Flux cored Arc Welding is presently the fast evolving arc welding process. Flux cored wires are like tiny tubes filled with various metallic and non-metallic powders to improve the metallurgy and chemistry of the weld metal and to produce fluxes which enable some desired welding features. This process is well established for unalloyed and high alloyed steels and also for creep resistant steels. The creep resistant steels of type P11, P12, P22, P23, P91 and P92 are weldable by using of similar flux cored wires. Flux cored wire welding process (FCAW) compared to other welding processes offers some general benefits like easy handling, higher productivity and a significant lower risk for defects as weld porosity and lack of fusion which are well recognized by welders.
The production of flux cored wires is more complicated compared to the other electrodes. Flux cored wires are usually delivered on similar baskets as solid wires for the use in the Gas Metal Arc Welding (GMAW) process. Welding equipment similar to normal solid wire welding can be used and the application in automatic and robotic welding systems. The fuse of flux cored wire can provide the GMAW process with the beneficial effects of the Shielded Metal Arc Welding (SMAW) process, control of slag metallurgy, protection of the weld pool from the surrounding by a slag covering and improved out-of position weldability.
The costs of cored wires are remarkably higher compared to stick electrodes or solid wires. Economic evaluation is often done only by comparison of the purchasing costs for similar amounts of different the electrode types, but it should be considered that flux cored wires have benefits in welding. This decreases the working time in establishing the joint due to less rework and faster achievable welding speeds. Also, higher deposition rates and faster travel speeds are achieved with flux cored wires.
Since the creep resistant steels are designed to operate at elevated temperatures for very long times, therefore steel microstructures with stable precipitates like carbides and nitrides embedded in a strong bainitic or martensitic matrix are required. Such desirable microstructures are achieved with a very well balanced chemistry of carbon, chromium, molybdenum and some special elements like vanadium, aluminum, columbium and/or boron, provided by flux cored wire technology.
Adapted from: “GMA-Welding of creep resistant steels with flux cored wires
(FCAW): perspectives and limitations” By G. Posch, S. Baumgartner, M. Fiedler,
Böhler Schweißtechnik Austria GmbH, 8605 Kapfenberg, Austria, Europe
First, we embed an interesting video on Inconlel 8″ pipeline welding.
Please visit our parent blog, http://blog.weldwell.com. We invite you to post all your comments / problems / enquiries freely and be served by our panel of welding experts.
One of our customers asked a few technical queries on interpass temperature of Inconel / Incoloy materials welding and fabrication. The alloys are as follows:
(I) SB444 UNS number N06625 (Nominal composition: 60Ni-22Cr-9Mo-3.5Cb)
INCONEL Alloy 625:
(ii) SB407 UNS number N08800 (Nominal composition: 33Ni-42Fe-21Cr) INCOLOY Alloy 800:
(iii) SB729 UNS number N08020 (Nominal composition: 35Ni-35Fe-20Cr-Cb) INCO Alloy 20:
(iv) SB423/SB705 UNS number N08825 (Nominal composition: 42Ni-21.5Cr-3Mo-2.3Cu) INCOLOY Alloy 825:
The technical queries on interpass temperature of Inconel / Incoloy welding are:
Question (1): During welding of these alloys, what is the maximum permissible interpass temperature against each of the above mentioned material?
We consulted our welding expert and could provide solutions to their problems as shown:
Control of interpass temperature is an important component of a weld procedure (WPS) but is not as critical for high nickel alloys as for carbon steel, low alloy and stainless
steels. Generally it is a recommended practice that control of interpass temperature is included as an integral part of the weld procedure and a maximum interpass temperature of 175 0C is used as a guideline in many cases. Sometimes, tight interpass temperature control from 500C to 650C is used to control the exposure to interpass temperature within the sensitization range to a minimum.
Welding engineers are aware of some cases where the temperature should be controlled at lower levels at about 950C, and applications requiring higher temperatures of about 2300C with acceptable performance. The qualification and execution of weld procedures on these materials must take into consideration all the above in addition to the base material, thickness, condition, final application of the component etc. It is normally the responsibility of the welding engineer within an organization, as he has access to all relevant information.
Question (2): Is there any reason for restriction of interpass temperature to such limit?
Answer: Even the stabilized alloys when held at intermediate temperatures long enough will suffer degradation. Control of interpass temperature during welding also minimizes the risk of grain growth in heat affected zone (HAZ), in the parent material. It can also reduce the formation of surface oxides on weldments that can be retained in the molten weld pool as inclusions. Such inclusions can result in NDT or premature component failure. Formations of surface oxides on underlying weld beads should be removed or cleaned otherwise they may add to molten weld pool inclusions.
Before we discuss further, we embed an interesting welding video.
