JPH0717922B2 - Heating method for producing iron powder by finishing reduction of atomized raw material iron powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heating method for producing iron powder by finish-reducing atomized raw material iron powder, and more specifically, a non-reducing element such as Cr and Mn and carbon. In order to include the pre-alloyed atomized raw material iron powder as a raw material, when producing iron powder by finish reduction annealing this, in the preheating process of preheating the atomized raw material iron powder from room temperature to the finish reduction temperature, The present invention relates to a heating method capable of preheating under a condition that a temperature rising time is shortened without causing a bumping phenomenon of a raw material iron powder, and further allowing a finish reduction of the raw material iron powder to proceed rapidly.

2. Description of the Related Art The demand for sintered iron powder parts is increasing year by year, and in particular, the demand for alloy steel powder for parts that require high strength and high toughness tends to increase. As the strengthening alloy element, for example, inexpensive Cr and Mn are preferable, but when the steel powder pre-alloyed with Cr and Mn is manufactured by the conventional water atomization-gas reduction method, these elements have an affinity with oxygen. Since it is strong, it is difficult to reduce the amount of oxygen contained in the steel powder. As a method for deoxidizing the alloy steel powder containing Cr and Mn, for example, vacuum reduction described in JP-B-58-10962 is proposed, and low-oxygen steel powder can now be produced. .

An example of a heat treatment furnace used for preheating reduction of atomized powder in the production of this low oxygen steel powder is shown in
It is as described in 61-19004. In this heat treatment furnace, a preheating chamber, a reduction annealing chamber, and a cooling chamber are arranged side by side, and the boundaries of each chamber are partitioned by a movable door. Further, in this preheating chamber, a raw iron powder consisting of atomized powder containing a non-reducing element and carbon is preheated and dried,
Next, in the adjacent reduction annealing chamber, the preheated atomized powder is deoxidized and annealed by utilizing the carbon contained therein. This reduction-annealed steel powder is cooled in a cooling chamber to produce low-oxygen steel powder.

When the heat treatment furnace of this structure is used for reduction annealing of the raw iron powder, as shown in JP-B-58-10962, in the case of heating up to the finishing annealing temperature of 800 to 1300 ° C. in a reduced pressure atmosphere of 20 Torr or less, , 650-800 ℃ in the preheating room as the previous stage
Up to.

In this preheating chamber, rapid heating is desired to improve productivity.

However, when heated rapidly, a gas is suddenly generated from the raw iron powder in the preheating chamber, and the raw iron powder rises in the preheating chamber (hereinafter referred to as bumping phenomenon). When this phenomenon occurs in the preheating chamber, the raw material iron powder scatters in the preheating chamber and damages the heater.

In particular, this bumping phenomenon appears remarkably when carbon is contained together with the non-reducing elements such as Cr and Mn.
For this reason, when using atomized powder containing a non-reducible element or carbon as the raw material iron powder, in order to prevent this bumping phenomenon, the temperature is slowly raised at a temperature of about 200 ° C./hr and then rapidly increased in the preheating chamber. It is necessary to prevent the generation of gas. However, at such a rate of temperature rise, preheating takes a long time, and in the preheating-reduction annealing-cooling step, the preheating step is rate-limited, resulting in a decrease in productivity.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention aims to solve the above problems, specifically, preheating atomized raw material iron powder, when producing iron powder by finish reduction, in this preheating process, bumping phenomenon It is an object of the present invention to propose a temperature rising method during alloy steel powder finish reduction annealing that is suitable for shortening the preheating time without generating it.

Means for solving the problem and its action That is, the present invention, atomizing raw material iron powder containing a non-reducing element and carbon, through a preheating process of heating while raising the temperature from room temperature to 650 ~ 800 ° C., 800 ~ 1300 When producing iron powder by finish reduction annealing at a temperature of ℃, from this room temperature to 650 ~ 8
The preheating process up to 00 ° C is performed in a depressurized atmosphere of 20 Torr or less, and preheating is performed so that the temperature is maintained at 300 to 650 ° C for 10 to 30 minutes to prevent bumping of the raw iron powder, and then finishing. The reduction annealing process is also characterized by being performed in a reduced pressure atmosphere of 20 Torr or less.

