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The best temperature performance can be obtained by brazing stainless steel with nickel-based brazing filler metal. When brazing with nickel-based solder, the size of the assembly gap has a great influence on the strength and plasticity of the joint, and a small gap means good performance.
Take nickel-based B-Ni74CrSiFeB(C) and B-Ni7CrSi brazing 1Cr13 and 1Cr18Ni11Nb stainless steel as an example. When the joint gap is extremely small, the tensile strength of the joint brazed with these two types of brazing filler metal is basically the same as that of the base material. The strength and plasticity are also good; when the gap increases to 0.05mm, the strength and plasticity of the joint drop sharply; when the gap reaches 0.1mm, the plasticity of the joint has tended to zero. The reason is that nickel-based brazing filler metal often contains more boron, silicon, and carbon due to the requirement of melting point, so that the brazing filler metal is composed of many non-metallic brittle compounds.
During the brazing process, elements such as boron, silicon, and carbon in the brazing filler metal diffuse to the stainless steel to form complex brittle compounds. When the gap is extremely small, the content of these elements in the brazing seam is small, and the diffusion distance is short, so they can be fully diffused within the brazing time, so that the brazing seam structure becomes a solid solution of chromium in nickel; when the gap is large, the boron in the brazing seam As the content of silicon or carbon increases, the diffusion distance also increases. These elements are too late to diffuse to the base metal. Therefore, a continuous brittle layer is left in the brazing joint, and the strength and plasticity of the joint drop sharply.
Because the atomic diameter of carbon and boron are small, and they are easy to all diffuse away; the atomic diameter of silicon is large, which mainly diffuses into the crystal, and the diffusion speed is slow. Therefore, the stainless steel brazed with B-Ni71CrSi solder with high silicon content is more likely to appear. The continuous brittle phase layer, so that the B-Ni71CrSi solder has a more obvious effect on the gap, which is not more than 10μm in the normal brazing range. Therefore, when brazing with this solder, the assembly gap should be small.
Suitable for vacuum brazing and gas-protected brazing of carbon steel, stainless steel, high-temperature alloys and some cemented carbides.