Content In Welds Research Articles

Machine learning (deep learning) and visualization assisted ferrite content prediction in austenitic stainless steel

The ferrite content of 202 austenitic stainless-steel welds was predicted based on Machine Learning (ML), and the data set was analysed by manifold learning, feature engineering, and other methods. Multiple ML methods such as K-Nearest Neighbors (KNN), Support Vector Regression (SVR), Ensemble Learning (EL)、Multiple model Merging (MM), and Artificial Neural Network (ANN) performed algorithm model building and model tuning on the data set and evaluated the prediction performance of the model. The ML visualization and ML interpretation tools are used to demonstrate in detail the comparison of the prediction performance of ferrite number (FN) of various ML models and the effect of welding parameters on FN prediction. SVR, Gradient Boost, Xgboost, Catboost, Voting, Stacking, and MLP regression models demonstrate precision prediction and generalization. The coefficient of determination ( R 2 ) of the MLP model was 0.956 on the test set, which showed generalization and robustness. The visual data analysis and ML sample tracking methods are used to optimize the model. An ANN model with high prediction accuracy was proposed, and the R 2 of the test set was 0.972. This paper reveals the comprehensive application of ML-assisted material design and data sample visual tracking in the field of materials. • PyTorch deep learning framework to improve prediction accuracy. • Welding parameters are used to analyse welding parameters’ effect on ferrite content in welds. • 13 kinds of algorithms are selected for modelling and training. • Visualization tools explain the model prediction and feature importance. • The determination coefficient of the neural network model is 0.972.

A Study on Microstructure, Residual Stresses and Stress Corrosion Cracking of Repair Welding on 304 Stainless Steel: Part II-Effects of Reinforcement Height.

The repair reinforcement height is an important parameter of repair welding, which may have a great influence on structural integrity. In this paper, the effects of repair welding reinforcement height on the microstructure, microhardness, residual stresses and stress corrosion cracking (SCC) behavior of a 304 stainless steel-repaired joint were investigated by experimentation and simulation. With an increase of the repair weld reinforcement height, the δ ferrite content in weld and fusion zone is obviously reduced, and the ferrite shape is gradually changed from the skeleton to the worm shape. With the increase of repair welding reinforcement height, the microhardness and residual stresses decrease gradually. The tensile strength and elongation for higher repair weld reinforcement height are larger than those with lower repair weld reinforcement height. The higher the repair weld reinforcement height, the harder it is for SCC to occur. The repair welding in 304 stainless steel is recommended to be repaired no more than two times.

Uvođenje novog termina - Gustina feritnog broja (FND) za merenje feritnog broja zavarenih spojeva na tankim limovima od nerđajućeg čelika serije 300

Delta-ferrite content in austenitic steel welds is a crucial parameter to control, since a number of properties depend on this. A FeritScope® is commonly used commercially to measure the Ferrite Number (FN) of the welds which takes advantage of the fact that the retained delta-ferrite phase at room temperature is magnetic whereas austenite is not. However, the readings obtained from the FeritScope® are influenced by a number of constraints such as sheet thickness, weld clad thickness, etc. Although some correction factors have been introduced by the FeritScope® manufacturer to account for these influential conditions, some other geometrical features of the welds were also found to influence the measured FN; for example, despite being a major influential parameter, there is no factor introduced to correct the measurement inconsistencies associated with smaller weld crown widths. In addition, the results obtained on measuring the FN using a FeritScope® contradicted the trends that were expected considering the literature. This research introduces a term called Ferrite Number Density (FND) to represent the ferrite content, in which the measured FN is further proportioned with the cross-sectional area of the weld bead, thus eliminating its dependency on the geometrical size of the weld. It has been established from this research that for welds completed on sheets thicker than 2.4 mm, the FN can be directly used as an indicator of the ferrite content in the weld; however, for thinner sheets, the FND must be used to indicate the ferrite content of the weld, if a FeritScope® with an apportioned size probe is used, e.g. in this case an FGAB1.3-Fe probe. Use of FND eliminated all the contradictions obtained between experimental data and literature for thin sheet welds.

