SU800237A1 - Method of low-temperature nitrocarburization of steel articles - Google Patents

Description

one

The invention relates to chemical-heat treatment, in particular, and to processes of low-temperature nitrocementation.

There is a method of carbonitriding l, 3 gas environment containing vol.%:

Ammonia7-12

Carbon dioxide 3-5

NitrogenErest

The parts to be carbonitrided are loaded into the furnace and heated to 200-250 ° C, 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 to 560-570 ° C. To reduce the cost of processing parts, it is possible to heat them from 200-250s to 560-570s in a single nitrogen atmosphere, and then apply ammonia and carbon dioxide. The shutter speed of parts at 560-570s is 4-6 hours, then the supply of gas and carbon dioxide is stopped and, after purging with nitrogen, the parts are unloaded and cooled in air, water or oil.

There is also known a method of low-temperature carbonitriding of metal products by heating them.

to 500-620 0, soaking at this temperature in a nasi-gasy gaseous medium and subsequent cooling during the process in the working space of the inert gas furnace, in particular nitrogen, during the process. Cyanuric acid 2 is used as saturation medium.

To carry out a known method, the parts are loaded into the furnace and heated to 200-250 ° C. When the indicated temperatures are reached, nitrogen is poured into the furnace and further heating to

500-620 ° C are carried out under nitrogen. This avoids oxidation of the surface of the parts. After heating the charge at 500-620 ° C, cyanuric acid is introduced into the furnace, which, as a result of thermal decomposition, becomes a supplier of active nitrogen, carbon and oxygen.

As a result of processing, an oxycarbonitride layer is formed on the surface of the products, which has a high hardness (Hji, 750-850 kg / mm) and wear resistance; fatigue strength of steel cut specimens

40X reaches the level of 48-50 kgf / wi.

The inert gas — nitrogen used in the known method — protects the surface of the products from oxidation during heating and cooling, and is also a carrier gas for the saturating medium.

However, in practice, the use of nitrogen in large quantities is difficult. To obtain it, it is necessary to have a special production of a nitrogen station, since the use of bottled gas is not always possible and expensive, and its storage in large quantities is difficult.

The purpose of the invention is to increase the wear resistance of machined parts.

This goal is achieved by the fact that cyanuric acid and crude exogas are used as saturating medium, which is introduced in the amount of 3-10 per 1 m of the furnace working space.

The method is implemented as follows.

After loading parts in the oven serves crude exogas. It can also be supplied after heating parts up to 150-200 ° C. Exogas is the product of burning natural gas with sufficient excess air (usually under production conditions, the excess air ratio is 0.9-0.95). After removing the moisture, the crude exogas has the following composition, vol.%:

Lzot85-90

Carbon dioxide 10-12 Hydrogen Up to 2.0.

Further heating to 500-620C is carried out in the atmosphere of unpurified exogas. This avoids the formation on the surface of the parts of the oxide film of a considerable thickness that prevents the subsequent incrustation.

After heating the charge at 500-620, cyanuric acid is introduced into the working space of the furnace.

Cyanuric acid (3HCNO) is a non-toxic, white, odorless powder. As a result of its thermal decomposition, nitrogen, carbon, and oxygen are released. Cyanuric acid is loaded into the furnace, periodically backfilling it through a special device.

The specific amount of the substance to be loaded depends on the size of the furnace working space, the number of parts being processed and is selected experimentally. In the same way and set the frequency of 5 backfill. The holding time for carbonitriding is determined on the basis of the required layer thickness and the type of workpiece. In the proposed process, it is 1-5 hours.

o During the aging process at 500620c, the carbon dioxide gas interacts with exogas with hydrogen released during the decomposition of cyanuric acid with

5 the formation of water and carbon monoxide, which actively interacts with the products being processed, additionally naps their surface with carbon and oxygen.

Q As a result of processing, an oxycarbonitride layer is formed on the surface of steel samples or parts, having a high hardness within Hg.Q 730-820 kg / mm, a higher

 wear resistance and durability 48-50 kgf / mm (for samples with a notch). Untreated exogas, acting as a protective atmosphere and carrier gas, simultaneously enhances the carbonizing effect of the saturating medium and accelerates the nitriding reaction due to the high oxygen potential. In addition, exogas is cheap and its production is available to every enterprise that has urban gas.

After the end of the shutdown, the cyanuric acid supply is stopped, the furnace is turned off and the parts are cooled in the exogas stream together with the furnace.

0 to 150-200 0. If it is necessary to quickly cool the parts after the end of the stove, the furnace is rinsed with ecogas to displace the working atmosphere, then the parts are unloaded from the oven and cooled in water, oil

. or other mediums.

An example. Carbon nitrous carbonated parts are carbonitrized for 2.3 and 4 hours at 57 (f C during the thermal decomposition of cyanuric acid. As a result of processing on parts of the hydroxycarbonitride layer.

The results of the comparative tests of the samples are presented in Table 1.

Table 1

As can be seen from the results of the tests, in the proposed and well-known methods, the rate of formation of the nitro-cemented layer is high (first of all the oxycarbonitride layer). Consumption of a substance containing a saturating medium (cyanuric acid is the same as in the known method. For a four-hour regime, about 12 g of a substance per hour is required with a furnace working space of 0.01 m. As a result of the increased carbon and oxygen content in oxy-.

750

Claims (2)

1. USSR author's certificate number 548660, cl. C 23 C 11/18, 1977. 2. Authors certificate of the USSR 627181, cl. C 23 C 11/18, 1976. carbonitride layer, the samples have wear resistance 1.5-2 times higher. Comparative tests of the samples treated with lime and the proposed methods were carried out on a machine with reciprocating motion, with lubrication at 750 kg / cm. Test duration 7 hours. The counterbody was a plate of steel P18. Wear is determined by changing the height of the samples. The test results are presented in Table. 2