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TipTig, Autogenous dissimilar welding, Nanostructured coatings, more on brittle fracture, WeldCraft August 03, 2009 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#072 - TipTig: An Improved Welding Process, Autogenous Dissimilar Lap Welds?, Filler Metals for Nanostructured Coatings, more on Brittle Fracture, WeldCraft Pro, Hybrid Welding, Stress Corrosion Cracking and more... DON'T USE REPLY to send us your messages! Use Contact Us instead. This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. You are urged to pass-along this publication to your friends, if you like it, and if you want to help them.
If you received this from a friend and if you like what you read, please subscribe free of charge and you will also receive a bonus book on Practical HARDNESS TESTING Made Simple. Note: References to articles or other documents are given here in one of two forms. If the links are "live" (usually underlined or otherwise highlighted) they are operated with a click of the mouse. If they are URL's (Uniform Resource Locator), which is the analogue of an address, they begin with "http://..." or "www.". These are not live and must be copied and pasted entirely into the browser (after having been selected with the mouse or otherwise). If they are long they may be displayed in two or more lines. In that case one has to care that the URL be copied completely in a single line without any space, and Enter.
1 - Introduction 2 - Article - An Improved Welding Process 3 - How to do it well: Autogenous Dissimilar Lap Welds? 4 - Filler Metals for Nanostructured Coatings 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - More on Brittle Fractures 8 - Site Updating: Hybrid Welding, Stress Corrosion Cracking 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: WeldCraft Pro 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction This 72nd issue of Practical Welding Letter starts with the promised presentation of an important improvement of the classic Gas Tungsten Arc Welding process, described as a real revolution. This innovation, whose claimed advantages seem overwhelming, promises remarkable advantages in ease of learning and performance, in speed and in economy of welding, and in quality. Although in use for some years already in Europe, it is only presently being introduced to the United States by Ed Craig (www.weldreality.com), a renowned expert who saved an untold number of stalled welding processes all over the world. Readers having significant interests in GTAW would possibly gain by exploring this improved process and by taking part in upcoming workshops to get first hand impression. Then, further down the page, one can see a discussion concerning the suitability of performing autogenous welding (without filler metal) in an overlapping joint of dissimilar materials. The original discussion in the Welding Journal is too complex to be summarized in a few sentences, but it is important to get a clue of how seemingly simple cases should be examined in depth if one wants to understand what happens in reality in the weld metal. The article coming next, points to current research aimed to improve the properties of coatings by embedding nanostructured powders into coating layers to improve wear resistance. The efforts are remarkable, as it is believed that this approach will in time provide considerable progress. For the time being, however, to the best of our knowledge, there is no universally applicable process or new material capable of solving most of current problems. Following the perplexed reaction of a reader to the note on Impact Testing appearing in PWL last issue, I try to remind that even materials known to be generally ductile may occasionally fail by brittle fracture. It is worth remembering. The Pages of this Month, added to the Welding Advisers website, are dedicated to Hybrid Laser-Arc Welding, a synergistic process of many advantages, and to Stress Corrosion Cracking, a dangerous occurrence that could undermine the stability of important structures, if overlooked during design and construction. Finally the Contribution of David J. Keats is gratefully acknowledged, presenting an underwater candidate welders training Course that enjoyed recognition as suitable preparation towards certification issued by the UK’s largest engineering awarding-body EAL (EMTA Awards). The other usual sections can be found at their place. Enjoy your reading and your vacation if you take one as we too will take soon. Use the Contact Us form to let us have your comments and feedback. (Don't use Replay). 2 - Article - An Improved Welding Process Not every day one has the chance of announcing an Improved Welding Process. But this time, as briefly mentioned when presenting the last Survey, that many readers helped to fill by kindly contributing their answers, we have the rare and lucky opportunity of revealing this new approach, likely to change completely all that was known up to now about Gas Tungsten Arc Welding. I was advised of this breakthrough by my mentor and friend Ed Craig, who was so impressed by the results, that hastened to secure to himself the distribution rights for the USA, Australia, Mexico, Brazil and other countries. Ed Craig plans to hold scheduled work shops (demonstration and training courses) where interested persons will have the opportunity to see the process in action and to be exposed to its benefits. The new process is called TIP TIG by the inventor, Ing. Siegfried Plasch from Austria. It consists in a wire feeder that superposes a to and fro motion (at 15 Hz frequency of oscillation), upon the regular feeding of a filler wire whose tip dips in the molten puddle created in the workpiece by a special water cooled tig welding torch. The oscillation motion modifies the surface tension of the liquid molten metal, with the surprising result that