Single Bead Weld Research Articles

Physical simulation of low temperature phase separation during multipass welding of super duplex stainless steel

This study aimed to investigate the degree of low-temperature phase separations and 475 °C -embrittlement in physically simulated multipass super duplex stainless steel (SDSS) welds. A single bead weld was produced using gas metal arc welding and multiple thermal cycles with different peak temperatures were applied using a Gleeble physical simulator with fixed and moving jaws to simulate the influence of constrained designs, to mimic the welding of thick SDSS components. The samples were studied using atom probe tomography and the results were correlated with toughness and ferrite microhardness. The results showed that the microhardness of the ferrite in the constrained simulated multipass reheated weld increased from 304 HV to 374 HV after 5 min aging at 475 °C. The amplitude of the Cr concentration of the same sample, showing the level of Fe-Cr phase separation, increased from 1.025 to 1.045 after 5 min aging at 475 °C. Despite the clear development of phase separation in the ferrite, the toughness did not drop. It can be concluded that reheated SDSS welds are not susceptible to 475 °C -embrittlement during short fabrication times of up to 5 min for the austenite level of 50%.

Detection of Defects on Single-Bead Welding by Machine Learning Methods

This study classified the defects that were encountered on single-bead welding, which was made by MIG/MAG welding machines in Hürsan Press company. 2250 images were taken on weldings that were made by five different welders. This study classified defects into three classes as good welding, porosity, and discontinuities. The images in the dataset, which have three classes, were classified by two stages. In the first stage, the texture features of the welding area were extracted. In the second stage, Artificial Neural Networks (ANN) method classified the extracted features. Sensitivity, specificity, accuracy, precision, and F-score metrics were used to measure the classification performance. 1500 images were used to train the system and training and validation performances were obtained as 94.03% and 94.19%, respectively. 750 images were used to test the performance of the proposed method and the test performance was obtained as 94.31%. The proposed method detected a defect on single-bead welding in 0.98 seconds.

Residual stress measurement round robin on an electron beam welded joint between austenitic stainless steel 316L(N) and ferritic steel P91

This paper is a research output of DMW-Creep project which is part of a national UK programme through the RCUK Energy programme and India's Department of Atomic Energy. The research is focussed on understanding the characteristics of welded joints between austenitic stainless steel and ferritic steel that are widely used in many nuclear power generating plants and petrochemical industries as well as conventional coal and gas-fired power systems. The members of the DMW-Creep project have undertaken parallel round robin activities measuring the residual stresses generated by a dissimilar metal weld (DMW) between AISI 316L(N) austenitic stainless steel and P91 ferritic-martensitic steel. Electron beam (EB) welding was employed to produce a single bead weld on a plate specimen and an additional smoothing pass (known cosmetic pass) was then introduced using a defocused beam. The welding residual stresses have been measured by five experimental methods including (I) neutron diffraction (ND), (II) X-Ray diffraction (XRD), (III) contour method (CM), (IV) incremental deep hole drilling (iDHD) and (V) incremental centre hole drilling (iCHD). The round robin measurements of weld residual stresses are compared in order to characterise surface and sub-surface residual stresses comprehensively.

Optimization of a multi-channel parabolic guide for the material science diffractometer STRESS-SPEC at FRM II

Neutron strain diffractometers usually use slits to define a gauge volume within engineering samples. In this study a multi-channel parabolic neutron guide was developed to be used instead of the primary slit to minimise the loss of intensity and vertical definition of the gauge volume when using slits placed far away from the measurement position in bulky components. The major advantage of a focusing guide is that the maximum flux is not at the exit of the guide as for a slit system but at the focal point relatively far away from the exit of the guide. Monte Carlo simulations were used to optimise the multi-channel parabolic guide with respect to the instrument characteristics of the diffractometer STRESS-SPEC at the FRM II neutron source. Also the simulations are in excellent agreement with experimental measurements using the optimised multi-channel parabolic guide at the neutron diffractometer. In addition the performance of the guide was compared to the standard slit setup at STRESS-SPEC using a single bead weld sample used in earlier round robin tests for residual strain measurements.