Hereinafter, the structure of the present invention and its operation will be described in detail.

First, in the present invention, the atomized raw material iron powder that is atomized containing a non-reducing element such as Cr and carbon, 20To
After the preheating process of raising the temperature from room temperature to 650 to 800 ° C in a reduced pressure atmosphere of rr or less, the preheated raw iron powder is further
Finish reduction at a temperature of 800 ~ 1300 ℃ in a reduced pressure atmosphere of 20 Torr or less, and in this preheating process, hold the reduced pressure iron powder in the temperature range between 300 ~ 650 ℃ for 10 ~ 30 minutes, and in the preheating process. The so-called bumping phenomenon of the raw iron powder is suppressed.

In this way, when preheating from room temperature to 650 to 800 ° C, the bumping phenomenon is avoided, so the temperature rising rate is, for example, 300 ° C / hr, 400
The temperature can be raised up to ° C / hr and productivity can be greatly improved.

That is, in the conventional example, as shown above, in a reduced pressure atmosphere.
In the preheating process of raising the temperature to 650-800 ℃, in order to avoid the bumping phenomenon, heating is done slowly at a heating rate of about 200 ℃ / hr at maximum. However, this preheating takes time.

Therefore, when we investigated the cause of the bumping phenomenon, it was found that the bumping phenomenon was caused by steam gas and CO generated from the raw iron powder during preheating.
It was found to be due to gas. In particular, due to the temperature difference in the raw iron powder packed bed, a difference occurs in the steam gas and CO gas generation time, and the gas generated with this time difference spouts the raw material iron powder in the surface layer portion slightly sintered from the inside, It was found to occur by going out of the raw iron powder packed bed.

In addition, at 800 to 1300 ° C, and further, finish reduction annealing is performed in a reduced pressure atmosphere of 20 Torr or less to accelerate the progress of reduction and to finish this reduction in a shorter time. Heat up to 650-800 ℃.
In order to avoid the bumping phenomenon of the raw material iron powder in the surface layer during this preheating process, the temperature is kept at 300 to 650 ° C for 10 minutes to 30 minutes, for the following reason.

If the temperature range to be held is 300 to 650 ° C, if it is less than 300 ° C, the water contained in the raw iron powder cannot be completely removed, and the bumping phenomenon occurs when the temperature is raised in the preheating process.

Further, when the temperature exceeds 650 ° C, CO gas is generated from the raw iron powder and the surface of the packed layer of the raw iron powder starts to sinter. For this reason, the raw iron powder that has begun to be sintered is blown up by the steam or CO gas generated from the inside of the packed bed, and the bumping phenomenon occurs.

In short, in the preheating process, if the temperature is kept in the temperature range of 300 to 650 ° C for 10 minutes or more, the steam can be completely removed and the surface of the raw iron powder is not sintered and bonded. Therefore, a vapor escape path is formed in the packed bed of the raw iron powder by the steam gas, and the steam gas and the CO gas that is temporarily generated are discharged to the outside of the system through this, and the bumping phenomenon does not occur.

The reason why the holding time is 10 minutes or more is that if the holding time is shorter than 10 minutes, the above-mentioned holding effect cannot be obtained, and the bumping phenomenon occurs when the temperature is raised after the holding. Further, the upper limit of the holding time is determined in consideration of productivity. About 30 minutes is preferable from the viewpoint of productivity.

Further, the reason why the finish reduction annealing after the preheating process is performed at 800 to 1300 ° C is that the reduction of the raw iron powder is incomplete at 800 ° C or lower and the sintering proceeds at 1300 ° C or higher.

Furthermore, the reason why the finish reduction annealing is performed in a reduced pressure atmosphere of 20 Torr or less is that the reduction progresses slowly when the finish reduction annealing is performed in an atmosphere exceeding 20 Torr.

Further, the water vapor generated in the preheating process is the water in which the steel powder is adsorbed, the iron hydroxide and the compound water are generated during the temperature rise.

Further, CO gas is generated by the solid solution carbon in the raw iron powder reacting with oxygen in the oxide.

Examples Hereinafter, the present invention will be specifically described based on Examples.

