JPH108183A - Production of steel for mechanical structural purpose excellent in machinability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel excellent in machinability by separately producing compounds forming composite inclusions in which forms are regulated by premelting and mixing the same to a molten steel. SOLUTION: A steel for mechanical structures such as an SC material in JIS is melted, and on the other hand, apart from the steel, compounds forming composite inclusions capable of improving the machinability of the above steel are separately produced by premelting. As these compounds, seven kinds of oxides such as CaO, Al2 O3 , SiO2 are used, furthermore, the ones easily addable to the molten steel are suitable, and powdery or granular ones are preferably used. Thus, in the steel for mechanical structures after casting, solidifying and rolling, the composite inclusions composed of gehlenite, anorthte or the like in which forms are regulated are dispersed to improve it machinability. Then, since Ca is not singly added to the molten steel, in the case S is contained in the steel, there occurs no failure accompanying the clogging of the nozzles of a ladle, a tundish or the like caused by the formation of CaS.

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 steel for machine structural use suitable for producing steel for machine structural use having excellent machinability.

[0002]

2. Description of the Related Art Machine structural steel such as carbon steel for machine structural use and alloy steel for mechanical structure is used for automobile parts (bolts, nuts, gears, shafts, rods, arms, etc.) and machine tool parts (bolts, nuts, gears). , Splines, shafts, cylinders, etc.) are used for a remarkably wide range of applications as materials for various mechanical structural parts. In some cases, it is also used in large quantities as sintering steel in which the C content is set low and a surface hardening treatment is applied after machining.

When various parts (for example, screws, bolts, nuts, precision mechanical parts, etc.) made of such steel for machine structural use are manufactured by cutting, not only mechanical properties but also machinability are required. And Pb, S, Se, Te, Bi and the like as machinability improving elements.
In some cases, a steel for machine structural use which is excellent in machinability and contains an appropriate amount of two or more kinds is used.

In order to further improve the machinability, it is conceivable to increase the amount of these machinability improving elements. However, if the content of these machinability improving elements is too large, other materials may be used. There is a limit to the increase in the amount of the machinability-improving element to be added, because the properties are rather deteriorated, and the productivity is reduced when a larger amount is to be contained.

[0005] On the other hand, the machinability of steel for machine structural use is also improved by controlling the form of inclusions by adding Ca. The improvement of the machinability by the addition of Ca is obtained by reducing the tool wear and extending the tool life by coating the tool with the morphologically controlled oxide contained in the steel during cutting. It is something that can be done.

[0006]

However, when such improvement in machinability by adding Ca is applied to steel for machine structural use having a high S content, the addition of Ca leads to the formation of CaS. However, during casting, there is a problem that the nozzle of the ladle or the dundish is likely to be clogged, and the frequency of replacing the nozzle is increased, which may lower the productivity.

In addition, when Ca is added by adding Ca alone or by adding a Ca—Si wire, it is necessary to control the components between Al, Si, O, etc. to form inclusions. For this reason, there has been a problem that it is sometimes difficult to stably obtain a more preferable form of inclusions that can improve machinability.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is intended to prevent the generation of CaS even in steel for machine structural use having a high S content, and to provide a nozzle for casting. Obstruction can be prevented and the form control of inclusions that can improve machinability can be easily and reliably performed, and a steel for machine structural use with excellent machinability can be obtained. The purpose is to be able to.

[0009]

According to the present invention, there is provided a method for producing a steel for machine structural use having excellent machinability, comprising the steps of: When manufacturing machine structural steel with improved machinability by including, separately producing a compound that generates the composite inclusions by pre-melt, mixing the compound into molten steel of the steel component for mechanical structure, The present invention is characterized in that a steel for machine structural use containing the composite inclusion of which form is controlled in the steel after casting and solidification is obtained.

