Stainless steel and magnets

C

Chrome Horn

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Aug 26, 2009
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Should all stainless steels be attracted by a magnet to some extent?

There's a pretty good draw with what knives I have with S30V, 154CM, M390 and others. I ask because I just got a stainless steel sling shot that exhibits almost no attraction. There are a lot of cheap zinc alloy knockoffs which can be extremely dangerous, breakage and facial injuries have occurred. Kinda worried.
 
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There's some stainless steels that aren't magnetic. IIRC 300 series stainless steels aren't. I have absolutely no idea why, but there's gotta be some scientific reason a metal that's primarily iron doesn't attract a magnet. You see this a lot in restaurant kitchens with tables/counters/whatnot. Stainless steel surfaces that you could soak in salt water for a decade and it won't rust. Weak magnetic attraction, or none at all. I'm pretty sure that any steel that's of cutlery grade (quality cutlery anyway) will attract a magnet.
 
I looked this up once, and it's true. Most stainless is not magnetic, it's the manufacturing process and/or treatment that changes something on the molecular level.
My stainless slingshot and water bottles aren't magnetic, well the slingshot is barely.
I don't think it's a judge of quality, maybe more of a circumstance.
 
300 series stainless is non-magnetic, but not non-ferrous as they have small amounts of iron but are mainly high percentages of nickel and chromium. If you have a powerful enough magnet you will feel a slight attraction. No good for knives, can't be hardened due to lack of iron. 400 series has enough iron to be very magnetic while having enough chromium for corrosion resistance. Other stainless alloys have high corrosion protection but have enough iron to be magnetic. I think the alloys like S30V, 60, 90 etc group and H1 have corrosion protection due to the addition of nitrogen, vandium, niobium and other good stuff. I am not sure of the details but there are many here who are. They will probably chime in soon.
 
Has to do with Austenite and Martensite formation during the heat treatment process.

http://en.wikipedia.org/wiki/Austenite

http://en.wikipedia.org/wiki/Martensite

Basically, Austenite is non-magnetic while Martensite is magnetic. Martensite formation is the change in molecular structure in the steel that is only achieved at certain temperatures and pressures, and which produces hardened steel.

Or in a broad generalization, hardened steel will be more magnetic than non-hardened steel.
 
SOLEIL said:
300 series stainless is non-magnetic, but not non-ferrous as they have small amounts of iron but are mainly high percentages of nickel and chromium. If you have a powerful enough magnet you will feel a slight attraction. No good for knives, can't be hardened due to lack of iron. 400 series has enough iron to be very magnetic while having enough chromium for corrosion resistance. Other stainless alloys have high corrosion protection but have enough iron to be magnetic. I think the alloys like S30V, 60, 90 etc group and H1 have corrosion protection due to the addition of nitrogen, vandium, niobium and other good stuff. I am not sure of the details but there are many here who are. They will probably chime in soon.
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While not completely true, the high alloy content steels will have a lesser quantity of Iron in them. Thus, you are right that these HAC steels would be less magnetic than other steels with fewer alloying element concentrations.

The difference in Iron content between 300 and 400 series isn't great enough for any appreciable difference to be seen magnetically, assuming they have the same ratio of non-Austenite phase Iron in them.

It's just that you don't often see people heat treating 300 series.
 
As Cynic states it depends on the crystal structure. There are three structures in steel , austenite, martensite and ferrite. Only martensite and ferrite are magnetic.Good knives will be martensitic .Table knives will be austenitic. Stainless pots are normally austenitic though some are ferritic for use with magnetic 'burners' .
 
316 and 314 stainless have almost no magnetic attraction. All 400 series has a very high magnetic attraction due to it's higher iron content. 300 series can not be heat treated well due to it's low iron content. Looking at scrap yard/recyclers designations 300 series and other stainless that is almost non-magnetic is listed as non-ferrous. It really isn't as it does contain small amounts of iron. 300 series just has a very low iron content.
 
Cynic2701 said:
Martensite formation is the change in molecular structure in the steel that is only achieved at certain temperatures and pressures, and which produces hardened steel.
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I think it mostly has to do with how rapidly the steel is cooled. If it is cooled rapidly, the carbon can't diffuse fast enough and equilibrium pearlite doesn't have a chance to form, so martensite forms instead.
 
Does this explanation from Answers.com have truth to it?

Some stainless steel is magnetic, and some is will exhibit only an extremely weak response to a magnetic field. It is the austenitic stainless steels that are generally thought of as being nonmagnetic. Let's review a couple of things to get to our answer.

The primary metal alloyed into stainless steel, the one that combines with the iron (steel, actually, since there is carbon included with the iron) is chromium. The presence of sufficient chromium in stainless steels allows these metals to resist corrosion. Note that the stainless steels are stain resistant, and not completely stainless. Anyway, the chromium can be thought of as a "glue" in the metal matrix that prevents magnetic domains in iron from aligning themselves with an external magnetic field.

If the magnetic domains in stainless steel, that is, the iron in this alloy, was "free to rotate a bit" within the metallic crystal structure, then the steel would be capable of conducting magnetic lines of force or of becoming magnetized. As it is, in many of the austenitic stainless steels, magnetic domains, which do exist, cannot rotate to align themselves to conduct magnetic lines of force. Nor can these alloys be magnetized to any appreciable degree. We also must note that cold working like drawing or swaging can "free" magnetic domains and cause the alloy to then exhibit ferromagnetic properties.
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This sounds like a question to ask mormon.org
 
Planterz said:
This sounds like a question to ask mormon.org
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"Fuckin' magnets, how do they work?" :D

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Tsujigiri, you might want to clean the language up a bit for General.

Noctis3880 said:
Call me a humorless bastard, but I don't get that one:confused:.
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The "magnets" thing is an internet meme. mormon.org has a chat room where missionaries are available to answer questions about LDS. Naturally, it's a popular target for trolls, who instead of asking them about mormonism, they ask them how magnets work, or whatever. They do it "for the lulz".

Fair warning, neither link above is particularly safe for work or around young kids.
 
I use magnetic strips from kitchen devices to display my knives. i cover them with black fabric so as not to scratch blades.

I can tell you:

440c
s30V
S90V
Elmaxx
AUS 8/10
VG10
CPM 154
CM154
M4
D2

stainless blade steels all stick to magnets well in this fashion.
 
We used to use a magnet as a quick way to determine if a SS tank or piece of equipment was made out of 316 SS or 304 SS. As Soleil said, the 316 series is virtually non magnetic.

You may want to check out this forum for slingshots if you haven't already looked at it. I've made a couple of board cut sling shots just for fun.


ric
 
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Not entirely off topic, but 316L is some serious stuff. All of the stainless steel control panel housing on the offshore oil and gas platforms are made of that and like someone had posted earlier it is for all practical purposes immune to corrosion from water, salt water and some chemicals and is apparently also pretty tough. The stuff is sick, too bad can't be hardened for blade material.
 
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