Weld Filler Metal for 422 SS 2

[metengr]

mcguire;
One of the areas that I deal with are weld repairs to large high pressure, intermediate pressure and low pressure steam turbines - which can include rotating blades or stationary blades commonly called partitions or 1st stage flow nozzles in the high pressure steam turbine.

In some cases we have had to perform weld repairs to blade tips or tenons and stationary partitions fabricated out of AIS type 422 stainless steel. This material was used by Westinghouse and GE on steam turbines that were designed for service temperatures above 1000 deg F. Typically, the work horse material is AISI Type 403 or 410 SS. However, above 950 deg F, the strength of 403 or 410 SS drops considerably, thus the need for AISI Type 422 (.23% C, 12.5 Cr, 0.5 Mn, 1.0 Mo, 0.8 Ni, 0.02 P, 0.018 S, 0.38 Si, 0.23 V and 1.0 W).

Unfortunately, the only filler metal I have seen used for weld restoration of this material is a nickel-base, like Inconel 82 or 92.

However, I stumbled on a filler metal that was developed by Bohler Thyssen called Thermanit MTS 4Si. The filler metal composition (0.2% C, 0.3 Si, 0.6 Mn, 11 Cr, 1.0 Mo, 0.4 Ni, 0.5 W and 0.3 V) is the closest I have seen to matching 422. The mechanicals look close. However, the only statement mentioned by Bohler Thyssen for high temperature strength and creep properties for this filler metal is they match a European grade of 422. I was at a Materials Conference in October of last year and ran across one of the Bohler Thyssen engineers and all they could tell me was that this filler metal has been around and extensively used in Europe.

Do you have any additional information on this filler metal in terms of elevated temperature properties? I would like to use this filler metal for future weld restoration of our AISI 422 steam turbine bucket tips and tenons versus using Inconel.

 

[mcguire]

If you can find a copy of the Metals Handbook, Desk Edition, page 16-4, shows the YS, TS, and creep rupture for various such martensitics above 1000F. The European alloy should behave like 422, which is a major improvement over 410. Anything with stable carbide, such as WC, NbC, or VC will produce these effects, and the more the better.

 

[mcguire]

Metengr
In case you don't have access to that book the YS looks like nearly double for 422 vs. 410 and the same for stress rupture. Tensile strength is about 80% higher.

 

[unclesyd]

Here is a thread on welding 422 SS. Checkout the post by stanweld.

thread725-31486

Have you looked at the properties of Hast C276 (ENiCrMo-4).
We welded a lot of material for high temperature service with this rod.

 

[metengr]

unclesyd;
The problem that I have is that after weld restoration of the 422 bucket tenons, the covers have to be peened back on. This is where I have concerns using the Ni base filler. The work hardening characteristics are completely different between Ni base and 422, and as such we had to struggle with qualification of new peening procedures. We have had Ni base welded tenons in service, with no reported problems (5 years).

On the nozzle partition trailing edges we can experience local steam erosion. In this case, I would rather match the 422 base material, in lieu of using Ni base filler. In-service inspection are much easier with met MT, in lieu of using Liquid Penetrant. Also, we have developed cracking along the weld fusion zone between the Ni-base filler and 422 base metal from mechanical fatigue.

 

[stanweld]

Bohler Thyssen MTS 4 Si was developed for welding X20 CrMoWV 12 1, which has been used extensively in Europe for supercritical boiler tubing. Requires high (450F) preheat and PWHT at near 1400F.

 

[EdStainless]

That was my question Stan, PWHT.
You basically have to re-heattreat the blades.

I would guess that the size and distribution of the carbides would be critical in getting the best properties. Doing this off of a repair could be tough.

How about a Ni filler with less Cr and Mo? It still will be difficult to test, but should work harden less.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

I have run across references to cracking of 422 SS when laser welded with 625 wire. I'm still trying to relocate the paper.
It should show up on Metadex. I am no long able to access it.

Interesting welding consumable site. As they say they make special heats they may have an insight on welding 422 SS.

http://www.usweldingcorp.com/main.htm

 

[metengr]

The PWHT would be performed locally using either a salt bath or resistance heaters to control temperature. The PWHT will be slightly lower than 1400 deg F because I do not want to over temper the bucket BM properties. Essentially, only the bucket tip would be PWHT'd to reduce stress and hardness of the BM HAZ, and weld deposit. PWHT is also performed after weld restoration of tenons using Ni base filler - I see no reason why this would not work with the Thyssen MTS 4Si.