(Welding video by high speed camera from youtube.com)
Our customer further enquired as shown:
Question (3): Since the specified four alloys are stabilized and not getting sensitized, why interpass temperature should be restricted to 1750C? Why it should not be higher, say 2500 C? Is there any other associated problem? Kindly explain.
We contacted our expert again and fond the solution as explained here:
The four alloys mentioned are among the non-stabilized ultra low carbon alloys that require very restrictive interpass temperatures. For example, C-276 has very low carbon and is
not stabilized such that its TTT diagram has a C curve that is a few minutes
away from zero time at about 7050C to 8350C. It is logical that with lower interpass temperature, the alloy will cool faster through the sensitizing temperature range and allow the alloy to
maintain its corrosion resistance. Alloys 625, alloy 20, and INCOLOY 825
are all stabilized and additionally, INCOLOY 825 is given a stabilizing anneal before it
leaves the mill.
However, INCOLOY 800 has a small addition of Ti, but it does not require stabilization against sensitization as it is normally not used in oxidizing acids, where the grain boundary sensitization can be damaging. Generally 1750C is used as interpass temperature for this alloy without damage.
The next question from our customer was as follows:
Question (4): For above four alloys, during welded pipe manufacturing by SAW process, how do you control interpass temperature? SAW is a continuous welding process generating high heat input. If you decide to wait after every pass till temperature is lowered, you have to wait for a long time due to poor cooling rate. This will affect productivity. Is there a way out?
Our welding experts opined as:
The mass of the pipe may normally be great enough to take care of the heat input of SAW and not present a large interpass temperature problem. If this type of problem is present, it would be proper to do the first welding pass to seal the joint, subsequently fit the pipe with end caps and flow water through the pipe as the balance of the joint is welded. For gas shielded processes, one should be careful that free convection currents in welding do not lift the shield gas and result in oxidation of the weld beads. Shrinkage stresses from the higher interpass temperatures can result in some distortion of the pipe, unless the pipe is restrained during welding and cooling.
Here is an example of how we assist our viewers.One of our clients asked the following questions about welding problems in aluminum alloys. We found a suitable article, “Common Mistakes in Design of Aluminum Weldments” By Frank G. Armao, Senior Application Engineer, The Lincoln Electric Company, Cleveland, Ohio, and adopted a suitable answer. You are also invited to ask your own questions. Before we answer this, we embed an interesting welding video.
(A welding Video from you tube filmed by a high speed camera)
Q. Is aluminum weld crack-sensitive? What are important considerations in aluminum alloy welding?
A. In aluminum weld, the alloy selection, choice of filler metal and the choice of welding process depend upon the composition of base metal. Welding aluminum structures are not more difficult than steel structures; it should be approached differently than steel welding.
Most aluminum alloys are weldable, but some of the strongest aluminum alloys are difficult to weld, (welds show hot cracking) using conventional techniques. Alloys prone to hot cracking are not proper choice for structural applications. Crack-sensitivity of welds depends on the alloy composition and choice of filler metal. Weldable alloys have a composition that falls either above or below the crack-sensitive zone.
For example, alloy 6061 welds are crack-sensitive; the crack-sensitivity can be reduced to acceptable levels by using high silicon or high magnesium filler metal as it reduces cracking sensitivity. In alloy 7075, it is difficult to choose crack-resistant weld filler metal.
Aluminum has high thermal conductivity, higher solidification shrinkage than steel and high coefficient of thermal expansion, which can cause distortion given improper weld design and may affect weldability.
Q. Which are non-heat treatable series of aluminum alloys? Are they crack-sensitive?
A. Aluminum alloys of 1000, 3000, 4000, and 5000 series are non heat treatable. Alloys such as 1100, 1188, or 1350, are basically commercially pure aluminum, they are softer and weaker, have good corrosion resistance and good weldability; they are used for their high electrical conductivity.
They can be strain hardened by cold work. After cold working, these alloys are given an annealing treatment (O-temper annealing). In case of 5000 series, there is a zone of cracking maxima at approximately 2.5% Mg, so alloys such as 5052 should not be welded without suitable filler metal. Weld filler metal with a high Mg content such as 5356, can be used to reduce crack sensitivity.
Furher enquiry by our client:
Our client subsequently enquired and fortunately, we could find ansers in the same article as quoted above. For the benefit of welding fraternity, we report the questions and answers here, as this is of general interest to aluminium welders.
Q. Which are heat treatable aluminum alloys? How they are heat treated? How to avoid crack sensitivity in such alloys?
Alloys in 2000, 6000, and 7000 series are heat-treatable alloys. These alloys can be heat treated by age hardening the material at approximately 400°F (205°C) for a few hours. Since arc welding process heats the HAZ to higher temperature, so welding is like an additional heat treatment for the HAZ. Some welded components are given a solution heat treatment, while the rest may become over-aged in the HAZ.
