Metal-cored Wire Research Articles

Double Jointing of High Strength Pipelines

With the increasing use of thermomechanically processed steels for pipelines, the alloy content of each steel grade decreases from year to year. Using welding processes which result in high dilution of the weld metal by parent material, such as conventional submerged arc welding, it becomes increasingly difficult to achieve the very high weld metal yield strength demanded when welding X80 and X100 steels, especially when strain-based design is used. For X80 steels, submerged arc welding with tubular wires and with twin arcs can allow high productivity to be maintained while limiting the heat input and dilution, and satisfactory results produced by this route are presented. Special boron-containing wires can also be used where high dilution cannot be avoided. For X100 steels, the use of gas metal arc welding with a fixed welding head and a rotating pipe, combined with a narrow bevel preparation, allows excellent mechanical properties to be achieved without excessively high alloy contents in the welding wire. Because of the small joint volume, productivity need not be unduly lower than that of submerged arc welding. Substitution of metal-cored tubular wire for solid wire can give a further increase in productivity.

Effect of welding procedure on wear behaviour of a modified martensitic tool steel hardfacing deposit

In the last years hardfacing became an issue of intense development related to wear resistant applications. Welding deposits can functionalize surfaces and reclaim components extending their service life. Tool steels are widely used in hardfacing deposits to provide improved wear properties. Nevertheless systematic studies of wear behaviour of new alloys deposited by hardfacing, under different service conditions are scarce. In this work the effects of shielding gas, heat input and post-weld heat treatment on the microstructural evolution and wear resistance of a modified AISI H13 martensitic tool steel deposited by semi-automatic gas shielded arc welding process using a tubular metal-cored wire, were studied. Four coupons were welded with different welding parameters. The shielding gases used were Ar–2% CO 2 and Ar–20% CO 2 mixtures and two levels of heat input were selected: 2 and 3 kJ/mm. The as welded and 550 °C–2 h post-weld heat treated conditions were considered. From these coupons, samples were extracted for testing metal–metal wear under condition of pure sliding with a load of 500 N. Chemical compositions were determined; microstructure and microhardness were assessed. It was found that content of retained austenite in the microstructure varied with the welding condition and that heat-treated samples showed secondary hardening, associated with precipitation phenomena. Nevertheless, as welded samples showed higher wear resistance than heat treated specimens. Under these test conditions post-weld heat treatment led to a reduction in wear resistance. The best wear behaviour was observed in samples welded with low heat input and under the lowest oxygen potential shielding gas used here, in the as welded condition. The intervening mechanism was mild oxidative. These results were explained in terms of the relative oxidation resistance stemming from different welding conditions.

Effect of post-weld heat treatment on the wear resistance of hardfacing martensitic steel deposits

The effect of different post-weld heat treatments on the microstructure and wear resistance of martensitic deposits were studied. The deposit was welded using a metal-cored tubular wire, in the flat welding position, on a 375 × 75 × 19 mm SAE 1010 plate, using 98% Ar–2% CO2 shielding gas mixture and with an average heat input of 2.8 kJ/mm. The samples were heat treated at temperatures between 500 and 680°C for 2 h. Chemical composition, Vicker's microhardness and wear properties with AMSLER tests in a sliding condition were determined. In the as welded condition, the microstructure was principally composed of martensite and retained austenite. Significant variations in wear resistance and hardness were measured for different tempering temperatures. For the different heat-treated conditions, it was observed that the decomposition of retained austenite to martensite and carbide precipitation was associated with the tempering of martensite. A secondary hardness effect was detected with maximum hardness of 710 HV for 550°C heat treatment temperature. The best performance in wear test was obtained for this condition. Wear rates for the different conditions were obtained and mathematical expressions were developed. For each case, wear mechanisms were analyzed.

Microstructure and Performance Characteristics of Parts Produced via GMAW Surfacing Rapid Forming

The new metal-cored wires with Fe-Si-Mn-Ti-B microalloyed series were prepared to meet demands of GMAW surfacing rapid forming technology. The microstructure and performance characteristics of parts produced with them are both investigated. Its continuous metallographic microstructure along the deposition height direction shows obvious layered characteristic due to the special thermal cycles and cooling conditions. The microhardness values of intermediate sections of the part are higher than those of surface sections, which closely relates to their microstructure. The tensile strength, yield strength and broken elongation percentage of the part are 575MPa, 530 MPa and 10.14%, respectively. The fracture mechanism of the part belongs to quasi-cleavage crack. Therefore, the self-made metal cored wires are acceptable for forming some structure parts.

