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PWL#004 - Submerged Arc Welder, F/M for Alum. Alloys, Fatigue Failures, sorting Stainless Steel
November 30, 2003
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Practical Issues, Creative Solutions
How to select your Submerged Arc Welder.

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Date: December 2003 - Practical Welding Letter - Issue No. 04

------------------------TABLE of CONTENTS---------------------------

==> 1 - Introduction

==> 2 - Article: Your Submerged Arc Welder

==> 3 - How to do it well: Sorting unweldable stainless

==> 4 - Filler Metal: Selection of Aluminum Alloys

==> 5 - In the press: Recent Welding and related Articles

==> 6 - Terms and Definitions Reminder

==> 7 - Article: Fatigue failures

==> 8 - Site Updating

==> 9 - Readers' Contributions and Short Items

==>10 - Explorations: beyond the Welder

==>11 - Correspondence: a few Comments

==>12 - Bulletin Board

==>Unsubscribe link
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1 - Introduction

This new issue of Practical Welding Letter is the first one where we could enjoy the help of some targeted feedback, pointing us in the direction of certain items which seem to be requested by at least a certain number of readers. We hope that the trend of providing us with the readers' wishes will continue, to improve the relevance of the content.

After the presentation of the Feedback Form (sorry for the technical problem of the first trial) we were delighted to see a substantial stream of input from our readers. We are encouraged by the positive feelings expressed in many of your messages and we certainly wish to provide significant information.

As expected we have now more subjects on hand than can be dealt with in a single issue but, if not now, we will do our best to answer in one of our next publications. Although not as diffused as other forms of manual joining, the Submerged Arc Welding process seems to gather quite a bit of interest: therefore we undertake to handle it in some depth.

Aluminum alloys are in demand as a subject to learn more on, and filler metal selection is possibly not obvious: that is why a section is dedicated hereafter to supplying at least some information on the criteria to keep in mind when selecting the filler metal most suitable for the job at hand.

Some articles referred to in the review of the Press deal with problems of Welding Education and Training. It appears to be a hot subject, because apparently there is a perceived and persistent lack of experienced welding professionals. It was therefore justified to dedicate one page of the Site to this problem, as indeed was done.

Now more than before we urge our readers to take a few minutes of their precious time and to let us know their comments and wishes. Use the prepared form: click here.
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2 - Article: How to select Your Submerged Arc Welder

Note: This subject came up as requested by some of our readers, who were so kind to provide us with their feedback, as urged by us to do so in the Form we provided in the Subscription page of our Site. We are glad to know what interests you more, and we will deal in next issues with other demanded subjects.

Submerged Arc Welding (SAW) is best suited to provide high productivity solutions to manufacturing problems arising when welding relatively thick material (over 6.3 mm = 1/4") in flat or horizontal position with long joints making the most of mechanized set-ups. Multiple passes are applied when a single pass would not provide an acceptable solution, either economically or metallurgically. Although semi automatic manual application is also possible, it is much less attractive than the above.

The process consists in establishing in the joint an electric arc between a running electrode (driven by power rolls through contact tips), in the form of a solid or a cored wire, and the workpiece, under the cover of a granulated flux. Mechanical means provide the relative motion of the joint relative to the electrode holder.

Advantages: High deposition rate and speed of welding. Use of not so skilled workforce. Suitable to operate even in presence of moderate air drafts. No need for protecting gases. No visible arc and no fumes, friendly to the environment. High quality generally available. Suitable for depositing hardfacing or corrosion protective layers. Suitable for adjusting the chemistry of the deposit by proper composition of the flux. Suitable to the manufacture of heavy wall tubes.

Limitations: Needs precise set up and fixtures. Needs manual or mechanical removal of fused slag. Usually not suited for thin sheets (less than 3 mm ~1/8"). Only for flat or horizontal position.

The most important part of the equipment is the power supply, which must be rated to the provision of elevated current for as long as needed. That means Duty Cycle = 100%, that is nonstop operation. See the Amperage Rating section in the following.

Direct Current

Direct Constant Current from a power supply exhibits a drooping characteristic curve expressing the dynamic relationship between current and voltage.

The System has usually a voltage sensitive control device that varies the electrode feed rate in response to a change in arc length: feed is increased (to reduce arc length and voltage) when voltage goes up, or reduced (to increase arc length and voltage) when voltage decreases.

