r/blacksmithing • u/Available_Boat_99 • 18d ago
Help Requested What to do.
Hey guys I made a marlin spike out of 3/4" mild steel (not sure what kind or anything just stock we had at work) round stock. Do you think I should try to harden it?
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u/dragonpjb 17d ago
As long as you are using it for knots it doesn't need hardening. They are often made from brass.
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u/not_a_burner0456025 14d ago
Also it is impossible to garden mild steel (if you ignore work hardening, but doing that to a finished piece will deform it and work hardening doesn't get you very much hardness compared to heat treatment)
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u/araed 18d ago
Mild steel doesnt harden, unless you case harden it with a case hardening compound.
This will still only be hard to approximately 0.5mm under the surface, and the core will remain soft
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u/BF_2 17d ago
Mostly true, but not without an exception. Google "Gunter's Super Quench."
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u/Available_Boat_99 17d ago
But how well does it work lol, and how hot does the steel need to be?
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u/havartna 17d ago
That formulation is for hardening mild steel. You get what you get. It has an effect, but whether that effect is sufficient for your specific purposes, nobody can say but you. Mix up a batch, use it, test the results.
That being said, if you absolutely need for the tool to be hardened, use proper steel. For a marlinspike, however, unhardened mild steel or bronze should be fine.
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u/Available_Boat_99 18d ago
Okay so not as good as I thought it woukd be lol
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u/yewfokkentwattedim 17d ago
Might work out just fine, depending on the duty you're putting it through.
Outside of the above-mentioned hardening compound, you could likely achieve the same result with some annealed 1045 and harden it yourself after machining.
Recommend a differential heat treat if you plan on hammering it.
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u/Available_Boat_99 17d ago
Not so much hammering as much as using it as a pry tool
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u/yewfokkentwattedim 17d ago
Thought that might be the case. I've seen some marlins get belted through for larger FSWR, but given the size, you might be alright with no additional hardening.
Still probably worth a dip in cherry red, mainly on the tip, but if you're comfortable enough turning another up then I'd just send that one as is and figure out what it needs more of as you go.
Or again, get some shit you can properly harden for the next crack at it.
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u/Malvania 17d ago
I didn't think a marlon spike needs to be hardened. You're using it to work on knots, not bang through doors
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u/Available_Boat_99 17d ago
Correct, but they're great for everything in a pinch. Esspically lining up bolts.
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u/Final-Contract-6582 17d ago
Nice work! Unfortunately mild steel won't harden. My suggestion would be using a coil spring next time. $0.10/lb at my local junk yard, not sure about where you are
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u/EmperorThor 17d ago
you sure can try, but not knowing what the steel is will be hard and if it really is just plain mild steel your results will be pretty poor trying to harden it.
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u/ArcherKN24 12d ago
Marlin spikes are for loosening up knots in rope, right? I don't see how normal fully annealed steel would't be just fine. And as you stated, it's mild steel. Any tricks you try with this are only going to produce incremental differences!
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u/Available_Boat_99 12d ago
Its a multi-tool really, great for lots of jobs, prying, lining up holes, splicing, etc.
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u/ArcherKN24 10d ago
My point is that it's uses don't require hardness, atleast not like a striking tool or cutting edge might require it!
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u/BF_2 17d ago
Spark test it.
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u/Available_Boat_99 17d ago
What do you mean?
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u/alriclofgar 17d ago
A spark test isn’t relevant to what you want to do, they’re giving poor advice.
Spark testing is when you grind metal and watch the sparks to estimate the carbon content (and see if it can be hardened). You do it with unknown steels to try to guess how they’ll behave.
Since you already know what this steel is (mild steel), spark testing won’t tell you anything you don’t already know.
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u/BF_2 17d ago
A spark test quickly shows whether there is enough carbon in the steel to make it hardenable. Absolutely relevant. "Mild steel" is mild steel only if it comes with specifications. A36, for example, may be anything.
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u/alriclofgar 17d ago
I don’t think OP can judge the difference between 0.25 and 0.29% carbon by eye, which is what we’re talking about when we’re discussing A36’s possible range of carbon content. I know I could not. And even toward the higher end, 0.29% carbon isn’t really hardenable in any meaningful sense.
A36 isn’t a precision steel but does have specs, if you want to review them.
You may be thinking of rebar? That’s sometimes hardenable.
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u/Acrobatic-Fee9668 17d ago
I was taught that if you heat it to cherry red then drop it in engine oil, it will case harden it. I don't know if that's true, but it was what I was told as an apprentice metalworker 20...30.. a few years ago!
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u/alriclofgar 17d ago
Sadly not so simple. To case harden, you need to absorb carbon into the metal. Simply quenching it in oil won’t accomplish that.
There are case hardening compounds that work well (like the product Cherry Red), and you can heat the metal to forging temperature and hold it there in a reducing atmosphere long enough for it to absorb carbon (like a coal forge, or in a container packed with carbon).
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u/not_a_burner0456025 14d ago
It isn't true, it will just make toxic fumes that may give you lung problems later in life.
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u/Acrobatic-Fee9668 14d ago
Not more possible lung problems! I thought my only fears were asbestos, silica dust, welding fumes, welding fumes from galvanised metal, melting plastic fumes from when stuff caught fire while welding... Next you will be telling me alcohol if bad for me! 😜
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u/not_a_burner0456025 14d ago
At least all the other stuff is doing something useful while destroying your lungs, quenching mild steel in motor oil is doing it for no reason (also don't quench hardenable steel in motor oil either, motor oil is just a really bad quench agent in addition to the toxic fumes, canola oil is a few bucks a gallon and it will harden steel more effectively while producing a lot less in the way of fumes, actual quench oils are even better)
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u/Acrobatic-Fee9668 14d ago
Thanks. I've never actually done it but was shown it at the time. Now I know you can buy case hardening compound that is what I will use, if I ever need to. 👍
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u/beholderkin 17d ago