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PWL #034 - Weld Quality, Stainless to Cast Iron Weld, Brazing Copper, Surface Engineering, SMAW tips June 01, 2006 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. Weld Quality, Stainless to Cast Iron Welding, Brazing Copper, Surface Engineering, Shielded Metal Arc Welding tips, Buried Gas Metal Arc and more... This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. We actively seek feedback to make it ever more useful and up to date. We encourage you to comment and to contribute your experience, if you think it may be useful to your fellow readers.
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Practical HARDNESS TESTING Made Simple.
1 - Introduction 2 - Article: Weld Quality 3 - How to do it well: Stainless to Cast Iron Welding 4 - Filler Metal for brazing Copper 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: Surface Engineering 8 - Site Updating: Shielded Metal Arc Welding Tips 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contribution: Buried Gas Metal Arc 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction You may have received two weeks ago the Mid May Bulletin, (that we published and distributed to all our subscribing readers), containing links to valuable Internet Resources easily reachable for downloading highly informative material. If you missed it, you can get it now by clicking on We hope that this initiative is well received, and we plan to continue it in the coming months, concentrating on various welding related subjects, if we get positive feedback from our readers. Please use the Contact Us button from the NavBar on each Website page. This 34th issue of Practical Welding Letter opens with an overview on Weld Quality which is a very important ingredient in the economic well being of any welding enterprise. We then present an addition to a short note, published in our FAQ page, relative to welding of Stainless Steel to Cast Iron. Some pertinent comments will add insight to those working on these materials. Brazing copper is well known and applied, but a few less evident points may add information to those who occasionally need to implement it. Our next featured article is devoted to Surface Engineering, a multi faceted complex of processes and materials that are needed for the practical and flawless working of many mechanisms and machines. It is a vast discipline served by many experts who may know only their own limited field. Research and progress require vision, dedicated efforts and funding that may repay many times the investment, when reaching success. The Page of this Month in our Website is dedicated to tips on one of the oldest arc welding processes, Shielded Metal Arc Welding, that is still the first one usually thinks of whenever welding is needed, because of its versatility and usefulness. We know of two Reports on the welding industry. As we think that they offer important information and insight, we indicate in the Press Section 5 how interested readers can download them. One, on the economic impact of welding activities, shows findings on the present status of welding in the USA. The other, on the Vision for the Future of Welding, proposes how society should tend to reach its objectives. Robotic welding has strict demands in terms of precision and tight tolerances of assembled elements. One application for automotive construction was studied for easing the preparation requirements. It is reported in the Contributions department. Other sections are to be found as usual. For your comments and feedback please use the Contact Us button on the NavBar on any page of our Welding Advisers Website. 2 - Article: Weld Quality Discarding defective pieces is not a suitable policy to implement weld quality. The most convincing argument demonstrating that weld quality is not only affordable but that it is in fact an economic proposition, is probably the one summing up all the hidden costs involved in a sloppy operation that gives only minimum thought to assuring weld quality. Consumers and customers are becoming increasingly aware of the total costs of any fabricated implement, so that the purchase cost by itself is playing only a limited part in the comparison of competitive offers. The expectation is for objects reliable, durable and without problems for the whole lifetime of operation, possibly with a recoverable residual value upon decommissioning. Therefore the risks and the cost to the user, associated with loss of service, maintenance, repair and replacement are so great that the provider neglecting the requirements of a sensible weld quality program jeopardizes the very essence of his/her own operation. A page of our Website devoted to the subject of compulsory requirements in manufacturing and on the formal approval needed to gain Certification from appointed Authorities is visible by clicking on Weld quality relates directly to reliability of performance of any manufactured item throughout the whole lifetime of service and operation. In order to meet these requirements, that include quality and fitness for purpose, any welded product must be:
It is customary to refer to quality levels, except that these are concepts difficult to quantify. Therefore quality can be understood both qualitatively and quantitatively to signify the adequacy of an engineering product to its intended purpose and to user's expectations, or on the contrary its need of improvement. The usual guarantee offered by the supplier to the purchaser is intended as a proof of confidence of the manufacturer in all factors intervening in the manufactured product, although design details and material selection may be excluded from his/her responsibility as not being controlled by manufacturing operations.
