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 Post subject: Spending time with my friend, 52100 :)
PostPosted: Thu May 08, 2014 1:41 pm 
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Still feeling the effects of a nice 48 hour stomach bug, I figured it'd be a good time to share some of my experiences with 52100 steel with y'all.

Recently got a heat treat oven and was sitting on 30 blanks of my 230 gyuto in 52100, so decided it was time for them to play. :)

Not wanting to grind entire chef knives to find out how my heat treat was doing, I decided to grind some smaller blades and see how things go first. (Josh Dabney was kind enough to heat treat my first blades in 52100). So, I created what I'm now calling a "mini-prep" knife, or maybe just "tall petty" (I'll work those details out later) by simply cutting a smaller design out of my already existing 230 blanks. That's what the pictures in my previous thread were.

Also, I used the handles that were cut off of the original 230 blank to create nice test pieces. I'm also going to make "shanks" from these test pieces as well, these are going to be fun. :) Here's a picture of test pieces that I broke at different intervals along the way during heat treat to inspect the grain.
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52100 steel is known for needing precise temperature control to get the most out of it, so I want to be extra sure I know I'm doing the best I can with it. You can research all you want until you are blue in the face, but the only way to be sure is to inspect the grain yourself. This way I can confidently tell someone I'm giving them the best I can do. That, and you don't always know the condition of the steel you are working with. Even though a company may sell you some steel as "annealed", some annealing processes are different than others and more thorough. It's just best to completely reset the steel yourself and then you can be sure of consistency to your own methods.

Some of you may already know what I'm about to type, but for those who don't know much about steel I'll give you a basic run down of what I do and why I do it.

The first step I do after shaping the blank is normalizing. Normalizing is used to reduce big grains and stresses in the metal from forging and over heating. When the temperature gets above a certain point the grain size of the steel will grow. Small grain is desirable in steel because big grains tend to chip out and are brittle. There are a few methods that I've seen people use to normalize. Hardening temperatures for 52100 are between 1475 and 1550f and forging takes place a bit above 1700. I've seen a method to normalize that calls for bringing it to 1650 then quenching, 1450 quench, then 1250 and air cool to black, then quench. I have also seen a method of the same but all air cooling insteading of quenching. After some testing, I settled on the air cool method. No point in quenching more times than is necessary and there is no benefit.

The normalizing method I settled on is probably overkill, but it's what I'm doing. Between each step the blade is air cooled until black (so that it's 900f or below) but kept above 400 before going back in the oven. I do 1600, 1550, 1500, 1450, 1400, 1350, 1250 air cool to black then quench. This ensures the grain is brought down gently and thoroughly. The steel I received is already annealed but I do this anyway because it's what you are paying for when you buy one of my knives.

After that the steel is hardened. As stated before, the hardening temps for this steel are between 1475 and 1550. After 1550 you can still harden but you will be getting bad grain growth. The closer to 1475 you get the less retained austenite there will be (desirable for knives) but the thing is that 52100 has a little bit of chromium, and in order to make chromium carbides you need to be a little hotter. I was told that 1525 is a good temp for this; I inspected grain at 1550 with no visible growth so I know 1525 is fine. I did soak the steel at 1250, then 1440 before going to 1525 to ensure it was heated nice and even. Hold for 12 minutes and quench in canola oil.

Tempering is done a little below 400 degrees to give an edge that won't roll that easy but won't be too chippy for a little heavier-handed user. For kitchen knife application I've been told we can temper at 325 to give a harder blade, around 62-63 Rockwell. While this takes and holds the best edge, you can potentially have chipping if you come into contact with bone or heavy chopping on a harder surface. For someone used to Japanese blades this probably wouldn't be a problem. After some testing I decided to temper between 350 and 375 to reduce the chippiness. Testing included swinging the blade full-force at a blank of pine. Pine is nice and soft but will make an edge fail if it is too thin or too hard. If you have a nice tough edge it will turn pine in to mince. My blades are triple tempered; 1 hour for each cycle and complete cooling in between.

