What went wrong? 1095 (Kiln heat treat)

Robert_Phelps

Robert_Phelps

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Nov 29, 2005
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I made a knife out of the last piece of 1095 I had (Admiral), and it broke while trying to fix a bend... and I'm not quite sure what could have gone wrong.

It was heat treated in my (24") paragon.. I let the knife sit in the kiln while getting up to temp (1500) then I let it soak for 5 minutes (It was a knife around 10" overall) After making sure my mouth was held right, I quenched edge down into parks 50 (my quench pan then wasn't quite long enough, so the tang [full tang] was left exposed) I kind-of had to angle it in, but the entire blade portion was submerged. I washed it off with hot water and soap and stuck it in an oven with 2 hard fire bricks in it at 400 (checked with an additional oven thermometer) for two one hour tempers. Days later, I noticed the blade had a slight bow to it over the whole length, so I sort of grabbed each end and put some weight on it over the corner of my workbench... after flexing a centimeter or so it snapped clean in two halfway through the blade. The grain looked really smooth. It acted like it wasn't tempered, but it had even turned a nice gold color in the oven.

Sorry for the long explanation. :o Any ideas? I guess my oven thermometer could have been wrong... or the odd quench could have done it... (Still hunting for a longer quench pan)
 
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Robert_Phelps said:
I made a knife out of the last piece of 1095 I had (Admiral), and it broke while trying to fix a bend... and I'm not quite sure what could have gone wrong.

It was heat treated in my (24") paragon.. I let the knife sit in the kiln while getting up to temp (1500) then I let it soak for 5 minutes (It was a bowie around 10" overall) After making sure my mouth was held right, I quenched edge down into parks 50 (my quench pan then wasn't quite long enough, so the tang [full tang] was left exposed) I kind-of had to angle it in, but the entire blade portion was submerged. I washed it off with hot water and soap and stuck it in an oven with 2 hard fire bricks in it at 400 (checked with an additional oven thermometer) for two one hour tempers. Days later, I noticed the blade had a slight bow to it over the whole length, so I sort of grabbed each end and put some weight on it over the corner of my workbench... after flexing a centimeter or so it snapped clean in two halfway through the blade. The grain looked really smooth. It acted like it wasn't tempered, but it had even turned a nice gold color in the oven.

Sorry for the long explanation. :o Any ideas? I guess my oven thermometer could have been wrong... or the odd quench could have done it... (Still hunting for a longer quench pan)
Click to expand...

need pics
 
Well, it happened a few weeks ago, the tang area had been drilled for weight reduction (not much to salvage) and the tip of the blade I ended up tossing in the last clean up. No pics available.

This is basically it.
brokebladeex.jpg


...Looking back now I have to wonder if it just didn't temper right? it broke nearly right between the two points where I was applying pressure to fix the bowing. I was barely putting weight on it when it snapped.
 
Well, for starters, a 1095 bowie blade isn't really designed to flex 1cm with a 400F temper. 1095 can be spring tempered if desired (not for a knife ,though), but at 400F it will still be too brittle to flex.

A 400F temper on fully hardened 1095 will yield a Rc in the Rc 63-64 range. - way too brittle to be bending it. At 500F it will drop to Rc60, and at 600F Rc57.

A bowie is a heavy fighting knife, It isn't designed to shave with, slice tomatoes ,or flex like a sword. It is designed to be tough and easily resharpened.A double temper at 550 would yield a great 1095 blade with much better survivability than a 400F temper would.

I can't understand the mindset that wants to temper 1095 knife blades at 350 and 375F. There are times when that is the right temperature, but in most knife uses, it is too low, and yields a blade that is too hard and brittle. The why of a Rc 63 camp knife or fighter escapes me.

Now, I will explain why many folks (especially from a while back) use such low tempers and say, "I get a great blade and never had one break.....". IF the austenitization was done properly, and the quench was done in such a way that ALL the austenite was converted to martensite...then the blade would end up as quenched at Rc 66-67. (Now , we all know that most of us don't hit this theoretical high point.) Then if that perfect blade was tempered at a controlled 400F, it would drop to about Rc 63-64...(and many of us don't use a controlled oven for tempering).

