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To etch or to temper first, that is the question...


Jason W

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Good evening all I have a question about my next step. This is my second attempt at a knife and my first san mai so be gentle, I know it looks like a butter knife : )

I did a "traditional" san mai where I made a well in the spike and inserted a piece of high carbon then forge welded them together and drawn it out. If you look closely you can see where the high carbon is on the edge. At this point I've hand sanded it down to 600 grit and want to know whether I should temper it then etch or etch then temper? 

Any comments, critiques or blasts are welcome. 

Cheers!

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Are you tempering in a vacuum furnace?  If not then the oxidation will occlude the etching.  Usually the finer grades of finishing is done AFTER heat treat.

We also do NOT suggest waiting to temper after hardening' I had a friend who hardened a blade late at night and decided to draw temper on it the next morning---it was in three pieces when he went down to the workbench in the morning.  Temper as soon as possible after hardening!

Also the blade should have been left at least at the thickness of a US dime before hardening and then tempering so a 600 grit finish is a total waste as it will get finish ground after hardening and tempering.

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What you didn't mention was as Thomas kind of stated- is it quench hardened yet? 

Thats going to preclude etching yet altogether. And I second Thomas on the tempering- as soon as possible... that high carbon is going to pretty brittle compared to the lower carbon steel in the spike.

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Thanks Thomas I appreciate that. I'm tempering it now, hopefully it stays in one piece. I don't have a vacuum furnace, just a toaster oven so we'll see what happens there. 

What do you recommend to use as an etchant? I went down to Canadian Tire, Home Depot and Walmart, none of which have Ferric Chloride. They looked at me like I was going to make a batch of meth or something : ). I do have muriatic acid and I grabbed some instant coffee. I'd rather use the coffee but either works. Does one make a more dynamic colour difference than the other?

Yes I did harden it last week : /

Ah well, live and learn 

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Not sure where you are located... but by any chance you still have a radio shack around?

They have ferric chloride.

Barring that- a really higher tech computer parts shop? Ferric chloride is used in etching copper circuitry.

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A lot depends on what you want out of your etch---topography?  Usually the strong mineral acids work, HCl, H2SO4, HNO3; but diluting them gives better definition. I've used salt and vinegar, heated, to get low topography but good definition with bandsaw blade and pallet strapping.  Lime juice has been used historically.

Nothing says you can't etch with one thing to get topo and then clean and etch with a another to get colour.

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Good morning! So I finished tempering last night in my easy bake and it doesn't look too bad. I tempered at 425f for 2 hours. I'm a little concerned about the blue on the edge since it's pretty thin and really surprised about the straw on the spike. Can I assume the blue edge is from the spring steel insert? Interestingly enough the spike has an "H" on the head so I'm assuming it's high carbon. 

As for the ferric, Amazon is the route I went. It should be delivered before Wednesday and was cheaper than ordering online from Walmart. They wanted 17 dollars plus 16 dollars shipping.

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From all the research I've seen, done, heard- even the "h" marked spikes are on the lower end of carbon content.

Doesn't matter now anyways if you forge welded in an edge. Lol...

Just a note for you if you haven't figured out a tank for the ferric yet- i just took a 2" diameter piece of pvc pipe about 14" long. I glued on a cap on one end, and a threaded clean out cap on the other. It will be my ferric dip tank, going to solidly mount to the wall in my shed, where I can hang & dip my blades to etch without being in the way. Lol.

Most use 3" pvc for blades that might have more curvature... but for now 2" will cover what I need.

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"High carbon" rr spikes are still on the low end of carbon content for a good knife. Those are marked HC. Not sure what just the H stands for but not high carbon as far as I've ever heard. Certainly would expect it to be low carbon steel. 

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Thanks Steve I'll check that out and thanks Welshj that's a great idea. I was on the way home today from doing errands with the wife wondering how I should set up a dip tube. Your timing is impeccable. 

