KR20130087618A - High-carbon steel wire having excellent drawability and fatigue properties after drawing - Google Patents

Abstract

High-performance, high-carbon wire rod with very low disconnection rate during drawing and excellent fatigue characteristics after drawing, even in stringent applications in which the inclusions after wire rolling are fine. (% SiO ₂ ) = 40 to 95%, (% CaO) = 0.5 to 30%, (% Al in an oxide-based nonmetallic inclusion (hereinafter referred to as a "size target inclusion") having a diameter of 1 µm or more and a circle equivalent diameter of 1 µm or more. ₂ O ₃ ) = 0.5 to 30%, (% MgO) = 0.5 to 20%, (% MnO) = 0.5 to 10%, and (% Na) = 0.2 to 7%, (% F) = 0.17 The ratio of the number of inclusions (hereinafter referred to as "composition target inclusion") satisfying the to 8% and the number of inclusion inclusions / size of the target inclusions x100 is 80% or more.

Description

HIGH-CARBON STEEL WIRE HAVING EXCELLENT DRAWABILITY AND FATIGUE PROPERTIES AFTER DRAWING}

TECHNICAL FIELD The present invention relates to a high carbon steel wire rod and a valve spring wire rod excellent in drawing property and fatigue resistance after drawing.

After wire drawing, the wire rod of the present invention is used, for example, steel cords for automobile tires, small wires for cutting silicon for solar cells or semiconductors, automotive engine valve springs, long rubber belts, various wires for aircrafts, bridge ropes, and the like.

In general, the high carbon steel wire rod provided for drawing is capable of high speed drawing and needs to be excellent in fatigue resistance after drawing. One of the factors adversely affecting these properties is a hard oxide-based nonmetallic inclusion. ·

Among the oxide inclusions, monolayer inclusions such as Al ₂ O ₃ , SiO ₂ , CaO, TiO ₂ , MgO, or binary MgO · Al ₂ O ₃ or 2MgO · Al ₂ O ₃ have a high hardness. High and inviscid. Therefore, in order to manufacture high carbon steel wire rods excellent in freshness, it is necessary to increase the cleanliness of molten steel and to soften oxide inclusions.

As described above, Patent Document 1 discloses a method for producing high carbon steel having good freshness as a method of increasing the cleanliness of steel and softening the nonmetallic inclusions. In patent document 2, the manufacturing method of a micro fine wire is disclosed. The basic idea of these techniques is limited to ternary oxide-based nonmetallic inclusions of Al ₂ O ₃ -SiO ₂ -MnO.

In Patent Document 3, by the Spanish company tight area in the non-metallic inclusions in the ternary phase diagram of _{Al 2 O 3, SiO 2,} MnO, has been proposed to improve the freshness of the product. Patent Document 4 discloses a method of reducing harmful inclusions and improving freshness by regulating the amount of Al added in molten steel.

Patent Document 5 relates to the production of steel cords having a non-viscosity inclusion index of 20 or less. After Al deregulation, CaO-containing flux is blown into the ladle molten steel together with a carrier gas (inert gas), followed by Ca, It is proposed to soften the inclusions by blowing an alloy containing one or two or more of Mg and REM.

Among the above methods, the method of modifying ternary nonmetallic inclusions is difficult to control stable composition. On the other hand, the method of controlling a multi-type nonmetallic inclusion is difficult to achieve the reduction of the size and number of inclusions, and to secure ductility. Therefore, improvement of freshness and fatigue resistance after drawing is difficult.

Therefore, Patent Document 6 defines the range of the total oxygen content in a certain range, controls the amount and composition of the non-viscous inclusions, reduces the size and number of the non-viscous inclusions, and ensures the ductility, thereby providing the amount of the non-viscous inclusions and The size distribution is made to be in a preferable state, and the inclusion composition is added to SiO ₂ and MnO to be modified to a poly-based oxide inclusion that selectively contains Al ₂ O ₃ , MgO, CaO, and TiO ₂ to soften the inclusions. High carbon steel wire rods with excellent remarkability, drawing property and fatigue resistance after drawing are realized.

In addition, Patent Document 7 discloses a method of defining the size of hard high SiO ₂ inclusions and reducing the amount of expensive deoxidation alloy used.

In addition, in order to control nonmetallic inclusions to be easier to draw at a lower melting point, some methods of utilizing alkali metal compounds have been proposed. In patent document 8, the method of controlling the amount of alkali metal compounds in a nonmetallic inclusion to 4 to 24% by using the mixture of a Si type | system | group deoxidizer and an alkali metal compound is proposed, and extending | stretching is proposed.

Further, Patent Document 9, the _{Al 2 O 3 -CaO-SiO 2} - there is a MgO-MnO based excellent fatigue strength, characterized in that it contains 0.5 to 10% of an oxide of an alkali metal in the low melting point inclusions Si deoxidized steel is proposed .

