4140 Pre and Post Heat Requirements

By TimGary (****)

Date 11-19-2010 19:28

Can anyone please share with me pre and post heat requirements for welding 4140.

A typical application would be:
Welding 4140 x 1" thick lifting eye to:
1 1/2" thick A36 plate.

Normally, I would pre heat this weldment to 250 degrees F min
Complete weld with out allowing interpass temp to get below 250 F
Post heat the lifting eye and about an 1' radius of base metal to about 300 degree F
Insulate for slow cool.

BUT... I want to be sure to get it right.
I'm in the process of writing a preliminary WPS for procedure qualification, and hope to skip the trial and error part.

Thanks for any advice,
Tim

By jarcher (**)

Date 11-22-2010 06:29

350 - 400 F preheat with an hour of 1150 F Stress Relief for each 1" of thickness. I must say this is a curious configuration though; this joint can never be any stronger than a 1" thickness (plus the area of any fillet around the padeye) of A36. You might want to put the question to the design engineer as to why the padeye needs to be 4140, a 1 1/2" padeye with CJP would develop the full strength of the base metal and not require post weld stress relief.

By 803056

Date 11-22-2010 14:22

4140 is not the material of choice if it is welded to ASTM A36. The assembly is only as strong as the weakest link which is of course the ASTM A36.

4140 is a chrome moly alloy steel with 0.4% carbon. The carbon equivalency is rather high. The preheat temperature is dictated by the base metal that requires the higher preheat, 4140 in this case, and I believe it should be higher than 300 degrees F. I've welded similar thicknesses where the preheat was between 550 and 650 degrees F with an immediate (no cool down) stress relief at 1150 degrees F for one hour.

You did not mention the welding process to be used. Needless to say it must be a low hydrogen process or if you use SMAW, you need to use low hydrogen electrodes that have been baked at a temperature of 600 to 700 degrees F for one hour before use to ensure low moisture content.

Good luck, but at least ask the designer why he is specifying the 4140 for the lifting eye.

Jarcher makes a good point regarding the design and selection of materials.

Best regards - Al

By TimGary (****)

Date 11-29-2010 14:36

Thanks for the replies,

I've succesfully argued against this weld joint design with management.
It was a result of a misunderstanding based on one guy's "stronger is better" philosophy.

Tim