JPH01100202A - Production of low-alloy steel powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing low-alloy steel powder used in powder metallurgy, and specifically relates to a method for producing low-alloy steel powder that suppresses variations in the amount of carbon in the powder. It is something.

[Prior Art] The low-alloy steel powder conventionally used in powder metallurgy is a metal powder that is made fine by molten metal, for example, by a gas atomization method, a water atomization method, a centrifugal atomization method, or the like. Since this metal powder is oxidized in the above process, it is reduced to a reduced metal under a mixed gas of nitrogen and hydrogen and pulverized to be used as a raw material for powder metallurgy. In this low alloy 11) rice cleaning process, it is necessary to adjust the amount of carbon contained in the low alloy steel because it changes the hardenability and mechanical properties of the low alloy steel. This carbon content iiiM is achieved by adding a predetermined amount of graphite powder to the molten metal. However, because some of the carbon contained in the molten metal is consumed or scattered during oxidation due to in situ oxidation and reduction under ammonia decomposition gas, the carbon in the raw material powder after reduction is
Since the amount varies from rod to rod produced, it is difficult to obtain a low alloy steel powder having a predetermined amount of carbon. However, the variation within the loft is small and is less than 0.02%.

[Problems to be Solved by the Invention] The present invention solves the problem that in the conventional manufacturing method of low-alloy steel powder, the carbon content varies from production rod to production rod, making it difficult to obtain a product with a specified oil content. The purpose is to solve the following problems. Since this carbon content causes variations in the hardenability and mechanical properties of the material, it is necessary to reduce these variations as much as possible.

In the present invention, carbon is not adjusted in the molten metal before the first step, but before the heat treatment in the second step, thereby suppressing the above-mentioned variation in carbon from production rod to rod. In other words, the present invention was accomplished by discovering that the variation in carbon content of low-alloyed steel powder obtained by forming a Blair alloy can be suppressed by performing reduction in an inert gas without adding carbon to the molten metal. It is.

[Means for Solving the Problems] The method for producing low alloy steel powder of the present invention includes a first step of spray cooling molten low alloy steel to obtain low alloy steel powder, and adding a predetermined amount of the low alloy steel powder to the low alloy steel powder. a second step of adding and mixing graphite powder and heating it under an inert gas to disperse the graphite powder as a solid solution in the low-alloy steel powder; and a third step of pulverizing the heated product. This is a manufacturing method that allows adjustment of w4 between carbons with little variation in carbon content between rods.

Low-alloy steel used for molten low-alloy steel is made by adding a third element to carbon steel in a manner suitable for the intended use, and structural alloy steel is a typical example. Examples of the elements added as the third element include silicon, manganese, chromium, nickel, molybdenum, tungsten, titanium, boron, aluminum, copper, and tin. The carbon content of low alloy steel to which this manufacturing method can be applied is 0 to 0.8%.

The first process is a step in which a cold W medium is sprayed onto the molten low alloy steel to form a powder. After adjusting the carbon content with this molten metal, the carbon content of the low alloy steel powder obtained by spray cooling is 0.
A variation of 0.1% is observed between 71 and 71. Therefore, even if the carbon content is adjusted in the molten metal, the carbon content in the low alloy steel powder obtained in the third step does not necessarily reach a predetermined level due to variations between lofts. Therefore, carbon m is not particularly adjusted here.

In the second step, the carbon content in the alloy steel powder obtained in the first step is determined, and graphite powder (2) necessary to form a predetermined carbon content is added. This graphite is carbon and can be used if it has a purity of 99% or more. Further, the particle size may be 50 μm or less. This graphite powder is mixed into low alloy steel powder and heated under an inert gas.

This inert gas may be any gas that does not participate in the oxidation or reduction of the powder during heating; for example, inexpensive nitrogen gas may be used. When heated under an inert gas, the low-alloy steel powder is usually not melted but remains in a powder or agglomerated state at temperatures below iooo°C. Therefore, it is considered that the graphite powder is used as a solid solution, dispersed, or reduced in the low alloy steel, and is uniformly dispersed in the alloy steel powder.