3 - How to do it well: Stainless to Cast Iron Welding As you may know, this is one of the Frequently Asked Questions.
Click on FAQ. An interesting supplement to the above presentation was published in a note by Damian J. Kotecki, Technical Director at the Lincoln Electric Co. and President of AWS, on page 14 of the March 2006 issue of the Welding Journal. Accordingly, the FAQ note above has been already updated with the following information. It is reported that, due to dilution with high carbon Cast Iron, weld metal from 309 or even 312 stainless steel electrode risks cracking because the composition of the deposited root pass layer results without any ferrite. Even if cracking is avoided by suitable preheating, both the weld metal and the Cast Iron heat affected zone result rather brittle. The problem stems from the carbon in the Cast iron combining with the chromium in the stainless (309 or 312) to produce, in the resulting weld metal, networks of eutectic chromium carbides in austenite. A better suggestion would be the use of electrode ENi-CI per AWS A5.15. Due to the complete absence of chromium from the composition of this last electrode, significant chromium carbides will not be produced. Furthermore this electrode would promote spheroidal graphite formation in the high nickel root pass, and also lower hardness results in the weld metal. However, even if cracking during welding is avoided, there is still the danger of cracking being produced later by shock loading due to the intrinsic brittle nature of the boundary layer. For a more complete review of the matter, interested readers are urged to seek the article mentioned above.
4 - Filler Metal for brazing Copper Copper and Copper Alloys are easily brazed metals. Many filler metal alloys are available, the selection being based on the composition of the metal, on the process employed, on shape and dimensions of components and on the predicted service conditions. In general heating for brazing will result in recrystallization and grain growth of the copper alloy being joined. While this fact may not matter for most applications one should be alert in those cases when the structure and their properties are important for electrical conductivity or other considerations. Copper alloys may be oxygen containing or deoxidized. Those that were not deoxidized will contain copper oxides dispersed in the material. If brazing is performed in furnaces whose protective atmosphere is based on hydrogen, at temperatures above 4800C (8960F), the reaction of oxygen and hydrogen will produce high pressure steam in the solid metal. Therefore tough-pitch copper should not be brazed in hydrogen atmosphere furnaces, but also torch brazing with oxyacetylene may cause embrittlement and should be avoided. Deoxidized coppers are readily brazed in hydrogen, sometimes even without flux by using a copper-phosphorus filler metal. However the use of flux is generally recommended as improved brazement properties are obtained. Copper alloys containing chromium or zirconium produce, upon heating, surface oxides that hinder the brazing process. In this case thorough cleaning is needed before, and the use of flux is necessary during brazing. Zinc containing copper alloys, known as brasses, can be brazed in general, but with more or less ease or difficulty depending on specific other elements content. Lead, a machining addition, and aluminum, a strengthening element, may prevent brazing at all if present in high proportions. Bronzes, an important class of copper alloys containing tin as a major constituent, include phosphor-bronze, silicon-bronze and aluminum-bronze. The first two should be stress relieved before brazing if work hardened, because of their tendency for hot cracking or hot shortness. Aluminum containing bronzes need special fluxes to overcome the tenacity of surface aluminum oxides. Copper-phosphorus filler metals are self fluxing when used to braze copper. Phosphorous based brazing filler metals should not be used on copper-nickel alloys because of the formation of the brittle intermetallic nickel-phosphide. High phosphorus alloys should not be used in sulfur containing atmospheres. Zinc containing alloys have higher liquidus and are anodic to copper, reducing corrosion resistance. Zinc may partially vaporize if overheated, leaving voids. Acceptable ductility of the brazed joints should be verified by checking the absence of objectionable brittle phases. The following Table lists a few copper-zinc and copper-phosphorus filler alloys.