The blade that you see broken in the pic was giving an inferior heat treat but still turned out to be a decent blade. It was given the quench method instead of the air cool, used higher temps, and fewer steps; The grain should have been decent but probably not the best it could have been. The blade was given a full height convex and taken to a near zero grind then edged. It was very thin behind the edge. While minor chopping didn't do anything to the edge, when I started taking big swing I started to see some damage after about 10 hard swings. The blade was digging into the soft pine and I was even twisting it a bit. (yes, I used it like an outdoor knife, I wanted to break it). After I saw the limitations of the edge I stuck it in the vice and hammered the heck out of it to see if would break. Bent it to 45 degrees a couple of times without breaking. Then repeated to hammer it very hard until it broke. I actually video taped the end of testing on my phone, might upload if there's enough request. (added; I just realized this blade was only heated to 1490 and also cold-hammered before hardening, which is a big No-No, so this blade was probably stressed a bit as well in that respect not to mention not heated hot enough during hardening.)

Well gotta go for a minute, be back soon. :)



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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Thu May 08, 2014 2:35 pm 
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Nice Shaun. I love learning about heat treatment of different steels. People don't realize how easy some are and how difficult others are.



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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Thu May 08, 2014 4:23 pm 
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No kidding, I though heat treating was a straight forward process but boy was I wrong! :)

In all fairness I'm sure the results on many of the already listed processes are pretty good, I just to be sure these edges don't fail when they are super thin.

The only other thing I've seen some people do that's different is doing multiple quenches or liquid nitrogen for a little extra hardness: Multiple quenching is supposed to refine the grain more like a powdered metal. There is supposed to be scientific data supporting this, although I've not seen it directly I wouldn't rule it out. I will play with multiple quenches when I get a little more time to experiment. As for right now the main thing you want is to not over-temp and be able to soak at a given temp for more than a few minutes is critical to getting the extra carbon into solution.

Simple tool steels like 1060, 1080 only need to be brought to a non-magnetic state (1425f) and then water-quenched. If steel has more than .8 carbon you then need to start soaking the steel to get all the carbon used up. 1095 steel will be no better than 1080 if you can't soak it for at least a few minutes. The problem is that a lot of guys who forge knives do everything in a propane forge with no temp control, they use eyesight and a magnet. While some can achieve good results it's no match for a good heat treat oven or salt bath if you can afford it. I soak my 1095 at 1450 for 15 minutes. Soaking steel for a time will not grow grain if you are in a "safe" temperature range, so anything more won't hurt or help it, we are just trying to soak long enough for all the carbon to get soaked up into the iron. Since 52100 has .95+ carbon, we soak it for 10 minutes or so.

I know I had more to add to this but for some reason it escapes me at the moment. Oh well, more later I suppose, finally feeling good enough to get some stuff done today.. it's been a rough past 2 days.

(edit:) Now I remember. It was about the annealing/normalizing process. The last step of normalizing calls for 1250 then air cool to black, then quench. The reason you quench after cooled to black is because you don't want it to cool slow below 400 degrees. If the steel cools too slowly then you get an undesirable type of pearlite for knives. You can anneal by going from 1460 to 1275 rapidly, then hold for 16 hours to get a "spheroidized" annealed state, which is better for machining but not for the hardening process. There are other ways to anneal as well but will not produce the same product.

There are 2 main factors when it comes to hardening (quenching fluids aside): 1 is temperature control, and the other is "what state was the steel in before it was hardened?"

You can have the best temperature control in the world, but if the steel wasn't in a good state before you hardened it then you aren't doing the best you can. So basically, just like I said earlier, all the steps in the normalizing process are to ensure I know what state the steel is in before I harden it. :)



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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Thu May 08, 2014 8:39 pm 
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Here's a shot of the blade I just finished a little while ago. This blade did the 7 step normalizing process before hardening, all air cool and quenched on the last step. This one was soaked for 12 minutes at 1525 and triple tempered a bit above 350 for 3 - 1 hour intervals.

Sharpened at around 15 degrees, I started with a 120 belt to establish the bevel, then to the stones: Shapton glass 320, then 1k, then 8k. It sharpened like good carbon, fairly stiff but still rolls, gets scary sharp very fast. This knife took a slightly better edge than last one as well. I can attribute this to a few factors, but bottom line is I'm impressed with results so far. I can not tell you how satisfying it is to grind and heat treat one of these blades from scratch. I know that when someone gets this blade they are getting something good.

