Ferrite Testing

Date 02-28-2007 20:50

To my knowledge there aren't any standards requiring ferrite testing (except base metals for Duplex). Even the nukes essentially gave it up. Its all in the hands of end users now. The reason was predominanly that the research guys were still trying to figure out a way to include cooling rates in all of the ferrite evaluations. This, and the fact that most research shows that even low levels of ferrite are efficient in eliminating the risks of cracking. I think that end users still require it in many instances because a minimum requirement is felt to be better than none. Just another level of verification and comfort. In my experience chemical verification (Schaeffler/WRC/etc.) from filler certs are often assumed to be a minimum verification standard and in the mind of many eliminate the need for redundant ferro-magnetic verification. The usual 4 to 13 range can quite readily be hit. The point is, high enough to eliminate cracking low enough to prevent intermetallics. Thats actually a pretty broad range as long a chemistries aren't out of wack.
In a sense the information added by FN is really the influence of the cooling rate.

By Soheyl Date 02-28-2007 21:02

thank you very much for your comprehensive answer

By PhilThomas (**)

Date 03-01-2007 00:51

Unless they have dropped it in the most recent version, Section III of the ASME Code does require a minimum ferrite number in some applications. They have changed the method for determination over the last few years from Schaeffler to Delong to WRC-92.

By js55

Date 03-01-2007 14:41

Thanks Phil. Jon may be able to help us here, he is currently into nukes.
There was a terrific article written some time ago, if I can ever find it in my archive-I can't even remember the author at this time-I'll post it in here if anyone is interested, that provides the history of the methods, the thinking behind them, and the current state. Anyone involved in ferrite evaluation should have at least a cursory knowledge of its history.

By jon20013 (*****)

Date 03-01-2007 17:15

Jeff; there is still a Nuclear Regulatory Guide in effect which requires stainless steels to have FN5 - 15. I thought most of the producers had adopted this practice? I certainly haven't had any problem in acquiring these materials. As for requirements, the NUREG Guide is the only thing I can think of that specifies this "suggested" limitation. That said, many utilities have adopted it as gospel.

By G.S.Crisi (****)

Date 03-01-2007 21:08

I think I've read or heard somewhere (but I'm not 100% sure) that WRC 92 has been replaced by a more recent diagram. Is that right ?
Giovanni S. Crisi
Sao Paulo - Brazil

By chuck meadows (***)

Date 03-01-2007 21:54

I, personally, haven't received or heard of any newer version of any diagram replacing WRC-92. I checked with our mill and they said the same thing. But, there might be something in the works, I don't know. As a manufacturer of stainless steel consumables we would certainly need to have the most recent...let me re-phrase that..the most accurate means of predicting ferrite in the filler metals.

By js55

Date 03-02-2007 14:43

I think I remember Kotecki doing a paper in Detroit a few years ago wherein he has a later version of the WRC92. It just may not have caught on yet. I think it centered on improvements to the martensite line, if memory serves.

By chuck meadows (***)

Date 03-01-2007 13:44

If testing is being done for a weld procedure and ferrite quantity is required, then the ASTM E 562 (point counting) is the most accurate. As has been pointed out, WRC-92 is the most accurate of the impherical diagrams being used.

By js55

Date 03-01-2007 14:49

I agree Chuck. If you really want to know, you have to look at it. They have never come up with an adequate equation for cooling rate, that I know of. Even though there have been some really good attempts.
But I think from a practical point of view if you have any ferrite at all you have greatly reduced the tendency to cracking. Some place for the 'junk' to go besides the austenitic grain boundaries-if memory serves on the mechanism.
An excellent WRC report-again the specific issue eludes me but their catalogue will list it-clarifies this. I think most levels specified increase this amount (I've seen 3 to 6 FN) as a cushion of safety and in recognition of measuring

By chuck meadows (***)

Date 03-01-2007 15:12

I agree that cooling down rate is vital in the determination of ferrite quantity, as is the weld technique. But, in reality, the pick up of nitrogen in the weld arc can lower the ferrite from (for an example) an 8 FN completely down to 0 FN. So, weld technique is, in my opinion, is as important as cooling rate. If you like, I will share a couple of papers relating to the different diagrams (Schaeffler, DeLong and WRC-88 and WRC-92). And also the prediction of ferrite usiing the different diagrams. These are papers I present in different stainless steel presentations. They're pretty interesting if you are interested. All I need is an e-mail address so I can send them to you.

