JP3537657B2 - Wire rod for steel wire and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire rod for a steel wire capable of maintaining a low tensile strength of a product in a billet continuous casting even when manufactured by low Al and open casting, and the steel. The present invention relates to a method for manufacturing a wire for a wire.

[0002]

2. Description of the Related Art Steel produced as a bar steel through a billet is cast into a billet mainly by a continuous casting method after completion of refining in a converter or the like. Free oxygen contained in molten steel at the completion of refining is removed as an oxide by adding a deoxidizing agent prior to casting. A typical deoxidizing agent is a composite deoxidizing using Al and Si. Al ₂ O ₃ and SiO ₂ as deoxidation products generated as a result of deoxidation are mostly separated by floating in molten steel, but a part thereof remains in molten steel,
At the time of continuous casting, it precipitates on the inner periphery of a nozzle for casting into a mold. In particular, Al ₂ O ₃ has a high melting point and precipitates around the casting nozzle, causing the nozzle to be blocked. In particular, in continuous casting in which a billet having a small cross section is cast, the cross sectional area of the casting nozzle is inevitably reduced because the cross sectional area of the mold is small, and nozzle blockage due to precipitation of Al ₂ O ₃ has become a serious problem. I have. By reducing the amount of Al contained in the steel by reducing the amount of Al added (to reduce Al),
There is known a technique for reducing Al ₂ O ₃ in steel and preventing clogging of a continuous casting nozzle.

When injecting molten steel into a mold, casting is usually performed using an immersion nozzle so that the molten steel stream does not come into contact with air in order to prevent oxidation of the molten steel in the mold. However, when the slab is reduced in cross section as in continuous billet casting, the immersion nozzle is easily clogged, making it difficult to use, and so-called open casting in which the molten steel flow is exposed to the atmosphere is performed. In this case, free air and nitrogen in the steel increase due to the entrainment of air into the molten steel during casting.

[0004] In producing a steel wire rod by the continuous casting method with a small-section billet, as a measure to prevent clogging of the casting nozzle, A
As a result of adopting open casting as a countermeasure for small cross section casting, compared with conventional high Al immersion nozzle casting or Al-less immersion nozzle casting, C,
Although the contents of Si and Mn are the same, the tensile strength (TS) of the product increases, and if the conventional manufacturing method is used,
There was a problem that a product that passed the TS standard was deviated from a higher TS. In order to bring the TS within the standard by changing the component content, it is necessary to lower C than before, and low carbon materials have a new problem of increasing the melting cost due to extremely low carbonization. .

[0005]

SUMMARY OF THE INVENTION In the present invention, when a steel rod is manufactured by continuous casting of a small-section billet, the TS content is increased at the same component content as in the prior art even when adopting open casting without using Al. An object of the present invention is to provide a wire for a steel wire capable of securing a value within a standard without any problem, and a method for manufacturing the same.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the gist thereof is as follows. The first is in weight percent, C:
0.02% to 0.22%, Si: 0.01% to 0.40
%, Mn: 0.20% to 0.60%, Ti: 0.005
% To 0.03%, B: 0.003% to 0.005%, Al: 0.005% or less, and total oxygen in the product is O: 0.006% to 0.02% And a balance of Fe and unavoidable impurities, and having a tensile strength defined by the following formula (1). TS ≦ 32 + 55 × Ceq (1) Ceq = C + 0.25 × Si + 0.2 × Mn where C: carbon content (% by weight) Si: silicon content (% by weight) Mn: manganese content (% by weight) TS: Tensile strength (kgf / mm ² ) The second is C: 0.02% to 0.22% by weight.
Si: 0.01% to 0.40%, Mn: 0.20% to
0.60%, Ti: 0.005% to 0.03%, B:
0.003% to 0.005%, Al: 0.005%
% Or less, wherein the molten steel comprising the balance of Fe and unavoidable impurities is subjected to open casting in which the molten steel flow is exposed to the oxygen of the atmosphere during continuous casting for billet and injected into a mold. )) Is a method for producing a steel wire rod having a tensile strength specified by (1).

