RC hardness question

T

The_cutting_edge

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May 25, 2009
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Hi guys I just recenly got a few knives back from HT they are all 440c. I have never used this steel before and is the first time I have sent blades to be HT'd. The blades came back and I am more than impressed with the job the company did. the blades are super clean and will require very little clean up to make them ready for handle scales. the only thing I was wondering is how much difference is there between a blade at 58 RC (which is what I requested) and a blade at 60-60.5 (which is what I got back). I was told that 58 would be a good cross between toughness and hardness. will 60-60.5 be too hard/brittle. and if they will be too hard what temp should I temper them at to bring them down. I dont have an RC tester so wont be able to check them myself. thanks for your help guys
Jason
 
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over 50 veiws and no replys... wont anyone help out a newb? I would like to start the finish work on these knives but would like to know if I need to draw the hardness back some before I get too far along with them.....
 
First off, I don't claim to have anymore knowledge about this than I have read here and a few other places, but my understanding is that smaller blades, say 6" or less are fine at a higher Rc and bigger blades benefit from a slightly lower Rc for more bending abuse. I typically don't use smaller knives for chopping, so edge chipping isn't a major concern.

This is my basic understanding which may be way offbase, so hopefully an expert will chime in soon.


-Xander
 
If the knives are not going to be abused (prying, chopping bricks etc) and will only be used for cutting soft materials, 60 HRC should be OK.
 
:o Oops. Those look familiar. I guess I missed the 58 request. It used to be that it was darn near impossible to get a 440C blade out of quench at more than 61 - and it was routine to aim temper for about 58/59. We now get them out of quench at 63/63.5 and routinely temper them back to target 60 (and we consider +/- 1/2 pretty good).

I apologize for missing your request and if you can spare the time to return them, I'll temper them back further and cover your shipping both ways. ... or if you want, send some back and compare their performance. Anyhow, sorry for the screwup and tell me how I can fix it.

I suspect you haven't had answers to your query because not many people have experience with 440C HT tis way.

Rob!
 
KnifeMaker.ca said:
:o Oops. Those look familiar. I guess I missed the 58 request. It used to be that it was darn near impossible to get a 440C blade out of quench at more than 61 - and it was routine to aim temper for about 58/59. We now get them out of quench at 63/63.5 and routinely temper them back to target 60 (and we consider +/- 1/2 pretty good).

I apologize for missing your request and if you can spare the time to return them, I'll temper them back further and cover your shipping both ways. ... or if you want, send some back and compare their performance. Anyhow, sorry for the screwup and tell me how I can fix it.

I suspect you haven't had answers to your query because not many people have experience with 440C HT tis way.

Rob!
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it's no biggie. Like I said I am more than happy with the results and as long as they arent going to be too brittle for normal use I have no issues. I didn't name you as I didn't want to seem like I was bashing you guys. I am deffinately going to be sending more blades your way in the future. you actualy wrote 58 on all 3 of them, it looks like b4 they were ht'd. stuff happens lol. thanks for chiming in
 
As the others have said, 60-60.5 is fine. You will love the slicing ability. I do my fillet and kitchen blades in CPM154 at 62,and have no problems.
 
They may be harder to sharpen but keep their edge longer. 440C with pro HT and cryo is good stuff :thumbup:

Kudos to Rob for offering to help you out. Mistakes do happen, glad it worked out for you.
 
Given the wear resistance of 440C, I don't see the 2 points making a big difference in finishing or sharpening.

I'm guessing that plate quenching, cryo and possibly even some variance in the tester gave you the 60RC. 58 was a target in the past because it was at the high end of what 440C hit. I have 59RC as the AQ hardness for 440C with air quench, your results seem correct with the additional factors.

The blades don't look like they are going to experience a lot of edge impact or flex, so I wouldn't worry about it. Though, at 60 they may break instead of taking a set when they're seriously flexed. Maybe Rob would be willing to do a test blade to see if that is the case.
 
you can just temper them in a kitchen oven to soften them a bit and perhaps gain some toughness... 450F for a couple hours should give you around RC58
 
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