Microstructure Of Base Metal Research Articles

Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas (MIG) welded with NiCrMo-3 and 307Si filler wires. The effect of filler wires on the microstructure and mechanical properties of joint was investigated, and the carbide precipitates were contrastively discussed. The results revealed that the microstructure of weld metal, heat-affected zone and base metal are austenite. Obvious grain coarsening occurred in the heat-affected zone (HAZ), and the maximum grain size grew up to 160 μm. In HAZ, C and Cr segregated at grain boundaries, the carbides was identified as Cr7C3. The dispersive (Nb, Mo)C phase was also found in weld metal with NiCrMo-3 filler wire. All the welded joints failed in HAZ during tensile tests. The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa, which is much higher than that with 307Si filler wire. In comparison to base metal, higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints, which was attributed to the precipitation of Cr7C3 phase and grain coarsening. The impact toughness around the fusion line is the worst for these two welded joints.

The influence of microstructure on CTOD fracture toughness of DZ125 base metal and brazed joint

The microstructure of the base metal zone and the weld zone of the DZ125 directionally solidified nickel-based superalloy brazed joint is studied by means of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and optical microscope. The CTOD fracture toughness of the base metal zone and the weld zone at 950 °C was tested respectively. The results show that the microstructure of the DZ125 alloy base metal grows with dendrites, the arrangement of the dendrites is close, the divergence angle is small, the dendrites are distributed with a uniform and fine γ′ phase, script-shaped MC carbides and petal-shaped γ/γ′ eutectic phases are distributed in the inter-dendrite zone. The uniform γ′ phase is distributed in the weld zone. At 950 °C, the CTOD fracture toughness of base metal and brazed joint is 0.080 mm and 0.048 mm, respectively. The fracture toughness of the base metal is higher than that of the brazed joint. The fracture morphology shows that the base metal has good toughness at 950 °C, while the weld zone has poor toughness at this temperature. It can be inferred that the long needle-shaped M6C carbides will weaken the structure performance.

Statistical optimization of parameters for enhanced properties of diffusion bonded AA6061 and AA 7075 aluminium alloys

The predominant complication when joining dissimilar aluminium alloys is due to the presence of brittle intermetallic and oxide films in the bonded region. However, to preserve the base metal microstructure diffusion bonding can be used. In this study, an effort was done to optimize the best process parameters such as bonding period, bonding temperature and bonding pressure for diffusion bonding of AA7075 and AA6061 aluminium alloys. Response surface methodology (RSM), a statistical approach which uses a series of designed experiments to achieve an optimum response was being adapted in this study to define maximum shear and tensile strength for the diffusion bonded aluminium alloy joints. The best bonding quality was observed when the temperature, pressure and time of bonding are 375 °C, 10 MPa, and 45 min respectively. The maximum shear and tensile strength attained are 55 MPa as well as 74 MPa respectively.

Effect of Aging Heat Treatment Conditions on the Mechanical Properties and Microstructure of Base and Weld Metal of Alloy 282 Superalloy

The effect of aging heat treatment conditions on the mechanical properties and microstructure of the base and weld metal of Alloy 282 superalloy was investigated. The aging heat treatment conditions employed in this study were as follows: two-steps (1010 °C for 2 hours plus 788 °C for 8 hours) and one-step at 788 °C, 738 °C, and 688 °C for 4 hours. The base metal with the one-step aged condition exhibited lower hardness but longer creep life than that treated with the two-step aged condition. The base metal subjected to the two-step aging exhibited the highest hardness and the shortest creep life, mainly due to the precipitation of Mo-rich M6C-type carbides and coarse <i>γ</i>' (Ni3(Al,Ti)) phase. For the weld metal, regardless of aging heat treatment conditions, creep elongation and life decreased significantly compared to the base metal, due to the coarse effective grain size and inhomogeneous distribution of <i>γ</i>' precipitates.

