Arc Zone Research Articles

Foveal contour interaction for low contrast acuity targets

Previous investigators reported the impairment of foveal visual acuity by nearby flanking targets (contour interaction) is reduced or eliminated when acuity is measured using low contrast targets. Unlike earlier studies, we compared contour interaction for high and low contrast acuity targets using flankers at fixed angular separations, rather than at specific multiples of the acuity target’s stroke width. Percent correct letter identification was determined in 4 adult observers for computer generated, high and low contrast dark Sloan letters surrounded by 4 equal contrast flanking bars. Two low contrast targets were selected to reduce each observer’s visual acuity by 0.2 and 0.4 logMAR. The contour interaction functions measured for high and low contrast letters are very similar when percent correct letter identification is plotted against the flanker separation in min arc. These results indicate that contour interaction of foveal acuity targets occurs within a fixed angular zone of a few min arc, regardless of the size or contrast of the acuity target.

The Deposit Features and Comprehensive Information Prospecting Model of Mengyejing Potash Deposits in Yunnan Province

Mengyejing potash deposit lies in brown-red and variedness salting-in nagelfluh formation of Cenozoic Mengyejing formation which is located at the back-foreland basin of Lanping-Simao bidirectional arc zone, and it is one of the few large-scale solid potash deposits in China. By integrated study systematically, Mengyejing Potash Deposit’s different scales of mineralization geological anomalies information:geological, geophysical, geochemical, and salt spring chemistry and remote sensing were extracted. A comprehensive information prospecting model of Mengyejing potash deposit is established. Tentatively identified deposits prospecting model of Mengyejing formation, negative gravity anomaly, salt spring chemical anomaly and geochemical anomalies as the core and is of a positive significance for this type of deposit’s prospecting.

Time constraints for the closing of the Paleo-Asian Ocean in the Northern Alxa Region: Evidence from Wuliji granites

The Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is the principal part of Shalazhashan Mountain. It belongs to the Zongnaishan-Shalazhashan Arc Zone, northwestern North China Plate, whose north is Engger Us Ophiolite Belt and south is Qagan Qulu Ophiolite Belt. The pluton was emplaced into Upper Carboniferous-Lower Permian Amushan Formation. According to the research about the original Carboniferous Amushan Formation, the lower and middle sections of the Carboniferous Amushan Formation consist of volcanic, clastic, and carbonate rocks, interpreted to represent the sedimentary association of a volcanic arc and back-arc basin; the upper section of the Amushan Formation is a molasse composed of silty shale, sandstone, gravel-bearing sandstone, and conglomerate. The Wuliji pluton consists mainly of biotite monzonitic granite, amphibole-bearing biotite monzonitic granite, and monzonitic granite. Geochemical analyses show that the pluton has both metaluminous and peraluminous characteristics, and on average has SiO2 > 70 wt%, Al2O3 > 14 wt%, and high contents of Na2O+K2O (8.5 wt%), which define a calc-alkaline series. In addition, REE patterns show enrichment of LREE and weak negative Eu anomalies (δEu = 0.3–1). Altogether, the samples are depleted in Nb, Ta, Ti, P, Sr, and Ba, and enriched in Rb, Th, and K. These geochemical traits are interpreted to reflect an arc component. A secondary ion mass spectrometry (SIMS) U-Pb zircon age of the biotite monzonitic Wuliji pluton in the Northern Alxa Region, Inner Mongolia, is 250.8 ± 2.0 Ma (1σ). Samples have ɛNd(t) values between −0.1 and 1.3, which suggests that the granites were derived from mixing between the crust and mantle. Based on the SIMS age and geochemical characteristics, Wuliji granite is interpreted to be a post-collisional granite, the result of mantle-derived melt and assimilated juvenile arc crust. However, according to the newest international stratigraphic classification standard, the upper section of the Amushan Formation is Lower Permian in age, indicating that the back-arc basin had already closed in Early Permian. We conclude that the Paleo-Asian Ocean represented by the Engger Us Ophiolite Belt subducted southward in Late Carboniferous, at the same time that the trench-arc-basin system formed in the Northern Alxa Region. The Paleo-Asian Ocean was closed in Early Permian and the Northern Alxa Region entered a post-collisional period in the Late Permian, as indicated by the Wuliji granites. This suggests that the genesis of the Wuliji granites is consistent with the pluton emplacement at the upper crust, which occurred widely in the northern margin of the North China Plate in Late Carboniferous to Triassic.

