SU1719461A1 - Method of carbonitriding of steel products - Google Patents

Abstract

The invention relates to the field of metallurgy, in particular to chemical heat treatment, in particular to methods of carbonitriding steel products, and can be used in mechanical engineering for hardening steel products. The goal is to increase productivity by intensifying the process. The method includes treatment at 840-860 ° C in a controlled atmosphere containing 5-15% by volume of natural gas; 60-80% by volume endogas; 5-35% by volume of a mixture of nitrogen with natural gas in the ratio (5: 1) - (7: 1), and the mixture of nitrogen and natural gas is heated to 2500-3500 ° C, for example, in a plasma torch. The method improves productivity by 1B-35%, while reducing processing time by 20-60%. 1 hp ff, 1 tabl.

Description

The invention relates to ferrous metallurgy, in particular to methods for processing finished metal products by carbonitriding their surface, and can be used in thermal shops of metallurgical and machine-building plants.

There is a method of carbonitriding steel, which includes exposure in an atmosphere containing carbon dioxide oxides, H2O2, saturated hydrocarbons, followed by cooling and quenching.

On the part surface, a diffusion layer is formed in the following mode: an isothermal exposure for 1.5 hours in a medium containing ammonia and products of pyrolysation triethanolamine, cooling in a furnace for 1.5 hours, followed by quenching.

The disadvantage of this method is the low productivity of the treatment process, mainly due to the low level of the nitriding process due to the weak excitation of ions formed during the dissociation of ammonia.

It is known the introduction of nitrogen in carbonitriding to intensify the process. Nitrogen introduced into the controlled atmosphere by this method is a carrier gas, does not participate in the process of saturating the surface of the part and only improves the mass transfer processes. Active nitrogen in

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This process results from the dissociation of ammonia.

Closest to the invention is a carbonitriding process. whereby the carbonitriding process is carried out at 840-860 ° C in a gas mixture of carbonizing gas and ammonia. The duration of the carbonitriding process depends on the depth of the saturating layer and is 1-10 hours.

The thickness of the layer varies in the range of 0.1-1.0 mm. A controlled endothermic atmosphere containing 5-15% untreated natural gas, 60-80% gas and 10-45% ammonia is used.

The disadvantage of this method of carbonitriding is the low productivity of the process, due to the fact that the saturation process takes place in the diffusion mode. Nitrogen ions formed during the dissociation of ammonia do not possess high activity, the process usually proceeds under conditions of low saturation rates.

The aim of the invention is to increase the productivity of the process of nitrocementation due to the intensification of the process by increasing the saturability of the controlled atmosphere.

To achieve this goal, according to the well-known method of carbonitriding steel products, which includes treatment at 840-860 ° C in a controlled atmosphere containing natural gas and endogas, a mixture of nitrogen and natural gas is additionally introduced into the controlled atmosphere in a ratio (5: 1 } - {7: 1) in the following ratio of components, vol.%: Natural gas 5-15; endogas 60-8D; a mixture of nitrogen with natural gas in the ratio (5: 1H7: 1) 5-35, and the mixture of nitrogen with natural gas is preheated to 2500-3500 ° C. Heating a mixture of nitrogen with natural gas can be carried out, for example, in a plasma torch.

PRI me R 1. Experiments on nitrocementation of parts were carried out on a CHAF furnace (chamber resistance furnace for carbonitriding). Processed parts of article 20. Pre-treated them by the method prototype. The controlled atmosphere was formed from a mixture of natural gas, endogas and ammonia, taken in a ratio of 10:70:20 (data are given in volumetric fractions). Nitrogen was not supplied. Heat treatment in a furnace at 850 ° C lasted 4 hours. The data on the change in the content of carbon and nitrogen in the thickness of the surface layer are given in the table.

The total carbon and nitrogen content in the surface layer at a distance of 0.05 mm for article 20 according to the technical conditions should be at the level of 1.0-1.3%, and the carbon content should be at the level of 0.7-0.8 % nitrogen 0.30-0.55%.

