temper times

[Bill Siegle]

I was asked by a friend why 3 two hour tempers? Why not 1 six hour? I couldn't really answer other than thats the way I've always done it. Anyone care to field this one? Thanks in advance.

Bill

 

[Arrow-Dynamics]

Hi Bill,
The cooling of the part (in this case a knife blade) to ambient temperature is part of the tempering/stress relieving process and is as important as the time in the tempering oven. The actual cooling of the part is the mechanism by which the matrix is stabilized…the heating time is only to make sure that the part is completely “soaked” through and through.

When steel is heated to the critical temperature (the point at which it becomes non-magnetic) it’s grain structure is transformed into Austenite. Austenite is characterized by a very large, irregular, and coarse grain structure. As it is quenched the grain structure is transformed to the hardened structure called Martensite. “As quenched” Martensite grain structure is very hard and fine but it is also very unstable and brittle. The tempering process allows the matrix to stabilize resulting in tougher and softer material depending on the tempering temperature.

Take care,
Cecil

 

[Bill Siegle]

thanks for the quick response. I was pretty sure the cooling was an important part of the process but I wasn't positive. Thanks