Structure and Stresses of Large Size Brazed Joints of Cermets and Steel

Abstract

Stresses in brazing joints of different differed in properties were appraised as a result of technological experiments and FEM analysis. Evaluation of microstructure and mechanical properties of large dimensional vacuum brazed joints of Ferro Titanit Nicro 128 sinters and precipitation hardened stainless steel of X5CrNiMoCuNb14-5 using copper as the brazing filler metal. Structure of the joint was described. Shear strength Rt and tensile strength Rm of the joints have been defined. It have been state, that the basic factors decreasing quality of the joint, which can occur during vacuum brazing of the Ferro Titanit Nicro 128 sinter Cu brazing filler metal steel joints are diffusive processes leading to exchange of the cermets and brazing filler metal elements and creation of intermetallic in the joint. It can have an unfavourable influence on ductility and quality of the joint. The effect of joint geometry structure on stresses and deformations as well as on the process of plate cracking has been determined. Results of numerical calculations of three-dimensional models of brazed joints for different sizes of surfaces brazed at a constant width of solder gap are presented. Results of the investigate proved that joints microstructure and mechanical properties depend on filler and parent materials, diffusion process during brazing, leading to exchange of the cermets components and filler metal as well as joint geometry. The thickness of the joints has an essential influence on the values of the local stress and the significant influence on the joint rigidity. In a case of the considered joints the values of the local stress differences have been considerable in dependence of a fixed load manner.