Composition Of Weld Metal Research Articles

Effects of oxygen and sulfur on alloying element vaporization rates during laser welding

Inadequate control of weld metal composition due to vaporization of volatile alloying elements is a serious problem in the welding of many important engineering alloys. Effectiveness of surface active elements such as oxygen or sulfur in blocking vaporization sites on the weld pool surface was investigated. Several iron samples doped with oxygen or sulfur were exposed to a carbon dioxide laser beam in pulsed mode. The time average metal vaporization rates and the emission spectra were compared with those obtained from ultra pure iron samples. Since the weld pool surface area and temperature distribution are affected by oxygen and sulfur, the true effects of these elements on metal vaporization rates cannot be easily evaluated from welding data. Therefore, rates of isothermal vaporization of iron and copper drops doped with oxygen or sulfur were determined both in the presence and the absence of low pressure argon plasma. These rates were compared with the rates of vaporization of ultrapure metal drops. Presence of sulfur or oxygen in metals always resulted in increased metal vaporization rates. The results are analyzed on the basis of interfacial phenomena.

The influence of inclusion chemical composition on weld metal microstructure

The effects of nonmetallic inclusions on weld metal microstructures were investigated. The inclusions were extracted from niobium microalloyed steel weld metal specimens, and examined with light and electron microscopic techniques. An EDS (Energy Dispensive Spectroscopy) system was used to determine the chemical composition of the inclusions. Correlation between weld metal and inclusion composition was established. Aluminum, titanium, sulfur, and iron were the most important elements in the inclusions that affect the final weld metal microstructure. Mn/Si ratio was also found to affect the amount of oxygen and acicular ferrite in the weld. The state of deoxidation, as indicated by the amount of FeO present in the inclusions, actually determines the recovery of alloying elements and the amount of oxygen in the weld pool. It also determines the chemical composition of the nonmetallic inclusions. Inclusions with high aluminum content tend to cluster together forming larger particles while pure silica or silicate particles are small and well disseminated in the weld metal. This explains the different inclusion size distributions observed in the weld specimens of different oxygen concentration. Consequently, the prior austenite grain size will be different resulting in different amounts of acicular ferrite and grain boundary ferrite.

Production of heavy-wall, high-strength SAW bent-pipe for arctic use.

High-grade bent pipes with heavy-wall (1.25 in. for API-5LX65 and 1.61 in, for API-5LX60) were produced by induction hot bending process for use in Arctic regions. Niobium and vanadium-added steel pipe, which is commonly used in the pipe line industry, was examined in this paper for both trial and production bending.The characteristics of the induction hot bending process and the properties of the bent pipe were investigated. By a combination of suitable bending temperature, proper chemical composition of weld metal and tempering after bending, good Charpy impact properties at -46°C and satisfactory CTOD value at -10°C were obtained. Tensile strength at bent, boundary and tangent portions was almost uniform longitudinally and circumferentially.

Inclusion phases and the nucleation of acicular ferrite in submerged arc welds in high strength low alloy steels

Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have been examined to study the inclusions and their role in the nucleation of acicular ferrite. Inclusion phases and compositions have been analyzed by electron diffraction and X-ray microanalysis. These analyses have shown that the inclusions contained many different compounds, the proportions of each depending upon both the flux and metallic additions. Six inclusion phases have been identified: galaxite (Al2O3 ⋅ MnO), a titanium-rich compound (probably TiO), a copper sulfide, a manganese sulfide, a silica, and an aluminum-rich phase. No correlation was found between the amount of acicular ferrite in the weld metal and either average inclusion composition or individual inclusion phases. No epitaxial relationships between inclusions and adjacent ferrite grains could be identified. It has been concluded that inclusions nucleate acicular ferrite by acting as inert substrates according to the classical theory of heterogeneous nucleation. Because most inclusions are multi-phase and are touched by several ferrite grains, it has also been concluded that each inclusion can nucleate several ferrite grains, due to local regions of high surface energy on the inclusion.

