Grain Boundary Embrittlement Research Articles

Electronic origin of grain boundary segregation of Al, Si, P, and S in bcc-Fe: combined analysis of ab initio local energy and crystal orbital Hamilton population

In steel, P and S cause serious grain boundary (GB) embrittlement, which is associated with high segregation energies. To investigate the origins of such high segregation energies of P and S, we applied the combination of ab initio local energy analysis and crystal orbital Hamiltonian population (COHP) analysis for the GB segregation of Al, Si, P, and S in bcc-Fe, which can provide local energetic and bonding views of segregation behavior of each solute, associated with the replacement between solute–Fe and Fe–Fe bonding at GB and bulk sites. The local energy analysis revealed that GB segregation of such solutes is mainly caused by the difference between local energy changes of Fe atoms adjacent to a solute atom in the GB and bulk sites, and that the local energy change of each Fe atom depends on the solute–Fe interatomic distance with a unique functional form for each solute species. The COHP analysis showed that such distance dependency of the Fe-atom local energy change is caused by that of solute–Fe bonding interactions, relative to the Fe–Fe ones, governed by the valence atomic-orbital characters of each solute species. P and S have smaller extents of atomic orbitals and larger numbers of valence electrons; thus, they greatly lower the local energies of Fe atoms at interatomic distances shorter than the bulk first-neighbor one, and they greatly increase those of Fe atoms at longer interatomic distances around the bulk second-neighbor one. Thus, high segregation energies of P and S occur at GB sites with short first-neighbor distances and reduced coordination numbers within the bulk second-neighbor distance. The GB embrittlement by P and S was also discussed by this local-bonding viewpoint. The combination of local energy and COHP analyses can provide novel insights into the behavior of solute elements in various materials.

Segregation and embrittlement of gold grain boundaries

Grain boundary (GB) segregation of solutes can significantly alter material properties, the effects of which have first been observed more than two hundred years ago. After an introduction that shortly summarizes the historic development of the study of segregation, this work conducts an investigation on the segregation tendencies of 27 alloying elements to an Au GB and a surface with first principles calculations, semi-empirical modelling, and a phenomenological model of segregation. The effect of alloying elements on GB cohesion are evaluated and both detrimental (Bi, Cl, As, K) and beneficial elements (Al and the 3d transition metals) for alloying are identified. By comparing to experimental results from over two centuries, the used methodology and the obtained results are validated. The main origin of the GB cohesion effect can be revealed, i.e. the size mismatch between alloying elements and Au.

Atomistic investigation of hydrogen induced decohesion of Ni grain boundaries

The embrittlement of metallic materials by hydrogen (H) segregation is widely observed, but not understood well on an atomic scale. In the present study, an atomistic investigation of H embrittlement of various grain boundaries (GBs) has been performed by mapping H segregation energy of trapping sites and examining the effect of H segregation on the decohesion of GBs. The simulation results show that under the equilibrium concentration of H atoms typical of embrittlement in Ni, in conjunction with local H diffusion process, the maximum reduction of tensile strength and fracture energy is 6.60% and 15.75% for Σ5 (210) ⟨100⟩ and Σ17 (530) ⟨100⟩ GBs, respectively. Inspired by experimental observations of the dislocation structures beneath intergranular failure features, further calculations reveal that the embrittling effect of H atoms in metallic materials can be largely facilitated by the boundary disruption and local stress state concentrated on the GB through the plasticity process. The findings directly provide a picture of H embrittlement arising from the cooperative action of H-induced plasticity and GB decohesion.

The influence of alloying on Zn liquid metal embrittlement in steels

In this study we investigate Zn liquid metal embrittlement at Fe grain boundaries (GBs) by employing ab initio density functional theory (DFT) simulations. We consider three different GBs and two common alloying elements in steels (Si and Al) and evaluate how the interplay of the elements affects Zn enrichment and embrittlement of the GBs. Our simulations show that Zn has stronger tendency to enrich at both GBs and surfaces than Al and Si. By increasing the amount of Al and Si in the bulk, Zn can be reduced at both GBs and surfaces. This is quantified for a large temperature range by the newly introduced replacement potency, which shows that compared to Al, Si has a larger potency to decrease the amount of Zn at GBs and surfaces. Regarding GB embrittlement, our results demonstrate that Si a small positive, Al a small negative, and Zn a strong negative effect on GB cohesion. In combination with Zn both Al and Si are able to somewhat reduce the detrimental effect of Zn.