High power fiber laser arc hybrid welding of AZ31B magnesium alloy

High power fiber laser–metal inert gas arc hybrid welding of AZ31B magnesium alloy was studied. The fusion zone consisted of hexagonal dendrites, where the secondary particle of Al8Mn5 was found at the center of dendrite as a nucleus. Within hybrid weld, the arc zone had coarser grain size and wider partial melted zone compared with the laser zone. The tensile results showed the maximum strength efficiency of 5mm thick welds was up to 109%, while that of 8mm thick welds was only 88%. The fracture surface represented a ductile–brittle mixed pattern characterized by dimples and quasi-cleavages. On the fracture surface some metallurgical defects of porosity and MgO inclusions around with secondary cracks were observed. Meanwhile, a strong link between the joint strength and weld porosity were demonstrated by experimental results, whose relevant mechanism was discussed by the laser–arc interaction during hybrid welding.

Effect of modified AA4043 filler on corrosion behavior of AA6061 alloy GTA welds

The corrosion behavior of the fusion zone of gas tungsten arc (GTA) welds of AA6061 alloy was studied. The role of GTA welding techniques such as continuous current and pulsed current (PC) with reference filler (AA4043) was studied. The role of the addition of different grain refiners such as scandium (Sc), zirconium, and Tibor to the reference filler was studied. Dynamic polarization testing was used to determine the pitting corrosion resistance of the fusion zone. Optical microscopy and scanning electron microscopy studies were carried out to find the mechanism of corrosion. Out of all the grain refiners studied, better corrosion resistance was observed with 0.5 % Sc addition to fusion zone through reference filler and PC technique.

Neoarchean suprasubduction zone arc magmatism in southern India: Geochemistry, zircon U-Pb geochronology and Hf isotopes of the Sittampundi Anorthosite Complex

The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541±13Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461±15Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715±180Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related~2530Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial176Hf/177Hf ratios and positive εHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth.

Microstructure of Laser-MAG Hybrid Welds of Sintered P/M Steel

The microstructure and mechanical properties of iron-based powder metallurgical steels jointed by CO2 laser-metal active gas (MAG) hybrid welding were investigated. The cross-sectional morphology of hybrid weld bead consisted of arc zone and laser zone. The microstructure of arc zone consisted of columnar dendrite and fine acicular dendrite between the columnar dendrites, but that of laser zone was composed of fine equiaxed dendrite. The MAG weld had obvious heat-affected zone (HAZ) zone, while hybrid weld had very narrow HAZ zone because of the rapid cooling rate. The phase constitutions of the joint determined by x-ray diffraction were α-Fe (ferrite) and Cu. The 2θ value of α-Fe (200) peaks of hybrid weld was smaller than that of sintering compact. Compared to MAG weld, hybrid weld had finer grain size, higher micro-hardness, and higher micro-strain, which was caused by the difference of cooling rate and crystallizing.

Influences of welding processes on microstructure and mechanical properties of modified 12 wt % Cr ferritic stainless steel

This paper presents the comparative evaluation of microstructural features and mechanical properties of a friction stir welded (solid-state), gas tungsten arc welded (fusion), electron beam and laser beam welded (high energy density) 409M grade ferritic stainless steel joints. Optical microscopy, ferritescope measurements, X-ray diffraction analysis, microhardness, transverse tensile, impact and bend tests were performed. The coarser ferrite grains in the base material are changed to very fine grains consisting duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. Fine dendritic columnar grain structure of alpha ferrite with grain boundary martensite was observed in fusion zone of laser and electron beam welded joints. On the other hand, grain growth was observed in fusion zone as well as high temperature heat affected zone of gas tungsten arc welded joint resulting in deterioration of mechanical properties.

