Rockwell testing carbon steel vs stainless steel Question

M

millejn3

Well-Known Member
If I use carbon steel calibration blocks to setup my Rockwell tester, will there be any type of variation when testing stainless steel ?
 
I sure hope not! I've not heard this question before, so will be following this thread to see what the experts say.

Ken H>
 
My thought is that the machine doesn't know what's sitting on it's anvil, it's just testing it's hardness.
 
That's my thoughts as well but I wanted to make sure,,,, Also was wondering how much faith I can put in the testing blocks that came with my import Rockwell Tester. The tester is consistently 1.5 to 2 points lower on all 3 of the C scale blocks. My thoughts are to order a quality set of USA made testing blocks to check it with. Any thoughts on this anyone?

Thanks,
Jeff
 
You are fine as long as the test block is in the same general hardness range as your work piece. Stainless or carbon wouldn't make any difference. Actually, I'm not sure they even make stainless test blocks. Anything high alloy is liable to have some honkin' hard primary carbides (maybe vanadium?) which could really get in the way of consistency. This isn't offered as any metallurgical knowledge - just experience. Every now and then on a stainless work piece, I'll get a WTF reading, while every other hit is right where it's expected to be.

In any event, be careful about implying more accuracy than your precision would justify.
 
millejn3 said:
That's my thoughts as well but I wanted to make sure,,,, Also was wondering how much faith I can put in the testing blocks that came with my import Rockwell Tester. The tester is consistently 1.5 to 2 points lower on all 3 of the C scale blocks. My thoughts are to order a quality set of USA made testing blocks to check it with. Any thoughts on this anyone?

Thanks,
Jeff
Click to expand...

If all three are out consistently, I'd guess the machine needs some tweaking. Yes, by all means get a high quality test block - but you don't need a set. What do you do that is more than three points off 60?
 
I just got this machine about 3 days ago. Until then I was just going by the normal recommended receipts found for CM154. Ramp to 1400 for 10 minutes - ramp to 1950 for 35 minute soak time - Then plate quench while using air between the plates - sub zero freeze - and then 2 tempers at 400 for 2 hrs - I have 5 knives that Im checking and all five are a consistent 59.5 to 60.3. But yet all 3 test blocks are consistently 1.5 to 2 points low. So my concern is that all 5 knives are 1.5 to 2 points higher. Which in turn makes me worry about the cutting edge chipping while in use... Now that I look back.. "That's a hole lot of worrying" :15: :biggrin:
 
millejn3 said:
I just got this machine about 3 days ago. Until then I was just going by the normal recommended receipts found for CM154. Ramp to 1400 for 10 minutes - ramp to 1950 for 35 minute soak time - Then plate quench while using air between the plates - sub zero freeze - and then 2 tempers at 400 for 2 hrs - I have 5 knives that Im checking and all five are a consistent 59.5 to 60.3. But yet all 3 test blocks are consistently 1.5 to 2 points low. So my concern is that all 5 knives are 1.5 to 2 points higher. Which in turn makes me worry about the cutting edge chipping while in use... Now that I look back.. "That's a hole lot of worrying" :15: :biggrin:
Click to expand...

The test blocks are what you use to set a standard and calibrate the machine to. The only way you could know if the blocks are off is if you had another set of blocks that were rated the same but gave different readings.

I think where you are getting off track is that the formula for the heat treating is more of a guide than an absolute. It is supposed to get you close. That is why you start tempering to a RC higher than you want and gradually work it down to your desired hardness. If you don't have the gear then you do as you have been doing. Follow the recipe and hope you are close.

So I would say trust the blocks and calibrate your machine to the blocks. You will want to do several testings on the block. You will know you have a good number when you get 3 consecutive readings that are really close to each other. Use that number and calibrate accordingly.

Also, you may notice that when you do your first 3 or so tests that you get a different reading each time and then the machine will settle in. If this is the case then consider it a warm up for the machine and it will be something that you will have to do each time you start using the machine after it has set a while.
 
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millejn3 said:
I just got this machine about 3 days ago. Until then I was just going by the normal recommended receipts found for CM154. Ramp to 1400 for 10 minutes - ramp to 1950 for 35 minute soak time - Then plate quench while using air between the plates - sub zero freeze - and then 2 tempers at 400 for 2 hrs - I have 5 knives that Im checking and all five are a consistent 59.5 to 60.3. But yet all 3 test blocks are consistently 1.5 to 2 points low. So my concern is that all 5 knives are 1.5 to 2 points higher. Which in turn makes me worry about the cutting edge chipping while in use... Now that I look back.. "That's a hole lot of worrying" :15: :biggrin:
Click to expand...

I agree with you. Presuming you used at least dry ice for cryo, that HT should have left you with 61-62. Sounds like your blocks may be about right.
 
I'm thinking I will run a test tomorrow. I have a small piece of CM154 3" long 2" wide 5/32 thick that I will HT and freeze then check the hardness both before and after normalizing.
 
millejn3 said:
I just got this machine about 3 days ago. Until then I was just going by the normal recommended receipts found for CM154. Ramp to 1400 for 10 minutes - ramp to 1950 for 35 minute soak time - Then plate quench while using air between the plates - sub zero freeze - and then 2 tempers at 400 for 2 hrs - I have 5 knives that Im checking and all five are a consistent 59.5 to 60.3. But yet all 3 test blocks are consistently 1.5 to 2 points low. So my concern is that all 5 knives are 1.5 to 2 points higher. Which in turn makes me worry about the cutting edge chipping while in use... Now that I look back.. "That's a hole lot of worrying" :15: :biggrin:
Click to expand...

You should come out around 59HRC to 61HRC with that recipe.

Your blocks will have some hand scratchy engraving telling you what the hardness is. What do you get when you test compared to how it is marked?
 
BossDog said:
You should come out around 59HRC to 61HRC with that recipe.

Your blocks will have some hand scratchy engraving telling you what the hardness is. What do you get when you test compared to how it is marked?
Click to expand...

I have a 61.3 block a 46.7 block and a 24.5 block. The machine is consistently 1.5 to 2 lower on all 3 blocks. My knives (the 5 that I have done) all measure 59.5 to 60.5. My only concern is than if the test blocks are correct, that would put my 5 knives 1.5 to 2 higher.
 
When I got my new bench machine in it had to be calibrated. Following the manual that might have been written in English, it took about a half hour of basically walking it into the correct calibration. It's not that hard, just a bit tedious.
 
Thanks for the help Tracy.... That's kind of what I figured. Its a long ways from China and I sure it wasn't in its own little padded room during that trip. Beings that all 3 test blocks are 1.5 to 2 lower than what is stamped on the block I pretty confident it just needs a little tweeking. If it was just one block I wont worry about it but all 3 being the same amount lower pretty much tells the story.
 
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