SU627181A1 - Method of low-temperature nitrocementing of metallic articles - Google Patents

Description

The invention relates to chemical heat treatment and in particular to processes of low-temperature nitro-cement

CII.

Various methods of low-temperature carbonitriding are known, in which the nitrogen-supplying agent is ammonia, and the carbon source can be various hydrocarbons, carbon dioxide, etc. The process is carried out at 550-620 ° C with a holding time of 3-8 h ( depends on the workpiece and the type of material). As a result of processing, a carbonitious layer or oxycarbonitride layer is sprayed on the parts, if the treatment is carried out in an oxygen-containing medium with a thickness of 10-0.3 µm and a diffusion layer with a thickness of 0.2-0.5 mm. For example, there is a known method of carbon cementation in a gaseous medium containing,%: Ammonia7-12

Carbon dioxide3 5

Nitrogen Else, {l}

Parts that are subject to cementing are loaded into the furnace and the dB 2OO25O is heated, then a mixture of gases: ammonia, carbon dioxide and nitrogen is fed into the working space of the furnace within the specified limits and continue heating until. To reduce the cost of processing the parts, it is possible to heat the parts from 200-250 ° to 56 ° -570 hours: in a nitrogen atmosphere, and then apply ammonia and carbon dioxide. Exposure of parts at 560-570 0 is 4-6 h, then the supply of ammonia and carbon dioxide is stopped, and after purging with nitrogen for 5 min, the parts are unloaded and cooled in air, in oil or water.

After processing the details significantly

5, their wear resistance, endurance resistance and fatigue strength are enhanced.

The development of processes of chemical heat treatment at the present stage requires a decrease in the cost of processing the parts while maintaining their properties. This can be obtained by using cheap technological materials and reducing the duration of the processes.

The aim of the invention is to reduce the exposure time.

The delivered chain is achieved in that cyanuric acid is introduced into the working space of the furnace as a source of nitrocement gas atmosphere.

Cyanurea kispot is a white powder and has the following chemical formula:

Oh and

with nkg | n

0 С

HN As a result of thermal decomposition

acid is a supplier of nitrogen, carbon and oxygen.

The method is carried out as follows.

Parts are loaded into the furnace and heated to 20 ° C-250 ° C. When the indicated temperatures are reached, nitrogen is supplied to the furnace and further heating to 500-62 ° C is carried out in a nitrogen atmosphere. This avoids the oxidation of the surface of the parts. After heating the charge at 5006-2 ° С, cyanuric acid is introduced into the working space of the furnace. The latter can be loaded into furnaces in various ways, for example, through a special loading opening in the furnace lid by means of periodic backfilling. The amount of acid fed to the furnace depends on the size of the working space of the furnace, the number of parts to be processed and is chosen experimentally. In this way, the frequency of filling is also established. The holding time for carbonitriding is determined by the required thickness of the layer and the type of workpiece. In the proposed process, it is 1-5 hours.

 As a result of processing according to this method, an oxycarbonitride junction is formed on the surface of steel samples or parts, which, like during processing by a known method, has a high hardness within 75 ° -85 ° kg / M fatigue strength of 48-50 jftrc / mm 1 For notched samples; High wear resistance, which was determined on a reciprocating machine, with lubrication under a load of 75Org / cm. Depreciation was determined by changing the sample size. Counterbody plate made of steel P18. The wear of specimens was tested for 7 hours at 0, O1-O, 03 mm.

The advantage of the proposed method is that the exposure time necessary for the formation of the oxycarbonitride layer is shorter than with the known methods, i.e., at the same time, a deeper layer can be obtained. It. confirmed by the results of comparative tests of the known method and proposed.

For example, after carbonitriding, according to a known method, parts made of steel 40X for 4 hours in a gaseous medium containing T vol.%:

Ammonia10

Carbon dioxide; gas4

Nitrogen Else, an oxycarbonitride layer 18 μm thick was obtained with a total thickness of the nitro-cement layer 0.4 mm.

When processing the same parts according to the proposed method for 4 hours, the thickness of the oxycarbonitride layer was μm, the total thickness of the nigro cement layer, “S, 45 mm,

The results of comparative tests of images processed at different extracts by the known and proposed methods are summarized in table.

As suggested by the test results, the proposed method provides a significant increase in the growth rate of the layer and, in the first place, the oxycarbonitride layer, which is an important fact, especially for wear-resistant parts.

The proposed method is cheaper than the known one, since the required amount of cyanuric acid is small, for carrying out the 4-hour mode, about 7 g of substance is required (the volume of the furnace is 0.01 m).

It should also be noted that storing cyanuric acid powder is much easier than ammonia in cylinders; it is non-toxic and odorless. The use of cyanuric acid greatly simplifies the gas distribution system of the furnace. Process

with cyanuric acid can be carried out on furnaces of any design.

Claims (1)

1. Copyright certificate N9548660, cl. C 23 C 11/18, 1977.