Why the long soak?

J. Neilson

J. Neilson

Joined
Feb 6, 2001
Messages
3,621
I am curious why such long soaks are needed for stainless steels. I work with both high carbon and 440c stainless following the recommended heat treating methods, but don't really understand why one place says soak for 5, 20 or 30 min. or why you cannot just bring the steel to critical and quench. The David Boye book on knifemaking (where I learned alot starting out, great book) says this type of hardening method is good on any steel with at least 1% carbon content. The 440c stainless I've used has a 1.2-1.5% carbon content. I've done some experiments with different hardening method including soak times (since every 5th blade or so I test to destruction I've had a few to play with) and for the most part have seen little difference in soak times quenched in warm oil. This is what happens when you learn knifemakeing from books and trial and error. Since I hate doing things without knowing why I'm doing them I was hoping for some opinions and input on what other knifemakers have experienced.

J.

www.mountainhollow.net
 
Well here's an answer for you. I don't know. However, I once asked, and was fortunate in that Ed Fowler answered, about heat treating 440C by the method used on non stainless steels (heat in a forge, oil quench). He said the best results he'd ever gotten with 440C were with the oil quench method, performed three times. The triple quench replaced the soak time in an oven and then some. While this doesn't directly answer your question, it might be that a more complete crystalline conversion occurs with soaking or triple quenching. If we're lucky he'll see this thread.
 
In the annealed condition, most of the carbon in the higher alloy steels is tied up w/ other elements in the form of carbides. The long soak times do 2 things. First, and least important to the knifemaker, they allow full heating of thick sections, say 1/2" or more. Second, the soak above the critical temperature dissolves some or all of the carbides in the austenite, freeing up the carbon to form martensite and harden the steel to the desired level upon quenching. Upon tempering, some of the carbides may reform, but they will be smaller and more evenly distributed than the ones in the annealed condition. The degree of carbon tied up in carbides, the length of the soak time, the amount of carbides that reform during tempering and the maximum hardness attainable are almost completely dependant upon the specific alloy.
 
It's so you'll have time to grind another blade.:D
sorry I had to say that.
Elwin sound's close to the nail head.
 
Having very little experience with SS (Kinda like an ugly girl at closing time) I decided to try Ed's method. I had some of the stuff and ground an ugly and usable blade (I thought it was fitting). I oil quenched it 3 times. It got hard. I don't know if it helped but I tempered it at 310 three times. It took an ugly shiny edge, cut OK, didn't snap until I bent it about 40 degrees in the vice. What else can I say. If I had a desire to make dishwasher safe knives I'd try some homegrown heat treating.:D :D :D
 
Long soak times have some negative effects on knife blades as they tend to grow grain. The multiple quench does everything that long soak times do except grow grain, thus the benefit. It was years ago that I worked with the 440-C. As I remember I used a faster oil than the Texaco Type A that I use on 52100. I used Brownell's Tough Quench that is a fairly fast oil and it worked better. I have misplaced my old experimental book, but it is in the shop somewhere. When I find it I will be able to give the exact formula.

The 440C that I used was forged down from a gate check ball out of the oil field. It made a pretty good knife.
 
Of course Ed is right as rain.
I proved it the other day as I'm sure
many have before in mistake or in testing,
with 3 blades of 154CM
I had a brain cramp off doing something else
and soaked them for about 2 hours at 1925
way to long for one setting and
yes grainy
you can see it in a mirror polish
looks like little tinny spots all over it.
2 hours on the draw is about right,,
I should say the first draw then of course
the nitro and draw (temper)again.
 
Peter and Dan: I thank you for giving the multiple quench a try, then testing the results. Knifemakers like you will continue to advance the quality of knives for more to enjoy.
Thanks and Take Care
 
Thanks Ed
Though I've worked with Hi carbon steels since
the early 70s for my knives, I've only worked
with the SS's, D2 .and other air quenchable steels  
for the last I think 5 or so years now.
it's been interesting at the least.

 Ed have you or know of anyone that has
looked into edge hardening stainless
with no heat to the spine?
I think I've found a way to do it and reasonably fast
I need to spend more time on it to be conclusive.
I don't want to waste time on ground that
has been possibly covered already.
I'll post it when the time comes.
Keep up the good work ED
 
I've tried edge quenching stainless(440c)in solid "Goddard's Goop" and got good results as long as I left the edge a little thick. Anything ground too thin, .025 of an inch, warped.

Hey Ed, tried that triple oil quench with 440c today. It's tempering for the third time as I write this. Will the triple quench method work with any other stainless steels; ATS-34 and so forth?:confused:

J.
www.mountainhollow.net
 
Hi J. Neilson
I'm afraid the way you hardened your 440
being an air quenchable steel you hardened it anyway.
so the spine is now hardened.
I'm talking about leaving the rest of the knife other than the
edge cold though out my process. you can do what your doing
with say O1 because this steel has to be quenched in something
other than air, mainly oil and some guys use water.
the goop will work too as Wayne uses.
 
Graymaker, You have asked a question that has been bugging me for a while.

I know of one smith that is also experimenting with an edge quench and I am curious of his results, hopfully I will get to talk to him againg soon.