Physical and Chemical Behavior of Welding Fluxes

Shielded-metal arc, submerged arc, and flux-cored arc welding processes (1) all rely on a flux to achieve an acceptable weld deposit. The welding flux for each of these processes must meet specific physical and chemical requirements to perform properly (2). A flux must have a melting range such that the weld metal solidifies before the molten slag does, and the resulting slag must have a density such that it floats to the top of the weld pool and collects there. The specific ranges of melting and density vary depending on the alloy being welded. The flux must also assist in main­ taining the arc plasma, in producing a shielding gas to protect the weld deposit from the atmosphere, and in limiting the amount of splatter. The flux viscosity is important because it controls the extent to which the flux can chemically alter the weld-metal composition, and it influences weld­ metal porosity, bead morphology, and the ability to make out-of-position weld deposits (3, 4). The flux must contain specific chemical additions to influence the weld metal's composition, microstructure, and properties.

極低温非磁性材料用溶着金属の機械的性質

Superconducting magnets in fusion reactor system produce enormous electromagnetic force which generates very high stress working on the containers of these magnets at cryogenic temperature. The candidate alloys for the structural material of containers are non magnetic stainless steels with improved yield strength and toughness at cryogenic temperature. Containers are produced as welded structures, so that these properties on the structural material are also indispensable for the weld metal.The chemical compositions of stainless steel weld metal are usually controlled to include a small quantity of δ-ferrite for the prevention of hot cracking in welds. The δ-ferrite is, however, ferromagnetic and causes the reduction in cryogenic toughness of weld metal. On the other hand, the weld metal of 19Cr-13Ni-5Mn type is known as fully austenitic one with very low susceptability on hot cracking in welds. The improvement of weld metal of this type resulted in the development of the fully austenitic weld metal of l7.5Cr-l6.5Ni-6.5Mn type with improvde cryogenic strengths. The effects of carbon and molybdenum contents on the tensile properties and Charpy impact properties were examined on this type of weld metal.Conclusions are as follows. It is possible to assure the yield strength of the weld metal of 2.3% molybdenum content higher than 1000 MPa when carbon content is higher than 0.07% and carbon plus nitrogen content is higher than 0.13%. While the weld metal decreases in the elongation and reduction in area as the addition of carbon, the weld metal which contains 0.13% of carbon and 2.3% of molybdenum indicates about 40% of elongation and about 300% of reduction in area at 4.2 K. The Charpy absorved energy and lateral expansion of the weld metal at 4.2 K are equal to those at 77 K. The weld metal decreases in the absorved energy and lateral expansion as the addition of carbon content, but the weld metal which contains 0.13% of carbon and 2.3% of molybdenum indicates about 60J of absorved energy and 0.8 mm of lateral expansion at 4.2 K. The relation between yield strength and absorbed energy at 4.2 K on the weld metal coincides with the lower limit line of absorbed energy of the stainless steels SUS304LN and SUS316LN of high yield strength.

Microstructural development in mild and low-alloy steel weld metals

The conditions for acicular ferrite formation and the overall transformation behaviour of mild and low-alloy steel weld metals are discussed in terms of deoxidation and alloying practice, solidification microstructure, and operational conditions. Selected weld metal microstructure and composition data are critically reviewed, and new semi-empirical correlations for predictions of the final mechanical properties of the weldment under various welding conditions are presented. The results of this review provide a systematic basis for future research which is required if a sound theoretical treatment of weld metal microstructure development is to be obtained.