By js55

Date 03-01-2007 15:22

Good point on N Chuck. And while the diagrams consider N as established in heats, they don't consider it as present from welding technique. I suppose you could chem test for N and then use the diagram. But ferro magnetic testing would be more practical as an evaluation of not only cooling but N as you say.

By chuck meadows (***)

Date 03-01-2007 16:00

Jeff,
That is why ferrite quantity is strictly a "prediction". Like you indicated, nitrogen is a factor in the prediction of ferrite both in the prediction of filler metal and as-deposited-weld metal. But, still, it is only an educated prediction. There is no way to factor in the amount of nitrogen picked up in the weld arc. And, we both know, nitrogen lowers the ferrite since nitrogen is a strong austenite former. The Nuclear Regulatory Commission has indicated, in their opinion, that 5-12 FN is optimum.

By Soheyl Date 03-01-2007 16:52

thanks, you can e-mail me those papers to ssoltani@fce.com

By Stephan (***)

Date 03-01-2007 17:06

Soheyl,

may I also add a quite good paper in regard for what you are looking for?

http://www.osti.gov/bridge/servlets/purl/14580-mGkMzM/webviewable/14580.pdf

Regards,
Stephan

By CWI555

Date 03-01-2007 23:56

Soheyl,

If your application is cryogenic I can understand why a specification would have it. Based on documents from Lincoln they state 3 - 6 FN for CrNiN and CrNiMoN weld metal for cryogenic applications. Quoting from Avestas low ferrite welds are sometimes stipulated for cryogenic applications and certain environments. This in my experience is the case for many cryogenic applications, especially LNG. If your project is for LNG and utilizing a 304L grade for transfer of the LNG (or other similar temp material) it is likely going to be the case. The primary purpose for this concern is the potential reduction in toughness for the material at hand. The cryogenic temperatures have a direct effect on your V notch values and any thing that can affect that such as to high a FN number is in question.

By chuck meadows (***)

Date 03-02-2007 00:17

Gerald,
You are 100% correct. If this is a cryogenic application, Section VIII of the ASME Boiler and Pressure Vessel Code requires any weldment intended for cryogenic service to qualify by Charpy V-notch testing to insure freedom from embrittlement and must meet the minimum of 15 mils lateral expansion opposite the notch on all three specimens. And, to insure that requirement, the lower the ferrite the better. Or, the more austenite the better.

By CWI555

Date 03-02-2007 02:47

More information can be found in 2004 ASME Section II Part C paragraphs A6 through A6.10.4. A quote from paragraph A6.1
" Ferrite may have a detrimental effect on corrosion resistance in some environments. It is also generally regarded as detrimental to toughness in cryogenic service, and in high temperature service where it can transform into the brittle sigma phase."

It is also noteworthy that anyone performing ferrite test, should read paragraph A6.3 through A6.6. of the same document if they want accurate results. In particular A6.5.

On another note, thanks for the info on section VIII Chuck, as it so happens I was just needing that information today. If you could tell me which verse it would save me a lot of look up.

Regards,
Gerald

By chuck meadows (***)

Date 03-02-2007 13:39

Gerald,
I'm out of my office today, so I can't give you the exact sentences that Section VIII state that, but it's pretty close to word for word.
On a side note, please...I agree 100% about sigma forming at high temperatures, but may I please add a side note to your comments.. As you said, sigma is detrimental to mechanical properties, especially ductility and impact toughness, but small levels can be almost relatively innoculous because the phase tends to be discontinuous in the microstructure. At higher levels sigma tends to form continuous networks in the ferrite bearing steels. It is these continuous networks that embrittle the steel. The amount of sigma that forms in the austenitic steels weld metal is always less than the ferrite content, because the sigma phase has a much higher chromium content than the ferrite it grows from. Therefore, a relatively high ferrite content is generally needed to promote sigma embrittlement. Although the actual sigma level is a function of the weld metal composition, it generally must exceed 15FN. Naturally this requires the steel to be exposed to the sigma temperature, 900-1650F, for a good length of time for this to happen. Just thought I would add that to your excellent post.

