JPH0448002A - Method for raising temperature at the time of executing finish reduction annealing to alloy steel powder - Google Patents

Abstract

PURPOSE:To execute finish reduction annealing for short time without developing bumping phenomenon by finish-annealing iron powder, which incorporates hard-to-reducing elements and carbon and is pulverized with atomizing method, in the condition of the specific reduced pressure atmosphere and temp. raising velocity. CONSTITUTION:Molten alloy steel incorporating the hard-to-reducing elements of Cr, Mn, etc., and carbon, is pulverized into powder state with the atomizing method. This atomized alloy steel powder is charged into a stainless steel-made pans 1 - 8 and charged into an annealing furnace with a carriage, and after making the atmosphere in the furnace to the reduced pressure condition of <=20 Torr, the finish reduction annealing is executed at 800 - 1300 deg.C. In this case, this is kept at the temp. in the range of 300 - 650 deg.C for >= 10 min on the way of raising temp. from the room temp. to 650 - 800 deg.C. The finish reduction annealing can be executed to the alloy steel powder for short time without developing the bumping phenomenon.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for raising temperature during finishing reduction annealing of alloyed steel powder. Finish reduction annealing of alloyed steel powder uses atomized iron powder as a raw material and reduces the heating time without causing bumping of the iron powder during the heating process to reach the finish reduction hot water temperature. This relates to the method of raising the temperature at the time.

Conventional technology The demand for sintered iron powder parts continues to increase year by year, and in particular, the demand for alloy steel powder for parts that require high strength and high toughness is increasing. As the reinforcing alloy element, for example, inexpensive Or, M +'+ are suitable, but Cr,
When copper powder pre-alloyed with Mn was produced using the conventional water atomization-gas reduction method, it was difficult to reduce the OWA contained in the copper powder because these elements have a strong affinity with oxygen. . As a method for deoxidizing such alloy steel powder containing Cr and Mr+, for example,
Vacuum reduction as described in Japanese Patent No. 10962 was proposed, and it is now possible to produce M bare copper powder.

The heat treatment furnace according to this proposal is disclosed in, for example, Japanese Patent Application Laid-Open No. 61-1900.
As described in Publication No. 4, by preheating and drying a raw material powder containing a refractory element and carbon, and by using carbon contained in alloyed copper powder, the raw material powder after preheating is heated to l112.
F11L is divided into a reduction annealing chamber at the annealing stage and a cooling chamber for cooling the reduction annealing powder, and these are arranged side by side in series, with movable doors provided at the boundaries of these winter solstice, so that each chamber is independent. The chamber is constructed to be a space, and each chamber is provided with an exhaust device for depressurization.

When using this reduction annealing furnace,
As proposed in the publication, the temperature is raised to 650 to 800 °C in a preheating chamber as a preliminary step to raising the temperature to the final annealing temperature of 800 to 1300 °C in a reduced pressure atmosphere of 20 Torr or less. When the temperature is raised rapidly to improve productivity, gas is rapidly generated from the copper powder, causing a phenomenon in which the copper powder flies up (hereinafter referred to as a bumping phenomenon). If this phenomenon occurs in the furnace, copper powder will fly into the furnace and damage the heater. In order to prevent this bumping phenomenon, the temperature is set at a temperature of 200°C/hr, for example, to prevent sudden gas generation in the preheating chamber.
The temperature must be raised slowly at a certain temperature, and therefore, a long time is required for preheating, and the preheating stage of the preheating-reduction annealing-cooling process becomes rate-limiting, resulting in a problem of reduced productivity.

Problems to be Solved by the Invention The present invention aims to solve the above problems, and specifically provides an alloy steel powder finish suitable for reducing preheating time without causing bumping in a reduction annealing furnace. How to raise temperature during reduction annealing! ! The purpose is to propose a plan.

Means for Solving the Problems and Their Effects Namely, the present invention provides a method for finishing raw material powder for atomized alloy copper powder containing a refractory element and carbon at a temperature of 800 to 1300°C in a reduced pressure atmosphere of 201'Orr or less. During reduction annealing, the temperature is raised from room temperature to 650 to 800°C, and the temperature is held at 300 to 650°C for 10 minutes or more.

Hereinafter, a detailed explanation of the configuration and the operation of the means of the present invention will be as follows.

The present inventors conducted intensive research on a method for suppressing the bumping phenomenon when deoxidizing raw material powder for atomized alloy steel (t) containing refractory elements such as Cr and carbon, and found that 20 T or 650~ in a reduced pressure atmosphere below r
It has been found that the bumping phenomenon of copper powder can be suppressed by maintaining the temperature of the steel powder in the temperature range of 300 to 650°C for a certain period of time in the process of raising the temperature to 800°C.

Further research was conducted, and the present invention was established based on the results of this research.

According to the research of the present inventor, in the conventional example, when the copper powder to be finish-reduced is heated to 650 to 800°C in a reduced pressure atmosphere in the preheating chamber, the heating rate is reduced to about 200°C to prevent the bumping phenomenon of the copper powder. A method of heating slowly at ℃/hr was adopted, but this method does not cause the bumping phenomenon of copper powder, but it takes time, so the inventors further investigated the cause of the bumping phenomenon of steel powder. By the way, 650-80 from Murohada
The bumping phenomenon that occurs when the temperature rises to 0℃ is caused by water vapor and CO gas, which are gases generated by steel powder, and the time for generation of this water vapor and CO gas is caused by the temperature difference in the copper powder filling stage. Therefore, it was discovered that this phenomenon occurs when gas generated from inside blows up a slight amount of iron powder on the sintered surface and exits to the outside of the copper powder filling (2).

