View Full Version : Weak Joints O/A
11-14-2006, 04:46 PM
I seem to have started to get the hang of dipping the rod into the pool and running the bead. On the surface it doesnt look half bad (1/8 inch steel butt joint). However when I put it in a vise and bend it with a hammer the joint breaks with just a few bends. When I look at the joint (after its broken) it is extremely grainy and dull. Even in areas where I got good penetration it breaks right at the joint and has a horrible grainy brittle appearance. I tried going to a slightly A rich flame but is didnt seem to help. Any Ideas ?
11-14-2006, 05:23 PM
Any chance you can get a photo?
You may not be doing anything wrong, there are many factors to be looked at.
Where does the fracture occur, center of weld, edge of weld, or base metal?
Did you achieve full penetration, because the sharp notch of a partial penetration weld will act as stress riser and help the weld to easily open up in a root bend.
Do you know what the base metal is, I guess I'm assuming it is a low carbon steel. This could have a huge affect on your weld properties though, if you happened to pick up something with higher carbon content or some alloy steel that is easily hardened in the heating/cooling cycle.
When you say it breaks with just a few bends, does this mean you bend it 90 degrees or more in one direction, and then bend it back in the opposite direction, and so forth? If so, that is a pretty severe test. Don't know the code standards for something this thin, but generally you are required to do face and root bends, bending the material through 180 degrees in one direction.
The grainy appearance is probably normal, since metals are composed of crystal structures called grains. The heat affected zone (HAZ) in the base metal next to the steel weld will undergo grain growth/coarsening due to the heat cycle and this does reduce ductility and strength in that area.
As I recall, a dull gray fracture is a ductile fracture (good type or fracture). If you could see it under a microscope it would show thousands of tiny "cup and cone" type dimples produced as the metal plastically deformed (stretched) during failure. A brittle failure (which is most feared because of its sudden catastrophic nature) would tend to be shiny and multi-faceted, because of the lack of plastic deformation and the flat fracture path right along the grain boundaries.
11-14-2006, 06:53 PM
Thanks for your advise. It begins to break on the return of a complete 90 degree bend. I put it in a vise alonng the joint and hammer it down to 90 then bend it back . Hard to see the grain with the pic
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