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PWL#113 - Welding semiaustenitic PH stainless steels, Manual Torch Brazing variability, AWS A5.10 January 02, 2013 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#113 Welding Wrought Precipitation Hardening Stainless Steels: Semiaustenitic PH Stainless Steels, Manual Torch Brazing quality variability, Newly Revised Specification AWS A5.10:2012, Research on Double Stage Plasma Arc Pipe Welding Process, Advancements in Hybrid Methods for Spray Coatings, Revised Bend Testing (R), Creep Test (R) and much more...
January 2013 - Practical Welding Letter - Issue No.113
The Mid December Issue of Practical Welding Letter, Bulletin 80, dealing with Laser Beam Welding was not distributed by e-mail but it is available at Bulletin 80 and from the Welding Resources Page.
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1 - Introduction 2 - Article - Welding Wrought Precipitation Hardening Stainless Steels - II 3 - How to do it well: Manual Torch Brazing. 4 - Filler Metal: New Specification AWS A5.10 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: Double-Stage PAW Process 8 - Site Updating: Bend Testing (R), Creep Test (R) 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Advancements in Spray Coatings 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
(Sponsored Links) 1 - Introduction Welding Advisers and Practical Welding Letter wish to all Readers and their Families a Happy and Prosperous New Year in good health and mood, full of professional and personal satisfaction. It seems we just started yesterday, but in fact PWL is entering its tenth year of publication. It is hoped that the content is generally interesting, sometimes informative, occasionally entertaining, and a few times helpful. This 113th issue of PWL for January 2013 opens with the second installment of the article on Welding Wrought Precipitation Hardening Stainless Steels. This time it is about the semiaustenitic types which can be easily formed in their solution treated state. Their advantage consists in their capability of undergoing hardening through a mild treatment, unlikely to introduce disturbing deformations. Welding is easily merged in the fabrication procedure. Hardening consists in a conditioning treatment, designed to destabilize the austenitic phase, so that it will transform to martensite upon cooling. A low temperature aging will complete the process. Then, following a Q&A note in a recent Welding Journal, we review the difficulties in maintaining manual torch brazing at a consistent quality level, and provide a few hints on how to keep it under control. The 2012 edition of the rewritten Specification AWS A5.10 on Bare Aluminum-Alloy Welding Electrodes and Rods contains alloys that were not included previously. Those who use this document should be advised of the new publication now available. Further down we introduce an experimental new process, practically a variation of existing and known techniques. The research looked after ways to optimize the results for a definite joint type. As it seems that the goal was achieved, it would possibly benefit those having similar requirements to follow up on experience to be gained with this development. We report on hybrid processes for plasma spray, used to obtain demanding coatings with quality characteristics. Those looking for advancement of the state of the art with specific applications in mind, might find here new ideas to study. Two more website pages on Bend Testing and Creep Test were revised in what amounts to a major upgrading effort, we hope readers will appreciate the results. All the other usual sections appear where expected. Titles of Articles from Practical Welding Letters can be found in the Welding Topics page, together with the needed links. The subjects treated in all the Mid Month Bulletins published to date are listed in the Welding Resources page. Please use the Contact Us form to send your comments, feedback or questions.