Effect of inhomogeneous microstructure on the deformation and fracture mechanisms of 316LN stainless steel multi-pass weld joint using small punch test

The local microstructural effect on the deformation behavior and fracture mechanisms in different zones of 316LN stainless steel multi-pass weld joint of the nuclear power plant was investigated by using small punch test. The results indicated that microstructure of the weld joint was highly inhomogeneous from region to region. The microstructure of base metal (BM) and heat affected zone (HAZ) was austenitic cellular crystal with twins, while that of as-deposited weld metal (WM) was duplex austenite-ferrite. By inducing multi-pass thermal cycles, at least five distinct morphologies of ferrite were identified in the WM. On the other hand, the deformation and fracture mechanisms in different zones of the multi-pass weld joint were strongly influenced by the inhomogeneous microstructure. The WM showed lower deformability than the BM and HAZ due to the deformability mismatch between ferrite and austenite. In BM and HAZ, the cracks tended to initiate at the slip bands and propagate along the slip bands. However, in WM, the cracks tended to initiate at the ferrite and ferrite-austenite interface and preferentially propagate along the needle-like ferrite. In the fusion zone (FZ), the plastic deformation always first occurred in the HAZ followed by the deformation of the WM near the fusion boundary. And the crack initiated at the region adjacent to the fusion boundary but did not propagate along the fusion boundary. Fractographic analysis demonstrated that the fracture model of all the specimens was ductile fracture except a few quasi-cleavage fracture features were observed in the HAZ.

Correlation between Microstructure and Mechanical Properties of Base Metal and HAZ of 500 MPa Steel Plates for Offshore Platforms

In this study, two types of thick steel plates are prepared by controlling carbon equivalent and nickel content, and their microstructures are analyzed. Tensile tests, Vickers hardness tests, and Charpy impact tests are conducted to investigate the correlation between microstructure and mechanical properties of the steels. The H steel, which has high carbon equivalent and nickel content, has lower volume fraction of granular bainite (GB) and smaller GB packet size than those of L steel, which has low carbon equivalent and nickel content. However, the volume fraction of secondary phases is higher in the H steel than in the L steel. As a result, the strength of the L steel is higher than that of the H steel, while the Charpy absorbed energy at -40 °C is higher than that of the L steel. The heat affected zone (HAZ) simulated H-H specimen has higher volume fraction of acicular ferrite (AF) and lower volume fraction of GB than the HAZ simulated L-H specimen. In addition, the grain size of AF and the packet sizes of GB and BF are smaller in the H-H specimen than in the L-H specimen. For this reason, the Charpy absorbed energy at -20 °C is higher for the H-H specimen than for the L-H specimen.

Experimental study to investigate microstructure and continuous strain rate sensitivity of structural steel weld zone using nanoindentation

In this study, a series of experiments consisting of continuous stiffness measurement (CSM) nanoindentation experiments, optical microscope (OM), atomic force microscopy (AFM) examinations, and finite element (FE) analysis were performed to study the microstructures, the indentation size effects, and the rate-dependent behavior of mechanical properties in three phases of SM490 structural steel weld joint. The microstructures of base metal (BM), heat-affected zone (HAZ), and weld metal (WM) were observed using OM examinations. The size-dependent behaviors of mechanical properties in BM, HAZ, and WM were characterized and interpreted through the strain gradient theory. The CSM nanoindentation experiments were carried out in the strain rate range of 0.01–0.1 s−1 to investigate the rate-dependent behavior of indentation hardness and continuous strain rate sensitivity. The results indicated that indentation hardness depended on not only the indentation size but also the strain rate of the indentation level. The strain rate sensitivity (SRS) of BM, HAZ, and WM showed the depth-dependent behavior. The SRS of WM is quite high, over 0.4 at the indentation depth of 200 nm, quickly drops to 0.1, and finally is around 0.0298 at large indents. Similarly, the SRS behavior in the case of HAZ is the same, however, the SRS values at larger indents are higher than those obtained in the WM region. At larger depths, the SRS values of the WM region are lower than those of BM and HAZ, while BM has the highest SRS value compared with WM and HAZ. The continuous SRSs of WM, HAZ, and BM are attributed to the change in the dislocation behaviors during the indentation process. The results of the present study can be used to access and understand the rate- and the size-dependent behaviors in structural steel weld zone.

