Re: [Harp-L] How the Turboslide actually works

[Joel Fritz <williemctell@xxxxxxxxx>]

There are two, more or less, families of stainless steel, the 300 series 
(austenitic) and the 400 series(martensitic.)  The 300 series has 
chromium as the principal alloying element and is non-magnetic.  The 400 
series has nickel as the principal alloying element and is magnetic.  
The 300 series is not hardenable by heat treatment while the 400 series 
is.  The 400 series is used for knives, surgical and dental instruments, 
and other applications where greater strength and wear resistance is 
required.  It's not bad stainless, just a different kind.  You don't 
want a knife made from 300 series stainless, trust me.  :) The tradeoff 
is somewhat poorer corrosion resistance than the 300 series.  The 300 
and 400 designations are for steels from mills. Cast steel uses 
different naming conventions.

Oh, if you try your magnet on something like a restaurant sink/counter 
combination made of stainless steel you'll probably find little magnetic 
areas near welds.  This comes from cooling from welding temperature that 
isn't quite rapid enough.  A dead giveaway is rust spots.  Rust will 
only occur where the weld didn't cool rapidly enough.   We have a cheap 
stainless colander with spot welded feet.  It's starting to get corroded 
around the welds.

There, I feel better.  Finally some of my heat treating experience comes 
in handy.  :)

Some of the rare earth metals are magnetic although they need to be 
alloyed with iron to be magnetic at room temperature and above.  You may 
have noticed neodymium magnet speakers, for example.

On a slightly more serious note, I wonder how well harp reeds made from 
17-4 stainless would work.  It hardens to "spring temper" at 900 
degrees.  The advantage would be forming the reeds in the annealed state 
and then hardening them at the relatively low temperature which will 
avoid the distortion that comes with a quench and temper heat 
treatment.  They'd be a bit more expensive than brass reeds.  :)  400 
series stainless has to be heated to 1850 degrees and cooled relatively 
rapidly to harden.  The reeds would come out like potato chips, or more 
accurately, tortilla strips.


On 6/9/2012 12:45 PM, Joseph Leone wrote:
> I'm going to assume the reeds are what 'I' like to call suspicious stainless. Like Dave, I am a MacGiver type. I checked around the house one time back when I was making custom knives. I had been surprised to fine that the stainless that I was working with attracted a magnet. Si I checked in the kitchen and found that 7 out of 8 stainless implements WERE magnetic. Except for out flatware (Ecco), most of my chef's knives attracted a magnet. Some where merely that you could hold the knife in your hand and the magnet would stick with enough flux field to hold the magnet in place. Some were so ignoble that you could hold the MAGNET and the knife would hang there. (To me, that's fairly crappy stainless).
>
> Ok, so I found that stuff coming from Sheffield and the U.S. were the least attractive, but stuff from Denmark, Germany, Sweden, Finland, and Japan were VERY attractive. I saw this as a bummer until I realized that (in actuality) you WANT the knives to have more carbon steel than they do nickel and chrome. Why, you say? Well, very good stainless is hard to sharpen well and when it IS sharp, it also looses it's edge quickly. Carbon steel is hard to sharpen but it HOLDS it's edge. So, in conclusion, lesser stainless is actually better for some applications. Now in this case, I think it was to save money BUT we wind up getting the benefit of this faux paux. OR..Brendan does. lolol
>
> smo-joe
>
> On Jun 9, 2012, at 1:00 PM, Joel Fritz wrote:
>
> > I'm curious how this works since copper alloys are non-magnetic.  :)