Effect of the Segregation of Embrittling Impurities on the Local Strength of Grain Boundaries in a Martensitic Steel

The finite element method and the results of delayed fracture tests of Charpy specimens are used to determine the local strength of grain boundaries in 18Kh2N4VA steel at various contents of phosphorus, antimony, and tin impurities. The embrittlement of grain boundaries is attributed to the adsorption enrichment of grain boundaries in impurities in initial austenite, which leads to weakening of the intergranular cohesion. Phosphorus is found to have the highest susceptibility to intergranular segregation: during the same heat treatment, its grain-boundary concentration is higher than that in steel with antimony or tin. However, the segregation of antimony is more dangerous than the segregation of phosphorus, since, at its lower intergranular concentration, the local strength of grains of quenched steel decreases as in the case of phosphorus segregation.

Fatigue crack growth in operated gas pipeline steels

Regularities of fatigue crack growth for pipeline steels of different strength are presented, and the changes in fatigue behavior of these steels after long term operation are analyzed. Threshold values of stress intensity factor range are lower for operated steels comparing to the corresponding values for as received ones. During the testing in the simulated soil solution NS4, a barely noticeable tendency to increase the threshold values of SIF was traced. It was explained by the appearance of intergranular fracture elements on the backgrownd of the typical flat fatigue relief already in the near-threshold region of fatigue crack growth curves in the soil solution. A higher relief of intergranular facets provided favorable conditions for occurrence of crack closure effect.Fatigue testing was performed using steel specimens after in-laboratory and in-service degradation, and it was shown that results for both degraded steels are very close to each other proving the validity of the method of in-laboratory degradation. A new methodic approach to fatigue testing of pipe steels is presented which allows simulating working conditions of gas pipelines, namely the hydrogen diffusion through the pipe wall to its external surface, and estimating its possible effect on SCC. It consists in evaluation of the influence of hydrogen reached the crack tip only due to its diffusion, on the crack growth. It is found that hydrogen absorbed by metal during the test providing such conditions, causes a leap of crack growth rate in the Paris region of the fatigue crack growth curve of the tested 17H1S steel. Intergranular mechanism of fracture detected on the specimen fracture surface is suggested as a clear evidence of embrittlement of grain boundaries as a result of its hydrogenation.

Microstructural evolution and high-temperature strength of a γ(f.c.c.)/γ’(L12) Co–Al–W–Ti–B superalloy

We characterized the microstructural features and mechanical performance of a model Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) alloy consisting of γ(L12)-precipitates in a γ(f.c.c.)-matrix. Scanning electron microscopy (SEM) was used to follow the isothermal aging of the microstructure at 900 and 1000 °C for 256 h, and 950 °C for 1000 h. The compositions of the γ'(L12)-precipitates and γ(f.c.c.)-matrix were evaluated by atom-probe tomography (APT) for solution-treated and air-cooled conditions, as well as in specimens aged at 950 °C for 16 and 100 h. Boron was shown to partition preferentially to the γ'(L12)-precipitates, and profiles taken across the γ(f.c.c.)-matrix channels in both aged specimens revealed confined segregation of Al at one of the two γ(f.c.c.)/γ′(L12) heterophase interfaces. After aging at 950 °C for 16 h, Co-5.6Al-5.8W-6.6Ti-0.12B (at.%) exhibited anomalous flow-strength behavior in the range 625–900 °C with a peak yield stress of 822 MPa between 800 and 825 °C. Compressive creep tests performed at 850 °C demonstrated a creep strength comparable to archival literature results for Co–9Al–9W-0.12B (at.%), despite a smaller γ′(L12)-volume fraction and lack of strengthening borides along the grain boundaries (GBs). The activation energy for creep in the temperature range 800–900 °C was 606 kJ mol−1. The post-creep microstructure consists of rafted γ′(L12)-precipitates perpendicular to the compression axis, consistent with the positive γ(f.c.c.)/γ'(L12) lattice parameter misfit character of this class of alloys. Creep failure could occur due to GB embrittlement caused by deleterious Ti-rich (L21 or B2) and D019 phases formed at the GBs during creep.

