Brittle Fracture Characteristics Research Articles

Study on the influence of primary peak temperature on the microstructure and impact properties of heat affected zone of a 1000 MPa grade hydropower steel

ABSTRACT The microstructure of various zones in the heat-affected zone (HAZ) of 1000 MPa grade ultra-high-strength steel were investigated by welding thermal simulation. The results showed that the grain sizes were smallest at 950°C, when it was at the fine grain section in HAZ. The continuous reduction in grain size was due to the recovery and recrystallization. Samples subjected to thermal cycles at lower than 950°C exhibited high impact absorption energy of more than 100 J, with distinct fibrous zones and shear lips on the fracture surfaces, indicative of high impact toughness. However, the impact toughness of samples from the CGHAZ, which underwent thermal cycles at higher than 1100°C, decreased significantly to about 10 J, with the fracture surfaces showing macroscopic brittle fracture features and covered entirely by cleavage planes. Microstructural analysis revealed that coarse grains and brittle martensite were the primary causes of embrittlement in the CGHAZ.

Role of stable‐structural yarns and fabrics on the tensile and bending performance of carbon fiber resin composites

AbstractThe component yarns and fabrics effected the formability and stability of preforms, and finally determined the performance of corresponding composites. In this research, four typical fabric structures of carbon fiber resin composites (CFRC) were introduced to conduct the comparative investigation. The stability of component yarns in natural state and in fabrics have been discussed at mesoscopic scale, and the main methods to improve the structural stability of preforms were proposed. Composites with and without stable‐structural fibers and fabrics were manufactured by the modified curing process, and the yarn cross‐sections in specimens were analyzed. The tensile and bending performance of these composite specimens was comparatively conducted to discuss the influence of stable preforms on the elastic properties. The fracture mode and mechanism of specimens were illustrated in meso‐scale. The results depicted that yarns and fabrics with stable‐structural cross‐section could ensure a high fiber volume fraction, reducing the curvature of load‐bearing yarns, and effectively reduce the yarn curvature along bearing direction. The high interfacial bonding strength of composites with stable geometrical fabrics exhibited the excellent in‐plane mechanical properties, and presented the obvious brittle fracture characteristics when the fibers fully exert their load‐bearing capacity.Highlights Stable‐structural fibers result in the prominent performance of composites. Performance of composites with stable preforms show the low dispersion. Stable cross‐section of component yarns can enhance the stability of preforms. Low curvature yarns lead to brittle fracture characteristics of composites.

Dissimilar unbeveled aluminum to steel butt joint achieved by laser-arc hybrid welding-brazing

In this study, unbeveled butt joints of 2 mm thick steel and aluminum plates were welded using a laser-arc hybrid process. The influence of welding speed and wire feed speed on joint weld formation, microstructures, and mechanical properties were investigated. The results indicate that using a laser-arc hybrid heat source enables good weld formation of steel/aluminum dissimilar metals without groove preparation, even under high welding speed conditions. The steel side interface formed Fe₂(Al,Si)₅ near the steel and Fe(Al,Si)₃ near the aluminum. As the welding heat input decreased, the thickness of the intermetallic compounds gradually reduced. With an increase in welding speed or wire feed speed, the tensile strength of the joint first increased and then decreased, reaching a maximum of 104.47 MPa. Cracks propagated rapidly along the intermetallic compound region, resulting in brittle fracture characteristics. The three-point bending test showed a maximum longitudinal bending angle of 53.82° and a maximum transverse bending angle of 36.54°.

Radiation and thermal embrittlement of RPV steels: the links of embrittlement mechanisms, fracture modes and microcrack nucleation and propagation properties. Part 1. Strategy, program and methods of experimental and numerical studies

Further development of local approach models is considered from viewpoint of links of local brittle fracture properties with embrittlement mechanisms and fracture modes for RPV steels. Strategy and program of experimental and numerical investigations have been developed that allows one to find how various embrittlement mechanisms and fracture modes are connected with the conditions of nucleation and propagation of microcracks resulting in brittle fracture of RPV steels. The experimental and numerical investigations are performed for 2Cr-Ni-Mo-V steel and A533 steel used for RPVs of WWER and PWR types. RPV steels are studied in the following states: (1) initial (as-produced); (2) thermally embrittled by a hardening mechanism; (3) thermally embrittled by a non-hardening mechanism; 4) irradiated. Experimental studies include testing specimens of different geometry (smooth and notched round bars, and cracked compact tension specimens), which allows us to obtain characteristics of brittle fracture under various stress triaxialities. Numerical studies performed with the probabilistic brittle fracture model Prometey aim to obtain the brittle fracture properties on micro- and macroscales for all the investigated states of the materials.Part 1 of the paper presents information concerning the investigated materials, the used procedures and methods. Part 2 gives the test results of smooth round bars of the investigated materials in various states and the stress-strain curves determined over wide temperature range. The experimental results for various specimens from the investigated steels in various states are represented and compared with the results predicted with the Prometey model in Part 3.