Further, Patent Documents 10 and 11 contain 0.5 to 20% of the LiO ₂ , Na ₂ O, and K ₂ O in the low melting point inclusion in the total amount of these LiO ₂ , Na ₂ O, and K ₂ O. A high-cleaning spring steel wire having excellent fatigue characteristics is disclosed. Among them, LiO ₂ , Na ₂ O, and K ₂ O are not equivalent, and particularly, by adding Li, which has strong deoxidizing power, as an origin of the generation of oxide inclusions, the effect is increased when an appropriate amount of LiO ₂ is contained in the oxide inclusions. It is described.

Patent Document 1: Japanese Patent Application Publication No. 57-22969 Patent Document 2: Japanese Laid-Open Patent Publication No. 55-24961 Patent Document 3: Japanese Patent Application Publication No. 54-7252 Patent Document 4: Japanese Unexamined Patent Publication No. 50-81907 Patent Document 5: Japanese Patent Application Publication No. 57-35243 Patent Document 6: Japanese Patent Application Publication No. Hei 4-8499 Patent Document 7: Japanese Patent Publication No. 3294245 Patent Document 8: Japanese Patent Publication No. 2654099 Patent Document 9: Japanese Patent Publication No. 3719131 Patent Document 10: Japanese Unexamined Patent Publication No. 2005-29888 Patent Document 11: Japanese Patent Publication No. 4315825

Non-Patent Document 1: Edited by the Japan Steel Association, Page 3 690

As described above, high carbon steel wire rods having high freshness have been supplied by securing cleanliness of molten steel, soft-nitridation of nonmetallic inclusions, and prevention of Al mixing.

By the way, in recent years, the wire rod which becomes a cause of disconnection by the expansion of the market of the small wire of thin wire rather than the steel cord for a car tire being aimed at the productivity improvement by the omission of the patterning after primary drawing in the wire drawing process of a wire rod. The inclusion size in the layer was much smaller than the conventional (20 µm or more), and the inclusion was not sufficiently stretched only by the conventional inclusion soft-nitriding technique, which made it difficult to cope.

In view of the above circumstances, the present invention is based on a multi-system control technique of an oxide-based nonmetallic inclusion, and also utilizes compounds other than oxides, thereby causing a special decrease in melting point and viscosity of the nonmetallic inclusion, By miniaturizing the inclusions, it is a problem to supply a high-performance high carbon wire rod having a very low disconnection rate during drawing and excellent in fatigue characteristics after drawing.

The inventors conducted detailed investigations on the relationship between the composition of the nonmetallic inclusions and the melting point and viscosity. As a result, by coexisting alkali metals such as Na and trace amounts of fluorine in the multi-component inclusions, the melting point and viscosity of the inclusions can be further reduced, and the formation of crystal phases can be suppressed. It was found that it could be refined.

In addition, the inventors have found that NaF molecules also have an effect of slowing down the formation of a crystalline phase of a nonmetallic inclusion.

The present invention has been made based on the above findings, and its main points are as follows.

(1) In mass%, C: 0.5 to 1.2%, Si: 0.15 to 2.5%, Mn: 0.20 to 0.9%, P: 0.025% or less, S: 0.004 to 0.025%, Al: 0.000005 to 0.002%, Ca: It is a high carbon steel wire rod containing 0.00001 to 0.002%, Mg: 0.00001 to 0.001%, Na: 0.000005 to 0.001%, F: 0.000003 to 0.001%, total oxygen content of 16 to 30 ppm, and the balance of Fe and unavoidable impurities. (% SiO ₂ ) in oxide-based nonmetallic inclusions (hereinafter referred to as "size target inclusions") having a short diameter of 0.5 µm or more, a long diameter of 1.0 µm or more, and a circle equivalent diameter (surface conversion diameter) of 1 µm or more, as seen in the cross section of the wire rod L direction. = 40 to 95%, (% CaO) = 0.5 to 30%, (% Al ₂ O ₃ ) = 0.5 to 30%, (% MgO) = 0.5 to 20%, (% MnO) = 0.5 to 10% The number ratio of inclusions (hereinafter referred to as "composition target inclusions") satisfying (% Na) = 0.2 to 7% and (% F) = 0.17 to 8%, the number of inclusions to be included / size to be included × 100 is 80% Characterized in that fresh and good fatigue characteristics after fresh high carbon steel wire rod of.

Here, (% SiO ₂ ), (% CaO), (% Al ₂ O ₃ ), (% MgO), (% MnO), (% Na), and (% F) are respectively SiO ₂ , CaO, the content of _{Al 2 O 3, MgO, MnO} , Na, F is (% by weight). (Hereafter, same)

 (2) Furthermore, REM: 0.000005 to 0.001%, and the said composition object inclusion satisfies (% T.REM) = 0.3-1.0%, (% S) = 0.05-0.2% at an average concentration. The high carbon steel wire rod excellent in the freshness and fatigue property after drawing of said (1) characterized by the above-mentioned.

Here, (% T.REM) and (% S) are the total of rare earth elements in inclusions, and content of S (mass%), respectively. (Hereafter, it is the same.)

(3) Furthermore, B: 0.0005 to 0.002%, The high carbon steel wire rod excellent in the freshness and fatigue property of the said (1) or (2) characterized by the above-mentioned.

