New Hard Coating Solution, Failure of Stainless Welded Studs, Selecting Active Brazing Filler Metal, Welding Dissimilar Metals, Pickling, Laser Beam Welding, Friction Taper Plug Welding and much more...

ADVANCE NOTICE We are now only Three Months before ISSUE 100 of Practical Welding Letter. We would like to Celebrate with you, our faithful Readers, this Special Occasion. If you were interested by what you read here along the years, we would like to ask you to send us, as a token of appreciation, a meaningful and interesting article reflecting your unique experiences. We will then publish your Contributions in the Special Issue 100, making it a remarkable and memorable event. Make a Note Now! - Don't forget...

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Please be advised that the Mid Month Bulletin is now integral with the regular PWL publication. You will find it further down, past the end of this Practical Welding Letter.
Don't miss it!

1 - Introduction

2 - Article - A New Hard Coating Solution

3 - How to do it well: Failure of Stainless Welded Studs

4 - Selecting Active Brazing Filler Metal

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Welding Dissimilar Metals

8 - Site Updating: Pickling, Laser Beam Welding

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Friction Taper Plug Welding

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

(Sponsored Links)

1 - Introduction

This 97 Issue of Practical Welding Letter opens by presenting a new Hard Coating. It is a commercial process with which we have no affiliation and there is no intention to advertise or promote it. However it might be exactly what some of the readers need just now, so that, if they wish, they can explore and evaluate it for their applications.

A question was received about failure of welded stainless studs. No details were given as to the failure itself, so that only an opinion can be expressed. By the way it is an example of the great cost incurred by someone who did not ask for advice.

Then tips are offered on how to select Active Brazing Filler Metal. The advice, from a renowned expert, suggests to make a few tests to optimize the application, if the production program justifies the expense.

Follows an article on welding dissimilar materials, which is probably a quite common occurrence not sufficiently studied. The characteristics that negatively affect mutual compatibility most, should be investigated first. And certainly one should deepen the search, if welding difficulties are found.

For the website update two new pages of this month are presented. The first, on Pickling, explains what it is and what it is intended to accomplish. The second explains some basic knowledge on Laser Beam Welding and on its essential characteristics.

Friction Taper Plug Welding is not a well known process but it is reported to have enjoyed successful performance in demanding service conditions both in aerospace and in energy generation applications.

The regular columns appear at their usual place. Enjoy your reading and let us have your feedback and comments using the Contact Us Form.

Bulletin #65, appended as PWL#097B past the end of the regular Practical Welding Letter issue, offers resources on Joining Incompatible Materials with several links to authoritative Internet Sources. Don't miss it!

2 - Article - A New Hard Coating Solution

A new process capable of producing advanced Chemical Vapor Deposition (CVD) coatings is introduced in an article published at page 21 in the August 2011 issue of Advanced Materials and Processes (AM&P), a monthly publication of ASM International (www.asminternational.org).

The reason to report on the above advancement here is to inform interested readers of the available solution. No endorsement or advertisement is intended and no claims are made as to the suitability of the process for definite applications.

The process called commercially Hardide offers a number of properties, that should be explored by those in search of a suitable solution to their problems of wear, erosion, aggressive and corrosive attack by certain acids.

The CVD coating is applied from the gas phase, and can uniformly coat complex shaped parts and internal surfaces.

It can be applied to a number of different metal substrates. It is said to have the ability to coat complex shapes and internal surfaces to a sizeable coating thickness, and to show toughness and ductility.

Hardide-T is described as a nanostructured material consisting of a metallic tungsten matrix with dispersed nanoparticles of tungsten carbide typically between 1 and 10 nm in size.

Nanostructured materials can have a combination of properties (like hardness and toughness) that are not common in macro or microstructured materials. Hardide-T is said to combine extremely high microhardness (1100 to 1600 HVN) with unique toughness, and crack and impact resistance.

The coating is reported to have successfully met harsh requirements in various demanding applications. It is suggested as a replacement for hard chromium plating to dispose of limiting and expensive environmental requirements. For more information readers may seek the article indicated above or look at the site, at www.hardide.com

3 - How to do it well: Failure of Stainless Welded Studs

Q - Recently I was sub-contracting to a company that was building an acoustic smoke stack for a gas turbine.
The outside casing was 3Cr12 stainless and the acoustic panels were held in by 304 stainless studs (8 mm dia) which had been welded with a stud welder. These studs failed in service. The temperature rises to 500 deg [C? F?] rapidly. It has cost the company a lot of money in re-work. Could this be carbide precipitation?

