SU1482976A1 - Method of gas nitriding of articles of steels and alloys - Google Patents

Abstract

This invention relates to the nitriding of parts from steels and alloys at 500-600 ° C in an atmosphere containing urea and ammonium carbonate. In order to increase the hardness of the products, ammonium carbonate is obtained directly in the reaction zone of the furnace by simultaneously supplying urea-containing oxygen gas, such as air, which is at the same time transporting means for supplying urea to the furnace. 1 hp ff, 1 ill., 1 tab.

Description

The invention relates to the chemical and thermal treatment of metals and can be used for surface hardening of parts made of various metals.

The purpose of the invention is to increase the hardness and speed of saturation.

According to a known method of nitriding parts from steel and alloys, consisting in heating to 500 - 60.0 ° C, aging at this temperature in the presence of urea with the addition of ammonium carbonate, ammonium carbonate is fed into the furnace zone along with urea. Ammonium carbonate is produced directly in the furnace zone by simultaneously feeding oxygen-containing gas with urea, which at the same time serves to transport the urea to the furnace.

The supply of urea to the furnace zone simultaneously with the oxygen-containing gas according to the proposed method makes it possible to obtain a saturated atmosphere containing ammonium carbonate, which decomposes, accelerates the process

saturating the surface with nitrogen directly in the reaction zone of the furnace, while no oxidation occurs on the surface of the parts and the hardness of the nitrated layer,

Using air as an oxygen-containing gas, the oxygen of which reacts in the furnace zone with the formation of ammonium carbonate, and the simultaneous transfer of urea with compressed air into the furnace without mechanical devices improves the processability of the nitriding process, therefore this feature is considered essential.

The method of nitriding parts from steels and alloys is that an oxygen-containing gas, such as air, is supplied to the furnace simultaneously with urea. Air oxygen at high temperature reacts with urea, and carbonate and active nitrogen atoms are formed in the workpiece area:

4CO (Shg) 2 (NH,) C03 + 2CQ2 + 2N.

(L

with

oo

YU

CP 1

oh

3148

Ammonium carbonate decomposes to form active nitrogen and carbon dioxide atoms, the latter shifting the reaction equilibrium toward the original substance CO, reducing the amount of soot that is formed, which allows nitrogen atoms to freely penetrate inside the parts, thereby accelerating the nitriding process.

The air supplied simultaneously with the urea into the furnace is at the same time the working medium for the transportation of urea, which allows the detection of the amount of moisture released during the reaction, which oxidizes the surface of the workpiece, and the appearance of rust on the surface.

Example. A tool with a diameter of 12 mm and mm samples of steel R6M5 are placed in a furnace heated to a temperature of 540–560 ° C. The furnace is sealed, then into the reaction zone from a bunker (bunker height 200 mm, outer diameter 120 mm, hole diameter under the bunker 7 mm)

To supply this amount of urea, which supplies urea in the amount of 1.0 kg / h.

This is necessary to maintain the composition of the atmosphere in the furnace without additional mechanical devices. For this, compressed air is supplied in pulses, with each pulse transporting a portion of urea into the furnace.

The drawing shows a diagram for implementing this method.

In the bunker 1 poured urea 2.

Through a tube, 3 pulses feed inactive nitrogen atoms, and then carbonate

air that moves the urea 2, which is lowered by the weight of the bunker 1 to zone 4, then through pipe 5 to the working zone of the furnace 6, whose temperature is 500-600 C.

The composition of the atmosphere in the furnace is determined by the amount of urea and the air supplied to the furnace. The amount of air supplied depends on the air pressure, the duration of the pulse and the pause between the pulses. The amount of urea supplied also depends on the size of the hopper 1 and the diameter of the pipe 5.

The amount of air required to obtain, as a result of the reaction, the amount of ammonium carbonate sufficient in order to speed up the process in the furnace zone is 0.3–20% by weight of the amount of urea supplied.

The amount of air is less than 0.3 May. does not ensure the passage of ammonium carbonate formation reaction. Since air is not only involved in the reaction, but is also a transporting means, the minimum amount of air is also determined from the condition of movement of a portion of urea running down the bunker 1 to zone 4 of pipe 5. Therefore, the minimum amount the air supplied to the furnace, taken equal to 10 wt.%.

Air supply in quantities greater than 30% by weight leads to heat transfer to the furnace through compressed air through the tube. Through a tube with a diameter of 10 mm, air is supplied in an amount of 6 m / h in pulses every 10 seconds for 0.8 seconds at an excess pressure of 0.5 atm.

In the reaction zone of the furnace, the oxygen of the air reacts with urea to form ammonium carbonate and .0

five

0

five

0

five

ammonium decomposes to form nitrogen and carbon dioxide. Nitrogen atoms penetrate into the surface layer of parts, the process of nitriding occurs. Since a significant amount of gases is generated in the furnace, to maintain an overpressure in the furnace of no more than 0.1-0.2 atm, it is provided with an outlet 10 mm in diameter to remove excess reaction products, with which most of the air entering the furnace is removed. Therefore, the amount of air supplied to the furnace must be increased by a factor of 20 to ensure how. obtaining the amount of ammonium carbonate required for the reaction; and transporting urea to the furnace.

After 15 min, the supply of urea and air to the furnace is stopped, the instrument and samples are taken out of the furnace and cooled in oil. As a result of saturation of the surface with nitrogen and carbon, the hardness of the layer is 1066 mm, the depth of the nitrated layer is 0.045 mm.

Saturation was carried out for 5 and 8 hours in a C-25 furnace at 570 ° C.

The table shows the average values of comparative tests of samples of steel 38KHMUA.

Thus, the nitrided layer obtained by the proposed method has greater depth and hardness and, as a result, greater wear resistance, and the same depth of saturation can be obtained in less time.

Claims (2)

1. The method of gas nitriding of products from steels and alloys, including heating to 500-600 ° C and diffusion saturation in a gaseous medium in a container containing urea, characterized in that, in order to increase the hardness, the gaseous medium additionally contains an oxygen-containing agent. V 2. A method of claim 1, characterized in that, in order to increase the rate of saturation, the oxygen-containing agent is fed into the container cyclically. Editor M.Petrova Compiled by I. Petrov Tehred L. Serdyukova Proofreader I. Musk Order 2787/22 Circulation 941 VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab., D. 4/5 Production and Publishing Combine Patent, Uzhgorod, st. Gagarin, 101 Subscription