Overheating 1080?

[onebagnomad]

I've heat treated a couple of small blades now using propane torches and canola oil but they came out pretty uneven (no surprise, right?). I'm on a tight budget and am now thinking of just throwing together a washtub coal forge just to have something that will give me an even heat. My concern is overheating (especially the edge side of my blade). I know 1080 is forgiving, but how forgiving? How hard is it to overheat 1080 and what are the consequences?

 

[Kevin R. Cashen]

Mr. Bagnomad, when I saw this thread I had my suspicions as to why it had gone unanswered, but your comment in “I've heat treated a couple of small blades now using propane torches and canola oil but they came out pretty uneven (no surprise, right?)”, indicated to me your willingness to advance and move to the next level of your craft despite your budget restrictions, and prompted me to help if I can. You will find a forge of any kind to be a pleasant improvement over your current tools. A coal forge with an enclosed fire can give surprisingly good results with a steel like 1080. I actually prefer using a coal forge with an enclosed fire over a gas forge if I have to demonstrate heat treating on the road. What I mean by an “enclosed fire” is a fire with a good bed below and a ceiling above to contain an atmosphere. This can be done with a hollowed out pile of coked coal or I prefer to make a tunnel of fire brick over the fire. This type of enclosure will hold in heat making an oven type arrangement, but just as important, it will make an oxygen free zone to work in and will keep your blade very clean.

Now about the overheating, and yes torches are very good at that. In 1080 the two main problems you will face are decarb and grain growth, as long as you don’t spark the steel, then it just needs to be thrown away. Grain growth will be the largest threat with this steel, keep things under 1500F (a dull orange, but that is hardly a proper description) and you will be alright. Above 1525F and you will have total solution and your grains will begin to grow. Expect to see this most at your tip and some on your edge. This is why I like the brick tunnel; it allows me to pass the tip through the other side and out of the fire until the rest of the blade is heated. I also heat the blade spine down in order to heat the thicker areas first and allow the heat to bleed more gently into the edge. The large grains will result in weaker steel. You will see significant losses in tensile (bend/flex) as well as impact strength. Your edges thus weakened will not hold up as well and will suffer micro blowouts that will result in quicker dulling.

 

[onebagnomad]

I appreciate the reply, Mr. Cashen. I know this post probably got a lot of unspoken "read the stickies" response. I've read your stickied post on working with different types of steels. While I've learned much from it, I'll be honest with you, a lot of the material in that post is just so far above my skill level at the moment that it's looking a bit Greek. I'm definitely on board with the small forge idea for a heat source. You mention keeping things under 1500F, I know a lot of people recommend the magnet test for 1080 but then say to go a couple of shades lighter before quench. I have partial color blindness so this method is less useful for me. Is there an inexpensive way to measure the temp of steel (even if only semi-accurately)? I've looked at various pieces of equipment, infrared thermometers being the most promising. The problem is it seems like the higher the temperature range you want to measure, the more costly the thermometer. I've got a feeling there is a really simple solution here that I'm just not seeing.

 

[me2]

You could use the "arrest point method". What that means is heating the blade until you see what looks like a shadow on the blade. It will get brighter and brighter, then seem to darken, then brighten back up. For 1080, this is when to quench. I've used it successfully on 1095, though it takes a lot of practice, and I have to do it in the dark to see the change. You can take a piece of scrap and do the heating until you can see the change.

Just use the same piece over and over, but don't quench when the temperature is reached, just let it air cool. Then when you are ready and think you have it right, quench the last time and break it. If the surface looks like gray velvet, you were right on. If it takes on a crystalline appearance similar to very fine rock candy, it was too hot. If putting it in a vice and pulling doesn't break it, but bends it, it didn't harden. Use gloves and eye protection. If you pull in a vice and it does break, its likely to shatter, so be careful.

Just so you don't get worried, the knife won't do this after its tempered. You probably knew that from the stickies you read, but I mention it for the benefit of anyone reading this that hasn't read them.

 

[David Wesner]

Hi Nomad, Brownells sells a product called tempilaq.
http://www.brownells.com/.aspx/pid=13124/Product/TEMPILAQ_reg_
$15 + shipping

Use per Brownells "Apply thin smear to surface to be treated. When desired temperature is reached, Tempilaq melts sharply. Disregard color changes, when Templiac melts, quench!"
They sell several different temperature indicating types. If I were doing it I would get the 1450*F Tempilaq.

Thanks for the earlier post Kevin. Everytime you post, I learn

me2, I think, is describing a phenomena called decalescence which is a very good method, but you'll need some practice to notice the change

 

[onebagnomad]

Hi Nomad, Brownells sells a product called tempilaq.
http://www.brownells.com/.aspx/pid=13124/Product/TEMPILAQ_reg_
$15 + shipping

Use per Brownells "Apply thin smear to surface to be treated. When desired temperature is reached, Tempilaq melts sharply. Disregard color changes, when Templiac melts, quench!"
They sell several different temperature indicating types. If I were doing it I would get the 1450*F Tempilaq.

