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  #1  
Old 09-05-2016, 10:38 AM
dtec1 dtec1 is offline
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more HT trouble

ok guys so now I am having another problem so that batch that didn't harden, I annealed it and re hardened 2 of them so as I always do I tempered the first one low I think it was 300 grinded bevels and did brass rod test...it was hard (so at least I know it did harden this time) so I increased temper to 310 still hard then 320 still a lil hard when I got to 330 it was just slightly soft not by much...so now that blade I put to the side and the other one that was hardened at the same time as that one has been laying in the liquid nitrogen while I was tempering that last blade as a test so 320 to hard 330 just barely soft very small amount of edge not "springing back" on the rod test it was hard to see but was there, so I figured with those results I took the other one out of the liquid nitrogen and tempered at 325... grinded and tested got a different result most of the blade seemed to be a lil soft same as the one at 330 (I guess if 320 is to hard and 325 is slightly to soft probilly better to go slightly to soft than to hard) but also right in the middle of the belly on the blade the edge rolled a tiny bit but also on the "rolled" part edge 2 or 3 tiny lil chips developed. this only happened in the middle of the blade. so I have 2 questions first how can you get a good HT if 320 is to soft and 325 hard?? I didn't think that lil of a difference could even make a signifigant change? second if part of that edge rolls as if soft but still has tiny chips on that rolled part what would that mean to soft AND to hard? that makes no sense. I have had nothing but problems with this batch of steel I am starting to wonder if its something to do with the steel being wrong first none of it hardend then I annealed all of it re harded 2 more and I know it hardend but the results aren't making sense to me at all. I have never had this many problems on a HT before I am almost tempted to throw it all out and start again...if it was only one or 2 blanks I would have already done that
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  #2  
Old 09-05-2016, 11:11 AM
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Naboyle Naboyle is offline
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I had a conversation with Ed Caffrey about stainless and carbon steels. What was explained to me....


Another biggie that I've learned with stainless..... when the heat treat formula recommends a "target" hardness.... get as close to that as you can. A lot of makers try to heat treat stainless as if it were carbon steel.... raising of lowering the tempering temp in hopes of achieving toughness or increased edge holding.... stainless just doesn't work that way. Miss the "target" hardness by a couple of Rc points, and you get an overage of undesirable things happening.....too soft and if simply will not sharpen, and if it does, the edge is dead when you cut ANYTHING with it. Too hard and the edge is so brittle that anything beyond the lightest cutting chores chips up the edge. Where as with carbon steel I can choose a grind, and adjust the hardness to work with that grind.....stainless requires the opposite approach. You have to nail the "target" hardness of the given stainless steel....THEN you have to figure out the type of grind that the target hardness will tolerate for the jobs you intend the blade to perform.
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Old 09-05-2016, 11:28 AM
dtec1 dtec1 is offline
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ok so when I started with 440 c I had made coupons and had them tested for Rc and grain size. each one was done slightly different (quenching temp, temper temp, and oil vs plate quench) I think 60 rc is where they say is "optimal" so what your saying is to do the same HT as the coupon I got a 60rc result and use that regardless of how it comes out on the brass rod??? when I say these last couple ones have been soft or hard I don't mean its really hard where it will chip on anything or to soft to sharpen I mean a couple very small chips when hard and just a lil bit of rollover that wont spring back its hard to see but is there when you look close...
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Old 09-05-2016, 11:40 AM
jmccustomknives jmccustomknives is offline
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I'm just curious if the problem isn't your oven? Do you think the heat is even throughout the chamber. Inconstant heat, hot spots and heat sincs could all cause problems. I wonder if there's a way to test that, I suppose they make a temp stic or some other indicator.
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Old 09-05-2016, 12:34 PM
dtec1 dtec1 is offline
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its a even heat oven and only a couple months old so..also I was doing fine up until this last batch that's why I am tempted to think the steel before the oven...I am going to order another bar tomorrow so then I can compare when I get that see if there is any difference there....but I guess anything possible I don't know how I would test that maybe heating it up and pointing a temp gun in to see if it matches what the oven says? I would have to get a much better temp gun than I have tho...
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Old 09-05-2016, 12:48 PM
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Ray Rogers Ray Rogers is offline
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If you are seeking perfection with stainless you will probably be disappointed. The brass rod test works well for carbon steel but with stainless about all you can hope for is that the edge doesn't chip much. As Ed suggested, do what the spec sheet says and don't try to tweak it too much. The spec sheet will usually give suggestions for what to change if you want more toughness vs hardness so use those suggestions if you feel the need. Other than that, real world testing is probably the best thing.

