Hardening and tempering in one step - water tub and torch method?

[doggonemess]

Greetings,

I recently had a conversation with a blade maker who told me that his method for hardening and tempering is as follows. Using a tub of water, he places all but the half inch of edge in the water. He then takes an oxyacetylene torch and heats the metal using slow circular motions until it is bright red. He continues evenly down the blade in this manner until reaching the end. When the color fades, he takes the knife out of the water and lets it finish cooling in the air.

This is very different from any other method I've heard of. Has anyone tried this themselves? Is this a standard practice I don't know about? The process seems logical, but at the same time, it seems to me that the blade wouldn't harden properly. The knife he showed me that used this method had a good, strong edge and seemed to be well made.

Any thoughts? 

Thanks!

[ThomasPowers]

Would totally depend on the alloy!  He's using a self quench as the cold metal abstracts the heat from the hot edge.

[doggonemess]

2 minutes ago, ThomasPowers said:

Would totally depend on the alloy!  He's using a self quench as the cold metal abstracts the heat from the hot edge.

If this works as a quench, that's great, but what about tempering? Wouldn't this method result in a really hard edge? Or does the heat moving down the blade serve to temper the region near the part being heated? If so, wouldn't the extreme heat nearest to the 'active' area destroy any tempering? It seems like it could work, but also that it shouldn't.

I did try it myself with a MAPP-Pro torch. FYI - MAPP-Pro isn't hot enough to get the metal glowing red when the rest of the blade is submerged. Good to know. The blade didn't really harden much - I managed to roll the edge by hitting a tree stump with it.

[ThomasPowers]

I picked a plant on the side of the road is it good to eat?   Why can't you tell me????? Whenever you discus heat treating WITHOUT stating the alloy it's a lot like that question. Not listing the alloy he used or the alloy you used is pretty worthless. Were you even using a hardenable alloy? We've had a lot of folks come through here that have made knives from mild steel and then want to know how to harden them.

That method almost certainly will not produce the best heat treat for any alloy I know. In someways it's like the japanese sword quench where they do not temper the edge but use the unhardened body of the blade to hold things together.  Note that the japanese have a very structured process to get that using very shallow hardening steel.

 

[Steve Sells]

while it may work, he has no control over tempering or hardening, much is left to luck

[ThomasPowers]

I strongly suggest you do NOT place you hand in the pan to see what temperature water he is using!

[Frosty]

I'm no bladesmith but have been heat treating tools as needed for decades. I wouldn't own a knife heat treated in that manner without being able to examine, hands on, a few examples of these blades tested to destruction. Eg, bent 90*. 

You'll be far more likely to be successful if you buy a knife making book and do it THAT way. There are world renowned blade smiths who are  published authors on the forum. And don't mix and match different techniques, methods and equipment until YOU have been doing it successfully for a few years.

When I teach I don't let students actually use chisels they've made and heat treated in my shop. We test them by wrapping them with a shop rag or in a short piece of rubber hose to act as a scatter shield in case they shatter when struck. The student hold them with a pair of tongs and give them a few good smacks with a 2-3 lb. hammer and we check the chisel and results on the mild steel test coupon. 

The chisel is the student's property of course, they can do with them as the wish AFTER they leave my shop but I recommend they be very careful if they use them. I'm always very careful using struck tools I've made. There are NO guarantees with home heat treating unless you have the equipment and expertise to use it. This is why most professional bladesmiths heat treat conservatively.

Frosty The Lucky.

[doggonemess]

2 hours ago, ThomasPowers said:

Whenever you discus heat treating WITHOUT stating the alloy it's a lot like that question. Not listing the alloy he used or the alloy you used is pretty worthless. Were you even using a hardenable alloy? We've had a lot of folks come through here that have made knives from mild steel and then want to know how to harden them

The steel he used was 1095. I used an old file since I didn't want to spend any money on an something I had little confidence in.

Sorry, the first responder asked the same question and I forgot to answer. Despite my post count, I'm actually somewhat experienced with this, having done it as a hobby for almost eight years. I did make the mistake years ago of trying to make a blade with mild steel, so I'm definitely not innocent of that. I've also made a bi-steel blade with a spring steel edge and folded wrought iron core; I love the way it turned out and would like to do it again. Hence, I'm very interested in differential tempering, especially if there are easier ways to do it than what I've read about.

