HIGH STRENGTH STEEL - YS 490 - 690 MPa

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HIGH STRENGTH STEEL - YS 490 - 690 MPa
Appendix 6 (p. 1/16)

• Consumables optimisation for the welding of high
  strength steels

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Main menu
Appendix 6 (p. 2/16)

• Over-matching approach
• Welding process
• Chemical composition optimization of S690 type
  consumables
• Impact of the lowering of diffusible hydrogen in
  high strength steels welding consumables

3
Overmatching
Appendix 6 (p. 3/16)

• Over-matching approach in the weld metal
  selection is a general practice.
• weld metal is required with strength higher than
  that of the parent metal to offset the potential
  problems such as a reduced toughness and presence
  of defects in the weld metal

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Overmatching
Appendix 6 (p. 4/16)

• Actual or theoretical overmatching ?
  ? Codes require a
  MIN YS value for the base material
  
  ? The actual YS of the base material should be
  very close to the min. or much more than the min.
  ? The weld metal YS, depending on the actual base
  material YS, could satisfy the over or the
  mis-matching requirement
  ? As practical approach is usually
  required min WM ys
  min BM ys 10 MAX BM ys

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Overmatching
Appendix 6 (p. 5/16)

• If the steel maker can accept this narrow range
  of YS (YS min 10) the YS WM and the YS BM
  could be of the same order of magnitude
• But if we want an actual OM and the steel maker
  does not accept YS min10 we have to consider an
  higher WM YS min (15,20,3040)
• In this case for YS 690 the min. WM ys should be
  793 - 828 - 897-966 MPa
• The highest YS (897 - 966MPa) induces impact
  properties reduction and it makes very difficult
  or impossible to meet all the requirements

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Overmatching
Appendix 6 (p. 6/16)

• Welding consumables are an industrial product
  that means that an acceptable range for the
  chemical elements is required
• The Standards (EN - AWS-) require an acceptable
  range of mechanical properties
• To compare the Codes requirements we can consider
  the following table

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Overmatching
Appendix 6 (p. 7/16)

• BM YS 500 50010 550 MPa - min WM
• BM YS 690 69010 759 MPa - min WM
• EN class YS TS E AWS class YS TS
  E
• 55 550 610 18 90
  540 620 17
• 62 620 690 18 100
  600 690 16
• 69 690 770 17(0) 110 670
  760 15
• (7.5) 120
  740 830 14
• 79 790 880 16(15)
  
• 89 890 980 15(30)

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Overmatching
Appendix 6 (p. 8/16)

• Impact and tensile properties requirement are the
  main concern for high productivity welding
  process (FCAW-SAW) because
  ? Heat Input
  ? chemical analysis
  of the weld metal ? dilution
  effect with the base material
  ?PWHT ? purity of the weld metal deposit affect
  the mechanical properties of the weld metal

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General trend Yield strength versus toughness
Appendix 6 (p. 9/16)
Looking for a minimum requirement on all weld
metal deposit induces an over matching of
properties on real application and a loss of
toughness
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Overmatching
Appendix 6 (p. 10/16)

• WELDING PROCESS
• welding parameters (WP)
  Amp-volt-speed ? Heat Input
  (HI)
• process with narrow range of WP
  ? low HI / low productivity
  
  shielding metal arc welding (SMAW)
  tungsten inert gas (TIG)
• process with wide range of WP
  ? high HI / high productivity
  Flux cored
  arc welding (FCAW) Sub
  merged arc welding (SAW)
  

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Overmatching
Appendix 6 (p. 11/16)

• FCAW - SAW
  ? considering a certain
  chemical analysis
• the welding parameters have to be precisely
  defined to reach the required YS and the welding
  parameter range becomes narrow
• YS and TS increasing ?Impact decreasing

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Overmatching
Appendix 6 (p. 12/16)

• chemical analysis of the weld metal
  ? purity of the weld metal deposit
  P,As,Sn,Sb are considered in Y (Brsucato
  Factor) Y(10Sb5Sn2PAs)/100 (ppm)
  ? O2 affects the impact
  properties before PWHT (basic flux-low oxygen)

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Overmatching
Appendix 6 (p. 13/16)

• chemical analysis of the weld metal
  
  ? dilution with the base material
  if we consider
  a certain chemical analysis defined to obtain
  certain mechanical properties in all weld metal
  (without dilution effect) this mechanical
  behaviour can be modified by the dilution effect
  and the welding material could be not allow to
  meet the requirement

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Overmatching
Appendix 6 (p. 14/16)

• PWHT effect on weld metal properties
  
  ? PWHT reduces the YS and TS but it could
  decrease the impact properties
  ? N2-V-Nb affect the impact properties
  after PWHT (precipitation on V-Nb nitrides) N2
  should be less than 0,006 in weld metal but the
  total amount of N2 in the weld metal depends not
  only of the welding consumable but also of the
  skinless of the welder mainly for manual process

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Hydrogen
Appendix 6 (p. 15/16)

• Hydrogen in the weld metal
  increasing the tensile properties the wed
  metal becomes more and more sensitive to the
  cold cracking
  ?
  Diffusible Hydrogen in the weld metal
  (as lower as possible)
  (Standards require max 5ml/100gr)
  
  ? preheat and interpass temperature during
  welding (Standards require 120 - 180C) ?Crack
  propagation depending on stress state - strength
  of material - plastic strain capacity ?Heat Input
  defined to reduce the stress state

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HIGH STRENGTH STEEL - 490 - 690 MPa
Appendix 6 (p. 16/16)

• ASPECTS TO DEFINE
• WHAT IS THE min WM YS NEEDED TO HAVE AN ACTUAL
  OVERMATCHING ?
• WHAT IS THE IMPACT PROPERTY REQUIRED TO THE WM ?
• IS THE PWHT NECESSARY?
• WHATS THE IDEAL CHEMICAL ANALYSIS Y (5-10)? -
  V-Nb??INDUSTRIAL PRODUCT
• WHAT IS THE MAX. DIFFUSIBLE HYDROGEN ACCEPTABLE
  FOR A PRACTICAL WELDED JOINT (5-3-2 ml/100gr)?