As a consequence of the electrode variable feed rate the voltage remains quite constant at the predermined value, while the power supply provides constant current during the welding process.

It is reported that this type is more difficult to set up because any change introduced either in the wire feed control or in the current has an influence on the other parameter.

This type of power supply is preferred for thick joints using relatively thick filler wire.

Direct Constant Voltage (or Constant potential) power supplies are self regulating. The voltage is set in advance at the power supply. The electrode is provided at a constant, predetermined feed rate. Current is determined by electrode size and speed: to increase the current one has to increase the wire feed and vice versa. So it is easier to set up.

This type of power supply is preferred for relatively thin materials to be welded at high speeds.

Polarity

With both types of direct current as introduced above one should be aware of the consequences of the polarity selected. Selection affects the shape of the bead, the dilution of the base metal and the deposition rate.

The least dilution and penetration is obtained with direct current straight polarity (electrode negative). This should be the choice for overlaying or hardfacing, and to reduce cracking tendency. For overlaying, the filler material can be in strip form, requiring proper rollers in the feeder. The plates should be clean, to limit porosity.

Conversely direct current reverse polarity (electrode positive) provides increased penetration with thinner beads, permitting decreasing grove width: this in turn permits the use of less filler (increased productivity) and lower heat input (less distortion). It will also produce less porosity even with rusty or not so clean plates.

Alternating Current

The shape of the bead will result somewhere in between the shapes of both polarities discussed above for direct current.

Alternating Current power supplies are used for SAW, with provisions for a square voltage wave shape. This modified wave form has a very rapid passage through zero voltage, which helps avoiding arc black out. Alternating current is beneficial at elevated current values, where direct current may be subject to magnetic blow interfering with welding.

For extremely high weld deposition rates, special equipment with double or multiple electrode may be employed but we are not going to deal with that here.

Materials

The process is used mostly for welding low carbon and low alloy steels. Filler metal is covered by AWS A5.17. If special requirements are not present (like minimum assured impact strength or fracture toughness), it can be used also for less weldable steels although with proper provisions, like special consumables, preheating etc. Stainless steel can be welded by this process.

Cast iron could be welded with nickel electrodes, although the application may not be simple.

Aluminum, magnesium, titanium, lead and zinc are not suitable for SAW.

Amperage rating

The amperage range of any available power supply determine in large measure the thickness welding capability of the equipment. As a guideline light gages (6 mm ~ 0.25") can be welded by 300 Amp. while heavy plates (25 mm ~ 1") may need 1000 Amp. or more.

The duty cycle determines the maximum percentage of welding time available in any ten minutes interval. A power supply with high maximum amperage but limited duty cycle, guarantees a higher duty cycle at the lower current level used in practice.

However it is quite unusual that a thick weld should be welded in a single pass: this is because too much heat would be input, too much filler would be used and much distortion would occur. And the welding speed would result unacceptably low.

Therefore it is customary to report in tables the current range for different filler wire sizes. It should be noted that different sources provide quite different parameters. The ranges displayed are large and show some overlapping. These are estimated values that are influenced also by flux, wire type, stickout, joint type, metal thickness and power supply.

At any given current value, changing to a smaller size increases the current density and provides for deeper penetration and thinner bead, while the arc results more stable and the deposition rate increases.

In the following Table I some initial parameters were listed for helping in setting up a Submerged Arc Welding operation for steel sheet and plate.

Table I
Submerged Arc Steel Welding Parameters
Wire Diameter Welding Current Deposition Rate
mm in A kg/hr lbs/hr
1.2 0.045 100-350 1-4.5 2.2-10
1.6 1/16 115-500 2.4-8 5.3-17.6
2.0 5/64 130-600 3.8-9.8 8.4-21.6
2.4 3/32 150-700 4.3-11.5 9.5-25.4
3.2 1/8 220-900 5.8-12.4 12.8-27.3
4.0 5/32 300-1000 6.2-14.3 13.7-31.5
4.75 3/16 400-1100 7.8-17 17.2-37.5
6.3 1/4 450-1500 9-19 19.8-42

Consumables

The composition of different fluxes is finely tuned to control the composition and the mechanical properties resulting in the weld, so that their selection should be based on careful consideration of the base metal and of the requirements.

It is the combination of the filler metal and of the flux that provides the required properties. It is recommended therefore to seek advice from the manufacturers for chosing suitable and compatible consumables.