Also, stop doing your blades in batches or, if you must do batches then do very small ones like 3 blades. Get 20 identical knives from any manufacturer and test them and you will find a wide range of hardness, toughness, and edge holding characteristics among them. That is the inevitable result of batching blades. If you want to be a knife manufacturer then learn to accept this fact. One of the main reasons people buy custom knives - whether they consciously know this or not - is that knife makers have the ability to control the HT carefully for each knife. That can't be done by any practical means with batches ....


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Old 09-05-2016, 01:33 PM
dtec1 dtec1 is offline
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ray..makes sense ill try to just stick to those coupons I made...the previous batch did seem almost perfect as far as the HT except 2 or 3 that I think was the oil getting to hot wich I guess is where you were going about doing batches. and even the one before that was a little better maybe I just got lucky on the first batches....Since I got the dewar there are no more "batches" obviously you know why I was doing that in the past not any more, this batch I had cut up and hted before I got the dewar then I realized they didn't harden right around the same time I got the dewar so when re hardening I did 2 purposely just to see if they did harden have one as a test knife but I am not going to be doing a lot at once any more with the dewar there is no point. Any way so if they cant be perfect would I be right to assume that having a little to soft is better than a lil to hard (kinda going on that fact I would rather a blade get dull than break)
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  #8  
Old 09-05-2016, 04:00 PM
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Ray Rogers Ray Rogers is offline
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Depends on the toughness of the steel. Most of the high end stainless I use made very tough blades so if it were too hard it still isn't likely to break but the edge might be a little chippy.

If it were too soft then the edge, again, might chip more than it had to but not necessarily fatally - depends on toughness. Good stainless is tough so if you get the hardness close to the spec - and the grain is good - then that should be a good working knife. Stainless knives generally don't have the very thin edges that you might put on a carbon blade so they aren't going to behave the same on a brass rod test....


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Old 09-06-2016, 08:48 AM
dtec1 dtec1 is offline
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Ray that is something I haven't heard about not putting a thin edge on stainless. maybe that could be a problem. do you mean how much of the edge you leave before the secondary bevel or the angle of the secondary bevel? or maybe both? is there any general rule of thumb on how thick to leave the edge or I know you don't do the secondary bevel on exact angle but is there any estimated angle you wouldn't go past?
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  #10  
Old 09-06-2016, 11:26 AM
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Ray Rogers Ray Rogers is offline
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There's no real rule of thumb about it. I'm sure it also depends on the steel. Generally though, if I try to put a thin edge on stainless it usually works fine as long as the edge doesn't get abused. Thin stainless edges seem to chip out (micro chips) more easily than the same edge in carbon steel. I'm referring primarily to the secondary bevel, the primary never had any problem being as thin as I wanted it to be ...


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Old 09-06-2016, 11:39 AM
dtec1 dtec1 is offline
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ok thanks ray, yeh I have never heard of the edge in stainless shouldn't be as thin. just another thing you have opened my eyes to I have found the bubble jig AND the edge pro is extremely efficient and acccurate for secondary bevel and sharpening...I can use it to say put a 17 degree secondary bevel on then have the edge pro set up for the same angle and sharpen very quickly....I am just thinking lately I have been doing 17 deg sec. bevel where as I THINK (not positive) the last batch of knives were at 19 deg maybe that is what this difference in rolling and slight chipping is from I don't know if 2 deg would make that much of a difference but it is another thing to test
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  #12  
Old 09-06-2016, 01:24 PM
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17 degrees is pretty thin and delicate for a general use knife on any kind of steel, more likely to be used on a kitchen knife. About 20 degrees is common on general usage knives and up to 25 degrees for a heavy chopper ....


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Old 09-06-2016, 03:30 PM
jimmontg jimmontg is offline
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Heh Heh Heh, Dave. I thought you knew what Ray told you. You shouldn't be double HT your knives. Once done they are done unless you want to do about a 20 hour anneal on 440C. All your stainless steels have long anneal times or they just harden if cooled too fast. Of course maybe you did anneal it right, but I'd hate to see you electric bill.
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Old 09-06-2016, 04:34 PM
dtec1 dtec1 is offline
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ok yeh I am going to go back to 19+ on the angle....I know about the anneal...I had HTed that whole batch (as I was still using the cooler for LN didn't have the dewar yet) when they didn't harden yes I annealed them and yes it was a LONG day yeh I know the oven is kinda set it and wait but lets say my oven is in the same room as my mothers washer and dryer so she knows when its on and is not to keen on me turning that thing on and not being close by if she had realized I turned it on and then went back to sleep for 2 hours I probilly would of gotten woken up by getting hit in the head with something
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Old 09-07-2016, 12:55 AM
jimmontg jimmontg is offline
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Talking LOL Ha ha ha,

Making me laugh Dave,
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