Customer Hardness Test

trentu

trentu

Joined
Mar 2, 2006
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Had a customer come to the shop to pick up a knife. I made it out of 440C like he wanted. After grinding out the blank I sent it off to heat treat. Got it back with a cert of RC56. Finished the blank and handle, an all went well.
When he picked it up and looked it over I told him to test her out. He shaved wood, cardboard, chopped rope and it stayed very sharp. Then he asked if it would stand up to taps from a ball peen hammer. I said try it.
He lightly tapped the spine and blade and disaster hit. The spine copied marks from the hammer and the taps on the cutting edge dented and rounded the edge easily. Is this normal or is it a bad temp?
Should an edge take taps from a ball peen hammer without expected marks and damage? Thanks guys and gals.
 
No it's a knife blade they are not made to be hammered on they are made to cut with. Maybe on the spine of the blade but not the cutting edge.
What was he trying to prove,is he buying the knife for cutting things or does he plan on using it as a hammer.
Test it on the purpose it was made to be doing, I don't test a tape measure on it's cutting ability or hammering ability.
 
Because of the thickness the spine will tend to be a little softer, this is desirable.

Bending of the cutting edge is not desirable.

George
 
Kinda what I thought but I am new to stainless blades. I usually make only carbons. I didn't know if you have someone oven heat treat stainless if the spine would be softer though.
 
Well, interesting that 56 Rockwell hardness on 440-C I always went to 58 but the blades were heat treated in a vacuum chamber and then freeze treated. The spine may not of shown a mark from the hammer but perhaps a spine edge would chip but that blade edge would have looked awful sick. This is certainly not the way to check the quality of the edge. Frank
 
The top plate on the cutlers stiddy I made (22# anvil) is heat treated 440c, 3/8" thick, about 10" long and on the draw I took it to 59Rc surface ground it and polished it. Every knife I've made for the last three or four years has been peened on that anvil and there is not one mark any where on the face of it.
Ken.
 
I usually avoid commenting on stainless related topics because it is out of my area of expertise, but HRC numbers are a constant regardless of the steel in this situation. HRC is a measure of deformation under penetrative load, so it will give you an idea of how much the blade will deform under load regardless of the steel. The steel however will determine whether things can still behave in a brittle manner while deforming, something that earlier generations of stainless like 440C were known for if not treated very carefully.

Anyhow HRC 56 tells me that the blade is going to deform, especially if the thing sliced up to your expectations at HRC56, indicating a lot of carbon locked up into carbide. If the penetrator sunk in deep enough to read 56 it stands to reason that a ball peen will sink in to some extent as well.

I also agree that I would not allow a customer to hit any of my blades with a hammer, a wooden baton- yes, but a hammer- no. Steel is steel, we can get it to do some very amazing things but we can't make it totally indestructible, if a person wants to hit a steel cutting implement with a hammer tell them to buy a cold chisel, but warn them that even that will mushroom over time:rolleyes:.
 
As already said, 56 is pretty soft. It is possible they didn't soak it long enough and the martensite is carbon lean? Quenched too slow?

A problem I have had on a high chromium steel is retained austenite. It is possible to have a blade that RC tests HRC 62 (folks, that is hard) but still suffers edge roll (not chipping) in use that shouldn't cause edge damage. (Kevin, if you think I'm nuts, I'll gladly mail you one).

By the way, I never sold one like that.

440C probably needs cryo as a part of the quench to reach its full potential.

I think most blade edges would tolerate light taps from a hammer without much damage. Though something like a straight razor is going to get messed up regardless. Kind of a weird way of evaluating a knife, but I wonder if perhaps the HT may need work?

I worked with 440C years ago as a hack machinist and had no idea how to HT it. Depending on who you used, perhaps they didn't realize it needs a long soak and cold treatment?
 
"He lightly tapped the spine and blade and disaster hit."

I think he is talking about little taps. A blade can be "tapped" through a small nail without mark off on the spine and very little edge damage. I don't think the customer was so over the top there.

Obviously if you tap the edge with a hammer you're going to dull it a little, but I don't think that is what he is talking about.
 
OK.

However, I can LIGHTLY tap annealed 440C all day, and not beat it up.

First guy that's pissed at me because my knife didn't work well as a nail or cold chisel will probably not be too happy with my response...

They may work like a champ for all I know, but I won't go around trying/suggesting/recommending that.
I've already got a piece of steel embedded in my skull from hitting a hardened pin with a hammer.
Lesson learned for me.
 
Brian Fellhoelter Knives said:
OK.

However, I can LIGHTLY tap annealed 440C all day, and not beat it up.

First guy that's pissed at me because my knife didn't work well as a nail or cold chisel will probably not be too happy with my response...

They may work like a champ for all I know, but I won't go around trying/suggesting/recommending that.
I've already got a piece of steel embedded in my skull from hitting a hardened pin with a hammer.
Lesson learned for me.
Click to expand...



Well I plan to bring my edge testing ball peen hammer to Blade Show this year and have a go at your whole lot. LOL!:D

Can't wait to see you guys at the show this year, BTW.
 
It could be entertaining though Andy.

Watching my pregnant wife come across the table and jump you like a spider monkey would be a sight to see..

;)

Ahh... good times.
We look forward to the show too.

Now back to your regulary scheduled thread.
 
Hit the edge with a hammer?! I'm surprised the guy didn't want to try and saw through some concrete as well....geez.
 
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