By js55

Date 03-02-2007 14:47

I too thank you for the Section VIII input Chuck. I had forgotten that VIII uses lateral expansion as well as III. I had in another location expressed my preference for LE measurement in impacts. And VIII is actually the queen mother of all codified impact testing. And given that III uses it also perhaps the other codes need to come around to their thinking.

By chuck meadows (***)

Date 03-02-2007 15:17

I agree, Jeff. It would make sense, at least to my peanut brain, that all codes would have the continuity of each other.

By js55

Date 03-02-2007 14:54

Chuck is dead on with the continuity of Sigma idea. I beleive its been shown that there is sigma present in virtually every SS weld with upper FN contents (especially those containing Mo like 316). Its just that it is so isolated and minimal that it is virtually meaningless.

By chuck meadows (***)

Date 03-02-2007 15:32

Agree again...The discontinuous network of sigma, usually less than 5%, can very well be in more than we might really understand or realize. On the same hand, sigma can be quite hard to find in the mocrostructure and even a small amount can have large effects on mechanical properties. Regardless, sigma is an intermetallic compound, and an intermetallic compound is a real compound, like a carbide, except that it forms from 2 metals, like chromium and molyybdenum. Forming this intermetallic compound steals the chrome and moly from their role in providing corrosion resistance. But worse, it embrittles the steel. Once these bad boys form, only a full anneal will cure sigma. Like you pointed out, the higher chromium and moly contents favor higher rates of formation and potentially larger volume fractions. That's why nitrogen is added to the austenitic and duplex grades as a retardant.

By js55

Date 03-02-2007 16:13

Chuck,
I remember a series of papers that came out a few years back and it was quite a stir. Our ability to 'see' things has improved astoundingly over the past couple of decades and discussions of the Sigma phenomena was starting to include language of 'fitness for purpose' thinking. In other words, just because we can detect it, do we really need to eliminate it. Even if we consider it as generally deleterious. Very similar to our thinking with slag, and porosity in welds. I still don't think it is settled yet, and perhaps rightly so since I still don't believe we understand fully the impact of Sigma in varying applications. For example, if Sigma is present in a weld that is intended to operate at high temp is the embrittlement a problem? Probably not. But what about start ups and shut downs or other cyclic regimes? Economics will always drive us one way (not unjustifiable-I mean, who wants to pay 20 bucks a gallon of desalinized water, or 25 dollars for a bottle of shampoo), safety the other.

By chuck meadows (***)

Date 03-02-2007 18:37

Jeff,
I agree with your line of thinking, especially the absolute need for resolution of sigma in all cases. I can see where embrittlement might not be as serious in certain applications and environments as it is in others. If embrittlement was the only by-product of sigma, I could fully agree, but sigma also robs the chrome and moly of it's corrosion resistance. So, even though the service won't warrant the absolute need for freedom from embrittlement, now we have the reduced corrosion resistance to consider. It is very impractical to try to quantify the amount of sigma in production pieces. I mean, how many project engineers will let an inspection firm do a destructive metallurgical test just to determine the amount of sigma? I think that the majority of Welding Engineeers and Metallurgist, working together, are trying to not eliminate sigma after detection, but specify grades of steel (stainless) that will delay the onset of sigma without compromising the corrosion resistance. Since it is very hard to experience sigma during weld thermal cycles (except Duplex), the "fit for service" condition is of the utmost importance. Even though some sigma may be present in certain applications, I don't think it is detrimental in every case, especially at lower quantities. But again, determining those quantities involves a costly and destructive metallurgical test. So, in my way of thinking, sigma should be avoided as much as absolutely possible. And sigma is just one intermetallic phase. That doesn't include chi and alpha prime.

By js55

Date 03-02-2007 19:01

Chuck,
Its interesting, the phenomena of reduced corrosion properties due to Sigma is actually quite similar to the 'sensitization' of austenitic SS's. Primarily the depletion of adjacent Cr and Mo. Only instead of a carbide its an intermetallic.
And your assemssment of the ability to quantify Sigma is right on as well, considering its chemical makeup varies to an extensive degree and that it actually looks so much like Chi phase. Though Chi will eventually age into Sigma.
I think impact testing is a good practical measure. It actually contributes to a real assessment of embrittlement while not actually quantifying the Sigma content.
As for corrosion resistance I would agree with you again, prior metallurgical examination of materials that delay or reduce the onset of Sigma/Chi formation is the minimum step necessary for confidence. This would also allow a quantification of Cr/Mo depletion into Sigma consistent with CrMo segregation into the ferrite phase. An absolutely unavoidable phenomena as far as I know. I mean, it does no good to concern oneself with CrMo depletion into Sigma if CrMo segregation into the ferrite phase is more extensive.
But having said all that, avoiding it as much as possible, I have to dispute with, since any adjustment in heat regimes that would do so are also beneficial to minimizing segregation, and the avoidance of the many other detrimental phases of these messy alloys.

