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- - By gsi (**) Date 08-18-2005 19:45
LOOKING FOR ANY GOOD REFRENCE MATERIAL ONLINE ABOUT FERRITE NUMBERS BEFORE PWHT AND AFTER PWHT ON STAINLESS STEEL
Parent - - By - Date 08-18-2005 20:02
gsi,
Any specific grade of SS? To be honest, very few grades, if any, of SS require PWHT other than a complete solution and anneal process, and most of the time that is not practical.

Chuck
Parent - - By gsi (**) Date 08-18-2005 20:13
MATERIAL IS 304H. WELD WIRE IS 308H WITH A FN OF 5-9. WE ARE DOING A SOULUTION QUENCH. BEFORE PWHT I HAVE FN IN BASE METALS AROUND 5 AND WELD METAL 6. AFTER PWHT THE FN DROP IN THE HAZ AND WELD METAL TO 1-2.
Parent - - By - Date 08-18-2005 20:20
What temp. is your PWHT? There is no need to PWHT 304 or 304H except in special occasions and then quench anneal at 1050C. PWHT will significantly lower the FN of a 304/304H, as it will in all the grades.

Chuck
Parent - By gsi (**) Date 08-18-2005 20:24
TEMP IS 1900 F AND QUENCH
Parent - - By - Date 08-18-2005 20:15
gsi,
Let me clarify something. Your martensitic, ferritic and PH grades of SS require PWHT. The most common austenitic and duplex grades do not require, or recommend, PWHT due to the possibility of sigma formation.

Chuck
Parent - - By gsi (**) Date 08-18-2005 20:23
THIS WAS A CUSTOMER REQUIRMENT. I'M ASSUMING THEY ARE DOING THIS BECUSE THE HAVE CONCERNS ABOUT INTERGRANULAR CORROSION. THIS IS OUTSIDE MY AREA OF EXPETISE AND WAS LOOKING TO LEARN AS MUCH AS POSSABLE
Parent - - By - Date 08-18-2005 20:31
That is the right quench anneal temperature providing it is not help at that temp. for an extended time. It is not uncommon for the FN to drop during this process. To be honest, 304/304H, welded properly with a 308/308H, is not likely to experience any carbide precipitation (intergranular corrosion).

Chuck
Parent - - By Jim Hughes (***) Date 08-18-2005 22:32
Chuck,
I'm just asking this question to learn, but isn't 304H high carbon? And if so wouldn't you have a more likely hood of experiencing carbide precipitation?
Jim
Parent - By - Date 08-18-2005 23:41
Jim,
With the austenitic grades, chromium carbides can precipitate on the grain boundaries if the steel is held in the temperature range of 800-1500F. This can be a factor in welding because some of the regions of the HAZ will be in this temperature range during welding. Normal welding thermal cycles are typically too short for this detrimental sensitization to occur. Now, chromium carbides by themselves do not lower the corrosion resistance. However, the Cr-depleted region immediately adjacent the carbides will reduce the corrosion resistance. By definition, this is called sensitization. Chromium and carbon atoms diffuse to the grain boundaries where Cr-carbides (Cr23C6) precipitate and grow. As the carbides grow, a narrow region in the vicinity of the grain boundaries become depleted in Chromium. This condition makes the alloy susceptible to intergranular attack (IGA). The kinetics of sensitization is a function of time, temperature and the carbon content of the steel. A 304/304H with a carbon content of 0.062% will suffer sensitization within a matter of a couple of minutes at 1200 to 1400F, while a 304L with a carbon content of 0.03% would not sensitize for about an hour. Reduced carbon levels provide sufficient time for welding without the onset of sensitization. If sensitization occurs, the carbides can be dissolved and the corrosion properties restored by a solution anneal heat treatment. Typical cycle for a 304 SS is 1900F followed by a rapid cool. So, in answer to your question, yes, a higher carbon content 304 is more prone to sensitization (chromium carbide precipitation) than a low carbon 304 if held in the detrimental temperature range.