Effects of flux composition on the element transfer and mechanical properties of weld metal in submerged arc welding

Submerged arc welding was performed using metal-cored wires and fluxes with different compositions. The effects of wire/flux combination on the chemical composition, tensile strength, and impact toughness of the weld metal were investigated and interpreted in terms of element transfer between the slag and the weld metal, i.e., Δ quantity. Both carbon and manganese show negative Δ quantity in most combinations, indicating the transfer of the elements from the weld metal to the slag during welding. The amount of transfer, however, is different depending on the flux composition. More basic fluxes yield less negative Δ C and Δ Mn through the reduction of oxygen content in the weld metal and presumably higher Mn activity in the slag, respectively. The transfer of silicon, however, is influenced by Al2O3, TiO2 and ZrO2 contents in the flux. Δ Si becomes less negative and reaches a positive value of 0.044 as the oxides contents increase. This is because Al, Ti, and Zr could replace Si in the SiO2 network, leaving more Si free to transfer from the slag to the weld metal. Accordingly, the Pcm index of weld metals calculated from chemical compositions varies from 0.153 to 0.196 depending on the wire/flux combination, and it almost has a linear relationship with the tensile strength of the weld metal.

Influence of Heat Input on Mechanical Properties of Multipass Low-Alloy Steel Weld Metal

Influence of heat input on the tensile strength and impact toughness of multipass weld metal made with AWS E81T1-Ni1 metal-cored wire was investigated. Welding parameters such as current, voltage and travel speed were varied independently to get different heat inputs. When it was increased by varying current, tensile strength of the weld metal increased even if more primary ferrite and wider columnar grains were observed. The increase is attributed to the higher recovery ratio of deoxidizing elements such as carbon, manganese and silicon due to the shorter reaction time in both wire tip and arc column. It also showed that impact toughness was influenced by the formation of reheated weld metal by subsequent passes and it decreased continuously with an increase of the amount of coarse grained region in the reheated weld metal.

하드페이싱 오버레이용접 비드형상에 미치는 GMA 용접조건의 영향

The relationship between GMA welding conditions and the bead shape of overlay weld was studied by using <TEX>${\Phi}1.6mm$</TEX> hypo-eutectic metal-cored wire designed for hardfacing against the severe metal-to-metal wear. As the welding voltage increased, the dilution also increased but the sudden drop of dilution was observed at <TEX>$30{\sim}33V$</TEX>. It was considered to be due to the decrease of penetration resulting from the change of transfer mode, from short circuit to spray. It was also found that the behavior of penetration with welding current was dependant on the transfer mode. The short circuit mode exerted the penetration to decrease while the spray mode did it to increase with increase of welding current. The former was considered to be responsible for the remarkable decrease in dilution at low welding voltage region. The change of transfer mode also had an effect on the behavior of bead width with welding current but it did not on the bead spreadability defined as W/H ratio. It was considered that the optimal welding conditions for multi-pass overlay welding could be obtained from the bead spreadability suitable for bead lapping and the dilution as low as possible in the spray transfer mode.

Effect of Mn and Ni on the Variation of the Microstructure and Mechanical Properties of Low-carbon Weld Metals.

Low-carbon weld metals with various amounts of Mn and Ni addition were made using metal-cored wires and Ar–2%O2 shielding gas, and their mechanical properties were evaluated. The objective of the research, aimed to develop welding consumables with better resistance to cold cracking, was to determine the optimum composition ranges of Mn and Ni, in the presence of carbon content less than 0.02%. The hardness of weld metals were found to increase linearly with Mn and Ni, which was attributed mainly to solid solution strengthening and in part to formation of hard phases. Varying Ni content influenced Charpy impact energy, the extent of which depended on Mn content. For a low-Mn composition, Ni addition increased hardness without sacrificing impact toughness whereas for a high Mn composition, Ni deteriorated the impact toughness seriously and caused intergranular fracture. The fracture path followed columnar grain boundaries that are identical to prior austenite grain boundaries since no d-ferrite phase formed during solidification. Accordingly, these boundaries without having ferrite phase were susceptible to cracking under dynamic loading. Based on hardness and impact resistance, the optimum levels of Mn and Ni were suggested to be 0.5–1% and 4–5%, respectively.

Effect of Inclusion Size on the Nucleation of Acicular Ferrite in Welds.

Low-carbon steel weld with a high density of oxide inclusions prepared using a experimental metal-cored wire has been examined to study the effect of inclusion size on the formation of acicular ferrite, and to understand the role of inclusion in the nucleation of ferrite lath. Depending on the ferrite morphology associated with inclusions, a total of 282 inclusions observed under TEM could be classified into two groups, i.e. the non-nucleant and the nucleant. Experimental results showed that the group of inclusions acted as nucleant were appreciably larger in size compared with those of non-nucleant resulting in the increased probability of nucleation with the increase of inclusion size, even though the chemical and structural natures appeared to be the same. The group of nucleant-inclusion was further divided into two types depending on the degree of nucleation, which was evaluated by the number of ferrite lath nucleated. Statistical analysis performed on inclusion size indicated that the larger the inclusion size is the more ferrite laths could be nucleated. Those laths nucleated from a large single inclusion have grown in many different radial directions and mostly had a different crystallographic orientation from those of adjacent ferrite laths. As a result of this study, it is demonstrated that larger inclusions are indeed more potent nucleation sites when compared with those of smaller size. Thus it could be concluded that the provision of the inclusion surface as for the inert surface for the heterogeneous nucleation of acicular ferrite lath would be the principal role of inclusions playing in the weld metal of low alloy steels. Other possible mechanisms were also considered, but they were unlikely to be operated in the present weld metal system.

