Self-shielded Flux-cored Wire Research Articles

Underwater wet welding of high-strength low-alloy steel using self-shielded flux-cored wire with highly exothermic Al/CuO mixture

Underwater wet welding processes with minimal energy consumption and high efficiency is the future goal for researchers in the field. Al/CuO exothermic mixtures in consumables for land welding process can improve welding process stability and decrease the electrical dependence of the welding process. To confirm the beneficial effects of Al/CuO thermite and gain a better understanding of metallurgical properties of the thermite welds in underwater environment, this study investigated underwater wet self-shielded flux-cored arc welding (FCAW-S) of high-strength low-alloy steel with highly exothermic Al/CuO mixture. The effects of Al/CuO thermite on arc stability, weld metallurgical behavior and melting characteristics of flux-cored wire were clarified. The ratio of chemical heat in the flux to the heat required to melt welding wire increased from 4.7% to 38.4% with the addition of Al/CuO, potentially accelerating the melting of flux-cored wires. The arc stability with thermite addition was superior to that without the addition of thermite. The presence of copper as a result of metallurgical reactions had a substantial impact on metallurgical behavior of underwater wet welds. The ferrite weld was a non-equilibrium Cu supersaturated solid solution, which increased the microhardness and tensile strength of wet welds. The measured cooling time proved that the incorporation of Al/CuO had the capacity to reduce cooling rate. The incorporation of 50 wt% thermite yielded a 7.8% increase in welding process efficiency compared to the base formulation. Current work provided an important direction for the development of a chemically self-heating flux-cored wire.

Effect of Nano-Y2O3 on the Microstructure and Properties of Fe-Cr-C-N-Al Surfacing Alloy

In this paper, Fe-Cr-C-N-Al-Y wear-resistant surfacing alloy was prepared by open-arc surfacing with self-shielded flux-cored wire. The wear properties of the surfacing alloy were analyzed using an MLS-23 rubber wheel wet sand wear tester. The phase composition and microstructure of the surfacing alloy were analyzed using X-ray diffraction, scanning electron microscope, electron backscatter diffraction and transmission electron microscope; the strengthening mechanism and wear mechanism of the alloy were discussed. The results show that the microstructure of Fe-Cr-C-N-Al-Y surfacing alloy is composed of M + γ-Fe + M7C3 + AlN. When the content of nano-Y2O3 is 0.456 wt.%, the formability of the surfacing alloy is the best, and the wetting angle is the smallest, which is 50.8°; AlN and M7C3 precipitate the most, and the microstructure grain is the smallest. At this time, the hardness value of the surfacing alloy is up to 62.3 HRC, which is 11.8% higher than that of the unmodified surfacing alloy. The minimum wear weight loss is 0.125 g, and the wear resistance is increased by 41.86%. The wear mechanism of the surfacing alloy is mainly a plastic deformation mechanism, and the material removal processes are microcutting and furrow wear. This study provides theoretical guidance for refining primary carbides and improving the wear resistance of high chromium cast iron.

The Efficiency of Thermite-Assisted Underwater Wet Flux-Cored Arc Welding Process: Electrical Dependence, Microstructural Changes, and Mechanical Properties

Alumino-thermic additions to the flux-cored wire can be utilized to enhance welding heat input, improve welding productivity, and minimize the dependency on power sources in the air environment. In this article, the influence of Al/Fe2O3 thermite on electrical dependency, microstructural characteristics, and mechanical performance during the underwater wet welding of Q235 steel was investigated. The results revealed that adding exothermic flux enhanced the underwater wet welding appearance. The basicity of the slag steadily decreased from 1.77 to 0.73 because of the formation of Al2O3. Thermite increased the quantity and diameter of inclusions in the underwater wet weld metal. The excessive addition of Al/Fe2O3 thermite resulted in agglomerated inclusions in the weld metal. Significant microstructural changes from grain boundary ferrite to acicular ferrite were mainly caused by the de-oxidation products of the thermite process. When thermite was added to the flux-cored wire, the ultimate tensile strength first increased and then decreased, while the microhardness of the underwater wet welds showed an obviously increasing trend. The addition of exothermic flux additions to the flux-cored wire can help generate chemical heat and increase the energy required to melt the wire. This study established a link between thermite addition and joint performance, paving the way for the development and application of thermite-assisted self-shielded flux-cored wire.

Comparative studies of the three-body abrasion wear resistance of hardfacing Fe-Cr-C-B-Ti alloy

In this research, the mechanical and tribological properties of two deposited metal of Fe-C-Cr-B-Ti alloying systems. In this study, comparative tests of the deposited metal hardfacing by two self-shielded flux-cored wires electrode were carried out: with an exothermic additive (110Cr4Cu5Ti1MnVB) and without an exothermic additive (140Cr15TiSi1MnVB). Abrasive wear resistance was evaluated using a slightly modified procedure on a standardized tribological machine for abrasive wear, according to the limits established by the ASTM G65. The results of studies of the efficiency of introduction of an exothermic addition CuO-Al system into the core filler of a flux-cored wire electrode were presented.

