Effect of nitrogen on properties of submerged arc weld metal

Abstract

A systematic study of the effect of nitrogen contents from 33 to 210 ppm on the microstructure and mechanical properties of submerged arc deposits has indicated that the optimum toughness occurs when the nitrogen content is about 70 ppm. The fracture appearance transition temperature was lower at the highest and lowest nitrogen levels. Changes in the microstructure and mechanical properties of the deposit were satisfactorily interpreted with the aid of a model in which the reaction sequence was Ti with O₂ then Ti with N₂, and then B with N₂.

MST/607     

Microanalysis of fine precipitates in a two-pass C-Mn submerged arc weld metal

Abstract

Precipitation of very fine particles has been observed by transmission electron microscopy in a C–Mn weld metal containing small amounts of chromium, niobium, and molybdenum. The precipitates were found in the bead from the first pass of a two–pass weld. The hardness of the bead from the first pass was found to be greater than that from the second pass. Precipitation had occurred from a supersaturated ferritic matrix as a result of the heat treatment of the first pass imposed during the second pass. The precipitates were analysed by atom–probe field–ion microscopy and found to be of the M₂X type, where M = Cr, Mo, Ni, and X=C, N.

MST/173     

The microstructure and phase transformations in duplex 316L submerged arc weld metals

Journal of Materials Science - The nature and kinetics of the δ-ferrite transformation in a series of duplex submerged arc 316 L weld metals has been studied under creep conditions at...     

Material variability in composition and structure of a Type 316 stainless steel submerged arc weld metal

Type 316 austenitic stainless steel submerged arc weld (SAW) deposited metal, produced by joining two heavy (50mm) thickness plates with a multipass procedure and using Type 316L filler metal, was characterized from both a compositional and structural point of view (optical and scanning electron microscopy observation, energy-dispersive X-ray elemental analysis and ferrite content and hardness measurements). Important features such as columnar grain macrostructure, mainly cellular-dendritic and a duplex (γ-austenite matrix plusδ-ferrite second phase) microstructure were observed according to the occurrence of a ferritic-austenitic weldpool solidification mode followed by a solid-stateδ→γ transformation. The weld deposited metal was characterized along the thickness by significant variations in composition and ferrite morphology, distribution and content because of the influence of the filler metal chemistry and the thermal cycles experienced by each pass during subsequent passes.     

Joining stainless steel parts by means of weld bonding

Recent published works in the field of weld bonding present new results relevant to project and design of structural metal joints. However, it is still difficult to find technological data in the open literature to support and control manufacturing conditions. Gaps of knowledge are easily found in the set up of process parameters, in the selection of adhesives and in the understanding of the long term performance of weld bonded joints in hostile environments. The aim of this paper is to contribute to an extension of the actual knowledge on the weld bonding technology and to provide useful insights into its application to the joining of stainless steel. The research is accomplished by the weld bonding of stainless steel test specimens using three different commercial adhesives with varying working times and different exposures to water. The relative performance and quality of the weld bonded joints is evaluated against alternative solutions based on adhesives and conventional spot-welding. The experimental investigation is supported by finite element computer simulations with the purpose of establishing the welding parameters that allow spot-welding through the adhesives.     

Thermal model of submerged arc welding

Abstract

A model for calculating the temperature field in submerged arc welding is presented. The algorithm is based on the method of elementary balances. Melting of the electrode rod and melting of the parent material followed by solidification of the pool of molten metal are considered. The calculated temperature evolution curves are compared with the results of experiments. The temperature evolutions at characteristic points of a welded joint are shown.

MST/1289     

Manual metal arc weld modelling: Part 2 Treatment of multipass weld

Abstract

The premature failure of parts designed to operate at high temperatures often occurs in low-ductility microstructures in a weld or its heat-affected zone (HAZ). Clearly, a knowledge of how the welding process variables determine these microstructures is essential to the designer of welding procedures. In an accompanying paper relationships are established which describe how the dimensions of single manual metal arc weld beads and their associated HAZs are related to the welding process parameters. Here it is shown how these relationships can be used to optimize the metallurgical properties of multipass welds by controlling the process parameters. The factors given particular attention are dilution of the weld metal by the parent material, refinement of the HAZ using controlled deposition, and refinement of the structure of the weld metal. Data for BOC Murex Suprex B welding electrodes and a mild steel substrate are used throughout for illustration, but the methods presented are applicable to other combinations of materials provided the correct material constants are used. The present work was prompted by a need to improve metal deposition rates during manual metal arc repair of foundry defects in large Cr–Mo–V castings. The practical implementation of the results is also considered.

