JPH05163550A - Sulfide-containing free-cutting steel excellent in machinability - Google Patents

Abstract

PURPOSE:To provide a continuously cast sulfide-contg. free-cutting steel wherein large Ca or Mg sulfide inclusions are uniformly dispersed and excellent in machinability. CONSTITUTION:The powder contg., by weight, 0.06-0.20% C, <=0.01% Si, 0.05-2.0% Mn, <=0.02-0.10% P, one of >=2 kinds among Ni, Mo, Cu, Cr and Pb as the elements for improving strength, etc., and the balance Fe with inevitable impurities and wherein an iron powder having 200-400mum average particle diameter and the powder of Ca or Mg sulfide having 10-30mum average particle diameter are mixed in >=3 volume ratio is kneaded. The pretreated powder is added to molten steel, and a sulfide-contg. free-cutting steel contg. 0.01-0.04% of the sulfide, having 10-30mum average particle diameter and excellent in machinability is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sulfide-containing free-cutting steel excellent in machinability and mechanical properties.

[0002]

2. Description of the Related Art It has been well known that carbon steel is mainly added with elements such as Pb, Bi and S, Se, Te, which are low melting point metals, to improve machinability of steel materials. However, although Pb remarkably improves the machinability of steel, it has the drawback of lowering the strength at high temperatures due to its low melting point. Similar to Pb, S also has a great effect on improving the machinability of steel, but it has a drawback that it plastically deforms during the rolling of the steel material and stretches to a length of several tens of μm, which lowers the toughness. In addition, manganese sulfide, calcium sulfide, and magnesium sulfide are known as sulfide-based intervening substances. These sulfide-based inclusions are plastically deformed by a vertical load in the secondary cutting shearing region and reduce the frictional force, thus improving machinability. However, compared to manganese sulfide, in particular, calcium sulfide and magnesium sulfide are produced by continuous casting, so that calcium sulfide and magnesium sulfide, which have a smaller specific gravity than molten steel, are uniformly distributed in the steel. Very difficult to disperse in.
Therefore, there is a demand for the development of free-cutting steel containing calcium sulfide and magnesium sulfide, which has excellent machinability by the continuous casting method. The reality is that sufficient steel has not been obtained.

[0003]

As described above, in the cooling process and solidification process of continuous casting, free-cutting steel having a small size of metal sulfide inclusions due to precipitation cannot obtain sufficient free-cutting property, and If the metal sulfide is directly added, the yield of addition to the molten steel is extremely poor, and uniform dispersion in the molten steel is almost impossible, which is an industrial problem.

[0004]

In view of such circumstances, the present invention provides a metal sulfide-containing free-cutting steel excellent in machinability by a continuous casting method in which large-sized Ca or Mg sulfide inclusions are uniformly dispersed. It is intended to be provided. The gist of the invention is as follows: (1)% by weight, C: 0.06 to 0.20% Si: 0.01% or less Mn: 0.5 to 2.0% P: 0.02 to 0 10% The balance is Fe and inevitable impurities, and the iron powder having an average particle size of 200 to 400 μm and the sulfide powder having an average particle size of 10 to 30 μm are mixed in a volume ratio of the iron powder to the Ca or Mg sulfide powder. The average sulfide particle size in the steel material is 10 to 30 by adding the pretreated powder mixed and kneaded to the molten steel as 3 or more.
A sulfide-containing free-cutting steel having excellent machinability, characterized by containing 0.01 to 0.040% of μm. (2) By weight%, C: 0.06 to 0.20% Si: 0.01% or less Mn: 0.5 to 2.0% P: 0.02 to 0.10% as a basic component, and Ni: 2.0% or less Mo: 0.5% or less Cu: 0.05 to 0.30% Cr: 2.0% or less Pb: 0.30% or less Includes one or two or more and balance Fe And unavoidable impurities. The sulfide-containing free-cutting steel excellent in machinability according to claim 1.

