Joint Strength of SUS304 Stainless Steel Joint Brazed with Fe-Cr System Alloy

Two kinds of new Fe-Cr system alloy brazing filler, Fe-Cr-based and Fe-based, have been developed as a substitute for expensive Ni-based brazing filler in brazing of SUS304 stainless steel. Joint strength of the joints brazed with new filler were investigated and compared with the joint brazed with Ni-based brazing filler. The following results were obtained in the study. P-rich phases were formed because Ni in the new Fe-Cr system alloy diffused from the brazed layer to SUS304 stainless steel when joint clearance was 10 μm. When joint clearance was more than 50 μm, a finally-solidified region appeared in the brazed layer, at the same time, most of P segregated and was enriched in the finally-solidified region. It was proved that the volume fraction of P-rich phases in the finally-solidified region varied with the increase of joint clearance and joint strength decreases with the increase of the volume fraction of P-rich phases. Compared with Ni-based filler, joint strength of the joint brazed with Fe-based filler was almost equal when joint clearance was under 200 μm. On the other hand, joint strength of the joint brazed with Fe-Cr-based filler was slightly inferior regardless of joint clearance. Still, joint strength reached approximately 100 MPa. The result indicated that joint strength of the brazed joint with the Fe-Cr system alloy was strongly affected by the P addition. It is possible that promoting of joint strength can be brought by lower addition of P.