Effects of titanium on grain boundary strength in molybdenum laser weld bead and formation and strengthening mechanisms of brazing layer

Molybdenum has tremendous application potential in the nuclear power field, but its application is limited by the grain-boundary embrittlement of fusion-welded joints made of it. In this study, titanium was selected as an alloying element to reduce brittleness of laser weld beads in molybdenum “cladding-end plug” socket joints. Brazing was also performed to enhance the joint strength. Joints with the same strength as base material and a hydraulic bursting pressure of 60 MPa were produced using a combination of the two methods. The analysis indicates the following. After being added to the weld bead, titanium was able to combine with the free oxygen, forming TiO2 and reducing the MoO2 content on grain boundary surface. Oxygen and MoO2 are both the main causes of the embrittlement of molybdenum grain boundaries. In addition, by taking advantage of the high melting point and thermal conductivity of molybdenum, a titanium foil pre-placed between the tube and rod in the socket joint was melted, forming metallurgical bonding, which further improved the bearing capacity of the joint. These results could facilitate application of molybdenum in nuclear power field and also provide a new approach for improving the property of socket joints made of refractory materials.

First-principles study on the grain boundary embrittlement of bcc-Fe by Mn segregation

Developing steels with high strength and ductility is needed in order to improve the mechanical reliability and environmental performance of engineering products. The addition of Mn is a key technology for developing next-generation high-strength steels. However, the addition of Mn leads to a serious side effect, grain boundary (GB) embrittlement, which decreases the mechanical toughness of steels. Understanding the mechanism of GB embrittlement due to Mn is an essential process for improving the toughness of steels containing Mn. In this work, in order to reveal the fundamental mechanism of GB embrittlement by Mn, the effect of Mn on the cleavage fracture of bcc-Fe GBs, especially the influence of the difference in the magnetic coupling state between Mn and Fe, is investigated using uniaxial tensile simulations of the bcc-Fe $\mathrm{\ensuremath{\Sigma}}3(111)$ GB with and without Mn segregation using the first-principles density functional theory (DFT). The uniaxial tensile simulations demonstrate that Mn decreases the cleavage-fracture energy of the GB. In particular, the ferromagnetically coupled Mn substantially decreases the cleavage-fracture energy of the GB, promoting cleavage fracture. When ferromagnetically coupled Mn is present in the bcc-Fe GBs, the electrons contributing to the bonds between Mn and the surrounding Fe atoms easily localize to the Mn atom with increasing stress, and the bonding between Mn and the surrounding Fe atoms rapidly weakens, leading to a cleavage fracture of the GBs at a lower stress and strain. This unusual behavior is derived from the stability of the nonbonding Mn as a result of its half-filled d shell. These results show that the local magnetic state in GBs is one of the factors determining the macroscopic mechanical properties of steels containing Mn.

Influence of hydrogen on the propagation of intergranular corrosion defects in 2024 aluminium alloy

To study the influence of hydrogen on the intergranular corrosion mechanism of a 2024 aluminium alloy, samples were hydrogen precharged by cathodic polarisation and then exposed to a NaCl solution. EBSD analyses and SEM observations showed that hydrogen increased the number of corroded interfaces and led to the embrittlement of low-angle grain boundaries which were not susceptible to corrosion without hydrogen precharging. The increase of the reactivity of the 2024 aluminium alloy in the presence of hydrogen gave a new insight into the intergranular corrosion mechanism: corrosion-induced hydrogen promoted the intergranular corrosion propagation and partially controlled the corrosion defect morphology.

Atomistic understanding of helium behaviors at grain boundaries in vanadium

Using first-principles calculations, we systematically investigated the interaction of He (helium) with high-angle grain boundaries (GBs) in vanadium alloy. Three representative grain boundaries were examined: Σ3(1 2 1) GB with a compact structure, Σ3(1 1 1) and Σ5(0 1 2) GBs with open structures. Our results reveal that Σ3(1 2 1) GB has higher resistance to He segregation compared with the other GBs, since the segregation energy of He at Σ3(1 2 1) is high and He atoms are hardly trapped. All three GBs can decrease the He diffusivity along GB compared with bulk diffusion in vanadium and provide obstacles for He migration between the GB cavities. For the effect of He on the theoretical tensile strength of GBs, the cohesive strength of V GBs is weaken significantly, especially for Σ3(1 1 1) and Σ5(0 1 2) GBs, which results from that He can deplete considerably the charge density of GB region and weaken the interlayer bonding strength of GBs. It is worth noting that the low content of He (when one atom segregates at GBs) decrease slightly the cohesive strength of Σ3(1 2 1) GB, indicating that Σ3(1 2 1) exhibits better resistance to He-induced GB embrittlement compared with the other GBs. The physical mechanisms involved in He behaviors in the three distinct GBs are discussed in detail.