Fluxes of two types are supplied: Fused fluxes are melted after mixing the ingredients, and then crushed, screened and packaged. They do not contain alloying elements or active deoxidizers.

Bonded fluxes can be blended more easily with useful additives. They are however more susceptible to contamination and moisture.

Filler metals for steels are listed in the following:
"Specification for Carbon Steel Electrodes and Fluxes for Submerged Arc Welding"
A5.17-89, AWS, 1989.

"Specification for Low Alloy Steel Electrodes and Fluxes for Submerged Arc Welding"
A5.23-90, AWS, 1990.

Relative motion

The accessories for providing relative movement as required depend on the application and are independent on the power supply selected, although the weld speed should be controllable as a function of other welding parameters.
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3 - How to do it well: Sorting unweldable stainless

Q: A batch of regular stainless steel fasteners to be welded on a sheet, was inadvertently mixed up with free-cutting stainless ones. As we are told that free-cutting stainless is not weldable, how can we sort out the weldable items?

A: Hopefully the batches, although unknown, are still separated: if this is the case you need only to examine representative specimens of batch A vs. batch B. It is quite straightforward to sort the types by microscopic examination, after grinding and polishing one surface of each one (a nondestructive process): the free-cutting material is peppered by sulfur particles readily standing out of the background. Alternatively you may try to weld: the nonweldable will crack right away...

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4 - Selection of Aluminum Alloy Filler Metal

Gas shielded arc welding processes, which can be performed without the use of flux, are the most employed for joining Aluminum Alloys. These processes permit full view of the welding being performed, allowing skilled welders to obtain quality work without costly flux removal and neutralization treatments.

This article is intended to provide information and guidelines for selecting the most appropriate Aluminum Alloy Filler Wire for any job, by highligting the principal concerns to be considered.

The accepted document governing the subject is:
"Specification for Bare Aluminum and Aluminum Alloy
Welding Electrode and Rod" ANSI/AWS A5.10-92,
American Welding Society, 1992.

Additional relevant data can be found in:
"Recommended Practices for Gas Shielded Arc Welding of Aluminum
and Aluminum Alloy Pipe", ANSI/AWS D10.7-86,
American Welding Society, 1986.

The following Table I lists the most important Aluminum Alloys Filler metal composition and melting range. The prefix ER indicating Electrodes and Rods is omitted from the list of items. The designations are followed by a number [x] which is used in Table II further down, for indicating the suggested selection according to specific criteria.

Table I
Filler Metal Designation, Composition and Melting Range
Alum. Nominal Composition % Melting Range
Alloy Si Cu Mn Mg Cr Ti Notes 0C 0F
1100 [1] - 0.12 - - - - - 643-657 1190-1215
2319 [2] - 6.3 0.3 - - 0.15 +0.18Zr
0.1V
543-643 1010-1190
4009 5.0 1.25 - 0.50 - - (1) 546-621 1015-1150
4010 7.0 - - 0.35 - - (2) 557-613 1035-1135
4011 7.0 - - 0.58 - 0.12 +0.55Be(3) 557-613 1035-1135
4043 [3] 5.25 - - - - - - 574-632 1065-1170
4047 [4] 12.0 - - - - - - 577-582 1070-1080
4145 [5] 10.0 4.0 - - - - - 521-585 970-1085
4643 [6] 4.1 - - 0.20 - - - 574-635 1065-1175
5183 [7] - - 0.75 4.75 0.15 - - 579-638 1075-1180
5356[8] - - 0.12 5.0 0.12 0.13 - 571-635 1060-1175
5554 [9] - - 0.75 2.7 0.12 0.12 - 602-646 1115-1195
5556 [10] - - 0.75 5.1 0.12 0.12 - 568-635 1055-1175
5654 [11] - - - 3.5 0.25 0.10 - 593-643 1100- 1190

Notes:

  • Aluminum percentage is the Remainder
  • (1) - ~ C355.0
  • (2) - ~ A356.0
  • (3) - ~ A357.0

    The primary factors commonly considered when selecting a welding filler alloy are:

    • Ease of welding or freedom from cracking
    • Tensile or shear strength of the weld
    • Weld ductility
    • Color match between the weld and base alloy after anodizing
    • Corrosion resistance

    A further consideration, not listed here, but sometimes important refers to the behavior of the weld to somewhat elevated temperatures, or to applications in very cold environments within the limits suitable to aluminum alloys.

