JPS5934126B2 - Production method of iron nitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing iron nitride as a nitrogen additive in steel.

The iron nitride in the present invention is mainly composed of iron and has a nitrogen content of 1 to 11 parts by weight, and may contain impurities of 5 parts by weight or less.

According to X-ray diffraction, Fe4N, Fe3N, Fe
2N alone or a mixture thereof.

Regarding the production of iron nitride, the following two reports have been made so far.

Literature (1) Journal of the Chemical Society of Japan, No. 53, p. 466, “On the relationship between two types of iron nitrides” by Shun Sato Literature (2) U.S. Patent No. 4,133,678 “Production method and product of ferroalloy” However, literature (1) is about the production of pure iron nitride on a laboratory scale for testing the chemical or thermodynamic properties of iron, and is not a practical method for industrially usable iron nitride. It is not related to iron, and there is no specific manufacturing method described.

Literature (2) is about iron nitride as a nitrogen additive in steel, but the manufacturing method is to first heat iron oxide powder with a particle size of 30μ or less at 760 to 870°C using H2 or CO gas.
Refund with.

Next, dry ammonia gas at a pressure of 200 mm or more of water column is passed through and nitrided at a temperature of 590 to 730° C. in a rotary furnace or fluidized bed to obtain iron nitride mainly composed of Fe4N with a nitrogen weight of 6 or more.

The time required for nitriding varies depending on the particle size, but
At 0μ, it is stated as 48 hours.

In contrast, in the method of the present invention, the particle size of the iron oxide powder used as a raw material is 5 mm or less, and the lower limit is set to o, o5 mm to improve air permeability and allow the reaction to proceed in a short time. .

In the present invention, 0. By cutting O 5 nm or less, air permeability is improved and the reaction is promoted, so that N=6% by weight or more can be obtained in about 20 hours from reduction to completion of nitriding.

The present inventors proposed a method using a furnace in which raw materials are continuously moved and discharged as a method for obtaining iron nitride (filed on January 9, 1980); Due to this method, there are operational problems such as fusion, sintering, etc., which may cause the raw materials to become immobile, and since it is a single furnace, it is difficult to finely adjust the temperature and the fermentation time. However, it has the disadvantage that the nitrogen content cannot be controlled.

The present invention improves these drawbacks, and by adopting the structure described in the claims, there is no problem in fusion and sintering, and temperature and reaction time can be easily adjusted. Therefore, it is possible to produce iron nitride with high nitrogen content,
Additionally, a method has been established that allows the nitrogen content to be adjusted.

The present invention will be explained in detail below.

First, the iron oxide used here has a particle size of 5 to 0.05 mm.
Oxidized iron powder, scale, calcined iron hydroxide, high-quality iron ore, etc. are used.

The scales are Fe2O3, Feso, , F
It has a layered structure of eO and Fe in various proportions, and the iron content is preferably around 70% by weight. Iron ore is also crushed and magnetically sorted to reduce the iron content to less than 1% by weight of gangue. A material with a weight ratio of about 70 is used.

In addition, magnetically selected iron oxide for catalysts may be used.

In addition, the particle size was set to 5 to 0.05 mm, which was 5m11L.
This is due to reasons such as the reduction reaction slowing down, and the reaction rate in the nitriding reaction and the N content of the product becoming low.

The reason why the thickness is set to 0.05 mm or more is that if there is a fine powder of 0.05 mm or less, air permeability will be extremely reduced and the nitriding time will be longer.

These iron oxide powders are first reduced in the reduction process, but for the sake of explanation here, the reduction and nitridation processes are divided into two processes each, for a total of four processes (preliminary reduction process, final reduction process). A description will be given of a case where the nitriding process, primary nitriding process, and final nitriding process) are performed.

FIG. 1 is a flow diagram showing the iron nitride production method consisting of the above four steps, where ■ is a final nitriding reactor, ■ is a primary nitriding reactor, ■ is a final reduction reactor, and ■ is a preliminary reduction reactor. be.

