Just for grins, I bought a 10" K Sab carbon chef's knife. I've been watching some old Julia Child vids and those carbon Sabs that she used looked so cool. I'm trying not to compare it to Japanese knives and judge it on it's own merits.
The F and F are very good. It's soft (HRC 54-56) but it takes a very wicked edge. Balance point is about 1/2" in front of the bolster but there is that pesky bolster.
It took a nice blue patina with warm rare beef but when I sliced a lemon the patina disappeared where the lemon touched the blade. I only have 3 other carbon knives and 2 of those are made from 52100. They were more difficult to get a patina and are surely less reactive to lemon (acids?) than the K Sab. I look it up and 52100 has 1.3-1.6% chromium. I cannot find what the makeup of the K Sab is but I'm thinking it may have no chromium. If anybody knows what the composition of the K Sab steel is, I thank you in advance.