By chuck meadows (***)

Date 03-02-2007 19:44

Geez.....You and Stephan are making me really use my brain cells, which sometime go into neutral this time of day. I love these kind of discussions, though.
You know, we have been talking about impact testing and later expansion and all these other things. I think the impact testing using lateral expansion as an acceptance criteria is primarily done for cryogenic applications, aren't they? If memory serves me correctly, isn't the ASTM A923 test used to demonstrate the absence fo intermetallic phases, while using the acceptance of 40 ft-lb at -40C (-40F) in applications other than cryogenic? I think this test was used and was found to correlate with the appearance of intermetallic phases in a metallographic examination and a loss of corrosion resistance. We have spoken about testing done for "suitability of service" and that would be the ASME UHA 51 test. Now, the UHA 51 is also a lateral expansion test using 3 samples with strength well below 40 ft-lb as acceptable for use, though. Unlike the impact testing for cryogenic applications, the UHA 51 impact test is done at minimal design metal temperature, a factor of design specirfic to each application. Boy, have we strayed off the topic of the original post...

By js55

Date 03-02-2007 20:18

Chuck,
I'm LMAO!! Yeah, it did turn into quite a stray. Though from ferrite through sigma to duplex ( I had to go back over the posts to verify) its a natural one. Garanteed this ones getting printed. Good points on A923 and UHA 51.
I think Stephen needs to hang out here a little more often. Clearly something valuable to offer.

By Stephan (***)

Date 03-02-2007 18:35

Dear Chuck,

I am impressed - what a discussion and what an expertise in Stainless!

May I humble ask..?

When a carbide is directly comparable with an intermetallic compound - and (metallic-) carbides are - as far as I know - mainly non stoichiometrical structures - are intermetallics also obeying non stoichiometric rules although they have defined relations in their composition (and having - sometimes - metallic character), or are the rules of constant proportions the reason for their formation?

Thanks for the great already stated information until here, and of course for brighten my brain in regard to my question!

Regards,
Stephan

By js55

Date 03-02-2007 19:11

I believe the current thinking is that Sigma/Chi and the others are formed due to local variances in the liquid chemistry. Cr and Mo, two primary elements of these phases naturally segregate to the ferrite phase, the primary location for Sigma/Chi formation, which forms first in Duplex, and this segregation provides a chemistry in approximation to that which is found in the solid intermetallic phases. It doesn't take much to tip the balance.

By chuck meadows (***)

Date 03-02-2007 19:12

Stephan,
What a challenging question !! And a great one... Without having to search my references, I will try to answer as best I can from my memory. I'm not sure I would compare a carbide directly to an intermetallic compound in the fact that an intermetallic compound is a product of two metals. This is not necessarily the case in carbides and nitrides. Intermetallic compounds are an actual chemical compound. I guess I'm having trouble associating stoichiometric and non-stoichiometric structures when relating to the formation of carbides as opposed to intermetallic compounds. I'm sure there can be a relationship, but it is not something I can define that easily. Sorry..
Oh, yes, I enjoy reading your post....

Chuck

By js55

Date 03-02-2007 19:31

Chuck,
I was really hoping you could help us out on this one because I didn't have a clue. I mean, I understand the meaning of stoichiometric but couldn't put it together in this context.

By chuck meadows (***)

Date 03-02-2007 19:49

Me, too..I'm having trouble with the relationship pertaining to carbides and nitrides and intermetallic compounds using stoichiometric and non-stoichiometric structures. I'm not sure I have ever been asked to compare them in this context. My initial thought was a carbide and a compound are not comparable in the text that Stephan was referring to.

Stephan, find the answer and educate us.....Please....

By Stephan (***)

Date 03-02-2007 20:10

Dear Chuck,

Sorry, I have seen there has happened a kind of "delay" between yours and my last reply?