MST/193b     

Residual stress reduction in the penetration nozzle weld joint by overlay welding

Stress corrosion cracking (SCC) in the penetration nozzle weld joint endangers the structural reliability of pressure vessels in nuclear and chemical industries. How to decrease the residual stress is very critical to ensure the structure integrity. In this paper, a new method, which uses overlay welding on the inner surface of nozzle, is proposed to decrease the residual stresses in the penetration joint. Finite element simulation is used to study the change of weld residual stresses before and after overlay welding. It reveals that this method can mainly decrease the residual stress in the weld root. Before overlay welding, large tensile residual stresses are generated in the weld root. After overlay weld, the tensile hoop stress in weld root has been decreased about 45%, and the radial stress has been decreased to compressive stress, which is helpful to decrease the susceptibility to SCC. With the increase of overlay welding length, the residual stress in weld root has been greatly decreased, and thus the long overlay welding is proposed in the actual welding. It also finds that this method is more suitable for thin nozzle rather than thick nozzle.     

A turbulent electric arc in a submerged jet

We have experimentally investigated the optical and electrical characteristics of a turbulent electric arc burning at the axis of a submerged jet.Translated from Inzheherno-Fizicheskii Zhurnal, Vol. 57, No. 4, pp. 533–538, October, 1989.     

Vision-based weld seam tracking in gas metal arc welding

A low-cost visual sensing system is developed to realize weld seam tracking in gas metal arc welding (GMAW). The system consists of a commercial CCD camera, narrow-band composite filter lens, an image capturing card, an industrial computer, a welding control unit, a GMAW power source, and a worktable. Images of root gap and its vicinity are captured in the GMAW welding process by the system. The captured images are processed by an algorithm on the basis of the analysis of gray characteristics of the root gap to get the offsetting information between torch and root gap centerline. The offsetting information is then used to realize weld seam tracking in the GMAW process. Welding seam tracking experiment is conducted by a simple proportional (P) controller. The results show that tracking error is basically less than ± 0.5 mm.     

Electrode melting and plate melting efficiencies of submerged arc welding and gas metal arc welding

Abstract

The effect of process variables such as current, voltage, electrode extension, electrode diameter, etc., on the electrode melting and plate melting efficiencies of submerged arc welding (SAW) and gas metal arc welding (GMAW) has been studied. It has been shown that there is an increase in the electrode extension or a decrease in the voltage and electrode diameter. For the same welding parameters, the electrode melting efficiency is higher when the electrode is negative. A similar relationship was observed for GMAW. The results also indicated that the shielding gas in GMAW also had an effect on the electrode melting efficiency. The plate melting efficiency of GMAW increases with an increase in the welding current, voltage, and electrode diameter, and decreases with an increase in the electrode extension. For the same welding parameters, the plate melting efficiency is lower when the electrode is negative. For SAW there is an increase in the plate melting efficiency with an increase in the welding current and voltage. It was also observed that the plate melting efficiency was lower for the negative electrode. Although there was an indication of a decrease in the plate melting compared with similar effects in GMAHI: this decrease in plate melting efficiency did not seem significant. An attempt attempt has also been made to develop numerical models to predict the electrode and plate melting efficiencies from the process variables.

MST/1096     

Residual stress prediction in submerged arc welded spiral pipes

Submerged arc welding (SAW) is generally the preferred method for joining the seam edges of large diameter spiral pipes. The quality control of the welded pipes usually consists of a hydrostatic test in which water is pumped into the pipe. High pressure hydrostatic tests can moderate tensile residual stress caused by the welding process.In this paper, three-dimensional finite element (FE) simulations of double SAW and hydrostatic test processes of spirally welded pipes are carried out in two simulation steps using the ANSYS commercial software. In the first step, i.e., welding, a new method, namely, unfurl-mapping (UM) is introduced to overcome the geometrical difficulties of defining the Goldak double ellipsoidal heat source of the welding process. UM virtually opens the pipe into a flat surface, and therefore, the spiral seam is mapped to a straight line. To discretize the pipe, fine brick elements are utilized for meshing the main computational zone. The rest of the model is meshed by coarse shell elements by applying the multi-point constraint technique. This non-uniform mesh structure reduces the computational requirements significantly and provides the ability to simulate the entire pipe. Therefore, in the second step, the hydrostatic test is easily simulated by defining a ramped internal pressure. The method is validated using hole drilling measurements performed before and after hydrostatic test for this research. It is observed that obtained results from the FE simulations are in good agreement with the experimental measurements.     

