Wetting and brazing characteristic of high nitrogen austenitic stainless steel and 316L austenitic stainless steel by Ag-Cu filler

In the present work, wetting behaviour of Ag-Cu eutectic filler on high nitrogen austenitic stainless steel (HNS) and 316L austenitic stainless steel (316L) base metals was firstly studied using a sessile drop method in high vacuum. The Ag-Cu eutectic filler exhibits completely different dynamic wetting process on the surface of HNS and 316L. The equilibrium contact angle of Ag-Cu/HNS system is lower and its wetting time is shorter than that of Ag-Cu/316L system. Subsequently, brazing experiments were carried out for HNS and 316L base metals using the same filler at 840 degrees C for a holding period of 5-30 min under high vacuum. Microstructural analysis shows that the 316L/316L joints are composed of alpha-Cu and fine Ag-Cu eutectic. The HNS/HNS joints consist of beta-Ag and coarse Ag-Cu eutectic. The optimal shear strength of HNS/HNS joints (290 MPa) is significantly higher than that of 316L/316L joints (175 MPa) because of the formation of diffusion layer. Therefore, HNS has tremendous potential to take the place of the traditional austenitic stainless steels for industry application.