WELDABILITY

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WELDABILITY

• The weldability of a material refers to its
  ability to be welded.
• Many metals and thermoplastics can be welded,
  but some are easier to weld than others.
• It greatly influences weld quality and is an
  important factor in choosing which welding
  process to use
• Weldability is simply a measure of how easy it is
  to make a weld in a particular material without
  cracks. If it is easy to avoid cracking, the
  material is deemed 'weldable'.
• For a weld to be truly successful, however, it is
  also necessary for it to have adequate mechanical
  properties, and to be able to withstand
  degradation in service (e.g. corrosion damage).

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• Thus, weldability is a measure of how easy it is
  to
• Obtain crack free welds
• Achieve adequate mechanical properties
• Produce welds resistant to service degradation.
• Weldability is not a fixed parameter for a given
  material, but will depend on joint details,
  service requirements, and welding processes and
  facilities available.
• This variability in weldability is illustrated in
  the following examples

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Example 1 Which of these two C-Mn steels is most
weldable?
  Steel 1 Steel 2
C 0.16 0.19
S 0.027 lt0.002
P 0.011 0.021
Si 0.20 0.28
Mn 0.61 1.38
Ni 0.03 0.01
Cr 0.02 0.02
Mo lt0.01 lt0.005
V lt0.01 lt0.01
Cu 0.03 0.005
Nb lt0.005 0.024
Ti lt0.01 0.002
Al lt0.001 0.047
CE IIW 0.27 0.43
Pcm 0.20 0.27
CEN 0.27 0.43

• The answer clearly depends on which type of
  cracking is of most concern
• Low restraint fillet onto thick steel - Hydrogen
  crack, steel 1 more weldable
• Restrained high dilution MIG nozzle weld -
  solidification crack, steel 2 more weldable
• Full penetration highly restrained T butt -
  lamellar tearing, steel 2 more weldable.

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Example 2Which of these materials is most
weldable? (welding a fairly thin walled (3mm)
pipe)Commercially pure titanium 316 L
austenitic stainless steel 22 Cr duplex
stainless steel 6 Mo high alloy austenitic
stainless steel

• The answer will depend on an individual's
  experience, and available facilities.
• The titanium expert knows that it is one of the
  easiest materials to weld - but he is very
  familiar with very good back purges, and the use
  of a trailing shield.
• The expert in austenitic stainless steel would
  see this level of control to be very difficult.
  He knows to watch out for solidification
  cracking, and is careful to check the penetration
  characteristics of each cast, and does not
  consider that these pose a significant risk.
• An expert in duplex stainless steels will tell
  you that it is much easier to weld than
  austenitic stainless steel, because there is no
  real risk of solidification cracking, and less of
  a variable penetration problem. But now, you
  generally need a filler.
• High alloy austenitic steel is similar to duplex,
  expect that with a Ni based filler there is a
  risk of microfissuring.

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• Example 3
• Consider Example 2, but now add that the weld
  will be operating in an acid, chloride containing
  environment at about 30C. Had the concern been
  purely about freedom from cracking, then duplex
  and titanium would have been on an equal footing,
  with the high alloy austenitic being the least
  weldable because of the risk of solidification
  cracking. Now, however, the duplex stainless
  steel becomes more of a problem, as it becomes
  necessary to work within quite a narrow heat
  input window. It can be difficult to pass
  procedure qualification tests involving corrosion
  tests with duplex stainless steels.
• Example 4
• Consider examples 2 and 3, but now add a
  toughness requirement. Now titanium is not so
  weldable, as near perfect shielding is necessary
  to avoid toughness degradation.

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Example 5Is AISI 4130 weldable?
The composition range for AISI 4130 is
C 0.27-0.34
S lt0.040
P lt0.035
Si 0.15-0.35
Mn 0.35-0.60
Cr 0.80-1.15
Mo 0.15-0.25

• It is not possible to answer this question
  without knowing the intended service. The answer
  would be different for a gear component, to
  operate in a warm oil bath, and a piece of
  wellhead equipment to carry sour gas.

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Weldability of materials- Steels

• In arc welding, as the weld metal needs
  mechanical properties to match the parent metal,
  the welder must avoid forming defects in the
  weld.
• Imperfections are principally caused by
• poor welder technique
• insufficient measures to accommodate the material
  or welding process
• high stress in the component.
• Techniques to avoid imperfections such as lack of
  fusion and slag inclusions, which result from
  poor welder techniques, are relatively well
  known. However, the welder should be aware that
  the material itself may be susceptible to
  formation of imperfections caused by the welding
  process.
• In the materials section of the Job Knowledge for
  Welders, guidelines are given on material
  weldability and precautions to be taken to avoid
  defects.

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• Material types
• In terms of weldability, commonly used materials
  can be divided into the following types
• Steels
• Stainless steels
• Aluminium and its alloys
• Nickel and its alloys
• Copper and its alloys
• Titanium and its alloys
• Cast iron
• Fusion welding processes can be used to weld most
  alloys of these materials, in a wide range of
  thickness.
• When imperfections are formed, they will be
  located in either the weld metal or the parent
  material immediately adjacent to the weld, called
  the heat affected zone (HAZ).
• As chemical composition of the weld metal
  determines the risk of imperfections, the choice
  of filler metal may be crucial not only in
  achieving adequate mechanical properties and
  corrosion resistance but also in producing a
  sound weld.
• HAZ imperfections are caused by the adverse
  effect of the heat generated during welding and
  can only be avoided by strict adherence to the
  welding procedure.

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• Imperfections in welds
• Commonly used steels are considered to be readily
  welded and can be at risk from the imperfections
• porosity
• solidification cracking
• hydrogen cracking
• reheat cracking.
• lamellar tearing
• Using modern steels and consumables, these types
  of defects are less likely to arise.

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• Welding Metallurgy and Weldability of Stainless
  Steels
• by John C. Lippold (Author), Damian J. Kotecki
  (Author)

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• New developments in advanced welding
• Edited by N Ahmed, CSIRO, Australia
•  - discusses the changes in advanced welding
  techniques - looks at new technologies - explore
  s mechanical and structural engineering examples
• summarises some of the most important of these
  and their applications in mechanical and
  structural engineering. begins by reviewing
  advances in gas metal arc welding, tubular cored
  wired welding and gas tungsten arc welding.
• A number of chapters discuss developments in
  laser welding, including laser beam welding and
  NdYAG laser welding.
• Other new techniques such as electron beam
  welding, explosion welding and ultrasonic welding
  are also analysed.
• The book concludes with a review of current
  research into health and safety issues. This is
  a standard guide for the welding community

US 275.00
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• Contents
• Gas metal arc welding
• Tubular cored wire welding
• Gas tungsten arc welding
• Laser beam welding
• Nd YAG laser welding
• New developments in laser welding
• Electron beam welding
• Developments in explosion welding technology
• Ultrasonic metal welding
• Occupational health and safety