Examples 1 to 2. Comparative Examples 1 to 3. Atomized raw powder having the chemical composition of the steel powder shown in Table 1, that is, raw iron powder, as shown in FIG. 3, 4, 5, 6, 7, and 8 were filled to a thickness of 80 mm or less, and they were loaded on a trolley 9 made of graphite having a stepwise configuration, and loaded into a furnace for preheating and reduction.

In the preheating chamber for performing this preheating, in the case of Comparative Examples 1, 2, and 3, the preheating temperature was set to 800 ° C., and the heating rate 200 ° C./hr, 300 ° C./hr shown in FIG. The experiment was conducted by raising the temperature from room temperature in three steps of 400 ° C./hr.

The experimental results are shown in Table 2.

In this case, the bumping phenomenon was not confirmed at the heating rate of 200 ° C./hr in the conventional method, but the bumping phenomenon was confirmed at the heating rates of 300 ° C./hr and 400 ° C./hr.

On the other hand, according to the method of the present invention, in the preheating chamber
When held for a minute and preheated, the heating rate was 300 ° C / hr, 400
The bumping phenomenon was not confirmed in Examples 1 and 2 when the temperature was set to be ° C / hr.

It can be seen from Table 2 that the present invention is advantageous in raising the temperature to 800 ° C. in a short time for improving productivity under the condition that the bumping phenomenon does not occur.

Examples 3 to 7. Comparative Examples 4 to 5. As shown in FIG. 3, the holding temperature was changed to 250 to 700 ° C. and the heating rate was 400 ° C./hr and the holding time was 30 minutes as in Example 1. The experiment was carried out. The experimental results are shown in Table 3. The bumping phenomenon was not confirmed at the holding temperatures of Examples 3 to 7 within the scope of the present invention, but the bumping phenomenon was confirmed at the holding temperatures of 250 ° C. and 700 ° C. of Comparative Examples 4 to 5.

Example 8. Comparative example 6. An experiment was conducted in the same manner as in Example 1 except that the holding time was changed to 5 minutes and 10 minutes, with a temperature rising rate of 400 ° C./hr and a holding temperature of 500 ° C.
The experimental results are shown in Table 4. The bumping phenomenon was not confirmed in Example 8 having a holding time of 10 minutes within the scope of the present invention, but the bumping phenomenon was confirmed in Comparative Example 6 having a holding time of 5 minutes.

<Effects of the Invention> As described above, the atomizing raw material iron powder contains a non-reducing element and carbon, and when these components are contained, the preheating by the method of the present invention is performed despite the fact that the bumping phenomenon is particularly likely to occur. Then, the raw iron powder is preheated from room temperature in a depressurized atmosphere of 20 Torr or less, and finish reduction at a temperature of 800 to 1300 ° C is also performed in the same depressurized atmosphere, particularly from room temperature to 650 to 800 ° C. In the process, 10 between 300 ~ 650 ℃
Preheat to hold for more than 1 minute. For this reason, in the preheating process from room temperature to avoid the bumping phenomenon of the raw iron powder, the preheating time can be shortened and the productivity can be greatly improved.

Furthermore, since it is in a reduced pressure atmosphere, finish reduction proceeds rapidly, and high-purity iron powder is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a trolley in which a tray is filled with atomized raw material iron powder used for carrying out the method of the present invention, and FIG. 2 and FIG. It is a graph which shows the relationship between preheating temperature and preheating time between each Example of an invention method, and a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Akaoka 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (56) References JP-A-55-138001 (JP, A) JP-A-64- 25901 (JP, A)

Claims (1)

[Claims] 1. Atomized raw material iron powder containing a non-reducing element and carbon is subjected to a preheating process of heating while raising the temperature from room temperature to 650 to 800 ° C., and then finish reduction annealing at a temperature of 800 to 1300 ° C. to obtain iron. When manufacturing the powder, this preheating process from room temperature to 650 to 800 ° C is performed in a reduced pressure atmosphere of 20 Torr or less, and preheated so as to be held at 300 to 650 ° C for 10 to 30 minutes, A heating method for producing iron powder by finish-reducing atomized raw material iron powder, characterized in that bumping of raw iron powder is prevented and subsequent finishing reduction annealing process is also performed in a reduced pressure atmosphere of 20 Torr or less.