Effect of Single Oxide Fluxes on Morphology and Mechanical Properties of ATIG on 316 L Austenitic Stainless Steel Welds

Tungsten inert gas (TIG) is a wide common process used in fabrication due to its low cost equipment, high quality and accuracy welds but has low productivity related to the low penetration depth in single pass. A new perspective, the Activated Tungsten Inert Gas (ATIG), in which the same equipment as TIG is used, except that a thin layer of activated flux is deposited on a workpiece surface. In this work, eight kinds of oxides were tested on 316L austenitic stainless steel. Three levels of welding current were used to study the effect of different activating fluxes on weld bead geometry and mechanical properties. X-ray Photoelectron Spectroscopy (XPS) was used for the first and the second level energy for different ATIG welds to analyze the relationship between the weld shape and oxygen content in welds. The experimental results showed that the weld profile is related to the thermodynamic stability of selected oxides and in relation to the energy provided. ATIG with TiO2, SiO2, MnO2 oxides presented the deepest welds followed by Cr2O3, Fe2O3, and ZnO. Finally ZrO2, CaO oxides had no effect on the weld depth. The ATIG welded joint showed better tensile strength than TIG. The ATIG hardness measurements carried out showed also better if not the same as TIG weld except for the Silicon oxide weld. Results of the impact test showed that, except for the titanium dioxide TiO2 which has a good benefit, the weldment using the other oxide fluxes exhibits worse withstanding to sudden shock than TIG welding.

Heterogeneity Estimation of Low-Cycled Steel Weld Probes

The heterogeneity of manual arc welded samples of low-carbon steel St3sp meant for bridge construction to be used in Cameroon has been investigated. The chemical analysis of the material was carried out and the arc welding processes used, then the probes were subject to mechanical testing such as tensile test, low-cycle fatigue test, and micro hardness study. A total inclusion of weld defects in the specific welded sample and especially in the cyclic loading specimes has been discovered. Premature fracture was revealed below the plastic limit in some probes during the tension and low-cycle test. A micro structural examination and micro hardness measurements were done in order to determine what exactly could be the reason of this catastrophic failure. The structural analysis revealed the differences in mechanical properties conditioned by phase distribution and carbon content in weld, heat affected zone and base metal. To determine the heterogeneity in mechanical properties the elastic modulus distribution has been calculated due to relationship between the micro hardness and materials strength.

Effect of B2O3 containing fluxes on the microstructure and mechanical properties in submerged arc welded mild steel plates

This paper represents a study on the effect of B2O3 additions in fluxes on the microstructure and mechanical properties of the weld metal formed during Submerged Arc Welding of Mild Steel plates. Five fluxes with about 2.5, 5, 7.5, 10 and 12.5% B2O3 were used with a low carbon electrode. Welding process parameters were kept constant for all the conditions. The microstructure of weld metal for each flux consisted mainly of acicular ferrite, polygonal ferrite, grain boundary ferrites and equiaxed pearlite. It was noted that the Vicker's hardness value was a function of boron content and shows a mixed trend. Impact Energy and Tensile Strength were increased with the increase in boron content in welds this can be attributed to relation with the higher acicular ferrite percentage. However an optimum level of toughness and tensile strength was available with 7.5% and 5% of B2O3 respectively. A qualitative comparison has also be done with fresh flux by means of full metallography and mechanically.

A Brief Review on Methods for Diffusible Hydrogen Measurement in Welds

Hydrogen is obnoxious in high strength steels because it poses the risk of causing failure of material well below its yield strength. Failures triggered by hydrogen in weld joints are generally known as cold cracking or hydrogen assisted cracking. Cracks are not permitted in the welds and any undetected cracks can severely affect the performance of welded components and this is a serious safety concern. Hydrogen enters in steel weldment during welding and remains in the weld joint either as Diffusible Hydrogen or as residual hydrogen. While the residual hydrogen is immobile and has no role in cold cracking, diffusible hydrogen is free to diffuse at or near ambient temperatures. Diffusible hydrogen is accumulated in the regions of stress and produces a tensile stress field that expands the crystal lattice leading to microcracks. Therefore, diffusible hydrogen content in welds should be reduced to levels that do not cause cracking. This brings forth the need for measurement of diffusible hydrogen content in welds. However, the diffusivity of hydrogen in steel is very high and hydrogen starts effusing out even before the start of the measurement. Therefore, development of standard procedure for diffusible hydrogen measurement is difficult. In spite of the intricacy, several methods were developed in the past few decades for the measurement diffusible hydrogen because of the growing interests in the still not so clear role of hydrogen causing HAC and the increasing demand for batch production of welding consumables. This paper presents a brief yet a systematic review of the methods for diffusible hydrogen measurement in steel welds.