Arc spray process for the aircraft and stationary gas turbine industry

Technological advances in arc spray have produced a system that competes favorably with other thermal spray processes. In the past, arc spray was thought of as a process for very large parts that need thick buildups. However, an attachment device known as the arc jet system has been developed that focuses the pattern and accelerates the particles. This attachment device, coupled with the in-troduction of metal-cored wires that provide the same chemistries as plasma-sprayed powders, pro-vides application engineers with a viable economic alternative to existing spray methods. A comparative evaluation of a standard production plasma spray system was conducted with the arc spray process using the attachment device. This evaluation was conducted by an airline company on four major parts coated with nickel-aluminum. Results show that, for these applications, the arc spray process offers several benefits.

Gas Pocket Generation in MAG Welding of Galvanized Steel Sheet.

The effects of welding parameters, wire compositions and others on the gas pocket (pit, blowhole) generation have been studied regarding MAG welding of galvanized steel sheets, and the mechanism of the gas pocket generation also has been investigated.As to the welding joint type and position, lap joint and vertical-down position make the number of generations large in comparison with others. The increase in welding current and speed or Ar content of shielding gas also furthers the gas pocket generation. In contrast, the application of metal-cored wire in CO2 welding or pulsed current welding machine in MAG welding with Ar-CO2 mixture gas reduces the generation. The increase in C, Ti and P content of the metal-cored wire is effective for the reduction of gas pocket generation. Through these investigations, special metal-cored wire for CO2 welding of galvanized steel sheets has been developed, and the wire is currently used in car manufacturing, house construction and other fields.Based on the above phenomena, zinc vapor seems to be the main cause of gas pocket generation. These phenomena can be mainly explained by the penetration depth which corresponds to the amount of zinc vapor, and by the stability of short-circuiting arc which influences the coming up and release of zinc vapor through the molten pool.

Development and Evaluation of Experimental Metal-Cored Electrodes for Submerged-Arc Welding of HSLA 100 Steel

The objective of this investigation was to develop and evaluate experimental electrode wires for joining HSLA 100 steel with particular emphasis on improvement of weld metal toughness properties. The work focused on the development of metal-cored wires with varying carbon and molybdenum contents for submerged-arc (SA) welding.The series of SA welds produced with the metal-cored wires, in combination with a highly basic flux, provided better toughness than achieved using the reference electrode MIL 120 S1.Optimum Charpy notch toughness was achieved with the intermediate carbon and molybdenum contents. In general, the results were attributed to the influence of weld metal chemistry on the final weld microstructure, specifically the formation of a relatively fine bainitic structure with some lath martensite and limited grain boundary ferrite in both the as-deposited and reheated weld metal regions. For increasing weld metal carbon (0.040–0.090%) and molybdenum (0.45–0.700/0) there was an increase in yield strength, hardness and tensile strength. With increasing carbon there was refinement of the microstructure, increased evidence of lath martensite, reduced (to almost no) grain boundary ferrite, and greater carbide precipitation. Changes in microstructure were much less pronounced with variation in molybdenum. In addition, increasing carbon was found to reduce the upper shelf energy, attributed to the high weld metal yield strength and increase in carbide precipitation (enhanced microvoid coalescence). Résumé Le but visé était la mise au point et l' évaluation de fils-électrodes expérimentaux pour le soudage de l'acier à haute résistance faiblement allié 100, en cherchant plus particulièrement à accroître la ténacité du métal fondu. Les travaux ont essentiellement porté sur la fabrication de fils à âme métallique d'une teneur en carbone et en molybdène variable pour le soudage àl'arc sous flux enpoudre.L'emploi de ces fils avec un flux hautement basique a permis d'obtenir des séries de soudures plus résistantes que celles produites avec l' électrode de référence MIL 120 S1. La plus haute résilience d'entaille à l'essai Charpy a été atteinte avec les teneurs moyennes en carbone et en molybdène. En général, les résultats ont été attribués à l'effet de la composition chimique du metal fondu sur la microstructure finale de la soudure, notamment à la formation d'une structure bainitique relativement fine renfermant un peu de martensite en plaquettes et une faible quantité de ferrite aux joints de grain, tant dans les zones de métal fondu brut de soudage qu'après réchauffage. L' élévation de la teneur en carbone (0,040–0,090%) et en molybdène (0,45–0,70%) dans le métal fondu s'est traduite par une augmentation de la limite d' élasticité conventionnelle, de la dureté et de la résistance à la traction. Le renforcement de la teneur en carbone a produit un affinage de la microstructure, une accentuation de la presence de martensite en plaquettes, une diminution (presque totale) de la ferrite aux joints de grain et une plus forte precipitation du carbure métallique. La variation de la proportion de molybdène a entraîné une modification beaucoup moins nette de la microstructure. Ilest apparu également que l'augmentation de la teneur en carbone réduisait l'énergie de la phase supérieure, phénomène attribué à la limite d'élasticité conventionnelle élevée du métal fondu et à l'amélioration de la précipitation du carbure (cupulation améliorée).