Creep and fracture behavior of long-annealed weld HAZ in CB2 steel

CB2 steel for thick castings has been designed and investigated in the frame of COST-522 and C0ST-536 R&D actions of EU to work at supercritical conditions of the steam main lines. The steel exhibits loss of impact strength and hardness after long annealing and also of strength and life when creep tested after the long annealing. The most serious decrease of properties appears in weld’s heat-affected zones during the creep tests. Differences in microstructures of base metal (BM) and weld’s heat-affected zone (HAZ) have been studied in initial state and after long-term annealing/aging for 10 kh and 30 kh at 625 °C, followed by creep testing. The initial as-cast microstructure of CB2 is inhomogeneous, and the welding thermal cycle causes additional separation of phases in the intercritical region. TEM observations revealed appearance in HAZ of large ferrite grains between compact colonies of spheroidal carbides, associated with the decrease of creep strength and life in the HAZ.

Correlation between Tensile Deformation Behavior and Microstructural Morphology of Nuclear Grade Austenitic Stainless Steel Weld Joints using Infrared Thermography Technique

Tensile deformation behavior of nuclear grade Austenitic Stainless Steel (SS) and its weld joints fabricated by Gas Tungsten Arc Welding (GTAW) and Activated flux Gas Tungsten Arc Welding (AGTAW) processes were studied and correlated with relevant microstructural morphologies using Infrared Thermography (IRT) technique. The microstructure of base metal showed a complete austenite phase. GTAW Fusion Zone (FZ) exhibited both primary ferrite and primary austenite mode of solidification. Meantime, AGTAW FZ exhibited only primary austenite mode of solidification A strain rate of 4.4x10-4 s-1 was used during the tensile test of the base metal and weld samples. The failure locations of the base metal, GTAW and AGTAW samples were noticed at the center of the gauge portion, the base metal side away from Fusion Line (FL) and Heat Affected Zone (HAZ) respectively. Temperature variations of the base metal and weld zones were recorded in the form of thermograms using the IR camera at the different stages of the tensile deformation. During deformation study, peak temperatures of 39.2 oC, 38.8 oC and 34 oC were observed at the base metal, GTAW and AGTAW samples respectively. The lesser peak temperature of the AGTAW sample compared to the base metal and GTAW samples indicated that the AGTAW sample undergone lesser deformation. Moreover, tensile deformation behaviors of the base metal and weld samples were correlated with their microstructural morphologies using corresponding temperature curves.

Corrosion Susceptibility and Functionally Graded Properties of Ti-35Nb-4Sn Alloy Processed by Laser Remelting

The effect of laser remelting on the corrosion susceptibility and mechanical properties of Ti-35Nb-4Sn (mass%) alloy is investigated across the remelted track profile. In comparison to the cold-rolled microstructure of base metal, recrystallization of heat affected zone (HAZ) improved plastic energy absorption and pitting corrosion resistance, by the reduction of active sites for pit nucleation. In fusion zone, however, passivation was compromised by the formation of dendritic microstructure with Sn enriched interdendritic region, where preferential pitting corrosion occurred. Fusion zone was the most anodic region and presented a corrosion potential difference of 35 mV, in comparison to the adjacent and most cathodic HAZ. Electrochemical impedance analysis showed that spontaneous passivation was most effective in base metal, that developed a thicker and more compact passive film. Local increase in elastic modulus and microhardness of fusion zone shows that laser remelting is a viable processing route for the manufacturing of biomaterials with functionally graded properties.