The 2000 series are high strength Al-Cu alloys used for aerospace applications. Most alloys in this series are non-weldable except 2219 and 2519, which are weldable. High strength alloy 2024 is used in airframes, is extremely crack-sensitive and almost impossible to weld by standard techniques and is riveted.
The 6000 series are generally weldable and used in structural work, as they are reasonably strong and have good corrosion resistance. Correct filler metal must be used to avoid cracking in 6000 series and these alloys may crack if they are welded without correct filler metal additions. This series is considered crack-sensitive, but they are weldable and are welded widely.
The 7000 series are very high strength Al-Zn or Al-Zn-Mg-Cu alloys that are used in various forms in aerospace and marine fabrication. With a few exceptions, the 7000 series are generally difficult to weld, and these alloys also show poorer corrosion resistance. The weldable 7000 series are 7003 and 7005 and 7039, which are used in light bicycle frames and baseball bats, in welded condition, and have better strength in as-welded condition over the 6000 and 5000 series.
As-welded properties of the heat treatable alloys may be lower than the properties of the base alloy, in such cases, post-weld heat treatment (PWHT) can restore the mechanical properties of welds in heat treatable aluminum alloys.
Q. What are recommended welding processes in aluminum welding? How to solve aluminum welding problems?
A. GMAW permits successful welding of crack sensitive aluminum alloys, when welded by oxyfuel gas or by manual welding. In aluminum, GMAW may be one with straight polarity, that is, electrode positive. It is possible to minimize distortion as increase in temperature in components can be confined to a narrow zone. Cracking in aluminum alloy welds can be reduced if cooling rate is higher. In many cases, a weld in an aluminum alloy may be weaker than the base metal being welded, unless proper process and filler metal is chosen.
Entrapped gas in aluminum weld (cause of porosity) can be due to contaminants such as grease, hydrocarbon cleaning agents, or due to moisture in electrodes or base metal. Moist air leaks in inert gas lines also can form such porosity, as gas does not get time to escape due to high solidification rates. Proper adjustment and control of electrode speed, welding current, and machine variables can avoid such problems. Constant voltage power supply can be used, with electrode speed adjustable in the range of 50 in/minute. For further details, you are invited to ask us at blog.weldwell.com and visit our site Weldwell.com
Adopted from: “Common Mistakes in Design of Aluminum Weldments” By Frank G. Armao, Senior Application Engineer, The Lincoln Electric Company, Cleveland, Ohio.
Recent developments.
MIG welding (GMAW) of aluminium- recent developments.
Aluminum is a very reactive metal, and bare aluminium will form an oxide layer on exposed surfaces. Aluminum welding of thin components are easier with AC TIG for a beginner. Due to the chemically reactive nature, aluminium welding is different from steel welding, and it requires appropriate settings.
With MIG, good results are possible with the efforts described below. The oxide layer can be removed from the aluminum surface immediately before welding. A stainless steel wire brush can be used to remove the oxide and generate a clean surface. The edges of the aluminum should be rounded with a file, if required. It’s best to use a new wire brush to avoid contamination, and to brush in a one direction only so the oxide does not get rubbed into aluminum.
Aluminum MIG welding is different from steel welding. There is a fine line between poor penetration and blowing holes. This is due to the combination of a low melting point of aluminium and high thermal conductivity. Also, the softness of aluminium wires may require push from back and pull from leading end of wire feeder.
Using power settings similar to the equivalent steel settings, and with about double the steel wire feed, moving the gun quickly seem to be better. Using thicker aluminium wires would reduce the chance of crumpling up in the feeder and reduce the wire speed. The problem with moving the gun very quickly is that the weld may not be a neat TIG weld.
Brass can generally be used as heat sink, as it has a much higher melting point than aluminum and it is comparatively chemically inactive which makes it a good material for heat sink. Brass heat sinks are more effective when clamped immediately after cleaning the aluminum surfaces to be welded.
Did you face similar problems in aluminium MIG welding due to oxides/ pin holes/ pyrophoricity of aluminium powders etc?
We welcome you to share your problems with us.
Further information on aluminium MIG welding is to come here.
As much as you need.
Thereafter, we embed an interesting video from you tube on MIG welding of aluminium.
Our Chit-Chat:
We visited some companies including:
1. Protech Engineers Pvt. Ltd.
2. Das offshore Engineers Pvt. Ltd,
3. Steel tech Engiuneers.
and others. There was a requirement of MMA/ SMAW process.After our visit, our engineers suggested that they convert to MIG/ SMAW process.
The advantages in this conversion are:
a. Saving of consumables,
b. Faster process, faster production.