Nonetheless, although your request honors me in an unspeakably way, I am not sure to be able finding out the "final secrets".

Honestly I was rather setting all my hope in You or js55...

However, I promise to do my best!

And who ever from us may find the reason first may shout out loud ;-)

Sincerely Yours,
Stephan

By Stephan (***)

Date 03-04-2007 00:37

Dear Chuck,
Dear all,

here is a first humble attempt to find an approach on what we have discussed about.

I have tried again to find any hints in regard to explain the physical mechanisms of intermetallic phases or compounds(?) or both(?) and if their origin may be based on stoichiometrical or other reasons. And... thanks Prof. "GOTTSTEIN" (Physikalische Grundlagen der Materialkunde - a SPRINGER textbook) and his explanations of physical material sciences I have experienced a kind of slight "enlightenment". And I hope very much that I will find the right words once again for explaining what GOTTSTEIN has described in a very - diplomatically expressed - scientific view on the matter of subject, being the object of our interesting theoretical exchange of thoughts.

Considering what I mean to have understood by reading the "high purity" theoretical explanations, I would like to start very simple in the field of alloying metals. Most of metallic materials are forming systems being fully miscible in melting condition. But there are also systems being totally immiscible in solid and liquid state. Well known, and thus being used here, is the system "Iron-Lead" showing a miscibility gap between liquid and solid state and is finally immiscible in both conditions. And as I understood, the miscibility gap at all, is the main factor for all further complex explanations in regard to the forming of intermetallic phases in different metallic alloys. What can be stated is, that in the predominant number of alloy systems the alloying elements are completely miscible whereas while solidification occurs this ratio is varying to a lower level of miscibility. This is, in solid state of these alloys governs limited solubility.

What I could find out is that the topic we are talking about is - as far as I have once mentioned already - totally tricky. This is being induced through the immensely high number of existing intermetallic phases and compounds, which lies in the order of ~ 5000(!). When I have read that, I was sure that we - my dear appreciated colleagues - have selected one of the "easier" things in metal physics ;-) .

Well, you remember, what I have asked was about any coherence in comparing non stoichiometric structures like Carbides with other structures like Sigma (FeCr) and if these compounds being now non stoichiometric or - what is being suggested by the term "compound" - rather stoichiometric in sense of chemical aspects, which means that the rules of constant proportions and thus constant valences should be able to be determined. But, as we have discussed already Hume-Rothery has clarified that in case of many intermetallic phases the composition - expressed by the empirical formula (e.g. FeCr) - does not fully predict the valence of what should be expressed by this formula. This was the main reason of my question. Why, when we have an empirical formula - normally expressing stoichiometry as the driving force for forming the compound, why do we then not also have a constant valence of the compound?

GOTTSTEIN - and at the latest then I saw, I am not the only one getting grew hair when talking about Sigma et al - described the discrepancies in dealing with intermetallic phases are being based on the typically "non chemical character" of these structures although - and this is important - chemical empirical formulism is being used to express their composition. Therefore he proposed firstly to find a common and clear terminology having the benefit of separation what is meant by using the term "compound" or "phase". He explained that the reasons of the origin of intermetallic phases are numerous and thus the definition of why intermetallic phases are being formed is complicated, additionally, since different interacting factors may be the reason for the origin of intermetallic phases. The very main reason is - as in most sequences in material science too - the enthalpy, which I do not want to deal with here further on (I hope you may agree).

Crucial point is, to recognize that the term "intermetallic compound" is a bit "misleading". In German he used "irreführend". Subsequently I would like to state the recommendations for the separation of technical terms in regard to "Intermetallic Systems"

1. The term "intermetallic compound" should be used when the composition of the substance is s t r i n g e n t stoichiometrical based. I.e. MgZn2 or NaTl. In German we say "Strichphase" which might be translated approx. with "dash-phase". These phases have a stringent composition, often being accompanied from solidus-line-maxima and being represented as a dash within the phase-diagrams. Therefore, following from that, in most cases, this term is not recommended to be used in most of intermetallic systems (You see, this replies my question already partially).