The third step is a step in which the agglomerated low-alloy steel heated in the second step is mechanically pulverized into a powder having a particle size corresponding to the number of cores. Any conventional known method can be applied to the pulverization. Ground low alloy steel is used as powder for powder metallurgy. The variation in carbon content in the obtained powder within the rod (within the sample) is 0.02% or less, and the variation between manufacturing lofts is also 0.02% or less. Therefore, it is also possible to use several rods at once.

[Operations and Effects of the Invention] In the method for producing low alloy steel powder of the present invention, the carbon content in the low alloy steel powder obtained by adjusting the carbon content in the second step is increased within the rod and between the rods. Variation is 0.
The hardenability and mechanical properties of alloy products using this low-alloy steel powder as a raw material do not change. Furthermore, since the variation is small, the yield of low alloy steel powder obtained is improved and productivity is improved.

Furthermore, low alloy steel powder having a predetermined carbon content can be easily produced with good reproducibility.

[Example] The present invention will be explained below with reference to Examples.

The carbon content of the low alloy steel used in this manufacturing method is 0.47% (after the first step). The low alloy steel used in this example contains Ni, MO, etc. in addition to iron and carbon.

The first step is to melt low alloy steel to form a molten metal.

This molten metal is pulverized by a water spray method.

Then, dry it to remove the attached moisture.

In the second step, a sample is taken from the alloy steel powder obtained in the above Wi1 step, the amount of carbon m in the sample is measured, a predetermined amount of carbon is replenished, the alloy powder is reduced by heat treatment, and the replenished carbon is This is the process of uniformly dispersing the powder into the alloy powder. The powdered carbon added during this step is considered to be dispersed in various forms such as solid solution and reduced form.

In the second step, heating is performed at 950° C. for 1 hour under nitrogen gas. This is a third step in which the obtained aggregates are pulverized and used as a product raw material. Grinding was performed using a hammer mill.

In the above manufacturing method, alloy steels with different carbon contents (1) were used, and the carbon contents before heating and after heat eroding were measured for each of five samples, and the measured value variation (R) was investigated. The results are shown in the table.

The comparative example is the same as the example except that the heating in the second step was performed at 950°C under a gas in which the ratio of nitrogen to hydrogen in the ammonia decomposition gas was 1 = 3, and carbon was added to the molten metal. This was done under certain conditions.

Before the second step in the table, samples were taken and measured after the amount of carbon in the table was added to the low-alloy steel powder after the first step, and there was no variation regardless of the amount of graphite powder added. The target value is 0.02 or less. After the third step,
In a study that investigated the variation in the amount of carbon contained in samples taken from alloy powder after heating under nitrogen gas, the variation was 0.02 when graphite addition 1 was 0.5%.
Although this is large, it is within the target, and in the case of no other additives and 0
．． The variation in carbon amount when adding 10% is 0.00
8, there is very little variation.

On the other hand, the variation in the carbon content in the metal powder after the third step in the comparative example increases as the amount of graphite added increases, and when the amount of carbon added is 0.1%, the variation becomes 0.066. It is larger than the m value of 0.02.

FIG. 1 is a graph showing the relationship between added carbon m and the amount of carbon in low alloy steel.

A straight line 1 with black circles in FIG. 1 indicates the amount of graphite added and the carbon content in the metal powder before the second step of this example, which increases linearly with the amount added. Straight line 2 with white circles shows the relationship between the carbon content in the metal powder and the added graphite after the third step, which also increases almost linearly in this case. Comparative Example 3 shows the relationship between the amount of carbon in the metal powder after the third step and the added graphite, which is not a straight line but a curve, and does not show a proportional relationship. Furthermore, when the amount of graphite added is 0.05% and 0.10%, there is a vertical line indicating the dispersion of the measured values.
In the case of 10%, the variation is more than twice that of 0.05%.

Even though there is no variation in carbon content when no graphite is added, the method of the comparative example shows large variation. This shows that the manufacturing method of the present invention is a method with little variation.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of added carbon and the amount of low alloy steel powder in this example. Patent applicant Toyota Motor Corporation

Claims (1)

[Claims] (1) A first step of spray cooling molten low-alloy steel to form low-alloy steel powder, and adding and mixing a predetermined amount of graphite powder to the low-alloy steel powder and heating the graphite powder under an inert gas. A second step of dissolving into the low alloy steel powder, and a third step of pulverizing the obtained heat-treated product. Steel powder manufacturing method.