A Table of Silver base brazing filler metal alloys, suitable also for brazing copper alloys, was published in the Issue No. 03 of Practical Welding Letter for November 2003. To see the Table click on PWL#003. Standards, Specifications, Recommended Practices and a Brazing Handbook reference were reported in a revised issue of our page on Brazing. A commercial source providing a page of links to basic data for some of the standard phosphor bronze alloys, including compositions and characteristic temperatures is available at http://www.brazing.com/products/Phos_Copper/ 5 - Online Press: recent Welding related Articles From the Fabricator: From TWI: European Brazing Alloys and Fluxes Two Reports From AWS: 6 - Terms and Definitions Reminder Backing left on is a procedure related discontinuity that consists in leaving inadvertently in place, by mistake, the partially fused metal backing that was used to support and shield the root side of a joint. This condition requires correction because it may cause stress concentration. Concavity, also known as insufficient throat, represents a deficiency in fillet weld metal resulting in less material (short throat) than prescribed by Code, Specification or drawing requirements. Application of adequate procedure should be enforced to avoid this discontinuity. Convexity refers to the useless and damaging excess of fillet weld metal consisting in larger than needed throat, as specified by applicable drawing. The sharp discontinuity at the toe junction (between base and weld metal) risks to act as a harmful notch that may initiate a crack. In multipass welding of groove welds it may interfere with slag removal. Cracks are fracture type discontinuities, characterized by sharp tip opening, that tend to propagate under stress. They are the most damaging and insidious of the defects never to be tolerated in any structure. Many different causes, to be singled out and eliminated, can be at the origin of their appearance. Hot Cracking, also known as hot shortness, develops at elevated temperature, usually when solidification and shrinkage stresses exceed the material strength at those temperatures. It can be influenced by the unwanted presence of phases still liquid at a temperature lower than that of metal solidification. Laps and Seams are base metal discontinuities that may appear during faulty rolling or forging processes when folds or openings are pressed on colder metal and fail to coalesce into the main body of the material. They appear as longitudinal surface imperfections. Although they may or may not be harmful, depending on the direction of stressing (either transversal or parallel) relative to the seam, these defects should be caught and rejected during Receiving Inspection. Porosity is a discontinuity consisting in the presence of voids or cavities of various shape and dimensions, due to the liberation of gases (because of their reduced solubility into molten metal during cooling) and their entrapment upon solidification of molten metal or during deposition of thermal sprayed material. Slag Inclusion, or the entrapment of molten slag into the solidified weld metal, is caused generally by improper electrode manipulation and/or by difficult access to the weld location. Viscosity factors of slag and metal when molten, and heating factors like low heating or too rapid metal solidification, may hinder entrapment avoidance.
7 - Article: Surface Engineering Surface Engineering as a group represents a large and growing set of technologies used to provide definite surface properties to the items treated. The three main classes of processes are the following:
Although in the consumer world the thought of "repairing" something is generally considered non economic and wasteful (despite the huge cost to the environment), in the industrial community there is a real need to recondition essential items to lengthen their useful life and save expensive assets by restoring surfaces and materials to original dimensions and quality. Reconditioning must be approached as an engineering project by taking into consideration service conditions, new materials, new processes and the experience gained from past applications. In fact there is no need to reproduce the exact makeup that was displayed by the item as it was when new. What is needed is renewed functionality that can be better achieved by such processes as surfacing or hardfacing with a suitable Surface Engineering process. Thermal Spraying processes started a century ago with the Flame Spray torch that used a copper alloy wire to provide new metal to rebuild parts. It was then followed by Arc Spray techniques but the real progress was achieved with Plasma Spray Torches and with the very large range of powders that were developed to suit the most exacting requirements. Plasma Spray knew real success in building up layers of protective materials and ceramics. One of the most interesting developments was the introduction of plasma spraying in vacuum that permitted to provide Thermal Barrier Coatings (TBC) to gas turbine blades to push their performance to stand even higher burned gas temperatures. The products, ceramic powders, were to be known as MCrAlY type powders, where M stands for a metal, usually Nickel, with Chromium Aluminum and Yttrium oxide, and YSZ or Yttria Stabilized Zirconia. Plasma Spray