Hardness testing & decarb

JTknives

JTknives

Joined
Jun 11, 2006
Messages
8,651
I'm having a slight issue that I never even considered befor I started heat treating for other people. The issue is measuring hardness on blades that have some decarb. I don't seam to have a problem with the 1084 I have done but I did a 15n20/1095 blade that had a good soak and I could not get an accurate hardness reading. I know it was good as I heat treated a 1084 blade at the same time (one blade at a time) and it came out screaming hard. But 1084 did not get the soak time. So my question is this. I want to be able to provide accurate hardness measurements to my customers as well as test and make sure there desired RC is hit after tempering. The only way I can see to do this is to remove the decarb from a small spot on the tang and test there. I'm hoping to add nitrogen to my oven in the future but until then I need some sort of solution. Any ideas, thanks guys.
 
I thought that the other commercial heat treated say they will grind decarb from an inconspicuous area on the knife for testing. I would expect to see a grind and divot on the handle if I sent something out.
 
Would a test coupon sent with the blades suffice?
Like you could ask people to send one in, you could test that and discard it?
 
I have some like that in the past and it works nicely. But all things considered it's still not testing the blade.
 
The blades i get back from peters has a grind mark close to the first pin hole on the tang.
 
A particular heat treater that comes highly recomended through this forum tests directly on the de-carb... :eek:
 
I've had both requested by the heat treat vendor. Some grind a spot on the tang and test, some offer a test spot on the riccasso if you want it for proof to the customer, and one asked for an extra tag piece of material to provide along with the blades. As a customer I trusted all of them, even if the tag wasn't the actual blade. I get your reservation there though.
 
JBC69 said:
A particular heat treater that comes highly recomended through this forum tests directly on the de-carb... :eek:
Click to expand...

From personal experance it's not accurate. Like I said 1084 seams to do ok. Maybe it's the 3 grain refining cycles I do as each cycle drops a good amount of scale off the surface and then the actual austenite is 1475 for 5min once the temp on the controller comes back up. But on other steels it has issues and it's not that it reads way off its just off from what it should be and I know it should be higher. I'm afraid that if you based your tempering numbers off testing through decarb your going to be at least a few points higher then what the test shows.

I did a 15n20 test and I was shocked. 15n20 does not scale up like 1085 during heat treating and when I did my hardness testing I was trying to test on decarb. I could not believe the numbers, thy just seamed wrong. I was getting like 62-63rc and I knew it should be higher. So I ground around .005 off one surface and re tested and low and behold I was 66RC.

My gole is to provide the best heat treat I can provide and solid numbers and accurate testing for my customers. So that's why I came here to see if cleaning up a small spot would be exceptable to others who want me to HT there blades.
 
JTknives said:
From personal experance it's not accurate. Like I said 1084 seams to do ok. Maybe it's the 3 grain refining cycles I do as each cycle drops a good amount of scale off the surface and then the actual austenite is 1475 for 5min once the temp on the controller comes back up. But on other steels it has issues and it's not that it reads way off its just off from what it should be and I know it should be higher. I'm afraid that if you based your tempering numbers off testing through decarb your going to be at least a few points higher then what the test shows.

I did a 15n20 test and I was shocked. 15n20 does not scale up like 1085 during heat treating and when I did my hardness testing I was trying to test on decarb. I could not believe the numbers, thy just seamed wrong. I was getting like 62-63rc and I knew it should be higher. So I ground around .005 off one surface and re tested and low and behold I was 66RC.

My gole is to provide the best heat treat I can provide and solid numbers and accurate testing for my customers. So that's why I came here to see if cleaning up a small spot would be exceptable to others who want me to HT there blades.
Click to expand...

If it gave you more confidence in your product, then I as the customer would have more confidence in it too. I would suggest you just make it your policy as part of the service offer, with a statement about why you insist on testing the actual knife. Write a general description of it that you can paste in a message when people inquire so you aren't explaining it every time.....here's what I offer....how I do it....and why I do it that way.
 
What was the layer count on your 15N20/1095 blade? It'll make a difference.
If you're doing testing on a pattern like the one below, it's quite likely you'd get different readings in different spots.
That's why we seek that 300 layer sweet spot, in a 1/4", so we have equalized carbon migration and a homogeneous steel.
Just an idea.
 
I'm about to embark on acquiring a Hardness tester myself. Having never done it so take this question as "I'm just trying to learn". Wouldn't the test piece have to be ground of decarb on BOTH sides to get a actual true reading. In my mind if one side of knife is laying on a table with decarb on it and the other side only cleaned where the point is wouldn't it be compressing the decarb on the back side?
 
I think you're right about removing scale on both sides. I don't do much carbon steel, but when I do it sprinkle both sides with borax powder (roach powder) to prevent scale build up. When ready for Rc test I'll just hit both sides with flat platen to clean up nicely, then test.

While I've wanted to buy a good product to prevent scale, the borax does a decent job and washes off in hot water.

Ken H>
 
No you don't have to remove decarb from both sides. The bottom side sets on a large surface of around a 1/2" or larger. The force is spread over that entire area. On the top side the diamond point actually creates a dent in the steel and measures how deep it went. The point is quite small which focuses the 150KG force into a tiny area.
 
Thanks guys. Yeah I'm goi g to be doing this from now on. I finely found a use for the box of 10,000 sanding rolls. Thy are small and go on a dremmel. Clean up a small patch and it tests great.
 
Good on you for your research on this. I just bought a hardness tester today and am eager to see where I'm at as well.
What's the maximum carbon steel dimensions you can heat treat? I have a short sword and some tomahawks I would like to cut out of some steel.
 
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