Daswulf  ya, I had read that spikes were on the lower end, that's why I thought it would be a good test to do a san mai on. That and my neighbour keeps bringing them to me lol. I made him about 20 hooks out of them for his stables and noticed some having the "HC" so I started doing some digging. 

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As for the tempering, the thinner parts will temper more and faster than the thicker parts. Or atleast in drawing color.

How is the hardness? Did it skate a file on the edge?

I'm admittedly caveman in this and still go by "skate a file good, file bites in bad."

There are much better ways to do things but in caveman world, how did you do? 

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Same way, I tried an oil quench first but I think I heated the oil too much so the file didn't skate. I'm using a gallon of olive oil and heating it with a hot piece of steel from the forge. The xxxx dog keeps drinking the oil so I don't have a gallon anymore but the dog's coat is so shiny! I do cover the oil now : ) I did a water quench the second time and that did it. I'm a hobbiest blacksmith so I don't have all the fancy stuff for knives yet.

Thanks for the heads up with the colours, once I get it sanded and etched I'll put up another picture. I'll definitely do more of these, it was a fun process and I can see lots of different things to improve on. I definitely didn't draw it out enough since the middle of the blade is quite a bit thicker than the spine and the well I made wasn't super clean on the end so there's a small space between the insert and the spike right at the transition from the blade to the handle. 

Wait, you meant after the temper did the file skate. Sorry I misunderstood. I haven't checked that yet but I will. Thanks for the suggestion.

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When they started using powered rr spike inserters they had to up the carbon content to make them resist bending with the power driving, so they brought them up to the border between low carbon and medium carbon steels.  You don't want high carbon in a spike as that also increases the brittleness. I live near a train track and I sure don't want brittle spikes failing and a train derailing and dumping ammonium nitrate, MEK, diesel, and chlorine out in a big mess!

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Jason, heating the oil increases the quench rate. Cold oil can be viscous  and not circulate fast enough for a good quench. By heating the oil you lower the viscosity allowing the oil to circulate faster, thus pulling the heat out faster.

You could have lost some of the carbon in the insert to carbon migration. (Carbon diffusing from the high carbon to the lower carbon at welding temperatures.) That maybe why oil quench wasn’t fast enough, but it still hardened in water.

David

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ThomasPowers that makes a lot of sense I sure wouldn't want spikes snapping either.

Goods I could see carbon migration as being an issue since I took me a few welds to get it set. I didn't really think too much about why we heat the oil other than it can't be a solid mass of course. I was told by one of my instructors a couple years back that the oil should be at 130f for quenching and assumed that if it was hotter than that it wouldn't harden. 

Rashelle I used spring steel from a coil spring I got down at the local 4 wheel mechanic shop. I went in, told him I was an amateur blacksmith and he threw me a couple that he just pulled off a truck he did an upgrade on.

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The ferric acid showed up today so I gave it a shot. It didn't turn out how I had hoped so hopefully you guys can give me some suggestions. I did a 3:1 ratio and dipped it a few times for 30 seconds then dipped it in water and cleaned it in between. I've also posted a picture of the spot where I need to improve next time when I'm making the well so the insert fits and welds better.

Unfortunately when I file tested it again is didn't skate so either I heat treat it again or start on the next one. Thoughts?20210112_181045.thumb.jpg.165de9dd80ce78f6ceaa059a432d0361.jpg

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So it skated a file after hardening in water, now after tempering in who knows really what temp (close to what you think). it won't skate a file. I'm thinking it may not be hard enough to hold a good edge. Why not sharpen it up and use it a good bit to see how it holds up? It is a spike knife without added handle material, so if it performs poorly you could re heat treat later. 

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If you're looking for a good even darker color- leave it in for a couple minutes at least. 30 seconds might be enough to show you the steel differences, bring out a hamon line... but that depends on how good your dilution ratios were. Lol...

Like das said- I'd try sharpening it first and see how it holds an edge. If you don't like the results from there- then you have your decision to try and re heat treat, or start again.

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  • Mod42 changed the title to To etch or to temper first, that is the question...

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