50% Nickel and 50% Chromium Material

Date 04-12-2005 22:15

No, there's not, and it can't exist.
Reason: 50% chrome and 50% nickel means that they're completely soluble in each other.
Now, the unit cell (or Bravais lattice) of nickel is FCC (face centered cube) whereas the unit cell (Bravais lattice) of chrome is BCC (body centered cube).
So, one of the four Hume Rothery's rules is not obeyed, although the other three are. But if just one of the Hume Rothery's rules is not obeyed, the components of an alloy can not be completely soluble in each other.
They can be partially soluble, and in fact nickel and chrome are, but not completely. And, as I told before, for an alloy to contain 50% of each component, they must be completely soluble.
Giovanni S. Crisi
Sao Paulo - Brazil

By peterbil (*)

Date 04-13-2005 04:08

Hi Professor,

Thanks for your reply. Do you know a website which discusses Hume Rothery's rules? I'm interested in this rules and want to have a detail if there's any or perhaps you could give us this rules by posting it here. Thanks again.

Roger

By Lawrence (*****)

Date 04-14-2005 01:22

http://www.mse.uiuc.edu/info/mse182/t148.html

http://www.cartage.org.lb/en/themes/Biographies/MainBiographies/H/Hume-Rothery/1.html

http://www.mse.uiuc.edu/info/mse182/t149.html

http://www.ecm.auckland.ac.nz/course/phys130/phase_diagrams1.pdf

::::Woosh...

The sound of three of the above four links going over my head :)

By - Date 04-13-2005 13:21

There is definitely a 50%Cr-50%Ni material. Please refer to ASTM A 560/A 560M - 93. This is the Standard Specification for Castings, Chromium-Nickel Alloy.
This specification covers chromium-nickel alloy castings intended for heat-resistant and elevated-temperature corrosion applications such as structural members, containers, supports, hangers, spacers, and the like in corrosive environments up to 2000F (1090C). As a matter of fact, there are three like compositions. One is called "50Cr-50Ni", another is called "60Cr-40Ni" and the last is called "50Cr-50Ni-Cb (R20501)". The usual rrecommended filler to weld these materials is a 625 filler.

Chuck

By - Date 04-13-2005 14:12

Now that we know that there is definitely a 50%Ni-50%Cr material, let me give you an example where it is used quite frequently. This material is quite common and is used frequently as burner tips for furnaces due to the very high heat it is exposed to. As the Welding Engineer for Avesta Welding, I have written numerous welding procedures using this material. As I relayed to Mr. Cristi, please refer to ASTM A 560/A 560M-93 for chemical composition, tensile properties, test specimens, number of tests and retests, and other supplementary requirements. But be assured, there is definitely a 50%Ni-50%Cr material that your question inquired about. Thank you. If you have any further questions about this material or how to weld it, I will be glad to help you.

Chuck

By peterbil (*)

Date 04-14-2005 03:25

Hi Chuck,

Thanks for your information I agree you really are an asset to this forum, I also commend you for making this forum an open forum by giving us very reliable information so keep up the good work. Please I would like to know information regarding welding of this material.

peterbil

By - Date 04-14-2005 03:58

peterbil,
Thank you for your kind words. I will never comment on anything in this forum unless I know it to be accurate and true, but also to be able to back up my comments by documented data.
First of all, there is no big deal when welding a pure austenitic material. It requires no formal preheat or post weld heat heat treatment. The austenitic phase of this material allows greater time at temperature without forming the sigma phase, which is the embrittlement of stainless steels. This material is susceptable to hot cracking during welding unless careful monitoring is observed. By this I mean careful control of the interpass temperature (300F or 150C), and allowing the weld to cool down rather slowly. A high nickel alloy will withstand a higher heat input than your 308, 309, etc., but it also takes longer to cool down, so the cooling rate should be somewhat slower. As stated earlier, a pure austenic material will perform at higher heat temperatures due to its austenitic structure, which will counteract the sigma phase for a longer period of time. All 3 of the alloys I mentioned have a carbon content of 0.10% max., so that is an advantage with high temperature service. Even better is the 50Cr-50Ni-Cb, in which the columbium with tie up the carbon and give better resistance to the high heat while resisting any detrimental intermetallic phases. Usually, the filler metal of choice is a 625 filler matrial. Again, this is a pure astenitic material containing approximately 60-63% nickel and around 20-25% chromium and 6% moly. Of course, the most important thing when welding any stainless steel is the ability to start out CLEAN. If you will just use everyday good welding practices you should have no problems. 50%Cr-50%Ni is a very commonly used material, so do not be afraid of welding it. It's strength and weldability is like any other pure austenitic material. I think you will do just fine welding it. Go for it !!