Mechanical characterization of Al2219-SiC metal matrix composites

The present work conducted an experimental examination to assess the tensile behaviour and microstructural characteristics of Al2219 metal alloy reinforced with 4 and 8 wt. % of SiC composites. The investigation employed the liquid metallurgical method to fabricate composites of the Al2219 alloy including SiC particles at weight percentages of 4 and 8. This work employed supplementary methods, including scanning electron microscopy (SEM), to determine the microstructural characteristics. An investigation of the mechanical characteristics of Al2219 alloy with SiC reinforced composites is conducted in accordance with ASTM Standards. Furthermore, the incorporation of silicon carbide particles into aluminium 2219 demonstrates remarkable characteristics in the field of composite materials, therefore augmenting its potential for a broad spectrum of uses. Enhancements in hardness and tensile strengths of the composites were achieved by combining different materials. The fractured surfaces of the Al2219-SiC composites displayed both brittle and ductile fracture characteristics, as indicated by their tensile test results.

Effect of annealing temperature on properties and second phase characteristics of 443 stainless steel hot-rolled sheets

Commercial 0.31 wt.% Ti 443 ferritic stainless steel (FSS) hot rolled plate was selected as experiment object. Microstructures and state of the second phase of steels annealed at different temperatures from 880 to 1080 °C were researched. The tensile and impact properties were tested, the microstructure was characterized, and the fracture morphology was observed. The results indicated that annealing temperature had a significant impact on the properties and second phase characteristics of hot-rolled 443 FSS plates containing titanium. The annealed microstructure of steel exhibited a ferrite structure with bcc crystal structure. As the annealing temperature increased, both strength and elongation decreased the trends hardness and impact value showed decreased at first, then increased and decreased at last. The fracture morphology gradually transitions from ductile fracture to brittle fracture characteristics. The fracture morphology gradually transformed from ductile fracture to brittle fracture characteristics. After annealing at 980 °C, the grain recrystallization was relatively complete with uniform size and mostly presented equiaxed grains. The (110) diffraction peak were weaken. Resorption of the second phase particle caused matrix lattice distortion and induced dislocation entanglement and blockage. The second phase particles determined by SEM-EDS were TiN and TiCN, which weakened the solid solution strengthening and increased the dispersion strengthening of the steels.

Progressive Failure of Water-Resistant Stratum in Karst Tunnel Construction Using an Improved Meshfree Method Considering Fluid–Solid Interaction

An improved meshfree method that considers cracking, contact behaviour and fluid–solid interaction (FSI) was developed and employed to shed light on the progressive failure of the water-resistant stratum and inrush process in a karst tunnel construction. Hydraulic fracturing tests considering different scenarios and inrush events of the field-scale Jigongling karst tunnel in three scenarios verify the feasibility of the improved meshfree method. The results indicate that the brittle fracture characteristics of the rock mass are captured accurately without grid re-meshing by improving the kernel function of the meshfree method. The complex contact behaviour of rock along the fracture surface during inrush is correctly captured through the introduction of Newton’s law-based block contact algorithms. FSI processing during inrush is accurately modelled by an improved two-phase adaptive adjacent method considering the discontinuous particles without coupling other solvers and additional artificial boundaries, which improves computational efficiency. Furthermore, the improved meshfree method simultaneously captures the fast inrush and rock failure in the Jigongling karst tunnel under varying thicknesses and strengths of water-resistant rocks and sizes of karst caves. As the thickness and strength of water-resistant rock increase, the possibility of an inrush disaster in the tunnel decreases, and a drop in the water level and an increase in the maximum flow velocity have significant delayed effects during the local inrush stage.