Development of Self-Shielded Flux-Cored Wires for Arc Welding of Low-Alloy Steels

Current aspects of the developing of modern self-shielding flux-cored wires composition for arc welding of low-alloyed steels are considered. Advantages and disadvantages of flux-cored wires of carbonate-fluorite, oxide and oxide-fluoride types of are shown in comparison. The effectiveness of gas shielding of molten metal at welding with self-shielding flux-cored wires of carbonate-fluorite type is analyzed considering the thermal properties of their cores. It is shown that to improve reliability of gas shielding at welding using the wires of this type it is important not only to ensure generation of sufficiently large volume of shielding gases at thermal destruction of the wire core, but also to control this process, providing gas evolution at all stages of heating and melting of the wire. The results of complex thermal analysis of the wire core mixtures containing, for example, lithium carbonate show substantially large heat losses for heating and melting of the wire core, which are accompanied by the development of energy-intensive processes of thermal destruction of core components. It is shown that the limitation of lithium carbonate content in the wire at the level of not more than 2 wt. % allows not only to preserve welding arc burning stability at the acceptable level but also to provide effective gas shielding of molten metal and easy separation of slag crust. The control of thermochemical reactions in the core is achieved by selection of its proper composition to ensure favorable melting of flux-cored wire and electrode metal transfer to the welding pool. Results of metallographic examinations of distribution and composition of non-metallic inclusions in metal of the welds made with wires of the oxide and oxide-fluoride types are presented. Main properties of the developed self-shielding flux-cored wires and recommendations on welding are given in conjunction with prospective fields of their application.

Corrosion resistance of niobium-added slag-free self-shielded flux-cored welding overlay in neutral solution

The niobium-added iron-based slag-free self-shielded flux-cored wire was developed and the effect of niobium addition on the corrosion resistance in neutral pH solution was investigated. The carbides, including NbC carbides, primary (Cr, Fe)7C3, and eutectic (Cr, Fe)3C carbides, remain intact after neutral corrosion, but the grain interface is corroded preferably for all the niobium-added welding overlays. The eutectic microstructure of 7.2 wt-% niobium-added welding overlay, which has more grain interface, leads to severe corrosion. When niobium addition reaches 14.4 wt-%, the welding overlay possesses the best corrosion resistance since more NbC carbides are formed, prophase austenite dendrite is precipitated, decreasing the grain interface, and chromium content is increased in the matrix of the hypoeutectic microstructure.

Comparative Evaluation of Self-Shielded Flux-Cored Wires Designed for High Strength Low Alloy Steel in Underwater Wet Welding: Arc Stability, Slag Characteristics, and Joints’ Quality

Comparative Evaluation of Self-Shielded Flux-Cored Wires Designed for High Strength Low Alloy Steel in Underwater Wet Welding: Arc Stability, Slag Characteristics, and Joints’ Quality

Investigation of Process Stability and Weld Quality of Underwater Wet Flux-Cored Arc Welding of Low-Alloy High-Strength Steel with Oxy-Rutile Wire

Abstract The paper described the experimental findings of underwater wet welding of E40 steel using self-shielded flux-cored wire with a TiO2-FeO-MnO slag system. The arc stability, weld quality and corrosion resistance with different heat inputs were studied. The results showed that the wet welding process of the designed wire displayed good operability in the range of investigated parameters. The microstructure and mechanical properties of the weld metal depended on the heat input. Due to the high fraction of acicular ferrite in the weld metal, the mechanical properties of the weld metal under low heat input had better tensile strength and impact toughness. Fracture morphologies at low heat input had uniform and small dimples, which exhibited a ductile characteristic. The diffusible hydrogen content in the deposited metal obtained at a heat input of 26 kJ/cm significantly reduced to 14.6 ml/100g due to the combined effects of Fe2O3 addition and the slow solidification rate of molten metal. The microstructure also had a significant effect on the corrosion resistance of the weld metal. The weld metal with high proportions of acicular ferrite at low heat input exhibited the lowest corrosion rate, while the base metal possessed a reduced corrosion resistance. These results were helpful to promote the application of low alloy high strength steel in the marine fields.

Hardfacing of Copper

The article discusses the primary issues of the hardfacing of copper elements exposed to intense abrasive wear, gas-abrasive wear at high temperature and in contact with liquid metal. In addition, the article presents test results concerning the surfacing of copper grade M1 performed using a self-shielded flux-cored wire providing weld deposit Fe14 and plasma powder surfacing performed using powder providing weld deposit Ni3 (in accordance with EN 14700).