    In the following Table II the above designations, indicated as [x], are listed as suggested choices for satisfying the criteria of each of the headings.

    The indications are not absolute and should always be tested to confirm their suitability to the requirements of any particular application.

    Table II
    Suggested Filler Alloys that satisfy specific Criteria
    Aluminum
    Alloys
    Ease of
    Welding
    Strength Ductility
    (1)
    Color
    Match (2)
    Corros.
    Resist.
    1100 to 1100 [3] [3] [1] [1][3] [1][3]
    1100 to 3003 [1][3][5] [3][5][7][8][10] [1][8] [1][7][8][10] [1][3]
    1100 to 6061 [3][5] [3][5][8][10] [8] [7][8][10] [3]
    2090 & 2095 [2] [2] [2] [2] [2]
    2219 to 2219 [2][5] [2] [2] [2] [2]
    2014 to 2014 [5] [2] [2] [2] [2]
    5052 to 5052 [3][7][8][10] [7][8][10] [8][9][11] [8][11] [9][11]
    5052 to 6061 [3] [7][8][10] [8][9][11] [8][11] [3]
    5083 to 5083 [7][8][10] [7][10] [8] [7][8][10] [7][8][10]
    5083 to 6061 [3][7][8][10] [7][10] [3][8][9][10][11] [7][8][9][10] [3][7][8][11]
    5086 to 5086 [7][8][10] [7][10] [8] [7][8][10] [7][8][10]
    5086 to 6061 [3][7][8][10] [6][7][10] [8][9][11] [7][8][9][10] [7][8][9][10]
    5454 to 5454 [7][8][10] [7][10] [8][9][11] [7][8][9][11] [9]
    5454 to 6061 [3] [7][8][10] [8][9][11] [7][8][9][10] [9]
    5456 to 5456 [7][8][10] [7][10] [8] [7][8][10] [7][8][10]
    6061 to 6061 [3] [6][7][10] [8][9][11] [8] [3]
    6061 to 6063 [3] [8][9][10][11] [8][9][11] [8] [3]
    7005 to 7005 [7][8][10] [7][8][10] [7][8][10] [7][8][10] [7][8][10]
    7039 to 7039 [7][8][10] [7][8][10] [7][8][10] [7][8][10] [7][8][10]

Notes:
  • Ease of welding is considered achieved when cracking is not observed.
  • Strength is evaluated in as welded condition, without heat treatments.
  • Ductility is assessed as a function of successful bend testing.
  • Color matching between base metal and weld metal refers to appearance after anodizing.
  • Corrosion resistance is indicated for exposure to water, plain or salted.

    Disclaimer: the information of this Table is made available in good faith, as collected from sources believed to be accurate.

    In particular cases following the indications may result in less then optimum outcome. Readers are urged to control by independent means if what published here is relevant to their problems. Practical tests are always recommended before selecting a particular filler metal for manufacturing applications.

    It is important to identify the types of base metals to be joined and to define the most important requirements of the weldment as these are the basic criteria for the selection of filler metal for welding Aluminum Alloys.

    Ease of welding and freedom from cracking are the most important requirements usually considered. If other considerations do not prevail, then aluminum filler metal ER4043 containing 5% Silicon is selected, for the great majority of welding jobs because it allows the easiest flow and welding without cracking.

    Welding of 1xxx and 3xxx alloys can be performed with fillers of 1100 material or even from strips from same sheets and also with ER4043.

    Of the 2xxx alloys, only 2219, 2090 and 2095 should be considered weldable, with filler ER2319, ER4043 and ER4145. However also 2014 has been welded with the same filler wires in certain situations (not recommended).

    The 5xxx alloys are best welded with fillers like ER5183, ER5356, ER5554, ER5556 and ER5654. Of these alloys containing Magnesium only 5052 can be welded with ER4043 without causing excessive brittleness.

    Alloys 6xxx should never be welded autogenously, that is without using any filler metal, because of their tendency to crack. Magnesium containing filler metal alloys (ER5xxx as above) can be used for better strength and ductility, and for better color matching after anodizing.

    Otherwise ER4043 and ER4145 can be employed provided a substantial proportion of these materials enter the weld bead: because of this the prepared gap should be larger than what commonly used. ER4047 should be preferred if ER4043 shows cracking.