Effect of weld metal composition and welding conditions on δ -ferrite and CVN toughness of austenitic-ferritic weld metal

In the present investigation, the effect of base plate and filler wire composition as well as of welding conditions on δ-ferrite contents and toughness of austenitic-ferritic stainless steel weld metal has been established. According to previous work, the δ-ferrite contents are not only depending on chemical composition but also on cooling conditions of the weld metal. The application of δ-γ-CCT diagrams is recommended. Increasing δ-ferrite contents lower the CVN toughness of the weld metal, which should be taken into consideration before recommending filler materials and welding conditions. In der vorliegenden Arbeit wurde der Einfluß der Zusammensetzung von Grundblechwerkstoff und Schweißzusatz wie auch der Einfluß der Schweißbedingungen auf die Ausbildung von δ-Ferrit und auf die Zähigkeit von Schweißgut aus austenitisch-ferritischem nichtrostendem Stahl untersucht. In Übereinstimmung mit früheren Arbeiten wurde festgestellt, daß die δ-Ferritgehalte nicht nur von der chemischen Zusammensetzung, sondern auch von den Abkühlbedingungen des Schweißgutes abhängig sind. Hierzu wird die Anwendung von ZTU-Schaubildern mit kontinuierlicher Abkühlung für den Umwandlungsbereich δ/γ empfohlen. Es zeigte sich, daß mit Zunahme der δ-Ferritgehalte die an ISO-V-Proben ermittelte Kerbschlagarbeit herabgesetzt wird; dies sollte bei der Auswahl von Schweißzusätzen und -bedingungen berücksichtigt werden.

The mechanical properties of thermite welds in premium alloy rails

In this paper the results of an investigation into the properties of 13 thermite rail welds produced using CrMo, CrV and chromium alloy rails, American Railway Engineering Association controlled-cooled rails (i.e. standard rails) and heat-hardened rails are reported. Various combinations of the rails were joined with weld metal produced by the aluminothermic reaction of “standard” and “alloy” thermite charges. After welding, the hardness profiles, the tensile properties, the impact energies and the macrostructures and microstructures of the welds were determined. Detailed examinations of the microstructures of the heat-affected zones and of the weld metals revealed that the thermite welding process produced welds compatible with rail service in that no martensite was ever observed in any of the welds regardless of the rail composition or of the weld metal composition. Despite the absence of martensite, very low impact energies (1.5–2.8 J at 293 K) were measured in Charpy V-notch specimens removed from the weld metals. The weld metals also exhibited only a 2%–6% reduction in area for tensile ductility. Predictably, all the weld metal fracture surfaces showed brittle-type transgranular cleavage. It was also shown that alloy weld metal is harder and stronger than standard weld metal. Depending on the preheat time, the Rockwell C hardness of alloy weld metal is approximately 28–34 HRC whereas that of standard weld metal is 20–27 HRC. Correspondingly, the tensile strengths and yield strengths of alloy weld metal were about 100–150 MPa greater than those of standard weld metal. Also studied were the properties and structures of specimens which straddled the region of minimum hardness along the outer edge of the heat-affected zone.

Effect of aging on interfacial structures of nickel-based transition joints

AbstractThe interfacial structures between 2·25Cr–1 Mo steel and Inconel 182 weld metal have been studied in the as-welded condition and after aging at temperatures between 630 and 700°C for times up to 6000 h. Examination of the as-welded specimens revealed a band of martensite ∼0·5 to ∼50 μm wide between the steel and the weld metal. During aging, precipitates developed in this band and led to arrays of interfacial carbides which showed two morphologies, depending on the initial width of the martensite band. Single lines of coarse carbides were associated with narrow bands, and finer precipitates were distributed within the wider martensite bands. Initially, the interfacial precipitates formed readily between 630 and 700°C, but on further aging at temperatures >675°C the precipitates dissolved. The effects of changing the welding conditions and weld metal composition on the development of the interfacial precipitates are considered. In comparison with nickel-based transition joints examined after longte...

Relationship of weld-metal microstructure and penetration to weld-metal oxygen content

The weld-metal oxygen content has been found definitely to influence the behavior of the welding process. Flux composition can alter the weld-metal composition, affecting weld-bead morphology, microstructure, and mechanical properties. Further research is necessary to understand the actual means by which oxygen and other weld-metal residuals influence the welding process and weld-metal properties.

