'Splain stainless steel to me

[Chik]

The thread about convection oven and induction hobs reminded me of something I've been wondering since the spring, which is when induction hobs entered my life. Someone please edumacate me about stainless steel.

We have All-Clad cookware that we've had since the early 90s. All of them work on the induction hob except for one piece: the pasta pot. I confirmed that it's not ferromagnetic because a magnet doesn't stick to it.

I realise that stainless is an alloy and comes in a variety of mixes, but doesn't it always include a fair bit of iron? I can prolly Google this, but where's the fun in that?

Also, what I find striking is that All-Clad used different alloys for different products or simply at different production lots. Despite their claim about their construction being very efficient in terms of heat conductivity, the pasta pot in question was always a bit shit in that regard -- it took ages for the water to boil whether over gas or electric hobs.

Anyway, I'm just mystified by this non-ferromagnetic stainless steel piece.

[Scott G.]

[snip]
Anyway, I'm just mystified by this non-ferromagnetic stainless steel piece.

Made from steel salvaged from a Soviet SSN, have you checked for radiation ?

[Kev inc.]

Is your pasta pot aluminum cored?

[thollandpe]

Two flavors of stainless steel are Ferritic and Austenitic.

Ferritic has a body-centered cubic (BCC) microstructure, like iron. So it's magnetic. No nickel in the alloy so they're usually cheaper.


Austenitic has a face-centered cubic (FCC) microstructure, like aluminum. Non-magnetic, pretty much. Most stainless is this: 304 or 18-8 (18% Cr, 8% Ni), 316 (more Ni).

[Chik]

Is your pasta pot aluminum cored?

They are all 3-layered construction, but I can't remember what the middle is. Prolly aluminium.

Two flavors of stainless steel are Ferritic and Austenitic.

Ferritic has a body-centered cubic (BCC) microstructure, like iron. So it's magnetic. No nickel in the alloy so they're usually cheaper.


Austenitic has a face-centered cubic (FCC) microstructure, like aluminum. Non-magnetic, pretty much. Most stainless is this: 304 or 18-8 (18% Cr, 8% Ni), 316 (more Ni).

Interesting. Thank you.

As an aside, my Reynolds 931 tubing is ferromagnetic. Reynolds say that it's 17% Cr, 4% Ni, and a bit of Cu: https://www.reynoldstechnology.biz/m...s/steel/s-931/ Do you reckon it's ferritic?

[thollandpe]

As an aside, my Reynolds 931 tubing is ferromagnetic. Reynolds say that it's 17% Cr, 4% Ni, and a bit of Cu: https://www.reynoldstechnology.biz/m...s/steel/s-931/ Do you reckon it's ferritic?

Austenite can be made slightly magnetic by cold working. You're stretching my decades-old metallurgy memory (yes I should work on my flexibility) but I think you can heat treat austenite into martensite.

That link says, "931 has a 17% Chromium, 4% Nickel, and Copper content, and is designated a stainless steel. When cold-worked and then aged/welded, this alloy cools to form a fine-grained, tough martensitic structure (precipitate) which offers builders ductile but strong fabrications."

Martensite is a body-centered tetragonal (BCT) microstructure which is a distorted BCC so I think that's why it's magnetic.

PS Will your bike heat up if you put it on your induction cooktop?

[echappist]

Two flavors of stainless steel are Ferritic and Austenitic.

Ferritic has a body-centered cubic (BCC) microstructure, like iron. So it's magnetic. No nickel in the alloy so they're usually cheaper.


Austenitic has a face-centered cubic (FCC) microstructure, like aluminum. Non-magnetic, pretty much. Most stainless is this: 304 or 18-8 (18% Cr, 8% Ni), 316 (more Ni).

Thanks for the post.

Were it not for your post, I wouldn't even begin to suspect that austenitic steel is largely non-ferromagnetic. Blind spots and assumptions. I may very well have bought stainless thinking all of it are compatible with induction.