Microstructure and mechanical properties of thick CLF-1 reduced activation steel weld joint made by electron beam welding joint

The effect of post-welded heat treatment (PWHT) on microstructure and mechanical properties of electron beam welded joint of 35 mm thick China low-activation ferrite steel CLF-1 was studied. The results showed that the hardness and microstructure of the joint for both the as-welded and the PWHT were uniform along the thickness direction, and the hardness behaved a W-shaped distribution. The joint microstructure was composed of tempered martensite and precipitated phases which were mainly chromium and tungsten carbides. A small amount of δ-ferrite existed near the fusion line in the fusion zone. With the increase of tempering temperature, the microstructure of joint and base metal didn’t change significantly. With the extension of tempering time, the precipitated phases of base metal grew and the joint microstructure didn’t change significantly. The suitable PWHT was suggested as tempering at 1013 K for 2∼4 h, which not only ensured the strength of base metal, but also greatly improved low-temperature impact energy of the joint at 253 K.

Effect of cathodic potential on stress corrosion cracking behavior of different heat-affected zone microstructures of E690 steel in artificial seawater

In this work, the stress corrosion cracking (SCC) behavior of E690 steel base metal (BM) and different heat-affected zone (HAZ) microstructures, i.e., coarse grain HAZ (CGHAZ), fine grain HAZ (FGHAZ), and intercritical HAZ (ICHAZ), was investigated at different cathodic potentials in artificial seawater by slow strain rate tensile tests, scanning electron microscopy and electron back-scattered diffraction measurements. The results show that the HAZ microstructures and BM exhibit different SCC susceptibilities: FGHAZ < ICHAZ < BM < CGHAZ, which are controlled by anodic dissolution (AD) at the open circuit potential. With the cathodic potential equaling to −750 mV, the SCC susceptibility of the four microstructures increases because of the synergistic effect of AD and weak hydrogen embrittlement (HE). At -850 mV, AD is inhibited, and the SCC susceptibility of BM decreases, while the SCC susceptibility of the HAZ microstructures increases. At a potential below -850 mV, the SCC susceptibility of the four microstructures gradually increases because of the augment of HE, and the SCC susceptibility of the HAZ microstructures is higher than that of BM. The distinction reveals that the HAZ microstructures have the greater HE susceptibility than BM.

Mechanical and corrosion behaviour of conventional and high-speed remote scanner laser welding for duplex stainless steel: A comparative study

High-speed remote scanner laser-welding is a relatively new technique that is being tried out at the Mittweida Laser institute to weld stainless steel sheets of high thicknesses; the material used was (1.4462) 8mm thick. For comparison, the material was welded also by gas tungsten arc welding (GTAW) or TIG. The welding processes were evaluated by several testing techniques; mechanical testing using (tensile testing and hardness). Optical microscopy was employed to investigate the phase changes and weld defects inside the material. Scanning electron Microscope investigated the grain size before and after weld with the precipitate. Electrochemical corrosion testing was used to evaluate the corrosion behaviour of the weld zone. For each experiment, base metal and heat affected zone (HAZ) have been selected. Microstructure investigation of HAZ revealed the formation of finer microstructures with different grain boundaries due to the melting and the resolidification of the base metal and extensive microstructure changes inside the materials. In comparison to TIG, many weld defects were observed and carbide precipitations formed at the grain boundaries. Hardness measurements revealed that hardness increases towards the centre of both laser and TIG. Tensile testing revealed that the weld has the potential to have very high strength approaching that of the original material, particularly for laser welding. Measuring corrosion rates shows that the welded material is more susceptible to corrosion and to pitting, the pitting potential was estimated reflecting higher pitting resistance for base metal than laser and TIG weld respectively, thus can be explained due to the formation of precipitates of carbide and ferrite particularly for TIG Weldament.

Investigating the Effect of Friction Stir Welding on Microstructure and Corrosion Behaviour of Al-Zn-Mg Alloy

In this work, Friction Stir Welding (FSW) of alloy 7039 was carried out in T4 temper and resulting microstructure and corrosion behaviour of developed weld were studied. FSW transformed the starting microstructure of base metal and formed stirred zone (SZ) and heat affected zone (HAZ) with varying microstructure and precipitate morphology. The observed zones in welded joints exhibited decreased protection to corrosion resistance than base metal. Dissolution of secondary precipitates in SZ and occurrence of precipitate free zones (PFZs) in HAZ enhanced susceptibility to corrosion of HAZ and weld nugget zone (WNZ) than base metal.

