Retained Austenite??

You read so much on the web about heat treatment of blades and the latest techniques used, I was wandering about the question of retained austenine and is it really much of a problem when it comes to treating a razor?
Firstly are you likely to get much if any retained austenite with a eutectoid steel like 1084? As for the higher carbon steels what is the issue around the austenite left after ht, is it likely to chip at the micro level?

Also for those that do the cryo treat, would a further tempering cycle be required in real terms considereing the function of a razor?

Deckard

It's a simple question with a simple answer. Some want it to be more complicated, but there lies the realm of marketing.

You have the concept understood. Iron can only combine with, or take up, a finite amount of carbon. The idea of eutectoid is that the balance between iron and carbon for steel is good. Adding alloying elements (chromium, molybdenum, tungsten, vanadium) all of which form their own carbides helped folks discover that higher carbon contents were possible. So if more is good, more is better? But there's a point where too much of a good thing has a price.

It's probably the retained austenite that is the general initiating point for blade fractures, since the martensite that forms after heat treatment is tougher. Tempering the initial martensite will convert a little of the retained austenite forming untempered martensite. Untempered martensite is more brittle (another source of fracture) than tempered martensite and will benefit from another tempering cycle. These cycles often come in threes, probably because there is no measurable advantage to doing more (the point of diminishing returns and practical costs).

Edges that are chippy could be simply too hard, the heat treatment may not have been the optimum for that particular steel (hardening and tempering) and there may be the possibility that the edge grind didn't remove enough material after heat treatment leaving behind some decarburized steel. For old razors, we will never know since the factories and methods are lost to review. These are only a few of the variables possible here.

After cryo, tempering is definitely required.

If you're looking to pick "the best" steel, I'd vote for a eutectoid steel and then batch heat treat multiple blades and record everything temperature wise. Then break them all to see what happened at the spine, at the edge, how the survivors shaved/honed etc. There is so much batch to batch variation what with old Ford bumpers and computer parts in the big ladles these days, each new batch of steel practically demands this ritual to know how it will perform.

Good question Deckard.

for the most part the more RA you can get rid of the better as tempered martensite is the better to have at the edge. alot of RA will act more like a over tempered blade makign wire edges that you have a hard time getting to brake off to get to a good clean edge

tho making your self crazy over RA (or some of the grain size dealings ) is not really worth it

a guy that makes a lot of clames oabout 52100 and grain size but claims that the way he does it works and that someone that does not forge or use his week long HT is not maxing out the steel (at the point of maybe 3 % difference and one that would not be able to be seen by most any end user)

Thanks guys.
I guess I'm looking to you seasoned smiths to offer some practical advice to a novice using simple steel. When I come to treat my first blade made of 1084, could I dispense with the cryo stage or do you think it's worth doing.
There aint no theoretical in my world.

Deckard :)

if cryo would help it would be so small that without scientific tools you would not see a difference

have you been over to hypefreeblades.com to read up on HT without all the bull crap yet

Not yet Lloyd, thanks for link.