The Effect of a Welding Technology on the Abrasive Wear Resistance of Joints in Abrasion-Resistant Plates

The article presents results of tests concerning the metal-mineral abrasive wear resistance of butt welded joints with abrasion-resistance overlay weld HARDPLATE 100S 5+3 made using a covered electrode with the solid core and the flux core as well as a self-shielded flux-cored wire. The significance of the above-named effect was determined using a completely randomized design. The scope of tests also included the analysis of the chemical and phase compositions, hardness measurements as well as the macro and microscopic metallographic tests of welded joints in abrasion-resistant plates.

Effects of electrode polarity on the droplet transfer mode in self-shielded flux-cored arc welding

Abstract Self-shielded flux-cored wires (AWS E71 T FCW) are widely applied in the fields of construction. In this study, the effect of the electrode polarity on the mode of droplet transfer and arc stability in self-shielded flux-cored arc welding was investigated by the high-speed video camera system and electric signal. The results showed that the change of electrode polarity determined different mode of droplet transfer. In direct current electrode positive (DCEP), droplet transfer mode presented the globular repelled transfer. And the area of the arc root decreased at the bottom of the droplet because of the metallurgical reaction effect of the flux core, it resulted in the relatively lager electromagnetic force acting on the droplet, which hindered the droplet transfer. Moreover, when the droplet was separated from the welding wire, the droplet was kept rotation state under the action of the resultant force couple. In the direct current electrode negative (DCEN), the electromagnetic force promoted the droplet transfer and droplet transfer mode shown spray transfer mode. Due to the particularity of the composition and distribution of the molten slag, the conductive path was generated easily at the connection between the droplet and the wire, it made the arc root climb up and wrap the droplet, the necking phenomenon appeared obviously. In DCEN or DCEP, arc voltage and arc current have little effect on the droplet transfer mode. At the same time, compared with the welding process in DCEP, the welding process in DCEN had the advantages of higher arc stability, fewer welding spatter.

Rare earth elements in self-shielded flux-cored wires and their effect on the weld toughing of U75V rail steel

Self-shielded flux-cored wire is a new type of welding material that has the advantages of outdoor and high-efficiency application, and it has been used widely for rail repair. A self-shielded flux-cored wire with high alkalinity and rare earth elements was taken for research, and the microstructure, inclusions, hardness and the impact toughness were studied. Rare earth elements could eliminate the oxygen and sulfur when they were added into the molten pool. The addition amount has been optimized to the range of 4% in the self-shielded flux-cored wire when used for rail repairing.

Rail surfacing repairing technique with self-shielded flux-cored wires

A newly self-protecting flux-cored wire was used for simulated U75V rail repairing and five welding process parameters were applied. The influence of welding parameter on the hardness and microstructure of the wire and solder layers was investigated. The single-pass welding process with different preheating parameters and post-treatment parameters were also taken into research. The results showed that the welding process parameters have a significant influence on the weld quality, and mismatched parameters will increase the welding defects. The number of welding layers has a great influence on the hardness and structure. Increasing preheating temperature and a post-heat treatment at a high-temperature can enhance the hardening effect.

Effect of Parameters Change on the Weld Appearance in Stainless Steel Underwater Wet Welding with Flux-Cored Wire

The underwater wet welding (UWW) technology is rapidly developing as a crucial method in the maintenance work of marine equipment and offshore platform. The rapid development of UWW technology has also exposed the problems to be solved urgently. Therefore, the influence of welding parameters on the weld appearance and welding spatters was investigated in this paper. The main welding parameters used in the study are welding current, arc voltage, welding speed and the contact tip-to-work distance (CTWD). Through the orthogonal test, it is found that, as each welding parameter increases within a certain range, the amounts of welding spatter decreases first and then increases, and the weld forming effect first becomes better and then deteriorates. The amount of wet welding spatter is mainly affected by the welding speed. When the welding speed is low, the splash is more, and the change of the welding current and the arc voltage has a little effect on the number of spatters. When the welding speed is large, the spatter is most with a small welding current and a large arc voltage. After evaluating the weld morphology obtained by welding under various parameters, a set of optimal parameters was obtained. The best parameters for the underwater wet welding of stainless steel with self-shielded flux-cored wire are determined to be 200 A-29 V-2.0 mm/s-15 mm (CTWD).

