is the brass rod test reliable???

[Doug Lester]

My problem with it is that I had a blade pass the brass rod flex test but fail in use, in this case chopping. Yes, I probably screwed up. I just find trying to cut through the brass rod more informative and easier to perform than trying to flex the edge against it. Just remember, as pointed out by others in this discussion, hardness is only part of the package. The ultimate test is in usage, where the rubber meets the road.

Doug

 

[One]

I agree, chopping into the brass rod is a little better test, but you still need something to compare with.

I suppose if I was making a lot of kitchen knives all the same and had some points of reference the standard brass rod test might be more useful, and there was that one time it did lead to further investigation on a student's blade.

I guess the only really good things about it is that it's quick and easy, and there's is the outside possibility that it could suggest some type of defect. So, for what ever it's worth I guess.

 

[One]

One last thought that could help sum it all up...

In the final analysis,… I think it is probably much more useful as a way to weed out significant defects, than it is as any type of standard for heat treating.

It might help spot tiny hair line fractures along the edge (if there were any), and be worth it just for that.

... now where did I put my brass rod?

 

[One]

… One more last thought,…

On that student’s knife where the end grain or "grain flow" was cut across diagonally near the point,… after the sodium bisulfate etch, it looked like the stringers might have partially separated from the matrix, possibly during the quench, forming hair line “tears“, although I didn't notice any change in deflection during the brass rod test, just the chipping out at those spots...

 

[One]

While you guys got me thinking about it,… here’s an illustration of what I’m talking about.

This is/was a 1095 Kiridashi I was working on. I etched it in sodium bisulfate to remove scale prior to hardening. I noticed this stringer right along the edge where the grain flow had been cut across. The blade of my student’s looked very similar, but it also had some fine dark lines running through the stringers, post quench.

… Anyhow, I scraped this Kiridashi before I even got to the heat treating or brass rod test.

 

[farmrbrnboy]

Thanks to everyone who posted on this thread. As it turns out, I was applying too much pressure and got plastic deformation. I could really see it on the Mora with a scanti grind. Hardly any pressure was required to flex the blade with elastic deformation, way less then when I was initially testing and got plastic deformation.

 

[me2]

There were reports of some 1095 with rather unforgiving carbide structure from the mill. Any chance to try a full normalizing to dissolve all the carbides and see if it's still there? If it's carbide, that should get rid of it.

 

[One]

me2, if you are referring to the stringer, I don't think it's a carbide. I did do a full normalization after the texture was hot forged in and also did some of the stock reduction on the bevel with a file. It’s also quite long and runs back over an inch into the blade, which you can’t see in the pic. I’ve seen this type of thing in 1095 and other steels from numerous reputable suppliers many times. It’s really not that uncommon. Some is a little “cleaner” than others, but figure it’s just somewhat typical with certain of types of steel. For that matter, virtually all steel has flaws and inclusions to varying degrees. Even the so called “clean” steels have them, they are just smaller and fewer. I think it is safer to assume that this can be a problem with any steel and that the flaws exist in the worst possible locations, than it is to assume that any steel is perfectly clean and homogenous.

The lesson I'm taking home is that it would have been better to take the time, modify my technique and forge the point so that the grain flow follows the profile of the edge, from now on, which would have been theoretically better from a structural stand point regardless of the stringer…

... and start using the brass rod test again just in case.

(On thicker stock I generally do forge the point, but need to change the way I’m doing the thin stock on these kiridashis etc. I think what I’ll do is hot cut them at an angle from the back side and then forge the tip or point back up from the edge side. This will basically, push the cut portion to the spine and get the grain flow to run parallel to the edge.)

 

[me2]

Can you estimate the temperatures of the hot forging and normalizing? I'm assuming you were going by color, but you may have a thermocouple in the forge, in which case estimating isn't necessary. I have seen cold laps, fins, and blow holes in structural shapes and plates, but it is pretty infrequent, maybe 10 times in 14 years. It does happen, but it's not nearly as common as it used to be. You are correct in that no steel is perfect. If it were without flaws, it would behave completely differently than it does.

 

[One]

I estimate the forging was between about 2000 and 1650, just a few whacks with the texturing hammer, maybe 3-4 heats total. Normalizing targeted at about 1650, 1550 and 1450 consecutively, then stress relieved at about 1200.

I occasionally use a magnet for temp., reference and also sometimes use ceramic cones and/or tempilstiks to check my eye. I always heat treat daylight in the shade and the muffle also helps block out most of the ambient light. I used a controlled electric furnace for over 10 years, which tremendously helped train my eye. I really haven’t missed the electric furnace and enjoy using the muffle furnace.

Anyway, this is should be more than enough about that for this thread….

The main point is just that the brass rod test might be useful in helping to weed out these types of defects and flaws etc., in the steel.... something to consider anyway, even if it's just one in a hundred.

 

[One]

Tip: The sodium bisulfate etch really shows the mechanical anisotropic grain flow better than some of the other acids.