Chromite–silicate chemistry of the Neoarchean Sittampundi Complex, southern India: Implications for subduction-related arc magmatism

The Neoarchean layered anorthositic complex at Sittampundi in southern India is known for its chromitite layers that are mostly associated with anorthosite (An90–100). The chromitites contain FeAl-rich chromites concentrated in layers between amphibole-rich layers with a dominant mineralogy of amphibole–spinel–plagiocase±sapphirine. The chromite-rich layers contain only amphibole and plagioclase. Mineral compositions illustrated by X-ray composition maps and profiles show subtle chemical differences. The chrome spinels are of refractory grade with Cr2O3 and Al2O3 contents varying between 34–40wt.% and 23–28wt.%. The chromite compositions are noticeably different from those in layered igneous intrusions of the Bushveld-Stillwater type. The existence of original highly calcic plagioclase, FeAl-rich chromite, and magmatic amphibole is consistent with derivation from a parental magma of hydrous tholeiitic composition that was most likely generated in a supra-subduction zone arc setting. In terms of mineralogy and field relations, the Sittampundi chromitites are remarkably similar to anorthosite-hosted chromitites in the Neoarchean Fiskenæsset anorthositic complex, Greenland. We propose that the Sittampundi chromitites formed by partial melting of unusually aluminous harzburgite in a hydrated mantle wedge above a subduction zone. This melting process produced hydrous, aluminous basalt, which fractionated at depth to give rise to a variety of high-alumina basalt compositions from which the anorthositic complex with its cumulate chromite-rich and amphibole-rich layers formed within the magma chamber of a supra-subduction zone arc.

The peripheral magma chamber of Ploskii Tolbachik, a Kamchatka basaltic volcano: Activity, location and depth, dimensions, and their changes based on magma discharge observations

The Klyuchevskoi group of volcanoes (KGV) in Kamchatka is the most powerful existing island arc and subduction zone volcanic center. The Holocene volcanic activity in the southern part of the KGV is concentrated in a large basaltic volcano, Ploskii Tolbachik (PT), altitude 3085 m and in its Tolbachik zone of cinder cones (TZ), length 70 km, which are similar to Hawaiian-type volcanoes and their rifts. A variety of different basalt types are erupted at a rate of 18 × 106 t/yr. This paper provides information on the PT peripheral magma chamber obtained by several independent methods. We used data on the evolution, eruptions, magma discharge, deformation, and earthquakes in the PT and TZ, as well as calculations that give the size of the PT flow-through magma chamber. The use of seismological and geodetic data places the chamber under the PT summit caldera, gives its transverse size as below 6 km, and the top of the chamber at a depth of 2 km. Our calculations give 4.9–5.8 km for the transverse chamber dimension, 3.2–3.9 km for its vertical dimension, 40–70 km3 for chamber volume, and about 4 km for the depth of chamber center. The information we provide makes the properties of this source of PT and TZ alumina-rich basalts clear, as well as those of the entire KGV complex plumbing system.

Carbon arc production of heptagon-containing fullerene[68

A carbon heptagon ring is a key unit responsible for structural defects in sp2-hybrized carbon allotropes including fullerenes, carbon nanotubes and graphenes, with consequential influences on their mechanical, electronic and magnetic properties. Previous evidence concerning the existence of heptagons in fullerenes has been obtained only in off-line halogenation experiments through top-down detachment of a C2 unit from a stable fullerene. Here we report a heptagon-incorporating fullerene C68, tentatively named as heptafullerene[68], which is captured as C68Cl6 from a carbon arc plasma in situ. The occurrence of heptagons in fullerenes is rationalized by heptagon-related strain relief and temperature-dependent stability. 13C-labelled experiments and mass/energy conservation equation simulations show that heptafullerene[68] grows together with other fullerenes in a bottom-up fashion in the arc zone. This work extends fullerene research into numerous topologically possible, heptagon-incorporating isomers and provides clues to an understanding of the heptagon-involved growth mechanism and heptagon-dependent properties of fullerenes.