Role of disordered bipolar complexions on the sulfur embrittlement of nickel general grain boundaries

Minor impurities can cause catastrophic fracture of normally ductile metals. Here, a classic example is represented by the sulfur embrittlement of nickel, whose atomic-level mechanism has puzzled researchers for nearly a century. In this study, coupled aberration-corrected electron microscopy and semi-grand-canonical-ensemble atomistic simulation reveal, unexpectedly, the universal formation of amorphous-like and bilayer-like facets at the same general grain boundaries. Challenging the traditional view, the orientation of the lower-Miller-index grain surface, instead of the misorientation, dictates the interfacial structure. We also find partial bipolar structural orders in both amorphous-like and bilayer-like complexions (a.k.a. thermodynamically two-dimensional interfacial phases), which cause brittle intergranular fracture. Such bipolar, yet largely disordered, complexions can exist in and affect the properties of various other materials. Beyond the embrittlement mechanism, this study provides deeper insight to better understand abnormal grain growth in sulfur-doped Ni, and generally enriches our fundamental understanding of performance-limiting and more disordered interfaces.

Effect of Aging Isothermal Time on the Microstructure and Room-Temperature Impact Toughness of Fe–24.8Mn–7.3Al–1.2C Austenitic Steel with κ-Carbides Precipitation

The microstructure and impact toughness of the as-cast Fe–24.8Mn–7.3Al–1.2C austenitic steel after solution treatment and subsequent aging treatment were investigated in the present work. Research on the κ-carbides precipitation behavior was carried out by transmission electron microscope. The results show that nano-sized coherent κ-carbides were obtained in the as-solutionized steel after aging treatment, which produced precipitation hardening. After being aging treated at 550 °C for 1 h, the steel with regular hexagonal grain structure exhibited a good combination of yield strength (~ 574 MPa) and room-temperature impact toughness (~ 168 J). In the present steel, the typical cube-on-cube orientation relationship between austenite and κ-carbides was observed. However, due to the long aging isothermal time and high C content, the coarse intergranular κ′-carbide was formed and grew along the austenite grain boundary, which caused this orientation relationship to be destroyed and a dramatical increase of the coherency strain energy at grain boundary. Furthermore, serious embrittlement of grain boundaries caused that cleavage cracks trend to propagate along the grain boundaries. Accordingly, the room-temperature impact toughness decreased sharply. After aging isothermal time prolonging to 13 h, the Charpy V-notch impact toughness was only ~ 5 J and fracture mode turned to fully brittle fracture accompanied with flat facets, shear cracks and well-developed secondary crack.

Effect of thermal exposure time on tellurium-induced embrittlement of Ni–16Mo–7Cr–4Fe alloy

The embrittlement of nickel-based structural alloys by fission-produced tellurium (Te) is a major challenge for molten salt reactors (MSR). In this study, the effects of thermal exposure time on tellurium diffusion in a candidate MSR structural alloy (Ni–16Mo–7Cr–4Fe) and the consequent mechanical property degradation of the alloy were investigated through surrogate diffusion experiments at 700 °C. The results show that some tellurium reacted with the alloy to form tellurides on the surface, while some tellurium diffused into the alloy along grain boundaries. Ni3Te2 and CrTe were the most stable reaction products at the tested temperature, and the formation of CrTe on the surface induced the Cr depletion at grain boundaries of the alloy. The diffusion depth of Te increased gradually with thermal exposure time, and the diffusion rate kept stable within the test duration of up to 3000 h. The Te diffusion in the alloy caused the embrittlement of grain boundaries, inducing crack formation and strength degradation in tensile test at room temperature.

