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This is my first foray into Stainless, might as well since I got the digital kiln...

First heat treat went well, only complaint is both blades have a bow in them.  The stock I bought was slightly bent in transport (I guess), but I straightened the two pieces I started with.

My problem is the following, while doing my "research" I'm sure I read about plate-quenching 14C28N, so at considerable expense I went and bought two suitable 30mm plates.

On the day I went to check the exact temperatures and hold times, and all I can find on the Sandvik site mentions oil quench.....?

I might be confused, most likely am, but since I found out that without a cryo cycle I won't get this steel over 60 HRC, so I was wondering if a plate quench might not be sufficient and solve some other problems as well.......

If any of you regularly use this alloy, I would appreciate some pointers or advice.

Thanks

Gerhard

PS: going by the hand sanding the two blades are plenty hard.....and I got them straight.

Edited by Gerhard
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I haven't used it (and hopefully never will, or any stainless for that matter).  So I can't help with personal experience.  

But I trust you were looking at this page from Sandvik.  

How the hardening parameters affect the product properties

  • Too high hardening temperature gives low hardness and bad wear resistance due to excessive content of retained austenite.
  • A low hardening temperature gives low hardness and reduced corrosion resistance.
  • Too long holding time at the optimal hardening temperature increases the amount of retained austenite and lowers the hardness.
  • Too short holding time at the optimal hardening temperature has the same effect as low austenitizing temperature.
  • The maximum hardness will be obtained at a retained austenite content of about 15%.
  • Deep freezing, i.e. cooling to below room temperature, increases the hardness by about 1–2 HRC.
  • With deep freezing, the highest possible hardness will be achieved by increasing the hardening temperature. Read more in the Sandvik hardening guide.
  • High cooling rate after hardening is necessary to avoid brittleness and reduced corrosion resistance. 600°C (1112°F) should be reached within 1–2 minutes and room temperature within 30 minutes.
  • Rehardening is generally not recommended as it will not give optimal product properties.
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11 hours ago, Jerrod Miller said:

I haven't used it (and hopefully never will, or any stainless for that matter).  So I can't help with personal experience.  

But I trust you were looking at this page from Sandvik.  

Indeed.

I treated a 5160 blade first so the kiln was at about 830C when they went in, hoping that meets the 600C under 2 minutes requirement......thing blades so.....

Worked on a timer exactly on spec, my blade thickness is between their last two options so I soaked for 17 minutes IIRC.

@Jerrod Miller I would appreciate even a guess from you.....

Would chucking the blades in the deep freeze actually help or are we talking dry ice type situation here?

Considering I'm quenching in garden variety Canola oil, do you think the plate quench is worth a try?

Unfortunately no easy access to a Rockwell tester....

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21 hours ago, Jerrod Miller said:

I haven't used it (and hopefully never will

Why is that? If I'm ever going to use stainless, this seems like the stainless steel that behaves closest to carbon steel. Easy to grind and polish, low carbide volume, fine grain, good hardness, takes a keen edge and excellent toughness. Of course, this is all based on feedback I've read...

@Gerhard Gerber

Most makers use plate quench on this steel because it has a tendency to warp. An oil quench would only make it worse.

Edited by Joël Mercier
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Gerhard,

The freezing is to convert the retained austenite.  As indicated from Sandvik, your soak temperature and cooling rate will determine the amount of retained austenite.  The more you have, the colder you are likely to need to go to convert it all.  I guess the real question is whether or not that 1-2 HRC and a little more impact toughness is worth the effort to you (austenite is not good with impact toughness).  Cooling to 600 C in a minute should be pretty easy.  You could probably even throw it between your plates and toss the assembly in the oil to cool.  

Joël,

The applications where stainless is pretty much a requirement are very few.  Pretty much just salt water environments (boaters and divers).  Given that situation, knives are at a greater risk of being lost (overboard).  As such, all the complications in production do not seem worth the effort for a custom knife, and those that are willing to pay for it won't be asking me -- they'll find someone MUCH better at knife making.  I'd recommend those applications to at least consider the knife as a consumable.  Buy a decent production knife, and when needed, replace it.  Any knife I make I expect to be well cared for, so simpler alloys will serve nicely.  

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4 hours ago, Joël Mercier said:

Why is that? If I'm ever going to use stainless, this seems like the stainless steel that behaves closest to carbon steel. Easy to grind and polish, low carbide volume, fine grain, good hardness, takes a keen edge and excellent toughness. Of course, this is all based on feedback I've read...

@Gerhard Gerber

Most makers use plate quench on this steel because it has a tendency to warp. An oil quench would only make it worse.

You sure you're not thinking of 13C26, Sandvik's version of Uddeholm AEB-L?  That's the one I have my eye on for those things that absolutely positively have to be stainless.  Devin Thomas loves the stuff, which is recommendation enough for me.  Of course, gotta get a heat-treat kiln first.