A Brief Review on Methods for Diffusible Hydrogen Measurement in Welds

Hydrogen is obnoxious in high strength steels because it poses the risk of causing failure of material well below its yield strength. Failures triggered by hydrogen in weld joints are generally known as cold cracking or hydrogen assisted cracking. Cracks are not permitted in the welds and any undetected cracks can severely affect the performance of welded components and this is a serious safety concern. Hydrogen enters in steel weldment during welding and remains in the weld joint either as Diffusible Hydrogen or as residual hydrogen. While the residual hydrogen is immobile and has no role in cold cracking, diffusible hydrogen is free to diffuse at or near ambient temperatures. Diffusible hydrogen is accumulated in the regions of stress and produces a tensile stress field that expands the crystal lattice leading to microcracks. Therefore, diffusible hydrogen content in welds should be reduced to levels that do not cause cracking. This brings forth the need for measurement of diffusible hydrogen content in welds. However, the diffusivity of hydrogen in steel is very high and hydrogen starts effusing out even before the start of the measurement. Therefore, development of standard procedure for diffusible hydrogen measurement is difficult. In spite of the intricacy, several methods were developed in the past few decades for the measurement diffusible hydrogen because of the growing interests in the still not so clear role of hydrogen causing HAC and the increasing demand for batch production of welding consumables. This paper presents a brief yet a systematic review of the methods for diffusible hydrogen measurement in steel welds.

Effect of preheat and post-heating on diffusible hydrogen content of welds

A systematic study was conducted to examine the effectiveness of pre- and post-heating to bring down the diffusible hydrogen (HD) content in the welds to levels that are unlikely to cause cracking. Specimens for HD measurement were prepared as per ISO standard 3690, and the measurement was carried out using standard mercury method and the newly developed hot extraction technique, which uses a hydrogen sensor. Results show that pre- and post-heating of the weld at lower temperatures are more effective than preheating alone at higher temperatures to bring down the HD content in the welds. Results also indicate that if the HD content of welding consumable is known, it is possible to choose the preheat and post-heat temperatures that will bring down the HD content remaining in the weld to sufficiently low levels so that danger of delayed cracking is minimum. Such information can help to optimise the pre- and post-heating requirements during weld fabrication, resulting in substantial energy savings.

Study on Weldablity of Dissimilar Steel between 16MnR and S31803

The weldablity of dissimilar steel between 16MnR and S31803 was analyzed and researched. By means of optical microscope (OM), the microstructure of the weld joint was investigated, which is welded by tungsten inert gas arc backing welding (GTAW) and manual arc filling welding (SMAW). The mechanical properties and corrosion resistance of the welded joint was also tested and studied. Results indicate that austenite and acicular ferrite distribute uniformly in the weld metal, which strengths the toughness and ductility of the joint. The austenite content in weld is higher than that in over-heated zone of S31803.The SMAW joint structure is coarsening than that of GTAW and has more austenite content. It is also observed that there are a decarburization layer and a carbon-enriched zone nearby the fusion line. And very small amounts of the third phase of harmful metal phase are found in the fusion zone of S31803 side. The welded joint shows the excellent mechanical properties and corrosion resistance. The impact toughness of the weld metal is higher than in HAZ of 16MnR side, and the impact toughness at GTAW side and in HAZ is superior to the SMAW side.

水素侵入による980MPa級溶接金属の低温割れ限界条件

Prevention of weld cracking is primely important for ensuring the integrity of steel construction. Especially, for high strength steel weld, which is susceptible to hydrogen cold cracking, it is important to clarify the critical condition for cracking in order for expanding use of high strength steel applications. In this study, critical conditions of hydrogen content and residual stress in the high strength steel weld with tensile strength level of over 980MPa were investigated. Cold cracking test was conducted using Y-grooved constraint weld joint by intentionally introducing hydrogen gas, and critical hydrogen content in the weld metal to cold cracking was determined. Cold cracking occurred in the weld metal from the root, bottom portion in the weld metal, when hydrogen content exceeds about 2ppm, and fracture surface was typical grain boundary fracture caused by hydrogen embrittlement. Then, residual stress distribution in the weld meal was measured by neutron diffraction technique. Same Y-grooved weld joint with no cold cracking was used for stress measurement. Neutron beam was filtered by 2mm×2mm slit to measure the residual stress in the small region. Reference sample without residual stress was prepared by introducing multiple saw cuts with small intervals in the same weld joint, and lattice spacing of stress free condition was first measured. Then, lattice spacing in the three different directions along the centerline of the weld metal were measured to calculate residual stress in the three directions. All portions in the weld metal center showed tensile residual stress. The root portion showed highest tensile stress of over 1110MPa in the transverse direction, which is the same as the crack opening direction. Therefore, it is considered that high level of tensile residual stress is the key factor for cold cracking. Hydrogen concentration to the root region by pressure stress was discussed in terms of local hydrogen content condition for cracking.

Effect of activating flux and shielding gas on microstructure of TIG welds in austenitic stainless steel

The aim of this research is to study the effect of an activating flux, two shielding gases (100%Ar and 50%Ar z 50%He) and a range of weld currents on the microstructure of autogeneous A-TIG welds on an austenitic stainless steel. Metallographic, Mössbauer, X-ray diffraction and magnetic permeability methods were used in the study to evaluate ferrite content in the welds. The increase in welding current coarsened the microstructure and increased the retained ferrite content in welds made with and without flux. The activating flux increases the ferrite content and changes the distribution of ferrite in the welds. The influence of flux on ferrite content is less significant in Ar/He than in Ar shield welds. The process of filling steel samples, currently used in the Mössbauer method, drastically changes the microstructure of the parent and melted austenitic stainless steels.