Not sure if I'll turn this knife into another sacrificial lamb or not: I know the grain is fine and my eyes, even aided with a 60x loupe, will not be able to detect the grain difference. I will continue to use this knife hard and take a few swings into the pine wood. If there is no chipping this time then I'm good to go. I've already abused it a bit but no microchipping, it's staying sharp.... very sharp. All the long nights last week are finally paying off.


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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Thu May 08, 2014 8:43 pm 
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I also might shrink the butt of the handle a bit; While the big butt looks good it kind of gets in the way... ;) ;) ;)



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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Thu May 08, 2014 9:05 pm 
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Just got back from testing the edge of this last knife by swinging hard into the pine plank I had from earlier: No edge damage! Still very sharp! Nice. :)

The last knife failed because I hammered it while cold to straighten it (didn't know it would hurt so much but I know to never do that again) and also not as good of normalization beforehand. These things have the biggest effect on if the knife is going to chip out or not. I could have followed the hammering by a normalizing and it would have helped a lot but the steel was probably already cracked. I am pretty sure that the fact that I changed the soak from 1490 to 1525 didn't do much for chipping, that will help with wear resistance and corrosion resistance more by making more chromium carbides. The retained austenite at these levels is so low that I don't care if I'm closer to 1475, I'd rather my chrome get tied up properly. Splitting hairs here, but that's what we're in the business of sometimes! :mrgreen:

Now that I know heat treat is good I can move forward with these babies and put them for sale. I hope to do this with every steel I work in the future so that you all know exactly what you are getting. I enjoy sharing my experiences with anyone willing to read. Thank you if you did read all of this, and please shoot some question if you want!

(edit: Just realized I never mentioned hardness! Going to send one off for testing soon, but so far I estimate these to between 61 and 62 Rockwell. I've tested a lot of knives, just take my word on it for now lol! The main thing is that it performs good first.)



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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Fri May 09, 2014 1:49 pm 
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Did a quick video with my phone this morning for you guys. I know all the wall of words from yesterday might bore you, so here's some action!




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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Fri May 09, 2014 5:47 pm 
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That's really cool stuff Shaun! I had to hit Wikipedia to get the low down on all those processes :-).


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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Fri May 09, 2014 6:07 pm 

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I most enjoyed the explanation of your process, but the violence was interesting, too.


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 Post subject: Re: Spending time with my friend, 52100 :)
PostPosted: Fri May 09, 2014 6:38 pm 
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Violence? Oh you have no idea! ;) Kidding aside, I mainly wanted to show that the heat treat is good and has a fine grain. Bigger grain would have chipped out a bit on that test, I've done it many times before with other blades. When I first started heat treating 1095, I did it by eyesight. A few blades got overtemped, and while they took a good edge they would chip a bit on that test, no matter if I tempered them a little higher or not. When I got the heat treat right it would create a near indestructible edge (chopping wood). Believe it or not I only have 1 personal carry knife that I made for myself; a mini-tanto in 1095 with g-10 scales that I heat treated in coals. I got lucky and did a differential heat treat on the first try, so the spine was already soft after the quench, meaning I got the temp near perfect on the rest of the blade. I actually took a ball-peen hammer to the spine almost as hard as I could swing; and while it dented the spine the edge just laughed it off. (I was hammering the knife through a Christmas tree trunk, I may upload pics later of the blade, it's travels in the other car with my lady.)

Thanks Steve, I was waiting for some people to chime in! I know metallurgy isn't a sexy subject, but since I need to know it lately I've been a bit obsessive. :) I really want people to know what is going into their knife, not to mention it's really satisfying to know you are making a great blade for someone to enjoy.

The grind on this knife performs very good, it's boarding the "laser" category for sure, but I think I can fine tune things a bit more. I'm doing a convex grind all the way down to the edge, so there's a lot more steel backing the edge up. Combine a convex grind with tough steel and you have potential to make things really thin behind the edge without losing too much toughness.

Admittedly, you will never put your knife through what I did in the video doing kitchen tasks, it's good to know your knife is capable of taking a little abuse. I, personally, never have chipping issues with my harder Japanese blades because I'm careful, but I also realize that many users are not careful and will abuse the blade. Time to start pumping these puppies out and getting feedback!



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