Residual Stress Measurement by Neutron Diffraction in a Single Bead on Plate Weld - Influence of Instrument and Measurement Settings on the Scatter of the Results

Residual stress measurements on a single bead weld on a steel plate had been performed at the High Flux Reactor of the Joint Research Centre in 2003. For these measurements a relatively old diffractometer had been used. The results obtained were characterized by significant scatter of the data, and the measurement quality suffered from the short movement ranges of the specimen positioning table as well. In 2008, a second, nominally identical, specimen from the same activity was investigated on a second diffractometer, which allowed the repetition of the residual stress measurements using different measurement settings. The present paper compares the old and the new measurement results, with a view to assessing the impact of the instrumental settings on their quality. It has been found that the overall stress distributions from the 2003 and the 2008 measurements were in fact very similar. Nevertheless, the new settings used, such as in-situ specimen rocking, extended measurement duration, increased density of measurement positions and spatial resolution among others, have been found to have considerable impact on the real and on the apparent scatter of the experimental results showing that the presented methodologies can be used for improvement of neutron diffraction measurements.

NET TG1: Residual stress assessment by neutron diffraction and finite element modeling on a single bead weld on a steel plate

In the context of the efforts of Task Group 1 (TG1) of the European Network on Neutron Techniques Standardization for Structural Integrity (NET), the Joint Research Centre (JRC) participated in the experimental round robin campaign for residual stress analysis on a single weld bead on a steel plate. In parallel, the University of Patras (UP), in collaboration with the JRC, contributed to the corresponding numerical analysis round robin exercise. Neutron diffraction measurements were performed on a specimen, designated as A12, using the residual stress diffractometer at beam tube HB5 at the High Flux Reactor (HFR) in Petten, The Netherlands. Several line scans of strains and stresses were performed in accordance with an experimental protocol devised for this exercise and their results are presented in this paper. Two scans were made along the weld longitudinal direction beneath the upper surface of the plate, three were made in the weld transverse direction, and three through the thickness of the plate. The measured residual stresses are presented in detail. The measurements confirm that the stress distribution around this single weld bead on a plate is intrinsically 3-dimensional. The procedure followed by UP in the numerical assessment of the problem is presented in detail. The numerical results are presented in direct comparison to the JRC measurement data.

NET TG1: Residual stress analysis on a single bead weld on a steel plate using neutron diffraction at the new engineering instrument ‘STRESS-SPEC’

Non-destructive analysis of phase specific residual stresses and textures is only possible by diffraction methods. The new neutron diffractometer STRESS-SPEC was installed at FRM-II in Munich, Germany, for this purpose. It is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The results of measurements on a single bead on plate weld within the framework of the European Network on Neutron Techniques Standardisation for Structural Integrity (NET) are presented here, in order to demonstrate the reliability and accuracy of the instrument by comparing previous results from other neutron diffraction facilities by using a Bayesian statistical approach.

Predicción numérica de la microestructura de la zona afectada por el calor (ZAC) durante el proceso de soldeo SMAW en el acero al Cr-Mo-V

Cracking associated with welds operating in high temperatures and high pressure, is a problem of consideration. The performance of welded joints, both during fabrication and operation depends strictly upon the microstructure of the heat-affected zone (HAZ), which, in a steel of a given composition, is a function of welding conditions and joint geometry. The methodology of prediction of the dimensions of the zones containing different sizes in the HAZ grain of a single-bead weld of 1.25Cr-1Mo-0.25V steel using SMAW deposition process is described. The standard heat-flow equations have been used to determine weld thermal cycles in conjunction with basic metallurgy including phases-transformation, grain growth kinetics and empirical equations to describe the effects of welding variables on weld bead dimensions.

高マンガン鋼のガスシールドアーク溶接(第1報)

A series of study was carried out to realize automatic welding of austenitic manganese steel rail which had been conventionally performed by manual arc welding process.Using austenitic manganese steel as base metal, 16 Mn-16 Cr wire as electrode, and mainly CO2, A and N2 singly or mixed as shielding gas, build up welding was performed. Further, with the welding conditions varied, single bead welding was made. The mechanical properties. chemical composition and microstructure of weld metal were investigated on these welds.For any shielding gas used, the mechanical properties of deposited metal are satisfactory. Impact value is particularly good in the case of A-N2 gas;This is presumably partly due to relatively small contents of non-metallic inclusions. Among the welding defects, hardly any crack occurs, but blow holes are observed more often in N2-CO2 gas and in A-O2 gas containing considerable quantities of O2.As for the chemical composition of deposited metal, with an increased CO2 or O2 content of shielding gas the consumption of manganese in welding increases and as the result the manganese content of deposited metal decreases (transfer efficiency of manganese is about 80% for single use of CO2 gas). The decrease of chromium content is small but it shows the same tendency as manganese content. Nickel content hardly depends on the composition of shielding gas. Meanwhile, if the N2 content of shielding gas is large, the N content of deposited metal also grows large (0.49% for 20% CO2-80% N2). The deposition efficiency is high when the shielding gas is rich in A; and it is low when the gas is rich in CO2, N2 and O2.Under high arc voltage and under low welding current, the weld metal surface is liable to develop blow holes (pits), accompanied by a drop in the deposition efficiency and an increase in spattering, if the shielding gas is rich in CO2. In this case the manganese content of weld metal is lower than in others.If the welding is performed in appropriate shielding gas under appropriate welding conditions, use of 16 Mn-16 Cr welding wire will assure weld metal having high mechanical properties and almost free from any welding defects.