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34 minutes ago, Alan Longmire said:

You sure you're not thinking of 13C26,

Those are very similar. The one with added nitrogen (14c28n) has a bit higher working hardness and even better corrosion resistance because the nitrides fill every tiny pores in the steel.

Aldo's version(nitroV) is even better so I've heard...

Edited by Joël Mercier
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@Joël Mercier Thank you for confirming about the plate quench, so I stick to the Sandvik recipe? 

@Jerrod Miller Well both blades went flying at some point and hit cement tip first, they are plenty tough, so not worth the effort I guess.

 

12 hours ago, Jerrod Miller said:

The applications where stainless is pretty much a requirement are very few.  Pretty much just salt water environments (boaters and divers).  Given that situation, knives are at a greater risk of being lost (overboard).  As such, all the complications in production do not seem worth the effort for a custom knife, and those that are willing to pay for it won't be asking me -- they'll find someone MUCH better at knife making.  I'd recommend those applications to at least consider the knife as a consumable.  Buy a decent production knife, and when needed, replace it.  Any knife I make I expect to be well cared for, so simpler alloys will serve nicely.  

I've asked that question here before, and from the answers I could only conclude that many of you are lucky to have such educated clients.

My mentor is Swiss, lives and makes knives here in deepest darkest Africa, sells to tourists staying at their tented camp as well as regular international customers.  He switched exclusively to stainless following too many complaints about rusting knives when the people get back home.

He lives in the desert, rust is not an issue.

It took a very strange set of circumstances for me to buy a digital kiln, but I have it now and that's opened the door to SS.

The two steak knives I made and the kitchen knives I have on order are all headed to people who would not know better.

 

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  • 2 years later...

IMG_8418.jpg

 

Working on a k-tip out of 14C28N.

Got it at -- or as close to -- 1940F as I could for 5 min, then did two 120min cycles of 400F, cool, 400F, cool...  

And no matter what I do, I can't get her to bite into onions the way I want.  Maybe it's on me for trying a 70-30 grind but I feel like it could be more in the heat treat, as I don't have a heat treat oven, used the forge.  Any ideas? 

IMG_8418.HEIC

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3 hours ago, Bill F. said:

I can't get her to bite into onions the way I want.

This could simply be a matter of edge geometry

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11 minutes ago, Joshua States said:

simply be a matter of edge geometry

I second that. Even a mild steel blade would slice onions very easily with the right geometry. Of course, it wouldn't cut for long though...

 

Judging from your photo, it seems extremely thick behind the edge. I suggest you take a look at a commercial chef knife and and also take a few thickness measurements and compare to your blade.

Edited by Joël Mercier
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20 minutes ago, Joël Mercier said:

thick behind the edge.

This much I've been aware of.  Kinda like a haircut, at least I can take more off.  

As it is, it is about .815 at top of the spine where the handle would start.  Might just opt for a 50-50 bevel and take more off.  

I still think I need to dial-in the HT process better, though.

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@Bill F. check the first reply from Jerrod, it's quoted from the manufacturer's site.

With the modern stainless steels its best to stick to the heat treat recipe as close as possible, I get very good results with this steel and I now need to sand less post-HT thanks to the advice here to plate quench.

The last one I made did the job, doubtful hunting guide cut his finger testing the edge, then proceed to to unzip most of an oryx and the edge is still good.

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3 hours ago, Gerhard Gerber said:

heat treat recipe as close as possible

That's the nice thing about this.  I can at least redo it and try again.

I do think the biggest issue is getting the temp steady at 1922... much harder to do with a forge vs. HT oven.  

 

I guess it's time to get some aluminum plates! 


I'll make another round going that route this weekend.  Thanks! 

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I've got a very bad memory so I have notes, but I do recall 14C28 you start by holding at somewhere around 800C for a number of minutes, then you ramp to over 1000C and hold again before quenching.

Many (all?) stainless steels have heat treat recipes with holds at different temperatures, and I have to assume they're not specifying this just to entertain us, something has to happen in that steel at (e.g.) 800C before you can go on to the next step......for optimal results.

Only people like @Jerrod Miller and a few others understand what's happening in there, in my case it's monkey see monkey do. :D 

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I'm opting to get some plates soon, which I figure can't hurt either.  

After some more stock removal/re-profiling, I'll post my results here.  I don't wanna give up.  I really want to make this steel work; it's perfect for this use!  

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4 hours ago, Bill F. said:

That's the nice thing about this.  I can at least redo it and try again.

Note that the manufacturer of the steel says that you will not get optimal results when re-hardening.  

