JPH05161947A - Manufacture of magnesium-containing free-cutting steel by continuous casting - Google Patents

Abstract

PURPOSE:To obtain a manufacturing method for a magnesium-containing free- cutting steel by a continuous casting uniformly dispersing magnesium sulfide inclusions. CONSTITUTION:Mixed powder beforehand uniformly mixing iron powder of 50-300mum the average grain diameter and the magnesium sulfide powder of 5-30mum the average grain diameter and having >=4vol. ratio of the iron powder and the magnesium sulfide powder, is added into a molten steel in a tundish and/or a mold in the continuous casting. By this method, the magnesium- containing free-cutting steel having excellent machinability is manufactured by the continuous casting method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnesium-containing free-cutting steel by continuous casting in which magnesium sulfide inclusions are uniformly dispersed.

[0002]

2. Description of the Related Art Conventionally, manganese sulfide and calcium sulfide are well known as sulfide-based intervening substances. These substances are plastically deformed by the vertical load in the secondary cutting shearing region, and improve the machinability in order to reduce the frictional force. It is presumed that magnesium sulfide has the same effect as these free-cutting substances, but it is the fact that it is not used because there is no suitable method for adding magnesium to steel. In addition, since the oxide free energy of magnesium is smaller than that of calcium, it is less likely to be oxidized than calcium, and more easily forms sulfides than manganese. is expected. Further, if a method for uniformly dispersing magnesium sulfide having a specific gravity smaller than that of molten steel in steel is developed, it is expected that it can be used as a free-cutting substance.

[0003]

As described above, it is the actual situation that it is not utilized because there is no suitable method for adding magnesium to steel. However, if a method of uniformly dispersing magnesium sulfide having a smaller specific gravity than molten steel was developed in the steel, it could be used as a free-cutting substance, and various studies have been conducted, but the addition yield to molten steel is extremely poor,
Moreover, it is almost impossible to uniformly disperse it in molten steel, and it has not been industrially put to practical use.

[0004]

SUMMARY OF THE INVENTION The inventors of the present invention have made various investigations in view of the above circumstances, and as a result, intend to provide a method for producing a magnesium-containing free-cutting steel by a continuous casting method having excellent machinability. Is. The gist of the invention is that iron powder having an average particle size of 50 to 300 μm and an average particle size of 5 to 3 are used.
In the tundish of continuous casting, a mixed powder obtained by uniformly preliminarily mixing 0 μm magnesium sulfide powder in a volume ratio of iron powder and magnesium sulfide powder of 4 or more, or
And a method for producing a magnesium-containing free-cutting steel by continuous casting, which is characterized by adding to molten steel in a mold.

[0005]

The present invention will be described in detail below. In the present invention, the lower limit of the average particle size of the magnesium sulfide powder is set to 5 μm in order to secure machinability. If the upper limit is more than 30 μm, the machinability will be saturated, so 30
It was set to not more than μm. The reason for adding magnesium sulfide powder as a mixed powder instead of adding it separately is that magnesium sulfide powder aggregates to form powder and increases in volume, and since it has a smaller specific gravity than molten steel, it is added separately. This is because they do not float and remain in molten steel. The agglomerated magnesium sulfide powder was separated into individual magnesium sulfide powders and mixed with iron powder to reduce the volume. The reason why iron powder is selected is that when it is added to molten steel, it does not float separately.

In order for the magnesium sulfide powder having an average particle diameter of 5 to 30 μm to be mechanically attached to the surface of the iron powder and uniformly dispersed, the lower limit of the average particle diameter of the iron powder is preferably 50 μm or more. The upper limit is preferably 300 μm or less, because if the size becomes too large, the magnesium sulfide powder and the iron powder are likely to be non-uniformly mixed. The volume ratio of the iron powder and the magnesium sulfide powder is set to 4 or more in order to increase the surface area of the iron powder and facilitate the attachment of the magnesium sulfide powder. When the mixed powder is added to the molten steel in the ladle, oxide-based inclusions and complex inclusions are easily generated. Therefore, the mixed powder is added in the tundish and / or
Limited to molten steel in rud. Next, the present invention will be specifically described with reference to examples.

[0007]

EXAMPLE A mixed powder was produced by placing iron powder and magnesium sulfide powder in a container together with a tungsten carbide ball and mixing them with an agitator. Table 1 shows the average particle diameters of the iron powder and the magnesium sulfide powder at that time. The average particle size was classified by sieving various meshes, a particle size distribution chart was prepared, and the average value was displayed. At this time, it is desirable that the surface of the iron powder be as uneven as possible. Also,
The hardness is preferably soft, and a component close to pure iron is suitable. Low-carbon steel was melted in a high-frequency melting furnace with a capacity of 100 kg, poured into a 100 kg mold, and press-molded mixed powder was added to the casting flow. The addition of magnesium sulfide was 70 kg in each charge. On the other hand, the comparison material is 100k
It was manufactured by injecting Mg wire into a g mold. Each of the cast pieces was formed into a round bar having a diameter of 50 mm by hot casting and then normalized at 920 ° C. for 2 hours.

Table 2 shows the steels A, B, C according to the manufacturing method of the present invention.
And the chemical compositions of comparative steels D, E, F, G, and H and the flank friction width VB measurement results are shown. D, E, F, and G use mixed powder, but the particle size of iron powder or magnesium sulfide powder is outside the scope of the present invention, and H is the current manufacturing method, that is, adding Mg wire to the mold. It is the steel produced by this. The cutting conditions are as follows. Tool material: cemented carbide P
20, Cutting method: Longitudinal turning, Cutting speed: 130m /
min, feed: 0.25 mm / rev, cut: 1.
Tool wear (VB) was measured by cutting for 40 min under the conditions of 5 mm and no cutting oil. The Charpy test piece was sampled in the direction parallel to the forging direction.

[0009]

[Table 1] MgS in Table 1: Magnesium sulfide powder, average particle size: μ
m, volume ratio: iron powder / magnesium sulfide

As is clear from Table 2, the inventions A, B,
C, the tool wear is extremely small. Steel having a particle size of iron powder or magnesium sulfide powder outside the scope of the present invention, D,
It can be seen that E, F, G and H are inferior in either tool wear or impact value.

[0011]

[Table 2]

[0012]

As is apparent from the above examples, according to the present invention, it becomes possible to produce a magnesium-containing free-cutting steel by a continuous casting method having excellent machinability, and the industrial effect is extremely remarkable. There is.

Claims (1)

[Claims] 1. An iron powder having an average particle size of 50 to 300 μm and a magnesium sulfide powder having an average particle size of 5 to 30 μm are mixed in advance by uniformly mixing the iron powder and the magnesium sulfide powder in a volume ratio of 4 or more. A method for producing a magnesium-containing free-cutting steel by continuous casting, characterized in that powder is added to molten steel in a continuous casting tandem or in a mold.