(4) Further, Cr: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Cu: 0.05 to 1.0%, Ti: 0.001 to 0.25%, Nb: 0.001 to 0.25%, V: 0.001 to 0.25%, Mo: A high carbon steel wire rod having excellent freshness and fatigue property after drawing according to any one of (1) to (3), which contains one or two or more of 0.05 to 1.0% and Co: 0.1 to 2%.

Industrial Applicability According to the present invention, a high-performance high carbon wire rod can be obtained in which the inclusions after wire rod rolling can be made fine, and the disconnection rate at the time of drawing is very low, which can cope with stringent applications such as small wire, and also has excellent fatigue characteristics after drawing.

Hereinafter, the present invention will be described in detail. First, the detail of the mechanism of this invention is demonstrated. In addition, unless otherwise indicated, "%" shall mean "mass%."

The conventional multi-system control technique of nonmetallic inclusions is a technique of lowering the melting point and viscosity of the silicate inclusions. Of these silicate inclusions, Na and F are very affinity. From a micro point of view, Na ions and F ions are located adjacent to each other and affect the melting point and viscosity of the silicate inclusions as NaF molecules.

Whereas the NaF-containing oxide starts to melt at a temperature of 1200 ° C. or lower, the Na ₂ O alone oxide or F (eg CaF ₂ ) alone oxide does not start melting unless the temperature is higher than 1200 ° C. That is, by coexisting Na and F, a very low melting point can be realized.

The melting point of 1200 ° C. or less is a temperature close to the wire rolling temperature (1000 to 1200 ° C.) as well as to the cold rolling (1150 to 1300 ° C.) of the breakdown process of the continuously cast slab. Conventionally, the stretching at the time of rolling of an inclusion has been considered to mainly occur in the lump rolling process. However, when Na and F coexist in an interference | inclusion, an interference | inclusion is extended not only in a pulverization rolling process but a wire rod rolling process. Therefore, by coexisting Na and F, it is possible to refine | miniaturize a inclusion significantly.

In the nonmetallic inclusions, there are potentials in which various crystal phases are formed depending on the composition thereof. However, when the crystal phase is actually formed and it grows large, it becomes a starting point such as disconnection. On the other hand, addition of NaF molecule has the effect of remarkably slowing the formation of the crystal phase in addition to the effects of lowering the melting point and lowering the viscosity. As a result, since the starting point of disconnection etc. reduces, the disconnection rate at the time of drawing becomes very low.

In addition, the effect of Na and F on inclusion elongation depends on the amount of NaF calculated in inclusions, and when the amount of NaF increases, elongation is improved. In this case, the calculated NaF amount refers to the mass% of NaF in inclusions when Na and F are bonded at a molar ratio of 1: 1.

If the balance between Na and F is bad and excess Na or F is present, there is little effect on inclusion stretchability. For this reason, it is good to add so that (% Na) and (% F) may be 1: 1 by molar ratio, ie, 1: 0.83 by mass ratio.

Patent documents 8 to 11 disclose a method of utilizing an alkali metal oxide represented by Na. However, neither document mentions the necessity for coexisting Na and F based on silicate-based multi-element inclusions. That is, the technical idea of this invention and this invention differ.

Next, in this invention, the reason etc. which determined the content rate of each oxide which comprises an oxide type interference | inclusion are demonstrated.

First, the reason for limitation of the total amount of oxygen in steel is demonstrated. In the wire rod with a total oxygen content of more than 30 ppm, the amount of non-metallic inclusions increased, so that the avoidance of disconnection was not sufficient in the workpiece used for strict applications, so the upper limit was 30 ppm. On the other hand, when a large amount of strong deoxidizer such as Al or Mg is used, it is easy to make the total oxygen amount less than 16 ppm. However, in order to control the composition of the non-metallic inclusions in the wire rod of the present invention, the total oxygen is 16 ppm or more. need. When the total oxygen amount is less than 16 ppm or more than 30 ppm, the die life becomes extremely bad. A more preferable range of the total amount of oxygen is 17 to 25 ppm.

Next, control of the composition and form of the nonmetallic inclusion in the present invention will be described.

The steel wire rod of the present invention is an oxide-based nonmetallic inclusion (size target inclusion) having a short diameter of 0.5 μm or more, a long diameter of 1.0 μm or more, and a circle equivalent diameter (surface equivalent diameter) of 1 μm or more, as seen in the cross section of the wire L direction (length direction), ( % SiO ₂ ) = 40 to 95%, (% CaO) = 0.5 to 30%, (% Al ₂ O ₃ ) = 0.5 to 30%, (% MgO) = 0.5 to 20%, (% MnO) = 0.5 to Inclusions (composition to be included) satisfying 10% and satisfying (% Na) = 0.2 to 7% and (% F) = 0.17 to 8% are the number ratio (number of inclusions to be formed / size to be included × 100 80% or more).

In the wire rod L section, inclusions having a short diameter of less than 0.5 µm are inclusions having a small original size or being easily deformed during rolling. Inclusions having a long diameter of less than 1.0 µm and a circle equivalent diameter of less than 1.0 µm are inclusions having a small original size. These inclusions are unlikely to cause deterioration of freshness or fatigue properties.

