Filler Metal to weld ASTM A743 CA6N 1

[mahadhatu]

Gurus ,

My attempts to locate a filler metal to weld ASTM A743 CA6N have failed. If any one you have an idea about this please reply. I think the strength levels this grade at room temperature are excessively high for the 410NiMo electrodes. Please post your comments if you have tried using the 410NiMo for CA6N.

Thank you in advance.

Mahadhatu

 

[metengr]

Yes, we have used ER410NiMo filler metal for weld repairs on large steam turbine components on a regular basis. No problem with weldability, performance or sourcing of the wire. The 410NiMo exhibits good ductility in the as-welded condition. The only caution with this filler metal is that you need to cool the weld area to ambient temperature prior to any post weld heat treatment.

 

[mahadhatu]

Thank you Metengr. That input has surely put me way ahead. My concern is that the mechanical properties demanded by CA6N are very high compared to CA6NM and I am skeptical as to the 410NiMo being able to achieve it unless there is a PWHT capable to doing that.

 

[metengr]

mahadhatu;
The CA 6N is a modified version of CA 6NM. The CA 6N contains about 11% Cr - 7% Ni and the stated mechanicals are 140 Ksi min UTS and 135 Ksi min YS with 15% min elongation. This is an age hardening martensitic stainless steel with aging performed at 800 deg F.

Any welding on this material will adversely affect the strength of the base because it is age hardened. So, welding needs to be performed with minimal preheat and strict controls on interpass temperature with NO PWHT. The 410NiMo has a about a 110 Ksi min UTS and 91 Ksi min YS with 17% elongation. However, these properties are stated for an 1150 deg F PWHT after welding, which you will not be performing for CA-6N.


My suggestion is to run a coupon with the ER410NiMo filler metal on the CA-6N base material and perform ASME Section IX bend and tensile testing. I see no problems with bend testing. The tensile results will speak for themselves.

 

[mahadhatu]

Here is what I found out till now,

I used 410NiMo filler metal to weld the coupons. The coupons were in the aged condition. Preheat was about 250F and interpass was 350F. I waited about 5 mins between passes to bring the temperature in the desired range. Welding was done at high speed with small beads to minimise heat input.

The weld bent ok but the base metal tore about 1/2" away from the fusion line. To verify if the base metal would bend, I bent the base metal by itself and it bent ok. So there is this region about 1/2" away from the fusion line and extends to may be 1" away from the fusion line which is getting adversely affected by welding.

I tried doing the 800F aging cycle hoping to strengthen this region but did not work either.
Any comments as to how I can eliminate it?

Thanks, Mahadhatu

 

[metengr]

mahadhatu;
The preheat is too high for the base material. You need to have minimum preheat for CA-6N. In other words weld at ambient temperature and keep the interpass at or below 300 deg F. My guess is that the heat input from welding and the preheat resulted in a local band of reduced ductility, as you described.

The 800 deg F aging treatment needs to be performed after a re-solution anneal for it to be effective.

 

[mahadhatu]

Metengr,

You are right about the 800F aging treatment not being a suitable PWHT for this material. I also tried to do a complete heat treatment, the 1900F, 1500F and 800F on the weld coupon and still ended up with the same problem where the bend specimen broke about 1/2" away from the weld fusion line.

The weld metal passes the bend test and the base metal passes the bend test but this 1/4" to 3/4" zone away from the fusion line seems to get affected drastically and the change appears to be difficult to reverse.

This has been a frustrating few weeks. I have one more chance to weld on a set of plates. Do you think I should use SMAW or GMAW process to weld this material?

I will post my next result soon.

Mahadhatu

 

[metengr]

mahadhatu;
I would use SMAW versus GMAW. Remember, do not preheat (70 deg F) and keep the interpass temperature at or below 300 deg F. What is your weld prep and thickness of the plate material?

 

[mahadhatu]

My weld plate thickness is 1/2 inch. I will post my results for your information. Thanks for your input.

Mahadhatu

 

[GRoberts]

Could there be something in the bend test itself that may be contributing? What bend thickness and radius are you using? What type of bending fixture. CA6N only requires 15% elongation in the supplemental information of A743. Are you accounting for that in the bend radius or specimen thickness? Due to the different strength of the 410NiMo and CA6N, are you using a wrap-around bend fixture instead of the plunger type in order to get a non-kinking bend?