the whole equilibrium of the phases is altered, permitting deeper penetration, absence of spatter, release of porosity, higher deposition rate and welding speed (3 to 10 time faster) and finally higher quality that translates in less rework and improved productivity. It is stated that welders using TIP TIG will easily master the process and pass qualification tests after short training sessions. This easy to use process has been successfully applied to all of the common metals, in all welding positions, to all joint configurations and also for overlaying. The results, relative to weld speed, costs and weld quality are defined as amazing, many times better when compared to regular Tig, Mig and FCAW. The process is equally applicable to manual welding, where it is said to permit welding with one hand holding the composed torch, while the other welder's hand rests idly or helps keeping the torch firmly, and to mechanized welding, where the welder becomes a machine operator. Depending on the application one can work either with cold wire technique (where no preheat current is running through the wire) or with preheated hot wire technique. Many existing GTAW power sources can be used. In this process welding current and wire feed speed are independent variables controlled separately. A few parameter settings (wire feed / weld amp) will cover most of welding procedure specifications for most applications. For more information, including details on the first Free TIP TIG Workshop, see: http://www.weldreality.com/TIP-TIG-Welding.htm http://www.tiptig.co.uk/ www.cyberweld.co.uk/tiptig.html (Photos and Videos) Additional information will be gladly published here as soon as available. 3 - How to do it well: Autogenous dissimilar lap welds? Among the best columns published in the Welding Journal are the Q&A, covering different subjects and written by most competent Authors who explain in depth the reasoning behind the discussion of the treated cases. For readers eager to learn from "Case Histories" this is most recommended reading. In the July 2009 Issue, on page 18, the situation described and analyzed concerns fillet welds of mild steel flat metal overlapping stainless steel sheets or plates. The inquirer asks if it would be feasible to perform those joints using autogenous (without additional filler metal) Gas Tungsten Arc Welding. The answer is provided by Damian J. Kotecki, past President of AWS and a renowned authority in stainless steel welding. The analysis of the case is instructive in itself inasmuch as it shaws the depth to which one must dig if one wants to understand the risks connected with the application, as the variable dilution rate can only be guessed. It would be possibly misleading if I tried to summarize the neat exposition, therefore I will abstain, except perhaps for the final conclusion that autogenous welding in this case is not recommended. Interested readers are urged to seek the original article mentioned above, a reprint thereof they can obtain from AWS.
4 - Filler Metals for Nanostructured Coatings Many attempts to enhance mechanical properties of coatings are made by using nanoscaled powder materials. The reasoning is that, similar to the effect in oxide dispersion strengthened bulk materials, hindrance of dislocation movement and synergetic effects of matrix material and nanoparticles are expected to improve coating performance. Various projects currently aim to produce nanometric metallic (Co- and Ni-based alloys) and ceramic powders (tungsten and chromium carbides) to obtain composite spray powders and thermally sprayed nanostructured coatings with higher wear and corrosion resistance. Production of nanopowders uses high-energy milling methods performed in liquid nitrogen and magneto hydrodynamic atomizing. To obtain nanostructured coatings, cold gas dynamic spray and HVOF spray methods are used. The aim of these developments is to obtain an increase in abrasive wear resistance of coatings up to 50% without increase in hardness and decrease in toughness. Thermal Spray Coatings Performance of Plasma Sprayed Nanostructured and Conventional Coatings Nano Powders improve Wear Resistance of
Coatings 5 - Online Press: recent Welding related Articles and Videos Directly downloadable from Friction Welding (video) The 10 Must Have Hand Tools Of Every Welder (Commercial video) ORBIMATIC Orbital Welding Systems Germany (Commercial video) Why should you choose induction heating? 6 - Terms and Definitions Reminder Friction Welding Force is the compressive force applied to the faying surfaces from the time when there is relative motion between the contacting workpieces to generate friction welding heat until the application of the forging force. Longitudinal Weld Test Specimen is one with its major axis parallel to the weld axis. Orifice Throat Length is that of the constricting orifice in the plasma arc torch or plasma thermal spray gun. Push Angle is the same as the travel angle when the electrode is pointing in the direction of the weld progression. It is the angle (less than 900) between the electrode axis and a line perpendicular to the weld joint axis, in a plane formed by the electrode and the weld axis. Shoe is a metal block used in a variety of manufacturing operations to form or support the part being processed. In welding a backing shoe maybe cooled and fixed or sliding to define the surface where the weld metal will solidify without joining to it. Toe Crack is that starting at or near the junction between the weld face and the base metal. Virgin Flux is new, unused granulated flux for submerged arc welding, made from new raw materials. Weld Tab, is a disposable additional element of the same material, located at either end of a joint for starting or ending on it the weld likely to contain local imperfections. 