JPS621806A - Manufacture of atomized high-carbon steel powder - Google Patents

Abstract

PURPOSE:To obtain atomized high-carbon steel powder contg. a very small amount of hollow or porous particles by adding a deoxidizing agent to molten steel and regulating the temp. of the molten steel to reduce the amount of O in the steel to a value below the limit of deoxidation caused by a C-O reaction and by atomizing the molten steel. CONSTITUTION:When molten steel contg. >=0.2wt% C is atomized, a deoxidizing agent is added beforehand to the molten steel and the molten steel is kept at a proper temp. according to the deoxidizing agent to reduce the amount of O in the molten steel to a value below the limit of deoxidation caused by a C-O reaction. One or more among Si, Ti, Al, Zr, B and Ca are used as the deoxidizing agent. Plural kinds of deoxidizing elements produce a more significant effect than one kind of deoxidizing element.

Description

Detailed Description of the Invention (Industrial Application Field) The invention disclosed in this specification is a method for producing dense C-containing (>0.2 wt%) atomized steel powder with no pores or with very few pores. Regarding manufacturing technology, 0.2 wt of C
Select and add an appropriate deoxidizer to high carbon molten steel containing % or more,
By maintaining the temperature of the molten steel in the tundish appropriately, molten steel adjusted to [%0] below the deoxidation limit by C-0 reaction is prepared, and by atomizing such molten steel, the CO gas generated during atomization creates a hollow space. This paper proposes an advantageous method for suppressing the formation of porous particles or porous particles.

The steel powder obtained by the method according to the present invention can be processed by powder metallurgy, thermal spraying, etc. in areas that require heat resistance, wear resistance, corrosion resistance, etc.
It is used when processing by welding method etc.

(Example) Conventionally, copper powder with a high carbon content (202wt%) has been produced by an atomization method or the like, but such conventional production methods often produce hollow particles or porous particles. With these powders, the packing density decreases,
Consolidated materials, welded materials, thermal sprayed materials, overlay materials, etc. have problems such as increased shrinkage, decreased density, and residual coarse pores. On June 10, 1971, a technology to prevent the formation of hollow or multi-shaped particles of atomized steel powder containing high C content was developed.
The publication ``Atomized Metal Powder'' published by the Japan-Soviet News Agency (Original Publishing) states that it can be atomized with an inert gas such as N2 to form dense particles; Currently, the gas atomization method is used.

Other conventional techniques include the method disclosed in Japanese Patent Publication No. 49-38547 and the method disclosed in Japanese Patent Publication No. 58-158.
There is a method disclosed in Japanese Patent Application No. 843.

(Problems to be Solved by the Invention) First, the method disclosed in the above publication "Atomized Metal Powder"
The problem is that cold forming is difficult because only irregularly shaped copper powder can be produced. On the other hand, Special Publication No. 49-28101,
Japanese Patent Publication No. 48-38547 mentions the formation of hollow and porous particles that occur during water atomization of C-containing molten steel; for example, in Japanese Patent Publication No. 48-38547, [%C] is 0.2.
It merely suggests that the following water atomized steel powder is substantially uniformly solid (dense), and also that
No. 58843 and Japanese Patent Application Laid-Open No. 158844/1987 disclose that hollow particles are recognized when [%C] exceeds 0.40, and that the content increases significantly when it exceeds 0.80. Only. Therefore, in the case of conventional technology, the relationship between [%C] and the generation of hollow particles is not necessarily clear, and the reality is that there is no technology to prevent the generation of hollow particles, etc., except for the inert gas atomization method. Therefore, the development of effective technology has been awaited.

(Means for Solving the Problems) The present invention, as a means to overcome the above-mentioned problems that occur when producing high carbon content (>0.2 wt%) atomized steel powder, By adding a deoxidizing agent to molten steel and adjusting the desired molten steel temperature determined in relation to the deoxidizing agent (tundish), the amount of [%O] in the steel was reduced to below the deoxidation limit due to the C-O reaction. The present invention provides a method for producing dense, high-quality, high-carbon steel powder with very few hollow or porous particles by obtaining molten steel and atomizing it.