In the present invention, since Al-less is used as a countermeasure for clogging of the casting nozzle, the elements contained in the molten steel during continuous casting and having deoxidizing ability are Si and Mn. When molten steel having such a component is injected into a mold openly, oxygen is taken into the molten steel by entanglement from the atmosphere at the time of injection. Since the deoxidizing agents Si and Mn have weak deoxidizing ability, the incorporated oxygen is not deoxidized in the initial stage after the mold injection,
It remains as free oxygen. However, as the solidification of the steel proceeds in the mold and below the mold, concentration occurs due to segregation of the contained elements at the solidification interface, and the oxidation reaction between free oxygen remaining at this stage and Si or Mn proceeds, resulting in solidification. Non-metallic inclusions, which are fine deoxidation products, remain in the layer.

[0008] These fine non-metallic inclusions remain fine in the steel during and after rolling. As a result, the tensile strength is increased by the dispersion strengthening mechanism using the fine nonmetallic inclusions. It is clear that dispersion strengthening works because it is much smaller than the oxides present in normal steel, and there are many. That is, in the continuous casting of small-section billets, the fact that the tensile strength of the wire rod of the product increases when Al-less open injection is performed is caused by a fine oxide based on oxygen taken into steel. Revealed.

Conventionally, excess A when deoxidized with Al
l, forming a compound with nitrogen in the steel and fixing the nitrogen, did not affect the strength, but the nitrogen entered into the steel during open casting did not form a compound, It was clarified that the solid solution strengthening of the steel was caused, which was also one of the causes of the increase in the tensile strength of the wire. Therefore, it is necessary to fix nitrogen in a form that does not contribute to strengthening, and it has become clear that B is effective as an element that fixes the nitrogen and does not affect nozzle clogging.

The present invention is based on the elucidation of the mechanism of the increase in tensile strength as described above, and does not add Al which causes clogging of a casting nozzle and does not adversely affect clogging of the nozzle. It is characterized in that Ti is added to effectively remove oxygen. Ti is Si or M
Since it has a deoxidizing ability stronger than n, it can react with oxygen entering as a result of open injection in the mold to form an oxide, and can be floated and separated in the mold before being taken into the solidified layer. In addition, since it is Al-less, there is no problem of clogging of the casting nozzle.

Although the reduction of TS can be realized by the addition of Ti, the present invention can further fix the nitrogen by adding B to steel to further reduce the TS.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the contents of other alloy components except for total oxygen are graded from the analysis values of molten steel in a tundish. Since the total oxygen is intended for oxygen taken into the product as a result of the open injection, an analysis value from the product after the wire rod rolling is adopted.

In the present invention, the formation of alumina as a deoxidation product is prevented by reducing the Al content in steel to 0.005% or less. Ti: 0.005% or more
As a result of performing deoxidation mainly with Ti alone or Ti and Si by setting 0.03% and Si: 0.01% to 0.40%, a deoxidized product is mainly composed of TiO ₂ and SiO _2. In addition, it is possible to reduce the precipitation of nonmetallic inclusions in the continuous casting nozzle as compared with the case where the main component of the deoxidation product is alumina.

In the open casting into the mold in the continuous casting, oxygen is taken into the molten steel because the flowing from the tundish to the molten steel surface in the mold comes into contact with the air in the atmosphere. Even if measures are taken to prevent oxygen entrapment as much as possible, the oxygen in the molten steel in the mold increases by about 30 ppm as compared with the case of immersion nozzle injection. If the deoxidizing element is only Si and Mn without Al, the oxygen mixed in the molten steel cannot be sufficiently deoxidized and remains as free oxygen. As solidification progresses in the slab, enrichment due to solute distribution of impurities occurs at the solidification interface, and oxygen and Si, Mn that existed independently until then combine to form a very fine and dispersed oxide, It is taken into the solidified layer without floating in the molten steel. As described above, the fine oxides increase the tensile strength of the steel. In the present invention, the molten steel in the mold contains 0.005% to 0.03% of Ti, and T
Since i has a stronger deoxidizing power than Si or Mn, oxygen mixed by open injection is quickly deoxidized by Ti,
The deoxidized product floats in the mold, reaches the surface and is removed.

