Why some Inconel is magnetic and others are not
Why some Inconel is magnetic and others are not
(OP)
So Im fairly new here, and have a question with regards to why some inconel is magnetic and some others are not. Im assuming right now that it has to relate to the elements in the material. Inconel 600 series a Ni-Cr is magnetic, where a 718 series is Ni-Fe is non-magnetic.Thanks in advance.
RE: Why some Inconel is magnetic and others are not
Second, the tradename "Inconel" is a marketing device, it does not mean anything metallurgically. The alloys that are marketed under that general name are all high in Ni content, but very different in alloy elements and properties.
the name is used to distinguish Ni based alloys from Fe based alloys (called Incoloy). Both were originally trademarks of the International Nickel Company, later know as INCO, and now held by Special Metals, a division of PCP.
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RE: Why some Inconel is magnetic and others are not
http://www.specialmetals.com/
RE: Why some Inconel is magnetic and others are not
RE: Why some Inconel is magnetic and others are not
I think EdStainless was trying to indicate that Alloy 600 is not ferromagnetic at ambient/room temperature and above. Unless your application is intended for cryogenic applications, then neither Alloy 600 nor Alloy 718 should exhibit magnetism. If you review the datasheets from Special Metals or one of the other producers of these alloys, they should reference the Curie point/temperature. I am not expert enough in metallurgy of nickel-based alloys to address how alloy content affects magnetism, but I would assume for a given microstructure (single-phase solid solution, multi-phase precipitated structure, etc.) the higher the Fe content the higher the Curie temperature.
RE: Why some Inconel is magnetic and others are not
You'll also note the permeability you mentioned was 1.010, hardly over 1. That's at room temperature, and means that you get an increase in an applied magnetic field of 1%, not really enough to be ferromagnetic.
RE: Why some Inconel is magnetic and others are not
although this is off topic it still some what relates. The difference in magnetic properties is due to the structure of the material at room temperature. The structure is due to (in most cases) the chemistry and thermal processing of the steel.
Nickel is added to stainless steel to stabilize the austenitic phase. Most 300 series stainless steels contain sufficient amounts of nickel so the structure is austenitic at room temperatures.
300 series stainless steel (also know as Austenitic stainless steel) has "higher" nickel contents and consists of a single phase, (austenite) which is non-magnetic.
Most 400 stainless steels have "lower" nickel contents and have a martensitic or ferritic structure (both of which are magnetic).
Does the above apply as well to high nickel alloys. Is it possible that 2 pieces of 718 Alloy based on how it was processed could create/ destroy magnetisim.
RE: Why some Inconel is magnetic and others are not
Most of these high Ni alloys will not become magnetic under any room temperature. If they do it usually means serious trouble, such as carborization.
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RE: Why some Inconel is magnetic and others are not
RE: Why some Inconel is magnetic and others are not
INCONEL alloys should not exhibit magnetic properties ... they are non-magnetic. The only time I have known of INCONEL alloys to be magnetic is after long exposure in a severely carburizing atmosphere such that all the surface chromium is combined with carbon and effectively removed from the metallic matrix. But under normal conditions, all INCONEL alloys should be non-magnetic. If you have a product that is supposed to an INCONEL product and it is magnetic, I would suggest that you have it analyzed to verify its identity.
RE: Why some Inconel is magnetic and others are not
The phase stability in cold work is related to their high temp phase stability.
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RE: Why some Inconel is magnetic and others are not
If one starts with pure nickel, and progressively alloys it with more and more chromium, it goes from being magnetic at room temperature, to being non-magnetic.
The same is true of cobalt. Common high temperature alloys based on cobalt, e.g. Haynes 188 & 556, L-605, have sufficient Cr in them to be non-magnetic at room temperature.
The most common reason for a piece of Inconel alloy 600 (UNS N06600, nominal 76%Ni 15.5%Cr bal Fe) to be magnetic is, as has been said, that it has been carburized. Carburization forms chromium carbides, removing Cr from the matrix. Once enough Cr is occupied being a carbide, the Ni matrix becomes low enough in Cr to be magnetic at room temperature.
Hot corrosion from various alkali metal salts also can make Inconel 600 magnetic. In this case the Cr selectively oxidizes and not only becomes a chromium oxide, or alkali metal chromate, it may be physically removed from the chunk of metal in question.
The same thing happens to the common heat resistant alloy RA330 (UNS N08830), mominal 35%Ni 19%Cr 1.2%Si 1.5%Mn balance iron. It has long been practice amongst heat treaters to check their alloy fixturing with a pocket magnet. If the metal is strongly magnetic, it cannot be weld repaired, for one reason or another. Carburization makes the metal too brittle to weld without base metal cracking. Hot salt corrosion physically penetrates the metal with salt & makes weld repair both unpleasant and ineffective. If magnetic, just sell the fixture as scrap & buy a new one.
I never did catch why you cared that your 600 alloy was magnetic, or what it had been used for?
RE: Why some Inconel is magnetic and others are not
RE: Why some Inconel is magnetic and others are not
RE: Why some Inconel is magnetic and others are not
Mate45, There are a number of the Ni based alloys that become slightly magnetic after aging because of the slight change in matrix chemistry and the associated shift in CP.
Most common alloying elements lower the CP of Fe and Ni. The only exceptions that I know of are Mn in Ni and V in Fe, these raise the CP.
There are a lot of common alloys and compounds that we think of as nonferromagnetic that at common cold temperatures are ferromagnetic. I have seen this mess up more than one application.
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RE: Why some Inconel is magnetic and others are not
I had the following experience about 20 years ago when I was a construction superintendent at a shipyard:
The ship's Damage Control Assistent would go around with a small magnet to ensure ferrous fasteners were not used in the firemain system which had CuNi piping, bronze valve, and should have monel 400 NiCu fasteners.
He found his magnet had attraction to some of the fasteners, and got very upset, while I was amused. I convinced the yard to remove a few of these fasteners with the DCA standing there, I handed the fasteners to the DCA and had him re-check them with his magnet. There was no NO attraction. I had the fasteners reinstalled and retorqued, and they were now weakly attracted to the magnet.
Real story, and a very good example of stress affecting magnetic properties.