"Rehardening is generally not recommended as it will not give optimal product properties."  -Sandvik

 

I would not even dream about heat treating stainless steels without having a thermocouple controlled heat source (forge or oven).  These things get quite finicky.  

 

2 hours ago, Gerhard Gerber said:

Many (all?) stainless steels have heat treat recipes with holds at different temperatures, and I have to assume they're not specifying this just to entertain us, something has to happen in that steel at (e.g.) 800C before you can go on to the next step......for optimal results.

There are a few different things that are happening with the tricky heat treats.  One reason for the "lower" temperature soaks, sometimes there will be more than one recommended, is to make sure all the steel is up to temp, therefore as you go hotter and things start to change it happens all at the same time.  The things that are generally happening that we are concerned with is the dissolving and/or precipitating of carbides.  When you have a lot of austenite at room temp with these alloys you will often get very small precipitated carbides when given a bit of heat.  The graphs for amount of conversion for a given chemistry for various times at various temps get a bit tricky to go through.  As an example, the wear resistant alloys we make at work get a soak at 1850F to get these carbides to precipitate out.  But they are very different chemistry from these blade alloys (ours have lots more carbon and we have gigantic primary carbides).  Anyway, the key thing is that these heat treat procedures are shooting for consistency in the overall structures within the steel.  They do a lot of testing to find out what the optimal times and temps are needed to get the right dispersion of the right sized carbides.  The cool thing about playing with the carbide particle size and distribution is that it affects the overall chemistry of the surrounding steel matrix.  When you precipitate carbides out you get small deposits that are higher in Cr and C concentration than the surrounding steel.  Likewise, when you dissolve a chunk of carbide you get more Cr and C available to the steel matrix.  But both the precipitation and dissolution of these carbides are diffusion based, so it takes time for these atoms to move around.  And that time is based on the temperature.  

 

Did anyone else notice in the original Sandvik notes that ideal quenching results (maximum hardness) will result in about 15% retained austenite, but cryo treatment to convert all of that will only add 1-2 HRC?  I find that pretty neat.  

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23 minutes ago, Jerrod Miller said:

consistency in the overall structures within the steel

I saw a good YT vid that explained that a bit, or at least normalizing at my level :-)

I think other than stock removal (and following Sandvik's method... not other peoples' "hacks" I've seen online) and finding a way to get my forge more dialed in for temperature is what I need to do.  

 

23 minutes ago, Jerrod Miller said:

cryo treatment

In regards to that -- and I suppose in reference to my parenthetical -- do you think the freezer is analogous to my forge, in that it might not be the right thing for the job?  I wasn't even trying the freeze step, but I've seen a lot of guys talk about popping knives in there, and it seems to me that they're probably just really lucky... or wrong, and you would want to do it with an environ with much more control and precision.  That's the name of the game here with all of it, control and precision.  

 

Also, thanks for taking the time to write that.

I learned a great deal, it made my lunch break more enjoyable, and I appreciate the thoughtfulness!  @Jerrod Miller

Edited by Bill F.
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When going with any of the cold treatments, it seems to me that control isn't nearly as important as getting cold enough.  Your freezer isn't likely to do too much.  Those are typically around 0F to -15F.  Ideally you want to be more like -100F or colder.  Dry ice is generally the starting point for these things.  "Cold" treatments are often considered at least -150F (colder than dry ice), and "cryo" at least -310F.  That being said, I know there are alloys out there that do tend to respond to dry ice levels.  Often people will say either "cold" or "cryo" when referring to either process, more as a generic term.  I try to not get hung up on that terminology, and as such I probably am less careful using it myself than I should be.  

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Just for the record, Larrin over at knifesteelnerds.com has done some testing that shows the lower carbon Sandvik and Uddeholm-Bohler steels like AEB-L and 14C28N do see a slight increase in hardness and toughness after an hour in a standard household freezer versus as-quenched.  Not nearly as much as the factory-recommended -100F soak, but better than nothing.  Other alloys like CPM154 really need the liquid nitrogen treatment to get decent toughness.  

 

AEB-L and 14C28N are both around 0.65% C and 13% Cr, which is their way of keeping the carbide size low. Don't supply enough carbon or chrome to make big ones! :lol:  

 

https://knifesteelnerds.com/2019/03/04/all-about-aeb-l/

 

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9 hours ago, Alan Longmire said:

after an hour in a standard household freezer versus as-quenched. 

I thought I might have seen a credible source, but couldn't think of it.  I'll be.  

Hmm.  Now I'm tempted to get an Evenheat... 

 

10 hours ago, Jerrod Miller said:

hung up on that terminology

I know exactly what you mean! 

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I think that you are starting to see the light.  The alloys used and the heat treating equipment need to match each other.  It's just like that if you only have a forge  to austenize the steel in you need to stick with a simpler alloy, like the 10XX group.

 

Doug

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