The reason why the content of Al is set to 0.005% or less is that
There exceeds 0.005%, the composition of the resulting non-metallic inclusions becomes Al ₂ O ₃ mainly because inclusions melting point can not be prevented nozzle clogging increases. Note that the Al content includes Al existing as an oxide.

The reason why the lower limit of Ti is set to 0.005% is that the lower limit of 0.15% is used.
If it is less than 005%, the deoxidizing power will be insufficient, and it will be the same deoxidizing as Si alone deoxidizing, and the ability to deoxidize and remove the oxygen contained in the molten steel in the mold by open injection will be insufficient, improving the tensile strength of the product. Because they cannot do it.

The reason why the upper limit of Ti is set to 0.03% is that when the amount of added Ti is increased and combined with the total oxygen in the steel, if the amount becomes excessive, TiC precipitates. If it exceeds 03%, the dispersion strengthening of TiC works.

The invention of a product defines the range of total oxygen in the product. The present invention is based on the premise that open injection is performed during continuous casting, and as a result of the open injection, the total oxygen in the product is in a specific range. The lower limit of total oxygen in the product is 0.006%
Although the present invention is directed to an Al-less open cast continuous cast material, if open casting is performed, oxygen is mixed into the mold, resulting in the inclusion of deoxidizing elements such as Ti and Si as described in the claims. Even if it does, oxygen is taken into the product, and the total oxygen in the product is always 0.006% or more.

Regarding the upper limit of the total oxygen in the product, when the total oxygen is high, part of the oxygen is not dissolved in the steel but dissolved in the steel once, and the pores in the steel are cooled during the cooling of the steel. Gas), and a high pressure is generated depending on the oxygen concentration in the steel. If the total oxygen exceeds 0.02%, the gas pressure becomes high and it will not adhere in rolling or cold working, so the upper limit of the total oxygen in the product was made 0.02%.

In the invention of the production method, the range of the total oxygen in the product is not specified. The reason for this is that since the open injection is performed during the continuous casting as a component of the manufacturing method, it is not necessary to newly specify the total oxygen in the product.

The reason why the lower limit of Si is set to 0.01% is that it is not industrially feasible to reduce the lower limit of Si by a commonly used refining method. The upper limit of Si is set to 0.
The reason for setting the content to 40% is that if the content of Si exceeds 0.40%, the toughness is reduced and the desired quality cannot be obtained.

The reason why the lower limit of Mn is set to 0.20% is to secure the heat treatment property of the steel material. The upper limit of Mn is 0.6
The reason for setting it to 0% is that if it exceeds 0.60%, the cold workability of the steel is lowered and the required quality cannot be obtained.

The reason why B is set to 0.003% to 0.005% is that if less than 0.003%, the effect of nitrogen fixation is not recognized, and if it exceeds 0.005%, the crystal grain boundary of the wire is This is because segregation causes embrittlement.

As for N, if N in the product is less than 0.003%, B in steel becomes excessive and flakes occur.
Further, when N exceeds 0.005% in a product, there is a problem that embrittlement occurs during heat treatment. However, when manufactured by the continuous casting method employing the open injection according to the present invention, N contained in the product as an unavoidable impurity is 0.0%.
Since the content is not less than 03% and not more than 0.005%, no problem occurs.

[0025]

EXAMPLE A molten steel with a molten steel volume of 240 tons was produced by the converter refining method, C, Si, Mn, and Al were added to the molten steel pot during the tapping of the converter, and Ti was placed above the molten steel pot after tapping. Was added.

In the continuous casting method, the mold size is 125
mm × 125 mm, casting speed 2.6-3.2 m / mi
Casting was performed under the conditions of n. As the casting nozzle, a nozzle having an inner diameter of 18 mm was used. Cast nozzles are in principle alumina graphite unless otherwise noted.

After the billet manufactured by continuous casting was inspected, the billet was heated to 1000 ° C. or more in a heating furnace, rolled to 5.5 mmφ in a wire rod rolling mill, and wound into a coil through a cooling process by air cooling.