Effects of process parameters on arc shape and penetration in twin-wire indirect arc welding

In this study, the effects of variable parameters on arc shape and depth of penetration in twin-wire indirect arc gas shielded welding were investigated. The variation of arc shape caused by changes of the parameters was recorded by a high-speed camera, and the depths of penetration of specimen were measured after bead welding by an optical microscope. Experiments indicated that proper parameters give birth to a concentrated and compressed welding arc, which would increase the depth of penetration as the incensement of the arc force. Several principal parameters including the distance of twin wires intersecting point to base metal, the included angle, and the content of shielding gas were determined. The arc turned more concentrated and the depth of penetration increased obviously as the welding current increased, the arc turned brighter while unobvious change of penetration occurred as the arc voltage increased, and the deepest penetration was obtained when the welding speed was 10.5 mm/s.     

Laser arc hybrid weld microstructure in nickel based IN738 superalloy

Abstract

A study of the microstructural characteristics of laser arc hybrid welded nickel based IN738 superalloy was performed. Laser arc hybrid welding produced a desirable weld profile in the alloy, similar to what is usually obtained during laser beam welding, and no cracking occurred exclusively in the fusion zone. Elemental partitioning pattern in the fusion zone was studied by electron probe microanalysis and calculating the volume fraction of the weld metal that resulted from the consumption of the filler wire. The result showed that Ti, Ta, Nb, Mo, Al and Zr partitioned into the interdendritic regions of the fusion zone. SEM and TEM examination of the fusion zone showed the presence of secondary solidification reaction constituents, which consists of MC type carbides. The study further revealed that non-equilibrium liquation of various second phases that were present in the alloy prior to welding contributed to intergranular liquation in the heat affected zone (HAZ), which consequently resulted in extensive HAZ intergranular cracking during welding. Although laser arc hybrid welding appears promising for improving the weldability of nickel based IN738 superalloy, a suitable weldability improvement procedure is required in order to minimise HAZ intergranular cracking and thereby enhance the applicability of this technology to the joining of the superalloy.     

Numerical simulation on interaction between TIG welding arc and weld pool

The interface deformation between welding arc and weld pool is important in dynamic coupling numerical simulation on arc and pool. To reveal the interaction between welding arc and weld pool, unified mathematic model of TIG welding arc and pool was established in this paper. The moving interface was solved by updating the calculation region of arc and weld pool continually. Fluid flow and heat transfer of TIG welding arc and weld pool were analyzed basing on this model. The weld pool shape calculated by dynamic coupling welding arc and pool is more close to the experiment than that of non coupling calculation.     

Numerical analysis of weld pool geometry in globular-transfer gas metal arc welding

The weld pool geometry and its dimension in the globular-transfer mode during gas metal arc welding (GMAW) were numerically analyzed by using the thermal conduction model, which considered the influence of the deformation of weld pool surface on heat flow in the quasi-steady state. According to the features of the globular-transfer mode, the additional heat energy from molten metal droplets was treated as a plane or volumetric heat source term to correspond to different welding conditions. The weld pool surface profile was predicted while considering the effect of droplet impingement on the depression of the weld pool. The bead-on-plate GMAW experiments were performed under different welding conditions to validate the model of numerical analysis. It has been found that the predicted results agree well with the measured ones.     

Manual metal arc weld modelling: Part 1 Effect of process parameters on dimensions of weld bead and heat-affected zone

Abstract

The properties of a weldment are determined largely by the size and distribution of microstructural regions within the weld metal and heat-affected zone (HAZ). It has been appreciated for some time that these properties may be controlled by adjusting the parameters of the welding process, although until recently this was done mainly qualitatively. Means of achieving more quantitative control are now beginning to be applied. In this paper measurements of the sizes of the weld bead and HAZ are presented for single manual metal arc weld beads. The process variables investigated were electrode type, gauge size, welding position, polarity, welding current, preheat, and welding velocity. Functional relationships between the process variables and the size of the weld bead and HAZ are determined. The generality of these relationships is examined by analysing measurements made previously on other materials. The results are discussed in terms of the theory of the welding process and, as shown in two accompanying papers, they can be used to develop models of multipass manual metal arc welding on which a practical welding procedure may be based.

MST/193a     

活性剂涂敷量对A-TIG焊熔深影响的研究

常规TIG焊生产效率低,单道焊可焊厚度小,活性化TIG焊（A-TIG）,同常规TIG焊相比可大幅度地提高焊缝熔深,从而提高焊接效率,针对不锈钢材料,通过宏观断面分析方法研究了单一成分的活性剂（SiO2,CaF2,TiO2,Cr2O3和NaF)对焊缝熔深的影响,结果表明：同常规TIG焊相比,上述5种活性剂在涂敷量较小时,焊缝熔深均随活性剂涂敷量的增加而明显增大,氧化物活性剂增加熔深的作用效果大,氟化物的作用效果较小;5种活性剂在熔深增加能力上均有一个饱和点;电弧收缩和熔池表面张力梯度的变化是活性剂增加熔深的主要原因。