Some effects of flux physical properties on weld-bead formation, in the SAW process

The study of fundamental arc-welding process characteristics is important for controlling both the formation of and the mechanical properties in weld metals. Automated and semi-automated welding procedures require accurate knowledge of the effects on weld-bead dimensions of changes in process variables, in order to fill joints rapidly without defects. In the SAW process, one such variable is the type of flux used. Two classes of flux properties are important: flux chemistry and reactivity, which affect weld-metal composition and properties; and flux physical properties, which can be intrinsic, e.g., viscosity and surface tension, or extrinsic, e.g., particle size. Physical properties affect (or allegedly affect) bead dimensions, welding speed, and weldingcurrent capabilities. Much recent work on the SAW process has been concerned with the chemical composition and mechanical properties of weld metals.

Prediction of weld-metal composition during flux-shielded welding

It is well known that the slag and metal do not reach equilibrium during fluxshielded welding, due to the short reaction times and large thermal gradients inherent in the process. Nonetheless, many investigators have attempted to define the effective equilibrium by empirical analysis of experimental data. The results of these analyses have generally been contradictory and, in most cases, have lacked a firm scientific basis.

The application of neutron diffraction to a study of phases in type 316 stainless steel weld metals

Neutron diffraction techniques have been utilised to study the phases in type 316 austenitic stainless steel weld metal, both in the as-welded condition and after stress-relieving and ageing heat-treatments. The amounts of the principal crystallographic phases present in bulk specimens have been measured. Two compositions of weld metal were selected to provide a “low” (6%) and “high” (16%) initial ferrite level and the subsequent volume fractions of transformation products were measured after heat-treatment. Some retained ferrite was observed in all the heat-treated specimens, ranging from 4% for specimens of both initial ferrite levels treated at 625°C for 1000 h, to around 1% for the specimens treated at 850°C for 6 h. The high initial ferrite specimen produced 0.9% of sigma phase after the 850°C treatment and 0.2% sigma after the 625°C treatment. The low initial ferrite specimen produced 1.5% M 23C 6 carbide after both heat-treatments. The results compare well with previous findings on similar samples of weld metal using optical and electron microscopy.

Tempering of 2.25 Pct Cr-1 Pct Mo Low Carbon Steels

The effect of carbon level on the tempering behavior at 700°C of 2.25 pct Cr-1 pct Mo steels having typical weld metal compositions has been investigated using analytical electron microscopy and X-ray diffraction techniques. The morphology, crystallography and chemistry, of each of the various types of carbides observed, has been established. It has been shown that each carbide type can be readily identified in terms of the relative heights of the EPMA spectra peaks for iron, chromium, molybdenum, and silicon. A decrease in the carbon level of the steel increases the rate at which the carbide precipitation reactions proceed, and also influences the final product. Of the carbides detected, M23C6 and M7C3 were found to be chromium-based, and their compositions were independent of both the carbon level of the steel and the tempering time. The molybdenum-based carbides, M2C and M6C, however, showed an increase in their molybdenum contents as the tempering time was increased. The rate of this increase became greater as the carbon content of the steel was lowered.

Factors Influencing Stress-Corrosion Cracking of High-Strength Steel Weld Metals

The stress-corrosion cracking (SCC) behavior of high-strength steel weld metals, as indexed by KIscc, was examined with emphasis on the relative influences of yield strength, electrochemical potential, welding process, and weld metal composition. The weld metals were from weldments fabricated by the gas metal arc (GMA) or gas tungsten arc (GTA) process. Filler metals with four different compositions—designated 120S, 140S, AX140 and HY-130—were used. The multi-pass welding procedures and their associated thermal cycles produced very complex martensitic-bainitic type microstructures. The GTA weld metals were considerably more fine-grained and more highly tempered than the GMA weld metals. This enhanced the fracture toughness of all four of the higher strength GTA weld metals but improved the SCC properties of only two GTA weld metals—HY-130 and 140S. The effectiveness of microstructural influences on SCC behavior is correlated with the sulfur content of the weld metals assuming that hydrogen is the cause of SCC in these materials. The role of sulfur is presumed to be that of catalytic poison for the hydrogen recombination reaction which increases opportunities for nascent hydrogen absorption. The results show that the weld metals with improved SCC properties contain the lower concentrations of sulfur.