The tensile strength (TS) of the steel material after rolling (5.
(5 mmφ) was cooled to room temperature and measured with a standard Instron-type tensile tester.

Steels having components (other than total oxygen) shown in Tables 1 and 2 were melted, billets were produced by continuous casting according to the above-mentioned method, and wires were produced.

[0030]

[Table 1]

[0031]

[Table 2]

No. 1 in Table 1. 1 to 17 are production results of the examples of the present invention. All the results of the analysis of the alloy components in the tundish are within the scope of the present invention. All casting nozzles were selected for open injection. As a result of adopting open injection, the total oxygen analysis result in the product was 0.00
6% or more. Despite Al-less and open injection, since Ti is contained within the scope of the present invention, deoxidation in the mold proceeds, and the reduced diameter of the product is 0.1 μm.
m is suppressed, and the tensile strength satisfies the expression (1) of claim 1.

Table 2 shows the production results of the comparative examples. No. 1
Nos. 8 to 20 are Al-less, open implantation, and do not contain Ti. No. Reference numerals 21 to 23 denote Al-less and open implantations, and the content of those to which Ti is added is lower than the lower limit of the present invention. As a result, no. In all cases of Nos. 18 to 23, the number of inclusions in the product increased due to insufficient deoxidation in the mold, and the tensile strength did not satisfy the expression (1) in claim 1. No. In Nos. 24 and 25, the Ti content was equal to or higher than the upper limit of the present invention, and as a result, the tensile strength was not satisfied with the formula (1) of claim 1 due to the reinforcement by Ti. No. 2
In Nos. 6 and 27, the total oxygen in the product was higher than or equal to the upper limit of the present invention, and as a result, voids were generated in the product after rolling. No. 28
Nos. 30 to 30 employed immersion nozzles as casting nozzles, unlike the production method of the present invention. Therefore, the total oxygen in the product is out of the lower limit of the range of the components contained in the steel of the present invention. Also, the nitrogen in the product is at a low level. The use of an immersion nozzle eliminates oxygen entrapment in the mold, so there is no increase in the number of inclusions in the product, and consequently the tensile strength is high.
It is natural that the expression (1) is satisfied. However, due to the presence of excess B relative to the amount of nitrogen, segregation occurs at the crystal grain boundaries of the slab during solidification, and cracks are generated on the surface of the slab.

No. In 31, 32, B is less than or equal to the lower limit,
As a result, the tensile strength does not satisfy the expression (1) in claim 1. No. 33 and 34 had B equal to or more than the upper limit, and the tensile strength satisfied the expression (1) of claim 1, but cracks occurred in the products.

[0035]

According to the present invention, the same Ceq is obtained even when the billet continuous casting method by Al-less open injection is adopted.
, The tensile strength of the product was as low as that of the immersion cast material, and it was possible to manufacture a product capable of maintaining the TS upper limit without intentionally lowering Ceq.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (2)

(57) [Claims] 1. C: 0.02% to 0.22% by weight
%, Si: 0.01% to 0.40%, Mn: 0.20%
０．６0.60%, Ti: 0.005% to 0.03%, B:
0.003% to 0.005%, Al: 0.005%
% Or less, and the total oxygen in the product is O: 0.006% or more.
0.02%, the balance consisting of Fe and unavoidable impurities, and having a tensile strength defined by the following formula (1). TS ≦ 32 + 55 × Ceq (1) Ceq = C + 0.25 × Si + 0.2 × Mn where C: carbon content (% by weight) Si: silicon content (% by weight) Mn: manganese content (% by weight) TS: Tensile strength (kgf / mm ² ) 2. C: 0.02% to 0.22% by weight
%, Si: 0.01% to 0.40%, Mn: 0.20%
０．６0.60%, Ti: 0.005% to 0.03%, B:
0.003% to 0.005%, Al: 0.005%
% Or less, wherein the molten steel comprising the balance of Fe and unavoidable impurities is subjected to open casting in which the molten steel flow is exposed to the oxygen of the atmosphere during continuous casting for billets and injected into a mold. A method for producing a steel wire rod having a tensile strength defined by the expression (1) described above.