'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.

[hampco]

A former employer once told me: "There are two things to know about stainless steel: it aint stainless and it aint steel."

[e-RICHIE]

A former employer once told me: "There are two things to know about stainless steel: it aint stainless and it aint steel."

and, according to my opinion, the most overrated and misunderstood material to have ever been added to the menu.

[htwoopup]

A former employer once told me: "There are two things to know about stainless steel: it aint stainless and it aint steel."

Ha, when I was working summers at a boat builder that built 12 meter America’s Cup racing sailboats the grumpy shop foreman made us polish and polish and polish stainless fittings….”They call it stain-less not stain-free, boy”. I wish I could type the accent and anger with which he said it.

[Mark Kelly]

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?

I think it easiest to explain it in terms of Curie temperature.

All ferromagnetic materials have a temperature above which they lose their ferromagnetism and become paramagnetic, discovered by Pierre Curie and named in his honour*. For example in iron this is about 770 oC so if you get ordinary iron red hot it loses its ferromagnetism. It also changes crystal structure to austenite: the two are related, the crystal structure affects the way the electron spins can interact which determines the Curie point. When the iron cools the crystal structure reverts back and it regains its magnetism.

Room temperature austenitic alloys have components (Nickel) that stabilise the austenite so it remains in that state when cooled. Usually you can't heat treat an austenitic alloy because there isn't any phase change on cooling.

If you work harden them the crystal structure changes again.


Caveat: metallurgy has probably changed since I was an aeronautical engineering student in the 70s.





* It has to do with the way electron spins couple to create magnetic moment. Heat disrupts this; I think that's due to electron phonon interaction.

[Mark Kelly]

Addendum too late to edit:

Thinking about it while I made a coffee, saying the crystal structure affects the electron interaction is ass about: the crystal structure is determined by the bonds between the atoms which are mediated by electron interaction.

[Mabouya]

As a buddy of mine at work once told me, "It's called stain LESS, not 'will not ever stain at all.'"

[Chik]

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

Yeah, I think it can heat up a few sausage rolls.

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.

Yeah, well, that makes two of us. Current production should be labelled whether it's induction hob compatible. (I believe All-Clad moved to a 5-layer construction partly for compatibility reasons.) The problem is older equipment that pre-dates induction hobs, like our stuff. We have other older stuff from Mauviel, but fortunately, they work on induction.

In Europe, the market for new cookware that's not compatible with induction hob is disappearing. Even if you look at upmarket suppliers like La Cornue, they're offering induction versions -- even though I think it defeats the point of getting a La Cornue unit.

If you look at any starred restaurant in Europe whose kitchen had been fitted out in the last few years, they are almost invariably equipped with induction hobs, partly for compliance reasons (having gas cookers installed new has become a nightmare from a regulatory standpoint) but also for its significantly lower running costs.

[j44ke]

Yeah, I think it can heat up a few sausage rolls.



Yeah, well, that makes two of us. Current production should be labelled whether it's induction hob compatible. (I believe All-Clad moved to a 5-layer construction partly for compatibility reasons.) The problem is older equipment that pre-dates induction hobs, like our stuff. We have other older stuff from Mauviel, but fortunately, they work on induction.

In Europe, the market for new cookware that's not compatible with induction hob is disappearing. Even if you look at upmarket suppliers like La Cornue, they're offering induction versions -- even though I think it defeats the point of getting a La Cornue unit.

If you look at any starred restaurant in Europe whose kitchen had been fitted out in the last few years, they are almost invariably equipped with induction hobs, partly for compliance reasons (having gas cookers installed new has become a nightmare from a regulatory standpoint) but also for its significantly lower running costs.

There's a kitchen tool district a block from Dehillerin in Paris - roughly Rue Montmartre and Rue Etienne Marcel - that I visited last time to buy pots, and the range of choices was pretty extraordinary, all of them induction compatible. I think there must be an EU requirement that all the pots have to be stamped with the "international symbol" for induction if they are compatible. I asked the gentleman at A. Simon if a particular pot was induction compatible and he said "But of course. They all are. We only sell for induction." Which isn't 100% accurate but accurate enough that he was nearly right.

[Chik]

There's a kitchen tool district a block from Dehillerin in Paris - roughly Rue Montmartre and Rue Etienne Marcel - that I visited last time to buy pots, and the range of choices was pretty extraordinary, all of them induction compatible. I think there must be an EU requirement that all the pots have to be stamped with the "international symbol" for induction if they are compatible. I asked the gentleman at A. Simon if a particular pot was induction compatible and he said "But of course. They all are. We only sell for induction." Which isn't 100% accurate but accurate enough that he was nearly right.

I believe there are, or were, 2 types of induction hobs, so some cookware can be compatible with one but not the other. That said, I think it's unified in the EU, but if you're shopping for other markets, you may want to confirm whether it will work on just one or both.

PS, I should go have a wander through that neighbourhood since I'm in the market for a pair of tongs with non-metallic tips that are not black plastic, which seems harder to find than I had expected.

[j44ke]

I believe there are, or were, 2 types of induction hobs, so some cookware can be compatible with one but not the other. That said, I think it's unified in the EU, but if you're shopping for other markets, you may want to confirm whether it will work on just one or both.

PS, I should go have a wander through that neighbourhood since I'm in the market for a pair of tongs with non-metallic tips that are not black plastic, which seems harder to find than I had expected.

Check TOC or Mora. They have a lot of utensils. Dehillerin might also but it is a bit of an archeology project.

[echappist]

Yeah, I think it can heat up a few sausage rolls.



Yeah, well, that makes two of us. Current production should be labelled whether it's induction hob compatible. (I believe All-Clad moved to a 5-layer construction partly for compatibility reasons.) The problem is older equipment that pre-dates induction hobs, like our stuff. We have other older stuff from Mauviel, but fortunately, they work on induction.

In Europe, the market for new cookware that's not compatible with induction hob is disappearing. Even if you look at upmarket suppliers like La Cornue, they're offering induction versions -- even though I think it defeats the point of getting a La Cornue unit.

If you look at any starred restaurant in Europe whose kitchen had been fitted out in the last few years, they are almost invariably equipped with induction hobs, partly for compliance reasons (having gas cookers installed new has become a nightmare from a regulatory standpoint) but also for its significantly lower running costs.

I'm surprised that not all of your cookware is from Stabu/ Le Creuset. Issue solved, as cast iron is ferromagnetic ;).

That was completely tongue-in-cheek, of course. Now I expect to hear that even Le Creuset is merely mid, and those in the know (like yourself) use something even better.