magnetic material 1

[verdon]

Is there a list of materials that are magnetic. When I test a material with a magnet, what does it tell me. I know it has to contail Fe Ni or Cobalt but how for instance for a CuNi alloy when will it respond to a magnet, CiNi90/10 or CuNi70/30 etc. (and how for naval brass/ muntz metal etc). How does the magnet behave with stainless steel (304, 316 etc).
I'm mainly interested in carbon steel, stainless steel and copper alloys.
Thanks for any response.

 

[hacksaw]

generally not considered a reliable method for distinguishing alloys

 

[verdon]

But are there thumb rules?

 

[EdStainless]

Yes, but the rules are different for each alloy group. You also need a way to measure 'how magnetic' something is.
The simplest system is the Severn Gage. It is a simple magnet lift off measurement that is proportional to permiability.
In austenitic stainless the values should be very low, but they will be higher in unannealed welds. You will also see some mag in cold worked material.
In Cu/Ni you should only see mag if the heat treatment was wrong.
We can talk more if you are interested.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[verdon]

Thanks, I will check the Severn Gage.
What is permiability, is it "how strong a metal reacts to a magnet"?
I know that for CuNi90/10 we can measure the Ferrite number (for us it should be below 2,5 otherwise our Eddy Current tester won't function, it will give a very unstable readout). Is that what you are also referring to with wrong heat treatment?
And I'm told that CuNi70/30 cannot be Eddy Current tested but why is not clear to me, it may not have to do with magnetism.
Do you know if nodular and grey cast iron are magnetic? (I don't have samples so I cannot test on forehand).
Many questions but if some are answered I allready happy.

 

[EdStainless]

Irons, cast irons and carbon and alloy steels are all stongly magnetic.
You can easily ET 70/30 by using a saturation field around your test coils. This is a common practice with ferrous alloys.
But 70/30 should not be magnetic at all. I thought that these alloys were nonmagnetic as long as the iron was in solution. When iron rich precipitates formed at the grain boundaries they became slightly magnetic. I am looking for a reference.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[metengr]

Here is some background information on Cu/Ni alloys from copper.org. There is information regarding ferromagnetic behavior related to nickel content above 68.5 w/%, and the solubility of iron. I did not see anything related to improper heat treatment.

http://www.copper.org/applications/cuni/txt_DKI.html#1.3

 

[EdStainless]

I have found a couple of references that give mag. perm. for rapidly cooled material as <1.02 and for slow cooled as 1.2. I would expect this to be single phase (non-magnetic) material. Otherwise the Fe would not help strengthen the alloy and improve surface film toughness.
It may be that the corrosion effect is only in specific environments. I'll keep looking.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[verdon]

Thanks. I've been away so now only i'm reading your reply. I will check the reference.