Okay I made a knife to be used as a skinner (posted in the forums a little while back). It was tested for hardness(several tests with in a 1/2" area. the results were from 69-72Rc. It was my under standing that 1095 would not exceed Mid 60's as quenched let alone after a temper is drawn.. How is this possible? Is my heat treat data incorrect? The test equipment was calibrated and I believe to be accurate. 

 

The knife was heated and then quenched in vegetable oil (about 100-110F), scuffed with a scotchbrite pad and then straight into a 425F oven for about 1hr 15mins. The blade was a medium-dark straw color, darkest on the edges and the tip area. I knew it was hard but I did not think it would be that hard. 

 

Any one willing to shed some light on this?

 

 

The charts state that top end hardness is about 68 Rc with about a 52 Rc after drawing at the temps you stated.  69-72 Rc could be within tolerance for the tester as quenched but are you certain that the oven reached the desired temp by using a calibrated thermometer?

 

You could obtain a set of tempering files and have a second method of comparison.  I believe MSC and other suppliers sell them for not much money.  Basically, they are a set of files tempered to specific hardnesses.  You start at the top (hardest) and move downwards until the file slides and no longer bites into the steel.  The hardness of the test specimen would subsequenty fall between those last two file ranges.

Commercial charts are usually dealing with 1" round bars for the Jominy End-Quench Test, thin sections may get even harder in fast quenches, or you may be experiencing some carburization of the surface.

 

Are you testing with a calibrated Rockwell hardness tester, or some other method? You are aware that uneven surfaces seldom can be easily or accurately measured.

 

 

Just how far down this particular rabbit-hole are you prepared to go? :huh:

I'm with the "Chart based on 1" cross section" blade less than 1/4" will go harder crowd.

no way it got to 72 RhC, perhaps RhB.  Recheck calibration while I move this lost post to the knife section.  We have a lot of info there just because of the thin sections dont match up with the published data for 1in or more thickness. I am interested in finding out what is really going on tho :)

My rockwell tester had test coupons so you can see wot a known sample checks out at with your machine

I have not talk to the man who did the actual test, but after I talked to the knife owner I think the blade was not properly secured and perhaps flexed or shifted during the test. I appreciate all the input.

Untempered martensite has a maximum theoretical hardness of about Rc 65.