Grain Boundary Segregation of Substitutional Solutes/Impurities and Grain Boundary Decohesion in BCC Fe

The segregation of certain impurities to grain boundaries (GBs) which induced by neutron irradiation in Reactor Pressure Vessel (RPV) steels may have adverse effects upon their mechanical properties. In this work, ten symmetrical <110> and <001> tilt GBs in BCC Fe were created based on Coincident Site Lattice method, the GBs segregation embrittling potency was simulated by adding phosphorus, copper, nickel, and manganese to the boundaries and free surface (FS) using molecular static method. We have addressed both high- and low-angle tilt grain boundaries. Systematic Molecular Statics simulations were performed employing recent Embedded Atom Method (EAM) potentials. We show that P will strongly bind to GBs and FS; P and Cu have a detrimental effect on the GB cohesion, and segregation of these two elements will lead to GB embrittlement.

Hydrogen embrittlement of grain boundaries in nickel: an atomistic study

The chemomechanical degradation of metals by hydrogen is widely observed, but not clearly understood at the atomic scale. Here we report an atomistic study of hydrogen embrittlement of grain boundaries in nickel. All the possible interstitial hydrogen sites at a given grain boundary are identified by a powerful geometrical approach of division of grain boundary via polyhedral packing units of atoms. Hydrogen segregation energies are calculated at these interstitial sites to feed into the Rice–Wang thermodynamic theory of interfacial embrittlement. The hydrogen embrittlement effects are quantitatively evaluated in terms of the reduction of work of separation for hydrogen-segregated grain boundaries. We study both the fast and slow separation limits corresponding to grain boundary fracture at fixed hydrogen concentration and fixed hydrogen chemical potential, respectively. We further analyze the influences of local electron densities on hydrogen adsorption energies, thereby gaining insights into the physical limits of hydrogen embrittlement of grain boundaries.

The effect of alloying elements on the ductility of Al-Mg-Si alloys

Experiments were conducted to document the combined effect of different alloying elements on the microstructure and associated stress-strain behavior of extruded Al-Mg-Si alloys, with a special emphasis on the ductility to fracture characteristics. Four alloys with different concentrations and relative amounts of Mg, Si, Fe, Cu, and Mn were selected for examination. In order to obtain an accurate description of the strength-ductility relationship, tensile testing was performed with a laser extensometer, and scanning (SEM) and transmission microscope (TEM) studies were carried out to correlate the microstructure and fracture characteristics with the stress-strain behavior. Excess-Si (Mg/Si<1.73) was found to have a detrimental effect on the ductility of Al-Mg-Si alloys without the presence of additional alloying elements, leading to fracture occurring partly intergranularly. This was linked to the segregation of free Si at grain boundaries, forming coarse Si-particles, and the formation of Mg2Si particles during solution heat treatment. Adding Fe and Cu improved the ductility and strength, which could be attributed to a lower solvus temperature and increased formation of primary particles, resulting in less free Si for embrittlement of grain boundaries. The highest ductility was found by introducing Mn, which in addition to tie up free Si to second-phase particles, suppressed recrystallization by forming dispersoids. The most desirable combination of tensile strength and ductility was found in an excess-Mg alloy (Mg/Si>1.73) with additions of both Mn and Cu.

Atomistic study of hydrogen embrittlement of grain boundaries in nickel: I. Fracture

Hydrogen ingress into a metal is a persistent source of embrittlement. Fracture surfaces are often intergranular, suggesting favorable cleave crack growth along grain boundaries (GBs) as one driver for embrittlement. Here, atomistic simulations are used to investigate the effects of segregated hydrogen on the behavior of cracks along various symmetric tilt grain boundaries in fcc Nickel. An atomistic potential for Ni–H is first recalibrated against new quantum level computations of the energy of H in specific sites within the NiΣ5(120)⟨100⟩ GB. The binding energy of H atoms to various atomic sites in the NiΣ3(111) (twin), NiΣ5(120)⟨100⟩, NiΣ99(557)⟨110⟩, and NiΣ9(221)⟨110⟩ GBs, and to various surfaces created by separating these GBs into two possible fracture surfaces, are computed and used to determine equilibrium H concentrations at bulk H concentrations typical of embrittlement in Ni. Mode I fracture behavior is then studied, examining the influence of H in altering the competition between dislocation emission (crack blunting; “ductile” behavior) and cleavage fracture (“brittle” behavior) for intergranular cracks. Simulation results are compared with theoretical predictions (Griffith theory for cleavage; Rice theory for emission) using the computed surface energies. The deformation behavior at the GBs is, however, generally complex and not as simple as cleavage or emission at a sharp crack tip, which is not unexpected due to the complexity of the GB structures. In cases predicted to emit dislocations from the crack tip, the presence of H atoms reduces the critical load for emission of the dislocations and no cleavage is found. In the cases predicted to cleave, the presence of H atoms reduces the cleavage stress intensity and makes cleavage easier, including NiΣ9(221)⟨110⟩ which emits dislocations in the absence of H. Aside from the one unusual NiΣ9(221)⟨110⟩ case, no tendency is found for H to cause a ductile-to-brittle transformation for cracks along GBs in Ni, either according to theory or simulation for initial equilibrium H segregation and with no, or limited, H diffusion near the newly-created fracture surfaces. The NiΣ3(111) twin boundary does not absorb H at all, suggesting that embrittlement is more difficult in materials with higher fraction of such twin boundaries, as found experimentally. Experimental observations of cleavage-like failure are thus presumably caused by mechanisms involving H diffusion or dynamic crack growth.

