When you weld something that hard there are really huge stresses when it cools. Hardness is high, ductility low. Those stresses will be relieved upon shrinkage. I would guess that 'shoulders' could very well be an issue, but a material with less hardness and therefore less tendency to cracking will wear even faster.
Hello mountainman, in many instances hardsurfacing is used over the top of softer deposits. Even though you may see cracks on the surface of the hardfacing application, those cracks aren't necessarily detrimental, they are there as a result of the contraction rate of the hardsurfacing deposit. Part of the hardness of this material means that it doesn't have much in the way of elongation ability, elasticity, or ductility, thus it cracks. Think of it in terms of certain candies that have a chocolate covering, as you bend the chocolate covered bar it may crack the chocolate covering but the chocolate still sticks to the caramel or whatever else is under it. In a sense certain hardsurfacing materials act similarly. I used to build up crusher rolls for a crushing plant, we would use E7024, E7014, E7018 to do the initial build-up and then finish the roll with a layer of hardsurfacing rod. The underlay of weld would act somewhat as a buffer for the hardsurface on top and would allow it to have some give. If you put too heavy or thick of a layer of hardsurfacing on, large chunks might break out instead. There are also different types of hardsurfacing material, some are designed to resist impact, others are designed to resist abrasion, yet others are designed to resist abrasion at high temperatures, there are really many different types of these materials, most with very specific applications and uses. Having said that, many will exhibit the cracking and it is acceptable, others may not exhibit any cracking and even if they do, it may be acceptable as well. The folks that select specific types of these materials for application need to take this into consideration when they specify or choose a certain material. Hope this helps somewhat, Best regards, Allan
As usual, good explanation Allen.
To take it a bit further, most hardfacing material is very, I stress VERY, hard. It sometimes ranges into the high 60's and mid 70's RC. Usually one layer will not exhibit much cracking because of the dilution with the softer material, but as the hardfacing is built up, the weld mix gets less and less ductile, and at some point becomes unable to contract as the part cools. That's when it starts to crack the hardfacing weld bead and almost always are transverse to the weld bead. These cracks don't usually propagate into the base metal, and are totally normal. We use one specific SMAW rod that will not stack more than 3 layers because of the extreme hardness. The weld material becomes so hard that it will start chipping off in chunks as the part cools. One other very important thing with this type of rod is that proper ventilation. Due to the different alloys in the stuff, the smoke is really really bad on your lungs.
My apologies to the original poster since his post was not really asking about hardfacing.
The process we used was a single layer open arc process (solid wire with a powder mix) with ~5% or less dilution. The mix was designed to realize an M7C3 Cr/Fe Carbide with a Brinell equivelent of ~1700 (though Brinell's typically max at about 600).
The mix was ~5% C, 30% Cr, 3% Mn, and Fe balance (though a variety of chemistries and hardnesses was available. Our specs were 55 RC min. with ~20 cracks per foot (foot, not inch as I mistated).
very interesting, learn something new everyday. thanks.
JJ
oh damm is not this a helluva thread
js55
Was this company in Houston? I ask as I worked for them for several years in the 70's and 80's. Buckwelding, some called it.
fredspoppy,
Houston for sure. Never heard the Buckwelding thing though.
I don't want to let Charles' post slip by without more discussion. Not being an 1104 guy, though not totally ignorant of it either, the idea of acceptable crater cracks, though I'm sure having heard it, never seriously impinged on my mind (though I'm sure at the time I went huh?). But as Charles says, this is a very interesting (and I have to admit somewhat troublesome in my mind)state of affairs for pressure (sometimes very high pressure and temp and perhaps even cyclic service) retaining, CJP (to borrow the AWS D.1 terminology) circumferential groove welds.
Tapco/Triten. I was with them '79-'84. The technical term was "bulk welding", meaning powdered additions to open arc and sub arc welding. Many a plate of chrome carbide overlay was manufactured using that method.
Small world. When I arrived they had just decided to bring back their hardfacing operation from Monterrey Mexico and restart it in Houston. AND, they had just acquired Capitan Corrosion Overlays from Capitanescu and were bringin them down from Canada. So we were doing hardfacing and corrosion at the same time, seperated by a couple of walls. The bulk welding open arc process, as you probably well know, was at one time, maybe even when you were there, proprietary, invented by the old man, one of the truly knowledgeable old guard of fusion welding minds from the 50's and 60's. But its pretty widespread now. Tapco was sold off and moved around the corner on Little York.
It didn't work out between me and them but there were still some pretty good guys there.
Yeah, it means the stress is off of it now so grind it out and burner in der. Thats if it's still in one piece.;-) J/K I have no idea, but this is good trivia. You could make a game out of this.
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