I have heard of Wayne Goddard giving D-2 a soft back draw, and posted a question about it on anougther forum with out much luck. If D-2 can be given a soft back, what about ATS-34? How is this done?

I personaly detest stainless, but living in southern MS, a lot of people will sacrifice cutting ability for ease of care.:rolleyes:
 
Actually I've used "goop" edge quench and a point down oil quench both followed by annealing the spine with a roebud(440C can be quenched in air or oil and I don't believe harden quite equally) and have gotten similar results. "Goop" is mainly more pleasant and cleaner, though salts from the animal fat in the goop are suppose to help in the hardening some how...sorry, not a chemist here. Also, after edge quenching stainless I've found it's a good idea to anneal the spine of the blade regardless of the quenching method as extra insurance. You can't be too careful in making a working knife. Plus, that blue is such a pretty color, unless you see it when grinding! Any ideas on keeping the spine cold during quenching, Greymaker, I'd love to hear.

J.
www.mountainhollow.net
 
J. Neilson, the way I harden most hunting sized carbon steel blades is with a torch, heating the lower 1/3 of the edge to non-magnetic, then quench. On anything larger like a bowie I have to use my forge to get an even heat, then edge quench.

I havent' tried it with stainless, but should work if non-magnetic is close to criticale temp. for stainless?
 
Gentlemen: I am very pleased to read about the experimenting going on with some other steels. There are many variables, try to keep them seperate so as not to contaminate your results.

You can build some thick steel blocks blocks that look like a sandwich, welded together with a gap in between then, heat them hot enonough to heat the blade to critical, the blade is only sunk into the sandwich a little over the level you want to harden the blade, when the edge portion is over critical, quench the blade. It doesn't take too much practice to learn this method.

The 440 blades that I did were heated with a torch, only bringing a little more than the lower third to critical. I still haven't located that experimental book but will look again tomorrow and will be able to supply more information.

I have never found the soft back draw to be necessary when everything that comes before is done right.
 
J
I still think your spine is still hard because of the
time it takes to anneal stainless
because of the slow decent of temp you need ( hours).
you can't just heat the spine like say O1 it won't happen
if your heating the whole blade to critical. I maybe wrong
in the way I think your heating your stainless to edge quench.
please tell me the process your treating your 440C.?

heating the edge the way Ed is saying I see can be
an alternative to what I've been working on.
but if I'm right in the way I want to do this it will
dispense any of that, it will truly do away
with the oven or forge for the hardening part but the edge
will still have to be drawn down.
it will be easier than heat treating O1
with a torch.
the spine will be cool
there is a pun in there..:p


J... please what is a "Roebud"for annealing,,?
 I've been back in the woods to long I guess

Will.. yes I think so on any air quenchable steel if this
turns out right.
I think other than the ease of sharpening say in O1,
stainless would be the steel that most will use if
you can do the heat treat faster than say The O1's
of steels. I don't want tell just how I'm doing this
 right now until I know it'll work the way I say
 but I'm confident it will..
I use 154CM witch is close to ATS34 I believe it is way more
steel than the 440C though 440C is tuff 154CM will hold
a better edge.
 if both are heat treated to maximum and comparing
apples to apples here.
just my Opinion in the use of both.
 
Graymaker, I think J. Neilson is refering to a 'rosebud' torch nozel, basicly just a big fitting that puts out a big flame.

I've tested 440C and ATS-34 and 154CM and found that there is very little differnces at the same hardness levels, ecept that ATS-34 and 154CM are a lot tougher at say 60R. 440C is most often drawn back to 57-58R. At those hardness levels both should be about the same toughness, but ATS-34 and 154CM will hold better edges. 440C is also slightly more corosion resistant. The one thing I have found is that cryo is a definate pluss for stainless. I wont consider makeing a SS blade without it.

The one thing more than lack of edge holding and ease of sharpening that bugs me about stainless is a conventional heat treat leaves the entire blade the same hardness. To me that is just asking for trouble.

My main concern is to get the most out of any steel I use. I know your not supposed to use a knife as a pry bar, but often a knife is at your side and the tool you need is way off yonder way.
 
Hey Will
yes I now know, JD e-mailed me on it to.,
I know what a rosebud is (;>))
I've  been welding for years,
J put in the post "Roebud" just a typo
I should have seen it was missing the :s: I had a brain cramp.
anyway being that you can't simply anneal just the spine
with a torch I thought a "Roebud" no S was something
I had missed out on.
I agree with your thoughts on SS.
  I'm going to do some testing here shortly.
on my process. also I believe
  most SS was meant to be nitrogen soaked anyway.
if I'm ever wrong in something I say by all means jump on it..
 
I've played around with heat coloring titanium quite a bit. One way that I have found to selectively heat an area and not the rest of the piece is to submerge that which you don't want heated into water. Then, using a torch, you can heat just one part....like an edge.
 
peter
that's good for lower heats but I'm not sure about 1950 deg's for the SS
 now on O1
I use a water tube on the edge to differential temper O1
works great and it's out of this world fast and fool proof.
 see this picture with water running though the tube you can torch the back bone
until the cows come home.
 

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