Influence of accelerated aging on mechanical properties and aging behavior of glass fiber reinforced pipe

In this work, the accelerated aging test of GFRP in two thermal environments was conducted. The accelerated aging test was conducted at a constant temperature of 95°C for periods of 3000h to analyze and study the aging behaviors and mechanism under two environments. Resin defects caused by aging were found in the SEM images, and degradation of the fiber/resin interface was observed. Both the hoop tensile test and uniaxial compression test showed brittle fracture characteristics, and the strength of hydrothermal aging specimens decreased more significantly. Due to matrix degradation, uniaxial compression fracture after hydrothermal aging was observed that the resin exhibited poor adhesion. The decrease in the hardness of the outer resin layer was attributed to the development of the degree of molecular chain breakage. ATR-FTIR results showed that the accelerated aging process is accompanied by changes in the concentration of functional groups. The change in C-H intensity was attributed to the post-curing phenomenon. Accelerated aging resulted in the formation of carboxylic acids or esters and the introduction of hydroxyl groups. Thermogravimetric tests showed that accelerated aging did not change the thermal decomposition temperature of epoxy resins, but caused a decrease in resin content.

High-temperature tensile rupture property of (Nb,W) co-alloying TiAl-based alloys

In order to explore whether (Nb,W) co-alloying TiAl-based alloys with relatively higher W addition have better high-temperature tensile rupture property, Ti-44Al-4Nb-1 W-0.1B alloy is designed and prepared. Ti-44Al-8Nb-0.1B alloy and Ti-44Al-7.2Nb-0.2 W-0.1B alloy are also prepared for comparative study. The rupture property testing is carried out at 800 °C and different tensile stresses. The property data, macro/microstructure evolution, fracture surface, W content, crack failure behaviors are studied. The results show that the (Nb,W) co-alloying alloys have better rupture property than the pure Nb alloying alloy. For the (Nb,W) co-alloying alloys, the higher W contained Ti-44Al-4Nb-1 W-0.1B alloy has the better property under lower tensile stress, and the lower W contained Ti-44Al-7.2Nb-0.2 W-0.1B alloy has the better property under higher tensile stress. The relationships of rupture life t and stress σ for the three alloys are given. All the three alloys have a coupling fracture mode of ductile fracture and brittle fracture. The ductile fracture exhibits the typical dimple characteristics. The brittle fracture exhibits the typical trans-granular cleavage, river-like pattern and trans-lamella fracture characteristics. The higher the stress, the more brittle fracture characteristics there are. After rupture property testing, the (α2 + γ) lamella colony sizes of the three alloys all decrease, indicating that DRX and grain boundary slip occur not only along (α2 + γ) lamella colony boundary, but also inside it. The colony boundary regions have the stress concentration, where the B2 phase produces the better buffering and coordination, and as well as the dislocation tangles, DRX and grain boundary slip can be found by EBSD and TEM. EPMA results show that the more W added in the alloy, the more W content is in the (α2 + γ) lamella matrix, which is beneficial for the rupture property. However, more W addition will also lead to the formation of more B2 phase in the initial as-cast microstructure. So that, under higher tensile stress, when the stress intensity factor K is higher, the crack failure is more likely to occur.

Study on Thermal Cycling Reliability of Epoxy-Enhanced SAC305 Solder Joint.

In this work, epoxy was added into commercial Sn-3.0Ag-0.5Cu (SAC305) solder paste to enhance the thermal cycling reliability of the joint. The microstructure and fracture surface were observed using a scanning electron microscope/energy dispersive spectrometer (SEM/EDS), and a shear test was performed on the thermally cycled joint samples. The results indicated that during the thermal cycling test, the epoxy protective layer on the surface of the epoxy-enhanced SAC305 solder joint could significantly alleviate the thermal stress caused by coefficients of thermal expansion (CTE) mismatch, resulting in fewer structural defects. The interfacial compound of the original SAC305 solder joints gradually coarsened due to the accelerated atomic diffusion, but epoxy-enhanced SAC305 solder joints demonstrated a thinner interfacial layer and a smaller IMC grain size. Due to the reduced stress concentration and the additional mechanical support provided by the cured epoxy layer, epoxy-enhanced SAC305 solder joints displayed superior shear performance compared to the original joint during the thermal cycling test. After 1000 thermal cycles, Cu-Sn IMC regions were observed on the fracture surfaces of the original SAC305 solder joint, exhibiting brittle fracture characteristics. However, the fracture of the SAC305 solder joint with 8 wt.% epoxy remained within the solder bulk and exhibited a ductile fracture mode. This work indicates that epoxy-enhanced SAC305 solder pastes display high thermal cycling reliability and could meet the design needs of advanced packaging technology for high-performance electronic packaging materials.