The present invention will be described in detail below. In order to facilitate the addition of Ca or Mg sulfide powder to molten steel and to achieve uniform dispersion in molten steel, the present invention uses iron powder to attach Ca or Mg sulfide powder around iron powder. It is intended to increase the overall specific gravity. As the method, a mechanical alloying method, so-called iron powder and Ca or Mg sulfide particles are mixed in a ball mill, and mechanical compression, fracture, and joining are repeated, and Ca or Mg sulfide particles are uniformly distributed in the iron powder. A dispersed powder forms. Therefore, the average particle size is 10 to 3
Pretreatment is required to mechanically attach 0 μm Ca or Mg sulfide powder to the iron powder surface. The reason for setting the average particle size of Ca or Mg sulfide powder to 10 to 30 μm is that the lower limit of the average particle size of Ca or Mg sulfide powder is set to 10 μm in order to secure the finished surface roughness. Regarding the upper limit, if the size is too large, cracks tend to occur during the drawing process starting from Ca or Mg sulfide inclusions.
It was set to 0 μm or less.

The reason why these Ca or Mg sulfide powders are directly added to the molten steel is that, for example, FeS and FeCa are added and C is added.
This is because large-scale CaS cannot be dispersed by the method of precipitating aS. Further, the reason for adding Ca or Mg sulfide powder alone as a mixed powder is as follows.
This is because the Ca or Mg sulfide powder aggregates and increases in volume, and because the specific gravity is smaller than that of the molten steel, it floats and does not remain in the molten steel. The agglomerated Ca or Mg sulfide powder was mixed with the individual Ca or Mg sulfide powder to reduce the separation volume. The reason why iron powder is selected is that when it is added to molten steel, it melts without being separated and floated.

Thus, Ca having an average particle size of 10 to 30 μm
Alternatively, the lower limit of the average particle diameter of the iron powder is preferably 200 μm or more so that the Mg sulfide powder mechanically adheres to the surface of the iron powder and is uniformly dispersed. The upper limit is preferably 400 μm or less because if the size becomes too large, Ca or Mg sulfide powder and iron powder are likely to be non-uniformly mixed. The volume ratio of iron powder to Ca or Mg sulfide powder is 3
The reason for the above is that by increasing the surface area of iron powder, Ca or M
This is because the sulfide powder tends to adhere. In this way, the pretreatment powder was added to the molten steel to obtain an average sulfide particle size of 10 to 3
0 μm Ca or Mg sulfide 0.010 to 0.040
%, Ca or Mg sulfide must be 0.010% or more in order to secure machinability.
Since the toughness decreases as the content of Ca or Mg sulfide increases, its upper limit was made 0.040%. Furthermore, when the mixed powder is added to the molten steel in the ladle, the molten steel temperature becomes high and Ca or Mg
Since the sulfide powder will dissolve, the place where the mixed powder is added is C
A molten steel in the tundish and / or in the mold in which the a or Mg sulfide powder does not dissolve and the iron powder sufficiently dissolves is desirable.

[0008]

Next, in order to achieve the desired characteristics of the present invention, it is necessary to limit the amount of each constituent element to an appropriate range as described below. C: 0.06 to 0.20% If the content of C is less than 0.06%, the strength cannot be secured, and if it exceeds 0.20%, the machinability deteriorates, so 0.20. % Or less. Si: 0.01% or less Since Si increases hardness and deteriorates machinability, Si is 0.0
It is 10% or less. Mn: 0.5 to 2.0% Mn is added for deoxidizing, improving hot workability of steel, further improving hardenability, and improving strength and toughness of steel. In order to effectively develop such effects,
It is necessary to add it in the range of 0.5 to 2.0%. P: 0.02 to 0.10% P is required to be 0.02% or more for improving the machinability, and is preferably 0.10% or less from the viewpoint of hot workability.

Next, the reason why the strength improving element group of the second invention is defined in the proper range of the amount of constituent elements will be described. Ni: 2.0% or less Ni is an element that improves the toughness, but if it exceeds 2.0%, the cost increases, so it was made less than that. Mo: 0.5% or less Mo is an element that improves hardenability, but if it exceeds 0.5%, the cost becomes large, so the content is made less than that. Cu: 0.05 to 0.30% If Cu is less than 0.05%, there is no effect on machinability and grindability, and if it exceeds 0.30%, Cu segregates at the grain boundaries, and the solidification process of continuous casting. Since there are many surface flaws on the slab, 0.05
Was set to 0.30%. Cr: 2.0% or less Cr is an element that improves hardenability like Mo, but if it exceeds 2.0%, its effect is saturated. Pb: 0.30% or less Pb further improves machinability and imparts strength and toughness, but if it exceeds 0.30%, segregation of Pb becomes large,
Mechanical properties deteriorate.

