On Monday, July 16, 2018 at 8:43:05 AM UTC-4, Ignoramus22929 wrote:
On 2018-07-16, Gunner Asch wrote:
On Sun, 15 Jul 2018 21:28:36 +0100, David Billington
wrote:

On 15/07/18 18:57, Ken Grunke wrote:
Does anyone know what type of stainless steel is generally used for common butterknives? They seem to have the same temper as carbon spring steel, as I can't bend them. Looking for guidelines on heat treating, as I want to hot-forge the handles to make jaw harps, and might have to restore the blade's temper for springiness of the tongue.

Stainless cutlery is generally 18 -8, 18% Cr, 8% Nickel so 304. It can't
be heat treated to harden it only by mechanical working.


Correct.

Check them with a magnet, as most cutlery knives, in my experience, were 400 series
stainless and magnetic as iron.

That won't tell you what you think it does. This simple question actually is, unfortunately, pretty complicated to answer.

Once 300-series stainless has been heavily cold-worked, as in forging or coining, it's very magnetic. All of my flatware is highly magnetic and it's all 300-series steel.

400 series is used mostly for cutlery that needs to take and hold an edge, not for table flatware.It's less rust-resistant. Leave a 400-series knife in lemon juice or vinegar for a day or two, and you'll probably see what I mean.

Kitchenware manufacturers often use old steel designations, which complicated the issue. However, for out purposes, their 18-8 and 18-10 designations are equivalent to 300-series austenitic stainless. Almost all of your flatware is made of these grades. But put a magnet on them -- most of them are magnetic from the cold working. (Technically, they are "paramagnetic." They're attracted to a magnet, but they can't be magnetized themselves to any substantial degree.)

The only piece of 300-series stainless in my kitchen drawer that is NOT magnetic is an ice cream scoop. My guess is that it was annealed somehow, because the scoop has a pretty deep draw in it and thus is quite heavily cold-worked.

While we're at it, cutlery manufacturers sometimes use the designation 18-0.. That's 400-series stainless, which is quite magnetic. But they don't use it for flatware.

Ken may have drawn some incorrect conclusions from what we've said. For example, making a simple bend isn't going to contribute much to work-hardening his stainless. Also, heating to 400 deg F won't "anneal" his steel. If you soak it at the temperature for an hour or so, you probably will get some stress relief. But it takes a temperature over 1000 deg. F (aroun 1400, I think) to anneal 300-series stainless.

--
Ed Huntress