Chuck
Parent - By - Date 08-19-2005 00:02
Jim,
All of this is covered in the July edition of the AWS Journal that Jim Fritz and I co-authored. Look on page 27 "Chromium Carbide Precipitation". Without sounding prejudice, that article has a lot of good information concerning SS and the HAZ.

Chuck
Parent - - By MBSims (****) Date 08-19-2005 04:06
Chuck,

Good data. Since the desire for ferrite in an austenitic SS weld deposit is mainly to prevent hot cracking during weld solidification, it would seem a drop in ferrite level after solution anneal would not be detrimental. The ferrite has already done it's primary job and it not needed as much after the solution anneal in complete. There is a secondary benefit to having at least 5 FN in the weld since it tends to blunt the crack tip of an active stress corrosion crack and prevent it from extending into the weld deposit. This was demonstrated by GE, EPRI and others in the BWR pipe cracking program back in the '70s. If you go to the NRC web page at www.nrc.gov, look in the electronic reading room for NUREG-0313 Rev. 2 and you will find the technical data to support this.

We have had many welds in 304 (not 304L or 304H) that have indeed experienced IGSCC in the HAZ due to chromium depletion (sensitization). These were in heavy wall (1"-2"), large diameter pipe (12", 22", 28") pipe and were typically welded with relatively high heat input compared to what we might use today for SAW or SMAW. But they were welded properly according to industry welding practices at the time they were fabricated. Currently, we try to limit heat input on austenitic SS to 35,000 joules/in. to prevent sensitization.
Parent - By - Date 08-19-2005 11:35
Marty,
Excellent, thank you. Agreed that the drop in FN after solution anneal is not detrimental, but expected. As you pointed out, I also believe that heavy walled pipe, as the thicknesses you demonstrated, will tend to experience IGSCC at a more frequent rate given a "higher" heat input. Thankfully, technology has changed somewhat since the '70's. Avesta's stand on heat input is recommended at 38,000 J/in, but like you, I normally tell folks 35,000 J/in so as not to push the limits. I will check out the web site you shared. Thanks for sharing. This has been a very informative and interesting thread. Good info, Marty, thanks..

Chuck
Parent - - By - Date 08-18-2005 20:45
gsi,
I've written a couple of papers regarding ferrites and how they are calculated. They might familiarize you with what ferrites are, and how they are calculated, and other information you might find interesting. If you will give me your e-mail address, I will send them to you. My e-mail address is chuck.meadows@outokumpu.com

Chuck

Parent - - By G.S.Crisi (****) Date 08-19-2005 12:38
Chuck,
I'd thank you if you send those papers to me as well, including the article on Welding Journal.
Giovanni S. Crisi
Parent - By - Date 08-19-2005 12:50
Giovanni,
Good morning... I will send you the ferrite documents immediately, but it is probably going to be information you are already quite familiar with. These documents are geared to the person not familiar with ferrites and how they are calculated. They will be on their way immediately. Good hearing from you..Oh yes, I have the article that is in the Journal on disk. I will see if my co-author still has it on his computer, and will have him send you the text and the illustrations.

Chuck
Parent - - By - Date 08-19-2005 13:22
Giovanni,
I sent you the documents on the ferrites, but all were rejected to your e-mail address. I have the article from the Welding Journal on my computer, but it will not make it to you for whatever reason. Do you have another e-mail address?

Chuck
Parent - - By G.S.Crisi (****) Date 08-19-2005 21:25
Chuck,
check my correct e-mail address:

gscrisi@mackenzie.com.br

Notice that the address ends with a "br", which of course means Brazil.
Hope you're luckier next time.
Cheers
Giovanni
Parent - By - Date 08-19-2005 22:05
I'm very sorry. I typed in gcrisi instead of gscrisi. My stupid mistake. It is coming to you now.

Chuck
Parent - By - Date 08-22-2005 12:57
Giovanni,
I hope the information I sent you made it.

Chuck
Up Topic Welding Industry / Technical Discussions / FERRITE

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