Hardness tester question

K

knifemaker3

Joined
Dec 26, 1999
Messages
119
Hey guys,

I just recently bought a used Ames hardness tester. I just got done with a blade of 1095 hardening it. I tested it with the tester to see the as quenched hardness. It tested 43 Rc!!!!

As always, I hardended as follows, heat to non-magnetic, quench in slightly warm oil. I use a gas forge, NC Tool Lowboy.

I tested with an old file and the file slid. I started to sand just enough to get a bare place to judge tempering color and the blade showed a nice little crack. I went ahead since the blade was ruined and broke out the chip. The texture is a fine velvety gray.

My question is this. Obviously I'm getting the blades hardened. Yet, why is the tester not showing this?

The test blocks that came with the tester shows it to be very accurate when I test it with test blocks. It had a 30Rc and a 63.5 Rc test blocks that came with it. And they both test accurate.

What are your suggestions as to why it don't test the steel? Could I maybe getting some loss of hardness on the outside of the steel yet the inside is hardened correctly?

I've always just used files to test hardness on 1095 and never a tester.

What am I doing wrong? Or has the way I've been doing my hardning for 10+ years been wrong?

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Craig Blankenship
Blankenship Knives
http://www.blankenship-knives.com
 
Hi Knifemaker,
One thing to check...in order for a hardness tester to work properly and accurately, the part you're testing must be 1.) flat and 2.) the back of the specimen MUST be resting solidly on the "anvil" or support post.

For example, I once tested a piece of hardened O1 that should have indicated a hardness of about Rc 61. It actually tested around Rc 45. I was actually testing the ricasso of the blade which was relatively flat. After the normal "what happened" panic subsided, I noticed that there was a very slight bow in the tang that extended into the ricasso.

Remember that a hardness tester simply measures the distance the penetrator travels under a given weight...the further it travels, the softer the material. When I released the weight, the penetrator had to flatten out the bow in the tang before it actually began penetrating the steel. This made the reading much lower than it should have been.

Hope this helps,
Cecil

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Cecil Self
SELF Knives
Arrow-Dynamics Cutting Tools
www.arrow-dynamics.com
 
Hey guys,

Thanks for the answers. I was checking all the flat areas between the ricasso and tip of the blade. Never thought about it maybe having a slight bow to it. I'll check next time to make sure with a flat surface instead of just eyeballing it for straightness
biggrin.gif


This does clear up some stuff about testers. I wondered why none of my edges would show a proper hardness while the ricasso did. Just goes to show how much I know about hardness testers.
redface.gif


Thanks again for the quick response!

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Craig Blankenship
Blankenship Knives
http://www.blankenship-knives.com
 
The concern with 1095 is the ms point (super fast quench required). The knife has to be quenched in water or brine for it (in most cases) to harden in the thicker sections at the rc as the thicker sections.
The blade tested on the rc tester as stated above must be flat and not wobble or skew at all. Also there is a decarb layer on the steel after heat treat . This must be removed.

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Web Site At www.darrelralph.com
 
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