[0010]

[Examples] A mixed powder was prepared by placing iron powder and Ca sulfide powder or Mg sulfide powder together with a tungsten carbide ball in a container.
It was prepared by mixing with a Lumil. Table 1 shows the average particle sizes of the iron powder and the Ca sulfide powder or the Mg sulfide powder at that time. The average particle size is classified by sieving various meshes,
A particle size distribution map was created and the average value was displayed. At this time, it is desirable that the surface of the iron powder be as uneven as possible. 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 300 kg, poured into a 300 kg mold, and press-molded mixed powder was added to the casting flow. Ca for each charge
Or, the addition of Mg sulfide is 5 kg. On the other hand, a comparative material was manufactured by adding an iron-sulfur alloy to a melting furnace and then pouring it into a 300 kg mold. Both cast pieces have a diameter of 50 m by hot casting.
After forming a round bar of m, normalizing was performed at 920 ° C. for 2 hours.

[0011]

[Table 1] CaS in Table 1: calcium sulfide powder, MgS: magnesium sulfide powder, average particle size: μm unit, volume ratio: iron powder / magnesium sulfide powder.

Table 2 shows steels (1) to (1) manufactured by the manufacturing method of the present invention.
Chemical composition of (5) and comparative steels (6) to (8), Ca or M
The measurement results of the dimensions and the finished area of the sulfide inclusions are shown. Comparative steels (6) to (7) use mixed powders, but the particle size of iron powder or Ca or Mg sulfide powder is outside the scope of the present invention, and (8) is the current production method, that is, , A steel produced by adding an iron-calcium alloy to a melting furnace. The dimensions of Ca or Mg sulfide inclusions were measured with an optical microscope in the forging direction cross section, and the average cross section was shown. Finished surface roughness, tool material: high speed steel,
Cutting method: Flange cutting, cutting speed 80 m / min, feed: 0.05 mm / rev, cutting oil: the finished surface cut under the conditions of use was measured by a stylus roughness meter. As is apparent from Table 2, the diameter produced by the method of the present invention, 50
The size of the Ca or Mg sulfide inclusions contained in (1) to (5) of the mm round bar is significantly larger than that of the round bar (8) manufactured by the current manufacturing method, and the finished surface roughness is It can be seen that it is extremely small and excellent. The sizes of the Ca or Mg sulfide inclusions of the round bars (6) to (7) manufactured by adding the iron powder or Ca or Mg sulfide powder outside the scope of the present invention are the same as those of the steel of the present invention. However, the distribution of Ca or Mg sulfide-based inclusions in the mixed powder is non-uniform, so that it is found that the finished surface roughness is inferior.

[0013]

[Table 2A]

[0014]

[Table 2B]

[0015]

As described above, according to the present invention, the free-cutting steel containing Ca or Mg sulfide and having excellent finished surface roughness in which Ca or Mg sulfide inclusions having a large size are dispersed is toughness, It excels in both machinability and industrial effects.

Claims (2)

[Claims] 1. By weight%, C: 0.06 to 0.20% Si: 0.01% or less Mn: 0.5 to 2.0% P: 0.02 to 0.10% balance Fe and unavoidable And kneading of iron powder having an average particle size of 200 to 400 μm and sulfide powder having an average particle size of 10 to 30 μm with a volume ratio of iron powder to Ca or Mg sulfide powder of 3 or more. The sulfide average particle size of 10 to 30 is added to the steel material by adding the prepared pretreatment powder to the molten steel.
A sulfide-containing free-cutting steel having excellent machinability, characterized by containing 0.01 to 0.040% of μm. 2. By weight%, C: 0.06 to 0.20% Si: 0.01% or less Mn: 0.5 to 2.0% P: 0.02 to 0.10% as a basic component Further, Ni: 2.0% or less Mo: 0.5% or less Cu: 0.05 to 0.30% Cr: 2.0% or less Pb: 0.30% or less One or more types are included, The sulfide-containing free-cutting steel with excellent machinability according to claim 1, wherein the balance is Fe and unavoidable impurities.