Accordingly, in the present invention, oxide-based nonmetallic inclusions having a short diameter of 0.5 μm or more, a long diameter of 1.0 μm or more, and a circle equivalent diameter of 1 μm or more, which are seen in the cross section of the wire L direction, are referred to as “size object inclusions”.

Next, the reason for limitation of the composition range is demonstrated about a composition object inclusion.

For the soft nitriding and miniaturization of nonmetallic inclusions aimed at by the present invention, a combination of oxide compositions in a plural system is first required. The basis of the oxide composition is a five-membered system of SiO ₂ -CaO-Al ₂ O ₃ -MgO-MnO, and by simultaneously containing Na and F therein, the effects of softening and miniaturization of nonmetallic inclusions are exerted.

SiO ₂ is an important oxide that forms the duration of the silicate inclusions. If (% SiO ₂ ) is less than 40%, the poly-based inclusion of the base itself does not become a silicate inclusion, and the effect of the present invention cannot be exhibited. If (% SiO ₂ ) is more than 95%, it is not already a polymorphic inclusion, and deterioration in quality due to large SiO ₂ occurs.

 (% CaO) needs to be 0.5% or more in order to acquire the effect of the melting | fusing point and the viscosity fall by polymorphic inclusion. If (% CaO) exceeds 30%, CaO rich hard inclusions are produced, resulting in deterioration of quality.

When Al ₂ O ₃ is in an appropriate amount, it contributes to inclusion softening, but when (% Al ₂ O ₃ ) exceeds 30%, hard Al ₂ O ₃ inclusions are generated, and the quality is greatly deteriorated. If (% Al ₂ O ₃ ) is less than 0.5%, the effect of the multi-element inclusions cannot be obtained.

(% MgO) needs to be 0.5% or more in order to acquire the effect of the melting | fusing point and the viscosity fall by a multi-component inclusion. When (% MgO) exceeds 20%, harmful inclusions, such as oribin or posthenite (2MgO.Al ₂ O ₃ ), are produced.

(% MnO) needs to be 0.5% or more in order to acquire the effect of the melting | fusing point and the viscosity fall by a multi-component inclusion. (% MnO) is more than 10%, as the silicate inclusions, Spain four tight _- is a _{(SiO 2 MnO-Al 2 O} 3) inclusion is no longer exerted the effect of Na and F was added.

Na and F are very important components in the present invention. If (% Na) is less than 0.2%, there is no improvement effect of inclusion stretchability. On the other hand, when (% Na) exceeds 7%, the effect saturates, and a problem such as a sudden increase in the amount of oscillation upon addition of Na occurs. Preferably less than 4% is good.

In addition, when (% F) is less than 0.17%, there is no effect of improving inclusion elongation. When (% F) exceeds 8%, the effect saturates and damages such as a sudden increase in the amount of refractory loss increase. As described above, since Na and F become NaF molecules in the inclusions and exert their effects, the molar ratio of Na and F in the nonmetallic inclusions is 1: 1, that is, in a mass ratio of (% Na): (% F) It is recommended to add it as close to 1: 0.83.

Incidentally, when the oxide-based nonmetallic inclusions (size target inclusions) having a short diameter of 0.5 μm or more, a long diameter of 1.0 μm or more, and a circle equivalent diameter of 1 μm or more shown in the cross section of the wire rod were counted, inclusions satisfying the above composition among the size target inclusions (composition targets) It is necessary that the ratio of the number of inclusions (the number of inclusion targets / size of target inclusions x 100) should be 80% or more.

If the number ratio is less than 80%, it means that the effect of inclusion extension by Na + F is nostalgic. In addition, below 80% means that a certain amount of inclusions which do not belong to plural inclusions, such as MgO-based or Al ₂ O ₃ -based hard inclusions, are present.As a result, freshness and fatigue after freshening Properties are impaired.

The reason for defining the size of inclusions is to count only inclusions of a size that degrades freshness or fatigue characteristics.

In the present invention, Na and F are added together in the steel, Na and F are contained in the silicate-based oxide inclusions together, and the composition of the inclusions is controlled to ensure excellent freshness and fatigue properties after drawing. . In recent years, the use of steel wires to be thinner has been increasing, and in such applications, the high-carbon steel wire of the present invention exhibits particularly excellent performance.

The addition method of Na and F may be added as a NaF compound, and Na and F may be separately (for example, Na ₂ CO ₃ and CaF _2). Etc.) can also be added.

Further, if when the addition of F, at the same time added with a metal Si, since the gasified SiF ₄ is produced and, F is the yield deterioration is to be avoided.

By controlling (% T.REM) (content of the sum of rare earth elements such as La, Ce, and Nd) and (% S) in the nonmetallic inclusions, the freshness can be further improved. The reason for this is as follows.

REM (La, Ce, Nd, etc.) has strong affinity with S and enters in a polymorphic inclusion while fixing S in the form of REM oxysulfide (REM ₂ O ₂ S). Thereby, the amount of solid solution S in steel can be reduced, and precipitation of MnS is suppressed. MnS precipitated in steel may become a starting point of the disconnection during wire drawing, and the suppression of this precipitation improves the freshness and the fatigue property after drawing.

