The first Krenov plane I made I didn't incorporate a chipbreaker. That project was more about learning. It turned out to be a good little block plane. It was initially bevel up 25* iron on a 40* bed which I was able to take shavings on red oak of .003 thickness. To further experiment, I opened the mouth and flipped the iron over bevel down. With a mouth clearance of about 1/32 and no chipbreaker I was able to take wisps of wood from alder and QSWO that didn't register on my Starrett calipers.
I intend to make a whole set of planes in Krenovian style with my remaining bois d'arc. I get my bar stock for the irons/chipbreakers from MSCdirect.com. David Finck doesn't mention anything about hardening a chipbreaker. The color of the chipbreaker in his book looks like it has been oil hardened. The O1 stock comes soft, about 5 RC. I will definitely grind, shape, drill and tap before hardening. So the question: Is hardening the chipbreaker necessary? The only vintage iron I own is a #6 Union. I suppose I could take its iron and chipbreaker and have their hardness tested.