Combined effects of local residual stresses, internal pores, and microstructures on the mechanical properties of laser-welded Ti-6Al-4V sheets

Laser-welded Ti-6Al-4 V is prone to severe residual stresses, microstructural variation, and structural defects which are known detrimental to the mechanical properties of weld joints. Residual stress removal is typically applied to weld joints for engineering purposes via heat treatment, in order to avoid premature failure and performance degradation. In the present work, we found that proper welding residual stresses in laser-welded Ti-6Al-4 V sheets can maintain better ductility during uniaxial tension, as opposed to the stress-relieved counterparts. A detailed experimental investigation has been performed on the deformation behaviours of Ti-6Al-4 V butt welds, including residual stress distribution characterizations by focused ion beam ring-coring coupled with digital image correlation (FIB-DIC), X-ray computerized tomography (CT) for internal voids, and in-situ DIC analysis of the subregional strain evolutions. It was found that the pores preferentially distributed near the fusion zone (FZ) boundary, where the compressive residual stress was up to -330 MPa. The removal of residual stress resulted in a changed failure initiation site from the base material to the FZ boundary, the former with ductile and the latter with brittle fracture characteristics under tensile deformation. The combined effects of residual stresses, microstructures, and internal pores on the mechanical responses are discussed in detail. This work highlights the importance of inevitable residual stress and pores in laser weld pieces, leading to key insights for post-welding treatment and service performance evaluations.

Flexural mechanical properties of H-shaped steel-bamboo scrimber composite beams

To improve the torsional buckling resistance and enhance the load-bearing capacity and ductility of H-shaped steel beams with carbon reduction materials, the concept of combining H-shaped steel with bamboo scrimber has been proposed, in which the bamboo scrimber, an eco-friendly, lightweight, and high-strength material, promises significant structural benefits. Five full-scale specimens were designed and tested, including one H-shaped steel, two bamboo scrimber beams, and two composite beams. Additionally, further simulation tests were conducted using the verified finite element model (FEM). The experimental results revealed a remarkable increase in the ultimate bearing capacity of the composite beams by 96.5 % compared to bamboo scrimber-only beams and 72.7 % compared to steel-only beams. Meanwhile, distinct from the brittle fracture characteristics of the bamboo scrimber beams, which include instantaneous crack propagation and interlaminar cracking, the composite beams exhibited localized vertical cracks within the beam's tensile zone, effectively avoiding the torsional buckling issue of the H-shaped steel beam. The results further demonstrated that increasing the cross-sectional size of the composite beams can significantly enhance their flexural stiffness (up to 669 %), and reduce the deflection at the ultimate flexural moment. When the area of the bamboo scrimber in the cross-section was reduced with an unchanged steel profile, the initial stiffness dropped to 79 % without incurring any structural instability. Furthermore, by integrating the experimental and simulation results, a fiber element model for this composite beam structure is proposed to predict the maximum flexural moment value in the ultimate state. A corresponding calculation program was developed, and it is found that the calculated predicted ultimate flexural moment values exhibited negligible deviation from both experimental and FEM results, with AV of 1.0001, AAE of 2.21 %, and COV of 3.28 %.

Failure of a high-pressure flash gas pipeline from coal coke gasification to the cleaning section due to hydrogen-induced cracking

ABSTRACT The high-pressure flash pipeline of coal coke gasification leaked within one week after the operation. Further macroscopic observation showed that cracks appeared in the base material area near the weld. The medium transported by the pipe was low-concentration acid gas. Visual inspection, tensile testing, impact testing, chemical composition analysis, metallographic analysis, energy dispersive spectroscopy, X-ray diffraction analysis, and electron backscattering diffraction analysis were used to reveal the sources of cracks in the pipeline. It was found that the cracks were intergranular and filled with corrosion products. The chemical composition of the corrosion products is rich in Cr, S, and O. After the crack was opened, fracture features of ‘rock candy’ were observed, exhibiting brittle fracture characteristics. The cracks were caused by hydrogen-induced cracking along the grain boundary. On this basis, suggestions and countermeasures were put forward for the failure of the high-pressure flash gas pipeline.