[JHCC]

26 minutes ago, doggonemess said:

I used an old file

Old files can be anything from 1095 to case-hardened mild steel. I don't know if this would work for 1095 (although I suspect not; see below), but with a mystery steel, it's a total crapshoot.

As for the method itself, in order for the steel to harden, it has to be hot enough for the iron atoms to move from a body-centered-cubic crystalline structure (ferrite) to face-centered-cubic (austenite) which is then rapidly cooled to create a body-centered-tetragonal structure (martensite). I can see heating the entire blade, quenching the edge, and then allowing the entire blade to air-cool (thus allowing the residual heat to autotemper the edge), but I have a hard time seeing how the edge would get hot enough to harden using the method as described.

However, I am not a bladesmith and am open to correction on this from folks with more experience and better metallurgical understanding than me.

Please keep in mind  that there is a BIG difference between differential hardening and differential tempering. With differential hardening, you heat the entire blade and only quench the edge, thus creating a hard edge and an unhardened spine. With differential tempering, you heat and quench the entire blade, and then temper the blade by heating the spine until the edge reaches the proper temperature. Both result in a harder edge and a softer spine, but the differential temper will (all other things being equal) be a good bit stronger.

[Steve Sells]

I will relocate this to the knife section seeing how that is the way this is going, but i want to state that attempting to harden 1095 that way is a joke, this method leaves no soak time to get the carbides into solution, I suggest you read the HT sticky pinned to the top of the page

[doggonemess]

Thanks very much to all of you for your help with this topic. After searching for info on it and failing to find anything, I didn't know who else to ask.

26 minutes ago, JHCC said:

Please keep in mind  that there is a BIG difference between differential hardening and differential tempering. With differential hardening, you heat the entire blade and only quench the edge, thus creating a hard edge and an unhardened spine. With differential tempering, you heat and quench the entire blade, and then temper the blade by heating the spine until the edge reaches the proper temperature. Both result in a harder edge and a softer spine, but the differential temper will (all other things being equal) be a good bit stronger.

Good point, thanks for that. 

[Latticino]

I agree with John (JHCC).  The procedure you have described sounds like differential tempering, if the edge of the blade was submerged in the water and the spine heated and left to cool slowly.  Is it possible you misunderstood the smith (or could he have been deliberately been giving you mis-information)?  Even if this procedure is being used for differential tempering (after a full hardening quench) I would have my doubts on how effective it was, since heating to any glow would over temper the blade spine and there would likely be enough residual heat after leaving the water to autotemper the edge too far as well.

That being said there is a single step hardening/tempering process that is fairly common and I've used before.  I've done it with 4140 chisels and hammer heads, but it works with any shape that has some significant mass that you want to keep soft.  In this process you heat the entire piece up to transformation temperature (decalescence) then only quench the working edge for a relatively short count (just past the "nose" of the TTT chart).  Pull from quench media and quickly clean oxides off surface with sandpaper or piece of abrasive stone.  Then watch the residual heat from the rest of the piece "run the colors" to temper the edge to desired hardness.  Quench edge again to stop the process and repeat the color run if you will have residual heat.

[ThomasPowers]

For differential tempering, have you tried tempering tongs?   They seem easier to use with precision than a torch.

Differential hardening is tricky indeed, I've already mentioned the japanese method using shallow hardening alloys and applying clay to the spine to keep it from cooling quick enough to make the nose.

[Frosty]

The process you described in the OP sounds like something someone told you who is NOT a bladesmith. As described it wouldn't work very well if at all. 

This is one of the real problems learning things on the internet, the only qualifications you need to be an expert is a video camera and connection. Unless he demonstrates his technique and proves the blade I'd take ANYTHING he says about blades with a bunch of salt.

Don't sweat it we've all been sent down bad paths by a convincing BSer. And yes, you can BS a BSer, I know from experience.

Frosty The Lucky.

[JHCC]

Hey, I said I was sorry!