2. The term "Intermetallic phase" is being understood as a "neutral" determination under special consideration of the rules of thermodynamics. What was impressing me - and at the latest here I understood the main difference - was that in case of "phases" also the rules of "phase-variations" are being allowed. This is, it explains why I have read so often different percentage compositions of Sigma (FeCr). It may vary, since it has an allowed width of phase-composition(!). In case of FeCr-Sigma (our famous weld-metal phase) the variation-width of Chromium content within the area of existence of the phase is between 43... 49% Cr and thus the variation of Iron content within the phase is between 57... 51%. Another example for varying phase-width is the so called "epsilon-AgCd3" which has a variation width of 70... 82% Cd. The latter may only be an example, since I do not guess that we may be confronted with this phase anytime in welding.

So far so good, but the different (most important) mechanisms of intermetallic-phase generation are so complex that it would certainly impossible to deal with them within this humble post. Nonetheless they can - in a very strong simplification - be stated as following. I have allowed myself to prepare some small Portable Document Files showing the most important phases and compounds in a general treatment. I hope very much that these sketches can clarify the sequences and mechanisms in an understandable way.

Since as mentioned above, there are a number of interacting and overlapping sequences for intermetallic-phases formation:

· Phases determined by Valence

These kinds of phases (also called Zintl-phases) being originated due to different locations of atoms within the groups of the periodic table of elements. This is, strong electropositive elements are forming phases with strong electronegative elements. See also attachment Zintl.pdf, showing the binary phase-diagram of Ca (electropositive) and Silicon (electronegative). As can be seen, these phases have stringent stoichiometric induced structures ("dash-phases").

· Phases with high package density (Laves-Phases)

High density packed phases are being counted to the "Laves-phase-group". Depending on which elements react both can occur, either phases with stringent stoichiometric ratios or phases with phase-width variations. Identical Valence-Electron-Concentrations (VEC) and comparable metal-radii lead to homogeneous solubility. Differing VEC and atom-radii lead to defined package-density orientated compounds, see also the attachment Laves.pdf. These kinds of intermetallic systems having most an optimal ratio between the system forming element-radii (A/B). In case of the system Mg/Cu this Mg/Cu radii-ratio is 1.228 and thus a system with a high package density (~72%) can be formed. By the way, also Sigma-phase in welding is a kind of high-density package phase forming the transition to the Hume-Rothery-phases and having a phase-width, and thus a concentration-variation. See also attachment Sigma.pdf.

· Hume-Rothery-Phases

Basing on extremely intricate coherences - I beg your understanding for not treating here further - in regard to the so called Valence-Electron-Concentration (VEC) these phases are being originated. The elements of which the phases are formed of are located under "A2" (green accentuated) and "B1" (violet accentuated) within the period table of elements, see also attachment Hume-Rothery.pdf.

To be honest, when having a look onto the Iron-Chromium phase-diagram, where can be seen that Sigma has a variation in composition, it should normally have been clear for me that Sigma may not have a stringent stoichiometrical induced structure and should count to transition phases to Hume-Rothery. But due to I have been confused about the different meanings of chemical compounds (stoichiometric) and phases (stoichiometric or non stoichiometric) and covalent phases and Valence-Electron-Concentration (VEC) I was - honestly - unable to see what Sigma really is inside.

Dear Sirs, this was a very humble first attempt of creating clearness in a field of structure-chemistry which is not so easy to see through for a simple non academic - but "proud to be a" - welder like me!

I must admit - I love physics, but structure chemistry won't be my favourite topic in the future ;-) .

I do really hope now that you supernal stainless-steel-experts may correct me if I have explained or understood something wrong. To be corrected by you would be a honour and certainly never a disgrace!

I remain with greatest respect, best regards and in hope to reading soon from you,
Stephan

P.S. It's ~ 1.30 a.m. Sunday morning now where I live... Now as I have written this above I will find a bit of "relaxation" to have a nice rest of the weekend ;-) .

Attachment: Zintl.pdf (123k)

Attachment: Laves.pdf (101k)

Attachment: Sigma.pdf (120k)

Attachment: Hume_Rothery.pdf (142k)

By chuck meadows (***)

Date 03-02-2007 19:51

This seems to me to be more of a Metallurgist expertise than a Welding Engineering question. I do not propose to be any part of a Metallurgist...LOL

By js55

Date 03-02-2007 19:58

I've been accused of not even being any part of a welding engineer. But by a metallurgist. Ha!! I just think maybe he inhaled too much etchant, or spent too much time standing near an electron microscope.

By Stephan (***)

Date 03-02-2007 19:57

Chuck,
js55,

Sirs, you are the pure "madness" - please don't be angry, this is meant absolutely p o s i t i v e !!

