Creating welded bolt to replace forged bolt

[amorreale]

I am currently reviving an older bolt design which uses an EDT150 or 4140 QT stud that is threaded at both ends and is going to be welded to a nut on one of those ends. This in turn will create a bolt. We switched over to solid forged bolts a few months ago and we've been having problems with the heads popping off after preloading the bolts to the proper torque specification. The older welded bolts performed with much more longevity and had much lower instances of head failure. The only thing is that the welded style bolts were never heat treated after welding. The end of the stud that has the welded nut on it is chamfered to allow for a bevel weld. Any thoughts on normalizing and heat treatment after weld? Any thoughts/comments would be helpful. Thanks.

 

[metengr]

amorreale;
I read through your post and must have missed something. Your original style threaded stud/nut welded was used as a bolt. You had no reported problems. Now you have switched to a forged bolt and still weld the nut on the other end, correct? You refer back to a welded nut/stud and not having any problems, yet you are asking for post weld heat treatment recommendations for what - the old style threaded rod design or the new forged bolt design?

 

[amorreale]

The old style stud had a welded head on it. The newly forged bolts have forged heads. There is no welding taking place on the forged style at all. Since I'm revisiting the welded style again, I noticed that these old designs didn't have any post weld heat treatment and I'm wondering what kind to specify. I think I'm going to go with the 4140 qt versus the etd150 because of the slight ductility benefit, and when i say slight, i mean slight. I'm just basically wondering what kind of suggestions for normalizing / heat treatment would be suffice for a welded bolt like this one. The nut is standard nut material, grade 8. The weld rod is chronatron 333. I'm not a heat treatment expert, that's the problem, but i know it's probably necessary after welding.

 

[metengr]

amorreale;
I would suggest a post weld heat treatment for the 4140, the only problem is I do not know the strength level of the stud. If you can determine the tempering temperature used in the original heat treatment of the stud, stay 50 deg F below this temperature for your PWHT. Use 1 hr/inch of thickness as a guide for PWHT.

 

[amorreale]

metengr,

Thanks a bunch, i really appreciate your input.