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PWL#053 - Greetings, New Handbook Vol. 3, Welding Pb Brass, Filler for DFB, Ferrite in Aust.SS, DFW January 02, 2008 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#053 - Greetings, Welding Handbook New Volume, Welding Leaded Brass, Filler Metals for Diffusion Brazing, Ferrite in Austenitic Stainless Steels, Diffusion Welding, Examination Questions, Beware of 317LMN Castings! 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. 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.
1 - Introduction 2 - Article: Welding Handbook New Volume 3 - How to do it well: Welding leaded Brass 4 - Filler Metals for Diffusion Brazing 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - Ferrite in Austenitic Stainless Steels 8 - Site Updating: Diffusion Welding, Examination Questions 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contribution: Beware of 317LMN Castings! 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
a Happy and Prosperous New Year! This 53rd Issue opens with a short review of the latest Volume of the classic AWS Welding Handbook. It is one of a handful of books, frequently updated and reprinted, that should enrich the professional library of every person involved in welding. Only enthusiastic comments can be offered, because it is the work of a large team of exceptionally well informed experts that weighed every word and perfected every sentence so that it is almost impossible to find flaws in this book. Have you already this book? If not yet, you should. Next we deal with an actual question of a reader who got some cracks, upon welding, where he did not expect any. It is unfortunate that leaded brass is not suitable for welding. The following subject shows the characteristics of filler metals for diffusion brazing: this is a somewhat specialized process useful for delicate and expensive items. You should at least know what it is all about. Then an article reviews a few facts about the importance of promoting the presence of some ferrite in the welds of austenitic stainless steels. If you ever found weld cracks in these materials and overcame the difficulties, we would like to know how. Use the form of the Welding Talk page to describe your experience. The New Website Page of this Month describes Diffusion Welding, an expensive but highly successful process for the right materials and items. Furthermore we launched a New Initiative! See the details in Section 8... The Contribution in Section 11 is something special! A warning from a kind reader who cared to share with us his experience with a specific production problem that bothered him until the cause and the remedy were found. We are grateful to him for the information, in the name of the whole audience! We urge all readers to recall their experiences, to put them in writing and to send them to us with their comments. Use the form above or the Contact Us form that you will find in the last button of the NavBar in every page of our website. The other, regular columns are at their place as usual. We hope you enjoy this reading and we ask you to kindly find the time to recommend it to your friends: we will be glad and they will be grateful to you! 2 - Article: Welding Handbook New Volume The American Welding Society (AWS) is devoted, as everybody knows, to advance the Science, Technology and Application of Welding. Their Welding Handbook Volumes are fundamental knowledge necessary to everyone dealing with welding. The previous edition, the eighth, still represents useful reference materials at least for the subjects not yet covered by the new edition. Every new, revised, expanded or rewritten Welding Handbook Volume is reason for celebration. The last volume of the ninth edition, Volume 2, included arc and gas processes for welding and cutting, brazing and soldering. The fifteen Chapters and 669 pages of the present Volume 3 deal with all processes that were not covered by Volume 2 with a richness of detail and information rarely matched by other publications. Over 110 volunteer authors and reviewers from Academy, Industry and National Laboratories contributed to this book. The new Volume 3 that has been recently published, was eagerly waited for. It includes the Second Part of the process section that is devoted to the following Welding Processes: Resistance welding, projection-, flash- and upset-welding, Friction welding and Friction Stir welding. Solid State processes (ultrasonic- and explosion-welding), adhesive bonding, thermal- and cold-spraying, diffusion processes. High energy (Electron beam and Laser) welding. Other welding and cutting processes fill the last Chapter. As an example, Friction Stir Welding, a new process continuously expanding its reach, is treated thoroughly in Chapter 7 in what is probably the best and most complete monograph available on the subject. All other traditional and less used processes are presented in systematic way to outline the essentials, including advantages and limitations, and to detail applications and material suitability. Photos, diagrams, graphs, Tables, Standards and References help to the understanding of the text. Professionals who need complete and authoritative reference to welding processes will find in Volumes 2 and 3 of the Welding Handbook clear and exhaustive explanations and literature for further reading and learning. We are pleased to strongly recommend to our readers the addition of this third Volume to their bookshelf and also of the first two volumes if not yet in their hands. Two more volumes on Materials and Applications (ninth Edition) are still being prepared and will be published some time in the future. AWS WHB-3.9