is generally classified as an "allied process" to welding, meaning that a standard welding shop is a good starting point for establishing a thermal spray facility, because many of the consumables and production items are not extraneous to the basic technology. There is no need to develop manual skills, the processes being mostly mechanized or automated, but the success of applications is essentially based on equipment condition, on quality consumables and on proven schedules. Therefore it has become a practice, initiated by the important manufacturers from the aerospace field, to request qualification according to specific protocols intended to demonstrate the performance quality level by submitting definite test pieces to demanding tests. Those of our readers practically involved with Thermal Spray, may be interested to know that there is now an international formal Thermal Spray Certification Process administered by the German Association of Thermal Sprayers (GTS). See www.gts-ev.de But despite its glamorous success Plasma Spray found strong competitors first from the Detonation Gun process that realized stronger adhesion of the sprayed layers on the substrate, and then from the HVOF (High Velocity Oxygen Fuel) Thermal Spray Process. The newest addition to the family is not an even higher temperature process. On the contrary it is the Cold Spray, performed with gases accelerated to sonic or supersonic speed, but essentially at room temperature. A short note on cold spray was published at the section 9.3 in the Issue 22 of Practical Welding Letter for June 2005. It is visible by clicking on PWL#022. The evolution of the Cold Spray Technology was not easy or rapid, as it took at least three decades of much effort from different research organizations. But its success is now demonstrated by its capability to build from powders, thick coatings, freeforms and solid bodies of near net shape, at almost theoretical material density. This is remarkable because the process does not use, as powder metallurgy, the pressing of green powder bodies and then their sintering at elevated temperatures. In a recent review celebrating a century of achievements in Thermal Spray, published in the inaugural issue of the official Newsletter of the ASM Thermal Spray Society, there was an appreciation of the vitality of this industry, together with the expectation of much needed visionary leadership, excellence in technological innovation and entrepreneurship.
8 - Site Updating: Shielded Metal Arc Welding Tips The Page added this Month to our Website is dedicated to tips on one of the oldest arc welding processes, namely the Shielded Metal Arc Welding (SMAW), that is still the first one usually thought of whenever welding is considered. Mainly due to its versatility and relative ease of use, together with limited cost of equipment, it is the process of widest diffusion applicable to many different materials. See the page at Shielded Metal Arc Welding Tips. When you look for the subjects that you need, check first the Site Map. Or you can perform a Google search using the special query window appearing in almost all pages. By subscribing to our RSS feed (see instructions under the NavBar in anyone of our website pages) you are kept always updated. For sending us your comments or feedback, please use the Contact Us button that appears in the NavBar at the top left of every Welding Advisers website page.
9 - Short Items 9.1 - All-weld-metal test specimen is used to test deposited weld metal without any influence from dilution with base metal, and to report mechanical properties obtainable with welding electrodes. 9.2 - Anode is the electrode of an electrolyte cell where oxidation develops. Electrons flow away from the anode in the external circuit. Corrosion occurs usually at the anode and metal ions enter solution. In a direct current electric circuit, anode is the positive (electron-deficient) electrode. 9.3 - Bainite is a metastable microstructural aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures below the pearlite range but above Ms (the martensite start temperature). Bainite is usually further differentiated between upper and lower depending on the temperature of formation and on mechanical properties, harder than pearlite but softer than martensite. 9.4 - Ball Mill is a rotating hollow cylinder partly filled with metal balls (usually hardened steel or white cast iron) or sometimes pebbles, that is used to pulverize crushed ores or other substances such as pigments or ceramics. 9.5 - Elasticity is the property of a perfectly elastic material, deformed by mechanical stress, that recovers completely the initial shape and dimensions upon removal of the stress. Regular materials are not perfectly elastic and retain some deformation upon stress removal. 9.6 - Hardenability is a measure of the relative ability of a ferrous alloy to form martensite when quenched in a cooling medium from a temperature above the upper critical temperature. Hardenability depends on chemical composition and is commonly measured by the Jominy test, as the distance below a quenched surface at which the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure. Higher hardenability steels can reach higher core hardness even with mild quenching media (like air) in heavier sections than lower hardenability ones.