7 - Article - More on Brittle Fractures Referring to the note on Impact Test published (7) in the last issue of this newsletter, a kind reader wrote the following comment: "I take issue with the Comment in issue 71 concerning not labeling materials as ductile or non-ductile relating to notch toughness. It is common practice to label the solution annealed austenitic stainless steels and non-ferrous nickel & copper alloys and aluminum alloys as "notch-tough" or "ductile." Brittle fracture is never a concern down to -325F and for some of these materials (and all of the common aluminum alloys) down to -452F. For the nonferrous nickel & copper alloys and aluminum alloys, welding is not a concern for loss of notch-toughness." I asked the writer to expand somewhat the argument in a well organized article that I would have published with proper reference and affiliation, but he preferred not to add anything to the above mentioned note. While it is true that materials can be defined as brittle or tough depending on the macro aspect of their fracture in a typical uniaxial tensile test, one should understand that in reality the fracture aspect of complex engineering structures depends on many factors besides the basic material quality. In particular chemical composition, impurity elements and microstructural constituents may largely affect the behavior of materials under stress. Therefore in my opinion the common practice of labeling materials as notch-tough or ductile can be misleading if inducing someone to think that a "ductile" material will never fail in brittle manner. The following quotes are from ASM Metals Handbook Eight Edition Volume 10, Failure Analysis and Prevention, page 61: "Ductile and brittle are terms that describe the amount of macroscopic strain that occurs prior to final separation of a specimen or part as it breaks. Fractures that do not exhibit significant ductility (elongation or reduction in area) are considered to be brittle, regardless of whether or not there is microscopic evidence of plasticity on the fracture surface." "Fractures are not always exclusively ductile or brittle; often a fracture will exhibit both a ductile region and a brittle region." "Fractures in fragile materials occur in a brittle manner, whereas fractures in tough materials are usually ductile. A part made of a tough material, however, can sometimes fracture in a brittle manner, if that part contains a large enough flaw, or if there is sufficient elastic and plastic constraint." Besides the three main factors that cause brittle fracture in materials usually showing ductility in their fractures (low temperature, stress concentration and rapid application of stresses) one cannot ignore other endangering conditions. Embrittlement can be caused by several improper heat treatment conditions, by hydrogen absorption, by contact with certain liquid metals, by sigma phase (a structural instability) in stainless steels and nickel alloys, by conditions promoting stress corrosion cracking (in stainless steels, aluminum, titanium and copper alloys). It is worth remembering that usually labeled "ductile" materials can still fail, occasionally, by brittle fracture. See also the new page on SCC presented hereafter in section 8. 8 - Site Updating: Hybrid Welding, Stress Corrosion Cracking The Pages of this Month deal with subjects already briefly treated in the past as short notes in PWL. The first Page summarizes what should be known about Hybrid Welding, the composite process that, by combining two unrelated power sources and by adding filler metals, permits to obtain a powerful synergy providing results widely exceeding those available by the same separate processes in succession. The main obstacle to wider application is the difficulty to develop proper procedures. It is a difficult process requiring expertise, time and resources, normally available only within large and prosperous industries. Click on Hybrid Welding to see it. The second Page, on Stress Corrosion Cracking, describes the conditions normally associated with the occurrence of this treacherous failure mode. It may be particularly insidious because no evident signs of impending danger are remarked up to the sudden failure. Therefore a diligent search must be done in every case where even a remote chance of SCC should be taken into account, to make sure that all precautions were taken care of. In particular materials, design, fabrication methods, internal stresses and stress relief, and the nature of the mildly attacking service solutions must be assessed, complemented with appropriate non destructive testing techniques. Click on Stress Corrosion Cracking to see this page. Check regularly for new pages in the Web Site Map or subscribe to the RSS feed using the instructions given in every page (www.welding-advisers.com) under the Navigation Bar. For finding what you may need, use the Google Search Box which appears in almost every page of the website. More often that not there is some reference to your subject either in the website or in the collection of Practical Welding Letters. And if you do not find what you need you can always Contact Us using the usual form. 9 - Short Items 9.1 - Bakelite is a proprietary name for a phenolic thermosetting resin used as a plastic mounting material for metallographic samples. 9.2 - Basic Oxygen Furnace is a type of furnace for modern steelmaking consisting in a large tiltable vessel lined with basic refractory material (whose major constituents are lime, magnesia, or both). After the furnace is charged with molten pig iron (for about 65 to 75% of the charge), scrap steel, and fluxes, a lance is brought down near the surface of the molten metal and a jet of high-velocity oxygen impinges on the metal. The oxygen reacts with carbon and other impurities in the steel to form liquid compounds that dissolve in the slag and gases that escape from the top of the vessel. 