Crystalizing

[antq_colt_fan]

I havent posted anything in a while, but I have been a lurker here for quite some time.

I just recently got a gas forge built. It is made of firebrick and has chamber dimensions of 4x4x9 inches. I have been playing with it for a while and decided to try heat treating a blade I had ground out of what I thought was L6.

I did the first heating to critical and quench the blade in trasmission fluid. Without tempering I did the brass edge test. The edge curled and stayed that way. I thought that was odd, so I did the heat treat again and again the edge curled. I decided that maybe the quench medium was not right so I did the quench the third time with just water. The edge still curled. I was looking at the blade and was using my thumbs to kinda see how the blade flexed and 'snap', the blade snapped in two. The metal looked like it crystalized. Since I havent done any heat treating before, what the heck happened?

One other question. I am running about 10 psi on the gas. Should I expect to be using less or more? My burner is built like Ron Reil's.

Thanks for any help.

[Thingmaker]

How are you checking for critical, and how are you checking for L6?

[mete]

First the basics - all metals are crystalline - so the blade can't "crystallize !! It's a poor idea to assume what a saw blade is made from .If you have a "mystery steel" you should always test a piece to see if it will harden properly. What you probably saw was excessively large grain size from overheating. You should be about 50 F above critical and for lack of fancier instruments use a magnet to check.

[antq_colt_fan]

Critical was checked via the magnet test.

The material came from a farm implement and the part of the implement that was used is supposed to be L6.

This is not the first blade I have made from this material. It is my second. The first I heat treated via charcoal in a retrofitted charcoal grill with a blower attached to it, creating an incredible blast furnace. I heated the blade until what seemed like it should be long enough and tested it with a magnet and when it didnt stick, I tossed it in a pan of transmission fluid.
After tempering it at 450 for 45 min. I then cleaned it up. Finished it and took it to an aquintance at that time who made knives for a living and told him what I did. He looked it over and said that based on the hardness and the tempering time and temp and knowing what I took the material from said that it was most likely L6.

Yes, crystalizing is the structure of metal, I guess I should have said that it was very large grain and looked like cast iron.

So, the thought is that I got it too hot?

[antq_colt_fan]

Well I think I may have answered my own questions.

For one, I think I underestimated the efficiency of my forge. My forge heated the metal so fast I did not realize that I was reaching critical in a matter of a couple minutes. In my mind, the time that I thought it would take to reach critical, in actuality it was going well beyond that.

Two, I should have been more observant of the color range of the metal. The color was a somewhat yellow. As an estimate I had the blade in the gas forge for 5-7 minutes. So based on color I was reaching somewhere in the 2000 degree range.

Now, the "crystalizing" as I called it, from reading more and more about the heat treating process and grain growth. I think what I observed was grain growth from over heating the blade.

Would you agree?

[mete]

Yes !!! Keep learning !

[sdcb27]

And dont trust your eyes, color is a good "helper" but varies lighting conditions on your own shop can change the looks of the color as Mete said ,for lack of better use a magnet. For sake of exsperiment test your eyes at various light conditions with a magnet and i bet youd be amazed at the differances.

[Kevin R. Cashen]

The first time you pull a 1500F. blade out of salts (where there is no surrounding bright light sources to mess with your eyes) you will be astounded at how COLD 1500F actually appears. And then you will also get the queezy feeling at how badly you, and many,many others, have been overheating blades. I have come to believe that a VERY large number of knives being made have overheated tips, and I have also come to suspect that the morbid paranoia that bladesmiths have about blades that could break is the result of multitudes of folks habitually overheating without even knowing it.

[SteveA]

I normally run my Reil burner in a forge about that size at 4-5 pounds.

And I've done the magnet test starting well below critical, where the magnet still sticks, and going up. As Kevin said, just with that method I'm amazed how cold 1500 is.

Steve