Study on mechanical properties and molecular simulation of nano‐SiO2‐modified hybrid fiber reinforced polymer bar under the dry and alkaline environment

AbstractFiber reinforced polymer (FRP) bars have received extensive promotion and application in the structural engineering. However, due to the limitations inherent in using single material, FRP reinforced concrete structures often encounter issues, such as brittle failure and inadequate energy dissipation, particularly in complex natural environments and under various loading conditions. In this study, the preparation of nano‐SiO2‐modified carbon/basalt hybrid FRP bars was carried out using the pultrusion‐winding process and ultrasonic treatment. The objective was to investigate the influence of the fiber volume ratio and mass fraction of nano‐SiO2 on the mechanical properties of FRP bars under drying and alkaline conditions. Molecular dynamics simulations were performed to construct interface models between fibers and epoxy resin in order to elucidate the toughening mechanism of nano‐SiO2 and the degradation mechanism in alkaline conditions. The research results show that elevating the substitution rate of carbon fibers and incorporating nano‐SiO2 doping bring about alterations in the brittle fracture characteristics of BFRP bars and enhance the post‐yield performance and interlaminar shear properties of hybrid FRP bars, concurrently mitigating the degradation of mechanical properties induced by exposure to alkaline solutions. MD simulations indicate that the addition of nano‐SiO2 improves the binding rate of hydrogen bonds between BF and epoxy resin, resulting in a higher interfacial energy between BF/epoxy resin compared to CF/epoxy resin. Moreover, nano‐SiO2 effectively mitigates the impact of alkaline solutions on the formation of interfacial hydrogen bonds. The findings of this study serve as a valuable reference for the design and application of FRP reinforced concrete structures.Highlights Nano‐SiO2 modified B/CFRP bars made via extrusion‐winding & ultrasonic treatment. Improved mechanical properties and plastic deformation in Nano‐SiO2 modified B/C FRP bars. Nano‐SiO2 inhibits B/CFRP bars degradation in alkaline solution. Nano‐SiO2 bind more at BF/epoxy than CF/epoxy interface. Nano‐SiO2 reduces alkaline solution effect on interfacial H‐bonding.

Influence of coupled water and thermal treatments on the fracture characteristics of a typical sandstone

Understanding the fracture behavior of rock after coupled water and thermal environment is important for many geotechnical projects. This study examines the influence of coupled water and thermal treatments on the fracture toughness and characteristics of a typical sandstone under mode I and mode II loading conditions. Notched deep beam (NDB) specimens were utilized and subjected to soaking treatments at various water temperatures (23 °C, 60 °C, and 99 °C). The experimental results indicate a significant reduction in both mode I and mode II fracture toughness values, with reductions ranging from 15.4% to 13.2% for mode I and 26.1% to 8.9% for mode II respectively. As the water temperatures increase, a slightly rising trend is observed in both mode I and mode II fracture toughness within the examined temperature range. Sandstone specimens displayed typical brittle fracture characteristics at lower soaking temperatures. For mode I specimens, an increase in ductility was evident with higher soaking temperatures, while the ductile behavior is less pronounced in the mode II specimens. Based on the Maximum Tangential Stress (MTS) criterion and the Generalized Maximum Tangential Stress (GMTS) criterion, the predicted values of mode II fracture toughness and the fracture process zone (FPZ) were discussed. The results show that both the GMTS and MTS criteria exhibit inaccuracies in predicting the mode II fracture toughness of sandstone treated at different soaking water temperatures. However, the GMTS criterion, which incorporates T-stress, demonstrates smaller errors compared to the MTS criterion. The study shows that the radius r0 of the fracture process zone is not a constant under both mode I and mode II loading conditions. The calculation of the fracture process zone radius r0 in the GMTS criterion requires further theoretical and experimental study.

Effect of salt–fog spray environment on bending fatigue properties of 3D woven composites

In this study, the effect of salt–fog spray corrosion environment on bending fatigue properties of three-dimensional (3D) woven composites was investigated. Three test environmental conditions, namely a normal environment, two cycles of salt–fog spray corrosion environment, and four cycles of salt–fog spray corrosion environment, were designed. In addition, the salt–fog spray corrosion mechanism, the bending fatigue properties, damage mechanisms, and failure modes of 3D woven composites were studied. The results showed that the bending strength and bending modulus decreased by 5.5 and 9.3%, and 2.27 and 3.45% after two and four salt–fog spray cycles, respectively, compared with that of the normal environment. The bending fatigue properties of 3D woven composites were related to the applied stress and salt–fog spray cycles. The salt–fog spray environment was responsible for the degradation of the interface bonding strength. The maximum reduction ratio of bending fatigue life after salt–fog spray treatment exceeded 70%. The brittle fracture characteristics of 3D woven composite yarn were more pronounced with an increase in salt–fog spray aging cycles.