Eclogite origin and timings in the North Qinling terrane, and their bearing on the amalgamation of the South and North China Blocks

The amalgamation of South (SCB) and North China Blocks (NCB) along the Qinling-Dabie orogenic belt involved several stages of high pressure (HP)-ultra high pressure (UHP) metamorphism. The new discovery of UHP metamorphic rocks in the North Qinling (NQ) terrane can provide valuable information on this process. However, no precise age for the UHP metamorphism in the NQ terrane has been documented yet, and thus hinders deciphering of the evolution of the whole Qinling-Dabie-Sulu orogenic belt. This article reports an integrated study of U–Pb age, trace element, mineral inclusion and Hf isotope composition of zircon from an eclogite, a quartz vein and a schist in the NQ terrane. The zircon cores in the eclogite are characterized by oscillatory zoning or weak zoning, high Th/U and 176Lu/177Hf ratios, pronounced Eu anomalies and steep heavy rare earth element (HREE) patterns. The zircon cores yield an age of 796 ± 13 Ma, which is taken as the protolith formation age of the eclogite, and implies that the NQ terrane may belong to the SCB before it collided with the NCB. The ɛHf(t) values vary from −11.3 to 3.2 and corresponding two-stage Hf model ages are 2402 to 1495 Ma, suggesting the protolith was derived from an enriched mantle. In contrast, the metamorphic zircon rims show no zoning or weak zoning, very low Th/U and 176Lu/177Hf ratios, insignificant Eu anomalies and flat HREE patterns. They contain inclusions of garnet, omphacite and phengite, suggesting that the metamorphic zircon formed under eclogite facies metamorphic conditions, and their weighted mean 206Pb/238U age of 485.9 ± 3.8 Ma was interpreted to date the timing of the eclogite facies metamorphism. Zircon in the quartz vein is characterized by perfect euhedral habit, some oscillatory zoning, low Th/U ratios and variable HREE contents. It yields a weighted mean U–Pb age of 480.5 ± 2.5 Ma, which registers the age of fluid activity during exhumation. Zircon in the schist is mostly detrital and U–Pb age peaks at c. 1950 to 1850, 1800 to 1600, 1560 to 1460 and 1400 to 1260 Ma with an oldest grain of 2517 Ma, also suggesting that the NQ terrane may have an affinity to the SCB. Accordingly, the amalgamation between the SCB and the NCB is a multistage process that spans c. 300 Myr, which includes: the formation of the Erlangping intra-oceanic arc zone onto the NCB before c. 490 Ma, the c. 485 Ma crustal subduction and UHP metamorphism of the NQ terrane, the c. 430 Ma arc-continent collision and granulite facies metamorphism, the 420 to 400 Ma extension and rifting in relation to the opening of the Palaeo-Tethyan ocean, the c. 310 Ma HP eclogite facies metamorphism of oceanic crust and associated continental basement, and the final 250 to 220 Ma continental subduction and HP–UHP metamorphism.

Single-step synthesis and characterization of single-walled carbon nanohorns hybridized with Pd nanoparticles using N 2 gas-injected arc-in-water method

Single-walled carbon nanohorns (SWCNHs) hybridized with palladium (Pd) nanoparticles were synthesized by a single-step gas-injected arc-in-water method (GI-AIW) with a Pd wire inserted inside the anode hole. In the arc zone, carbon and Pd were vaporized simultaneously, leading to the formation of hybrid material of SWCNHs and Pd nanoparticles due to effective quenching. Based on TEM and CO chemisorption analyses, Pd nanoparticles were found to be embedded inside SWCNH aggregates. The size of Pd nanoparticles, determined by X-ray diffraction, was in the range of 3–6 nm when Pd wires with diameters of 0.1 and 0.3 mm were used. Using a Pd wire with a diameter larger than 0.5 mm results in larger Pd nanoparticles which tend to be exposed to the outer surface of the hybrid material. According to thermogravimetric analyses, the weight fraction of Pd nanoparticles is increased by increasing the Pd wire diameter although the yield of Pd nanoparticles decreased. SWCNHs hybridized with dispersed Pd nanoparticles, synthesized with 0.1 mm Pd wire, exhibited strong anti-oxidation resistance with a highly graphitic structure.