Improved weld metal safety at liquid nitrogen temperature

Cryogenic properties of austenitic weld metals deposited by covered electrodes vary widely from grade to grade. Within any specific grade, optimum properties may be obtained if weld metal is: low in ferrite (preferably 0 FN); low in nitrogen (preferably < 0.05%); low in carbon (preferably < 0.04%); high in nickel - (maximum permissible); and deposited by a lime-type electrode.Nickel was the only element investigated that improved weld metal toughness at cryogenic temperatures, suggesting that the nickel content of any specific grade should be maintained as high as possible.Thus, nickel, nitrogen, ferrite, and carbon contents combine as prime factors to be controlled for maximum toughness of SMA weld metal at cryogenic service temperatures. The type of electrode covering is of importance particularly if it is necessary to maximize properties.Regression analysis of the wide variety of materials tested at - 196°C (−320°F) resulted in the following model formulae.Toughness of weld metal deposited by lime-type electrodes:Lateral expansion (CVN) = 36.55 − 133.8 (%C) − 0.20 (%Mn) − 1.13 (%Cr) + 1.72 (%Ni) − 2.34 (%Mo) − 177.2 (%N) mils (1)Toughness of weld metal deposited by titania-type electrodes:Lateral expansion (CVN) = 33.72 − 133.8 (%C) − 0.20 (%Mn) − 1.13 (%Cr) + 1.72 (%Ni) − 2.34 (%Mo) − 177.2 (%N) mils (2)(Conversion factor: 1 mil = 25.4 μm). For known weld metal compositions, these models enable weld metal toughness at - 196°C (−320°F) to be reliably predicted.Regression analysis formula for lateral expansion calculations had a standard deviation of ± 0.17 mm (± 6.5 mils). This means that a calculated value of 0.56 mm (22 mils) was essential to reasonable assure a lateral expansion of 0.381 mm (15 mils) after testing at - 196°C (−320°F). If compositions are restricted to the ranges of AWS A5.4–69, low nitrogen heats of core wire become mandatory. Such stainless steel is not always readily available, posing a problem for the filler metal producer.

溶接部のじん性に関する研究 Ｉ Ｓｉ‐Ｍｎ系溶接金属のじん性とミクロ組織

Relations among Charpy impact properties microstructures and Si, Mn or O content about Si-Mn weld metal with submerged arc welding were investigated for the purpose of finding out the way to improve Charpy impact properties of weld metal.Results can be summarized as follows.(1) In Si-Mn weld metals, effects of Si and Mn content on Charpy impact properties are related with the change of microstructure and the decrease of oxigen content. And when the chemical composition of weld metal is the range of 0.10-0.25% Si and 0.8-1.0% Mn Charpy impact properties of weld metal is the best.(2) The growth of coarsened-grain ferrite and needle like ferrite on the microstructure deteriorate the Charpy impact properties, the growth of the mixed structure of them and fine-grain ferrite improve the Charpy impact properties.From these results it is thought the control of micro-structure is the most important factor for the improvement of Charpy impact properties on the weld metals.

溶接金属の気孔とそのガス組成

溶接金属の気孔とそのガス組成

Some Metallurgical Problems in Welding

The paper deals with various metallurgical problems associated with good welding in steel. Metallurgical background of defects like hot crack, hot tear, cold crack, weld metal and heat affected zone brittleness have been discussed from the point of view of weld metal and base metal compositions, impurities and deoxidation conditions. The role of oxygen, hydrogen and nitrogen and various inclusions, their distribution and morphology have been examined.