Chuck

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

Date 04-15-2005 00:18

Mr. Meadows is right. I've just taken a look at ASTM standard A 560/93 and it says what Mr. Meadows states.
Now, Mr. Meadows, I'm going to ask you a favor. You work for Avesta, a company that I know since 1978, so she's an old friend of mine.
Please tell me the brand name of Avesta's 50% Ni and 50% Cr alloy. I'm going to write a letter to Avesta in Sweden and ask them how it comes that nickel and chrome can be completely soluble in each other if one of the Hume Rothery's rules is not accomplished.
Thank you in advance.

Reply to Peterbil.
The four Hume Rothery's rules for two metals to be completely soluble in each other are the following:
1st. The two metals must crystallize in the same unit cell (also called Bravais lattice). This is not accomplished in the case of nickel and chrome, as I said above.
2nd. The maximum size difference between their atoms must be 15 %. OK. This is accomplished.
3rd. The maximum valence difference between the components must be 1 (one). OK, this is accomplished.
4th. Their electronegativity must be similar. OK, this is accomplished.

Giovanni S. Crisi

By - Date 04-15-2005 03:44

Mr. Cristi,
Respectfully, I think too much is being read into Hume Rothery's rules in this case. Using your logic, which is good, the same thing should apply to Alloy 690 (UNS06690) with a chemistry of 60Ni-30Cr, which is a solid-solution alloy, as is Alloy G-30 (UNS06030) and many other high nickel alloys.
Avesta does not produce the 50Cr-50Ni, 60Cr-40Ni, or the 50Cr-50Ni-Cb. I'm the Welding Engineer for the Welding Division of Avesta, not the Metallurgist. I decide and recommend filler metals based upon the chosen base metals, which is the Metallurgist's responsibility. But, I do know that these alloys are not uncommon and are used very frequently with no welding problems. They are treated like any other pure austenitic alloy when it comes to welding. I don't recall who manufactures the 50-50, but it is very evident that research has been done by ASTM or it wouldn't be listed.
Also, one thing that maybe was not stated totally correctly is that nickel has a FCC structure, as you said, only up to it's melting point. Please realize that the solubilty of Cr in Ni is 35-40%. I might be wrong, but when all is said and done, I don't think any of Hume Rothery's rules are compromised. I think it is being taken out of context in this case.
Thank you for your e-mail. I hope this forum benefits from discussions like these.

Chuck

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

Date 04-19-2005 22:53

Mr. Meadows,
I've accepted with pleasure your corrections because through them I've learned something new.
Don't get upset now if I take the chance to make a couple of comments on your last post.
1st. If the solubility of chromium in nickel is about 40%, as you say, the 30Cr - 60Ni alloy you mention is within that figure and the Hume Rothery's rule is obeyed.
2nd. Of course the FCC unit cell of nickel exists only up to the melting point. Cristalline and unit cells structures exist only in solid materials. When the material melts up the strucuture is lost. Atoms or molecules in liquid are in a disordered state, also called Brown's motion to honor the English scientist who discoverd it.
Now, regarding the 50Cr - 50Ni alloy, we must accept that so far nobody said that the Hume Rothery's rules aren't valid any more. So, we must find out some way to explain how the alloy exists.
In my opinion, the alloy is a solid solution of 40% chromium in 60% nickel, with an additional 10% chromium which is not in solution but is in free state as metallic chromium.
Does this makes sense?