As the deoxidizing agent, S i, T i + A I-, Z
r.

Preferable examples include one or more of B and Ca.

(Function) The present invention is based on adjusting the molten steel to be atomized in advance to have the following properties in order to avoid the above-mentioned disadvantages caused by the CO gas generated during atomization.

Regarding the point that the carbon content [%C] of molten steel is 0.20 or more; ■ Between [%C] and [%O] in molten steel, (C) + [
The reaction O]=CO occurs. Figure 1 shows the distribution of [%O] in actual furnaces such as converter furnaces, arc furnaces, high-frequency induction electric furnaces, crucible furnaces, etc. with respect to [%0] which is in equilibrium with [%C], and shows the Ct difference between the two. , that is, Δ[%0] = [%0] − [%0].

Ct becomes excess oxygen, and due to the influence of the solubility, which decreases as the temperature of the molten steel decreases as it cools during atomization, the (Ct) in the molten steel increases.
) to generate CO gas. The generated CO gas is trapped in the coagulated powder or ejected to produce hollow or porous particle powder.

Figure 2 shows steel powder being sprayed at a water pressure of 140 using a 10 mm nozzle.
The results are shown when atomized with kg 7cm2·G and water amount of 23017mln, and as the [%C] increases, the number of hollow or porous particles increases.

However, in the region where [%C] is less than 0.2, the amount of excess oxygen:
Since Δ[%0] is small and the activity of [C] is also small, dense copper powder can be obtained even if atomized without adding a forced deoxidizing agent. Therefore, the present invention targets molten steel containing carbon in [%C] of 0.20 wt% or more.

At this time, T i + N b, V, C are in the molten steel.
r.

Addition of elements that increase the saturation solubility of C, such as Mn, Mo, W, etc., reduces the activity of C and is therefore advantageous for obtaining dense particles.

On the other hand, Co, Ni, Cu, and 3b are present in molten steel.

Adding 4Sn, AJ, S, P, Si, etc. reduces the solubility of C and increases the activity of C, making it easier to generate CO gas during atomization, but when [%C] is 0
．． If it is less than 20 wt%, dense particles can be obtained.

The number of hollow particles in Fig. 2 is determined by mixing water atomized and dried powder with resin, molding, thermosetting, cutting and polishing, and using an optical microscope at 100x magnification to determine the number of hollow particles in 10 areas where there are 100 or more particles per field of view. The visual field was measured using a microscope.

(2) Types of deoxidizing agents; The types of deoxidizing agents applicable to the present invention will be explained with reference to FIG. Figure 3 shows [ for each 00 partial pressure of 1600℃ molten steel
Relationship between [%C] and [%0] and each deoxidizing element and [%C]
This shows the relationship between

At P co ” 1 atm, Si, Ti, A1
．． Zr.

If the deoxidizing agent contains one or more elements among B and Ca,
It is possible to reduce the C-containing molten steel to [%0] below the deoxidation limit due to the C-O reaction. Note that Ca is included as a deoxidizing agent in the present invention because it is clear from its standard free energy of formation that it has a strong deoxidizing power.

In addition, as a deoxidizing agent, Si, Ti, A/! , Zr.

B and Ca may be used alone or in combination. That is, [%○] can generally be lowered by adding a plurality of deoxidizing elements at the same time rather than adding a single deoxidizing element to molten steel. The most commonly used composite deoxidation is typically the case where Si and Mn are added at the same time.

Figure 5 shows PC,=latm, CC), (Si) alone and (0,50
%Mn+Si). As can be seen from this figure, by adding St and Mn simultaneously, the deoxidizing power becomes greater than when Si alone is used.