A - The company should have learned that suitable consultancy might have actually saved a lot of money in re-work. A failure investigation conducted by professionals would have easily spotted its cause. Carbide precipitation is not probable, due to the low carbon content of the steel. Furthermore carbide precipitation would probably affect corrosion resistance, not mechanical failure.

The probable causes of failure should be looked at in the reduced toughness and ductility because of grain coarsening and in formation of martensite in the 3Cr12 Heat Affected Zone following stud welding.

4 - Selecting Active Brazing Filler Metal

The use of Active Filler Metal for Brazing Ceramics was introduced in our website page (Click on the Link to see it). A page of links to resources on the same subject was published in Bulletin #064, in the appendix PWL#096B to our regular monthly page for August 2011.
Click on PWL#096 to see it.

A technical note in the Brazing Q&A section published in the August 2011 issue of the Welding Journal at page 24 discusses the criteria for the selection. The question was, what should be the preferred Titanium content for brazing a certain porcelain dielectric ring to a stainless tube.

The author points out that different factors play a role, sometimes in opposite directions. Preferentially one should select the brazing temperature and time such that a uniform reaction zone is formed on the alumina. Exceeding temperature and time will increase the reaction zone with a consequent loss of strength.

Increasing the titanium content plays in the same way, easing wetting of the ceramic surface but at the expense of increased brittleness. Residual stresses which increase with brazing temperature should be kept to a minimum to get sufficient strength.

The article recommends to perform brazing tests with different, competitive filler metals, to find out the most satisfactory material and parameters providing consistent acceptable results, due to the conflicting influences of many factors not known sufficiently.

Interested readers are urged to seek the reported article.

5 - Online Press: recent Welding related Articles

Internal condensation in your resistance welding machine
The Fabricator.

Special Permits, Enforcement Top DOT Agenda
Welding.

Welding Equipment Market to Reach $17 Billion by 2012
http://www.marketwire.com/press-release/-1550275.htm

Repair Rates in Welded Construction (Presentation - 22 frames)
http://www.twi.co.uk/content/Repair-Rates-survey-results-July11.pdf

TWI Connect - Jul-Aug 2011
http://www.twi.co.uk/content/conjuly11.pdf

6 - Terms and Definitions Reminder

Joint Filler is a metal plate inserted between the splice member and thinner joint member, to accommodate joint members of dissimilar thickness in a spliced butt joint

Low Pulse Time in pulsed power welding is the duration of the low current pulse

Nondestructive Proof Testing is performed to identify leaks by filling containers with water and applying a predetermined pressure

Preheat Current in resistance welding is provided as impulses to preheat the joint before applying the welding current

Rotational Spray Transfer (in GMAW) is a variation where a longer electrode extension and special gas mixtures are used to produce a helical pattern of very fine droplets to fill a larger gap.

Surfacing Weld is applied to a surface, not to make a joint but to obtain needed properties or dimensions

Throat Height, called also horn spacing, is the unobstructed vertical distance between arms in a resistance welding machine in the whole throat depth.

Wire Flame Spraying is a flame spraying process in which the coating material is supplied in the form of a wire.

7 - Article - Welding Dissimilar Metals

The need to weld together dissimilar metals, arises from the different service conditions (temperature, pressure, aggressivity of process media etc.) prevalent in different parts of complex structures like a boiler or a processing vat.

While solid state welding of dissimilar metals is generally quite possible if suitable methods are carefully selected and applied, fusion welding of dissimilar metals can be problematic.

This is the case of welds between Fe and Ti alloys or Cu and Al alloys. To check mutual weldability one should first check the melting temperature of both materials: if those are too different, then one will melt before the second starts to heat up, obviously not a promising condition.

Then the mutual solubility of each metal in the other should be examined. Limited solubility metal combinations gives rise to brittle intermetallic compounds that compromise the strength of any joint.

Two metals may be incompatible if the intermixing microstructures they produce are prone to cracking or to inferior corrosion behavior. Besides that, the Heat Affected Zone of each may contain unacceptably hard and brittle phases like martensite.

The mechanical properties of the weld metal, (depending on base metals, filler metal and dilution) and of each of the two heat affected zones, should be acceptable for service conditions, as can be proven by qualification testing.

If service includes heating, thermal expansion coefficients (CTE) should be quite similar, to avoid excessive thermal stresses. Besides that, if the joint is subjected to thermal cycles in service, thermal fatigue should be taken into account.

Therefore elastic modulus, yield strength at temperature and crack propagation behavior should be known, to avoid that destructive cracks propagate through the structure.

Microstructural stability can be compromised if thermal gradients promote interdiffusion of elements with consequent microstructural changes likely to affect mechanical properties. Carbon depletion in steel and carbide buildup in stainless can both have destructive effects increasing cracking likelihood. Corrosion behavior should be examined if galvanic cell can be formed causing corrosion in the more anodic metal or phase of the joint.

