Am I work hardening my 4130 tubing?

[GlennA]

I am experimenting with reducing the diameter on the end of thin walled (.028") 4130N tubing (5/8" OD). I'm using a technique like is used in metal spinning, simply applying pressure against the outside of the tube while it turns slowly on the lathe.

The result is good (I can get the end down to 3/8"), but I'm concerned that I may be making the material brittle. In experimenting with the technique I've succeeded in fracturing the end by forming too aggressively, but that can be avoided. The tubing is being modified for chain stays on a bicycle frame, specifically for the welding point to the rear dropouts which is a high stress area.

Am I weakening the material? If so, is there anything I can do to fix it?

 

[salmon2]

Yes, you sure did. A post heat treatment can re-store properties.

 

[GlennA]

Thanks for the confirmation. Can you suggest a heat treatment process? I heating equipment don't have access to an annealing oven large enough.

 

[salmon2]

I will suggest do a stress relief annealing, which is to heat the part up to a temperature, 50F below the tempering temperature, hold for an extended time (about 1 hour or more) and cool in still air.

As you can see I assumed that the tube was quenched and tempered before the spinning. You need to get the tempering temperature to set the annealing temperature, otherwise, you could change, not re-store, the previous properties.