Oil over water quench?

mete said:
You need fast followed by slow. The oil over water is just the opposite.
The limits of how big a bar can be through hardened is determined by the 'hardenability' [dependent on chemistry] and the speed of the quenchant.Many applications do not require through hardened.
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Besides distortion (a thin knife edge that may have fallen off center), cracking, warpage, etc. is there a danger, or downside in cooling too fast through martensite transformation ?

Would it be safe to say that as long as you've made it past the pearlite nose on the TTT chart and don't end up with any distortion in the knife after the quench is complete, that you're moving slow enough through martensite transformation stage? Even though you might be using the fastest of quenchants (whatever that may be) ?
 
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There are the obvious problems as you mentioned but there is one not visible - microcracks. These cracks may be internal and you may not know about them until the blade cracks in use.
The rule then is that it's best to quench no faster than necessary to get the martensitic structure.
 
Also remember two things. When mete says microcracks, the operative word there is micro! Even if they aren't internal, they can be very much to small for you to see.

The other thing that makes them a bitch, is the tendancy for cracks of any size to propegate. Those microcracks will not be invisibly small forever...
 
That would make a cool Demo. :D

... don't forget to bring your transmutation chips!
 
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