Strange grain

[shinobituazon]

Hi everyone!

 

This was a practice tanto I made a year ago. It is made from 5160 used leaf spring. I made this during the time that I kept telling myself that I can get hamon off 5160. I experimented with clay on this, heat treated 3x after the first and second attempt failed, but still no hamon. I never tempered it. Then I decided to just make this one a charcoal chopper instead. I broke it in two yesterday, and found the grain very strange. The spine(clayed portion) looked dark and rather soft, the edge is steely gray and hard (based on file tests).

 

 

Why is this so?

[Christopher Price]

The dark grey part looks pretty weathered, with rust in it. If you just broke it, it looks like that was the site of a crack that was there since forging... leaving the shiny stuff as freshly exposed.

 

5160 is terribly difficult to get a good hamon in. Not that it can't be done, but it's not easy and I have yet to accomplish it. Too much manganese to give any "activity". You can get a quench line, though, the difference between hard and soft, and this would show up after a mild etch.

 

Make another one with fresh steel (not used leaf spring, which may have many stress cracks in it from a lifetime of use), quench it with clay, and etch. You'll see the line, but not a great hamon, most likely. Break the blade, and examine the grain inside. The martinsite will look different than the unhardened portion, should have finer grain size, and a different character overall.

 

 

As for your pictured blade, I'm convinced you broke it on an existing crack and you're seeing a weathered/fresh transition. See if you can break it again somewhere else, and I doubt it would look the same.

[kb0fhp]

ABSOLUTELY CORRECT - the crack was pre-existing, and probably a quench crack, or a crack that formed at temperature. THe shiny part is the newly fractured surface, ad the dark areas are the region of the preexisting crack.....

[Brian Vanspeybroeck]

The dark stuff is just rust from the existing crack as has already been pointed out.The grain size at the edge is relatively *HuGe* compared to any of the hardened 5160 I have done break tests on. Properly hardened 5160 will never have that grainy, crystaline pattern like sand. It will look like grey velvet...like the end of a broken file.

 

My guess is that this is not 5160 and is more likely a 10XX steel that was over heated before the quench. Getting 5160 to exhibit grain that is this coarse in the hardened condition is very difficult to do because of the manganese and chromium content.

 

I'm not trying to upset you..just some observations.

 

Brian

[B. Norris]

Something else to pay attention to is that the size of the grains in the shiney section and the dark section look the same. Like Chris says, break it elswhere on the blade and see what you have. If you suspect that you have overheated the blade at some point you can throw a quench cycle into your normalization routine in order to achieve a finer grain. I have started to replace my second (of three) normalizations with a full quench into oil for this reason. Will it hurt the blade? No, you may have to straighten it a little though. Will it make the blade better? Possibly.

[Sam Salvati]

B, i find a good little technique is to normalise once, then quench twice using each heat to straighten the blade if it warps, then final quenching the 4th time.