We explained the advantages and they were so impressed that they decided to convert to GMAW/MIG process in their plants. They are now happy to convert to this process. You can join our group of satisfied customers.
Do you have similar problems and wish us to help you? Avail this opportunity as we welcome you to enlist your own comments (problems) here at the end of this page.
Next advancement:
Conversion of solid wire usage to F.C.W. wires, at
1. Weldon Engineers Pvt. Ltd,
2. Titan Engineering works,
3. GMM Pfaudler.
The advantages in our suggested process are:
a. Higher deposition rate ( 20% to 30% higher) in FCW process.
b. Compensation of loss of alloying elements possible,
c. Gas cover is not essential in shielded F.C.W.
Do you have similar problems and wish us to help you? Avail this opportunity as we welcome you to enlist your own comments (problems) here at the end of this page.
Further advancement can be achieved by:
Conversion of rectifier type power supplies to thyristor type welding machines.
The advantages offered by this equipment are:
a. Poer savings due to lower power losses in the machine,
b. More compact and lighter machine,
c. Absence of heavy transformer and rectifierunit.
Do you have similar problems and wish us to help you? Avail this opportunity as we welcome you to enlist your own comments (problems) here at the end of this page, and we will answer all your queries, free of charge, in this Blog
Check all of your enquiries inside our website Weldwell.com.
-This is a corporate blog of Weldwell Speciality Pvt Ltd & Nivek Agencies. For more information, please log on to www.weldwell.com
Our blog Welding Fraternity is commited to serve all in the weldimng community concerning all welding problems. You are wrmly invited to ask questions as well as share your exerience as a community. You are alo requested to visit our mother blog, blog.weldwell.com, and our site weldwell.com regarding your requirements.
Company : Weldwell Speciality Pvt. Ltd. ; Nivek Agencies (is a group company)
Address : Weldwell Speciality Pvt. Ltd. ; Nivek Agencies (is a group company)401, Vikas Commercial Centre, Dr.C. Gidwani Road, Chembur,Mumbai 400074. INDIA. Tel.: (91) (22) 6646 2000.
Prime Objective :
To provide complete solution for special welding needs of Customers.We specialize in arc welding. We market a wide range of Special gradesof welding consumables, equipments and accessorries.
Promoter : Mr. C. C. Girotra.
Product Profile :
Complete range of Arc Welding Consumables (Ferrous and Nonferrous)
Welding equipment and accessories
Consumable Inserts / Special Flux (for one side welding applications)
Flexible enclosures / chamber for Titanium welding
Soluble dam paper and film
Backing strips, Backing Flux and Purge Monitor
Our Principals : Authorised Distributors for:
Special Metals Welding Products Co. – U.K. (Formerly Inco Alloys)
Kobe Steels Ltd. – Welding company – Japan
Matsushita Industrial Equipment Co. – Japan (Panasonic Brand )
Kemppi OY – Finland
Huntingdon Fusion Technologies Ltd. – U.K
I. A. Barnes & Co. – U.K
We Stock:
In addition to the above, we also market product from the following
– Weldlogic (UK) make special purpose TIG welding machines
– TASETO – Japan make Stainless steel FCW
Spread all over India.
Industries Served :
Petrochemical and Refinery
Chemical
Heavy Fabrication
Power sector
Structural and Mechanical Engineering
Project Contractors
Associate Company : –
Eastwest Engineering & Electronics Pvt. Ltd.
– The associate company markets equipments,
accessories and consumables required for NDT such
as Radiography, Magnetic Particle and Ultrasonic
testing.
Check all of your enquiries inside our website Weldwell.com.
We provide complete solution for special welding needs of our Customers.We specialize in arc welding. We market a wide range of Special grades of welding consumables, equipments and accessorries.
Promoter : Mr. C. C. Girotra.
Product Profile :
Complete range of Arc Welding Consumables (Ferrous and Nonferrous)
Welding equipment and accessories
Consumable Inserts / Special Flux (for one side welding applications)
Flexible enclosures / chamber for Titanium welding
Soluble dam paper and film
Backing strips, Backing Flux and Purge Monitor
Our Principals : Authorised Distributors for:
Special Metals Welding Products Co. – U.K. (Formerly Inco Alloys)
Kobe Steels Ltd. – Welding company – Japan
Matsushita Industrial Equipment Co. – Japan (Panasonic Brand )
Kemppi OY – Finland
Huntingdon Fusion Technologies Ltd. – U.K
I. A. Barnes & Co. – U.K
We Stock:
In addition to the above, we also market product from the following
– Weldlogic (UK) make special purpose TIG welding machines
– TASETO – Japan make Stainless steel FCW
Spread all over India.
-This is a corporate blog of Weldwell Speciality Pvt Ltd & Nivek Agencies. For more information, please log on to www.weldwell.com
Posted by weldwell 