One should be cautious of unacceptable fusion welding processes like between steels and titanium alloys or between copper and aluminum alloys. In that case one should resort if possible, to solid state welding processes like friction welding, ultrasonic welding, explosion welding or magnetic pulse welding.

In general, if a transition part composed of the two metals can be welded by a suitable solid state welding process, then regular fusion welding processes can be performed separately for each side of the transition part connecting by fusion welding only similar metals.

In other cases a transition filler metal, separately acceptable by each of the impossible couple, can be made to bridge the dangerous contact and provide an acceptable joint. Alternatively it may be possible to consider an Electron Beam brazing/diffusion bonding approach with an appropriate interlayer.

When welding dissimilar metals by arc or Electron Beam processes, thermoelectric currents may form, similar to the operation of thermocouples, developing magnetic fields likely to cause arc blow, or uncontrollable deflection of the arc.

An article on Joining Incompatible Materials was published by this Author on April 10, 2007. It is available online by clicking on Incompatible.

See also, on this same subject, the link Resources published hereafter in Bulletin #65, appended as PWL#097B past the end of this regular Practical Welding Letter issue.

Find there several links to authoritative Internet Sources, on Joining Incompatible Materials.
Don't miss it!

8 - Site Updating: Pickling, Laser Beam Welding

The Pages of this Month added to our Website, deal with different subjects. The first is about an industrial process, usually highly mechanized and automated, performed continuously on the run of long coiled sheet metal, or in batches of highly repetitive lots of forged parts after they emerge from heat treatment furnaces and cool down to room temperature.

The acid attack called Pickling, removes heavy scale from the surfaces and prepares the material for further finishing or for shipping. This page is seen by clicking on the following link: Pickling.

The other page, reached by clicking on the link, describes in some detail the successful process called Laser Beam Welding. Advantages and Limitations are listed, along with the two different main Modes of operating, and gives some insight in the characteristics of suitable applications.

Generally updates like these are announced in our Welding Blog also available as a service to which any reader may subscribe to stay informed. See instructions below the Navigation Bar at the top left of each page from our website.

Updates can also be found in our pages Site Map and Index Page built to let readers find easily what they may be looking for.

You are urged to let your friends know of this website: they may benefit from the quite extensive information available freely to all readers and can ask questions that may help them.
Let us have your comments on the form of the Contact Us page.

9 - Short Items

9.1 - Atmospheric Corrosion is the gradual degradation or alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapor, and sulfur and chlorine compounds.

9.2 - Burr is a thin ridge or roughness dangerous to the bare hands, left on a workpiece, forgings or sheet metal blanks, resulting from cutting, drilling, punching, or grinding.

9.3 - Corrugating is the forming of sheet metal into a series of straight, parallel alternate ridges and grooves with a rolling mill equipped with matched roller dies or a press brake equipped with a specially shaped punch and die pair, to improve resistance to bending.

9.4 - Degassing is a chemical reaction resulting from a compound added to molten metal to remove gases from the metal. Inert gases are often used in this operation. Also a fluxing procedure used for aluminum alloys in which nitrogen, chlorine, chlorine and nitrogen, and chlorine and argon are bubbled up through the metal to remove dissolved hydrogen gases and oxides from the alloy.

9.5 - Electroplating is the deposition of an adherent metallic coating on an object serving as a cathode, for the purpose of securing a surface with properties or dimensions different from those of the substrate.

9.6 - Hot Working is the plastic deformation, hot forging and hot forming, of metal at such a temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening. Also controlled mechanical operations for shaping a product at temperatures above the recrystallization temperature.

10 - Explorations: beyond the Welder

Clearing the Table and Holding the Door: Constructing Social Norms
SA1.

Will Germany Become First Nation with a Hydrogen Economy?
SA2.

How to Prepare for a Hurricane in the U.S. Northeast
SA3.

Create Your New Job
https://www.welding-advisers.com/Create-your-new-job.html

Why Do London Riots Affect Everyone?
https://EzineArticles.com/?&id=6493596

11 - Contributions: Friction Taper Plug Welding

A process which is probably not widely known, Friction Taper Plug Welding (FTPW), introduced and developed by TWI (The Welding Institute, UK) has certain intrinsic advantages that could make it the repair procedure of choice in many instances where alternatives are less attractive.

In particular, as a solid phase Friction Welding process, it has all the advantages to be exploited whenever fusion welding is dangerous or impossible.