[Frosty]

2 hours ago, JHCC said:

Hey, I said I was sorry!

HUH? . . . Why? 

Frosty The Lucky.

[Cedar Crest Forge]

1095 is a common alloy, with very clear steps for the hardening and tempering process. I agree with everyone, there is no reason to reinvent the wheel. It's not like this new backyard process will produce a more consistent blade. Collectors like consistency, ie known properties. If they buy a 1095 knife, they expect 1095 performance..exactly as they have read about it.

[ThomasPowers]

However selling is often about the "sizzle".  Look at how many Railroad spike knives get sold yet they are not a good alloy for knives.

[JHCC]

True, but RR spike knives are more about the shape than alloy. 

[ThomasPowers]

KSOs at best!

[doggonemess]

Greetings again, all!

I have an update to this topic. The man who taught me this technique is a master bladesmith. He brought in examples of his work, including ones that survived testing. He has had his blades professional tested for Rockwell hardness, coming in around 60 HRC. He's definitely no BSer, and I've met quite a few. He can back up what he told me with actual evidence. On top of that, he brought one of his blades and did the hardening at the forge one day. I asked if it would work on a 5160 sword blade. He wasn't sure, but he was excited to try, having never worked with a long blade.

Below is the video, check it out if you're interested. I can attest that the blade is hard and flexible. I gave a hard stump a few good whacks and didn't see any deformation of the edge. Granted, this isn't a real test, but my own failures in tempering have taught me enough to know when the process failed. How good it is, I don't know, but it definitely can be sharpened and can cut without bending or breaking from the stress.

I've got some pictures, too, which I'll upload shortly. 

On a side note - the water was ice cold when we started and like warm bath water when we were done. That's A LOT of heat if it warmed up that much water that quickly.

Heat treating process: https://www.youtube.com/watch?v=vcJ5VI7zazo

Testing edge with file: https://www.youtube.com/watch?v=vsM5sGgBWOw

[doggonemess]

Here are a few pictures of the process and the results.

The sword is made from 5160, which he recommended for this technique. I may have been wrong before when I said he did this with 1095; if so, I apologize.

The thinness of the steel made it challenging - I'm glad that someone with a lot of experience did this part. It definitely reached transformation temperature all along the edge of the blade, but a less steady hand (mine) probably would have ended up burning it.

 

Below is the smith doing the work. His name is Bill, but I missed his last name. He's been making knives professionally for decades.

 

Here's the finished product.

 

The edge was good and hard. I can see from the color that the tempering went a little too far in a few spots, moving out of blue and into grey, but I don't fault him for it. This was the first time he'd worked a blade this thin and long, and it required a great deal of focus and effort to keep it as consistent as he did. Below is one spot that got cooked, but the rest of the blade was excellent.

NOTE - His blades that he showed me did not have this issue. He's far more skilled at blade crafting and my blade had very inconsistent thickness, making it almost impossible to treat evenly. When I watched him do this to a proper knife, the end result was perfect, no variation in the color.

 

Interestingly, the finished blades he showed me had edges that looked like hamon from proper katanas. Maybe this method produces a similar effect to the clay/water technique used by Japanese smiths.

[Steve Sells]

No it wont.  How can anyone expect to get it to harden evenly with a hand torch?  There is no way to get it all hard at once,  Some areas will partly cool on their own while others are heating, therefore there will be areas of non hardened material,  just a mess and hype over science ending up with a poor quality end result

[JHCC]

So just to repeat: he’s got the bulk of the blade submerged in water except the edge, he heats the edge until it’s glowing, keeps it in the water until the edge stops glowing, and then he lets it air-cool?

I’m no metallurgist, but this seems problematic for a couple of reasons. The torch heating might well get the edge above transformation temperature (to convert the ferrite into austenite), but is the water bath enough of a heat sink to cool the edge fast enough to convert the austenite to martensite (especially in a non-air-hardening steel like 5160)? Even if so, how does that martensite then get tempered to remove its brittleness, when there’s no more heat being applied?

[Steve Sells]

without the quench its mostly just normalizing which leaves a tough blade,  but as for an edge, well  I can put an edge on an Aluminum can quite easily but it wont last either