[0010] In the embodiment of the method for producing steel for machine structural use excellent in machinability according to the present invention, claim 2 is provided.
As described in the above, compounds that form composite inclusions are CaO, Al ₂ O ₃ , SiO ₂ , CaO.Al ₂ O ₃ ,
_{CaO · Al 2 O 3 · SiO} 2, 2CaO · Al 2 O 3
· SiO ₂ , CaO · Al ₂ O ₃ · 2SiO ₂ , and as described in claim 3, the compound that forms the composite inclusion is powdered or granulated by premelt. The powdery or granular compound can be mixed into the molten steel of the steel component for machine structural use, and as described in claim 4, the compound that forms the composite inclusion is The steel component for machine structural use may be mixed into the molten steel at the end of refining of the molten steel.

[0011] Similarly, in the method for producing a steel for machine structural use excellent in machinability according to the present invention, as described in claim 5, the composite inclusions whose form is controlled have a melting point of 1400-16.
It can be a composite oxide at 00 ° C., and as described in claim 6, the morphologically controlled composite inclusions are gehlenite (2CaO.Al ₂ O ₃ .SiO ₂ ) and anorthite ( CaO _· Al ₂ O 3 _· 2Si
O ₂ ), and the content of the morphologically controlled composite inclusion in the steel is 0.01 to 0.03% by weight as described in claim 7. As described in claim 8, the composite inclusion for improving machinability is MnS and 2CaO.Al ₂
O ₃ · SiO ₂ and / or CaO _· Al _{2 O} 3 _{· 2}
It may be in a composite form with SiO ₂ .

[0012] In the method for producing a machine structural steel excellent in machinability according to the present invention, as described in claim 9, the machine structural steel is a Cr-containing machine structural steel. And as described in claim 10,
One or two or more selected from Pb, S, Se, Te, and Bi in the steel components for machine structural use have a total content of 0.02 to 0.02.
The content can be 0.50%.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a machine structural steel excellent in machinability according to the present invention, the machine structural steel to be applied includes SC material of JIS G 4051 and JIS
G 4102 SNC material, JIS G 4103 SNCM material, JIS G 4104 SCr material, J
SCM material of IS G 4105, JIS G 410
6, SMn and SMnC materials, JIS G 4107, 4
The present invention can be applied to SNB material of No. 108, SACM material of JISG 4202, and other materials containing appropriate components.

In the present invention, while such a steel for machine structural use is melted, a compound capable of forming a composite inclusion for improving the machinability of the steel for machine structural use is separately manufactured by premelt. I do.

Compounds that form such composite inclusions include CaO, Al ₂ O ₃ , SiO ₂ , CaO.Al
₂ O ₃ , CaO.Al ₂ O ₃ .SiO ₂ , 2CaO.A
_{l 2 O 3 · SiO 2,} CaO · Al 2 O 3 · 2SiO 2
It is desirable to use one or more oxides selected from the above.

It is preferable that such a compound can be easily added to molten steel, and it is desirable that the compound be in the form of powder or granules.

Therefore, a powdery or granular compound is blown into the molten steel of the steel component for machine structural use, particularly preferably at the end of refining of the molten steel, and then the ingot is cast by ingot casting or continuous casting. And slabs, and are subjected to slab rolling, product rolling, and the like to obtain materials such as free-cutting stainless steel bars and free-cutting stainless steel bars.

Thus, composite inclusions whose form is controlled are dispersed in the steel for machine structural use after casting, solidification, and rolling. In this case, the composite inclusions are oxidized on the tool surface during cutting. The melting point is 1400-1600 ° C. so that the tool life is extended by being coated as an object.
It is desirable that the composite inclusions whose morphology is controlled are CaO-Al ₂ O ₃ -Si shown in FIG. 1 as Ca-based morphology-controlled inclusions.
Gehlenite (2C) in region I in the O ₂ ternary phase diagram
_{aO · Al 2 O 3 · SiO} 2) and, similarly anole site region II in the state diagram of FIG. 1 (CaO · _Al 2 O
₃ · 2SiO ₂₎ It is desirable to at least one of a.

It is desirable that the content of such composite inclusions in steel is in the range of 0.01 to 0.03% by weight. If the content of composite inclusions in steel is small, machinability is improved. The effect tends to be small, and if it is too large, it tends to adversely affect other properties such as mechanical properties.

