The impact of weld heat input on the mechanical characteristics of this steel was investigated in this study. The weld sample was an ASTM A304 grade A Flat Bar with a thickness of 5.00 millimetres. ...With the use of a data logger, a K-type thermocouple was installed in the drilled holes to measure the temperature fields at each of the places throughout the welding operation. The welding sample was created by varying three process parameters in the MIG welding process. Welding current, weld passes, and point of interest thermocouple position away from the weld centreline are the parameters. The experiment was designed using Taguchi's L9 orthogonal array to limit the number of experimental runs (DOE). To study the influence of weld heat input, the samples were subjected to mechanical and microstructure testing. The hardness test revealed that when the weld pass on the weld zone, HAZ, and base metal increases, the hardness value falls. The tensile test finding indicated that the tensile strength of samples 80A and 100A rises as the weld pass increases, however sample 60A decreases as the weld pass increases. The impact resistance increased when the weld pass was increased, according to the findings of the impact tests. The distance away from the weld centreline of the region subjected to a certain peak temperature increases as weld heat input increases, according to the weld thermal cycle. The value of the temperature fields increases dramatically as the heat source passes through the specific cross-section, where thermocouples are positioned. Later on, the temperature begins to drop at a slower rate. It's also obvious that when the distance between the measurement point and the weld centreline grows, the temperature drops.
The influences of the applied radial bending stresses on the corrosion behaviour of dissimilar weldments of two types of martensitic heat-resistant steel (F92/Co3W2) are investigated with NaCl–Na2SO4 ...deposited salts at 620 °C and 24 h employing a four-point bending jig. The applied external stress exhibits no obvious influence on corrosion products, which mainly consist of Fe2O3, Fe3O4, and FeCr2O4. However, the stress tends to aggravate the corrosion degree, and the weldments with stress addition yield more mass gain and greater corrosion scale thickness. Such phenomenon is more serious in the parent F92, implying F92 is more sensitive to the corrosion environment with stress. The corrosion scale of weldments without stress shows typical double-layer structure: outer Fe–O layer and inner Fe–Cr–O layer, while the weldments with bending stresses show interesting multi-layers (10 or more layers) with Fe-oxide and Fe, Cr-oxide alternately appearing. The mechanism for hot corrosion behaviour and the influence of hot corrosion on the local mechanical properties of different welding zones with and without stresses are further discussed.
•Hot corrosion behavior of F92/Co3W2 dissimilar weldments.•Corrosion layer changes from double-layer to multi-layer alternation after imposed stress.•Effect of stress on Co3W2 base material was weaker than that on F92.•Stress degrades microregions mechanical properties from nanoindentation results.
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In order to reduce the brittle Laves phase in nickel-alloy overlay welding from the outset, a numerical model has been established to predict Laves phase formation in ultrasonic ...field, by considering the molten pool as a liquid electric conductor which is composed of innumerable “electric wires”. The model predictions were verified experimentally. The prepared weldments were characterised using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and electron probe microanalysing (EPMA). Both simulation and experiments showed that the niobium distribution became more homogenous in nickel matrix and the volume fraction of Laves phase was decreased by over 90%, when 30kHz ultrasound was applied. It has been revealed that the high-frequency current, passing through the tiny “electric wires”, will generate ultrasonic field right inside the molten pool. The inside ultrasonic Ampère’s force is the predominant factor that directly makes the liquid metal vibrated at high frequency. This effect alleviates niobium segregation and makes the nickel dendrites more branching and tortuous in overlay weld, which reduces the amount of Laves phase.
•A special geometry of cylindrical notched tensile specimen is proposed for measurement of materials’ flow stress-strain curve.•The proposed method can obtain material’s flow stress-strain curve ...directly without performing the well-known Bridgman correction.•The proposed method can be applied to obtain the flow stress-strain curve of each individual material zone of a weldment.
Structural integrity assessment of weldments requires the input of flow stress-strain curve of each individual material zone. To cope with these challenges, a cylindrical cross weld tensile specimen with a notch located either in the weld metal, base metal or possibly heat affected zone has been previously developed by the authors to determine the true stress-strain curve for the material zone of interest. The disadvantage of this notched tensile testing method as well as the standard tensile testing method using a smooth specimen, is that the well-known Bridgman correction still has to be applied in order to obtain material’s equivalent or flow stress-strain curves. In this study, tensile specimens with various notch geometries have been scrutinized and a ‘magic’ specimen with a special notch geometry has been identified. By using this special notched tensile specimen, material’s flow stress-strain curve can be directly calculated from the recorded load versus diameter reduction curve and no Bridgman correction is needed. The method is very accurate for power-law hardening materials and becomes less accurate for materials with significant Lüders plateau in the initial yield region.
•A correction function is proposed to determine material's equivalent stress-strain curve with any axisymmetric notched tensile specimens.•No Bridgman correction is needed.•The proposed correction ...function can be applied to perfectly plastic materials.•The proposed correction function can be used to measure the equivalent stress-strain curve of each individual material zone in a weldment.
