SU676641A1 - Steel article working method - Google Patents

Description

less than metals (oxide density 3-5 g / cm, and steel density 7.8 g / cm), when they form, they fill the micropores of the ceramic coating, thereby increasing the adhesion by the type of mechanical engagement. At the same time, the heat resistance of the coating increases, since the formed nitrs play the role of a layer with a thermal expansion coefficient close to that of oxide-based ceramics. The nitride layer also ensures the corrosion resistance of the metal being protected.

Example. The surface of the product, such as steel casting, cleaned with metallic sand to form a matte surface. Then, thermal sputtering deposited aluminum oxide fraction 50-70 µm according to the accepted modes: plasma-forming gas consumption (argon H + hydrogen) 1.7, powder feed 10 g / min, conveying consumption, its gas (argon) 0.16 spraying distance 100 mm, burner power 20 kW. After spraying a layer of thick, other than 0.5-1.5 mm, the product is placed in an environment with active nitrogen, for example, in a retort of a shaft furnace into which ammonia gas is supplied. Nitriding is carried out in two stages: Stage 1 is carried out at 540 ° C, the degree of dissociation of ammonia is 30%, the flow rate is 5-6 l / min, aging for 8 hours, stage 2 at 560 ° C, the degree of dissociation of ammonia is 30%. After holding and slowly cooling (with a furnace) to room temperature, the finished product is obtained with a protective coating consisting of a layer of alumina and a nitride sublayer mechanically and chemically bound to the base metal and the layer of alumina. The strength of the protective coating without nitriding is 80.- 90 kg / cm with nitriding 130-150 kg / cm.

Example 2. A ceramic material made from a mixture of aluminum oxide and boron carbide with a film thickness of 0.5-0-0.7 mm (spray modes of Example 1) was applied to the inner working part of steel cast crucible by plasma spraying. The nitriding process is then carried out according to the mode in which the e-phase is formed on the steel surface. The resistance of a crucible with such treatment increases from 35-40 to 70-80 days of operation.

Example 3. A coating of zirconium oxide (modes of example 1) is applied on a core of steel 45, which forms a cavity in the cast of “Garnet sports. The zirconia (or alumina) coating works without peeling for 6 work shifts, and with subsequent nitriding, 15 work shifts.

Thermal stability tests are carried out by thermal cycling on: air at 20-600 ° C. Without nitriding, the coating peels off after 30 cycles, with nitriding after 70 cycles. The increase in corrosion resistance of steel in aluminum melts was tested experimentally. Samples coated with alumina, as well as with additional nitriding and processing known technology, immersed in molten aluminum at 720 ° C. Destruction with the first coating occurs after 30 hours, similar destruction of the second after 80 hours, destruction of the third after 30 hours.

Thus, the heat resistance of products increases by 2-2.5 times, and their corrosion resistance in aggressive media is 2.5 times.

Claims (1)

Invention Formula The method of processing steel products, including the preliminary gas-thermal spraying of ceramic materials, characterized in that, in order to increase their adhesive strength and heat resistance and increase the resistance of products in aggressive media, the product after spraying is subjected to nitriding to form a nitride layer.