Giovanni S. Crisi

P.S.
Does perhaps Sandvik, or Uddeholm, makes the 50-50 alloy?

By MBSims

Date 04-20-2005 01:16

Giovanni,

It sounds as though a 50%Cr-50%Ni alloy would have a 2-phase structure.

http://web.met.kth.se/dct/pd/element/Cr-Ni.html

You'll have to refresh me on the lever rule. If I look at the above Cr-Ni phase diagram at 400 C, wouldn't there be about 70% of the "Ni" phase and 30% of the "Cr" phase?

By - Date 04-20-2005 19:28

Mr. Crisi,
Your comments are always welcomed. I respect your input and your willingness to share your knowledge. All of your comments make sense to me, but I can't really explein how the alloy is structured, I just know it is a common alloy that is used in high heat applications. I guess I just blindly accept the ASTM as having the research ability to determine usability of such chemistries. I don't think Sandvik makes the 50-50, and since it Avesta's sister company, I would hope that I would be aware of it. Now, Uddeholm may make it, I'm not sure. I will search my library and see if I can find an old cert that lists the manufacturer.
Again, thank you for your comments and please, never feel that you might upset me. Sharing knowledge is one of the greatest things to share with our collegues. Thank you, sir.

Chuck

By sinamdar Date 05-25-2005 17:04

Mr. Chuck and Mr. Crisi,

I have just run into your interesting correspondence regarding A560 50Cr-50Ni materials. I work for ABB Lummus Global in the process furnace group. I am neither metallurgist nor welding engineer but a Mechanical engineer. We frequently use 50Cr-50Ni-Cb materials for cast tube supports. These materials are manufactured by number of foundaries specifically per order basis. To name a few, Metaltek (old Carborundum) in St. Louise. There are others if you need to know.

I need to know if welding between A335 P91 tube and A560 50Cr/50Ni using A617 or A625 wire will require any heat treatment? The HAZ hardness numbers are coming out high, BHN 340 or so. The weld is a type of lug (50/50) welded to a tube P91 in a platformer furnace.

Thank you in advance,

Shailendra Inamdar

By - Date 05-25-2005 20:53

Sir,
A335-P91 is the pipe specification of the Cr-Mo Steel product form. The tube specification is A199-T91. Regardless, as far as heat treatment, I don't think, using a 625 filler metal, that a formal PWHT would be "required". Of course, that should be a decision that your Metallurgist or Welding Engineer specifies. Based upon what you have told us, I believe that the cracking that is usually associated with the Cr-Mo steels can be avoided by using the 625 filler and using a high preheat and high interpass temperature. This is usually the technique used when a PWHT is not applicable when welding a Cr-Mo to a stainless steel or nickel alloy.

Chuck

By GRoberts (***)

Date 05-26-2005 03:28

Mr. Inamdar,
I do not know of any circumstances where P91 material should not recieve a proper PWHT. If P91 material is required, then obviously the pressures and temperatures involved are significant. Without PWHT, the HAZ in the P91 material, as you have found, will be hard and very brittle (in the neighborhood of just a few ft-lb at room temperature). It could easily significantly reduce the life of the equipement and pose a danger to those near the equipment.

By - Date 05-26-2005 11:58

Mr. Roberts,
Please refer to page 63 in Volume 4, Materials and Applications-Part2, American Welding Society's Welding Handbook, Eighth Edition, where it gives "preferred applications in which the weldment cannot be given a post weld heat treatment" when welding a Cr-Mo to an austenitic or nickel alloy.

CM

By MBSims

Date 05-26-2005 17:12

Chuck,

I agree with GRoberts, P91 is just not as easy to work with as P22 or P11. P91 is a martensitic alloy that must be tempered to perform safely. We've had a few failures where P91 was not properly heat treated, even in small NPS 1 piping. It just doesn't fall into the same category as the lower CrMo alloys as far as weldability goes. The 9%Cr content puts in just below a 410 SS with 12%Cr and it is extremely air hardenable.