Although it has been used successfully for documented repairs, even for repair of the Space Shuttle External Tank and for plugging the leaking boiler tubes of a power plant unit, the process, industrially exploited for over four decades, is still considered an emerging technology, and there is not off the shelf dedicated equipment currently available, so that prospective users must first build their own device.

Although suitable for fabrication, it is more often considered for repair situations, especially for underwater, radioactive, toxic and inflammable gas environments where traditional processes are more problematic.

FTPW requires drilling a tapered hole at the required location where a crack has to be repaired or where a weld has to be made. Then a tapered plug of the same material and included angle is friction welded into the hole.

This is done by rapidly rotating the plug clamped in a suitable chuck, and then stopping the rotation and applying pressure at the right time when the abutting surfaces are at welding temperature.

The result is that the complete conical surface of the tapered plug is now friction welded to the matching surface of the hole. There may be a need to grind excess thickness of the plug from both sides to have it flush with the plate.

The process is repeated by making additional holes along the crack that had to be repaired (or along the joint) and using as many plugs as necessary. It is true that FTPW is not a continuous process, and as such it is relatively slow, but its numerous advantages can be predominant.

In particular it can be applied under water, does not require skilled workforce, is performed with power tooling, not welding equipment, is highly repeatable and produces high quality, reliable welds.

This is one more process to be remembered when it could come in handy.

12 - Testimonials

From: Matthew Mackay
To: welding-advisers.com
Date: 28 Aug 2011, 10:37:13 PM
Subject: RE: courses

Thank you for your response.
I appreciate it.

From: Virendra Jaiswal
E-mail Address: Removed for security
To: welding-advisers.com
Date: 07 Aug 2011, 11:18:03 PM
Subject: Re: welding

Dear Sir,
Thank for your valuable reply.
Best Regards
Virendra

13 - Correspondence: a few Comments

13.1 - From time to time I receive blank forms, where the inquirer failed to input any feedback or question at all. I cannot understand or interpret the meaning of a non-message. So I leave it there without any comment on my part.

13.2 - Could anybody make sense of the following request: "required cold welding machine with all equipments"? It is a real request I got, the writer has probably no idea of the absurd of his/her message.

13.3 - Another example, from a Quality Engineer [?!]: "Photos [of] the machine and process [to] weld copper with copper and different size (the welding with the same size)". What can one make with this question?

14 - Bulletin Board

14.1 - ASNT Fall Conference and Quality Testing Shaw
Oct. 24-28 - Palm Springs Convention Center, Palm Springs, CA
www.asnt.org

14.2 - Heat Treat 2011, 26th Conf. and Expo.
Oct. 31-Nov. 2 - Duke Energy Convention Center, Cincinnati, Ohio
http://hts.asminternational.org/content/Events/Heattreat/

14.3 - 18th Steelmaking Conf.
Nov.1-3 - City Center Rosario, Rosario, Santa Fe, Argentina.
www.siderurgia.org.ar/conf11

14.4 - Can I Succeed Online?
You know the answer... YES! with SBI!

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Please continue to browse down hereafter for the Mid September Bulletin.

Copyright (©) 2011, by Elia E. Levi and
www.welding-advisers.com
All Rights Reserved

Mid Month Bulletin 65 - PWL#097B September 2011

keywords: Joining incompatible materials, Explosive Metal Welding, Acoustic Welding, Ultrasonic Plastic Welding,Friction Welding

PWL#097B - Resources on Joining Incompatible Materials, Welding of Dissimilar Metals, Solid State Metal Welding, Friction Welding, Friction Stir Welding, Explosive Metal Welding, Acoustic Welding, Ultrasonic Plastic Welding, Thermoplastic Compatibility Guide and much more...

However well informed and expert you may be, you could certainly benefit from a vast repository of online authoritative welding information.
The following may be just what you need...

Introduction

This Mid September Bulletin #065 is now integral with and appended to the regular PWL#097 publication. The subject of this Bulletin is a collection of Online Resources on Incompatible Materials Welding as an extension to our Article on Welding Dissimilar Metals, published above in Section 7.

Links to the Mid Month Bulletin Pages are listed in the regularly updated page on Welding Resources (Opens a new Window).

We urge our readers to Bookmark this page and to subscribe to our Welding Site Blog by clicking on the orange buttons under the NavBar in each Website page
(www.welding-advisers.com).
If you prefer not to subscribe, you may also click periodically on the Welding Blog button in the NavBar to see Updates.

The addresses reported hereafter were live and correct at the time of their publication. There is no guarantee that they will always be so, because they are administered by the sources themselves and are under their control.

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 selected them 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.