    However, if complete heat treatment is planned to be performed after welding, then filler alloy 4643 should be used, especially for thick welds, because it is heat treatable.

    Of the high strength alloys 7xxx, only 7005 and 7039 were designed to be weldable with the magnesium containing filler alloys 5356, 5183, and 5556. Other alloys of this series should not be fusion welded at all.

    For the casting alloys C355.0, A356.0 and A357.0, the filler alloys ER4009, ER4010 and ER4011 respectively should be used, because of their compatible chemistry and identical response to heat treatment.

    When considering the strength of the weldments, one must remember that for non heat treatable alloys, depending on strain hardening for their mechanical properties, the heat of welding provides annealing of the Heat Affected Zone, irrespective of welding procedure or filler metal.

    For heat treated alloys, on the contrary, annealing would be a much longer process. Therefore the Heat Affected Zone results in various layers of microstructures showing an array of properties. In general limiting peak temperature and heat input will cause a more contained damage.

    The strength of weldments performed in T4 condition may improve in time because of natural aging, even without resolutioning. Full solution heat treatment should be avoided when possible because of deformations associated with rapid quenching.

    However artificial aging should be omitted with filler alloys containing more than 3% magnesium (5xxx) because long heating can cause susceptibility to stress corrosion cracking (SCC).

    The following Tables III and IV list the initial parameters that can be selected for performing Gas Tungsten Arc Welding on Aluminum Alloys. The parameters should be adjusted as needed according to the particular conditions prevailing and the results obtained.

Table III
GTAW procedures for Flat Position Aluminum Welding
Base M. Thickn. Tungsten Size Filler Rod Size Current
mm in mm in mm in A
1.6 1/6 1.6-2.4 1/16-3/32 2.4 3/32 70-100
2.4 3/32 2.4-3.2 3/32-1/8 3.2 1/8 90-120
3.2 1/8 3.2 1/8 3.2-4.0 1/8-5/32 125-175
4.8 3/16 4.0-4.8 5/32-3/16 4.0-4.8 5/32-3/16 170-225
6.3 1/4 4.8-6.3 3/16-1/4 4.8 3/16 220-275

Table IV
Additional parameters in the same order
Passes Gas Cup Size Voltage Gas Flow
No. mm in V L/min cft/h
1 9.5 3/8 15-17 9 20
1 9.5 3/8 15-18 9 20
1-2 11.1 7/16 15-20 9 20
2 11.1- 12.7 7/16-1/2 15-20 12 25
2 12.7 1/2 15-20 14 30

Notes:

  • Groove joint.
  • Suitable for alternative current.

In the following Table V are listed the suggested initial parameters that can be employed for welding Aluminum Alloys with the Gas Metal Arc Welding with Filler Metal Electrode Wire.

Table V
GMAW initial parameters
Base Metal Thickn. Filler Wire Diameter Pass. Voltage Current Feed (Speed)
mm(in) mm in No. V A cm/sec ipm
1.6(1/16) 0.8 0.030 1 15-20 70-110 20-30 500-750
2.4(3/32) 0.8-1.2 0.030-3/64 1 18-22 90-150 20-30 500-750
3.2(1/8) 0.8-1.2 0.030-3/64 1 20-24 120-150 17-29 400-700
4.8(3/16) 0.9-1.2 0.035-3/64 2 22-26 130-175 10-25 250-600
6.3(1/4) 1.2-1.6 3/64-1/16 2 24-28 150-300 8-17 200-400

Notes:

  • Weld backing should be considered.
  • Pulsed current can be used for base metal less than 2.4 mm thick.
  • Typically pulsed current uses less amperes than constant current.
  • Otherwise use Direct Current Reverse Polarity (Electrode Positive).
  • Constant Current power supplies give more consistent penetration.
  • Wire should be kept always clean and dry.
  • Aluminum wires less than 1.2 mm can give problems in wire feeding.
  • Use forehand, push technique to remove aluminum oxide skin.
  • If the cleaning action is not sufficient, consider decreasing the voltage (arc length).
  • To provide sufficient gas coverage, the gas cup should be larger than weld + HAZ width.
  • Use 10 to 24 L/ min of Argon gas (20 to 50 cuft/hr).
  • Manual travel speed may range between 8 and 20 mm/sec (18 and 50 in/min), and even more for mechanized welds.
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5 - In the Press: Recent Welding and Related Articles

For those taking welding for granted, a sobering reminder from The Welding Institute, UK, is available in an article, actually a report of a Seminar, on Weld Failures and how to avoid them. Actually it is a call for managers and for everyone involved, on the Importance of Welding Education and Training. Note: The link that we provided was live in the past. TWI removed the page or filed it somewhere else where we are unable to find it. Sorry!

