Abstract
High temperature tensile tests were conducted on butt brazed joints of type 316 stainless steel. Two kinds of newly developed Ni-cu based filler metals, two kinds of standard nickel filler metals, BNi-2 and BNi-5, and a standard silver filler metal, BAg-21, were tested. Each of the joints was made to have a constant joint clearance of 50 micrometers. Tests were carried out at 298K, 423K, 573K, 723K, 873K and 973K, in air atmosphere.
Strengths of the nickel brazed joints were less than 300MPa at all the test temperatures. The relatively low strength were attributed to formation of brittle eutectic phase at the center of the joints. This indicates that the joint clearance for nickel filler metals should be controlled to be narrower than 50 micrometers to obtain practical strength in industrial applications. In the joints with BAg-21, the strength decreased drastically above 573K. This filler metal therefore would not be applicable for the joints used at high temperatures.
For the joint with Ni-Cu-Sn filler metal, one of the developed Ni-Cu filler metals, the strength was about 340MPa at 298K. The strength decreased gradually with the increase in temperature. At 973K, the strength was less than 100MPa. This filler metal is not applicable for the use at high temperatures over 600K, consequently. On the contrary, the joints with Ni-Cu-Mn filler metal showed about 400MPa of tensile strength from 298K to 723K. The result indicates that this filler metal can braze wide gap joints with better mechanical property compared to nickel filler metals, and can be used in high temperatures around 700K.