Microstructure and Wear Performance of Cobalt-Containing Iron-Based Slag-Free Self-shielded Flux-Cored Wire

A new type of cobalt-containing iron-based slag-free self-shielded flux-cored wire was developed for hardfacing. The influence of cobalt additions on the microstructure and wear performance of the hardfacing was investigated. The cobalt-containing iron-based hardfacing alloy has a typical hypereutectic microstructure consisting of primary M7(C, B)3 carbide, and a eutectic of M3(C, B) carbide and austenite (part of which subsequently transformed into martensite). Cobalt promoted the formation of austenite and changed the morphology of the primary carbide and eutectic colonies. The morphology of primary carbide became fragmented with increasing cobalt due to the possible impeding effect of cobalt to the movement of the M7(C, B)3/liquid interface. Different structures of the eutectic carbides were observed—the chrysanthemum structure for 1.42 wt.% cobalt, the skeleton form for 2.88 wt.% cobalt, the radial stripe 4.37 wt.% cobalt and the discrete stripe for 5.75 wt.% cobalt. Wear loss of the hardfacing alloy containing 2.88 wt.% cobalt was the smallest among all the alloys, owing to the large primary large carbide and skeleton-shaped eutectic carbides, the proper amount of austenite phase separating the M7(C, B)3 and M3(C, B) carbides, the solid solution strengthening by cobalt in the matrix, and the high hardness of the alloy. Moreover, the wear resistance has a tendency to decrease with the increase in velocity as well as load.

Effect of simultaneous addition of ferroniobium and ferrotitanium on properties of hardfacing

ABSTRACTThe slag-free self-shielded flux-cored wire with simultaneous addition of ferroniobium (Fe-Nb) and ferrotitanium (Fe-Ti) was developed to fabricate the iron-based hardfacing alloys. The transfer coefficients of Nb and titanium of slag-free self-shielded flux-cored wire were 91.2 and 63.8%, respectively. The changes in microstructures indicate that Nb and Ti addition shifted the carbon concentration in the remaining liquid to one corresponding to the near eutectic state owing to the formation of (Nb, Ti)C which consumed carbon. The wear loss of the hardfacing alloy with 18 wt-% Fe-Nb and 6 wt-% Fe-Ti addition was the smallest among all the alloys owing to the formation of reinforced uniform quadrangle-shaped (Nb, Ti)C carbides in the refined microstructure and the highest hardness.

自保护药芯焊丝激光-电弧复合堆焊参数对熔滴过渡的影响

自保护药芯焊丝激光-电弧复合堆焊参数对熔滴过渡的影响

Influence factors of X80 pipeline steel girth welding with self-shielded flux-cored wire

For girth weld of high-pressure oil and gas transmission pipeline, there is impact toughness values deviation phenomenon with self-shielded flux-cored semi-automatic welding technology. The macro-images, microstructure and mechanical performance of girth welding joint have been investigated by OM, SEM, TEM. The results show that there are several factors of impact toughness unqualified values of weld joints, such as welding heat input, coarse grain zone and a chain of M–A organisations, Al2O3 and Zr Precipitates particle sizes and distribution et al., which are the main unqualified reasons of welding impact toughness of the semi-automatic self-shielded core butt welding process of X80 pipeline steel.

Failure Analysis and Research Progress of Resurfacing Welding Material of Coal Mill Roller

Failure mode of coal mill roller was comprehensively analyzed and current situation of mill roller repair was elaborated. Process characteristic and application effect of metal cerement and high chromium cast iron building-up materials were expounded in the article. Owing to excellent wear resistant and low cost, high chromium cast iron building-up materials have been applied widely. The current research situation of self-shielded flux-cored wire with high chromium cast iron was summarized and the existing problem and probable solution were pointed. Key word: Coal mill roller, Abrasive wear, Flux-cored wire, Resurfacing welding

Effects of titanium additive on microstructure and wear performance of iron-based slag-free self-shielded flux-cored wire

In this investigation, a new slag-free type of iron-based self-shielded flux-cored wires (SSFCW) with varying titanium content was developed to fabricate experimental hardfacing alloys. The titanium can be transferred to the weld pool using magaluma powder and graphite in the wire as stronger deoxidizers. The phase composition and microstructure of the as-prepared alloys were characterized by X-ray diffraction and scanning electron microscopy. The wear behavior of SSFCW was investigated using a HT-500 pin-on-disk tribometer. The results showed that TiC was preferentially formed in the alloy. It acted as the nucleus of the primary M7(C,B)3 (M=Cr, Fe mainly) carbides; and that it decreased the amount of M7(C,B)3 when titanium was added into the wires. When 24wt.% ferrotitanium (Fe–Ti: containing 30wt.% Ti) was added, the microstructure of the alloy changed from a hypereutectic structure to a hypoeutectic one due to the formation of TiC, which consumed carbon. The addition of titanium to iron-based SSFCW improves the wear resistance of the alloy with respect to the higher hardness and refined microstructure. The wear loss of the sample with 24wt.% Fe–Ti was the smallest among all the samples.