From the Canadian Welding Association an article relates on programs and initiatives to spread Welding Education in Canada. A strong drive from industry is essential. The article published in the Spring 2003 issue of Canadian Welding Association Journal is now (03/2006) available to members only. See
http://www.cwa-acs.org/index.html

From AWS Welding Journal an article titled "Spot welding: still in the Driver's Seat" explains that robotics, repeatability and economy drive the quest for new and improved machines.
Note - Unfortunately the link is no longer supported by AWS. Readers may search the Welding Journal, November 2003 Issue.

For gaining a comprehensive view on the Aluminum Industry in the U.S. one can click here.

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6 - Terms and Definitions Reminder

Do you remember what is...

Autogenous weld: A weld made by fusing the base metal without the addition of filler metal.

Burn Back: A condition where the electrode wire is not properly fed to get the melting of the tip outside the torch, far from the contact tip (especially for thin, soft aluminum wire).

Magnetic Arc Blow: A powerful deflection of a welding electric arc, due to the influence of a magnetic field present at the location interfering with the field generated by the welding current. Particularly troublesome with direct current.

Stickout Distance: The distance between the last electrical contact to the electrode wire and the weld. (In Metal Inert Gas, in Flux Cored and in Submerged Arc Welding).

Would you want other terms being presented in next issues? Let us have your feedback on the Form. Click here.

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7 - Article: Fatigue failures

It is widely recognized that the majority of failures occurring in mechanical elements of structures or machinery are due to the fatigue phenomenon.

It is therefore quite important to understand their origins and the prevention means applicable to the elements designed to substitute the failed ones.

Fatigue is the progressive formation and propagation of cracks in a material subjected to repeated or alternating stresses (due to cyclic loads or forces), lower than its static yield strength limit. The final rupture occurs when the remaining section is no longer sufficient and able to sustain the normal operating forces.

Generally the appearance of the fracture presents a telltale aspect which is easily recognized as due to fatigue, and possibly other clues pointing to the origin of the failure. Characteristic features, commonly called "beach marks", represent progressive stages of crack development, and are the single most important distinctive sign of fatigue.

One of the first tasks of the investigation is then to determine, from the appearance of the fractured surface, assuming that it has not been obliterated by contact wear successive to the fracture, the mechanism generating the failure.

If it can be concluded with a fairdegree of certainty that fatigue was involved, then the most common course of action would be to plan the substitution of the element with a new one designed to better perform the task of that which ruptured, trying to improve its performance by taking into account the operating factors.

The contribution of an expert Metallurgist assisted by the equipment and know how of a modern Laboratory can be invaluable, especially if the case is complicate or tyed to legal responsibilities, or if environmental or operational conditions like humidity, heat, vibrations, very high speeds, impact loading, or corrosive agents are involved.

However, for the simpler cases (i. e. a broken shaft), there are a number of less expensive solutions which may be preferred by the one who has to pay for.

The properties to be looked for are hardenability, that is the capability to harden through the depth of the part, and hardness after heat treatment, taken as an indication of strength.

Where can inexpensive help be found? At those providers whose metallurgical expertise is included in the product or service they market and sell.

Service Centers representing reputable materials manufacturers are not only stock keepers of metals: the best of them know their products in depth and are familiar with applications similar to the one for which a new piece of steel (most often) has to be selected from the overwhelming assortment.

They may have informative leaflets displaying composition and properties, usage and treatments, availability and costs. They are worth listening to, they know what they say.

Even before cutting the first chip, the Heat Treatment job shop that will be charged with the processing of the part should be involved in the project and asked for advice. He/she could be requested to test the hardness of the broken part, to obtain an indication of baseline properties which should be improved upon. At the same time one should inquire if some surface hardening might be present.

A proper metallurgical investigation would try to pinpoint the cause of failure (faulty design, defective material, improper treatment, surface damage or pure high cycle fatigue).