Large deformation analyses of problems such as plastic forming, ductile fracture with finite element method need a full range of material's equivalent stress-strain curve or flow stress-strain curve. The equivalent stress-strain curve determined from the smooth round bar specimen should be corrected after diffuse necking, since tri-axial stress state occurs in the neck. The well-known Bridgman correction method is a candidate, however, it is not accurate as the strain increases. Furthermore, it is impossible to measure the equivalent stress-strain curve of each individual material zone in a weldment with cross weld tensile tests. To cope with these challenges, a correction function and an associated test procedure are proposed in this study. With the proposed procedure, the true stress-strain curve from any axisymmetric notched tensile specimen can be converted to the material's equivalent stress-strain curve accurately and no Bridgman correction is needed. The proposed procedure can be applied to both perfectly plastic and strain hardening materials. The equivalent stress-strain curve of each individual material zone in a weldment can also be measured with the proposed procedure.
Display omitted Assumed material’s equivalent stress-strain curve was used for numerical tensile tests with axisymmetric notched tensile specimens. By observing the true stress-strain curves from the tests, a correction function was proposed, with which true stress-strain curve from an axisymmetric notched specimen can be corrected back to material’s equivalent stress-strain. Material in red can be undermatched, overmatched or evenmatched with the base material in yellow.
The reinforcement particles present in a metal matrix is a key factor to improve the strength of weld joints. In the present work, in-situ Titanium diboride (TiB2) and ex-situ Boron carbide (B4C) ...particles were separately reinforced with Al 4043 matrix by ultrasonic cavitation assisted stir casting process. The fabricated composites were cut into composite filler rods to the required size and shape from the reinforced nanocomposites using wire-cut EDM. The TIG welding process was performed on Al 6061 plates using Al 4043 composite filler rod under optimized welding conditions. The tensile strength and microhardness of both type of particle reinforced weldment were compared. Addition of 2 wt% of TiB2 and 2 wt% B4C particles separately produced 59% and 41% higher microhardness compared to base metal weldment respectively. An increase in tensile strength of 201% and 128% respectively was observed when compared to base metal weldment. The High Resolution Transmission Electron Microscopy (HRTEM) and Field Emission Scanning Electron Microscopy (FESEM) were used to characterize the microstructure of B4C and TiB2 reinforced weldments. The re-melting behaviour of TIG welded joints was also investigated for the formulated nanocomposites.
Beside their high mechanical strength, duplex stainless steels are a suitable choice in highly corrosive environments. These types of steels are used in steel bridges more and more frequently exposed ...to low temperatures and fatigue loads. However, for low temperature applications, it must be guaranteed that brittle fracture is avoided since duplex stainless steel shows a toughness-temperature relationship similar to that of carbon steel. For this reason, in the frame of the German national FOSTA research project “P 1390”, comprehensive investigations have been started into the material selection of duplex stainless steel to avoid brittle fracture considering the fracture mechanic based background of EN 1993-1-10. For this purpose, Charpy-V impact tests and fracture toughness tests have been systematically carried out for various duplex stainless steels in order to create the basis for the development of toughness requirements for new duplex classes. The validity of the already existing Master Curve concept and the applicability of the transition temperature correlation for duplex stainless steels based on experimental fracture toughness and Charpy-V impact tests have been investigated. The aim of this contribution is to present first results of these investigations.
•A comprehensive investigation has been started and first results are presented based on Charpy-V impact and fracture toughness tests.•The highest nickel content in 1.4462 resulted in the lowest transition temperature followed by lean duplex 1.4662 and 1.4162.•The 3 °C temperature shift per percent of cold deformation in transition curve according to EN 1993-1-10 appears suitable for tested duplex steels.•Lower fracture toughness values are achieved for the specimens fabricated from thicker plates for both duplex 1.4462 and lean duplex 1.4162.•The results confirm that the transition temperature correlation in accordance with EN 1993-1-10 is valid for the studied duplex stainless steels.•The Master Curve approach presented in ASTM E1921 which was developed for carbon steel material is also valid for the tested duplex stainless steels.
•The corrosion of the weldment was studied by a coupled multi-ring form array.•The localized corrosion was caused by unlike compactness of the corrosion product.•The risk caused by the non-uniform ...circumferential corrosion was evaluated.
A novel corrosion system defined as coupled multi-ring form sensor array (CMRSA) was designed and fabricated to study the non-uniform corrosion performances of pipe weldment immersed in the CO2 saturated solution of different pH. The macro-cell currents flowing among heterogeneous welding areas, i.e. base metal (BM), heat affected zone (HAZ), and welding metal (WM), and the micro-cell corrosion inside of each welding area were explored. In conjunction with electrochemical measurements and surface characterization, it is found that all the welding areas would suffer active corrosion in the pH = 4 solution. While the HAZ suffered severe localized corrosion due to the local defects of the corrosion product film in the pH = 6.6 solution. Based on the dispersion interval analysis of the localized corrosion rate, the pipeline corrosion risk caused by the non-uniformity of circumferential corrosion could be estimated.
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