By - Date 05-26-2005 21:33

Marty,
If this was a P91 to P91 weldment, I would totally agree. Based upon proven WPS's, backed up by successful PQR's, the P91 welded to the 50Cr-50Ni-Nb using a high preheat (min. of 400F) and a high interpass temperature acts as a tempering treatment. The characteristics and metallurgical properties of the diluted weld metal when welding a P91 to a 50Cr-50Ni-Nb using a 625 (approx. 63% nickel) is totally different than a P91 to P91 weldment. Since there is a difference of opinions regarding the "required" heat treatment, the post should consult his Metallurgist or Welding Engineer for the required heat treatment based upon all variables. We can all give our opinions, but the final decision should be up to him.

Chuck

By MBSims

Date 05-26-2005 22:21

I agree, the decision is best left to the responsible parties. Your filler metal recommendation is a good choice. There should be no problem obtaining reliable weld deposit properties with the 625, it's the P91 HAZ that causes a problem. We've seen hardnesses over HB300 in as-welded P91 and occasionally they are not reduced sufficiently by even a "correct" PWHT in the recommended 1380-1400 F range. I haven't seen any creep-rupture data on P91 weldments in the as-welded condition, but would expect the HAZ has lower properties than would be seen with PWHT.

I'm interested in whatever info or references you can provide on welding procedures that produce an acceptable temper in the P91 HAZ. This has been the subject of recent research at EPRI using various filler metals and so far they haven't found a method that produces reliable results.

By - Date 05-26-2005 23:18

I don't think there is any strictly one "acceptable" temper method. Every spec. or customer requirement can differ based on many things. That is why it should be up to the post to determine his procedure based on his conditions. I am quite sure that an elevated preheat and elevated interpass temperature will lower somewhat the hardness in the HAZ of the P91. If that is acceptable to his requirements, that's another thing. Your information was sent today.

Chuck

By M-Squared (**)

Date 12-09-2005 17:59

Have run into situations in the past where we had to weld P91 pipe to Stainless Steel pipe and the question of PWHT always came up. The final fix that we used was to weld a “Butter Pass” (or two) onto the weld prep face of the P91 pipe with an acceptable filler metal for the dissimilar weld joint, (in your case use the 625). After welding you can grind/machine to smooth finish and perform a PWHT on the buttered P91 pipe per specification requirements. After PWHT, weld the P91 pipe to the SS pipe with no additional PWHT (Essential you are welding P91 to 625.

This is just a suggestion but I hope it helps or sparks some other ideas.

By Stephan (***)

Date 03-31-2007 15:48

Dear Prof. Crisi,

"Does this makes sense?"...

... what a wonderful question, in my opinion one of the most interesting ones on the forum!

Has it actually ever been clarified by now?

Every little feedback would be greatly appreciated.

Thank you and regards,
Stephan

By palooza Date 12-08-2005 19:11

Hi !!
Does anybody know where can I find pictures from the microstructure of Ni-Cr alloy??
In fact I have to study the microstructure of 50Ni-50Cr-Nb and I realy can not find something ...
I need some photos in order to compare them with my photos from the lab ..

Thank you in advance !!!!

PS My english is miserable...Sorry...

Christos ,Greece.

By MBSims

Date 12-09-2005 01:05

Try here:

http://www.iasmirt.org/F1546.PDF

By palooza Date 03-28-2007 11:52 Edited 03-28-2007 11:57

By CWI555

Date 03-28-2007 19:50

The dark areas I believe are chromium rich phase, the light areas nickel rich phase, It appears to have been somewhat annealed, probably around 2000 to 2200F for a short time and water quenched. Also looks like some minor agglomeration of the chromium phase.
Please refere to ASM Metals handbook vol 7 atlas of microstructures of industrial alloys. My edition is an old one (8th edition.) US library of congress #27-12046

Regards,
Gerald