Evaluación de la resistencia mecánica de la unión soldada en la aleación de aluminio 6261

Se estudia la relación entre la temperatura pico, la microdureza, la microestructura, la ubicación de la falla y la resistencia en la zona térmicamente afectada de juntas soldadas por el proceso GMAW en aleación de aluminio 6261-T6 y T5. Se logró una buena correlación de los resultados con la distribución de los precipitados reportados en la literatura. Los perfiles de temperatura pico se compararon con los perfiles de microdureza. Se encontró un punto de mínima microdureza en la ZAC con un valor menor del 70% del metal base, donde también se presentó la falla en tensión, correspondiendo a una temperatura de 380°C

Influence of Electrode Argon-Hydrogen Co-Injection on Carbon Content in a Alternating Current Ladle Furnace

About 80 kg low carbon steel was refined in a multifunction ladle furnace (AC-LF) with alternating current supplying. The argon-hydrogen gas mixtures were injected into the electric arc zone through one hollow graphite electrode. The flow rate of the gas mixtures was 3 m3/h. Results of the tests and the calculation based on the plasma local equilibrium thermodynamics and metallurgical thermodynamics theories show that, when the argon-hydrogen gas mixtures are injected into the electric arc zone, the carburetion rate is 4.7×10-6 per minute for the steel heated by conventional AC-LF, which is 1.26 and 1.51 times of the heats blown 90%Ar-10%H2 and 80%Ar-20%H2, respectively. The carburetion rate is reduced by 20% at least when argon-hydrogen gas mixtures are blown into the furnace. When H2 content in the gas mixtures reached 20% from 0, the decarburization rate increased but the total reaction rate decreases by 1.59×10-6 per minute.

A long-term earthquake forecast for the Kuril-Kamchatka arc for the period from September 2010 to August 2015 and the reliability of previous forecasts, as well as their applications

We describe results from the ongoing 2008–2010 work on long-term earthquake prediction for the Kuril-Kamchatka arc based on the patterns of seismic gaps and the seismic cycle. We provide a forecast for the next 5 years, September 2010 to August 2015, specified for all segments of the earthquake-generating Kuril-Kamchatka arc zone. For 20 segments we predict the phases of the seismic cycle, the normalized rate of small earthquakes (A10), the magnitudes of moderate earthquakes to be expected with probabilities of 0.8, 0.5, and 0.15, the maximum possible magnitudes, and the probabilities of great (M ≥ 7.7) earthquakes. It is shown that the forecast given for the previous 5 years, from September 2005 to September 2010, was found to be accurate. We report the measures that were taken for seismic safety and retrofitting based on these forecasts.

Provenance analysis of upper Cretaceous strata in the Tethys Himalaya, southern Tibet: Implications for timing of India–Asia collision

The provenance of upper Cretaceous strata in the Tethys Himalaya provides critical constraints on the closure time of the Neo-Tethys Ocean and the initial India–Asia collision. This paper reports detailed petrographic studies, in-situ detrital zircon U–Pb ages and Lu–Hf isotopic analyses, whole rock Nd-isotopes, and Cr–spinel electronic microprobe data from upper Cretaceous clastic sedimentary rocks of the Tethys Himalaya near Gyangze, southern Tibet. The Berriasian–Coniacian Jiabula Formation consists of black mudstone, chert and minor quartz arenite, and is dominated by detrital zircons with Archean–Cambrian U–Pb ages which were most likely derived from the Indian continent. Overlying conformably is the Santonian–Maastrichtian Chuangde Formation, which consists of red shale, limestone and chert. The Chuangde Formation is in turn overlain by the late Maastrichtian–late Paleocene Zongzhuo Formation, which is composed of black mudstone and lithic sandstone enclosing various olistoliths of sandstone, limestone and chert. The Rilang conglomerate is a lens which is located within the upper part of the Zongzhuo Formation and consists of an upward-thinning and fining succession of volcanic conglomerate, sandstone and black mudstone. The Zongzhuo Formation and the Rilang conglomerate record an abrupt influx of Cretaceous zircon grains with juvenile Hf isotopic compositions, arc-related Cr–spinels and positive εNd (0) sediments, suggesting an arc and suture-zone provenance. The change in provenance of upper Cretaceous strata from the southern Indian continent to a northern arc and suture zone is attributed to either (1) initial collision between the Indian plate and Lhasa terrane, or (2) initial collision between the Indian plate and an intra-oceanic arc. We prefer option (1) that the initiation of India–Asia collision occurred during Maastrichtian (~ 70–65 Ma).