(% T. REM) of the composition-containing inclusions is preferably controlled in the range of 0.3 to 1.0%, and (% S) in the range of 0.05 to 0.2%. If (% T.REM) is less than 0.3%, the S fixation ability is insufficient, and if it exceeds 1.0%, the concentration of REM oxide in the nonmetallic inclusion increases, and the stretchability may not be sufficiently improved. On the other hand, if (% S) is less than 0.05%, the amount of S fixed is too small to have no effect, and if it exceeds 0.2%, CaS or the like may be generated in the nonmetallic inclusions, and the stretchability may not be sufficiently improved.

In addition, the disconnection based on MnS is less frequent than the disconnection based on oxide-based nonmetallic inclusions. Therefore, first of all, it is necessary to appropriately control the composition of the oxide-based nonmetallic inclusion in steel.

Next, the definition of the component composition of the steel of the present invention will be described. So-called kilted steel is used for the piano wire of JISG3502, the hard steel wire of JISG3506, and the oil temper wire for valve spring of JISG3561 used as a high carbon steel wire. In consideration of this JIS standard, ease of manufacture, and practical use, the present invention defines a component range as follows.

Namely, in mass%, C: 0.5 to 1.2%, Si: 0.15 to 2.5%, Mn: 0.20 to 0.9%, P: 0.025% or less, S: 0.004 to 0.025%, Al: 0.000005 to 0.002%, Ca: 0.00001 To 0.002%, Mg: 0.00001 to 0.001%, Na: 0.000005 to 0.001%, F: 0.000003 to 0.001%, and if necessary, Cr: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Cu: 0.05 to 0.05 1.0%, Ti: 0.001 to 0.25%, V: 0.001 to 0.25%, Nb: 0.001 to 0.25%, Mo: 0.05 to 1.0%, Co: 0.1 to 2%, or a steel containing one or two or more.

Moreover, when REM: 0.000005 to 0.001% is contained, the effect of this invention becomes large. In addition, when B: 0.0005 to 0.002% is added, steel excellent in freshness and fatigue properties after drawing can be obtained.

C is an economical and effective element for strengthening steels. 0.5% or more is required to obtain the required strength as a hard wire. However, if it exceeds 1.2%, the ductility of the steel is lowered and embrittled, and the secondary processing becomes difficult, so it is made 1.2% or less. More preferred concentration of C is 0.51 to 1.1%.

Si and Mn are necessary for deoxidation and inclusion composition control, and are not effective at Si: less than 0.15% and Mn: less than 0.20%. Moreover, although it is effective also as a reinforcing element of steel, steel will embrittle when Si exceeds 2.5% and Mn exceeds 0.9%. More preferred ranges of Si and Mn are 0.16 to 2.3% and 0.25 to 0.85%, respectively.

P deteriorates drawing workability in high carbon steel and deteriorates ductility after drawing work. Therefore, content of P needs to be 0.025% or less, and 0.020% or less is more preferable.

S also deteriorates the wire workability and deteriorates the ductility after the wire work. On the other hand, in order to secure the descalability of the steel, it is necessary to secure the S concentration to some extent. Therefore, the concentration of S is made 0.004 to 0.025%, preferably 0.005 to 0.020%.

Al is an element which affects the composition of the inclusions of the present invention, and at least too many predetermined inclusion compositions cannot be obtained. Therefore, the concentration of Al is made 0.000005 to 0.002%, preferably 0.0002 to 0.001%.

Ca is also an element influencing the inclusion composition of the present invention, and too much, at least, a predetermined inclusion composition cannot be obtained. Therefore, the concentration of Ca is made 0.00001 to 0.002%, preferably 0.000013 to 0.0015%.

Mg is also an element which affects the inclusion composition of the present invention, and too much, at least, a predetermined inclusion composition cannot be obtained. Therefore, the concentration of Mg is set to 0.00001 to 0.001%, preferably 0.000011 to 0.0008%.

In addition, Na and F are very important components in the inclusion composition of the present invention, and Na and F concentrations in the steel affect the inclusion composition.

Na is an element which affects the composition of the inclusions of the present invention, and if too many, at least a predetermined inclusion composition cannot be obtained. Therefore, the concentration of Na is made 0.000005 to 0.001%, preferably 0.000007 to 0.0005%.

F is also an element which affects the inclusion composition of the present invention, and too much, at least, a predetermined inclusion composition cannot be obtained. Therefore, the concentration of F is made 0.000003 to 0.001%, preferably 0.000005 to 0.0005%.

The steel of the present invention may further contain the following components.

Cr has the effect of making a pearlite lamellar fine, and increasing the strength of steel. The amount required for obtaining this effect is 0.05%, and further addition is good. However, when added exceeding 1.0%, since ductility is inhibited, an upper limit shall be 1.0%.

Ni also strengthens the steel by the same effect as Cr. To obtain the effect, addition of 0.05% or more is preferable. When added exceeding 1.0%, since ductility falls, an upper limit shall be 1.0% or less.

Cu has the effect of improving the scale characteristics and the corrosion fatigue properties of the wire. To obtain the effect, addition of 0.05% or more is preferable. When added exceeding 1.0%, since ductility falls, an upper limit shall be 1.0% or less.

