S41008 (410s) P7 PWHT Conditions?

[moseley]

I have a project currently underway which involves .500" SA-240 Type 410s (P7 Gr. 1) and the client is imposing a MDMT/CET of -20°F. We have completed the production impact plates as required by ASME VIII-1 (UHA-51(h)) and according to UHA-32 the PWHT of this material is required to be performed at 1400°F minimum. The WPS used utilized E410 filler metal. My question is that the PWHT is required be performed at 1400°F with a specified cooling rate from soak to 1200°F at 100°F/hour maximum then below 1200°F, "after which the cooling rate shall be sufficiently rapid to prevent embrittlement". With this being said, I performed the PWHT as follows: From 600°F to 1400°F maximum heating rate of 400°F/ hour, held at 1400°F for 1.0 hour, from 1400°F to 1200°F maximum cooling rate was 100°F/ hour, then pulled the coupon from the oven and allowed to cool in still air. When I sampled the impact tests for the Weld & HAZ as required, my results were VERY low....lateral expansion < .003". My question is has anyone experienced this, if so, what was the process to ensure that the material maintained the ductility needed for acceptable results at lower temperatures. Note: The material was "tested" prior to purchase and the reports did show lateral expansion results >80 (before 1400°F PWHT), and > 70 (after 1400°F PWHT). Thanks for any advice anyone may have in advance. Thank you.

 

[metengr]

Why did you use 410 filler metal? The 410S is a ferritic grade of stainless steel that can be welded with no PWHT if an Inconel or other non-hardening type of filler metal is used in production welding. In your case, you have a air hardenable filler metal, 410 stainless steel coupled with a base material that upon PWHT can result in local embrittlement if cooled too slowly - in air.

 

[DonRoss]

metengr is correct; according to ASME VIII Div 1, Table UHA-32 it is allowed to use E(R)NiCrFr-2 or -3 or E(R)NiCrMo-3 filler for 410 materials without PWHT.

metengr, what are your thoughts on using Low Carbon, 0.020% C Max. ER410NiMo instead of the E(R)410 filler? I also found the ER410 Filler to fail impacts miserably; however, using ER410NiMo yielded great results @ -50°F.

 

[metengr]

Agree, I think the 410 NiMo would be a better selection over 410 filler metal. The coupon needs to be cooled to room temperature and then PWHT per the above and rapidly cooled below 1200 deg F with moving air or liquid quenching.

 

[moseley]

I agree with all of your recommendations. The 410NiMo filler metal was actually the one specified, however before getting me involved the use of 410 SMAW was used. And before I require them to start cutting all of the welding out (as I am thinking I need to anyway) I was only wanting to cover all of my bases Metallurgical wise so the client fully understands why this will be delayed. I am beginning to lean in the direction of having this cut out and redone the original way I had proposed and remove PWHT from the equation. However, I still have the dilemma of the Impact strength to deal with (-20°F). I have some of the base material (as received, without any additional PWHT from the manufacturer) and am getting the Lateral expansion values of this material prior to welding. The first round showed values at 3-5 mils. Is a 15 mil minimum, at -20°F, easily achieved for this type of material or is this something that is not readily achieved?

 

[DonRoss]

I would think 410 SS would be at least sufficient enough for temps as low as -40°F; however, I'm beginning to realize that it is not and
-20°F may be its lower limit.

According to ASME VIII DIv 1, UHA-51(e) - Exemptions from Impact Testing for welding procedure Qualifications. Impact testing is not required for the following combinations of weld metals and MDMTs except as modified in UHA-51(c):

UHA-51(e)(3) - for the following weld metal, when the base metal of the similar chemistry is exempt as stated in UHA-51(d)(3), then the weld metal shall also be exempt at MDMTs of -20°F and warmer:
(a) Austenitic Ferritic Duplex Steels;
(b) Ferritic Chromium Stainless Steels;
(c) Martensitic Chromium Stainless Steels.

Therefore, if the material is equal to or less than 1/4" thick and MDMTs of -20°F and warmer then impacts are exempt. Unfortunately, this is not the case for my qualification.

 

[moseley]

Already attempted that route. I have a .500" thickness. Thanks

 

[metengr]

The 410S is a ferritic stainless steel with low carbon content that should be able to meet the required impact and MLE at -20 deg F if it has been properly annealed. This material will not harden by heat treatment. The issue is to weld using a filler metal that does not require PWHT. If you require PWHT for the 410S, you need to cool quickly to avoid reduced toughness as mentioned in the Code.

Read up on this material

http://www.aksteel.com/pdf/markets_products/stainless/ferritic/410S_Data_Bulletin.pdf