Brian,

Yes, I agree we have to try these tests in our shop to determine the quality of the product. This aspect of knife making is often left to others when a maker farms out the heat treat. That is where the ABS really shines. It teaches the principles of metalurgy and then proves them to us. However we have to take the information home and figure out how it works in our shop.

That's why it's good to go to shop visits and Hammer Ins to see how others do it and compare their methods to yours. It takes a certain amount of humility to make the necessary changes.

BTW, when you break the hardened steel, you might try wrapping a rag around it to catch all the pieces. Lin

What steel was used for the demonstration? Believe it or not this is very important to the methods and results.

This is a post I put on swordforum back in 2004 that illustrates the effect that alloying can have on grain refinement and how the methods must be adjusted for it. I have revisited it before on other forums and got very negative reaction to my intruding on others grain refinement threads, so I post it here with humility and some trepidation, but I have faith the smiths of the ABS will welcome it as a learning opportunity.

…The first series of images are of 1084 that has been heated to approx. 2100F. and then normalized at different temperatures without cooling to room temp in between. The bar was heated to 2100F. and then a specimen was sliced off, quenched and broke to reveal the grain. This was all done before the parent bar cooled below critical.

Image #1 is the steel grain structure as it was at 2100F. Image #2 is a specimen that was sliced off after the bar had cooled to the point that it just started to regain magnetism and was then reheated to approximately 1450F. Image #3 is a specimen from the same bar that was allowed to cool to around 1000F and was then reheated to approx. 1450F. and sliced, quenched and broke.

The results are obvious to see. #1 shows marked grain growth, #2 shows a very rapid reduction in grain size simply by heating from a stage at which some pearlite could begin to form. #3 shows a very nice grain from yet another reheat after complete pearlite was allowed to form. The grain is fine but the break is not clean due to the formation of fine pearlite before I could get the slices quenched. I could do this better, the next time, if I were to put a bucket of water directly below the cutoff saw and have the hot pieces drop straight in.

No forging was done on these pieces; all the grain refinement was the direct result of recrystalization from a microstructure that produced increased nucleation of the fresh grains. With 1084 this can be done by cycling at a relatively high temp without letting things go cold; the bar never did drop below 800F.

Now we have the next series of images:

This is L6 steel. #1 is heated to approximately 2100F. then sliced and quenched. #2 is from the same bar after it has cooled to approx 1100F. and then reheated to approximately 1500F and then sliced. #3 is from the same bar that has been allowed to cool to about 950F. and then reheated to 1500F then sliced, quenched and broke. #4 is the same bar allowed to cool to around 700F and then reheated to 1500, sliced quenched and broke…

This is a very graphic illustration of how alloying pushes the temperatures all around for these effects. It is quite simple, in order refine austenite grain you need to make new and smaller austenite grains, just reheating the same grains can only grow them. So to accomplish grain refinement you need to make another phase out of the austenite and then make new tiny austenite grains from that new phase on the reheat.

For 1084 that will begin to happen very easily and quickly at around 1100F when it makes pearlite, so simple cycling to dull red or black is more than enough. But alloying like chromium, and others, retard pearlite formation to increase hardenabilty. The L6 reheated from 1100F or 900F shows no improvement and actually gets larger in grain size, until you reach 700F and it finally begins to make a new phase (upper bainite), and then the grain reduction is very marked and immediate.

I have had people contact me wondering why they could not refine the grain of such steels and I gave them the simple cure of using the magnet on cooling. On cooling the magnet can be much more useful than on heating since it will tell you exactly when a new phase has been created and you can reheat to successfully recrystallize the austenite.

A tip for breaking steel- since I have to do a lot of it for metallurgical testing and analysis, I first score the piece (always keeping it cool) with a fine flex-shaft cutoff wheel and then fold a piece of duct tape over it. Suspend it between the wide open jaws of a post vice and give it a good sharp stroke with the peen of a cross peen hammer as precisely on the scored area as possible. All steel breaks in a cleaner and more brittle like fashion with sudden impact type loading, so this works much better than bending or pulling on it. The duct tape will keep the pieces contained both for safety and retrieval, I came up with this when I got real tired of searching my shop for the pieces after I broke them, some I never did find and had to repeat tests.

Kevin, the steel in the above test was 1084.

Are you kidding? No need to be shy here. I was hoping you'd give us some insight into this subject. I am amazed at the vast diference that 250 degrees makes in the L-6. It stands to reason that alloys would influence this aspect of a steel's behavior too. I, for one, welcome any other photos or examples you have. Thanks for helping out here. Lin

Kevin, thank you for posting and complete with good pictures, you are the man. While it may take me a bit to wrap my brain around your information, I always find it useful and really good stuff. We look forward to you sharing your knowledge on threads like this, it is exactly what we want. Thanks again.

Brion