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mekilljoydammit
Jan 28, 2016

Me have motors that scream to 10,000rpm. Me have more cars than Pick and Pull

OK, crash course in metallurgy. There's two basic types of stainless steel, austenitic and martensitic. Austenitic is very corrosion resistant and not magnetic; it's also not very hard. They're alloys like the 300 series (304, etc) stainless. Martensitic is less corrosion resistant and are at least kind of magnetic if not as magnetic as some carbon steels, an example alloy is 440C but there's lots of others.

Any proper stainless kitchen knife will be martensitic stainless.

edit: Or true enough for the purposes of explaining.

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fart simpson
Jul 2, 2005



Lipstick Apathy

All of my stainless steel knives are magnetic.

AVeryLargeRadish
Aug 19, 2011

WolfDad is Best Dad.


mekilljoydammit already said it but yeah, any actual knife steel is magnetic enough to be used with magnetic knife holders, the only time I see austenitic steel used in good knives is if they are using cladding, but knives clad in soft steel are still magnetic enough to be used with magnetic knife holders because of the core steel that actually forms the edge of the knife is plenty magnetic enough on its own.

Zorak of Michigan
Jun 10, 2006

Waiting for his chance

Conclusion: the message is not "stainless knives do not stick to magnets," but, "if your knife is not sticking to a magnet, it is probably made from the wrong type of stainless steel, and you should replace it with a good knife."

Steve Yun
Aug 7, 2003

I
ANALYZE
CARTOONS


Grimey Drawer

I have several speed openers from Winco, some have STAINLESS STEEL stamped on them and they don't stick to magnets, some say 301 and stick to magnets.

Magnets on speed openers is great because you can stick them on your refrigerator door

totalnewbie
Nov 13, 2005

I was born and raised in China, lived in Japan, and now hold a US passport.

I am wrong in every way, all the damn time.

Ask me about my tattoos.


301 stainless is austenitic but is also high work-hardening. Austenitic stainless steels can gain magnetism through work-hardening.

This is due to partial transformation of austenite in the annealed condition to martensite after strain.

If you stick it in the oven during its self-clean cycle (or an 800 C furnace if you've got one) you can probably anneal it and make it lose its magnetism.

301 stainless is a natural choice for your speed opener because you want something that's relatively hard but minimize heat treat for hardness. Work hardening is a good process to achieve this because you'll roll out your plates to make plates of the correct thickness, but 301 retains enough ductility to be stamped or otherwise formed into the final shape.

But 301 stainless hardness tops out at 40ish HRC while 420 stainless can achieve up to 50 with proper heat treat, etc. You sacrifice corrosion resistance in the 420 but you don't need all that much corrosion resistance in a knife (against water, and mild acids is really what you need, especially if you keep your knives clean and don't let food sit on it).

Something like a 440C is even better for hardness, with 60HRC achievable in those.

But you can hit even higher hardnesses by switching away from stainless steels altogether, though I'm not really sure what steels are used in carbon steel or if any tool steel knives exist (maybe/probably?).

totalnewbie fucked around with this message at Apr 11, 2018 around 18:16

Steve Yun
Aug 7, 2003

I
ANALYZE
CARTOONS


Grimey Drawer

Most mismatched username/post combo

mekilljoydammit
Jan 28, 2016

Me have motors that scream to 10,000rpm. Me have more cars than Pick and Pull

totalnewbie posted:

But you can hit even higher hardnesses by switching away from stainless steels altogether, though I'm not really sure what steels are used in carbon steel or if any tool steel knives exist (maybe/probably?).

A lot of tool steels ("stainless" or not) get used for higher end pocket knives and stuff. Good points on work hardening with 300-series steels - I was trying to give a high-level, pre-coffee overview.

SymmetryrtemmyS
Jul 13, 2013



totalnewbie posted:

301 stainless is austenitic but is also high work-hardening. Austenitic stainless steels can gain magnetism through work-hardening.

This is due to partial transformation of austenite in the annealed condition to martensite after strain.

If you stick it in the oven during its self-clean cycle (or an 800 C furnace if you've got one) you can probably anneal it and make it lose its magnetism.

301 stainless is a natural choice for your speed opener because you want something that's relatively hard but minimize heat treat for hardness. Work hardening is a good process to achieve this because you'll roll out your plates to make plates of the correct thickness, but 301 retains enough ductility to be stamped or otherwise formed into the final shape.