Thermal expansions and mechanical properties of electrodeposited Fe–Ni alloys in the Invar composition range

Electrodeposited Invar Fe–Ni alloys with 36 to 40 mass% Ni were prepared from plating baths containing saccharin as a stress reducer and containing various Fe2+ concentrations. The Invar Fe–Ni alloys contained of small amount of S (∼0.02 mass%). The coefficients of thermal expansion (CTEs) of the as-deposited Invar Fe–Ni alloys were approximately 9 to 11ppm/°C and were larger than those of pyrometallurgically produced Invar alloys. When the alloys were heat-treated at 400 to 500°C, their CTEs drastically decreased to approximately 5ppm/°C. Furthermore, upon heat treatment at 600°C, the CTEs reached approximately 2 to 4ppm/°C depending on alloy composition; these CTEs are comparable with those of pyrometallurgically produced alloys. The as-deposited Invar Fe–Ni alloys were mainly composed of metastable bcc phases, resulting in larger CTEs. When the alloys were annealed at 400°C or above, the equilibrium fcc phases became the predominant phases, accompanied by a drastic decrease of the CTEs. The bcc-to-fcc transformation led to a decrease of the CTEs and to thermal contractions. Upon the heat treatment, an S (sulfide) at bcc grain boundaries segregated not as a thin film but as a granular sulfide form at primary bcc grain boundaries in the electrodeposited Invar alloys. Upon heat treatment at 500°C or above, bcc grain eliminated accompanied by fcc grain growth and the granular sulfide agglutinated further. Consequently, the agglutinating granular sulfide was entrapped in the matrix grains or grain-boundary triple-points of transformed fcc grains. In addition, it is considered that these two-type morphologies of the sulfide, as a thin film at grain boundaries or as a precipitate, will be determined by grain growth form during an annealing. Ductile behavior of the electrodeposited Invar Fe–Ni alloys was confirmed, irrespective of whether the alloys were heat-treated. Upon heat treatment at 400 to 500°C, the Invar Fe–Ni alloys exhibited high strength with good ductility, consistent with their low CTE. After the heat treatment, no severe embrittlement of the electrodeposited Invar alloys was observed despite the codeposition of S because the S existed as a granular sulfide, thereby preventing grain-boundary embrittlement.

Effects of alloying on the behavior of B and S at Σ5 (2 1 0) grain boundary in γ-Fe

To get the atomic scale understanding of impurities induced intergranular embrittlement or enhancement and the control of these effects on austenitic stainless steels, behavior of impurities B and S at γ-Fe grain boundary (GB) and effects of alloying elements (Cr, Ni, Mn, Co, Mo) additions on the cohesive properties of the γ-Fe GB doped by impurities are investigated by performing density functional theory (DFT) calculations. The results showed that, as the GB enhancer and embrittler respectively, impurities B and S tend to stay at the interstitial sites of γ-Fe GB, while alloying elements also can segregate at the GB studied. The presence of all the alloying elements considered can inhibit B GB segregation to some extent due to the higher segregation energies and can impair the enhancement effect of B on GB cohesion. However, these elements almost have no impact on GB segregation and embrittlement effect of S, except for Ni, Mn and Mo:Ni and Mo inhibit and improve S GB segregation, respectively; Mn and Mo strongly enhance and reduce S-induced GB embrittlement, respectively. Moreover, the remedial effect of (Cr+Ni), (Cr+Mn) on S-induced GB embrittlement is also discussed. Additional atomic structure and total valence charge density analysis demonstrated and explained our conclusions.