2O6 forms at ∼700°C and Co4Nb2O9 at ∼900°C. They are structurally related to the rutile-type cassiterite and can thus trigger oriented (epitaxial) growth (local recrystallization) of SnO2 domains in different orientations on a single seed particle. While oriented growth of cassiterite on columbite-type CoNb2O6 grains can only result in the formation of contact twins, the Co4Nb2O9 grains with a structure comparable with that of corundum represent suitable sites for the nucleation of contact and multiple cyclic twins with coplanar or alternating morphology. The twin nucleation stage is followed by fast densification accompanied by significant SnO2 grain growth above 1300°C. The twin nuclei coarsen to large twinned grains as a result of the preferential and fast growth of the low-energy (101) twin contacts. The solid-state diffusion processes during densification and SnO2 grain growth are controlled by the formation of point defects and result in the dissolution of the twin nuclei and the incorporation of Nb5+ and Co2+ ions into the SnO2 matrix in the form of a solid solution. In this process, the twin nuclei are erased and their role in the formation of twins is shown only by irregular segregation of Co and Nb to the twin boundaries and inside the cassiterite grains, and Co,Nb-enrichment in the cyclic twin cores.

High-Temperature Oxidation Behavior of Cr-Ni-Mo Hot-Work Die Steels.

The oxidation of 3Cr3Mo2NiW and 3CrNi3Mo steels was studied at 600 °C in air, and the test results suggest that the parabolic rate law fitted the oxidation kinetics of both steels. The microstructure, morphology, structure, and phase composition of the oxide film cross-sectional layers of the two Cr-Ni-Mo hot-work die steels were analyzed using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The influences of Cr, Ni, and Mo on the high-temperature oxidation resistance of the two Cr-Ni-Mo hot-work die steels are discussed, and the oxidation mechanism is summarized. Heat-treated samples were analyzed using electron backscattered diffraction (EBSD) to obtain inverse pole figures (IPFs) and average sample grain sizes, and the percentages of twin grain boundaries (TGBs) (θ = 60°) were also measured. After heat treatment, recrystallization was observed in both steels with a large portion of twin grain boundaries. After 10 h of oxidation, the dense chromium-rich oxide layer that formed in the inner oxide layer of 3Cr3Mo2NiW steel effectively prevented the continuation of oxidation. The inner oxide layer in 3CrNi3Mo steel formed an adhesion layer with a network structure composed mainly of Ni- and Cr-rich spinel oxide, without forming a barrier to prevent oxidation.

Effects of carbon addition on microstructure and mechanical properties of Fe50Mn30Co10Cr10 high-entropy alloy prepared by powder metallurgy

To improve the mechanical properties of Fe50Mn30Co10Cr10 high entropy alloy (HEA), a series of carbon-containing HEAs based on Fe50Mn30Co10Cr10 were successfully prepared by powder metallurgy. The effects of carbon content on microstructural evolution and mechanical properties of the as-sintered HEAs were investigated. The improved FCC phase stability and the decreased Σ3 twin grain boundary proportion as the increase of carbon content are mainly due to the increased stacking fault energy. As the carbon content increases, the phase structure of the as-sintered HEAs changes from FCC + HCP phases to FCC phase and then to FCC + M23C6 phases, and the deformation-induced martensitic transformation from FCC to HCP weaken gradually. The solid solubility of carbon in the as-sintered Fe50Mn30Co10Cr10 HEAs is below 2 at.%. A large number of carbides can be observed in the microstructure of the alloys at higher carbon content. The yield strength of the alloys increases approximately linearly with carbon content, while the uniform elongation first increases and then decreases. The (Fe50Mn30Co10Cr10)98C2 HEAs with nano-carbides and ultrafine manganese oxide exhibited a yield strength of 362 MPa, an ultimate tensile strength of 792 MPa, and uniform elongation of 36.7%, showing simultaneous improvement in strength and ductility compared with the carbon-free alloy. This is due to the joint contribution of multiple strengthening mechanisms in the carbon-containing HEA. Interstitial solid solution strengthening and grain boundary strengthening act as the dominant strengthening mechanism. Alloying with carbon element is a feasible method to enhance the mechanical properties of HEAs prepared by powder metallurgy.

Simulated migration behavior of metastable Σ3 (11 8 5) incoherent twin grain boundaries

Molecular dynamics simulations are used to examine the migration behavior of one incoherent twin, a Σ3 (11 8 5) / (8 11 5) grain boundary. The boundary is known to exhibit non-Arrhenius boundary migration that slows as temperature increases. This behavior is examined in 165 metastable structures of the same boundary and in a large simulation cell where smaller length scales can have less of an effect. The metastable boundaries show diverse migration behaviors from non-Arrhenius to Arrhenius, though the majority of them exhibit non-Arrhenius behavior. The large simulation cell sizes show no dependence on system size, eliminating concerns about the effect of facet nucleation on the migration in periodic simulation cells. However, facet structures play an important role in the migration of the metastable boundaries. Boundaries with larger facets typically migrate faster than those with smaller facets and with defects in the boundary structure.