But 301 stainless hardness tops out at 40ish HRC while 420 stainless can achieve up to 50 with proper heat treat, etc. You sacrifice corrosion resistance in the 420 but you don't need all that much corrosion resistance in a knife (against water, and mild acids is really what you need, especially if you keep your knives clean and don't let food sit on it).

Something like a 440C is even better for hardness, with 60HRC achievable in those.

But you can hit even higher hardnesses by switching away from stainless steels altogether, though I'm not really sure what steels are used in carbon steel or if any tool steel knives exist (maybe/probably?).

Tool steel and carbon steel knives are pretty common up to 63HRC or so, 65+ in some extremely well tempered knives. ZDP189 knives are getting more common for instance, and offer high hardness (on par with Blue Super or White #2) along with good durability (comparable with or better than VG10). Tool steels offer the best of both worlds, but the price is accordingly higher.

FordCQC
Dec 22, 2007


This is a highly rated sharpener that's on sale at Amazon: https://www.amazon.com/ChefsChoice-...uct_top?ie=UTF8

Anyone used this or a similar model? Would you recommend it?

Chemmy
Feb 4, 2001



Those things gently caress up your knives.

AVeryLargeRadish
Aug 19, 2011

WolfDad is Best Dad.


FordCQC posted:

This is a highly rated sharpener that's on sale at Amazon: https://www.amazon.com/ChefsChoice-...uct_top?ie=UTF8

Anyone used this or a similar model? Would you recommend it?

Pull through sharpeners rip apart the edge of the knife, by mangling the edge it basically makes the knife finely serrated, but the knife will dull in a few minutes of use afterwards because the torn up edge breaks down very quickly. If you want something simple and hard to screw up I would go with a ceramic rod, though eventually any knife needs a proper resharpening.

totalnewbie
Nov 13, 2005

I was born and raised in China, lived in Japan, and now hold a US passport.

I am wrong in every way, all the damn time.

Ask me about my tattoos.


mekilljoydammit posted:

A lot of tool steels ("stainless" or not) get used for higher end pocket knives and stuff. Good points on work hardening with 300-series steels - I was trying to give a high-level, pre-coffee overview.

Oh for sure, but people love to generalize (e.g. "magnetic = ferritic = hard!") so I really wanted to steer people away from that generalization. Non-magnetic knives are probably guaranteed crap, though.

SymmetryrtemmyS posted:

Tool steel and carbon steel knives are pretty common up to 63HRC or so, 65+ in some extremely well tempered knives. ZDP189 knives are getting more common for instance, and offer high hardness (on par with Blue Super or White #2) along with good durability (comparable with or better than VG10). Tool steels offer the best of both worlds, but the price is accordingly higher.


Yeah, I meant I don't know which grades of those particular steels are used. It's annoying that the knife industry hides their compositions behind proprietary steel grades because it makes it difficult to judge which knives are even worth testing for the high end stuff. Also, there's so much dependence on heat treat, etc. that maybe it's not even worth worrying about it and the real test should just be microhardness testing on the blade. That said, I'm not entirely confident in the ability of knife reviewers to properly assess the hardness of knife blades, as you really want to test the knife edge (not the bulk of the blade), but microharness testing is sensitive to specimen preparation, etc that people who aren't familiar (or aren't in a qualified lab) wouldn't necessarily know or be able to do properly.

For example, see here for an article about proper microhardness testing of cutting blades: https://www.qualitymag.com/articles...ardness-testing

Steve Yun posted:

Most mismatched username/post combo

I know a few things. Just a few.

totalnewbie fucked around with this message at Apr 12, 2018 around 15:09

No Wave
Sep 18, 2005

Yogg-Saron fan #1


FordCQC posted:

This is a highly rated sharpener that's on sale at Amazon: https://www.amazon.com/ChefsChoice-...uct_top?ie=UTF8

Anyone used this or a similar model? Would you recommend it?
The electric chef's choice models are quite nice, though quite expensive. Don't have any experience with non-electrics.

FordCQC
Dec 22, 2007


AVeryLargeRadish posted:

Pull through sharpeners rip apart the edge of the knife, by mangling the edge it basically makes the knife finely serrated, but the knife will dull in a few minutes of use afterwards because the torn up edge breaks down very quickly. If you want something simple and hard to screw up I would go with a ceramic rod, though eventually any knife needs a proper resharpening.