3 - How to do it well: Welding leaded Brass Q: We are welding a cylindrical brass part (60Cu+37Zn+3Pb with approximatively 2% impurities) with stainless steel pipe, by oxyacetylene flame. The Brass part section is 3.5 mm thick where it is being welded and the rest of the part is 8.5 mm thick. A: The stainless steel pipe should be of the weldable type, not prone to sensitization, otherwise it could become easily corroded. See our page on Stainless Steel Welding. The filler metal and the flux used were not specified but this is not the main thing. However the fusion process selected is not suitable for the application, because lead (Pb), added for improving machinability, causes the brass to become hot-crack susceptible upon welding. Therefore this alloy should not be fusion welded. If arrangements can be made to produce overlapping joints with small clearance, brazing could be performed instead of welding, with silver base alloys. Otherwise substitution of the said copper alloy with unleaded brass should be considered. 4 - Filler Metals for Diffusion Brazing Diffusion Brazing is similar to conventional Brazing in that a fusible filler metal undergoes melting to promote the joining of two or more members. A significant difference is however that Capillarity may or may not be used for driving the molten filler metal into the brazing joint clearance. In this process however, the filler metal has a composition very similar to that of the base metals, but includes melting temperature depressants that cause its melting at a temperature that does not affect the base metal. This is the case for example of nickel where small additions of silicon or boron reduce the melting point of the filler metal, so that it melts and wets the base metal at the brazing temperature. The depressants then diffuse out of the joint. At that point the change of composition causes the brazing filler to solidify. The temperature is maintained for quite longer a time to promote homogenization, so that in the end the joint line (in a section) may be indistinguishable from the unaffected material. This process is also called Transient Liquid-phase brazing. In a slightly different method, the filler metal is of such a composition that it forms with the base metal a low melting alloy (called eutectic) that melts right in the joint. An example is that of titanium that forms eutectic with copper at a temperature lower than the copper melting point. Here the diffusion stage, that can last even a few hours, at variance from the diffusion welding process (see section 8) is needed to obtain homogeneous structure and properties, once the joining is already completed. Brazing filler metals may be those used for regular brazing, if they are chosen so that diffusion will alter their composition once joining is performed. As such they should meet the requirements of AWS Specification A5.8 or equivalent. They can be in the form of powder, foil or wire, usually ready to use for the given joints as preforms. Occasionally the brazing cycle is combined with heat treatments as needed. The brazed joint should develop mechanical properties as good or better than those of the base metal. 5 - Online Press: recent Welding related Articles From TWI From Lincoln Electric From Hobart Welders Students learned more than just Welding 6 - Terms and Definitions Reminder Backing Shoe is a nonconsumable cooled backing device (sometimes sliding along the joint) used to contain molten weld metal in electro gas welding and electro slag welding. Bit is the copper tip of a soldering iron used to heat and solder the joint. Diffusion Brazing is a process that produces coalescence (joining) by heating and melting in place a suitable filler metal. The temperature is held long enough to have the brazing temperature depressing elements in the filler metal diffuse away from the joint to get properties approximating those of the base metals. Electron Beam Gun is the device where a beam of electrons is generated under vacuum and accelerated toward the target. It consists in a glowing filament (cathode), a grid and an anode. Globular Metal Transfer is an operating mode of Gas Metal Arc Welding of such a current that the filler metal is fused in large drops transferred to the work. Shrinkage Void is a cavity formed by shrinkage in the weld, unfilled by additional molten metal because of early solidification. Spray Metal Transfer is an operating mode of Gas Metal Arc Welding of such high a current that the molten filler metal is sprayed in a stream of fine drops. Weave Bead is produced by oscillating the electrode transversally to the weld while also moving it longitudinally along the joint. 