Thanks to you both for replying so fast and detailed...

Please let me very shortly describe the background for my question.

I have busied myself a longer time ago with some aspects in regard to the physical mechanisms and sequences in formation of intermetallical phases.

What I have learned at that time - besides it is very complex chemistry which sometimes was able to burst my poor head - was, that a lot of different kinds of varieties of the typus of only one intermetallic phase can occur. E.g. I have found out that only for the "famous Sigma-phase" approx. 50(!) Sigma-phase varieties can be formed.

But very interesting amongst others was, that many different metallic structures are being based on covalent or ionic bond-structures. These ones are being counted as "chemical compounds" in sense of real compounds.

Others again, and these ones are the ones we are most talking about in coherence with welding high-alloyed steels have no "real chemical compound character" but being also expressed by formulas as FeCr (Sigma). Hume-Rothery has expressed as first - as far as I know - that these kinds of formulas do not reflect the correct valency of elements being included in the "compound" or better "phase". But unfortunately I have never found someone who could explain in a way that my small would be able to understand it, on what then the mechanism forming of the intermetallics is based on. I would have supposed, that it might be geometrical reasons, i.e. basing on the size of the atomic radii which have to fit in a specific relation and thus - in combination with the predications of Hume-Rothery - the formation of e.g. Sigma may have the reason in geometrical aspects. But I really do not know...

Another reason might be - as js55 expressed - small variations in the liquid chemistry. But then - as far as I understood it correctly - the entire mechanism would be influenced by stochastical factors which would let me ask why is there a l w a y s a defined relation between - in case of Stainless Steel Weld Metal Sigma - Ferrite and Chromium?

O.K. I see i must prove further patience, but I am sure someone of you wonderful Stainless-Steel-Welding-Metallurgists may answer my question one day!

Once more a heartfelt "Thanks" (also for your kind words!) and my very best regards,
Stephan

By js55

Date 03-02-2007 20:06

Stephen, you are indeed talking way over my head. But I believe I grasp an 'iceburg tip' of your intent. As inadequately as it may be, the final 'always' of your statement may be answered, I have read that at the temperatures that Sigma is formed Sigma is actually quite stable and ferrite only metastable, therefore if a chemical imbalance occurs Sigma is actually favored. I am sure I have not come close to answering your questions, but that may be the best I can do.

By Stephan (***)

Date 03-02-2007 20:11

Thanks again a lot js55!

By js55

Date 03-02-2007 20:36

Dont think I helped much but it was an interesting discussion nonetheless. And Chucks complainin about strainin his brain. Yeah, yeah. Chuck's probably on the road somewhere, sittin in some Me and Ed's Pizza Parlor sippin Heinekins and pullin this stuff off the top of his head, shippin it from his laptop through a satelite, while I'm strugglin to strain through the onset of a geriatric stupor tryng to remember something I read years ago. With the lady in the office next to me wondering why i'm groaning.

By chuck meadows (***)

Date 03-02-2007 20:57

OMG Jeff...I'm glad I read this post..I had tears in my eyes before I finished reading it. Made my weekend...Thanks Guys..

By chuck meadows (***)

Date 03-02-2007 20:31

Stephan,
Like Jeff, I will try to tackle this after some much needed rest this weekend. Your concerns are very formidable and deserve an answer, but an answer that is correct. I'm about ready to share a glass of wine with my lovely wife and put this stuff on the back burner until next week. Stephan and Jeff...it's been great..Have a good weekend, my friends..

By Shane Feder (****)

Date 03-03-2007 01:19

My head hurts!!! LOL
Have a good weekend everyone.
Regards,
Shane

By CWI555

Date 03-04-2007 01:22

I have to agree, half of the previous thread was way over my head. Where and how individuals can rattle information like that off the tops of their heads is beyond me.

By ssbn727 (*****)

Date 03-04-2007 06:56

That's because Stephan's "yankin our chain" so to speak when he states ever so humbly that he's nothing more than a welder who just happens to enjoy physics but, can't seem to know the slight variances between elementary metallurgy and welding metallurgy half of the time... However his mastery of beyond basic applied physics to advanced concepts & constant referencing to "Empirical" formulas which require more than just proficiency in basic math... His rather recent command of english with regards to his use of the language, much more eloquent than when he first started to post, a quantum leap in articulation that seems nothing less than miraculous - Capish???

