Weldability of Steel

[xr4titis]

Hello Forum,

Anyone aware of a scale comparing weldability of steel to carbon content? I am specifically attempting to compare ASTM A27 70-40 (%C = .25) to ASTM A148 90-60 (%C = TBD)

Gracias

 

[dbooker630]

You can use the International Institute of Welding formula for Carbon Equivalency.

C.E. = C% + Mn%/6 + (Cr%+Mo%+V%)/5 + (Ni%+Cu%)/15

You also must take into account the Mn and Cr content, as Mn should be limited if C is above .25%, but Mn can be increased slightly if C is below .25%. At our site we also adjust Cr but that is not in ASTM A27 spec. A148 is more focused on mechanical properties with chemistries set by the caster and/or purchaser.

Section size can also be a factor. With larger sizes you may want to restrict CE, especially if the chemistry is off grade.

Jominy hardenability can also be compared at the J4, J8, and J12 positions using SAE J406.

 

[xr4titis]

Thank you,

I've seen the carbon equivalent formula (which puts A27 at %C = .583) and I know this material is very good for welding, however that is where my knowledge ends as far as relating %C to weldability.

 

[dbooker630]

What is your stock thickness? A CE of .58 is on the high side, especially if the stock is > .500".

 

[xr4titis]

I guess that's why you shouldn't trust wikipedia. The formula I was using included Si/6. Without that, CE = .45 (assuming Max Mn). Casting wall thickness in the area of weld is around .75" but these things have been used unchanged in the industry for decades.

 

[metengr]

I would like to add that CE and weldability are not necessarily synomonous - higher CE means poor weldability. The CE is used to establish the need for preheat requirements and, need for PWHT. This does mot mean that weldability is poor, only necessary precautions are required.

 

[HgTX]

There are a lot of CE formulae out there. Finding a different one doesn't mean the one you were using is wrong. Check the codes & standards associated with your industry.

Hg


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[xr4titis]

For the archives, the link below leads to a MIL spec that summarizes all the different CE formulae and their criteria for "good" (no preheat required) weldability.

http://www.metalwebnews.org/ftp/welding-design-TI-809-26.pdf

Thanks for all the replies!

 

[jehan17718]

metengr:

As always your erudite posts on this site help clear many basics. I just had a few queries/ concepts to be cleared.

1. As a thumb of rule, does a low %C in steel equate to better weldability than a steel with a higher %C content?

2. As a thumb of rule, does a higher CE in steel equate to lower probability of the steel cracking post welding?

Thks in advance.

-jehan

 

[metengr]

jehan17718;

1. As a thumb of rule, does a low %C in steel equate to better weldability than a steel with a higher %C content?

Given that all other variables in this comparison are equal between steels, yes. Carbon has the greatest influence on strength level in iron-base alloys - the higher the carbon content the higher the strength. With that, higher carbon means that more caution is required for welding to achieve similar results (sufficient ductility and avoidance of delayed cracking). CE should be used to determine the application of preheat and post weld heat treatment requirements. This is really the value of CE use for welding.

2. As a thumb of rule, does a higher CE in steel equate to lower probability of the steel cracking post welding?

I believe what you have meant to state was lower CE, not higher? If lower CE, the answer is yes. The reason is that if a harmful (fresh martensite) microstructure forms as a result of thermal gradients during welding, the hardness of this harmful microstructure will be lower in magnitude in comparison to the harmful microstructure formed in higher carbon steels, and will not be as prone to delayed cracking.

 

[salmon2]

hardenability/CE is directly and inversely related to weldability. Higher CE means poor weldability as other person pointed out it does not mean high CE is not weldable, but instead more caution/processes needed - people can call this poor weldability.

Just one non-relevant comment, I do not think Cr and Mo should share same coefficient because I think most people know that Mo is considered much more powerful hardenability agent than Cr, and therefore more expensive.

 

[jehan17718]

metengr,

thanks for clearing my concept and yes I did mean "lower CE" and not "higher CE".

-jehan

 

[dik]

xr4titis:

The current IIW and AWS formula for CE includes the Si%/6, the orignal formula presented by Deardon and O'Neill did not include it.

Dik