Grain growth in pulse reverse electrodeposited copper foil: Contrasting effects of duty cycle during deposition and annealing

The present study reports the opposite effects of the duty cycle in a pulse reverse electrodeposited copper foil during electrodeposition and further annealing. With increasing duty cycles from 60 to 90 %, while the average grain size decreases from 8.5 ± 6 μm to 4 ± 2.7 μm, the fraction of twin boundaries and crystallite size increase continuously in the as-deposited conditions. After annealing at 1050 °C, the average grain size increases, and the fraction of coherent twin boundaries reduces with an increase in the duty cycle. The differences in the anodic period at different duty cycles regulate the twin probability and grain size during deposition, while the stored energy governs the twinning probability during annealing. Interestingly, after annealing for 6 h, significant fractions of interconnected twinned regions are visible in all Cu foils. These results show that it is possible to maintain a high fraction (>60 %) of twin boundaries in high-temperature annealed Cu foils.

Atomistic modeling of Σ3 twin grain boundary in alloy 800H

Grain boundary engineering (GBE) has become an important thermomechanical processing strategy to enhance the physical and mechanical properties of polycrystalline metals in microstructure design. Solute segregation at grain boundaries can alter the electronic and strain energy states of the lattice and can impact the mechanical behavior in materials such as dislocation activity and yield strength. The twin boundary is one special type of grain boundary and has been of particular interest because of its role in deformation processes. The present work investigates twin grain boundary segregation induced strengthening in alloy 800H at temperatures of 300 K and 1000 K using Molecular Dynamics and Monte Carlo simulations. The simulations predicted no segregation preference of solute atoms (Ni and Cr) at coherent grain boundaries, but a significant segregation tendency to incoherent grain boundaries at a higher temperature during the simulated time. Shockley partial dislocations were formed and associated with Cr clusters. Deformation twins were found to only nucleate at the incoherent grain boundary. This solute segregation at the incoherent grain boundary increases the stress required to activate such a dislocation nucleation process. These findings extend the current understanding of the yielding behavior in alloy 800H, and more importantly, shed light on using GBE strategies to produce high-performance polycrystalline metallic materials.

Tailoring hydrogen embrittlement resistance of pure Ni by grain boundary engineering

By using thermo-mechanical processing, 99.996 wt.% pure Ni with different grain boundary characteristics were fabricated (Sample #1, 700 ℃ × 10 h + cold rolling reduction 50%+ 650 ℃ × 2 h; Sample #2, 700 ℃ × 10 h + cold rolling reduction 50%+ 900 ℃ × 5 min). Hydrogen embrittlement sensitivity of the two samples was determined by using high-pressure hydrogen charging, low strain rate tensile test and SEM fractography. Compared with Sample #1, hydrogen embrittlement index of Sample #2 increased from 0.52 to 0.71. The effects of grain size, grain boundary type and grain boundary curviness on hydrogen embrittlement of pure Ni were discussed. The results indicate that: 1) special grain boundaries including twin grain boundaries may have a marginal effect on tailoring hydrogen embrittlement resistance in pure Ni; 2) increasing grain boundary curviness is an effective way to improve hydrogen embrittlement resistance of Ni.

Friction stir welding of CoCrNi medium-entropy alloy: Recrystallization behaviour and strengthening mechanism

Dynamic recrystallization (DRX), deformation-induced mechanical twins, and strengthening mechanism of CoCrNi equi-atomic medium-entropy alloy (MEA), welded by friction stir welding (FSW) at different welding speeds, were systematically investigated in this study. The results indicated that FSW led to grain refinement in the stir zones (SZs) with diameters fluctuating in the range of 2.1–9.6 μm. The hardness was improved from ∼154HV (base material, BM) to 238–263HV (SZ) by FSW. The yield strength and ultimate tensile strength of the optimal SZs were 601 MPa and 844 MPa, respectively, which were 260% and 134% higher than those of the as-received material, respectively. Analyses of DRX behaviour indicated that discontinuous DRX (DDRX), continuous DRX (CDRX), and geometric DRX (GDRX) were successively activated with increasing strain during FSW to facilitate grain refinement. The larger the grain size, the higher the fraction of mechanical twins. However, the thickness of the twins had a negative correlation with the grain size. Although a few HCP structures were formed on the twin boundaries, grain refinement and dislocation hardening mechanisms remained dominant in enhancing the mechanical properties of the SZs. The strength-ductility synergy by FSW, under low heat input conditions, was caused by the formation of thin mechanical twins in fine equiaxed grains. Thinner twins were more effective in transferring and homogenising plastic deformation, thereby contributing to the postponing of plastic instability and further promoting an excellent combination of strength and ductility. These findings confirm that FSW is a promising approach for strengthening the MEA for superior performance.

The Role of Grain Boundaries in the Corrosion Process of Fe Surface: Insights from ReaxFF Molecular Dynamic Simulations

Intergranular corrosion is the most common corrosion phenomenon in Fe-based alloys. To better understand the mechanism of intergranular corrosion, the influence of grain boundaries on Fe-H2O interfacial corrosion was studied using molecular dynamics simulation based on a new Fe-H2O reaction force field potential. It is found that the corrosion rate at the polycrystalline grain boundary is significantly faster than that of twin crystals and single crystals. By the analysis of stress, it can be found that the stress at the polycrystalline grain boundary and the sigma5 twin grain boundary decreases sharply during the corrosion process. We believe that the extreme stress released at the grain boundary will promote the dissolution of Fe atoms. The formation of vacancies on the Fe matrix surface will accelerate the diffusion of oxygen atoms. This leads to the occurrence of intergranular corrosion.