Good to know. I actually have access to professional knife sharpening at a reasonable price, but the turnaround is a little long for my taste. I was hoping to find an easy in-home solution but this is probably one of those things you can't really shortcut I guess.

Submarine Sandpaper
May 27, 2007

ASK ME ABOUT HOW I GHOULISHLY CELEBRATE THE DEATH OF CHILDREN TO TEACH THEIR PARENTS "A LESSON"


Grab like a king 800 from amazon for ~20 bucks and use it twice a year. It won't work well for a major edge repair but is fine enough to not need another stone for a generic kitchen knife.

mekilljoydammit
Jan 28, 2016

Me have motors that scream to 10,000rpm. Me have more cars than Pick and Pull

totalnewbie posted:

Yeah, I meant I don't know which grades of those particular steels are used. It's annoying that the knife industry hides their compositions behind proprietary steel grades because it makes it difficult to judge which knives are even worth testing for the high end stuff. Also, there's so much dependence on heat treat, etc. that maybe it's not even worth worrying about it and the real test should just be microhardness testing on the blade. That said, I'm not entirely confident in the ability of knife reviewers to properly assess the hardness of knife blades, as you really want to test the knife edge (not the bulk of the blade), but microharness testing is sensitive to specimen preparation, etc that people who aren't familiar (or aren't in a qualified lab) wouldn't necessarily know or be able to do properly.

For example, see here for an article about proper microhardness testing of cutting blades: https://www.qualitymag.com/articles...ardness-testing

What's your industry? I'm a mechanical engineer doing testing stuff in small engines, but knives are interesting to me.

You're completely right about some of the "proprietary" grades, but truth to tell if you do some digging, most of the really high end knife makers are using off-the-shelf grades. A lot of the CPM tool steels are popular for various uses - some of the blends may be proprietary to Crucible but they publish heat treat guides. If you're know about microhardness testing and stuff, I'm willing to bet that you know where to dig for alloy composition - Rockwell C around 60-62 after tempering, various carbide forming alloying elements help with wear resistance, some balance to avoid too low of toughness. And yeah, heat treat is going to be a bugaboo... some of the steels that people are trying to make knives out of end up with such a fiddly heat treat schedule that it's probably pointless.

It's fun to figure out though.

totalnewbie
Nov 13, 2005

I was born and raised in China, lived in Japan, and now hold a US passport.

I am wrong in every way, all the damn time.

Ask me about my tattoos.


mekilljoydammit posted:

What's your industry? I'm a mechanical engineer doing testing stuff in small engines, but knives are interesting to me.

You're completely right about some of the "proprietary" grades, but truth to tell if you do some digging, most of the really high end knife makers are using off-the-shelf grades. A lot of the CPM tool steels are popular for various uses - some of the blends may be proprietary to Crucible but they publish heat treat guides. If you're know about microhardness testing and stuff, I'm willing to bet that you know where to dig for alloy composition - Rockwell C around 60-62 after tempering, various carbide forming alloying elements help with wear resistance, some balance to avoid too low of toughness. And yeah, heat treat is going to be a bugaboo... some of the steels that people are trying to make knives out of end up with such a fiddly heat treat schedule that it's probably pointless.

It's fun to figure out though.

I work for an automotive supplier but have a degree in materials engineering.

But I'm an engineer, so things like doing HRC testing on the blade bulk rather than the knife edge annoys me, because it leaves open the possibility of poor heat dissipation/cooling during grinding causing your edge to lose a lot of the hardness it would otherwise have. While I'm willing to be that it's NOT the case that the edge is significantly softer than the bulk material, I hate leaving open that possibility, right?

FYI for others: Grinding causes heat and insufficient cooling means the edge of your blade gets hot; hot = transformation of hard martensite to soft austenite. Therefore, it's possible for bulk blade to be harder than the edge.

Stangg
Mar 17, 2009


A group of friends clubbed together a while back for my 30th and got me a set of Pro Cook X100 knives (3.5in paring knife, 5in utility knife, 8in chefs knife) and was wondering what the general consensus is on how good they are. From my own research hardened steel is long lasting but quite brittle, does this mean that I'm at more risk of messing them up trying to sharpen on stones by myself?

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Submarine Sandpaper
May 27, 2007

ASK ME ABOUT HOW I GHOULISHLY CELEBRATE THE DEATH OF CHILDREN TO TEACH THEIR PARENTS "A LESSON"


You're good, it's vg10. It's just brittle in the sense that you shouldn't chop bones or the like with it.

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