Etch or heat treat

[RICK LOWE]

I've got two blanks ready for handles. Both are from the same piece of 1084. Stock removal, file worked and etched. I'm using white vinegar to etch. Both blades came up with a mottled look on the edge about 1/4" off edge. I've done several other blades the same way, but never seen this effect. Heat treat was standard for me, which has resulted in very consistant results with 1084. There is a very nice differential line on both blades. Just concerned that a problem has popped up and I don't know why. Paranoia rears it's ugly head in the newbies shop. Thanks!
Rick

[SKIVIE]

Possibly because its dirty ? Maybe oils from your finger and the etch didnt take place in those spots ? Just things running through my head. Before I etch, I always clean the blade real well with Acetone.

Shane

[RICK LOWE]

I always use a lot of acetone before etch. When I first put these in the vinager, they didn't seem to want to kick off with the bubbles, so I took 'em out and recleaned. That helped get the process going, but the motteled area showed up. Can I go back and sand to satin and do it again?

[Ray Rogers]

You can sand it and re-etch as often as you like. Although I don't really know the cause of your problem my gut feeling says that you'll get the same result when you re-etch.

I think the situation is the result of the heat treat. When you sand one of the blades look at it very carefully under strong light and at different angles. I think you'll be able to detect those same splotchy patterns in the polished steel but it's harder to see until the etch is done. I have seen this happen on blades that were ground too close to their finished size before heat treating as if it were some kind of effect due to the high heat and thin cross section of the steel (notice the effect is in the thinnest part of the blade). For that reason, I grind my blades entirely after the heat treat is done and that seems to avoid this effect on all but the thinnest of steel as it seems to be near the surface and will get ground away if you have enough extra material to remove ....

[RICK LOWE]

Thanks Shane and Ray!
I didn't see anything different while sanding, but then I'm looking for scratches. It may have seemed a little easier to sand than normal, which is my concern on heat treat. The file did skitter nicely after the quench. Any comments on normalizing a couple of times and then heat treat again? Ray, I follow what you're saying about grind, but these are mic'ed at the same as other blades I've done. I grind to about 2/3 of finish before h/t and finsh after.
Rick

[Ray Rogers]

Again, I'm not really sure that the heat treat is the culprit here but Ihave noticed much less of this problem when I have more metal to remove afterwards. I HT in an electric oven so my HT conditions are very consistant. If you use a forge or a torch, perhaps this problem comes from the steel getting too hot (at least in thin sections) or maybe not hot enough.....

[fitzo]

Not saying this is the case here at all, but splotchy dark areas can sometimes indicate localized overheating. Might have some grain growth there.

[RICK LOWE]

Mike, your thought is what is bothering me. I work in a forge and try to follow shadows and color before checking with a magnet, but could have gotten a little hot before coming out to the quench. Can I fix this or are they headed to the waste bucket?

[Jason Cutter]

I am agreeing with ALL the responses provided thus far. I think you have nothing to lose. I suggest :-

1) Sand the surface back to a clean, unetched surface and then re-etch the blade. This time, while etching remove the blade and scrub the blade well with a bit of steel wool or even just a clean rag dipped in etchant or just water and then back again into the etchant. Repeat a few times. If it is just a problem with surface oil, this should fix the problem.

2) If the pattern is still there, Grind and sand it back even further, then re-etch and finish. I often find that the heat treat causes enough surface decarburisation that results in these splotchy patterns that disappear once you grind past them. But you will need to grind a fair bit, up to 1/32inch deep.

3) If they are still there, you may have grain structure problems (excessive grain growth)that is through-and-through the steel. In this case, you have a "failed" heat treatment attempt. You can choose 2 options.

a) Re-heat treat the steel - if the grain growth is that bad, you'll need to re-anneal the blade at least once, before re-hardening. However, if the blade is already very thin, you may not have any more steel to play with for grinding after heat treat.

b) in that case, you could turn this into a test blade. Place the blade in a vise and break the blade through where the problem is. Examine the gain structure and KEEP the blade for future reference.

Hope this makes sense. This is my own troubleshooter flow chart that I use for similar problems. Jason.

[mete]

I would assume that the mottled look is due to oxide scale or decarburization that hasn;t been ground off.

[RICK LOWE]

Thanks everybody for the thoughts! Yesterday, before reading Jason's post, I really did his number 3 suggestion. I annealed overnight, then 2 complete normalizing cycles, and then another heat treat. Due to what Ray said, I was very careful to let only about half the thin edge get to non-magnetic before quenching. Hand sanded to 600grit, cleaned VERY carefully and etched. No mottled effect this time. Don't know if sanding and cleaning would have been the answer. My gut just told me the problem was grain growth. It's always a super bonus to have these responses to help with problems. Thanks again.
Rick

[mete]

If that's grain growth you would have a VERY brittle blade !