Effect of pre-weld heat treatment on the microstructure and mechanical properties of electron beam welded IN738LC joint

Influence of pre-weld heat treatment on the microstructure and mechanical properties of electron beam welded IN738LC superalloy was investigated systematically. The microstructure of as-cast base metal (BM) mainly consisted of “ogdoadically” diced cube γ′ particles, fanlike γ-γ′ eutectics, MC carbides, Cr–Mo borides and Ni–Zr intermetallics. Grain-boundary liquation cracking was observed in the HAZ of as-cast joint, resulting from the segregation of elemental boron. Pre-weld heat treatment had a significant influence on the size, volume fraction and distribution of γ′ particles. It also decreased the non-equilibrium segregation of boron during cooling, which inhibited the formation of grain-boundary liquid film and liquation cracking. The precipitation of MC carbides and nanoscaled γ′ particles in the fusion zone (FZ) improved the micro-hardness of the FZ. The micro-hardness of the BM and the HAZ were influenced by the volume fraction and the size of γ′ particles. All the joints fractured in the BM at RM and 900 °C. The as-cast and water quenched (WQ) joints failed with a quasi-cleavage fracture mode at RM and 900 °C while the tensile fracture of furnace cooled (FC) joint showed a ductile rupture at RM and 900 °C.

Effect of microstructure on corrosion of welded joints of X80 steel in water saturated supercritical CO2

Purpose The purpose of this paper is to research whether microstructure varieties of zones at welded joints pose a tremendous effect on its corrosion in SC-CO2. Design/methodology/approach The interrelation between the corrosion and microstructure of base metal (BM), fine grain heat affected zone (FHAZ), coarse grain heat affected zone and weld metal (WM) in welded of X80 steel in water saturated supercritical CO2 was studied by using optical microscope, weight loss test, electrochemical measurements and surface analytical techniques. Findings The all subzones of X80 weld joints were attacked by SC-CO2 corrosion and showed flower-like corrosion scale spots consisted of granular FeCO3. The most severe corrosion appeared at WM due to lower proportion of ferrite to pearlite, but the slightest corrosion displayed at BM. GHAZ with larger grains and more polygonal ferrite exhibited more severe corrosion than that at BM. Due to its smaller grain, FHAZ displayed comparatively more severe corrosion to that at BM. Originality/value There exists close interrelation between the corrosion and microstructure of the welded carbon steel in water saturated supercritical CO2.

Pengaruh Ketahanan Aus Baja SA 516-70 Setelah Mengalami Pelapisan Elektroda Sandvik 29 8 2 Lr Dan 25 10 4 Lr

SA 516-70 is a low carbon steel which is used for marking of boiler, high pressure tank and heat exchanger. Steel of SA 516-70 is applied for corrosion and wear resistance equipment. Weld surfacing can be used to overlay new components to their original dimensions. All are welding processes can be used for overlay as well joining applications. In this research two types of electrodes used are Sandvik 25 10 4 LR and Sandvik 29 8 2 LR. Weld surfacing process was used GTAW process using DCEP. The welding parameter used are as follow: welding current between 110 A to 112 A, welding voltage between 12 to 13 volt and travel speed between 173 to 191 mm/ minute. The weldments was then conducted hardness testing, metallographic examination, EDAX and X-Ray Diffraction ( XRD ). Samples for hardness testing were taken from base metal and to the filler metal layer. EDAX testing was taken from metal to the outer layer layers, while XRD testing was conducted on the base metal, layer 1 and layers 3. The results that the high hardness value of 356 Hv was Found on at layer 1 using sandvik electrode 29 8 2 LR. The base metal microstructure was reveled some ferrite and pearlite structure.The cromium dilution using sandvik electrode 29 8 2 LR was higher than that of sandvik electrode 25 10 4 LR. From all data investigations was concluded that the usage of sandvik electrode 29 8 2 LR is better performance than use of sandvik electrode 25 10 4 LR.