9.3 - Dip Coat in investment casting, is an extremely fine ceramic precoat applied as a slurry directly to the surface of the pattern to reproduce maximum surface smoothness. This coating is surrounded by coarser, less expensive, and more permeable investment to form the mold. 9.4 - Fibrous Fracture is the gray and amorphous fracture that results when metal crystals elongate before fracture occurs. When a fibrous fracture is obtained in an impact test, it may be regarded as definite evidence of toughness of the metal. 9.5 - Metallurgy is the science and technology of metals and alloys. Process Metallurgy is concerned with the extraction of metals from their ores and with refining of metals; Physical Metallurgy, with the physical and mechanical properties of metals as affected by composition, processing, and environmental conditions; and Mechanical Metallurgy, with the response of metals to applied forces. 9.6 - Pattern is a form of wood, metal, or other material around which molding material like sand is placed to make a mold for casting metals. Or a form of wax- or plastic-base material around which refractory material like ceramic slurry is placed in layers to make a mold for casting metals. Or a full-scale reproduction of a part to be used as a guide in cutting. 10 - Explorations: beyond the Welder Pizza tossing art unlocks secrets of tiny motors A Personal Electron Microscope (Commercial site) ATR - National Scientific User Facility (with video) NASA's Spitzer Images Out-of-This-World Galaxy Materials Podcasts - from ASM International 11 - Contributions: WeldCraft Pro I am glad to announce that I have been authorized to introduce, to the readers of Practical Welding Letter, "WeldCraft Pro", a self-teach Course especially prepared by David J. Keats of Speciality Welds. The course is designed to equip commercial divers with the skills necessary to produce high quality fillet welds underwater. The course is available to all training providers, to run, under license, through Speciality Welds' 'test-centre' status, with certification issued by the UK’s largest engineering awarding-body EAL (EMTA Awards). The programme is also recognized by IMarEST - Institute of Marine Engineering, Science and Technology. David J. Keats, president of Speciality Welds has been involved in the welding industry for over 34 years, of which 26 have been connected with underwater welding and training. David wrote the UK’s first formally approved qualification in underwater wet welding in 1991, and has been teaching wet welding skills since 1990. He has recently produced the first ever approved, self-teach training package. The purpose of this package is to offer to interested welding schools and to individual students a unified and approved syllabus and learning material, in view of making sure that essential knowledge is effectively learned and assimilated by the candidates. The fact that the Course is approved by the Certifying Authority EAL in the UK means that it covers all essential aspects of the preparation required. Course Outline The training is designed to equip commercial divers with the skills necessary to produce high quality fillet welds. Students will be introduced to all the relevant theory associated with the MMA welding process, together with relevant safe working practices, etc. Each specific topic is covered by a lecture where the learning outcome is clearly identified. See details at An intensive, closely supervised training course, delivered by one of the world's leading experts, provides both theoretical and practical hands-on experience for both wet and dry welding. The course consists of a series of lectures together with written and practical assignments and ultimately culminates in an end of course examination and welder qualification test. The practical exercises concentrate on developing the skills necessary to produce defect free fillet welds, through a number of well-planned and proven exercises and the theory is covered by a series of lectures covering 9 learning outcomes, which include the following:
For more information see the Speciality Welds website at I am grateful to David Keats who graciously permitted to present this note here. 12 - Testimonials The following are excerpts from the Feedback and Comment section of the Survey: Thanks for taking the time to set up and maintain the site. [...] Well done and keep the faith! Nothing to say for further improvement because I am satisfied the way it should be, I find it very useful to improve my craft. Just keep on publishing useful and informative materials. Thanks a lot. You provide very useful information. Keep up the fine work! You are doing a great job...Thanks Happy with it as it stands, thank you Keep up the Good Work Just keep on doing your best. It is highly appreciated"
From: Mahsa Seyyedian Dear Elia LEVI, 13 - Correspondence: a few Comments 13.1 - Some participants in the Survey complained that somehow they did not get the Hardness Book. If you are a subscriber and you want the book, please write me a note. 13.2 - Referring to our last Mid Month Bulletin, a kind reader advised that: Following this advice I added the alternative address in the Resource. I added also in the same revised edition a new link to videos from The Fabricator. 13.3 - Some readers send me the form with name and affiliation, but do not tell me a thing. What should I learn from a blank form? 14 - Bulletin Board 14.1 - LOET 2010, 9th Int'l Conf on Brazing, High-Temperature Brazing
and Diffusion Bonding 14.2 - Welding of Corrosion Resistant Alloys Conf. 14.3 - FABTECH International & AWS Welding Show Weld Cracking VII. - Nov. 16 - during FABTECH above
Important AnnouncementFor assembling at no cost your own Encyclopedia Online,
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Click on this Logo NOW! Copyright (©) 2009, by Elia E. Levi and See you next time...
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