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Interesting. I just read a bit about martempering in Verhoeven's book. It helps prevent quench cracks. I will have to give this a try. Might be a bit tricky to interrupt at the right time though

Sounds to me like the steel is too soft. Either over tempered, pulled from quench too soon, or overheated during buff.

Have you measured the bevel angle?

My understanding of the two temper cycles is that on cooling from the first cycle, retained austenite is converted to fresh martensite and the second cycle tempers this fresh martensite.

It should be long enough to bring the steel close to the temperature of the oil. If you stop the quench too early you run the risk of the internal heat bringing the steel back up to above 200 C and...