Humbled by Heat Treating Results. Questions/Discussion.

[Rick Marchand]

Karl... I think he is was implying that there may be a chance that the OP had the Rockwell tester set to a different scale (other than "C" ) for his reading. I don't think that is the case but it may account for the dramatic difference.(not sure how the different scales work out on a Rockwell machine.)

 

[Stacy E. Apelt - Bladesmith]

I have heard no one mention decarb.

There are a lot of things involved with a good HT.
Too low a temperature is the number one cause of low hardness.
Too slow a quenchant is number two.
Decarb is number three.

I would grind a quick edge on the blade and test the edge to see if it is hard enough. The brass rod test is probably good enough to tell you what you want to know.

What type of forge are you using? Is it suitable to evenly heat a large blade?

As pointed out, the magnet only tells you when the blade is getting close to the target temp. It is a matter of experience to know when it is about 50-100°F above non-magnetic.

For a blade the size you stated, you need a much larger tank and oil volume than you used. Optimally, the tank should be 4-6" deeper than the blade length and 4" wider than the blade width. That works out to be around 2-3 gallons for a knife the size of yours. Without proper size and volume, you can not get an even quench on a large blade.
Here is a thread on that subject:
http://www.bladeforums.com/forums/s...fect-of-oil-volume-and-agitation-in-quenching

 

[butcher_block]

did you retest the heal after the other parts 9making sure the tester anvel was fully seated (i have got a soft first test only to retest and have it right on spec )

while not the best oil it stil should have done ok i say do it again and get as much of the blade in th4 quench as you can

 

[David Wesner]

What type Rockwell Tester was used ?

Did it have a compound sine plate type anvil that placed the surface to be tested perfectly perpendicular to the diamond ?

The reason I ask is, because of distal taper and unusual geometry, a knife edge is an extremely difficult item to get an accurate Rockwell reading, unless you have a special tester.

Ideally a test piece should be surface ground clean, and perfectly flat and perpendicular to the diamond. Also zero mush factor on the anvil - as in none.

No offense meant Don, but PH.D. or not, I question your teachers quench recommendation and also his depth of hardness comment for a thin knife shaped item made using 1084.


Professor Ping :thumbup: That great Rick !! LOL

 

[Don Nguyen]

which rockwell scale are you using? is their one that would read it that differently

I used three different testers set to Rockwell C, one of them a quite fancy and cool electronic one. I consistently got the same results from all three testers.

I have heard no one mention decarb.

There are a lot of things involved with a good HT.
Too low a temperature is the number one cause of low hardness.
Too slow a quenchant is number two.
Decarb is number three.

I would grind a quick edge on the blade and test the edge to see if it is hard enough. The brass rod test is probably good enough to tell you what you want to know.

What type of forge are you using? Is it suitable to evenly heat a large blade?

As pointed out, the magnet only tells you when the blade is getting close to the target temp. It is a matter of experience to know when it is about 50-100°F above non-magnetic.

For a blade the size you stated, you need a much larger tank and oil volume than you used. Optimally, the tank should be 4-6" deeper than the blade length and 4" wider than the blade width. That works out to be around 2-3 gallons for a knife the size of yours. Without proper size and volume, you can not get an even quench on a large blade.
Here is a thread on that subject:
http://www.bladeforums.com/forums/s...fect-of-oil-volume-and-agitation-in-quenching

About the decarb, how "deep" would that affect the blade? For future blades, what advice would you give to account for decarburization (especially using sub-par heating mediums)?

I don't know much about the forge itself, but it uses natural gas and 2 burners. Also scales the blade pretty heavily, but I can get a relatively even heat on it (I say relative, because it looks even to my eye, but that doesn't say much at all). I also don't really have another method at this moment to judge temperature, so I was trying to use the magnet as a guide, but I'll be more careful when checking throughout the whole blade.

I do think most of my problems came from the poor planning with the quench tank. I'll probably have to suck it up and get another gallon...

did you retest the heal after the other parts 9making sure the tester anvel was fully seated (i have got a soft first test only to retest and have it right on spec )

while not the best oil it stil should have done ok i say do it again and get as much of the blade in th4 quench as you can

I had hoped that was the case, but I went back to test on the heel, and it was still very soft. I had the same results on two other testers set up for Rockwell C as well.

What type Rockwell Tester was used ?

Did it have a compound sine plate type anvil that placed the surface to be tested perfectly perpendicular to the diamond ?

The reason I ask is, because of distal taper and unusual geometry, a knife edge is an extremely difficult item to get an accurate Rockwell reading, unless you have a special tester.

Ideally a test piece should be surface ground clean, and perfectly flat and perpendicular to the diamond. Also zero mush factor on the anvil - as in none.

No offense meant Don, but PH.D. or not, I question your teachers quench recommendation and also his depth of hardness comment for a thin knife shaped item made using 1084.


Professor Ping :thumbup: That great Rick !! LOL

I can't remember the makes and models of the hardness testers, but I was only using a standard flat-faced anvil. If the surface tested is not perpendicular to the diamond (just a few degrees from distal taper), how much can that affect the reading?