10 - Explorations: beyond the Welder Explore the National Academies at The Tragedy of False Confessions Hybrid Transit Buses Scientific American Observations Blog Outback Australia Travel Guide
11 - Contribution: Buried Gas Metal Arc A new development, studied especially for producing lap joints in aluminum alloys sheet, plate and shapes by robotic or mechanized processes, was introduced by the Product Manufacturing Division of Alcoa, a manufacturer of aluminum products. The process is presented in an article appearing at page 28 of the April 2006 issue of the Welding Journal. It is known that welding with robots requires dimensionally accurate parts consistently assembled within tight tolerances, which is the main factor that contributes to high costs. Torch oscillation, that was introduced as a means of easing on those requirements, severely penalizes the economy of operation. Locating aids like vision or touch tracking systems cannot help effectively. The reported development involves abandoning the struggles to produce acceptable fillet welds in lap joints, in favor of seam welds to connect two elements by running the weld parallel to the planes of both components, to obtain partial penetration in the bottom element, much as what is done with high energy welding processes. Except that the research used GMAW, a much more economic process. The modification, that is given the name of Gas Metal Buried Arc Welding (GMBAW), introduces the concept of "burying" the arc deep into the metal, by establishing parameters that provide high current densities that restrict the arc increasing its penetration power. It becomes therefore possible to join assemblies by robot or mechanized processes with favorable economic productivity, despite relaxed requirements as to the relative positions of torch and workpiece, using regular GMAW equipment. The experiments reported demonstrate the feasibility and the economy of the process and open the way to exploitation in a number of industries where design with this type of joint is adequate for the required performance. Interested readers are urged to seek the original article referred to above. 12 - Testimonials From: "graham mcmann" (e-mail removed for security) Hi Elia, From a grateful cswip [Certified Senior Welding Inspector] welding & pcn level II u/t [Ultrasonic Testing] inspector your advice/articles are very much appreciated. thanks again g mcmann (applied inspection wakefield)
From: Alan Nixen (e-mail removed for security} Thanks, Elia.
13 - Correspondence: a few Comments A kind reader sent in a news clip presenting a welding process called HHO, that uses a hydrogen oxygen flame made with gases derived from water electrolysis. (See Electrolysers, in PWL#033, section 11). As far as we know the process has yet to gain endorsement from the major Institutions that research and develop new welding processes. When we learn on positive comments it will be our pleasure to report on them in a future issue of PWL. We occasionally receive questions from e-mail addresses that cause our answer messages to bounce back. We do not know why. We have no other way to reach such a person unless he/she tries again from a different address. So, if you do not get our response, which may be blocked despite our intentions, please try again, possibly from a different address.
14 - Bulletin Board 14.1 - Microscopy and Microanalysis 2006 and International Metallographic Society (IMS) Annual Convention, Chicago, Ill. - July 30-Aug. 3, 2006 http://mm2006.microscopy.org/ 14.2 - The Next Industrial Revolution: Nanotechnology & Manufacturing 14.3 - Browse through our other new Website titled Home Surveillance Guide where you will find useful tips and guidance for setting up your own most effective Security System for a limited budget. 14.4 - Next time you are confronted with tough choices that you are in pain to decide among them, in any possible field of human activity, please use the following service, available to anybody at no cost, offered by SiteSell, our Web Host. We think that also politicians, ministers, bankers and other people with power, not only regular persons, could profit from the use of Choose-It!, the powerful and versatile software that helps people decide for the best. Try it, click on Choose-It!
Copyright (c) by Elia E. Levi and See you next time. |
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