Ti, Nb, and V have an effect of increasing the strength of the wire rod by precipitation strengthening. In all cases, less than 0.001% is ineffective, and more than 0.25% causes precipitation embrittlement. Therefore, the content is made into 0.001 to 0.25%. Moreover, it is effective to add these elements also in order to make the (gamma) particle size at the time of patterning small.

Mo is an element which improves hardenability of steel. In the case of the present invention, the strength of the steel can be increased by the addition thereof, but addition of excessive amounts hardens the steel excessively, making processing difficult. Therefore, Mo addition range is made into 0.05 to 1.0%.

By containing 0.1 to 2% of Co, ductility improves by the effect of suppressing formation of the cornerstone cementite of the roughened steel.

B improves hardenability of the steel and, when present in austenite in a solid solution state, concentrates at grain boundaries to suppress the formation of non-pearlite precipitation such as ferrite, pseudo pearlite, and bainite, and improves freshness. If the amount is too small, this effect cannot be obtained, so the lower limit is made 0.0005%. On the other hand, when too much is added, precipitation of coarse Fe ₃ (CB) ₆ carbide in austenite is promoted, which adversely affects freshness. Therefore, an upper limit is made into 0.002%.

REM is an element influencing the inclusion composition of the present invention. Even if there are too many REMs, since at least the predetermined | prescribed inclusion composition for further improving freshness cannot be obtained, it shall be 0.000005 to 0.001%.

Next, the manufacturing method of the high carbon steel wire rod of this invention is demonstrated.

The steel of the present invention can be melted by a simple ladle refining after tapping the ladle after completing the refining in the converter or converter. As simple ladle refining, CAB (captured argon bubbling), SAB (shielded argon bubbling), and CAS (component adjustment by SAB) described in Non-Patent Document 1 can be used.

If the total oxygen content in the steel is 30 ppm or less, the mixing of converter slag flowing out from the converter into the ladle at the time of tapping is extremely suppressed, and the calm time of simple ladle refining (after ladle refining and continuous casting start) Time) is secured for about 20 to 40 minutes, and it is effective to promote floating separation of oxides. It is also effective to prevent air oxidation of molten steel between the ladle and the tundish and between the tundish and the continuous casting mold.

On the other hand, if the total amount of oxygen in the steel is 16 ppm or more, Al or Mg, which is a strong deoxidation element, is not added to the steel extremely, but only minimal addition to Ti is required, and simple ladle refining is not performed for a long time. Can be realized.

Specifically, it is about 25 to 40 minutes by dissolving synthetic slag and stirring with molten steel, secondary deoxidation and component fine adjustment, molten steel temperature adjustment, and argon bubbling in ladle. Then, argon bubbling in the ladle allows uniform mixing of the components, the coolant, and floating separation of the inclusions.

If full ladle refining, such as vacuum degassing, is performed, since the possibility that the total amount of oxygen in steel will be less than 16 ppm becomes high, it is unpreferable.

From the target size inclusions in the steel, (% Al ₂ O ₃₎ is to over 80% in number ratio not greater than 30%, it is necessary to attempt to prevent Al incorporated in the steel. Not only Al is used as the deoxidizer, but also Fe-Si and Si-Mn as alloy iron added at the time of tapping may use alloy iron having a low Al content.

For example, although ordinary Fe-Si contains about 1.5% of Al, low Al-Fe-Si having an Al content of about 0.01 to 0.10% can be suitably used. It is also effective to use a refractory having a low alumina content as the ladle refractories in order to make inclusions having 30% or less of (% Al ₂ O ₃ ) at 80% or more in the number ratio.

In addition, since some Al is necessarily mixed with Al in alloy iron added to steel or alumina in ladle or tundish refractory, (% Al ₂ O ₃ ) has an inclusion rate of 0.5% or more and 80% or more by number ratio. You can do

(% CaO) and (% SiO ₂ ) in the inclusions are used to adjust the content of CaO and SiO ₂ of the slag component on the ladle in simple ladle refining, and to make the total amount of oxygen in the above-described steel to 30 ppm or less. By employ | adopting manufacturing conditions, it can be within the scope of the present invention.

Specifically, the basicity (CaO / SiO ₂ mass ratio) of the slag on the ladle is adjusted by adjusting the component and the amount of the synthesized slag of the SiO ₂ -CaO system added to the ladle. The basicity of the slag on the ladle may be 0.9 to 1.3. In addition, by adopting the production conditions such that the total amount of oxygen in the steel is 30 ppm or less, it is possible to prevent the increase of the inclusion (% SiO ₂ ) due to the oxidation of the Si component in the steel.

In addition, the content of (% MgO) of the inclusions in the range of 0.5 to 20% and (% MnO) in the range of 0.5 to 10% is based on incorporation from the MgO source in the refractory, oxidation of Mn in the steel, and the like. This can be achieved within the scope of the present invention.

As described above, the addition of Na and F in the steel to the inclusion of (% Na) = 0.2 to 7% and (% F) = 0.17 to 8% of the inclusions both result in the present invention. It can be contained within the range of.

