It's no real trouble to weld simple high and low carbon steels, but when you get into complex alloy steels like 5160, 51200, some of the alloying elements really mess with the welds. I'd avoid trying to weld them at all costs. They are, for our intents, pretty much weld-proof. If the weld does stick, they'll fail in the heat affected zone. They behave strangely.
I've not tried to work 51200, but most of my knives are made from 5160 spring steel. This is pretty much what you'll find in the average leaf or coil automotive spring, a near endless source of material. While it benefits from an elaborate HT regime, not unlike 51200, it does respond quite reasonably to old-school heat-quench-temper too. I've found the finished blade to be quite tough, compared to similar 1085 blades, but slightly softer if I temper them the same. Their extra toughness allows me to leave the temper a shade or 2 cooler, to achieve a similar result to a plain carbon blade.
Some bearing races are also made from 440 class stainless steels. If your old bearings aren't frosted with rust, they may be stainless.
Mokwepa, you asked a few posts ago about getting a blade to stay straight thru the quench. That's one I've fought since the beginning too. Here's what I've found....
First, make sure the blade is held for quenching with the spine up, edge down, and move it around in the quench fluid in an up and down direction. Side to side would cool one side faster than the other. That's a warp!
When I first made blades, I'd forge'em to shape, and on the last heat, I'd tap them about, trying to straighten them. Then I'd heat and quench. Half the time, they'd warp.
Now, after I spend that heat straightening them, I re-heat them and recheck them for straight. Sometimes they'll shift a bit. Very little work done in this heat. Repeat a couple more times, working out any last bends, but do not try to cause any shape change in the final heats, especially as it cools below red heat. Then, do the hardening heat, quench and check... Chances are, there was much less warping this time. I think these last 2, 3 or 4 heats is basically similar to a normalization. When we straighten on the last heat, we risk leaving distortions in the steel's structure, and the next heat/quench lets those distortions pull the blade about.
That's the sense I can make of it, anyway.
HSO: Ice bucket. Will remember that, next time some newbies are about....
J
Im glad you can quench horizontal, i battled to find a container tall enough to hold enough oil. On my next knife (a bowie, im going to at least try it) ill do as you say and hopefully get it straight first time.