The jig is up there Stephan!!! Come out and trutfully reveal thy self!!! WHO ARE YOU REALLY???
If you're going to tell me that you're not intelligent enough to further your studies in welding metallurgy, welding physics, materials science or welding engineering, then please elaborate to us WHY???

Also, You seem very familiar with Thyssen Krupp's metallurgical info... are you associated with them in any way??? If I'm barking up the wrong tree so to speak, please accept my apologies but, my "Spider senses" are really off the scale with your input lately with respect to being real skeptical about you being just
a "humble" welder and nothing more. One more thing if I may ask, you were born 09/12 of what year?

BTW CWI555, did you check out that new H&K 416?

Respectfully,
Henry

By CWI555

Date 03-04-2007 07:26

HK 416 had it's roots in the G36, which robbed the armalite AR18 short stroke gas system. It's more or less a reversed engineered version eliminating some of the short comings of the AR/M16 line. The design first came to light in 1959 by armalite, license was sold to the english sterling and the japanese howa company, which ended production somewhere in 79 80 time time frame. I have one of the AR 180 semi only versions and yes it's ugly but far more reliable than it's AR counterpart. From the inside it's an AR180 at heart, I believe there is some international patent disputes currently underway as HK patented a short stroke gas system for the G36 which is more than just passingly similar to the AR 180. It's a fine weapon but not really new in design where it counts.

By chuck meadows (***)

Date 03-04-2007 14:30

I forwarded Stephan's "inquiry" along to a noted Ph.D. Metallurgist that specializes in stainless steel and he thought I was joking. It appeared to him that these topics of Stephan's are more or less dissertation papers (research papers) of opinions of a combination of highly educated Metallurgist and Material Scientists that are discussed at various conferences. He also noted that there are many ways to access these subjects (mainly on the internet) and post them on the Forum and seem technically "out of this world" when using the metallurgical terms and wording in Stephan's post. He said all of Stephan's post could have been posted in "every day" language that more than just a small handful of people would understand. He also said he had his own "opinion" that differed on a few of the comments in Stephan's his post. I would cringe to think that Stephan posted these things as a means to try to impress others in this forum. Regardless, whether I receive criticism from this post or not, I will try to still give accurate information within my line of expretise in terms and language that everyone in here can understand and apply to their everyday careers. If that is not good enough, I will gladly discontinue my participation in this Forum. To those of you that I might have offended, I'm sorry. For those of you that I didn't, God bless you.

Chuck

By CWI555

Date 03-04-2007 16:34

Chuck,

To my mind, whether or not the post are technically sound is the only thing that matters. I have to agree with SSBN in that I doubt very seriously He's "just a humble welder". Stephen may in fact be a welder, but it's clear that there is more to it. In Stephens defense, he shouldn't need a defense if the comments are factual. It doesn't really matter where they came from as long as that tenant (being factual) holds true. Inversely, it seems to me that more comments of that nature would be beneficial to the forum. I think all the welders who have experience, have been maligned at one time or another with comments to the effect of it's "just a welder", or referred to in upper management halls as a "labor resource", in short not giving them the status of a "Professional". That perception is in no small part responsible for the lack of willing intelligent young potential welders for not wanting to begin a career as a welder. Their parents, and society, in many cases portray them as a notch up from knuckle draggers. Any one who's ever welded for a living or has been around it in any form of reality knows that couldn't be furthest from the truth. It takes a great deal of intelligence to weld, far more than most understand. (I speak of welders not of rod burners)
Various management types peruse this forum from time to time, and comments such as yours and others tend to be an eye opener when they come across it. No one should ever have to be apologetic for showing above average intelligence.
Speaking for myself, I may not initially understand the comments, but I am the kind that will take up the challenge and not let it rest until I do understand what was said. As a welder and an inspector, I enjoy reading your comments and others like them.
If someone doesn't understand the comments, they need to break open the books until they do understand. it not only furthers their understanding of their chosen career, it furthers their minds, and the results of that will eventually raise the awareness of just what is involved in welding.

If you said anything offensive to me it would be your comment about discontinuing your participation and the subsequent apology. You've got nothing to apologize for, and I believe I speak for many when I say your comments are a great asset to the forum.

Regards,
Gerald