At this time, Na, and addition method of the F above may be added as NaF compound, Na, for the separately (for example, F, Na ₂ CO ₃ and CaF ₂ Etc.) can also be added. In addition, when F is added simultaneously with the metal Si, SiF ₄ is generated and gasified, and the yield of F is deteriorated and should be avoided.

In order to make (% T.REM) in 0.3-1.0% and (% S) in 0.05-0.2% in an interference | inclusion, REM may be added by several ppm equivalent in steel. REM added in the steel reacts with S in the steel to form a REM oxysulfide and coalesces with the silicate inclusions. As a result, (% T.REM) = 0.3-1.0% and (% S) = 0.05-0.2% can be contained in an average concentration in composition composition inclusion.

Example

The solvent of this example was implemented by LD converter. In the stepping out of the ladle from the LD converter, only a small amount (less than 50 mm thick) of LD slag was discharged using a so-called dart-type converter slag waste paper jig.

In addition, at the time of tapping, deoxidized alloy iron, such as a peat material for component adjustment of C, Si, Mn, Fe-Si, Fe-Mn, Si-Mn, was added. The deoxidation ferroalloy used what does not contain strong deoxidation elements, such as Al and Mg as much as possible. In addition, argon was blown from the ladle bottom during or after the tapping.

The molten steel in the ladle after the lecture is a so-called killed steel deoxidized by Si, Mn or the like. After moving the ladle to the molten steel refining position, after adding a SiO ₂ -CaO-based synthetic slag into the ladle, argon was blown from the ladle bottom, the molten steel in the ladle was stirred, and the CAB simple ladle refining was performed. Was carried out.

Next, a secondary deoxidizer was added to the molten steel as alloy iron. The secondary deoxidizer includes metals Ca, Al, Mg, Si, and the like. If necessary, Na, F, REM were added in the molten steel in the ladle. NaF was added when Na and F were added together, Na ₂ CO ₃ when Na was added alone, and CaF ₂ was added when F was added alone. When adding F, it added at the timing different from addition of the alloy containing Si and a secondary deoxidizer.

After adding the secondary deoxidizer, the component fine adjustment was further performed, and the ladle molten steel refining was completed. After completion of the ladle molten steel refining, a continuous casting time (about 20 to 40 minutes) was ensured so that the total amount of oxygen in the steel was 16 to 30 ppm, followed by continuous casting. Molten steel is continuously cast from the ladle via a tundish, but at that time, sealing is performed with an inert gas in order to extremely suppress air oxidation between and in the tundish in the ladle. After the obtained cast steels were subjected to light oil fractionation, steel sheet rolling, and steel sheet correction in the slab heating furnace, 5.5 mm diameter wire rods were produced by wire rod rolling through the heating furnace.

Investigation of the number and composition of nonmetallic inclusions cuts a 0.5 m long sample from one coil of a 5.5 mmφ wire rod, cuts a small sample of 11 mm in length from any 10 places in the L direction (length direction), It carried out by fully irradiating the longitudinal cross section passing through a centerline. The number and composition of nonmetallic inclusions were made into the size target inclusions with oxide type nonmetallic inclusions of 0.5 micrometer or more in diameter, 1.0 micrometer or more in diameter, and 1 micrometer or more in circular equivalent diameter, and the composition of each inclusion was analyzed by X-ray spectroscopy.

Among the size object inclusions, those falling into the composition range of the present invention were used as composition object inclusions, and the number ratio (the number of inclusion object inclusions / size object inclusions × 100) was evaluated. Moreover, the average composition of all the size object inclusions was also calculated. However, for REM and S, the average composition of inclusion targets was calculated.

Then, the 5.5 mm diameter wire was drawn to 0.175 mm diameter or less, and the drawing characteristic and the die life were investigated. As for the freshness characteristic, the disconnection frequency with respect to a fixed freshness was made into the disconnection index, and the disconnection index 5 or less was favorable. The die life was evaluated as the index of the maximum allowable life of the current process material as 100 and the longer life. Dice life index of 100 or more is good.

Moreover, in order to evaluate a fatigue characteristic, the rotational fatigue test was done about 0.175 mm (phi) fresh wire. In the rolling fatigue test, the stress was varied in various ways, and the number of repetitions was examined until it broke. The stress cut at 100000 times of repetition was corrected by the coefficient of tension of the mechanical test, evaluated as a stress index, and the stress index 15 or more was made favorable.

Tables 1 to 4 show the results of the inventive examples and the comparative examples. Numerical values outside the scope of the invention are underlined.

Ex. In 1-24, all the favorable results were obtained. No. Although 8-18 is the level which added REM other than Na and F, in this case, die life and fatigue characteristics improved. In addition, 19-24 is the level which added B to steel, and confirmed the improvement of die | dye life and fatigue characteristics further.

Next, the result of a comparative example is demonstrated. No. 25 is No. when Na and F were not added. 26 is No. when only Na is added. 27 is a case where only F is added alone. In all, the number ratio of inclusions (number of inclusion inclusions / size of inclusion inclusions × 100, hereinafter referred to as “inclusion number ratio”) was zero, and the disconnection index, die life, and fatigue characteristics were all deteriorated as compared with the examples of the present invention.

