Questions on a failed 3V heat treat

Outline your heat treatment for us.

Hoss

 

Just a comment, but there is no need of advantage to the overnight soak in the dry ice bath. Five or ten minutes is sufficient. Once the blade reaches the -90°F temp, the Mf is done. It probably won't hurt to leave it, but isn't necessary. The best method of HT is to do the first temper immediately after the blade reaches the Mf.

A dry ice bath is to reach the Mf point.
Cryo, in liquid nitrogen at -320°F requires a longer time to create changes in the structures and form eta carbides. Overnight won't hurt in cryo, but it really only needs an hour or so.

 

Theoretically it is better to go straight to tempering after cold treatment to Mf, rather than waiting over night yes? Or am I remebering wrong?

 

There can be a minor danger to long cold treatments for the same reason many datasheets recommend tempering right away (the steel is brittle and may crack without tempering). That said, I’ve never heard of a knife cracking in cryo overnight apart from laminated blades, probably because of the thin cross-section used in knives. I often leave knives in cryo overnight to let my furnace cool down to temper in.

Leaving in liquid nitrogen for extended periods of time does not lead to any benefits either, I have written about that extensively in the past.

 

If you left them in dry ice slurry over night and the reach room temperature they may crack from the stress waiting to be tempered.

 

This is a problem. This steel is forming most of its martensite in this temperature range. You want a relatively rapid quench at first that gradually slows down a little during the martensite formation temperature range. It is usually okay to dunk hot steel into water most of the time, but never during the primary quench.