Heat Treating Media
Published: 11 years ago
http://www.northarmknives.com
Heat treating is probably the second most important step to making a knife, the first being the steel is actually in the shape of a knife! During heat treat the steel undergoes a change in structure making it much harder than its soft annealed state. This hardness is what gives a knife its ability to hold an edge a long time and also to take a good sharp edge.
The first part of the heat treat is the hardening (or austenitizing) phase; the blades are brought up to a very high critical temperature and then cooled very rapidly to room temperature between aluminium plates. After this step the blades are very hard and also very brittle.
The second step is the tempering phase which slightly reduces the hardness but brings down the brittleness a lot making the blade much tougher; The blades are brought to a lower temperature (typically a few hundred degrees Fahrenheit) and held there for 2 hours. The blades a re cooled and an identical second tempering step is preformed.
Every type of steel has a slightly different heat treat "recipe". Depending on its chemical composition the temperatures used will vary. The steel we use (CPM S35VN by crucible industries) is in a group of high alloy steels that require extremely high temperatures to properly harden. The knives are hardened at 2000 Fahrenheit and tempered at 600.
The extreme temperature of the hardening phase will badly damaged the steel through oxidation and decarburization if it isn't protected. To prevent damage each blades is wrapped in a pouch of thin stainless steel foil with double folded seams.
We do all of our heat treat in house using an evenheat electric kiln.
Heat treating is probably the second most important step to making a knife, the first being the steel is actually in the shape of a knife! During heat treat the steel undergoes a change in structure making it much harder than its soft annealed state. This hardness is what gives a knife its ability to hold an edge a long time and also to take a good sharp edge.
The first part of the heat treat is the hardening (or austenitizing) phase; the blades are brought up to a very high critical temperature and then cooled very rapidly to room temperature between aluminium plates. After this step the blades are very hard and also very brittle.
The second step is the tempering phase which slightly reduces the hardness but brings down the brittleness a lot making the blade much tougher; The blades are brought to a lower temperature (typically a few hundred degrees Fahrenheit) and held there for 2 hours. The blades a re cooled and an identical second tempering step is preformed.
Every type of steel has a slightly different heat treat "recipe". Depending on its chemical composition the temperatures used will vary. The steel we use (CPM S35VN by crucible industries) is in a group of high alloy steels that require extremely high temperatures to properly harden. The knives are hardened at 2000 Fahrenheit and tempered at 600.
The extreme temperature of the hardening phase will badly damaged the steel through oxidation and decarburization if it isn't protected. To prevent damage each blades is wrapped in a pouch of thin stainless steel foil with double folded seams.
We do all of our heat treat in house using an evenheat electric kiln.