Further, the composite inclusions for improving machinability include MnS and 2CaO.Al ₂ O ₃ .SiO ₂ and / or
Alternatively, by forming a composite form with CaO.Al ₂ O ₃ .2SiO ₂ , it is possible to further improve the machinability while reducing the influence on other properties such as mechanical properties. Sometimes it is done.

[0021]

According to the method for producing steel for machine structural use having excellent machinability according to the present invention, there is provided a steel for mechanical structure having improved machinability by including complex inclusions whose form is controlled in the steel. Upon production, a compound that produces the composite inclusion is separately produced by premelt, and the compound is mixed into molten steel of a steel component for machine structural use, and the form-controlled composite inclusion is cast in steel after casting and solidification. Since the steel for machine structural use contained in the above-mentioned alloy contains composite inclusions consisting of morphologically controlled gehlenite and anorthite in the cast and solidified machine structural steel, the machinability is reduced. It is an improved machine structural steel.

In the method of the present invention, since Ca is not added alone or in the form of Ca-Si or the like to the molten steel of the steel component for machine structural use, S is contained in the steel for machine structural use. In the case, CaS is generated and there is no trouble that was conventionally observed with nozzle blockage such as a ladle or a tundish,
Further, in comparison with the conventional method in which it was difficult to obtain a composite inclusion having a desired morphology control when Ca was added, the compound for producing a composite inclusion separately manufactured in the present invention is a steel component for a mechanical structure. Since it is mixed into the molten steel, the desired inclusions with controlled morphology are surely present in the steel after casting and solidification, and a steel for machine structure with excellent machinability is obtained. Will be done.

In addition, Pb, S, S
e, Te, and Bi are contained in a total of 0.02 to 0.50% of one or more selected from e, Te, and Bi, so that machinability can be improved without lowering mechanical properties. Further improvement can be achieved.

[0024]

EXAMPLE In the example of the present invention, No. 1 in Table 1 was used. 1 to 1
In addition to melting the molten steel of the steel component for machine structure shown in FIG.
CaO.Al ₂ O ₃ , which is a compound for forming composite inclusions in a separate premelt by adjusting the contents of a, Al, Si, and O
And CaO.Al ₂ O ₃ .SiO ₂ powder were produced, and the powder was mixed into molten steel as a steel component for machine structural use. After casting, slab rolling and product rolling were performed. _A steel bar for a machine structure according to an example of the present invention having a content of ₂ O ₃ · SiO ₂ and / or CaO · Al ₂ O ₃ · 2SiO ₂ was produced.

[0025]

[Table 1]

On the other hand, in the comparative example of the present invention, the addition of Ca for controlling the form of the oxide-based inclusions was carried out by using a Ca—Si wire using No. The molten steel of the steel components for machine structure shown in Nos. 1 to 10 was smelted and cast, and after casting, slab rolling and product rolling were performed to produce a steel bar for machine structure of a comparative example of the present invention.

[0027]

[Table 2]

Next, a machinability evaluation test was carried out on each of the machine structural steel bars under the conditions shown in Table 3. Table 4 shows the results.

[0029]

[Table 3]

[0030]

[Table 4]

As shown in Table 4, in the embodiment of the present invention, a compound for forming composite inclusions separately manufactured by premelt is mixed into molten steel, and after casting and solidification, the composite inclusions whose form is controlled are formed in the steel. Since the materials are dispersed, the machinability is good and the variation in machinability is considerably small.

On the other hand, in the comparative example, by adding Ca as Ca-Si during the smelting of the steel for machine structural use, a composite inclusion having a controlled morphology is formed. In some cases, it is difficult to form inclusions, so that the machinability is slightly inferior or the machinability greatly varies.