Influence of Microadditions on the Resistance to Brittle Fracture of Welded Joints of Oil Pipelines

On the basis of the results of testing of influence of modifying microadditions (Ce, Y, Ba, Ca, and Zr) on the characteristics of the resistance to brittle fracture of a weld metal of welded joints of oil-and-gas pipelines, their optimal content in welds is determined. We propose mathematical models for numerical prediction of the crack resistance of welded joints.

Comparative study of methods for determining the diffusible hydrogen content in welds

Summary This paper presents a comparative study on the glycerine, mercury and gas chromatography methods for determining the diffusible hydrogen content in welded joints. The effects of the variables of time and temperature for hydrogen collection are also considered. AWS type E9018‐M electrodes were wetted, then dried at different temperatures for different times in order to obtain a wide range of diffusible hydrogen contents. The results showed that the collection time may be reduced when the sampling temperature is increased. The gas chromatography and mercury methods give similar results, much higher than those obtained with the glycerine method, without the need to use liquid nitrogen for preparation of test specimens. The gas chromatography method presents less scatter of results and a shorter sample collection time due to the increased sampling temperature. The use of equations found in the literature for comparison of the results obtained by the different methods is also discussed.

Improvement of notch toughness and soundness in longitudinal seam weld of line pipe.

Multiple-electrode submerged arc welding process with three or four electrode is used for the production of longitudinally welded pipe. Increased welding speed is limited by the properties of flux against weld defects such as undercutting and slag inclusion and the toughness of weld metal deteriorated by impurity gas contamination.A flux with a solidification temperature of 950 to 1050°C and with a viscosity of 2.5 to 4.5 poise at 1400°C can minimize slag inclusion and undercutting. Welding of heavy wall thickness UOE pipes with a heat input above 100kJ/cm requires a flux with a high melting point and high viscosity.In order to obtain good notch toughness of weld metal at low temperature service, it is necessary to control the nitrogen content foreffective utilization of titanium and boron in weld metal. Optimum range of titanium to get high notch toughness is shifted by nitrogen content in weld metal.HAZ notch toughness of high strength line pipe is affected strongly by carbon and boron contents in base metal. Excellent notch toughness of HAZ was obtained by decreasing the carbon content in base metal below 0.05wt%.

鋼材の溶接遅れ割れの研究(第3報)

In the previous reports, the authors studied the effects of various factors on the occurence of cold cracks including root cracks, toe cracks and under-bead cracks in the heat-affected zones of base metals. They proposed the preheating temperatures necessary for the prevention of these cold cracks as a function of the chemical composition of steel, the groove shape, the restraint and the hydrogen content in weld metal.There have arised cases where not only base metal cracking but also weld metal cracking must be considered in the selection of the preheating temperature, especially for the welding of steels with lower carbon contents. A number of cold cracking tests have thus been conducted in order to find the necessary preheating and inter-pass temperature, θpr*, for preventing cold cracking in multi-run weld metals.The θph* is given by the following empirical equation as:θph*(°C)=120+120 log (HJIS/3.5)+5(hω-20)+8(σB-83)where, HJIS is the diffusible hydrogen content in weld metal by the JIS method (0.1 to 40 ml/100gr), hw the weld metal thickness (15 to 40 mm) and σB the tensile strength of weld metal (60 to 90 kgf/mm2).

アルミニウム合金溶接継手の気孔に関する研究(第3報)

The welding conditions have complicated influence on the porosity in aluminium alloy welds. The authors reported in their first report that the heat input in welds influences considerably the gas content in welds and further in their second report that several different inspection methods presently available of welding porosity have respective merits and demerits.In this report (the third report) an attempt is made to simplify and analyse the welding conditions in the case of experimental welding which influence the porosity in aluminium alloy welds. The apparatus prepared for the purpose is schematically shown in Fig. 1.The following results were obtained :1) The increase of heat input in welds decreases the percentage voids of porosity in spot deposit (Fig. 6) ; the same result was also obtained in practical welding. Since the increase of heat input decreases the cooling rate of molten pool, it is clear that the cooling rate has remarkable influence on the welding porosity.2) Heat input of welds, however, is a complicated factor for welding porosity. It is therefore considered necessary to divide the factor into two minor ones, i.e., the cooling rate and the temperature of molten pool, and then investigate both, As the result of temperature measurement in molten pool during welding, it was found that the temperature and the porosity in weld deposits simultaneously increased linearly with the welding current.