2 - Article - Welding Wrought Precipitation Hardening Stainless Steels:
This is the second article in the series. The first one is at (2), PWL#112. Semiaustenitic Precipitation Hardening Stainless Steels include types 17-7 PH, PH 15-7 Mo, AM-350 and AM-355. The solidification mode of Semiaustenitic PH Stainless Steels is to delta-ferrite. This, on cooling, transforms partially to austenite. The Semiaustenitic PH Stainless Steels, like 17-7 PH, have the Martensitic Start temperature (Ms) below room temperature. Thus austenite is stable down to room temperature. Therefore also the as welded structure of the above steels fusion zone, consists of austenite within a ferrite matrix. As such, they remain soft and ductile, being largely austenitic, after being air cooled from solutioning temperature of 1025 - 1065 °C (1875 - 1950 °F). They can be easily formed in suitable tools, without cracking. After that, they are thermally conditioned to destabilize the austenitic phase. They are submitted to a treatment at 930 - 955 °C (1710 - 1750 °F) that precipitates carbon and alloying elements from the austenite. Upon cooling to room or sub-zero temperature (if required), the austenite transforms to martensite. Further aging at 480 - 565 °C (900 - 1050 °F) tempers the martensite and precipitates strengthening particles so fine that cannot be seen by optical microscopy. These alloys are readily weldable in any condition without cold cracking. The amount of delta-ferrite present in the microstructure after welding depends essentially on composition, but particular welding conditions may increase its content. An excessive volume fraction of delta ferrite in the weld metal may cause susceptibility to hot cracking. The composition of welding filler metals has been adjusted to reduce the amount of delta-ferrite in the weld metal. Therefore the use of autogenous (without filler metal) welding is generally not recommended. Although the use of matching filler metals is preferred, regular austenitic stainless filler material can be used, if the response to heat treatment in the weld is not critical. Strength will result lower but ductility and toughness will improve. GTA (Tig) Welding is most used for thin sheet metal of semiaustenitic PH steels. For welding 17-7 PH and PH 15-7 Mo which contain aluminum in their composition, the use of Helium is preferred to Argon as a shielding gas. Helium minimizes the formation of a continuous film of aluminum oxide on the weld pool. Also the underside has to be gas shielded. GMAW (Mig) is used for thicker plates, with shielding gas composed of 75%He-25%Ar. Post Weld Heat Treatment is necessary to develop suitable mechanical properties. Depending on requirements, weldments can be postweld hardened without reannealing. To improve weld ductility, without remarkable strength increase, welds can be reannealed after welding and before hardening. As for Resistance Spot Welding, cleanliness is of paramount importance. Compared to welding schedules for austenitic stainless steels, welding times should be longer, weld currents lower, and electrode force higher by 10 to 20%. Welding is done before or after final hardening. For judging of the effective strength of spot welds, readers are referred to the note published (11) in the last issue of Practical Welding Letter. Click on PWL#112 to see it. 3 - How to do it well: Manual Torch Brazing Readers fighting against the variability of results and quality of routine manual torch brazing, especially if from a large group of brazers, are addressed to an article written by Tim P. Hirthe in the Brazing Q&A section of the December 2012 issue of the Welding Journal at page 16. Answering to an inquirer who asked how to take the manual aspects out of the operation in order to achieve more consistency, the Author recognizes the difficulties. Training is important but there is a limit to he willingness of operators to follow instructions. The basics of the process should be understood and practiced. Proper cleanliness and correct clearance must be assured. The somewhat reducing flame should heat the base metal parts, not the filler. This is probably the most important message that brazers should absorb. Standardizing equipment and procedures throughout the company may make it easier to control the process. Infrared temperature sensors may help, as other sophisticated feeders. Gas flow rates can be held consistently under control. Alternate heating methods like hand held inductors may be suitable in certain cases. Concluding the article, the Author recognizes that there are no simple answers to the concerns of the inquirer. Interested readers are urged to seek the original article to glean useful information.
4 - Filler Metal: New Specification AWS A5.10:2012 Those who work regularly with Aluminum filler metals should better be advised, in case they don't know yet, that a revised document was recently released. ANSI/AWS A5.10/A5.10M:2012 (ISO 18273:2004 MOD)
Specification for Bare Aluminum-Alloy Welding Electrodes and Rods The new document adopted the ISO standard dealing with these materials. It includes now many new metals used mainly in Europe, and specifies the chemical composition of all the materials described. The AWS Specification differs from the international document in that it requires further testing to verify the soundness of weld metal deposited by the GMAW process. It also specifies the results to be achieved in the tests to meet requirements. Therefore materials specified to AWS A5.10 (1012 Edition) meet also the requirements of the less stringent ISO standard. The opposite however is not necessarily true, in that those ISO materials are not required to meet, besides composition, additional test requirements. An extensive note by Tony Anderson introducing the new edition of the above AWS Specification was published in the Aluminum Q&A section of the December 2012 issue of the Welding Journal at page 14. Readers are invited to check it for their benefit.