If the information is important to you as we hope, you may save the selected pages in a suitable folder on your Computer for easy reference. You are welcome to forward this page to those of your friends who may profit of this information.

Resources

Joining incompatible materials
http://www.thefabricator.com/article/TECHCELL/joining-incompatible-materials

Adaptive continuous acoustic welding system for incompatible materials
http://www.freepatentsonline.com/y2007/0257086.html

Joining Incompatible Material Combinations (Section 7)
Click on PWL#043.

Filler Alloy Selection For Aluminum Welding
Alcotec.

How to Avoid Cracking in Aluminum Alloys
ESAB.

Welding of Dissimilar Metals
Key to Metals.

Weldable Combinations for Inertia & Direct Friction Welding
http://www.spinweld.com/weldable-materials.php

Friction Welding Using Insert Metal
http://www.aws.org/wj/2004/03/036/

To Clinch or Spot Weld...That Is The Question
http://weldingdesign.com/gases/news/gwd_11309/

The cold welding process is being used for more and more high-volume applications.
Assembly Mag.

Welding of Dissimilar Materials
EWF.

Percussive arc welding
http://www.twi.co.uk/content/kscco003.html

Friction Welding
http://www.mtiwelding.co.uk/friction.html

Dissimilar Materials Welding
http://www.dielectrics.com/dissimilar-materials-welding.html

Procedure for Manual Welding Dissimilar Metals
http://www.g-w.com/PDF/SampChap/59070_5810_CH19.pdf

Welding metals of dissimilar strengths
http://www.thefabricator.com/article/arcwelding/welding-metals-of-dissimilar-strengths

Factors to Consider When Welding Dissimilar Strength Carbon and Low-Alloy Steels
http://www.hobartbrothers.com/aboutus/welding_dissimilar_metals/

Welding Dissimilar Steels
http://www.weldingcourse.net/2010/11/welding-dissimilar-steels.html

Friction stir welding of dissimilar alloys – a perspective
http://www2.matse.psu.edu/modeling/papers/10STWJ_DebRoy.pdf

Welding Dissimilar Metals Guide
http://metalspinning.wordpress.com/2009/12/15/welding-dissimilar-metals-guide/

Welding processes join dissimilar materials
Drilling Club.

Dissimilar Metal Welding for Stainless Steel
http://frepd.com/2011/03/13/dissimilar-metal-welding-for-stainless-steel/

Dissimilar Metal Welding: Solving Weak Weld Issues in Axial Welded Parts
http://cit-hadley.com/whitepapers/weak-weld-problems.html

Guidelines for Dissimilar Welding
http://www.weldingcourse.net/2010/04/guidelines-for-dissimilar-welding.html

Feasibility and optimization of dissimilar laser welding components
http://doras.dcu.ie/574/

Dissimilar Welding
http://www.matsceng.ohio-state.edu/wjmg/dissimilarWelding.htmlx

Mechanized TIG Welding Station for Joining Similar and Dissimilar Materials
http://weldingdesign.com/operations/main/mechanized-tig-welding-station-0822/

Simulation: welding dissimilar classes of materials
http://www.ilt.fraunhofer.de/eng/101629.html

Laser welding of dissimilar material
http://ethesis.nitrkl.ac.in/1829/

Laser Welding of Dissimilar Sheath Metals (abstract)
http://www.scientific.net/MSF.580-582.493

Explosive Metal Welding
http://www.pacaero.com/products/explosive-welding-metals.htm

Explosion Welding of Dissimilar Metals
http://www.highenergymetals.com/

Explosion Welding (EXW) Technology
http://atlasuhv.com/#/index.php/technology/atlas-explosion-welding-exw-technology

Heat Generation in the Inertia Welding of Dissimilar Tubes
http://www.aws.org/wj/supplement/dave10-01.pdf

Friction Welding Using Insert Metal
http://www.aws.org/w/a/wj/ochi.html

Ultrasonic welding of dissimilar plastics
http://meditec.mi-verlag.de/en/2011/03/09/ultrasonic-welding-of-dissimilar-plastics/

Polymer Materials for Ultrasonic Plastic Welding
http://www.powerultrasonics.com/content/polymer-materials-ultrasonic-plastic-welding

Ultrasonic Plastic Joining Methods Related to Welding
Power.

Frequency is important in ultrasonic plastic welding machines
Plastemart.

Thermoplastic Compatibility Guide
http://www.dukane.com/us/Documents/Thermoplastic%20Comp%20Guide.pdf

Comparison of Common Thermoplastic Welding Techniques - Copyright Dielectrics 2007
Dielectrics

28 Polyesters
Download.

Friction Welding of Similar and Dissimilar Materials: PMMA and PVC.
Free Library.

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