7 - Article - Ferrite in Austenitic Stainless Steels Austenitic Stainless Steels are considered the most easily welded than all other types. The term Austenitic refers to the main face-centered cubic (fcc) phase in their microstructure, called austenite, that is maintained by alloying additions over a wide range of temperatures. Their composition determines not only the microstructure but also important physical properties. Most important are (besides corrosion- and oxidation-resistance) Thermal Conductivity, about half that of other steels, and the Coefficient of Thermal Expansion (CTE) considerably greater. These characteristics influence their welding penetration, warping (deformation) and residual stresses, requiring adaptation of the techniques to obtain acceptable results. The major concern while welding these stainless steels is their tendency to cause solidification cracking unless the weld metal contains more than 3% ferrite. This phase is body-centered cubic (bcc) like the main constituent of iron base alloys at normal temperature (alpha ferrite), except that it is present at elevated temperatures and is therefore designated as delta ferrite. The primary phase appearing upon solidification may be either austenite or ferrite. The austenitic phase is more susceptible to weld solidification cracking. The main precautions that can be exercised to minimize weld cracking involve alloy selection, process optimization and postweld heat treatment. A useful concept that was developed with experience along the years is that of equivalence, whereby the elements active as ferrite forming (Cr, Mo, Nb) are normalized by multiplying their percentage with an empirical factor and then summed with the Chromium percentage to give a composite Chromium equivalent. Similarly the percentage of austenite forming elements (Ni, C, N and Cu), each one multiplied by its factor, are summed up to give the Nickel equivalent. While the exact proportions and influence of the single elements are still a matter of debate, in general the adoption of the concept has permitted the drawing of useful diagrams starting with that of Schaeffler (in the 1940s), modified by DeLong (1973) and further updated by the Welding Research Council (WRC) first in 1988 and then in 1992. The use of these diagrams permits to predict the structure of the resulting weld metal by dilution of base with filler metal of different compositions. The diagrams delineate regions identified by the main or composite structures of the weld materials as pointed by composition (Austenitic, Austenitic-Ferritic, Ferritic-Austenitic, Ferritic) depending on the primary structure solidified. Similar diagrams determining the same zones by slightly modified criteria were developed by other researchers. It is not uncommon to use all available diagrams to check the results obtained with any one of them. Unfortunately the boundaries defining these structures may move by cause of other parameters like heat input and solidification speed or constraint conditions. Furthermore quite large uncertainties exist in compositional analysis determination, and the exact effect of impurities unaccounted for, as well as the influence of process and parameters. One must remark that the amount of ferrite that is found at room temperature is only a fraction of that resulting immediately after solidification, because of transformations occurring in the solid state phase while cooling. The use of commercially available instruments for determining the Ferrite Number, based on ferromagnetic characteristics of the ferrite phase, can help in giving an idea of the ferrite content. One must remember however that it is almost impossible to determine the absolute ferritic content of austenitic stainless steels specimens, and that significant differences may be found among specimens made under the same conditions. Finally welds performed with high energy density processes may differ significantly from those welded by traditional means. The differences are attributed to rapid solidification speeds and also to microstructures not known from processes with slower cooling rates. In conclusion the development of suitable welding procedures for austenitic stainless steels must take into account the composition of weld metal and the general guidelines briefly summarized here. 8 - Site Updating: Diffusion Welding, Examination Questions The New Page of this Month deals with a process which achieved remarkable success with certain types of welded items characterized by high strength, high quality and low weight, generally for aerospace applications. In fact specific items cannot be welded successfully in any other way. The process is expensive because of costly equipment and long welding cycles. It is too expensive for being used for more simple applications where other welding methods give adequate results more economically. Anyhow anyone involved in welding should know its advantages and limitations. Click to see the new page on Diffusion Welding. On another subject we just started a New Initiative!, as announced above in the Introduction. This page (still empty at this early time) will include all Questions sent to us by readers who were just Certified or that work on preparing themselves for Certification. Contributors are invited to send in also the answers to their own or to others' questions. In due time this page will hopefully become a useful learning aid for all welders and inspectors working on Certification. Help us make it a rich and informative page! Send us your Contributions to this Questions page! Follow the continuing expansion and updating of this Website by checking regularly the Site Map. You may also subscribe to an RSS service to be notified of new pages or watch periodically the Welding Blog. 9 - Short Items 9.1 - Electrolytic Grinding combines grinding with a conductive abrasive wheel, the cathode, while the workpiece is kept anodic, under a suitable electrolyte, permitting simultaneous machining and electrolysis. 