HRC 57-59 ?

I know I read about this in the past but I seem to have forgotten about it again, what do they mean when they say "57-59" Rc (like the S6)? So what's the hardness, 57 or 59? Or is it 58? Or am I just making you guys laugh with my question? <img src="/ubbthreads/images/graemlins/blush.gif" alt="" />

The question about it being differentially or uniformly hardened never really got verified in one of the threads..or did it?

Hi, x!

The hardness of the steel can vary throughout the blade and from blade to blade. Steel is a mixture of metallic crystals and S7 likes to form both martensite and bainite crystals when the steel is hardened. The martensite is hard and quite tough, but the bainite is slightly softer (yet much tougher and more flexible). Patti or Dan mentioned a heat-treatment process they use called martempering. Martempering relieves the internal stress of martensite crystals in a way that's less stressful on steel than traditional quenching followed by tempering. It also increases the chances of bainite forming in the steel (if you want to get more technical, the bainite in S7 is usually lower bainite and the martensite is usually lath martensite - both of those are insanely tough). What the extra bainite does is cause variances in the steel's hardness. Even the martensite will have various levels of hardness.

The RC scale is neat, but only provides a sole point of reference. That point of reference is the depth of a dimple a diamond point makes in the steel with a set amount of weight (the smaller the dimple, the harder the steel). While harder is better than softer to a point, it doesn't tell the entire story. There are some very hard steels which will stay sharp forever so long as they only cut food on a wooden or plastic board (what's called "Japanese" cooking knives comes to mind), but can easily be ruined when used outdoors. There are other very hard steels which need an edge thicker than a cold chisel or else they'll rapidly dull, and heaven help anyone who cuts metal with them and doesn't expect to do a lot of sharpening. And then there are steels used in the same range of hardness as ScrapYard's SR77. Most lack the impact toughness and several lack the ability to take a fine edge. Those steels have their advantages, too, but not as survival knives, hard use tools, or harder use entertainment.

Hope that helps.

Nice answer Thom - your knowledge is appreciated! <img src="/ubbthreads/images/graemlins/thumbup.gif" alt="" /> Tom

Thank you Tom, very informative <img src="/ubbthreads/images/graemlins/thumbup.gif" alt="" /> Nice to hear more good things about S7 <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> I kind of understood more on the bainite/martensite subject as well, Thanks!

Thom is the resident guru of steel!

You're right about that Paul <img src="/ubbthreads/images/graemlins/thumbup.gif" alt="" />

Well, I have another one for Thom..Have you any insight on S5 steel?

I know this is the S7 club, but I can't resist asking. And I can't resist asking because after reading about it on CPM (Crucible), the charts say it's tougher than S7. And they actually list things such as concrete breakers and hammers for it's uses. So naturally, I imagined S5 on a scrapper <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Thanks for the kind words. I sure don't deserve them, though.

I've only seen S5 on paper/internet. Looks to be tougher and more open to a variety of heat-treatment methods. S7 is used for jackhammer bits, though, so it's a bit tougher than needed and SR77 looks to be tougher still (will need bowie to confirm <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> ).

Need a Bowie for confirmation...now that is going to be fun!

Thanks! Perhaps your right.. otherwise, S5 would/should be more popular.

I can't wait to hear and see comparison (destruction) tests on SR77, SR101 and INFI.

INFI INFI INFI! Hmm am I on the wrong forum? <img src="/ubbthreads/images/graemlins/confused.gif" alt="" /> Err no cuz I hate micarta! <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />

I don't hate it, but I do looooove Res-C....I just got in a new toy that has Blk Paper Micarta....and it is o so nice!

I saw your pic, that knife is just plain gorgeous even with micarta! Yep fine catch there GF. Just as well it wasn't a CS blade as stumps seem fatal to them... <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />

Thom, that was a great post!! I enjoyed reading it, and learning. I learn something new everyday!!

Life is a learning experience... you stop learning and breathing at the same time! <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />