Help in identifying the mechanism(s) of rods failures is needed and will be greately appreciated.

Short description:
It is a 1" dia, 5" long metal rod welded to the lid and protruding into a mixer where dry material is mixed with water. Impactive type of force is expected during the mixing process to be applyed to the rod, trying to bend it. The rest of the description is in the attachment.

Thanks in advance

Dave

Pin_Break.doc (160 KB, 32 downloads)

The fracture surface appears to show fatigue across most of the surface. Typically, the heat-affected-zone adjacent to the weld nugget has the highest hardness, and correspondingly, the least toughness. That's why fracture occured just below the welding level.

Post weld annealing and blending of the part surface after welding could help make the part more resistant to cracking. Shot peening of the surface would be an added plus.