1 is an ammonia gas cylinder, 2 is an inert gas cylinder, 3
is a dryer, 4 is a moisture remover, 5 is a heating device, 6 is an exhaust gas cleaning device, 7, 8, 9.10 is a gas analyzer,
. . . Each of the reactions in (■) is controlled to a predetermined temperature by 11 temperature recording controllers.

The iron oxide powder is first reduced to 700 to 110 in the preliminary reduction step (■).
It is heated to 0℃ and discharged from the final reduction step in the next step (①), the residual rate of NH3 is less than 20% by volume, and the N2/N2 ratio is 1/6.
It is half-reduced by a gas with a composition of ~1/3.

Here, in the case of claim 3, since the gas discharged from the final reduction process contains N20, it is once taken out of the system, cooled to below 100°C to remove 20 minutes of N20, and then After adjusting the ratio to 3/7 or less, it is returned to the preliminary reduction step.

Figure 2 shows the relationship between oxidation and reduction of Fe in an N2-N20 atmosphere. According to this, at the reduction temperature of 700 to 1100°C, which is limited in the present invention, N20/H
It can be seen that iron oxide can be reduced to iron if it is 2-3/7 or less.

In other words, even if the ammonia decomposition gas is once used for reduction and discharged from the nitriding process, N20/H2-3/7
If it is below, it can be used for reduction (such as one that has been dehydrated).

In the final reduction step (2), the exhaust gas from the next primary nitriding step (2) is used as is.

The reduction temperature here is 700 to 1100℃, and the Fe content is 95
It becomes iron powder with a weight ratio or higher and moves to the primary nitriding process (①).

Therefore, in the present invention, firstly, the raw material iron oxide powder is converted into N2, which is discharged from the nitriding process and further used once in the reduction process.
0/H2-3/7 or less ammonia decomposition gas 700~
Reduction treatment at 1100°C, then ammonia residual rate discharged from the nitriding process less than 20% by volume, N2/H2-1
Further reduction treatment shall be carried out using ammonia decomposition gas of /3 or less.

Next, this is sent to the nitriding process, where it is nitrided.
Here, as in the reduction process, the nitriding process is performed using the ammonia decomposition gas once used for nitriding.

Figure 3 shows 530℃ and 620℃170 after reducing iron oxide.
This figure shows the relationship between the nitriding time and the nitrogen content when nitriding was carried out with ammonia gas at a volume ratio of 50 to 100 at each temperature of 0° C. with an ammonia residual rate (value in parentheses in the figure).

According to this, the nitriding speed decreases as the ammonia residual rate of the ammonia decomposition gas used decreases.

On the other hand, as the nitriding temperature increases, the nitriding speed increases.

In other words, when reducing iron powder is nitrided using ammonia decomposition gas with a low ammonia residual rate, if it is treated at a higher temperature, the effect is almost the same as when using ammonia decomposition gas with a high ammonia residual rate. You can see what you can get.

Therefore, in the nitriding process, first, the treatment temperature is set at a high temperature of 5508C to 700℃, and the residual rate of ammonia used in the nitriding process is 20 to 60% by volume N2/H2-1/3.
A primary nitriding treatment is performed using the following ammonia decomposition gas, and a final nitriding treatment is performed at 350 to 550°C using an ammonia decomposition gas with an ammonia residual rate of 100 to 60 by volume, N=6.
Obtain more iron by weight than above.

At this time, the reaction temperature in the primary nitriding step (■) in Figure 1 was 700℃.
The temperature changes continuously from ℃ to 550℃, and ammonia gas passes through this, so atomic N is constantly generated as the temperature rises, making efficient nitriding possible, and achieving the high temperature range shown in Figure 3. The property that the nitriding speed is very fast is fully utilized, and even coarse iron powder can be nitrided in a short time.

In the final nitriding step (2), the temperature range from 600°C to 350°C is passed through which the nitrogen concentration reached is maximum.

Thereafter, the gas is switched to a sealing gas such as nitrogen gas, and after cooling, the iron nitride is discharged.

The reason why the final nitriding temperature was set at 350°C is that the nitriding reaction rate drops extremely below this temperature, and the reason why the maximum nitriding temperature was set at 700°C is that the produced iron nitride would decompose at higher temperatures. .

