Effect of the Prior Microstructures on Diffusion Weldability of SUS 304 Stainless Steel

Abstract

Fine grained microstructure enhances grain boundary diffusion, so diffusion weldability of fine grained material may be better than that of coarse grained material.
Three types of diffusion welding specimens were prepared. Each abutting surface had coarse grained microstructure, fine grained microstructure, which was prepared from friction weld interface, and cold-worked microstructure. Third one was expected to change into small recrystal at diffusion welding temperature. These were welded by various diffusion welding conditions. And, tesnile strength and microstructure of weld, and deformation of specimens were examined in order to estimate the effect of prior microstructures on diffusion weldability.
Obtained results were as follows;
(A) Very fine grained microstructure, in which grain diameter was about 7 μm, was hardly to change into coarse grain even keeping at 1000°C.
This specimen could be joined at lower diffusion welding temperature than coarse grained specimen, in which grain diameter was about 100 μm.
(B) Cold-worked specimen started joining with onset of recrystallization into small grain.
Diffusion weldability of this one was between that of fine grained one and that of coarse grained one.