A335P9 / AISI 420 WELDING

Date 11-18-2008 15:42

Peter,

Judging by your name and education I assume you from somewhere in Scandinavia, or maybe UK?
Be aware that the welding and PWHT of x20 can be a little complicated.

Can you be a little bit more specific on your question?

3.2

By Peter IWE Date 11-18-2008 16:17

Thank you for your quick answer.
Unfortunately you didn`t guess in case of my provenience:) I come from East Europe.
But sometimes I am working in Scandinavia:)
As I wrote before we need to qualify new PQR for joints between A335P9 (tube) / AISI 420 (rod dia 20mm). Operating temperature is contained between 550 - 610C degrees.
I consider using Bohler FOX KW 10 or FOX SKWA as a filler metal and PWHT in 750C degrees during 2h, and very slow cooling.
I don`t know what can I write moreover?

P.S.
I am sorry for my english:) I`m still learning.

By 803056

Date 11-18-2008 17:00

You should consider annealing the AISI 420 and the ASTM A335 P9 before welding and PWHT the assembly after welding. The filler metal should be selected with PWHT in mind.

The AISI 420 is martensitic stainless steel that is air hardenable. You want to weld it in the annealed condition so that there is sufficient ductility to prevent cracking while welding it. Sufficient preheat is also required to prevent cracking. Post weld heat treatment should be used to relieve residual stresses and to produce the mechanical properties you are looking to develop.

The A335 is also an alloy steel that requires high preheat and low hydrogen practices like the AISI 420 MSS. The welding conditions that apply to the AISI 420 MSS also apply to the ASTM A335.

You should consult with a metallurgist that can provide you with specific directions regarding the preheat and PWHT for the combination you have in mind and how best to attain the mechanical properties required in the final state.

Best regards - Al

By Peter IWE Date 11-18-2008 20:06

Thank you for your directions.
You are writing about annealing before welding. As I understand "annealing" means preheat before welding? According to informations concerning AISI 420, the preheat should be carried out above Ms temperature (more less 300 deg.). The same concerns interpass temperature.
I am not sure which consumable will be correct. I am thinking about: FOX KW 10 (http://www.alruqee.net/rtc_final/My%20Documents%5CRTC%20Web&CD%5Cwelding%20consumbales/bohler/217en00.pdf)
or FOX SKWA (http://www.alruqee.net/rtc_final/My%20Documents%5CRTC%20Web&CD%5Cwelding%20consumbales/bohler/234en00.pdf)
PWHT 750C deg / 2h.
What fo you think about it?

By 803056

Date 11-18-2008 22:07

Annealing is specific to the base metal being annealed, but in general it is a heat treatment that results in a soft ductile material.

Carbon steels are annealed by heating them above the temperature required to transform the base metal into austenite where the carbon and other alloying constituents are in solution with the iron. Then the steel is cooled very slowly to allow the carbon to precipitate as the austenite decays into ferrite and pearlite.

Copper is heated to a full red heat and quenched in water to anneal it. Just the opposite of carbon steel.

Annealing involves temperatures well above the typical preheat temperatures associated with welding. As I said, this is a job that should involve a metallurgist familiar with welding related problems.

Best regards - Al

By js55

Date 11-20-2008 20:41

You might want to consider 309 SS for the filler metal. P9 has a min spec TS of 60ksi. 309 will certainly meet this. And with the austenitic filler H2 solubility is high and diffusivity is low meaning the H2 will be trapped in the austenitic filler to 'protect' the martensitic base metal from H2 cracking.
You might also consider cooking it at the high end of the range. The high carbon 420 will respond to heat treat more than the P9 reducing 420 HAZ hardness.

By GRoberts (***)

Date 11-22-2008 00:06

JS,
You are usually spot on, but in this case, I would worry about using an austenitic filler due to the stresses created during heating and cooling cycles. A nickel based alloy would probably be a beter choice to reduce that stress. It provides all the advantages you mentioned for the 309 without the stress concentration drawback. Also, if the PWHT is over 1175F or so (or for a long time), I would worry about embrittlment of the 309 due to high ferrite content.

By js55

Date 11-24-2008 03:24

Greg,
You know, thats an interesting point. And in light of your post I would have to say I agree. You sorta caught me sleeping. I pulled the 309 info out of some notes I had from the ASM Handbook, but I'd have to say I too think a nickle alloy would be a better choice and would challange the ASME Handbook on this.