9.2 - Epitaxial Growth is that of an electrodeposit or vapor deposit in which the orientations of the deposited crystals are directly related to crystal orientations in the underlying crystalline substrate. 9.3 - Equiaxed Grain Structure (or equiaxial) is a microstructure in which the grains have approximately the same dimensions and possibly the same properties in all directions. 9.4 - Fatigue Strength is the maximum repeated stress a material can withstand for a given number of cycles befor failing. 9.5 - Microwave Processing is a new technology extending the advantages of microwave heating (at low temperatures) to industrial processes where water is absent. (Water is the main ingredient of food, readily coupled to microwaves in home appliances). In materials processing, high temperatures must be reached by coupling of microwave energy to atoms or atomic groups other than water. Research overcame the much greater technical complexity of this goal, succeeding in realizing high-temperature microwave processes that use 20% of the energy and take less than 20% of the time needed to process materials with conventional means. 9.6 - Riveting consists in joining two or more members of a metallic structure by means of metal rivets introduced from one side in prepared holes, the stem being upset by mechanical blows while counter pressure is applied on the existing rivet head. 10 - Explorations: beyond the Welder Motion of RNA Molecules Utility Solar Thermal Electricity A Global Emergency Solving a Puzzle 5 Pillar Affiliate Program 11 - Contribution: Beware of 317LMN Castings! Note: A kind reader published the following Contribution in a new Welding Talk page. We publish it again here for your convenience. We are a manufacturer of chemical processing equipment, and as such, we frequently weld base materials that must be strong and highly resistant to corrosion. On a daily basis we weld Duplex, Super Duplex [Stainless Steels], High-nickel alloys and titanium. We recently experienced a problem while welding a high molybdenum version of 317L stainless steel. The material is UNS S31726 containing 4-5% Mo. We were welding flanges or couplings to matching grade 1/2" wall pipe. Our coupling joint sees rugged service and must be able to withstand torque and bending loads. We prepare the joint by machining a double "J" groove into the coupling and sliding the coupling onto the pipe. We call the side of the coupling that is flush with the face of the pipe the Face side and the inboard groove is the Radius side. We normally weld the face side complete and then start the radius side. In this case we were welding with an ENiCrMo-3 electrode, SMAW process, maintaining 300 0F interpass. We found that our radius side BASE metal was indicating micro-cracks alongside the weld edge. I guess it would be safe to say the cracks were in the HAZ (Heat Affected Zone). The cracks were oriented parallel to the axis of the weld, and only in the base metal. We were surprised to encounter the problem. Welding information for 317LMN is very basic. The only rule is to use a high moly filler metal. We started to investigate and noticed something odd on our Material Test certificates: the mechanical properties appeared questionable. Our paperwork showed an Elongation value of 26%. We expected to see a minimum of 40%. We also noticed the document made no reference to forging. We visited the vendor's website and found that the flanges were produced by a spinning casting process. We are in the process of double-checking the chemical analysis of the material at an independent laboratory. I suspect we are going to find elements such as sulfur, phosphorus and possibly lead are out of specification. I would suggest to your readers that they specify forged 317LMN if they plan on welding product forms other than plate or pipe. [Note: - We are grateful to Paul from New York State for this instructive and interesting Contribution. We urge all readers having practical experience with uncommon aspects of welding applications to share them with our audience by taking the time to type a short note in the page mentioned above. It is easily done. Such contributions will be highly appreciated by all concerned with similar problems.] 12 - Testimonials Date: 04 Dec 2007, 04:13:56 AM First Name: Jaspal Jaspal Singh
From: Hotchkiss, Jerry - Siemens Happy Holidays! 13 - Correspondence: a few Comments A reader found some weld defects that may delay the startup phase of their installation: he asks me to give some technical reasons that will help him decide to postpone the repair of these defects until a later date. The information given is minimal. Do you think a serious answer can be given? Welding of stainless 303? A skeptic reader asks about that. We would have thought that this old problem was disposed of long ago in our website page on Stainless Steel Welding. It is really so difficult to dig out the information one needs? [Hint: use Google Search]. Readers ask for Welding Instructors or even for welding schools near home (without saying where home is). I try my best to be of help, but unfortunately sometimes my answers fall short of expectations, I am sorry. 14 - Bulletin Board 14.1 - Materials Innovation in an Emerging Hydrogen Economy 14.2 - WESTEC 2008 Exposition & Conference 14.3 - It is time that you Build your Encyclopedia Online! 14.4 - Contribute to the benefits provided by this newletter to all readers by adding notes from your welding expertise to the Welding Talk page.
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