are we doing anything to the grain structure?

It has been my belief that the grain structure shouldn't be affected as long as the heat was maintained properly and kept below the transition point.

Here's my concern with this process. We are trusting that the colored oxides (I guess they are oxides)are an accurate indicator of the temperature of the steel. As oxide formation is affected by the availability of free oxygen in the atmosphere and can also be by humidity, how much can these colors be trusted? I think I have seen evidence that the formation of these oxides can be dependent on the atmosphere. If you heat just one side of a piece of steel with a torch, the side opposite the torch flame develops bright oxide coloration. On the side where the flame is being played on the steel, the atmosphere of the flame hinders the formation of the oxides, so it doesn't display the same coloration. As I heat the blade on both sides with a torch, I have to wonder if the colors that I am seeing are an accurate indicator of the heat. What effect does the flame atmosphere and also the water used to keep the edge cool have on the forming of the colored oxides?

I always adjust my torch flame to be very slightly oxidizing; though I'm not certain that is the best setting. I know that I tend to over analyze everything. But inconsistencies in a process make me crazy when I am trying to achieve consistent results. My concerns about the accuracy of the oxide colors are one reason why I repeat this process several times. I use my intuition about how much heat I have applied with the torch as much as I do viewing the colors to decide when I have heated the blade to the correct temperature.

Brion,

One hates to admit their early mistakes, but I had many. Back when I was learning to bladesmith I would go visit or call Don Hastings. On a trip down to his shop I took a couple of blades without handles or guards. Don asked me if I wanted to test them. These were the first knives I had shown Don and we took the larger one about a six inch blade and cut with it. It did okay and Don pointed out lots of things to improve on the grind. He asked me if I had broken any of them and I had not. I took the hint and we broke the blade we had been cutting with. The grain structure of the edge was okay, not great, but okay. As you followed broken section toward the spine the grain size became very coarse and then about 3/16th from the spine the grain size was very fine by comparison to the rest of blade. Don asked a couple of questions about drawing the back of the spine and then pointed out that I had likely gotten the spine hot enough to turn it into austenite reforming the grain structure. I remembered the spine showing an bright orange color as I moved my oxyacet torch across it. Of course at the time I thought this was a good thing to make sure the back of the blade was really softened. Now this is early 1980s and I was pretty naive if not ignorant. Lots to learn.

So, I likely had a fine pearlite but given the cooling rate of the blade with its edge in the pan of water, I could easily have had some untempered martensite along the spine. Obviously, that would actually have weakened the blade unless I had re-tempered it. But at the time I did not know that. Here is the error I made. Don had described spine drawing and it made sense. My lack of knowledge then took it another step. If heating the spine made the blade stronger, then I was going to REALLY heat the spine and really make sure it was softened and tough. Too much of good thing is often not a good thing. So I am very careful not to get the spine too hot either.

Dan

After reading my post I should add that the reason all this difference in grain size took place was likely because I was not normalizing the blade correctly. Don pointed this out. So I had some coarser grain size in the blade as a whole. Without that we might never have noticed that the spine (with its fine grain size) was being over heated. I had messed up the whole thing. The only good part was that with Don's help I had learned a couple of valuable lessons. Yes, break your knives, test them and then try to figure what is happening.

Dan

That's some darned good advice - right there:

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Yes, break your knives, test them and then try to figure what is happening.

Dan

Reverse engineering.

I have a hard enough time trying to engineer it in forward!

|quoted:

Reverse engineering.

Dan,

Your two posts describe my first test blade, perfectly!

I have enjoyed this topic, and reading the responses you guys have experienced. It helps shorten the learning curve.

This topic has a lot of meat in it, so to speak!