L6 surface texture

SBranson

SBranson

Joined
Oct 29, 2006
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Hi. I'm using L6 (Aldo's) for the first time and I forged out a sort of Napoleonic Briquet sabre. I'm cleaning it up and I'm at 60 grit and there's a very strange texture to the steel. My first thought to describe it is "lizard skin". It's a very definitely grain pattern that I haven't seen in any other steel I've used.
I didn't do any special annealing or anything, just what I would normally do for a sword. I forged it, with descending heats at the end as I was cleaning up the lines, did a couple thermocycling heats in the forge.
Once I get it a little cleaned up I will do some proper grain refinement in my paragon.

Anyway, I will try to take a photo but I'm pretty sure that the way I have to get the light to bounce off the surface the photos won't work.

Anyone know what's going on?

Thanks
 
I can't really help myself, but I know Bruce Culberson has worked with Aldo's L6 before. Maybe he's seen this before too.
 
I've used Aldo's L6. Gotta be careful with low temperature forging with L6... the stuff practically air hardens!. I'll take it you didn't perform any soaks during the HT? I am thinking that the texture you are seeing in the blade has something to do with alloying and the possibility that you didn't get everything into solution. I have found that you can't give L6 a regular high carbon HT and expect it to perform like "L6". I'm not implying that you improperly HT'd it because I don't know what you did... but an open forge HT leaves many variables open for stuff to happen... or not happen.

Rick
 
It's not heat treated yet. And I didn't really "forge" it cold or anything, just that while cleaning up the lines and tweaking things, it was forged on the the cooler side of the range.. Anyway, that's not really the issue I don't think and probably doesn't bear mentioning.

Rather than do my usual thermocycling 1600,1500,1450,1400 for W2, I just did a couple cycles in the forge. I wanted to check on proper pre-heat treatment regimes for L6 and decided to clean up the profile and do some initial grinding.

I'm sure it's some alloying elements but I have never seen this before. Is it something normal or some way I can use to "verify" my pre-heat treatment regime?
 
I have used Aldos L6 on some full tang axes and a dozen or so stock removal knives. I never noticed what you are describing.
Is it possibly a bit of surface decarb that will go away with more grinding?
 
I don't think it's that as I think I'd have ground past that. Here's a couple videos. You can see it best right at the edge of the light reflection. It almost looks like damascus.
I'll watch it after I've done some proper grain refinement and see if it goes away or changes.

Anyway, I just thought it a strange phenomenon and wondered if it was indicative of something like forging temperature, lack of proper grain refinement, etc...
And it is a pretty even pattern throughout the blade and not limited to one spot or anything.

[youtube]xhPx9LGNUWc[/youtube]

[youtube]6ch34aAV6Rk[/youtube]
 
It's toast, Stu... you had better just send me the blade for disposal.;)


Now I get it... this is pre HT. Adequate thermal cycling should remedy any alloying issues. I would suggest a higher initial normalization heat(1650F-1700F) to get everything into solution. I would also do that for the W2 but not sure how that would effect your Hamon so don't mess with a good thing. Aldo's L6 is highly spheroidized and I am not sure what your forging regime could do with that. Any number of things could be going on. Just be sure to correct it before final HT
 
Ha.. for a second there you had me.. Ha

I did a couple of the higher 1600-1700s in the forge but I've just set the kiln for K.Cashen's regime 1400/1hr (my kiln can be upwards of 100F hotter near the back) then cool to 1200 at 40F/hr and hold for another hour.
I put anti-scale on the blade just for protection and I'll see what happens when I start grinding again.

I'll post back if there's a difference or not.

When I'm working W2 I consider the final straightening and stuff as my descending heats as far as the forging stage and then so the thermocycling as mentioned before.
My kiln seems to run a little hot so I add one more cycle at 1385F which seems to be just below critical.

On another note about L6. I was planning to use Parks #50 and do an interrupted quench only because it's that or canola but now I'm favouring the latter.
Will the blade droop in the quench like W2 does?
 
Kevin's regime is for spheroidizing and is usually done after grain refinement. I do it after a quench on my last 1475F thermal cycle. Spheroidizing makes it really soft for cold working. You pretty much have to do that to L6 if you have heated it past 1450F.

I would use the canola over P50. L6 shouldn't be as prone to tip-dip... but it really depends on cross section thickness and temperature and quench mechanics.( I quench spine down to help avoid dip.).
 
Thanks for the extra info Rick and for the tip on the edge down quench. I'm so used to W2 I wouldn't have thought of that.

For the info I used I took it straight from Kevin Cashen's page:


"Recommended Working Sequence For L6

Forging: Start forging at 1800 to 2000 °F (980 to 1095 °C). Stop forging at 1550 °F (845 °C)

Normalizing: Heat to 1600 °F (870 °C). Work is cooled from temperature in still air. Normalizing will result in significant hardening requiring subsequent annealing before machining.

Annealing: Atmospheric protection against decarburization or carburization is required unless all surfaces will be removed by machining before final heat treatment and use. Heat to 1400 to 1450 °F (760 to 790 °C). Use lower limit for small sections and upper limit for large sections. Holding time varies from about 1 hr for light sections and small furnace charges to about 4 hr for heavy sections and large charges. Cool slowly at a rate not faster than 40 °F (22 °C) per hour until 1000 °F (540 °C) is reached, after which faster cooling will not affect final hardness. Typical annealed hardness is 18 to 25 HRC

Grinding or Machining

Stress Relieving (Optional): Heat to 1200 to 1250 °F (650 to 675 °C) for 1 hour per inch of cross section. Cool in air.

Hardening: Austenitize at 1500 to 1550 °F (790 to 845 °C) for 10 to 30 min and quench in warm, agitated oil.

Tempering: As-quenched hardness as high as 63 HRC. Temper at 350 to 1000 °F (175 to 540 °C) for a corresponding approximate tempered hardness of 62 to 45 HRC ."

I'm in the annealing stage and throwing in the stress relief on the tail end since I've done most of the pre-heat treat grinding.

For HT, I was thinking of following Stacy's advice to bring it up to 1200 and hold for 10 mins but am curious as to his 1455F for 10mins over K.Cashen's 1500F-1550F.
 
Kevin gives you the industry standard and some of his own findings. You'll have to find out what works best for your application, along with the equipment you use.
 
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6 hours in the kiln later and I did a quick pass on both sides with 120x and the texture is gone.
 
Good to hear. Can't wait to see the sword!
 
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