SU604503A3 - Method of heat treatment of articles - Google Patents

Description

The invention relates to heat treatment and can be used in the plants of the metallurgical and engineering industries in the processing of steel products in a controlled atmosphere.

There is a method of heat treatment of steel, according to which methane 1 is added to the protective atmosphere of the furnace in order to reduce its decarburization.

There is also known a heat treatment method in which a cooled mixture of dissociation products of ammonia and methane 2 is used as a protective atmosphere.

The methane in the furnace space cannot be used to determine the carbon potential of the atmosphere, which makes it difficult to carry out the process normally and can negatively affect the quality of heat treatable products.

The aim of the invention is to improve the quality of heat treatment.

This is achieved by the fact that the dissociation products of ammonia are introduced into the furnace by uncooled, and the amount of methane formed inside the furnace is maintained at a value corresponding to its equilibrium concentration. The amount of methane in the furnace atmosphere is controlled by changing the amount of ammonia dissociation products fed into the furnace, and a hydrocarbon containing at least two carbon atoms, such as propane, is used as the hydrocarbon fed into the furnace.

The proposed method is carried out as follows.

The products of ammonia dissociation directly after thermal decomposition (non-cooled) are fed into the furnace space, and the content of methane in the furnace atmosphere is changed to control their content in the product. The introduction of uncooled ammonia dissociation products allows an active furnace atmosphere to be obtained.

Methane gas formed inside the furnace space is active and, in the presence of the molecules of ammonia dissociation products, is suitable for indirectly determining and regulating the carbon content on the surface of the products. The amount of methane produced must be maintained at a value corresponding to the chemical equilibrium of the carbon content on the surface of the product. Use for indirect

determining the carbon content on the surface of the processed methane products makes it possible to reliably regulate the carbon potential of the atmosphere and improve the quality of the thermally treated products.

In the carburizing process, activated molecules of ammonia dissociation products help to maintain the activity of methane molecules formed in the furnace to react with the surface of the products.

During decarburization, a certain amount of activated hydrogen of dissociated ammonia reacts directly with carbon atoms on the surface of the product. The reaction of carbon atoms with two hydrogen molecules, accompanied by the formation of a methane molecule, proceeds at an acceptable and technical point of view with only activated hydrogen, which is obtained by using uncooled ammonia dissociation products.

To regulate the amount of methane formed in the furnace space, the amount of ammonia dissociation products fed to the furnace is changed. On decarburization, the amount of methane produced is reduced, and the amount of ammonia dissociation products introduced is appropriately reduced to maintain methane at the desired value.

In order to increase the amount of methane in the furnace atmosphere, an additional hydrocarbon is introduced into the furnace space, containing at least two carbon atoms in the molecule. Thus, the required amount of methane in the furnace atmosphere results from the endothermic cleavage of a higher molecular weight hydrocarbon in an activated form within the furnace space. The methane molecules introduced into the furnace space, such as natural gas, are in a passive state and prevent the indirect determination of surface carbon through methane equilibrium.

Example. Carbonized heat treatment at 930 ° C is subjected to a sample of steel C15. Ammonia dissociation products serve as the furnace atmosphere, to which, depending on the methane content in the furnace atmosphere, propane is added. The transition of carbon occurs in the carburized phase with the subsequent chemical equilibrium of the corresponding decarburized diff: the 11011 phase. At different concentrations of methin in the carburized phase, the values given in the table were obtained.

Thus, as in the processing of low alloyed C15 steel, and other chromium alloyed steels, surface oxidation does not occur.

Stove atmosphere

1.00, 45

1.5

2.0

Formula and suggestions

Claims (3)

1. A method of thermal processing of steel products, including the flow of ammonia and hydrocarbon dissociation products into the furnace, characterized in that, in order to improve the quality of heat treatment, the products of ammonia dissociation are introduced into the furnace by non-cooled, and the amount of methane formed inside the furnace is maintained at a value corresponding to its equilibrium concentration. 2. A method according to claim 1, characterized in that. . ::, Product from 0.8 to 0.9 50 to control the amount of methane in the furnace atmosphere, change the amount of ammonia dissociation products fed to the furnace. 3. The method according to paragraphs. 1 and 2, different J, because a hydrocarbon containing at least two carbon atoms, for example, propane, is used as a hydrocarbon fed to the furnace. Sources of information taken into account in the examination: 60 1. Oxidation and decarburization of steel. 5 under teach, ed. prof. A.I. Vashchenko. “Metallurgists, 1972, p. 244. 2.- Petrov N. P., Troshkin I. T., 604503 6 M., Selov B. P. Thermal treatment of steel in controlled atmospheres. M., “MashinostroBeniya, 1969, p. nineteen.