By skipping the quest for the cause, one implicitly assumes that the failure occurred by chance as a consequence of one or more contributing factors, that will not necessarily duplicate if the marginal conditions are improved.

The heat treater will not only suggest the best treatment to perform (most often hardening and tempering) and by what equipment, but will advise at which stage in the machining sequence of operations the processing should take place, will provide useful tips for control deformations and may offer to take care of Hardness Testing for control, and of Magnetic Particles Inspection for assuring the soundness of the part.

In addition he/she may be familiar with finishing processes, like burnishing, shot peening or phosphatizing which will add value to and improve the properties of the final product. Shot peening in particular is a process designed to induce on the surface of the treated parts compressive residual stresses that may effectively prevent the occurrence of fatigue failures.

A sketch of the part and the taking of dimensions will probably be done in house with great care: a few remarks are in order here.

Depending upon the exact position of the failure, one should consider that sharp fillets or notches, known in general as stress raisers, may have a nefarious influence on fatigue life: they should be avoided or reduced in intensity (larger radius etc.).

Normally the smoother the surface finish the better, except that grinding is known to introduce tensile stresses which are harmful and even tiny cracks which are ruinous; grinding control, if applicable, should be performed by a certain procedure known as "Nital Etch".

The Heat Treater may know where to do that, especially if he is involved with treating gears. Summing up, although fatigue failure may have heavy and costly consequences on maintenance and availability of equipment, it can be controlled for the future if the new design and possibly improved procedures take care of most of the influencing factors which have been outlined above.

It should be added that, if the breakdown of important pieces of equipment could have harmful economic consequences, not to say personal danger to people, one should always search for cracks especially in rotating parts, during sessions of planned maintenance.

This is the only way to prevent fatigue failures, by retiring the damaged part while still functioning but before final rupture. Special crack detection techniques are available for performing this non destructive inspection.

Is this subject important to you? Let us know your comments and wishes. Use the prepared form: click here.
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8 - Site Update

We are proud to inform our readers that we released and posted in the Site a new page on Welding Education and Training. To reach it click here.
We believe this new page provides useful information especially to those willing to consider Welding as their promising new career for life. We are ready to listen to your comments and suggestions. Let us have your feedback on the Form. Click here.

We also added two new pages on the Site on how the Welding Advisers Site was conceived and built. One page deals with the lessons learnt from a book that opened unseen horizons to us, teaching what is important and how one must prepare to achieve results. To see this page click here.

The other page explains how the amazingly simple tools readily available to everyone are used in practice to realize one's project of building a new site. To go through this page click here.

Of course the original page announced in the last issue, detailing the story of why and how the Welding Advisers Site was conceived and built in a do-it-yourself simple and powerful way, is still there for our readers to see. Clickhere.

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9 - Readers' Contributions and Short Items

In the previous issue I proposed the idea, for those of you who create welded Artwork, to create a forum for exchange of tips and ideas, and to show off your creations. One reader expressed interest, but not enough to send in his Contribution. I repeat the invitation to the larger readership.

Maybe some of you have special experiences interesting and useful to fellow welders: you are urged to share them with all of us, as well as comments on what you find in PWL and what you would like to read.

Continuing as in the last issue, for lack of original readers' contributions, I will briefly deal with different subjects that were raised by readers as items of interest.

Welding of ASME SA335 P22 material, (2.25Cr 1Mo) creep resistant steel.
Used for piping and tube joining in power generation plants of not so recent design. The steel is hardenable and susceptible to hydrogen induced cracking.
Main precautions: maximum cleanliness and preheating to 150 0C (300 0F) to avoid hydrogen embrittlement. SMAW and GTAW are used successfully. However FCAW is problematic because manufacturers cannot assure a dry core.

Welding of thick carbon manganese steel plate.
Austenitic manganese steel must be kept relatively cool to avoid embrittlement. The lower carbon grades with high manganese content include various amounts of additional alloying elements. They are usually weldable by SMAW, GTAW and EBW. It is essential to weld without preheating, possibly with additional cooling, and to keep low heat input and buildup. No Preheating, cooling may be used if necessary. Limit time at heating. Maintain a short arc. Keep low welding current. When possible, make several passes. Low interpass temperatures are recommended. Do not post-heat. Electrodes for welding: EFeMn-A EFeMn-B EFeMn-C.

