Thread: forge ideas

Originally Posted by Mike Blue

Do you need to do this for every blade? The ABS spends a good deal of energy specifying a differentially hardened blade in their testing criteria. There are a lot of folks making Japanese style hamon on their blades. By definition, those are not fully hardened. Some steels do not through harden and others do. Which of those are best for razors?

I agree that you are better off understanding metallurgy when heat treating, but I want to know how tempering produces bainite. And explain the difference between tempered martensite and bainite. Why is one better or worse than the other? How does this play into the world of razors?

Differentially hardened blades are technically fully hardened, the part of the blade that is hardened (under the hammon) needs to be fully hardened like any other blade, on one of these though there is a boundary where a softer steel structure comes into play. the came thing goes for case hardened blades. the cutting part needs to be fully hardened, if it is connected to a piece of softer steel that is okay, as long as the soft steel is not your cutting edge.

Yes some steels harden to different depths, that is mostly with case hardened steels relative to amount of carbon that penetrates the steel during carburization; the other case is when thick sections are hardened where internal heat can temper out the quench from the inside/cool too slowly. Razors are so thin that any of these issues become irrelevant, unless you were differentially heating a 4/8ths razor with a huge spine I don't think you could cause those types of problems. Something else would be preventing the blade from hardening. Martensite is a very hard crystal structure formed from rapid cooling of austenite, the carbon gets trapped in the martensite.