In the method of the present invention, final reduction annealing is performed at temperatures between 800 and 1300°C, since reduction of the copper powder is incomplete at temperatures below 800°C, and sintering progresses at temperatures above 1300°C. If finish reduction annealing is performed in an atmosphere exceeding 201 o r r, the progress of reduction will be slow;
Reduction is performed in a reduced pressure atmosphere of 0 Torr or less. This reduction baking Il! In order to complete the reduction in a short time, it is effective to raise the temperature to 650 to 800°C in a preheating chamber. It is necessary to maintain the temperature in the range of 300 to 650°C for 10 minutes or more so that the bumping phenomenon of the copper powder described above does not occur even if the temperature is rapidly raised to 650 to 800°C. The reason why the temperature range to be maintained is 300 to 650°C is that if the temperature is lower than 300°C, the moisture contained in the copper powder cannot be completely removed, and a bumping phenomenon occurs when the temperature is raised later. In addition, when the temperature exceeds 650°C, CO gas is generated from the copper powder and the surface of the cylinder filled with copper powder begins to sinter. This is because a squeaking bumping phenomenon occurs. Therefore, the water vapor is removed by holding it in the temperature range of 300 to 650°C for 10 minutes or more, and the water vapor is used to charge the air. It is necessary to form a path for degassing within Is.

The reason why the holding time was set to 10 minutes or more was because the effect of holding for 10 minutes could not be obtained and bumping phenomenon would occur during the subsequent raising m. Further, the upper limit of the holding time is determined in consideration of productivity, and for example, about 60 minutes or less is sufficient, but from the viewpoint of productivity, about 30 minutes is preferable.

Note that adsorbed water, iron hydroxide, and compound water of the copper powder are generated as water vapor during heating, and the solid 7fJlfl element in the iron powder reacts with Wl and elemental elements in the oxide to generate CO gas.

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

Examples 1-2. Comparative Examples 1 to 3゜Atomized raw copper powder having the chemical composition shown in Table 1 was filled into eight stainless steel saucers to a thickness of 80+ug or less as shown in Figure 1, and they were stacked in steps. It was loaded onto the constructed graphite trolley and carried into the furnace for reduction.

The preheating temperature at the end of preheating is 800℃, and the furnace internal pressure is 0.0ITo.
Temperature increase rate 200°C/hr shown in Figure 2 in rr, 30
The experiment was conducted in three stages: 0°C, notar, and 400°C/t+r. The experimental results are shown in Table 2. No bumping phenomenon was observed at a heating rate of 200°C/111° in the conventional method, but a bumping phenomenon was observed at a heating rate of 300°C/hr and 100°C/hr.

Even if the heating rate is 300°C/hr or 400°C/hr, the bumping phenomenon can be prevented by holding the temperature at 500°C for 30 minutes using the method of the present invention! v Not approved.

From Table 2, it can be seen that the present invention is advantageous in raising the temperature to 800° C. in a short time to prevent bumping from occurring and to improve productivity.

Table 1 Chemical composition (wt%) Table 2 Experimental results Table 3 Experimental results Examples 3-1. Comparative Examples 4-5゜As shown in Figure 3, the holding temperature was changed from 250 to 700℃, and the heating rate was 400℃/l+r as in Example 1.
, the experiment was conducted with a holding time of 30 minutes. Real wA conclusion song 3rd
Shown in the table. Although no bumping phenomenon was observed at the holding temperature of Examples 3 to 1 within the range of the present invention, the holding temperature of Comparative Examples 4 to 5 was 250°C and 700°C of Example 8. Comparative Example 6 An experiment was conducted in the same manner as in Example 1, with the holding time changed to 5 minutes and 10 minutes, at a temperature increase rate of 400°C/hr and a holding temperature of 500°C. The actual wA results are shown in Table 4. Although no bumping phenomenon was observed in Example 8 with a retention time of 10 minutes within the range of the present invention, the retention time was 5 minutes. 20T raw material powder for atomized alloy steel powder containing elements and carbon
When performing final reduction annealing at a temperature of 800 to 1300°C in a reduced pressure atmosphere of orr or less, the temperature is maintained at 300 to 650°C for 10 minutes or more during the temperature increase process from room temperature to 650 to 800°C. .

According to the method of the present invention, atomized raw material powder for alloy steel powder containing a refractory element and carbon is heated to 80% in a reduced pressure atmosphere.
During final reduction annealing at a reducing hot water temperature of 0 to 1300 degrees Celsius, the steel powder was kept at a temperature of 300 to 650 degrees Celsius for more than 10 minutes during the heating process from room temperature to 650 to 800 degrees Celsius, which caused the bumping phenomenon of steel powder. This has the effect of shortening the rising time from room temperature and improving productivity.

[Brief explanation of drawings]

Fig. 141 is an explanatory diagram, seen from the side, of a cart loaded with a saucer filled with atomized raw powder used in carrying out the present invention;
FIG. 2 and FIG. 3 are graphs showing the relationship between heating conditions and temperature for an example of the present invention and a comparative example, respectively.

Claims (1)

[Claims] 1) When finishing reduction annealing the atomized raw material powder for alloy steel powder containing refractory elements and carbon at a temperature of 800 to 1300°C in a reduced pressure atmosphere of 20 Torr or less, the temperature rises from room temperature to 650 to 800°C. 300-65 in warm process
A method of raising temperature during reduction annealing for finishing alloy steel powder, characterized by holding the temperature at 0°C for 10 minutes or more.