Effect of Niobium on welding and CTOD
Effect of Niobium on welding and CTOD
(OP)
Hi folks!
I have a question regarding the effect of Niobium (or Columbium) on welding. We have a requirement for forging a modified SA182 F22 grade (with 2.0% Cr max) and achieve an Yield stress of 80 ksi (min). The application is a sour, under water service and welding is involved. With this background, the move to enhance Nb/Cb percentage to improve chances of achieving mechanicals has been viewed as detrimental (with a welding perspective).
Our experience with Q & T SA182 F22 is consistent with an YS of 77ksi at best and with a Cr content around 2.25%. What happens if we increased Nb% to 0.06 or 0.08% to help achieve the required mechanical strength, with a welding perspective? (By the way does anybody know; what is the contribution of Nb% to the Jominy/Grossman hardenability equation?)
The modified spec requires V% to be under 0.01%, CE around 0.45%, J Factor value = 150 max. To top it all the material has to meet Crack Tip Open Displacement (CTOD) requirement as well. We have no experience with CTOD. We are a bit overwhelmed.
Any suggestions, guidance will be greatly appreciated.
Thanks in advance,
Cheers
I have a question regarding the effect of Niobium (or Columbium) on welding. We have a requirement for forging a modified SA182 F22 grade (with 2.0% Cr max) and achieve an Yield stress of 80 ksi (min). The application is a sour, under water service and welding is involved. With this background, the move to enhance Nb/Cb percentage to improve chances of achieving mechanicals has been viewed as detrimental (with a welding perspective).
Our experience with Q & T SA182 F22 is consistent with an YS of 77ksi at best and with a Cr content around 2.25%. What happens if we increased Nb% to 0.06 or 0.08% to help achieve the required mechanical strength, with a welding perspective? (By the way does anybody know; what is the contribution of Nb% to the Jominy/Grossman hardenability equation?)
The modified spec requires V% to be under 0.01%, CE around 0.45%, J Factor value = 150 max. To top it all the material has to meet Crack Tip Open Displacement (CTOD) requirement as well. We have no experience with CTOD. We are a bit overwhelmed.
Any suggestions, guidance will be greatly appreciated.
Thanks in advance,
Cheers





RE: Effect of Niobium on welding and CTOD
RE: Effect of Niobium on welding and CTOD
I provided the J-Factor value to give a complete picture of the specification we are working to accompish. My idea of enhancing Nb% was to achieve 80 ksi YS and improve chances on passing CTOD. Customer and their welding sub cotactor feel that it will be detrimental to welding. I have no clue how they arrived at this inference.
Thanks again,
Regards
RE: Effect of Niobium on welding and CTOD
RE: Effect of Niobium on welding and CTOD
1) the niobium could push up the HAZ hardness causing you much pain in meeting ISO 15156 requirements
2) Niobium has a tendency to elevate the CTOD transition temperature and there could be a possibility of struggling with the CTOD requirements (you don't quote a temperature or acceptance criterion)
Dolby R E: 'The effect of vanadium and niobium on weld metal properties', Proc of Steel for Linepipe and Pipeline Fittings, The Metals Society, London, October 1981.
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Effect of Niobium on welding and CTOD
The post was really helpful. The acceptance criterion for CTOD is 0.049" (1.25mm) at -10deg. C (14deg F). Hope it does not pose a problem passing the test with Nb at 0.08% max.
Regards
RE: Effect of Niobium on welding and CTOD
In the reference you provided, I agree that vanadium will have a significant effect on weldability because of the tendency to form nitrides/carbides that resist tempering AND can result in increased reheat cracking susceptibility in comparison to Nb/Cb additions. For moderate to low heat inputs, and with vanadium held at or below 0.01% as per the modified specification posted above, the Cb/Nb additions should still play a significant role in grain refinement for increased toughness. Granted, higher heat inputs from SAW or electroslag welding can result in dissolution of carbides/nitrides forming a coarse-grained region in the weld fusion zone that is low toughness. Do you have specific reference regarding deliberate columbium additions for weld metal or are you referring to base metal micro-alloy additions, as well?
Source; Welding Metallurgy, by Kou
RE: Effect of Niobium on welding and CTOD
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Effect of Niobium on welding and CTOD
Sincerely thank Sjones, Metengr and Greenleader for sharing their thoughts on this bearbug issue.
Regards
RE: Effect of Niobium on welding and CTOD
RE: Effect of Niobium on welding and CTOD
Can somebody tell me what is the contribution of Niobium/Columbium to the Jominy hardenability equation. For instance the Carbon contribution is;
C=2*(SQRT(0.024*C%)).
I haven't found the equation for Nb/Cb. Any help??
Thanks in advance,
Cheers
RE: Effect of Niobium on welding and CTOD