[A Snake]

I'd have to see the break to be sure, but what you describe, sounds like the hubs may be too hard already. You might want to have someone do a hardness test at various points on both halves of the broken hub and at the point of breakage. I'm referencing other steel here, but I would estimate you should not exceed 48-50 Rockwell C scale if your hubs are 4140. Better they bend than shatter.

Questions for you: Does the break have very smooth edges and a fine textured look or is it a little rough textured with a rougher look to the inside of the break? How thick is the cross section where the break occurred?

Also, is the bearing surface part of the hub or does it come as a race and bearing set with race press fit into the hub?

Al