Does anyone have experience with the durability of stainless steel hardware in a wood stove firebox? Google shows conflicting claims from various manufacturers. I disassembled the stove this weekend and plan to reassemble it with hardware-store stainless steel bolts, as some of the originals have thinned down after about 30 years.
The fully assembled stove is locked together horizontally by tongue and groove joints between the panels. These bolts keep the plates in place if the stove tips or is moved, so they aren't tight and I don't think the higher thermal expansion of ss will cause problems. The other load-bearing bolts will stay mild steel.
Jim Wilkins fired this volley in news:5e7af89e- email@example.com:
The problem is that most corrosion-resistant steels lose much of that property at the heat encountered there.
The only solution to it is to protect the steel parts from the heat with a refractory brick (or panel) liner. If your stove never had a liner, it's tough to add one that's thick enough to do the job, and still not rob too much volume from the box.
Still, I'd rather have SS fasteners than merchant stock steel. At least there's the chance they won't be a solid lump by the time I must get them back out.
I guarantee that you'll hate yourself in the morning if you use SS bolts there. They GALL!!!!!!!!!!! Maybe use plain steel nuts with them. We have used SS bolts and nuts in the past in non-heted outdoor projects with really poor results. We put up on railing using some really pricey Allen head SS screws and SS nuts and had to take it down just a few months later because the color didn't match (that's another story). About half the fasteners galled so badly that they had to be ground off. When we went out and researched the problem, we got plenty of input from people saying, (essentially) "you dumbies, everybody knows that won't work!". Now, when we do use them, we coat the threads with Never Seize, the type with nickel, and that seems to work okay. But even then, it's hard to use because it gets all over everything if you aren't careful. I don't know if Never Seize can handle heat,though, so I wouldn't recommend it for your application unless you can get assurances that it will work there.
Someone did speculate the if you use a stainless steel of one type for the bolt and another type for the nut, that the problem goes away. I'd research that issue if you really want SS in there.
I always thought that coarse thread screws and square nuts were just the ticket for wood stoves. Don't they call 10-24 bolts "stove bolts" just for that reason? They come apart pretty well and aren't too hard to break off it needed. 30 years ain't to bad for the originals. As blacksmiths, we are often faced with forge repair. We almost always use plain steel fasteners in the forges. If nothing else, a quick burst from the old "gas axe" and the offending fastner is gone.
I just answered my own question with a magnet. The ones I replaced about 10 years ago -are- stainless and they are in very good condition after wire-brushing the crud off. The threads and the lettering on the heads are still crisp and the nuts turn freely. These are exposed to the flame at the top sides of the main firebox where they attach the upper smoke box. The lower ones that hold the sides to the base are original, were installed with NeverSeize in 1985, and came out easily although the exposed part was seriously eroded, more so in the cooler back end of the firebox.
Except for one hanging baffle the cast iron is in fine shape. I think it's a Scandia ripoff of a Jotul 118 from the 70's. The castings are marked Taiwan, the hardware is 1/4-20 with 10mm hex heads.
This is the stove I anneal and heat-treat in. A piece of steel coated in Ivory soap and left in overnight cleans up to a smooth grey with little or no scale. I modified the stove by drilling some small holes to let more secondary heated air into the upper smoke box and close down the main air intake until the flame shows some violet. At this setting it burns about 7-8 Lbs of wood per hour with no visible smoke. Below this rate it won't maintain a stable fire.
Jotul claims their original will burn all night "cigarette" style from front to rear but I have never been able to make this work without a lot of smoke. I arrange the fire muffle style with an air passage between the logs down the center and get a maximum of 2 hours of good heat.
Ivory or other sodium stearate soap bakes into a coating that protects hot steel to some extent. Another old formula I haven't tried is salt and flour.
Rub the moistened soap on tool steel before hardening it. As long as the part stays in a reducing flame the cutting edges don't degrade quickly at red heat, or scale in the air between the fire and the quenching bath. If I do it right I can sharpen the edges with a Dremel or hand whetstone rather than having to set them up on the surface grinder.
I harden small tools with a propane torch angled into a tin can with some charcoal in it, which contributes enough radiant heat of its own that the propane flame can get the steel up to hardening heat. When the steel doesn't attract a weak magnet I dump everything into a pail of water. The instructions for oil-hardening steel say that water is OK for small cross-sections.
Do this in a safe place outdoors and don't use a magnet strong enough to lift the part.
"Jim Wilkins" wrote: (clip) When the steel doesn't attract a weak magnet I dump everything into a pail of water. (clip) don't use a magnet strong enough to lift the part. ^^^^^^^^^^^^^^^^^^^ A jeweler once told me he does something like this to heat treat hair springs. He holds the spring over a quenching bath with a magnet, and then plays a torch on it until it drops off into the bath. Of course, his magnet is strong enough to lift the part.
Just be aware that for some steels, mostly of the high-alloy types IIRC, the critical temperature, at which the phase change is securely accomplished and the steel is ready for quenching, can occur at a slightly higher temperature than the Curie point, which is where ferromagnetism disappears.
In other words, for reliable hardening, give it the Curie point plus a very slight bump. This shouldn't be an issue with plain carbon steel.