Current trends in welding flux development

Welding flux makes significant contribution to weld-metal quality, productivity of welding process and rapid deployment of new materials. Deployment of new materials has been hampered because of lengthy trial-and-test experiments and paucity of methodology for modelling and optimisation in the traditional welding flux development. This paper discussed the contributions made to mitigate the drawbacks of traditional welding flux development in areas of experimentations, prediction modelling and optimisation. Limitations of current efforts were identified and suggested for future research, namely (i) current response models are limited to well-behaved flux systems and do not account for edge and additive effects of flux ingredients (ii) non-incorporation of stakeholder’s preferences concerning the relative importance of quality attributes (iii) lack of prediction and optimisation tools for determining optimal coating factor and flux heights for Shielded Metal Arc Welding and Submerge Arc Welding respectively and (iv) non-continuous response functions and concave regions of the trade-off surface are not considered.

Framework for incorporating stakeholders’ preferences in lifecycle welding flux design

Welding flux design involves optimising multiple quality attributes which are often conflicting and are of varying degree of concern to the stakeholders. The attributes are often selected as design criteria and are sometimes at different levels in the hierarchy such as primary, secondary and tertiary attributes. The articulation and incorporation of the opinions of stakeholders concerning the intensity of importance attached to each attribute at all the levels in the hierarchy in the optimisation process has remained a challenge. In this study, a framework was proposed for the articulation and incorporation of the preferences of stakeholders concerning all levels of attributes and illustrated with a lifecycle welding flux design case from the literature involving 5, 21 and 25 primary, secondary and tertiary criteria, respectively. Fifteen out of the 21 secondary criteria could not be further unbundled and were added to the tertiary criteria to make 40 lowest level criteria. The subjective judgements of stakeholders were converted to weighting coefficients using the analytical hierarchy process. The coefficients for the lowest level criteria were converted to global weights which were the preference indices for use in the optimisation models. Based on the values of , moisture pick-up, extrudability and slag detachability were ranked 1st , 2nd , and 3rd respectively and the respective 38th, 39th and 40th lowest level criteria were fume generation, dilution and charpy impart strength.

Reliability of Neural Implants—Effective Method for Cleaning and Surface Preparation of Ceramics

Neural implants provide effective treatment and diagnosis options for diseases where pharmaceutical therapies are missing or ineffective. These active implantable medical devices (AIMDs) are designed to remain implanted and functional over decades. A key factor for achieving reliability and longevity are cleaning procedures used during manufacturing to prevent failures associated with contaminations. The Implantable Devices Group (IDG) at University College London (UCL) pioneered an approach which involved a cocktail of reagents described as “Leslie’s soup”. This process proved to be successful but no extensive evaluation of this method and the cocktail’s ingredients have been reported so far. Our study addressed this gap by a comprehensive analysis of the efficacy of this cleaning method. Surface analysis techniques complemented adhesion strengths methods to identify residues of contaminants like welding flux, solder residues or grease during typical assembly processes. Quantitative data prove the suitability of “Leslie’s soup” for cleaning of ceramic components during active implant assembly when residual ionic contaminations were removed by further treatment with isopropanol and deionised water. Solder and flux contaminations were removed without further mechanical cleaning. The adhesive strength of screen-printed metalisation layers increased from 12.50 ± 3.83 MPa without initial cleaning to 21.71 ± 1.85 MPa. We conclude that cleaning procedures during manufacturing of AIMDs, especially the understanding of applicability and limitations, is of central importance for their reliable and longevity.

Reactions at the molten flux-weld pool interface in submerged arc welding

In submerged arc welding (SAW) of chromium (Cr) containing steels, Cr is usually added to the weld metal from the weld wire, and not from the welding flux. Manufacturing of weld wires of specific compositions is expensive and time consuming and cannot closely match all the desired alloy compositions. Therefore, the weld wire chemistry is usually over matched to the base plate composition. Better matching between the weld metal and base plate is possible if the weld metal incorporates Cr from Cr containing metal powder, instead of sourcing Cr from weld wire of limited Cr content. Because Cr is easily oxidised, the oxygen partial pressure in SAW must be controlled. This work illustrates the control of the oxygen potential at the molten flux-weld pool interface by using aluminium (Al) powder addition. The controlled oxygen potential at the molten flux-weld pool interface ensures increased Cr powder transfer into the weld pool, without interfering with oxygen transfer from the plasma arc to the weld pool. The objective of this work is to use targeted powder additions to better control Cr reactions in SAW to improve Cr metal transfer to the weld metal and maintain an acceptable level of oxygen in the weld metal.