The reason why there is overlap between 550°C and 600°C is that the temperature distribution in the furnace has a wide range due to the mass effect.

Next, in actual industrial production using the method of the present invention, each of the above steps can be carried out in the same reactor by switching the charging gas by operating the valves of the gas pipes arranged in each reactor.

In other words, in a method in which two furnaces are used for each process, if each furnace is A, B, C, and D, these furnaces are first used in steps IV, I, n, and I, and then used in B after the reaction is completed. Change the valve to charge NH3 gas and move to step 2. At the same time, C carries out the reaction of step 2 and D carries out the reaction of step 2. Iron nitride is taken out from A, and iron oxide is newly charged to it. Then, perform step I.

Next, after the reaction (2) in Furnace B is completed, NH3 gas is charged into Furnace C, and the other furnaces are switched in the same manner as above.

This method is repeated in sequence.

In this way, by using gas piping to switch the charging gas to each house, operation can be performed very easily without the hassle of replacing raw materials.

Examples of the present invention are shown below, and some comparisons with conventional methods are also made.

Example 1 Four reactors I, n, I, and IV shown in Fig. 1 were prepared, and the temperature in ■ was 530°C, the temperature in ■ was 700°C at the initial stage of the reaction, and the temperature was gradually lowered to 550°C, and the temperature in ■ was 530°C. 850℃, ■ is 850
Raw material (10-100 mesh scale) as °C
Charge ky to ■ and add 5 raw materials in the order of ■→■→■→■
It is moved every hour, and 2 kg of raw material is charged to ■ every 5 hours.

At this time, ammonia gas is blown in from I at a rate of 5 Nl/min and flows in the order of I→■→■→■.

Then, from (2), the product that has become iron nitride is taken out every 5 hours.

In this way, 6 kg of iron nitride was produced in 20 hours.

Table 1 shows the chemical composition of the raw material scale used here.

Table 2 also shows the nitrogen content of samples every 5 hours of the 6ky product manufactured in 20 hours.

As a comparative example, 2 kg of the same raw material as above was treated at a temperature of 900°C with a H2 atmosphere flow rate of 15Nl/min for 10 hours, then the temperature was lowered to 530°C, and 5N of decomposed ammonia gas was used.
Table 3
6 kg of iron nitride shown in Figure 1 was obtained.

Here, Table 4 shows the amounts of ammonia gas and H2 gas required to produce 1 kg of iron nitride using the method of the present invention and the comparative example.

As is clear from Table 4, the present invention does not require H2 or CO for reduction, and the amount of ammonia gas used can be extremely small.

[Brief explanation of drawings]

FIG. 1 is a flow diagram for explaining the method of the present invention,
FIG. 2 is a graph explaining the oxidation state of iron in the H2-H2O system, and FIG. 3 is a graph showing the relationship between reaction time and nitrogen content of iron nitride under various temperatures. ■・・・Final nitriding reactor, ■・・・Primary nitriding reactor, ■・・・Final reduction reactor, ■・・・・・・
...Preliminary reduction reactor, 1.. Ammonia gas cylinder, 2.. Inert gas cylinder, 3. Part...
・Dryer, 4... Moisture remover, 5...
Heating device, 6... Exhaust gas cleaning device, ? , 8
, 9゜10... Gas analyzer, 11...
・Temperature recording controller.

Claims (1)

[Claims] 1. Reducing iron oxide by heating it in an ammonia gas atmosphere,
A method for producing iron nitride by nitriding, the particle size being 5 to Q,
A first step of heating and reducing 05 parts mi of iron oxide at a temperature of 700 to 1100°C, and reducing the iron reduced in the first step to 3 parts mi.
The second step is nitriding with ammonia gas at a temperature of 50 to 700°C, the first step uses the gas discharged from the second step, and each step includes at least two
A method for producing iron nitride, characterized by using the above fixed reactor. 2 In the first step, a part of the hydrogen-containing gas is removed,
The method for producing iron nitride according to claim 1, wherein after removing the moisture generated in the reduction reaction, the hydrogen-containing gas is used again as the hydrogen-containing gas in the first step.