5 - Online Press: recent Welding related Articles Naval welding technique crosses over to computers Europe's first laser-welded CCB (cross car beam) is a fact Burning the torch on both sides The trend toward larger abrasive waterjet cutting tables TWI Connect - Issue 181 - November/December 2012
6 - Terms and Definitions Reminder Fused Thermal Spray Deposit is heated to coalescence on the substrate using a special technique. Hot Start Current is a brief current pulse used to stabilize quickly the arc as it is initiated. Induction Seam Welding is a resistance seam welding process where high frequency welding current is induced in the workpieces, to generate the heat required for joining the edges. Layer, in a weld joint buildup, is a stratum of one or more weld beads deposited to fill the joint space. Pulsed Spray Transfer referring to GMAW, is a spray transfer variation in which welding power alternates between background low current and peak current, where spray metal transfer occurs. This results in lower average power and lower heat input. Stress-relief Cracking occurs intergranularly in the heat affected zone or weld metal, because of residual stresses combined with heat from a post weld treatment. Testing Standards are documents that specify the means and the conditions to be used to perform testing of mechanical or other properties. Adherence to testing standards is essential for assuring the reliability of results. Welding Procedure Specification (WPS) is a document providing the required welding parameters for a specific application, to assure repeatability when implemented on suitable equipment by skilled welders. 7 - Article: Double-Stage PAW Process Innovations are generally proposed in response to certain needs. Here the research was directed to improve girth welding of pipes by a modified plasma arc welding. It is not specifically indicated for which range of dimensions and thickness the process would provide maximum advantage relative to current practice. In particular the experimental procedure was optimized for welding two pieces of 3.5-in. OD Schedule 10, 304 stainless steel pipe pipes butt joints without root opening and welded without filler metal. The article summarizing the research is titled Double Stage Plasma Arc Pipe Welding Process. Its subtitle reads: "An innovative arc process is developed to produce consistent complete joint penetration pipe welds of desired inner diameter convexity on open root joints at all positions with 50% heat input reduction". It was published in the Research Supplement of the Welding Journal issue of December 2012 at page 346-s.
It is downloadable from: The characteristics of keyhole mode and of melt-in mode welding are discussed and explained. Then the novel PAW mode, namely the double-stage PAW, is introduced. It uses a keyhole stage to build a partially penetrated keyhole and then a melt-in stage to finally reach complete joint penetration. The process is controlled and monitored by automatic feedback. The sought result is obtained by current pulsing in two periods: peak and base. Each peak period is further modulated. The first stage is interrupted before the keyhole fully penetrates. Then, a melt-in mode follows to complete joint penetration in a smoother and slower way with much lower penetration. In the experimental setup the goals of the demonstration were obtained, realizing acceptable welds of complete penetration and suitable surface appearance in joints without root opening. Heat input and weld pool width were reduced by 50% when compared with those of the GTAW process. With more development work and accumulation of practical experience, the range of successful applicability will be known with more confidence. This promising innovation should be worthy of follow up. Interested readers having similar problems might see the article indicated above and contact the Authors to check if the proposed improved process could benefit their applications. 8 - Site Updating: Bend Testing (R), Creep Test (R) The Pages of this Month are reviewed and updated issues, probably long overdue, of original publications prepared a long time ago. The first page, on Bend Testing reviews the various practical ways of performing such tests on properly prepared specimens. Relatively simple, the tests help to accept or reject representative test pieces. Bend Tests are most sensitive to defective welding, and play an important part as educational aids to trainees. Accepted Standards prescribing test methods and techniques are reported in the above page. Requirements are spelled out on material specifications or in applicable Codes. The other page on Creep Test refers to the study of materials capable to resist, up to a certain measure, to the consequences of heat. Materials with suitable characteristics may be approved for hot service under load, provided the maximum service temperature is known, and provided the maximum load will be limited by design. Heat resistant materials sustain load even under acceptable heat, but creep slowly, by progressive plastic deformation, changing their shape and dimensions under load. Materials of this kind must be removed from service well before they can collapse catastrophically. This information is essential for designing parts suitable for hot service conditions, and also for routine acceptance test of materials, to verify their adequacy to order requirements. Installations designed for hot service conditions, are usually regulated by mandatory standards known as Codes. These establish requirements not only for materials but also for fabrication and for the provisions to be applied for obtaining approval for use by the appointed authorities. Creep testing is performed according to techniques explained in accepted testing standards. Acceptance requirements are spelled out in material standards. A large amount of information is freely available in the Welding Advisers website. One can perform a search, by typing the requested terms in the box that appears in almost every page of the Welding Advisers website. Questions, comments and feedback are always welcomed. Don't use Reply, use the Contact Us form instead. 