Carbon equivalent F65 1

[bhoro]

My client asks for a carbon equivalent CE(IIW) of 0.40 for F65 forging flanges with the thickness of the weld neck of 25mm.
My supplier can not provide that CE and instead offers a CE of 0.44 (carbon content of 0.16%).

As far as I know, higher carbon equivalent means that the steel is less weldable, but in this case what will be the actual consequences if I accept a CE of 0.44 instead of 0.40?
What I can think is that I may need to use preheat for welding, is it correct?
How can I determine the preheat temperature?
Is there any other consequences beside possible need of preheat?

Bhoro

 

[SJones]

The first consequence will be that you receive a non-conformance from your client! Admittedly, 0.40 is a tough call for F65 at that thickness, but 0.44 is pushing things a bit far. There is more than one supplier of F65, try shopping around to get the value down closer to 0.40. The restriction is principally aimed at weldability but may also be a means of controlling material properties for resistance to certain degradation mechanisms.

You can get a guide for preheat temperature in ISO TR 17844

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[bhoro]

Steve,

Thanks for the response.

Forget to mentioned the forging thickest section is 200 mm. According to a number of suppliers we talked to that is the reason a CE 0.44 is needed.

Regarding the other aim of the CE restriction as you mentioned
"...may also be a means of controlling material properties for resistance to certain degradation mechanisms...",
I guess one of them is to limit the hardness right?
Any other degradation mechanisms influenced by CE of 0.44?

 

[SJones]

Indeed. 200 mm puts a different light on things and 0.44 will be good going.

Degradation mechanisms that could be affected by chemical composition:

- H2S cracking
- fracture
- hydrogen embrittlement

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[metengr]

To answer the second part of your post, the difference in CE between 0.40 and 0.44 is not going to significantly alter the preheat requirements for this material. Go back to your client and explain the reason for the increased CE. If they are reasonable, they should accept it.

 

[grampi1]

So you all think toughness and strength will be just fine at 0.44 but not 0.40 and 8" thick Q&T F65? Might want to check to make sure.

 

[PAN]

grampi1,

This depends on heat treatment procedure. I used to find problem with low impact value on this material...

 

[Guest102023]

CE = 0.44 is quite managable for welding. Steel makers probably need to bump the carbon to ensure making the property minima at that thickness.

A bigger but less obvious concern is the use of doping with V and/or Nb to achieve properties in thick sections. Caused me much grief one time with stress relief cracking. One of their diry secrets methought.