Thanks for the earlier post Kevin. Everytime you post, I learn

me2, I think, is describing a phenomena called decalescence which is a very good method, but you'll need some practice to notice the change

Wow, that seems like a perfect solution while I play around with other methods/equipment. Have you used Tempilaq yourself?

 

[David Wesner]

Wow, that seems like a perfect solution while I play around with other methods/equipment. Have you used Tempilaq yourself?

No sir, I have not used Tempilaq.
I know a few other Bladesmiths from the forum have used it successfully and hopefully, will chime in.
Like I had mentioned, I would try the 1450* and once it melts, give your blade a few seconds more to gain the 25*F (to ~ 1475*F) before quenching.

You might also use the Tempilaq to watch for the decalescence that me2 described.

Use it as an indicator for learning to judge your temps by eye, your eyes

 

[Kevin R. Cashen]

I appreciate the reply, Mr. Cashen. I know this post probably got a lot of unspoken "read the stickies" response. I've read your stickied post on working with different types of steels. While I've learned much from it, I'll be honest with you, a lot of the material in that post is just so far above my skill level at the moment that it's looking a bit Greek. I'm definitely on board with the small forge idea for a heat source. You mention keeping things under 1500F, I know a lot of people recommend the magnet test for 1080 but then say to go a couple of shades lighter before quench. I have partial color blindness so this method is less useful for me. Is there an inexpensive way to measure the temp of steel (even if only semi-accurately)? I've looked at various pieces of equipment, infrared thermometers being the most promising. The problem is it seems like the higher the temperature range you want to measure, the more costly the thermometer. I've got a feeling there is a really simple solution here that I'm just not seeing.

Reading my posts laden with Greek tech talk has lead many people to draw the hasty conclusion that I am somehow against simple, inexpensive, or low tech tools. As I have outlined in this very thread, I often embrace many of these tools myself just for the enjoyment factor, and I dare say that I have explored many of the simplest and basic aspects of our craft more deeply than those who claim to champion that approach. The only thing I oppose about this approach, or any other for that matter, is failing to be honest about it, to others of course, but most importantly, to ourselves. It is not until we recognize our limitations, that we can develop an effective plan to overcome them. Simply ignoring or failing to acknowledge them, is surrendering to the “ignorance is bliss” philosophy for our lives, which seems to work well for cattle, but not successful people. I will readily admit to looking for signs of that philosophy in posts to determine if my time is best used in ways other than enduring the rudeness or ingratitude that invariably accompanies it. You however exhibited your willingness to advance your knowledge and methods, which I feel deserves answers that can build a bridge to the more technical stuff which I am sure you will one day have use for as well.

The magnet stops sticking at around 1414F for iron, and iron is the only thing in 1080 you can work with for ferromagnetism. The temperature you want to shoot for in 1080 is 1475F. The magnet works because we and our eyes are not good enough in a forge (and certainly with a torch) to stop all heating at exactly the nonmagnetic point and the margin for error conveniently falls within the proper range for the steel. Since I do have the tools to hold at exactly the non-magnetic point, I have done experiments along these lines and have found exactly how undesirable the results can be unless you also have a chip of the Blarney stone in your pocket to help fortify the results.

Although 1080 is forgiving enough that even the Currie point (non-magnetic) would result in an acceptable knife. Having said all this I would strongly advise that you not follow any suggestion to go under the Currie point since the accidental over shooting of it is often the only thing that makes it effective.

Your absolute best shot with the tools at hand is probably the already suggested arrest point or what is called “decalescence”. When the proper crystalline phase in the steel for quenching is formed, it requires a greater amount of energy than the even heating can provide and this will result in a loss of outgoing energy in the form of heat and light manifested in what people refer to as the “shadow”. Practice heating a bar of steel again and again and you can train yourself to recognize the steel getting brighter and brighter and then suddenly developing a dimmer band before brightening again. This dark band is the steel undergoing the crystalline change you want, and at the high end of this before things get too bright is the best temp for any steel you do this way. If you learn this well it is more accurate than the magnet.

 

[Dan maltwood]

I have been having a similar problem with heat treating 1070 at a 3mm stock.

I’ve tried using the magnet test and a laser thermometer which does not work well at all , it seemed before I was concentrating on getting the perfect temperatures the blades were much better in sharpness and edge retention,I believe what I have done is over think the hole heat treat process and have probably been over heating as the blade edge is reading 60+ on the Rockwell scale but the edge literally just crumbles away and doesn’t get sharp in the slightest , after reading the previous post I have now realised what I used to do where I would watch the shadow pass through the blade and then quench which gave great results but I didn’t know the theory behind it until now thanks to you all.


I’m really hoping this solves my problem with the crumbly edge.

thanks again you bunch of legends