RU2105645C1 - Method of brazing of products - Google Patents

Abstract

FIELD: diffusion brazing of products containing components of molybdenum and steel. SUBSTANCE: a layer of copper coating, 12 to 15 um thick, and then a layer of nickel coating, 15 to 20 um thick, are applied onto the surface of a molybdenum plate. A layer of nickel coating, 12 to 15 um thick, and then a layer of copper coating, 20 to 25 um thick, are applied onto the surface of a steel plate. The plates are put on each other over the brazed surfaces and placed in a vacuum furnace for brazing, heated up to 600 +-10 C at a rate of 15 to 20 C/min, held for 30 to 35 min, the rate of heating is reduced down to 10 to 15 C/min and maintained up to the brazing temperature. Brazing is carried out at 1110 to 1120 C for 8 to 10 min. EFFECT: enhanced serviceability of products due to the increase of brazing temperature, thickness and density of the brazed joint.

Description

 The invention relates to the field of power engineering, in particular to the field of diffusion soldering of products containing parts from molybdenum and steel.

 Soldered structures containing molybdenum and steel parts are widely used in industry. Such designs are used in various fields of technology. In power engineering, they are used in conditions where their increased performance at high temperatures and pressures is required. In these designs, stringent requirements are imposed on the quality of the brazed joint, since it perceives loads as a relaxer to prevent cracking in brittle molybdenum.

A known method of soldering products containing parts of molybdenum and steel, including applying to the brazed surfaces of the parts layers of copper coating with a thickness of 12-15 microns, placing silver solder and soldering in vacuum 1 • 10 ^-2 mm Hg at a temperature of 920 ± 5 ^o C and a shutter speed of 5 min [1]
The known method allows to obtain soldered products, workable up to 1000 ^o C. Above this temperature and at elevated pressure, the product cannot work due to the low temperature of the soldered joint.

The objective of the invention is the creation of soldering technology that ensures long-term performance of products at temperatures up to 1300 ^o C and pressure up to 100 atm.

The problem is solved due to the fact that on the brazed surface of the steel part, a nickel coating layer with a thickness of 12–15 μm is first applied, and then a copper coating layer of 20–25 μm thick, and a nickel coating layer of 15–20 μm thickness is applied to the copper coating layer on the molybdenum parts , soldering heating is carried out at a speed of 15-20 ^o C / min to a temperature of 600 ± 10 ^o C, at which holding is carried out for 25-30 minutes, then the heating rate is increased to 35-40 ^o C / min, at a temperature of 1000 ± 10 ^o C spend exposure for 30-35 min, followed by a decrease in the rate of heat EVA to 10-15 ^o C / min and maintain it to a temperature of 1110-1120 ^o C, at which they are soldered for 8-10 minutes

 The technical result is an increase in the efficiency of the product by increasing the temperature of the solder, the thickness and density of the solder joint.

 The method in accordance with the invention is as follows.

 Solder products containing brazed plates of molybdenum and steel. Before coating the brazed surfaces, they are degreased, etched and washed in acidic solutions. Next, a layer of first copper coating 12-15 microns thick and then a nickel coating 15-20 microns thick with electroplating is applied to the brazed surface of the molybdenum plate. First, a nickel coating with a thickness of 12-15 microns and then a copper coating with a thickness of 20-25 microns is also deposited on the brazed surface of a steel plate using a galvanic method. The choice of material and coating thickness on the brazed surfaces of the plates is due to the following considerations. The choice of coating material is due to the fact that during the brazing of the plates, nickel diffuses into copper to form a solid solution of unlimited solubility and to obtain a high-density soldered compound. Application of copper and nickel layers on the brazed surface of each of the plates increases the thickness of the brazed joint, which allows it to absorb loads during operation without breaking, and prevent cracking in the molybdenum plate.

After coating, the plates are mounted on top of each other on the brazed surfaces and placed in a container for soldering. The container is evacuated to a vacuum of 1 • 110 ^-2 mm Hg. and placed in the working space of the furnace, where they solder the product. Initially, the heating under soldering is carried out slowly at a speed of 15-20 ^o C / min. At a temperature of 600 ± 10 ^o C spend exposure for 25-30 minutes During slow heating and holding, gases, in particular hydrogen, are removed from the surface of both plates. Next, the heating rate is increased to 35-40 ^o C / min, maintain this heating rate to 1000 ± 10 ^o C and when it is held for 30-35 minutes During heating and holding, the temperature of both soldered plates is equalized. After exposure, the heating rate is reduced to 10-15 ^o C / min and maintain it up to the soldering temperature. Such a decrease in the heating rate is necessary in order to maintain the identity of their temperatures before soldering.

Soldering is carried out at a temperature of 1110-1120 ^o C for 8-10 minutes During soldering, diffusion interaction of the base metal with the coating, as well as copper and nickel layers, takes place, moreover, the copper layer on the steel plate interacts with the nickel layers on both the steel and molybdenum plates, and the nickel layer on the molybdenum plate interacts with the copper layers on both plates. Since the soldering temperature is only 7-17 ^o C above the melting temperature of copper, the molten layers of the copper coating, being in a viscous (low-fluid) state, cannot leak out of the gap, but manage to dissolve nickel in themselves during the brazing time with the formation of a solid solution. As a result of these interactions, a dense solder joint is formed.

 The cooling of the container with a soldered product is carried out in air to room temperature. Next, the container is depressurized.

Metallographic studies of soldered joints of samples were carried out. Studies have shown the mutual diffusion of molybdenum and steel through layers of copper and nickel plating. No insoluble nickel layer was found. A high degree of density of the soldered joint was recorded. Its thickness over the cross section was from 40 to 80 microns. When the product was operated under extreme conditions (temperature 1300 ^o C and pressure 100 atm), no damage was found in the soldered joint.

Claims (1)

A method of brazing products of molybdenum and steel, including applying a layer of copper coating 12-15 microns thick on a brazed surface of a molybdenum part, heating and brazing in a vacuum atmosphere, characterized in that a nickel coating layer of 12 15 microns thick is first applied to the brazed surface of a steel part and then a layer of copper coating with a thickness of 20 25 μm, a layer of nickel coating with a thickness of 15 20 μm is applied to the parts of molybdenum on a layer of copper coating, heating under soldering is carried out at a speed of 15 - 20 ^o C / min to a temperature of 600 ± 10 ^o C, at which wire It is held for 25–30 min, then the heating rate is increased to 35–40 ^° C / min, at a temperature of 1000 ± 10 ^° C, exposure is carried out for 30–35 minutes, followed by a decrease in the heating rate to 10–15 ^° C / min and maintained to a temperature of 1110 1120 ^o With which soldering is carried out for 8 to 10 minutes