Environmental geochemistry of recent volcanic ashes from the Southern Andes

Environmental contextExplosive volcanic eruptions may have significant environmental repercussions for many Earth system cycles, particularly the water cycle. We investigate the potential contribution to local geochemical fluxes through water of five historical eruptions that occurred over a 20-year period in the Southern Andes. In all five cases, the major potentially toxic trace elements were arsenic, copper, fluoride, molybdenum, nickel, lead and zinc. AbstractThe potential contribution to the local geochemical balance of five historical eruptions that occurred during the 20th Century has been investigated in the Southern Volcanic Zone (SVZ) of the Andean volcanic arc of South America (Lonquimay 1988, Hudson 1991, Copahue 2000, Llaima 2008, Chaitén 2008). These ashes were characterised by SEMEDX and XRD, and their potential released geochemical fluxes were examined using water and nitric acid batch leaching tests. Leachates were analysed by ICP-OES, ICP-MS and ISE. The major contents removed correspond to SO42– and Cl–. The potential toxic trace element (PTTE) content was highly variable among the ash samples following this order: Chaitén > Copahue > Hudson > Llaima > Lonquimay. The trace elements with significant load in water batch leaching tests include Fe > F > B > P > Zn > As > Mn > Sr > Ba > Ti > Cu > Ni > Li > Rb > Co > Cr > Cd > Sb. Some of these elements (As, Cu, F, Mo, Ni, Pb and Zn) are included in the drinking water guidelines due to their potential toxicity and must be especially monitored in the environmental assessment of these ashfall deposits.

Early–Middle Ordovician nappe tectonics of the junction between the Kokchetav HP-UHP metamorphic belt and the Stepnyak paleoisland arc ( northern Kazakhstan)

The North Kokchetav tectonic zone is located between the Kokchetav HP-UHP metamorphic belt and the Stepnyak zone of Ordovician island arc and oceanic complexes. The Kokchetav zone is a collage of nappes (thrust sheets) that consist of basement gneiss and sedimentary rocks of the Kokchetav microcontinent, granite gneiss, mica schists with eclogite blocks, the Shchuch’e ophiolite, Middle Proterozoic felsic volcanics, and Arenigian siliceous-terrigenous sediments with olistostromes. The latter are of gravity-sliding origin and their clastic material includes quartz-muscovite and quartz-garnet-muscovite schists, gneiss, dolomite, and amphibolite. The sheet boundaries are marked by mylonite and Early Ordovician mica schists ( 40Ar/ 39Ar ages of syntectonic muscovite are 489–469 Ma). The North Kokchetav collage of compositionally diverse thrust sheets can be interpreted as a collisional zone. According to geological evidence, tectonic activity in the zone lasted as late as the Middle Ordovician. Syncollisional thrusting in the North Kokchetav zone was coeval with the latest dynamic metamorphic event in the Kokchetav belt. All events of retrograde metamorphism and exhumation of HP and UHP rocks in the belt have Cambrian ages, i.e., the rocks had been exhumed prior to the Early–Middle Ordovician collisions and the related orogeny.

Comparison of Friction Stir and Gas Tungsten Arc Weldments of Modified 12 wt.% Cr Ferritic Stainless Steel

AbstractThis paper presents the comparative evaluation of microstructural features and mechanical properties of a friction stir welded (solid‐state) and gas tungsten arc welded (fusion weld) 409 M grade ferritic stainless steel joints. Optical microscopy, microhardness, transverse tensile and impact tests were performed. The coarser ferrite grains in the base material are changed to very fine grains consisting of a duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. On the other hand, grain growth was observed in the fusion zone as well as heat affected zone of the gas tungsten arc welded joint resulting in deterioration of mechanical properties.