Effects of welding on the change of microstructure and mechanical properties of low carbon steel

Steel construction is mostly connected by using a welding technique. The result of the welding process can cause the change of mechanical properties of the welding zone. Therefore, it needs to be reviewed to guarantee the quality of the welding zone. This research aims to assess the effect of welding on the change of microstructure and the mechanic characteristic of welded connection. Low carbon steel was welded by using Shield Metal Arc Welding method (SMAW) with electrode E7016, diameter 2,6 mm. Type of notch used was single V with angle 70° and welding position was 1G. Then, the Charpy impact test, Rockwell hardness and micro-macro structure monitoring on the welding zone including base metal, Heat Affected Zone (HAZ) and weld metal, are conducted. The results show that the highest impact toughness value at metal welding area is 251 joule/mm2, and lowest impact toughness is at the heat affected area (HAZ) is 119 joule/mm2. Hardness values of welding zones are found of about 87,6 HRB for weld metal, 73,9 HRB for HAZ zone and 67,1 HRB for the base metal. The microstructure of weld metal zone, HAZ and base metal are included on ferrite and pearlite formed by welding on low carbon steel AISI 1010 observer by using an optic microscope.

Effect of Chemical Compositions on Microstructure and Mechanical Properties of Base Metal and HAZ of Bainitic Steel Plates

In this study, three kinds of bainitic steel plates are manufactured by varying the chemical compositions and their microstructures are analyzed. Tensile and Charpy impact tests are performed at room and low temperature to investigate the correlation between microstructure and mechanical properties. In addition, heat affected zone (HAZ) specimens are fabricated by a simulation of welding processes, and the HAZ microstructure is analyzed. The base steel that has the lowest carbon equivalent has the highest volume fraction of acicular ferrite and the lowest volume fraction of secondary phases, so the strength is the lowest and the elongation is the highest. The Mo steel has a higher volume fraction of granular bainite and more secondary phases than the base steel, so the strength is high and the elongation is low. The CrNi steel has the highest volume fraction of the secondary phases, so the strength is the highest and elongation is the lowest. The tensile properties of the steels, namely, strength and elongation, have a linear correlation with the volume fraction of secondary phases. The Mo steel has the lowest Charpy impact energy at -80 oC because of coarse granular bainite. In the Base-HAZ and Mo-HAZ specimens, the hardness increases as the volume fraction of martensite-austenite constituents increases. In the CrNi-HAZ specimen, however, hardness increases as the volume fraction of martensite and bainitic ferrite increases.

Characterization of Static Performance and Failure of Resistance Spot Welds of High-Strength and Press-Hardened Steels

The static performances and failure characteristics of resistance spot welds (RSW) of steel sheets were studied in this work. Both similar and dissimilar joints of press-hardened steel grade 22MnB5 and as-rolled high-strength steel grade 1000 were examined. From metallographic analyses and micro-hardness measurements, it was shown that the microstructures of base metal (BM), heat affected zone (HAZ) and fusion zone of steel joints were noticeably different. In particular, the HAZ close to BM or subcritical HAZ (SCHAZ) of 22MnB5 steel exhibited greatly decreased hardness due to occurring tempered martensite, in which carbide precipitation was clearly observed. Furthermore, tensile shear test and cross-tension test of the welded steel sheets were carried out. The determined maximum loads, energy absorbability and corresponding failure mechanisms were analyzed and compared. The RSW samples of similar steel grade 1000 provided the highest load-carrying capacity and absorbed energy in both tests. Due to the large hardness difference and soft zone in weldment of dissimilar steel specimen, failure loads and static absorbed energies were deteriorated up to 17 and 68%, respectively. The observed fracture occurrences of all investigated joints were pullout failure mode, in which BM and HAZ were the crack initiation sites of grades 1000 steel and 22MnB5 steel, respectively. The SCHAZ of welded boron steel considerably caused the failure onset in tension shear test, but seemed to have negligible effect on cross-tension test.