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Bill, ok seems to work for me today.
A lot that you have asked about has already been said on this forum but at risk of repeating some of it I will tell you how I do it. As you probably know the cryo cycle is used to help in the full transformation to martensite. Some steels do not fully transform when quenched down to room temperture. The higher alloy steels seem to benefit most from this step. If the transformation is not complete then the "retained" austentite can cause problems later. Over time it can transform by itself to martnensite which is then untempered and highly stressed. This can weaken a blade and maybe cause breakage later if there is enough of it. In addition I think it is best practice to get as close to 100% martnensite as possible and then temper it back. At least then we have some control of the crystal structure and do not have to guess at what the end result is. This is mostly a quality control step and some will argure that it is not necessary. It may not be necessary on some steels but I have found that on the CPM steels and 154CM that I can see a benefit. As soon as the blades are quenched down to room temp. I imerse in LN2 directly. I leave them in two hours. More time will not hurt anything, but does not seem to help either. Most of what is going to happen will happen in the first hour according to Ed Severson (metalurgists at Crucible now at a different steel company). As soon as the blade is removed and warmed up to room temp I temper at least once. I have read that it is best to keep the process moving and some steels can "set" and will not transform even in LN2 if enough time goes by between the quench and cryo cycle. I have never had a blade crack like my friend Ed Schemp has, probably lucky. On 154CM, 90V and 10V I can measure a one point hardness increase after the LN2 cycle. So I know on these at least there is a measurable change. All of this is based on what I have read, and discussions with some metalurgists that I have a lot of respect for. Hope this helps some.. Phil
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