PRI mme R 2. Conducted an experiment for this method. A plasma torch of the PGS-30 type with graphite electrodes was used as a gas heater. The operation parameters of the plasma torch N 23-30 kW, ZOOA. IN100-150B.

Before carbonitriding, parts from article 20 were thoroughly rubbed and washed in a 5% solution of caustic soda heated to 90 ° C for 10 minutes. After washing, the parts were rubbed and placed in the baskets with the clearance necessary for the free circulation of gases. After the working temperature was reached in the furnace with the help of conventional heaters, equal to 850 ± 40 ° C, the devices with the parts were loaded into the furnace. Through conventional channels, natural gas and endogas were supplied to the furnace, constituting 10 and 75% of the controlled atmosphere, respectively. 15% of the controlled atmosphere was formed from an additionally introduced mixture of nitrogen and natural gas, taken in a 6: 1 ratio. Before being fed into the furnace, this mixture was heated in a plasma torch, which was installed in the side wall of the furnace in the opening of the core to 3000 ° C. The gas temperature was estimated from the tables by the mean mass enthalpy of the gas, which in turn was determined from the heat balance of the plasmatron. The pre-calculated flow rates of gases (nitrogen and natural gas) introduced through the plasma torch were set using shop rotameters in the main lines. In the experiment, these costs were respectively 2.14 m / x and 0.36 m3 / h. After 3 hours of treatment, shutdown of the plasma torch. After the traditional oil quenching, parts were removed from the furnace. Samples of the metal were analyzed for chemical composition by removing layer-by-layer samples from the machined parts, the surface structure was examined using an electron microscope. The results of chemical analysis presented in the table showed that in 3 hours the content of carbon and nitrogen in the surface layer reached the required standards, i.e. the performance of the carbonitriding process, in contrast to the traditional method, increased by 25%.

PRI me R 3. In this example, the ratio of natural gas to endogas in a controlled atmosphere supplied through traditional channels was 5 and 60%.

respectively. 35% of the controlled atmosphere was a mixture supplied through a plasma torch. The ratio of nitrogen and natural gas in a mixture of 6: 1, the temperature of gas heating is 3500 ° C. Heating was carried out for 2.5 hours. During this time (see table), the saturation of the surface layer has time to achieve the required standards. The productivity of the process increases by 37.5%.

PRI me R 4. The ratio of natural gas and endogas in a controlled atmosphere, which were fed through traditional channels, was 15 and 80%, respectively.

5% of the controlled atmosphere was the mixture supplied through the plasma torch. The ratio of natural gas and nitrogen in a mixture is 6: 1, the heating temperature of the mixture is 3500 ° C. Heating was carried out for 3.4 hours. The productivity of the process increased by 15%.

EXAMPLE 5 In this example, all conditions were taken as in example 2, but the ratio of nitrogen and natural gas in the mixture, which was 15% of the controlled atmosphere, was 5: 1. The temperature of the mixture is 2500 ° C. The duration of the carbonitriding process was 3.2 hours. The productivity of the process due to the reduction in processing time increased by 20%.

Example 6. In this example, all conditions were also taken as in Example 2, however, the ratio of nitrogen and natural gas in a mixture of 15% of the controlled atmosphere was taken to be 7: 1. The heating temperature of the mixture is 3500 ° C. The processing time was 2.6 h, and satisfactory part quality was achieved. The productivity of the process compared to the traditional method increased by 35%.

Claims (2)

The formula of the invention was also 1. A method of carbonitriding steel products, including treatment at a temperature of 840-860 ° C in a controlled atmosphere containing natural gas and endogas, characterized in that, in order to increase productivity by intensifying the process, an additional atmosphere is introduced into the controlled atmosphere nitrogen with natural gas and the ratio (5: 1} - (7: 1) in the following ratio of components, vol.%: Natural gas5-15 Endogaz60-80 A mixture of nitrogen with natural gas in the ratio (5: 1) - (7: 1) 5-35, and the mixture of nitrogen with natural gas is preheated to 2500-3500 ° C. 2. The method according to claim 1, about t l and h and y and the fact that the heating of the mixture of nitrogen with natural gas is carried out in the plasma torch.