No. Since 28 is insufficient sealing in the tundish, the total oxygen amount is higher than the range of the present invention, the number of inclusions is large, and die life and fatigue characteristics deteriorate.

No. 29-32 is the level of inclusion count less than 80%. No. 29 has a Al ₂ O ₃ or MgO content is hayeoteumeuro using high refractory, Al ₂ O ₃ system, the MgO-based inclusions that are considered refractory due to the large number of inclusions present. As a result, the inclusion number ratio fell below, and the disconnection index, the die life, and the fatigue characteristics all deteriorated.

No. Since 30% (% SiO ₂ ) in the nonmetallic inclusions was lowered by changing the composition of the synthetic slag of SiO ₂ -CaO system, the inclusion number ratio was lower, and some hard ones appeared in the inclusions, and the disconnection index, the die life, The fatigue properties all slightly deteriorated.

No. 31, LD slag outflow was slightly higher, coarse SiO ₂ inclusions appeared in the deoxidation process, and (% SiO ₂ ) in the nonmetallic inclusions increased. As a result, the inclusion number ratio was lower, and the disconnection index and the fatigue characteristics deteriorated.

No. As the deoxidation alloy, 32 is not a low Al alloy iron, but ordinary alloy iron having a high Al concentration, and (% Al ₂ O ₃ ) in the nonmetallic inclusions is increased. As a result, the number of inclusions was lower, and many hard Al ₂ O ₃ -based inclusions were produced, and the disconnection index, die life, and fatigue characteristics were all very bad.

No. 33 had a high S concentration in the steel, and (% S) in the nonmetallic inclusions was higher than the range of the present invention, resulting in deterioration of the disconnection index, die life, and fatigue characteristics.

No. Since 34 added REM too much, (% T.REM) in a nonmetallic inclusion became a value higher than the range of this invention, and the disconnection index, die life, and fatigue characteristics worsened.

Claims (5)

In terms of% by mass,
C: 0.5 to 1.2%,
Si: 0.15 to 2.5%,
Mn: 0.20 to 0.9%,
P: 0.025% or less,
S: 0.004-0.025%,
Al: 0.000005 to 0.002%,
Ca: 0.00001 to 0.002%,
Mg: 0.00001 to 0.001%,
Na: 0.000005 to 0.001%,
F: 0.000003 to 0.001%
It is a high carbon steel wire rod containing a total oxygen content of 16 to 30 ppm, the balance of Fe and inevitable impurities,
Among the oxide-based nonmetallic inclusions (hereinafter referred to as "size target inclusions") having a short diameter of 0.5 µm or more, a long diameter of 1.0 µm or more, and a circle equivalent diameter (surface conversion diameter) of 1 µm or more, as seen in the cross section of the wire L direction, (% SiO ₂ ) = 40 to 95%, (% CaO) = 0.5 to 30%, (% Al ₂ O ₃ ) = 0.5 to 30%, (% MgO) = 0.5 to 20%, (% MnO) = 0.5 to 10% In addition, the ratio of the number of inclusions (hereinafter referred to as "composition to be included") that satisfies (% Na) = 0.2 to 7% and (% F) = 0.17 to 8%, the number of inclusions to be formed / size to be included × 100 A high carbon steel wire rod having excellent freshness and fatigue characteristics after being drawn, characterized by being 80% or more.
Here, (% SiO ₂ ), (% CaO), (% Al ₂ O ₃ ), (% MgO), (% MnO), (% Na), and (% F) are respectively SiO ₂ , CaO, the content of _{Al 2 O 3, MgO, MnO} , Na, F is (% by weight). The method of claim 1 further comprising
REM: 0.000005 to 0.001%
And the composition-containing inclusions satisfy (% T.REM) = 0.3 to 1.0% and (% S) = 0.05 to 0.2% at an average concentration. This excellent high carbon steel wire rod.
Here, (% T.REM) and (% S) are the total of rare earth elements in inclusions, and content of S (mass%), respectively. The method of claim 1 or 2, further comprising
B: 0.0005 to 0.002%
A high carbon steel wire rod having excellent freshness and fatigue properties after being drawn, characterized in that it contains a. The method of claim 1 or 2, further comprising
0.05 to 1.0% Cr,
Ni: 0.05 to 1.0%
Cu: 0.05 to 1.0%
Ti: 0.001-0.25%,
Nb: 0.001 to 0.25%,
V: 0.001 to 0.25%,
Mo: 0.05-1.0%,
Co: 0.1 to 2%
A high carbon steel wire rod having excellent freshness and fatigue properties after being drawn, characterized in that it contains one kind or two or more kinds thereof. The method of claim 3, further comprising:
0.05 to 1.0% Cr,
Ni: 0.05 to 1.0%
Cu: 0.05 to 1.0%
Ti: 0.001-0.25%,
Nb: 0.001 to 0.25%,
V: 0.001 to 0.25%,
Mo: 0.05-1.0%,
Co: 0.1 to 2%
A high carbon steel wire rod having excellent freshness and fatigue properties after being drawn, characterized in that it contains one kind or two or more kinds thereof.