OT-metallurgy question

xxclaro · Post by **xxclaro** » Mon Jan 21, 2008 2:00 am

It seems no matter what the topic, someone here knows the answers to almost any question. So let me throw this out there. I am trying to build a Sambura style spear, and need to aquire the proper steel. This spear is essentaily a 3 peice design, with a 2 foot wooden handle, a 2.5 foot front end and a 2.5 foot back end,both metal. It's about a 3/8 rod with spearhead welded to the front, and long tapered spike at the back. Cold Steel sells them, but I've tried theirs, and it bends very easily. I was thinking perhaps a type of spring steel could be used, something that would flex but not bend. Cold steel uses 5150 medium carbon steel. Speedy Metals sells some good tool steel and drill rod, but I don't know enough about it to know what to buy. Their spear works well, and it's easy enough to bend straight by hand, but I wonder how long before the metal fatigues and breaks. Anyone have expertise in this area?

Tycer · Post by **Tycer** » Mon Jan 21, 2008 4:33 am

Would tempering help? http://www.engnath.com/public/harden.htm

20cows · Post by **20cows** » Mon Jan 21, 2008 6:39 am

Tycer, thats some pretty good info! I'm slowly educating myself in that area and about ready to build a gas forge.

Thanks for posting the link.

BenT · Post by **BenT** » Mon Jan 21, 2008 9:03 am

RFDTV has a show on every once in a while about forging. It's really interesting. I think it's called Anvil and Forge or something like that.

I bought a gunsmithing book which was published from the 30's that talks about tempering steel for fabricating gunparts. It's good info to have. I'll also save that site on hardening for future reference.

mescalero1 · Post by **mescalero1** » Mon Jan 21, 2008 11:32 am

If you can locate an old Chevy 3/4 ton truck, try the bottom short spring in the leaf spring set.
This leaf has no curve set to it, grind slowly, use water to cool during grinding, be quick with the welder.
The steel takes a good edge, it will retain the spring "temper "
good luck

Ben_Rumson · Post by **Ben_Rumson** » Mon Jan 21, 2008 2:20 pm

You've got the spear ... Why not give annealing, hardening & tempering a go as per the info about 5150 Tycer has put you onto? A box of sand to bury the blade in will suffice to slowly cool the blade down.. Used motor oil will work for quenching.. I wonder though, how the people that used these blades originally dealt with bending.. As long as the blade isn't bending double I'd not worry too much about metal fatigue...

cutter · Post by **cutter** » Mon Jan 21, 2008 2:59 pm

Original iron speer heads, and other iron implements of war, were of a soft metal. Mostly because of that was the only material they had, but also because they could be easily repaired.

I stiff iron speer point may shatter on impact , where a softer one would bend. A bent speer can still function, but a broken one may not. A iron arrowhead, when bent could be easily 'cold forged' back into shape. If it were broken, it would require welding which required a blacksmith who was busy making new speer points and arrowheads.

Check out Dixie Gun Works, and Smokey Mountain Knife Works, for original speers. I believe SMKW has a large stock of original isukus, if you wanted to see how a 'real' one was made.

You can harden the tip and leading edge of the existing blade, using a axcetaline torch, scrap wood, coat hanger wire, and transmission fluid.
Strap the wood to the blade, exposing only the tip and leading cutting edge. Quickly, and evenly, heat the tip and edge to a dull cherry red, then quench in the transmission fluid. Make sure the transmission fluid is preheated. I like to heat a few 9/16 nuts to red, then drop into the fluid before I use it.
Heat and quench, heat and quench. It might take a few times to get it hard enough.
The wood keeps the heat contained in the parts of the blade you want to harden, it will burn away, but you can add more as needed.

Practice on a piece of scrap metal first...

octagon · Post by **octagon** » Mon Jan 21, 2008 5:39 pm

xxclaro: are you going to hunt with this spear?

bj94 · Post by **bj94** » Mon Jan 21, 2008 9:35 pm

For tools like knives and spears, you have to determine what the use is and then reach a compromise between hardness and ductility.

For instance if you take a piece of coathanger, you can bend it into a sharp bend and it will not break, and it will be fairly easy to bend. But if you tried to sharpen it, it would dull very easily.

The other extreme would be one of the more exotic knife steels. You can sharpen it and it will hold its edge pretty well, but try to bend it and before you have deformed it very far it will break like a piece of glass. Now it will take a lot of force to do this, but it will eventually break before deforming very much.

So the compromise is how hard do you want the steel to be to hold an edge, but how much do you want it to bend when necessary without breaking. In knife terms you can make a survival knife pretty hard to hold an edge, but if you start hammering on things the edge will chip, and if you try to pry open wooden crates you will break the end of the blade. This is why survival knives usually have what on the surface seems like a lower class of steel than some other modern knives. There isn't anything special about spring steel, it's just a high strength steel that resists a lot of stress without permanent deformation. In terms of this discussion it would also be brittle and maybe not suitable for all types of knife blades.

Well it isn't quite that simple. Some steels have better toughness characteristics than others. And this is where it really gets difficult because in addition to the steel chemistry being important, the heat treatment is also important.

Two interesting schemes have been used to work around this compromise. Some custom makers use differential heat treatment. They will forge a blade out of ductile steel, go into the heat treatment process, and then quench only the edge of the blade, thus leaving the rest of the blade more ductile than the edge.

The other scheme is to laminate steel. Morseth has done this, and Cold Steel has done this in their production knives. They use a thin layer of hard steel, then laminate a thick later of softer steel on either side. When this is ground into a knife blade, the hard core is exposed as the edge. Then when a blade is stressed in bending, the softer outside laminations can deform without fracture.

Now taking all of this in terms of a spear, if you get the metal hard enough to not bend, it might just break. Of course that doesn't mean you can't improve on the stock spear, but you have to search for that perfect compromise of hardness vs. ductility for your particular requirements.

xxclaro · Post by **xxclaro** » Mon Jan 21, 2008 10:45 pm

Well, sounds like this is going to be more compicated than I anticipated! I'm thinking of maybe making the shaft of spring steel and the head of a tool steel like D2 or something. I could slot the shaft and insert the head, welding along the sides of the shaft, adding support to the head. The Cold steel spear I referred t o isn't mine, I was using a friends. I hope to hunt with it, if I get proficient enough. Heat treating sounds interesting, but I don't know if I could heat the 2.5 foot lenght evenly with a torch. Maybe this summer I'll build a small outdoor forge and try that. Many thanks for all the help so far, you guys continue to amaze. Any suggestions on which steel to start with?

Gobblerforge · Post by **Gobblerforge** » Tue Jan 22, 2008 6:06 am

You may want to do some research to find what the traditional spears were made from. I would be surprised if the original ones were made from anything other than "wrought iron". Until Bessemer invented his furnace, steel was a difficult material to make and expensive to buy. As far as sharpness is concerned, a spear doesn't have to hold a razor edge. Sectional density will drive the spear into the target. The sharpness helps as it gets inside to cut vitals, but again, not as important as in, say a knife.
Might I suggest you try to find a Blacksmith for the job? I don't know where you live but there are smiths in all 50 states. Try
http://www.anvilfire.com/index.htm
or http://www.iforgeiron.com/
Someone there has done this already. I personally have made close to a dozen knives over the years, but never a spear.
Gobbler