Fracture behavior of graphene with intrinsic defects and externally introduced defects

Introducing and regulating defects to prepare functional graphene has become a research hotspot. However, most studies focus on the mechanical properties of functional graphene or the influence of a single defect, which cannot reflect the influence of multiple coupled defects on mechanical properties. In this study, molecular dynamics methods were used to investigate the fracture behavior of graphene under the coupled effects of intrinsic defects such as vacancies, cracks, and topological defects, as well as external introduced defects such as epoxy groups and hydroxyl groups. The results showed that the fracture behavior of graphene is strongly related to the defects' type, concentration, and functionality. Under the same conditions, the epoxy group has the strongest leading effect on fracture, followed by cracks, Stone-Wales topological defects, and hydroxyl groups. Based on the tensile simulation of defect-ordered graphene, the critical relative concentrations and functionalities of different defect types leading to fracture were further quantified and validated using an amorphous distribution model. In addition, the fracture mode dominated by epoxy groups is related to its functionality. Excessive or insufficient functionality will exhibit strong brittle fracture characteristics, and when the functionality is at a certain threshold, it will exhibit obvious ductile fracture characteristics; while hydroxyl-dominated fracture presents brittle mode. Finally, the coupled fracture mechanism was analyzed from the aspects of bonding characteristics and system energy. The research results can provide reference and reference for the theoretical research and technological development of graphene.

Influencing mechanism of nanoscale He bubbles on the crack propagation in TiT1.75 under tension

This work investigates the influence of the pre-existing He bubble on the crack propagation in TiT1.75 with molecular dynamic simulations. Under high strain rate tension, TiT1.75 exhibits typical brittle fracture characteristics with low fracture toughness at the microscopic scale, and the crack propagation path approximately follows the (111) plane with normal stretching direction. However, the presence of He bubble may change the stress concentration near the crack tip, resulting in the bending and even branching of cracks. The position relationship between He bubbles and crack tips is discussed, and the variation of the tensile strength with the distance and the angle is revealed. The total length and pattern of crack propagation are also presented. It is found that the tensile strength approximately linearly decreases with the He bubble concentrations, and the self-expansion and coalescence of He bubbles will gradually dominate the fracture process.

Effect of fan-shaped structure on high temperature tensile properties of nickel-based deformed superalloys

GH4742 alloy is a kind of precipitation-hardened superalloy, which is widely used in turbine disc, compressor disc, bearing ring and other parts due to its excellent high temperature mechanical properties. In this paper, high-temperature tensile comparison experiments were carried out at four temperatures, 1050 °C, 1080 °C, 1110 °C and 1140 °C, between alloy A containing a fan-shaped structure and alloy B without a fan-shaped structure. The results show that the tensile strength and plasticity of alloy A at 1050 °C are superior to those of alloy B. With the increase of temperature, the difference of tensile strength and plasticity between alloy A and B decreases gradually. By analyzing the fracture, both alloy A and B were found to have a large number of tough dimples, which showed ductile fracture characteristics. But alloy B was found to have some icing-like fracture at 1050 °C, which showed some brittle fracture characteristics. After 1110 °C, the difference in tensile strength and plasticity between alloy A and B almost disappears because γ′ phase is completely dissolved in the matrix. TEM results show that dislocations gather around the large-size γ′ phase, and for the small-size γ′ phase, dislocations tend to cut into γ′ phase directly. The results show that the existence of fan-shaped structure is beneficial to the high temperature tensile properties of GH4742 alloy, which has a certain reference effect on the production of GH4742 alloy in the future.

Improving laser welded joint performance of medium-Mn steel through C and Mn partition by intercritical annealing process

In this paper, the fracture failure mechanism of laser welded (LW) joints of medium-Mn steel is studied. And the mechanical properties of the joints were greatly improved by designated intercritical annealing (IA) process. Experimental results showed that the elongation of the as-welded joint of medium-Mn steel is very low, and the fracture shows typical brittle fracture characteristics. Electron probe micro-analyzer (EPMA) test showed that there were many Mn segregation bands in the joint, and electron backscatter diffraction (EBSD) surface scanning test further demonstrated that many Mn23C6 carbides were produced at the martensite grain boundary (GB) of the fusion zone (FZ), which was the main reason for the occurrence of brittle fracture in the FZ. The IA process improves the segregation of Mn element at the GB of the joint and reduces the intergranular brittleness. At the same time, more austenite was distributed by C and Mn elements, and more Fe3C phases were found near austenite in the EBSD diagram, which provided nucleation centers for the formation of austenite. The product of strength and elongation (PSE) of the IA treated joint was dramatically increased by 2693.65%.