This composite deoxidizing effect is caused by (Mn+47ri, (Mn+
Si+7N), (Cr+Si), (Cr+
Various combinations are possible, such as Mn+Si), (Cr+Mn+Si+Ajl), in short, Si,
Ti, Aj2. Any material containing one or more elements of Zr, B, and Ca may be used. - In addition, deoxidizing treatment by adjusting [%C] and adding a forced deoxidizing agent is carried out not only in the melting and refining process, but also in the molten steel processing, transportation, and transfer process, such as in the ladle, runner, and tundish. This can be done by adjusting the molten steel temperature.

■About molten steel temperature: The present invention applies to molten steel with [%C] of 0.20wt% or more to which the above deoxidizing element is added, and the molten steel temperature is further adjusted as explained below to cause a C-O reaction. For atomization adjusted to [%O] below the deoxidizing limit.

Prepare molten steel. This adjustment of the molten steel temperature will be explained with reference to FIG. 4, taking as an example Si, which is most commonly used as a deoxidizing agent.

FIG. 4 compares the deoxidizing powers of (C) and (Si) at P co '' 1 atm at each molten steel temperature.

As a result, in molten steel of arbitrary [%C], [%S
i) and the molten steel temperature.

(Example) Next, the present invention will be explained with reference to Examples.

Each charging raw material was mixed in anticipation of melting temperature rise loss so as to obtain steel with a predetermined composition, and melted in a high frequency induction electric furnace. After raising the temperature to a predetermined temperature, the molten steel was readjusted by adding ferroalloy, and the molten steel with the composition shown in Table 1 was tapped into a sufficiently preheated tundish.
The amount of water was 230J when injected by gravity from a 0mm diameter refractory molten metal nozzle! /min, water pressure 140 kg/c
N2 by an inverted conical high-speed water jet with a pressure of m2G.
Water was atomized in the atmosphere. After water atomization, it was allowed to settle naturally in a spray tank, the supernatant water was discharged, and the concentrated slurry was subjected to vibration dehydration and vacuum-dried at 200°C. This dried steel powder was mixed with a thermosetting resin, and after molding and curing, the cross section of the particles was cut and polished and examined under an optical microscope at 100x magnification, with 10 fields of view showing areas where 100 or more steel powder particles were present per field of view. The number of hollow particles, the equilibrium value of [%0] according to [%C], and the measured value of [%O] of molten steel are summarized in Table 1.

(Effects of the Invention) As explained above, according to the present invention, by adding a forced deoxidizing agent and adjusting the temperature of molten steel, the deoxidization limit due to the C-O reaction in molten steel can be reduced to [%0]. Since the molten steel was water atomized, it became possible to produce high-quality carbon-containing steel powder with very few hollow particles throughout the high carbon content region.

According to the present invention, not only can atomization be performed using an inert gas such as N2 and Ar, but also the same effect as described above can be obtained even when atomization is performed using a gas containing 02 such as air, and supersonic atomization method, Rotating disk method, vacuum atomization method, twin roll atomization method, crucible rotation method,
A similar effect can also be obtained by using an impact atomization method or the like.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the equilibrium values of [%C] and [%0] in molten steel and the measured values of [%C] and [%O] in an actual furnace. Melting IAC of steel powder atomized with water
A graph showing the relationship between the amount [%C] and the number of hollow particles, Figure 3 is a deoxidation equilibrium diagram of each deoxidizing element in molten steel, and Figure 4 is a graph showing the relationship between the amount [%C] and the number of hollow particles. )and(
Fig. 5 is a comparison graph of the deoxidation equilibrium values of Si).
It is a graph comparing the deoxidation equilibrium values of (C), (Si) and (0,50% Mn+Si) in 1600° C. molten steel at =1 atm.

Claims (1)

[Claims] 1. Oxygen content of the molten steel to be atomized, which contains 0.2 wt% or more of C, is reduced by selecting and maintaining a deoxidizing agent and a corresponding appropriate molten steel temperature. quantity C
A method for producing high carbon atomized steel powder, characterized in that atomization is carried out after the temperature is reduced to below the deoxidation limit by -O reaction. 2. The manufacturing method according to claim 1, wherein any one or more elements among Si, Ti, Al, Zr, B, and Ca are used as the deoxidizing agent. .