マルテンサイト型13%クロムステンレス鋼の熔接組織および急熱急冷による組織の挙動

Metallographic studies have been performed on the structures of weld metal and the heat-affected zone of 13% chromium martensitic stainless steel. The heat-affected zone was obtained by single bead welding, in which a single bead 10∼12 cm in length was placed on a 13% chromium stainless steel plate of 200×75×20 mm3. The isothermal austenitization diagrams (T-T-A diagram, Time-Temperature-Austenitization diagram) were determined for two specimens differently pre-heat treated. The specimen was heated in a salt bath, followed by rapid quenching in water, and then the T-T-A diagram was obtained from changes in hardness (Hv) and in matrix structure.The results may be summarized as follows: (1) In the specimen heated at 1050°C for 30 min and then oil quenched, the heat-affected zone is shaply divided into two parts; one is heated over the Ac1 point and the other is tempered at a lower temperature than the Ac1 point. This is characterized by hardness. (2) The hardness of the heat-affected zone approaches that of base metal by a short-time annealing at 700°C, but the chromium carbide is aggregated in the heat-affected zone. (3) By rapid heating and cooling, the 13% chromium stainless steels with varying carbon contents show a different hardness and an almost identical Ac1 point. The hardness curve exhibits a peak at a maximum heating temperature. (4) From the T-T-A diagrams of the specimens differently treated, it is clear that, in the rapid heating and quenching, a very short holding time is sufficient for hardening when the specimen is heated up to a specified temperature. (5) As to the different pre-heat treatment of the 13% chromium martensitic stainless steel, the austenitization time of the specimen that received only solid solution treatment is shorter than that of the annealed specimen.

被覆アーク溶接ならびにサブマージアーク溶接における冷却過程について

Cooling time, which has an immediate connection with root cracking in a high strength steel weld with its strength level of 60 kg/mm2 and below, from 800 to 300°C was measured for various welding conditions in the cases of welding with coated electrodes and submerged are welding, respectively. Experimental formulas for the estimation of the cooling time were obtained and these nomographs were shown.The main conclusions are summarized as follows:(1) Dimensions of heat flow in a weld were varied by any particular combination of welding condition, plate thickness and the shape of penetration.For the cooling process with two-or three-dimensional heat conduction in a weld, a relation between temperature T on a weld and cooling rate (dT/dS) as the temperature T is shown as follows :(dT/ds)T∞(T-T0)nwhere T0: initial temperature of platen: the exponent which is varied with dimensions of heat flow in a weldHence, the dimensions of heat flow was clearly shown as the gradient of a line in a logarithmic groph of (dT/dS) VS. (-T-T0).(2) In a finite plate, it was able to determine a minimum size of specimen, which is equivalent to an infinite plate for the given weld heat input, according to the temperature range of a weld thermal cycle to be considered. When they consider the cooling process to 500 and 300°C, the Value of T in the following formula should be chosen as, T*≤320 for 500°C and T*≤210 for. 300°C, respectively.Where T*=0.24ηJl/mc+T0(°C)η: thermal efficiency of arc, j: heat input (Joule/cm)l: bead length (cm), m: weight of plate (gr) andc: specific heat (Cal/gr.°C)(3) If thickness (t), initial temperature (T0) of plates and weld heat imput (J) are given in the case of single bead-welding, cooling time (s) from 800 to 300°C at manual arc welding and submerged arc welding can be estimated with the following experimental formula or nomographs by the present authors;S=K·Jn/(40-T0)2{1+2/πtan-1(t-t0/a)}

熱影響部の脆化について(第2報)

In this experiment the authors investigated the true reasons causing the brittleness in the range of heat-affected zone by observing Izod impact test, hardness measurement and Xray diffraction method in the single bead weld, and compared the states of the brittleness about both Killed and Rimmed steel. As the result it was recognized that the main factor to cause brittleness is the precipitation of super-saturated carbon in ferrite grain, and that state is used to caused by the rapid cooling from the neighbour-of A1 transformation point, and the most brittle part of Killed steel seems to somewhat above A1, Rimmed steel somewhat below A1, i. e. the mechanisms causing brittleness are somewhat different. The brittleness of Rimmed steel is more predominent than Killed steel.