304 SS stud weld on P91 pipe

[Itzik]

Hi,

I tried to weld 0.25'' 304SS on P91 with no PWHT. the welds look good, passed the hammer test and very good tensile strength (the stud brake not the weld) but when i cross sectioned the samples i found cracks in the weld. probably cold cracks. can you please advice how to eliminate these cracks with no PWHT? may be to try to weld feritic SS stud ?

please advice

 

[hotrodder]

Out of my league but i thought pre and post heat were mandatory with P91 to prevent hydrogen cracking and untempered martensite

 

[TechnicAl]

The only time Ive ever known this being done they used Inconel 625 as the filler, a preheat of around 250 oC and a PWHT (I dont have a record of what was used but it should be the same or 50 oC less than the original heat treatment as shown on the mill sheet)

Are you developing a procedure?

 

[Itzik]

The only time Ive ever known this being done they used Inconel 625 as the filler, a preheat of around 250 oC and a PWHT (I dont have a record of what was used but it should be the same or 50 oC less than the original heat treatment as shown on the mill sheet)

Are you developing a procedure?

yes, we weld the stud at 1000F

 

[Itzik]

its true but we weld it at 1000F. the untempered martensit is no problem now. the problems are the cracks

 

[TechnicAl]

what filler did you use
what process

 

[Itzik]

i use stud weld no filler

 

[TechnicAl]

Oh OK

I dont know anything about stud welding so Im not sure what happens to the components.

Having a guess it could be that the mixture of the 304 and the P91 has resulted in a martensitic weld but I really dont know.

You could maybe try welding 309L layer onto the P91 (preheating it) and then stud weld the 304 stud to the 309L layer. If you do, weld the 309L and check it for cracks before you do the stud weld.

 

[Itzik]

you are right, we do get untempered martensite in the weld, very brittle about 430HV. I also thought to stud weld 309L (its not critical for us 304).

 

[TechnicAl]

It might help but as I said I dont know much about stud welding ie dilution rates etc. Its not working as it is so its probably worth a try.