What is the reality for many folks is that they heat it up until non-magnetic+ and quench it in Godknowswhatkindof oil, then temper in a "400F" kitchen oven that swings +/- 50F.
This means that the Rc often starts at around Rc62-63 and drops to Rc 57. Those folks then post that data, or write an article on making knives on the cheap, and that procedure and temperatures get carved in stone as the "perfect HT". ( I left out the file they started with).

......Then someone ,like Robert, gets a Paragon and some Parks #50. He follows every detail of the HT, and nails it.....hard as glass. He then tempers in the oven, which he has meticulously checked to be accurate, and uses the old "tried and true" temper of 375-400F for 1095. He then breaks it and is stumped why. The WHY is that this misinformation on tempering (and HT in general) is so prevalent that it is quoted by many good and knowledgeable makers. I used to use the same info until I learned a little more about the metallurgy of HT.

The reality is that ,with proper regulated equipment, the HT can and often will be far better than the old timers were getting with their "by eye and a magnet" techniques ,and their mystic quench media blends.

I commend you,Robert, for doing it the right way ( I know, It is not the only way) and using controlled equipment. What you need is a good copy of the ASM Heat Treaters Guide, or something like it. That will give you a whole new look at what is going on in the steel, and how to control it.

BTW, We all break a blade from time to time trying to straighten it. I now check the blades while around 700-800F to straighten while they are still austentitic. Little bends can be gently tweaked later, but if there is a big bend or warp after the blade cools to room temp, I re-do the HT. Re-heating a martensitic blade to 400F won't be the same as bending a 400F austentitic blade. The austenite will bend by hand easily, the martensite will snap like glass.

Stacy
 
If you had all of your ducks in a row for steel set-up and then had a good quench as well, followed by proper tempering, trying to bend a hardened 1095 blade would be futile.
It sounds like you may have either got it full hard and then under-tempered it, or it had a hidden crack.
If I feel I did things right up to and including my quench on 1095, W1/W2, I do three two hours tempers at 425. Maybe higher with a little testing.
Two one hour tempers at 400 on full hard 1095 accomplished almost nothing.
It would still be brittle.

Looks like Stacy and I replied at exactly the same time!
 
Sounds to me like something went wrong when tempering. Hardened steel is very brittle and needs a good soak at the appropriate tempering temperature. But I'm sure you know that. Can you explain your tempering process?

When I was teaching workshops on tool making I would always take hardened tool steel (not knives) and smack it on the anvil and split it to illustrate the importance of proper tempering. The typical reaction was usually: :eek:
 
In my opinion, Stacy nailed your problem. You did every thing the right way, except for the temper heat. Try another, or a test piece, using Stacys recommendations and see how that works for you. I think you will be pleased with the results, but you might look into a better quench tank for your needs.
 
Karl B. Andersen said:
If you had all of your ducks in a row for steel set-up and then had a good quench as well, followed by proper tempering, trying to bend a hardened 1095 blade would be futile.
It sounds like you may have either got it full hard and then under-tempered it, or it had a hidden crack.
If I feel I did things right up to and including my quench on 1095, W1/W2, I do three two hours tempers at 425. Maybe higher with a little testing.
Two one hour tempers at 400 on full hard 1095 accomplished almost nothing.
It would still be brittle.

Looks like Stacy and I replied at exactly the same time!
Click to expand...


thats pretty much what I was thinking, I just wanted to see where the crack was--if it was from a stress riser.
 
If you are wondering about 2 seconds after the blade turns black in good quench oil, it should be stuck in a path to form as much martensite as it can even if it finishes cooling slowly and still hot enough that you can move it around for a while without breaking it. It is one of the amazing things I have found out by studying steel. The 600 degree steel as it cools from the quench will behave differently than if you reheated it to 600 and ruined the temper. Steel at 600 coming from the quench is easier and safer to bend than steel heated to 600f.
 
Well, I can't help with your problem, because I'm having issues of my own with 1095. However, it has been incredibly useful to read what everyone here has written in response to the issue.
 
I think under tempering was the cause.... and yes, my tempering temperature was a relic from when I had a one-brick forge and a pan of ATF, haha :o I'll temper higher then next time I have some 1095. Thanks for the help :thumbup:
 
This chart might offer a bit of assistance to some...


Also, the most heat treat and tool steel guides recommend 2 tempering cycles for simple carbon steels, with each cycle for two hours.



web.jpg
 
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