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1:10 am
March 21, 2011
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Can stainless steel be tested for hardness on a grinder the same way as mild or high carbon steel? What spark patterns do the various hardnesses of stainless produce at the grinder?
1:37 am
March 18, 2010
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To some extent you can check hardness on a grinder, but are you thinking of the grinder "spark" test? That is an indicator for carbon or alloy content. Stainless can be pretty soft and still difficult to grind. So I guess it would actually be a test for abrasion resistance.
“There are painters who transform the sun into a yellow spot,
but then there are others who, with the help of their art and their intelligence,
transform a yellow spot into the sun.” ~ Pablo Picasso ~
2:43 am
March 21, 2011
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OK, then a follow up question.
How do I know if a piece of stainless steel rod is hard enough to be useful in knife making? I picked up a piece at the scrapyard today. 1-1/8" x 36", they wanted $10 for the piece so I grabbed it. Can I test it by striking it with a cold chisel?
12:57 pm
May 13, 2010
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How about a file? Although just because it is not hard now does not mean it can or cannot be hardened
1:09 pm
March 21, 2011
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Yeah, I'll quench a chunk and see how it files.
1:16 pm
Odds are it's not a hardenable grade of stainless, or atleast not for knifes. That and are you sure it's stainless and not chromed?
Try air hardening a piece, then oil, then water but there really isn't any kind of water hardening stainless for knifemaking. Stainless also doesn't like to throw sparks like carbon.
1:35 pm
NWBA Member
April 22, 2010
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the only real way to know is either to pay for a test, or actually buy the right stuff in the first place.
Even in 300 series, which is NOT hardenable, there are at least 3 different very common alloys, and another half dozen possibles that show up once in a while.
Figure 2 dozen stainless alloys out there in common circulation.
If you are going to invest hours and hours making a knife, buy a ten dollar piece of the right stuff first.
90% chance, though, that its 304. Junkyard stainless almost always is.
Which will workharden, especially when you dont want it to, but actually anneals if you heat and quench it. And is NOT air hardenable, oil hardenable, or water hardenable.
440C, which is probably what you want, is literally ten bucks-
http://www.texasknife.com/vcom.....cts_id=333
Be aware, though, that almost no knifemakers heat treat this themselves. Its tricky, and requires expensive, very controllable heat treating equipment. Almost everybody sends it out to pros to be heat treated. Of course, you CAN do it. Be prepared to lose a fair amount in your learning curve, and to spend a reasonable amount on PLC controlled heating ovens.
5:59 am
March 21, 2011
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Thanks, guys.
I have so much to learn. [Image Can Not Be Found]
3:27 pm
September 7, 2010
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A simple thought; most of the best chef's knives are made from s/s and virtually all those are magnetic, so if a magnet does not stick it probably is'nt suitable.
Ian
6:40 pm
March 21, 2011
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Good idea, Ian. I tested my chef knives and like yours, mine are magnetic. The piece of SS stock in question isn't. So I don't know what I'll do with it. It can sit on the stock pile until I think of something. Maybe I'll heat a chunk of it just to see how it behaves.
7:30 pm
NWBA Member
Board Member
April 26, 2010
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"Martensitic stainless" is magnetic. This includes some of the 400 series, and also the "cutlery steels" like AUS10 or AUS8 or such things. One can magnetize these steels by rubbing them with a magnet - same as mild steel.
"Feritic stainless" is magnetic, but less so. One can only magnetize these steels weakly by rubbing with a magnet.
"Austenitic stainless" is not magnetic. This includes the kind commonly used for body piercings and kitchen pots and table-ware.
No matter where you go... there you are.
8:50 pm
NWBA Member
April 22, 2010
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If its non-magnetic, its almost certainly 3 series, most likely 304.
Which means it will forge just fine, although you have to hit it a bit harder than mild steel- average psi for the tensile strength is 1 1/2 to 2 times as much as A36.
304, heated to cherry red, and then water quenched, anneals to its softest state.
However, its pretty hard to tell the difference between annealed and work hardened unless you are either drilling it, or cold bending it.
9:22 pm
March 21, 2011
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Ries;9980 wrote: 304, heated to cherry red, and then water quenched, anneals to its softest state.
Really? Quenching this stuff softens it? How do you harden it? Quench from yellow?
9:45 pm
NWBA Member
Board Member
April 26, 2010
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Tom Allyn;9981 wrote: Really? Quenching this stuff softens it? How do you harden it? Quench from yellow?
You can work-harden it, like any metal. Or you can make it very very cold. Problem is, once it comes back up to room temperature, it is austenite again. Or maybe that's not a problem - or even an advantage - depending on what we do with it.
"Austenitic" means "made of austenite." "Austenite" is soft-er-ite. 😀 Austenite is what we get when we heat plain-carbon steel or low-alloy steel up above the "transition temperature." The transition temperature for 300 series steels is uber cold.
The 300 series are also magnetic when they are below their uber cold transition temperature. (Not that cold hard magnetic steel is of much use for most of us.:happy:)
No matter where you go... there you are.
11:12 pm
NWBA Member
April 22, 2010
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Essentially, what Lee is saying is - You CANT harden it.
It will work harden, which will destroy your drill bits, but not get it hard enough to use for a decent blade.
300 series stainless is no good for real knives.
It is very tough, hard to bend, and very resistant to weather. But it wont harden, in the temperature range that humans live in.
Toughness is an entirely different characteristic than hardness.
Stainless is used primarily for its corrosion resistance.
NO paint is needed, ever.
Means its great for exterior ornamental metalwork, as you never have to refinish.
4:45 am
September 7, 2010
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To add more washing to the water 310= non magnetic and is considered 'Furnace grade'
i.e. for use in high temp aplications, makes forging trickey:redcarded:.
So if you buy junkjard stuff ya never know what you gonna get.
Ian
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