The Sectors Workpieces and Drum Reel’s Die Cubes Electroslag Casting with Exothermic Electrical Conductive Fluxes

It has been established that the developed method of manufacturing workpieces for the sectors of the drums of X20CrMoWV3 steel reel’s and die cubes from X5CrNiMo steel using a solid start and exothermic flux significantly reduces the complexity of their manufacture. The cast reel’s drum sectors workpieces and die cubes, obtained by the electroslag remelting (ESR) method, had a smooth surface without corrugations, sinkers, and slag inclusions. Heat treatment provides the required mechanical properties and the absence of flocs in the cast electroslag metal. An effective way to increase the performance of electroslag processes is using the exothermic flux, which contain scale, ferroalloys, aluminum powder and standard flux (welding flux ISO 14174 – S F AF3, etc.) in quantities sufficient for the exothermic reactions to occur, which ensures the generation of additional heat in the starting period of electroslag processes and contributes to the accelerated induction of the slag bath of the required volume at the “solid” start both monofilar and bifilar schemes of conducting the process instead of the “liquid” start. Electroslag processes using an exothermic alloyed flux on a “hard” start allow to obtain (compared to existing methods of slag bath formation) an increasing in the output of a suitable metal 2...10 %; saving on melting 1 kg of standard flux 1.2...1.4 kW h; reducing of the starting time of the ESR process to 25 %.

Use of barium-strontium modifier for the manufacturing of welding flux based on silicomanganese slag

The possibility of using a barium-strontium modifier as a gasprotective and refining additive for welding the fluxes based on crushed slag from the production of ferrosilicomanganese is presented. The barium-strontium modifier BSK-2 produced by JSC “NPK Metalltekhnoprom” according to TU 1717-001-75073896–2005 was used as a material for the study. The base of the welding flux was silicomanganese slag produced by the West Siberian Electrometallurgical Plant. The research work on new welding fluxes and flux-additives was carried out using the equipment of the Scientific and Production Center “Welding Processes and Technologies” and the Center for Collective Use “Materials Science”. The use of barium-strontium flux additive was carried out in two ways. In the first option, the flux-additive was made by grinding barium-strontium to a dust-like fraction of less than 0.2 mm with further mixing with liquid sodium glass, drying in a furnace, crushing and separating a fraction of 0.45 – 3.00 mm. In the second option, the flux additive was used in the form of dust with a fraction of less than 0.2 mm. The additives were mixed at a ratio of 2 – 10 % of mass of the slag produced by silicomanganese. Surfacing of the samples was carried out with a welding wire of the sv-08GA grade on a substrate of steel grade 09G2S with a thickness of 20 mm. Quality of the deposited metal was studied, the chemical compositions (deposited layers, slag crusts, the used flux) were investigated by X-ray fluorescence method on XRF-1800 spectrometer and by atomic emission method on DFS-71 spectrometer. The degree of contamination with non-metallic inclusions (non-deforming silicates, point oxides, sulfides) was studied using OLYMPUS GX-51 optical microscope in the magnification range from 100 to 1000. The laboratory studies on the surfacing of steel samples have shown that due to introduction of a flux additive made from barium-strontium modifier, the metal is refined, and the concentration of sulfur and phosphorus decreases. The use of a mixture of a barium-strontium modifier with liquid glass as an additive is preferable to the use of an additive in the form of a dust. It was revealed that the best samples from the point of view of the degree of contamination of the deposited metal with nonmetallic inclusions are samples made using no more than 8 % of barium-strontium flux additive.

New submerged arc welding flux for hardfacing of Hardox steels

In this study, the usability of a new submerged arc welding flux was investigated to develop the surface properties of Hardox steels. In the hardfacing welding processes for Hardox 400 steel, four welding speeds resulting in varied heat inputs were applied. Through an analysis of the chemical composition, microstructure examinations, hardness measurements and wear tests, the possibility of hardfacing properties control due to the change of process parameters were determined. In the experimental studies, the hardness of the hardfacing obtained at a welding speed of 30 cm × min-1 was measured as 42 HRC while the hardness of the hardfacing obtained at a welding speed of 48 cm × min-1 was measured as 57 HRC. Moreover, in the wear tests, results consistent with the hardness values were obtained. It was understood in the light of the results that the use of high carbon ferro-chromium 20 wt.-% in a submerged arc welding flux mixture may be useful in improving hardness and wear properties of Hardox steels through hardfacing welding processes.