Why is there spatter in CO2 shielded arc welding?
The three filler metal transfer modes in GMAW (Short circuit at the least current, Globular at intermediate current and Spray type at higher current) represent a delicate balance involving the electrical arc conditions, the shielding gas present and its dissociation and ionization characteristics, and the forces acting on the fused tip of the filler electrode. Excessive spatter is usually a symptom of less then optimal global parameters. As this subject cannot be treated in a very short paragraph, it will be dealt with in a future issue if sufficient interest is shown by the readers.

Hot wire GTAW process. The hot wire process is used with the GTAW (TIG) or the PAW (Plasma) welding processes in applications where a high deposition rate of the filler wire is desired . Hot wire welding provides higher deposition similar to that of GMAW (MIG) but with better control of heat input, reduced dilution in overlay welds and deeper fusion in groove welds.

Welding together two dissimilar metals. To weld successfully one must first know exactly which materials are to be welded. Not all combinations are permitted or possible.
In general if one is low carbon and the second low alloy steel the filler can be low carbon as the weld will pick up some of the alloying elements from the more alloyed side.

With high alloy and especially with high carbon, preheat is needed to limit or prevent the formation of hard (martensitic) structures that may induce cracking.

When welding an austenitic stainless to a carbon steel, it is recommended to weld a transition layer (buttering) of high nickel on the carbon steel, and only after weld the part so prepared to the stainless steel.

Passivation of stainless steel. This finishing operation produces a (passive) protective layer of chromium oxide on the surface of stainless steel which provides an effective defense against corrosion attack from certain substances.

Before welding, any passive layer should be removed. On austenitic stainless steel passivation is usually done by immersion in an aqueous solution of nitric acid (mildly oxidizing) which has the additional advantage of eliminating all surface contamination traces of iron from previous manufacturing processes.

See complete information in ASTM A967. Specification.

Welding magnesium castings and shapes. Most magnesium alloys can be arc welded under protective gas, but weldability is widely varying among different types. In Magnesium-aluminum-zinc alloys high aluminum is helpful while zinc is detrimental. The problem may be "hot shortness" causing weld cracking. The selection of the most suitable filler metal and of special conditions like preheating, if necessary depends on the composition of the base metal and on the amount of restraint of the joint.

Strength of welded aluminium joints. This item is brefly treated in the article on Selection of Aluminum Alloy Filler metal. In general the strength is reduced locally in the Heat Affected Zone. If critical, thorough consideration should be devoted to the effects of welds on the strength of structures and assemblies.

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10 - Explorations: beyond the welder

Would you like to visit a big Library? Click here.

Or a big Museum? Click here.

Look at the birdie! Click here.

Maybe you would like to do something else? http://www.webexpeditions.net/

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11 - Correspondence: a few Comments

Questions are welcomed and we try our best to answer as promptly and as completely as we can. As already remarked, however, most of time the questions are incomplete so that it is difficult to figure out the real situation.

I would like to be able to convince the readers that essential information consists in detailed description of base metal designation, specification and condition, filler metal description, process applied and outcome obtained.

It would also help to understand the general situation, if it is a manufacturing problem, a theoretical issue, a research program or a school assignment.

And again, if the reader was helped by the answer I would like to know: I can only hope that this work brings valuable benefits to readers, so that they are encouraged to spread the notion of the Welding Advisers Site to their friends and colleagues, at home and at work.

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12 - Bulletin Board

12.1 - We would not want to make this a permanent feature of PWL, but we must admit to a mistake in which we incurred in our last issue: in the Title the issue number was erroneously written as No. 0030 instead of No. 003. We apologize for this.

12.2 - As our Hardness Book has by now reached quite a substantial diffusion we would like to have your comments as to whether it contains useful information for you and if you would like it expanded to include other subjects. On this and on any other one let us have your valued feedback. Use the prepared form: click here.

12.3 - For a description of how a very informative book helped us to prepare and publish this Site, click Make Your Site Sell.

12.4 - If you are curious as to how a seemingly complicate process (practically building an Internet Site) can be mastered by using simple tools, click on The Complete Site Build It! Reference Center.

12.5 - With many more requests of information than can be dealt with in a single issue, it is inevitable that not all subjects can be answered instantly. But the more you send in feedback the more your subject will stand out, especially if many readers request its presentation and discussion. So please send in your demands and they will be answered. Click here.

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