What are these lines from post HT?

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DukeHarley

Joined
Apr 11, 2014
Messages
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Hey guys got some horizontal(length ways) running down the blade. Since I heat treated and tempered I went to sand vertically and I can see these lines that show thru. They almost look like sanding lines but so far don't seem to be sanding out. I never once ran a file or sand paper in that direction. I can see some now on the other side that I've have not sanded since BEFORE HT. I never sanded between HT and tempering since I had a bit of warp in the blade.

Blade material is Aldo's 1084 heated past NM then quenched in warm canola oil. I then headed at 350 for 1 hour shimmed to remove warp and (2) 2 hour tempering soaks at 400-420. Also come to think of it I heat to orange at one point before quench due to talking with my son. So then I let it cool a bit to black and then I went ahead at did the above HT. I was kinda trying to do a grain refinement but due to not paying attention maybe went too hot??? Anyway what should I do now. Will the lines come out? should I finish or scrap the blade and chalk it up to a lesson learned? Maybe finish and give to a friend? Will these line hurt the blade performance? Just looking for some advice from other much more experienced than I.

Jay
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I will sometimes see those appear on blades of my own after heat treatment. I haven't really looked into what the exact cause is (but my guess is phase changes that occur as the blade is heated to various degrees and soak times in the forge/kiln.) Before heat treatment I usually sand mine to a clean 220 grit, and if those lines appear after HT, by going back to 180 - 120 grit I can always buff them out. Another thing you might do is give the blade a brief soak in hot vinegar and then clean with whatever grit of sandpaper you left off at - any fractures that might not have been visible before should show - IF they are there, that is. But since it was quenched in canola oil, there probably won't be any. Also, since this is 1084, did you soak it for several minutes? If so, 1084 doesn't require any specific soak time, as it has what might be considered the "golden" amount of carbon for 10XX steels.

Again, they look identical to ones that appear of several of mine, but go back a few grits and with patience they should be gone. Maybe someone who does know what exactly those are will post soon.
 
The steel goes through processes in productiuon that put "stresses" in it as well as actual banding of the alloys in some cases. These occasionally show up as differences in the look after HT. Some sand out, some don't, and I don't think it matters beyond aesthetics. These are referred to as "artifacts" of the rolling process.
 
Ahhh.......ok so it's not necessarily something I may have caused. I sanded with 80 and then 150 and they are still there. I'll go a bit further with the 80 or 150 and see if they sand out.

Jay
 
I have hard time figuring those line be alloy banding in 1084, but i won't swear about it...in fact they could be. :confused:
They looks like scratches...how did you profiled the blade? could be that you scratched it dragging on the bandsaw's or grinder's support-platen during profiling?
 
That is the exact question that I had last week but I could not get an angle to take a pic. Also used Aldo' s 1084. I finally sanded with 220 and they blended in and are gone. The answers to my thread suggested that I had not removed all the decarb. I'm glad I am not the only one with this issue. I'll be following this discussion.
 
Another idea is that sometimes when you harden a blade which has not been through a complete thermal cycle after grinding/filing, the grind lines (or the scratches whatever) could leave a stress (a kind of localized work hardened area so to speak) that responds to the ht in a way that it shows afterward and could be below the very surface.
Of course that imply the scratches would be there sometimes before you sanded them out. This could be possible even if you sanded to the bottom of the scratches or even a little below.
That's just an idea, but the subject has been covered here on BF somewhere in threads where people were troubleshooting ghost lines appearing on blades, and was resolved through thermal cycling.

Of course alloy banding from the mill remains as a possible cause, although from the pics to me they looks like different in this case...have you watched them in high magnification?
 
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