[0033]

According to the method of the present invention for producing steel for machine structural use having excellent machinability, a steel for machine structural use having improved machinability by including complex inclusions whose form is controlled in the steel is provided. Upon production, a compound that produces the composite inclusion is separately produced by premelt, and the compound is mixed into molten steel of a steel component for machine structural use, and the form-controlled composite inclusion is cast in steel after casting and solidification. Since the steel for machine structural use included in (1) and (2), composite inclusions consisting of morphologically controlled gehlenite and anorthite are present and dispersed in the cast and solidified machine structural steel, This has a remarkable effect that it is possible to produce a steel for machine structural use having significantly improved properties.

In the method of the present invention, since Ca is not added alone or in the form of Ca-Si or the like to the molten steel of the steel component for machine structural use, S is contained in the steel for machine structural use. In the case, CaS is generated and there is no trouble with nozzle clogging such as a ladle or a tundish, and it is difficult to obtain a desired morphologically controlled composite inclusion when Ca is added. Therefore, in the present invention, the compound for forming composite inclusions separately manufactured is mixed into the molten steel of the steel component for machine structural use, so that the desired inclusion-controlled composite inclusions are surely contained in the steel. Therefore, a remarkable effect that it is possible to stably obtain steel for machine structural use having excellent machinability without variation in machinability is provided.

[Brief description of the drawings]

FIG. 1 shows CaO—Al ₂ O ₃ —S showing a region in which gehlenite and anorthite, which are composite inclusions, are formed.
FIG. 3 is a diagram of an iO ₂ ternary system.

Claims (10)

[Claims] When producing a steel for machine structural use whose machinability is improved by including a composite inclusion of which form is controlled in the steel, a compound for producing the composite inclusion is separately produced by a premelt. Excellent in machinability, characterized in that the compound is mixed into molten steel of a steel component for a machine structure, and a steel for a machine structure containing the form-controlled composite inclusion in the steel after casting and solidification is obtained. Manufacturing method of steel for machine structural use. 2. The compound that forms a composite inclusion is CaO,
Al ₂ O ₃ , SiO ₂ , CaO.Al ₂ O ₃ , CaO.
Al ₂ O ₃ .SiO ₂ , 2CaO.Al ₂ O ₃ .SiO
_{2, CaO · Al 2 O 3} · 2SiO method for manufacturing a machine structural steel excellent in machinability according to claim 1 which is selected from among _2. 3. The method according to claim 1, wherein the compound that forms the composite inclusion is produced in a powdery or granular form by a premelt, and the powdery or granular compound is mixed into molten steel of a steel component for machine structural use. Method for producing steel for machine structural use having excellent machinability. 4. A machine structure excellent in machinability according to claim 1, wherein a compound forming a composite inclusion is mixed into the molten steel as a steel component for a machine structure at the end of refining of the molten steel. Steel production method. 5. The composite inclusion having a controlled morphology has a melting point of 14
5. A composite oxide having a temperature of from 00 to 1600 ° C.
The method for producing a steel for machine structural use excellent in machinability according to any one of the above. 6. The composite inclusion having a controlled morphology is at least one of gehlenite (2CaO.Al ₂ O ₃ .SiO ₂ ) and anolsite (CaO.Al ₂ O ₃ .2SiO ₂ ). 5. The method for producing a steel for machine structural use excellent in machinability according to any one of the above items 5. 7. The steel for machine structural use having excellent machinability according to claim 1, wherein the content of the composite inclusions whose form is controlled is 0.01 to 0.03% by weight in the steel. Manufacturing method. 8. The composite inclusion for improving machinability is Mn.
S and 2CaO.Al ₂ O ₃ .SiO ₂ and / or C
The method for producing a steel for machine structural use having excellent machinability according to any one of claims 1 to 7, wherein the steel is in a composite form with aO.Al ₂ O ₃ .2SiO ₂ . 9. The method according to claim 1, wherein the machine structural steel is a Cr-containing machine structural steel. 10. Pb, S, S in a steel component for machine structural use.
9. The machine structure excellent in machinability according to any one of claims 1 to 8, wherein one or more selected from e, Te, and Bi are contained in a total amount of 0.02 to 0.50%. Method for manufacturing steel.