Stacy E. Apelt - Bladesmith
ilmarinen - MODERATOR
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Knifemaker / Craftsman / Service Provider
- Joined
- Aug 20, 2004
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That is pretty much how it happens.
This is a great video clip of a sword in a water quench https://www.facebook.com/photo.php?v=245811752214385&set=vb.100003566854392&type=2&theater
You first see the "tip dip" as the edge cools and contracts. At this point the edge and spine are still austenite, which is very rubbery. The thermal contraction of the edge pulls the tip down in a negative sori. As the edge stays austenite ( because it missed the pearlite nose), the clay covered spine cools a bit slower and starts to convert into pearlite. Suddenly ( at the speed of sound), the edge converts into martensite, which expands because the lattice take up more space than austenite. At the same time the still soft pearlite is cooling and shrinking. This makes the blade rapidly curves upward. (You can hear and feel the shock waves caused by the rapid conversion of the martensite)
If the spine is has become partly martensite due to the clay falling off or being put on wrong, or the spine cools too much too soon...the blade will literally tear the edge apart in one or more places with a loud "TINK".
In an oil quench, the rates of cooling are just enough slower to have the martensite conversion not overcome the spine. This can cause the blade to cool with the tip remaining slightly dipped. Most of the time it is easily taken care of with a little adjustment while grinding, but on a long blade or sword, it can be a real issue to have. Quenching spine first is a method of avoiding this on heavy and large blades.
This is a great video clip of a sword in a water quench https://www.facebook.com/photo.php?v=245811752214385&set=vb.100003566854392&type=2&theater
You first see the "tip dip" as the edge cools and contracts. At this point the edge and spine are still austenite, which is very rubbery. The thermal contraction of the edge pulls the tip down in a negative sori. As the edge stays austenite ( because it missed the pearlite nose), the clay covered spine cools a bit slower and starts to convert into pearlite. Suddenly ( at the speed of sound), the edge converts into martensite, which expands because the lattice take up more space than austenite. At the same time the still soft pearlite is cooling and shrinking. This makes the blade rapidly curves upward. (You can hear and feel the shock waves caused by the rapid conversion of the martensite)
If the spine is has become partly martensite due to the clay falling off or being put on wrong, or the spine cools too much too soon...the blade will literally tear the edge apart in one or more places with a loud "TINK".
In an oil quench, the rates of cooling are just enough slower to have the martensite conversion not overcome the spine. This can cause the blade to cool with the tip remaining slightly dipped. Most of the time it is easily taken care of with a little adjustment while grinding, but on a long blade or sword, it can be a real issue to have. Quenching spine first is a method of avoiding this on heavy and large blades.