9 - Short Items 9.1 - Olsen ductility test is a cupping test in which a piece of sheet metal, restrained except at the center, is deformed by a standard steel ball until fracture occurs. The height of the cup at the time of fracture is a measure of the ductility 9.2 - Plating is the formation of an adherent layer of metal on an object; often used as a shop term for electroplating. 9.3 - Refining is the branch of process metallurgy dealing with the purification of crude or impure metals. 9.4 - Scouring is a wet or dry cleaning process involving mechanical scrubbing. Also wet or dry mechanical finishing operation, using fine abrasive and low pressure, carried out by hand or with a cloth or wire wheel to produce satin (matt) or butler-type finishes. 9.5 - Trace or tramp elements are Contaminant in the components of a furnace charge, or in the molten metal or castings, whose presence is thought to be either unimportant or undesirable to the quality of the casting. Their determination, when required, needs special instrumentation and precise procedures. 9.6 - Vickers Hardness Test is a microindentation hardness test employing a 136° diamond pyramid indenter (Vickers) and any of a series of loads, enabling the use of one hardness scale for all ranges of hardness from soft to very hard. Also known as diamond pyramid hardness test.
10 - Explorations: beyond the Welder California Meteor Broke Speed Record for Atmospheric Entry Please Play with Your Math: New Museum Opens in New York City Do You Accept the Science of Climate Change? [Excerpt] Sunlight Fuels Historic Sea-Crossing, Next Solar Effort Transcontinental Flight The Top 10 Science Stories of 2012 (10 pages) 11 - Contributions: Advancements in Spray Coatings As performance requirements increase for advanced systems, new surface engineering solutions must be sought. At the same time the economic drive demands ever lower manufacturing costs. One way to remain updated on current progress, is to browse regularly through publications reviewing research and applications. One such most useful publication is the International Thermal Spray & Surface Engineering (ITSSE), the Official Newsletter of the ASM Thermal Spray Society. It appears four times a year within the Advanced Materials & Processes (AM&P), a periodical of ASM International. The current issue, of November-December 2012, provides a recent overview of the present state of the art, and an account of various overlapping technologies, whose results are assessed in practical tests. It is possibly surprising to those not following the field evolution too closely, to discover that a number of hybrid methods were produced, combining different technologies to obtain coatings of improved properties. Examples of such hybrid systems, called tentatively Emerging Technologies, are plasma spray & physical vapor deposition (PS-PVD), suspension plasma spray (SPS), and thermal spray & chemical vapor deposition (CVD). Also laser cladding is mentioned, as a useful method capable of providing better properties. PS-PVD, typical of crossover technologies, is also called very low pressure plasma spray (VLPPS). Performed in a vacuum chamber at a level below 6 torr, it results in modified interactions, allowing the formation of very fine molten particles and deposits from the vapor. These new technologies improve the deposition rate of thin films and allow thicker deposits as may be needed for several applications. Another article reviews research work done for correlating process with properties while producing functional ceramic oxides by thermal spray. These material display useful electrical and magnetic properties. Optimization of the required properties is developed through techniques of process diagnostics and mapping strategies. Readers interested in these arguments are urged to seek the original publication and to dig deeper for references and links as necessary. 12 - Testimonials Name: Jamal Al-Anbari Thank you very much for all your interesting letters, they are very useful for me. [...]
Name: Srini Jeyakumar Usefulness: Excellent [...] Thanks again for answering my questions. 13 - Correspondence: a few Comments I should not complain of any peculiarities of the correspondence I receive. Nevertheless I an surprised anew whenever the questions have unexpected form. I used to expect a question mark at the end of a query. Apparently that is needed no more. One of my recently received inquiries looked like this: "I have a series of [...] in a series of pieces that [...]. These [...] have to be [...], on approximately [...]". Full stop. End of communication. No further explanation, no indication of the problems resulting by doing thing in a certain way instead of another. No question mark. No question. 14 - Bulletin Board
14.1 - LAM — 5th Annual Laser Additive Manufacturing Workshop. 14.2 - AWS 8th Shipbuilding Conf. 14.3 - Adhesion Society Annual Meeting & Expo.
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