JPH0959744A - High carbon steel wire rod excellent in wire drawability and aging resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a carbon steel wire rod excellent in wire drawability and aging resistance by specifying total oxygen concentration, residual Al concentration, and nitrogen content in the wire rod of a carbon steel containing specific percentages of C, Si, Mn, P, and S. SOLUTION: In the wire rod of a carbon steel having a composition consisting of, by weight, 0.5-1.O% C, 0.15-0.50% Si, 0.3-0.9% Mn, <0.020% P, <0.020% S, and the balance iron with inevitable impurities, total oxygen concentration, residual Al concentration, and nitrogen content in this wire rod is regulated to <=20ppm, 0.4-2.0ppm, and <=40ppm, respectively. By this method, the high carbon steel wire rod, minimal in the amount of >=1μm inclusions in the wire rod after hot rolling and excellent in wire drawability and aging resistance, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high carbon steel wire rod and a method for producing the same, and in particular, after hot rolling, the wire rod has a small amount of inclusions of 1 μm or more, and has cold drawability (wire drawing) and It is concerned with high carbon steel wire rods with excellent aging properties and their manufacturing technology.

[0002]

2. Description of the Related Art High carbon steel wire rods used for automobile tire cords and the like are hot-rolled to about 5.5 mmφ,
After that, cold drawing (drawing) is performed several times while applying patenting (a type of quenching), and finally 0.
The wire is drawn up to an extra fine wire of 15 mmφ.

During this wire drawing process, hard granular non-
If metal inclusions (hereinafter referred to as inclusions) are present,
Even if the matrix is stretched, inclusions do not stretch, and
If it exists in the normal shape, micro voids will appear around the inclusions.
When formed, the ductility of the wire is reduced, which causes disconnection. There
To refine inclusions in steel so as not to cause wire breakage
Therefore, in the steelmaking process, the composition of the deoxidized product during hot rolling
Al with good ductility₂ O _Three -SiO₂ -MnO ternary system state
It was necessary to adjust to the spessartite region in the figure.

As a method for adjusting the spacer tight region, the amount of Al in the ferroalloy added to the molten steel is adjusted to 1 t of molten steel.
How to control to about 10-50g per on
2-17490 gazette) and, in addition thereto, Mn /
A method of controlling Si to 1.7 or more (Japanese Patent Publication No. 57-229).
No. 69) has been proposed. However, in the above method, the amount of Al is regulated and deoxidation of molten steel is caused by Mn and Si.
Therefore, there is a problem that the deoxidizing power is weak, the residual oxygen amount in the molten steel after deoxidizing is high, and the cleanliness of the slab is poor.
In recent years, due to the further progress of ultra-thin tire cords and higher strength, the demand for finer inclusions has become even stronger, and it is necessary to reduce the inclusion amount of 1 μm or more and the oxygen amount in the wire rod after hot rolling.
It is not sufficient to adjust the composition of the inclusions alone.
Further, although the amount of Al is regulated and the composition is adjusted so as to become inclusions in the spacer tight region, the amount of residual oxygen in the molten steel is high, so the residual oxygen varies, and Al ₂ O in the generated inclusions is varied.
₃ There was also a problem that the morphology of inclusions varied due to changes in concentration, and it was difficult to make the inclusions fine during hot rolling.

In view of this, an improved method for deoxidizing molten steel is disclosed in Japanese Examined Patent Publication No. Sho 63-18646, in which the total amount of Al added to molten steel is changed by using a CaO—SiO ₂ slag or flux in a vacuum arc degasser. To 10 g / ton or less, and Japanese Patent Laid-Open No. 62-203647 proposed a method in which the refractory used in the refining vessel is a non-Al ₂ O ₃ system.

However, in the molten steel treatment using the vacuum arc degassing apparatus, it was possible to reduce oxygen, but the deoxidizing power of carbon in the molten steel became stronger than that of Al, and Al ₂ O contained in refractory materials, slag, etc. ₃ is reduced by C, remaining A in molten steel
l concentration increased. This dissolved Al is combined with oxygen in the molten steel temperature decrease after the treatment and continuous casting, and again Al ₂ O ₃
Therefore, there is a problem that non-ductile inclusions remain in the slab during hot rolling. At that time, even if a non-Al ₂ O ₃ system refractory is used, it is unavoidable that Al ₂ O ₃ is present in the slag due to mixing of converter slag and Al in the additive alloy, It was difficult to lower the residual Al concentration of the molten steel in the tundish during casting.

Further, as a method of adjusting inclusions for improving deoxidation of molten steel other than the above, Japanese Patent Laid-Open No. 53-76916 discloses, "Adopting a ladle refining method by Ar blowing to regulate oxygen mixture. At the same time, a reducing slag containing high-melting point CaC ₂ or the like is added with a synthetic slag obtained by adding 5 to 30% of a low-melting point alkali metal fluoride, oxide, or alkaline earth metal fluoride to promote slag formation. After acidification, Mg, Ca, T
i, Al, and Zr are added in appropriate amounts to form inclusions having good ductility ", or Japanese Patent Publication No. 57-35234.
"Under full Al regulation (5g / mol steel ton or less),
After pre-deoxidizing by blowing O-containing flux into the molten steel,
It discloses a method in which a small amount of Ca, Mg, or REM is blown into an inclusion having good ductility.

However, in the above method, the activity of the deoxidizing element used for adjusting the morphology of the inclusions is too high, and the addition amount of the deoxidizing element has a great influence on the morphology of the inclusions, and the inclusions having good ductility. It was difficult to stably generate In addition, the reducing slag containing CaC _{2 and the} like used for preliminary deoxidation and the CaO-containing flux cannot be completely floated up when they are caught in or blown into the molten steel, and they are aggregated with the subsequent deoxidized product and coalesced. There was a problem that it became a hard inclusion rather than doing it.

Further, Japanese Patent Laid-Open No. 4-110413 discloses
"The total amount of Al in molten steel is 0.010 kg or less per ton of molten steel, and the slag composition is (CaO / SiO ₂ ) = 0.7 to 0.9 and Al ₂ O ₃ ≤ in an arc heating type ladle refining equipment.
A method has been proposed in which, after treating molten steel to 10%, continuous casting is performed in a mold in a continuous casting facility and with electromagnetic stirring at the end of solidification. This keeps the amount of Al in the lower, the upper limit of by the slag composition and _{CaO / SiO 2 = 0.7~0.9, Al} 2 O 3 ≦ 10% and a _Al2O3 (Al ₂ O ₃ activity) To prevent the formation of inclusions having a high Al ₂ O ₃ concentration.

However, since the a _{Al2O3 of the} slag is large, the residual oxygen in the molten steel is high, the oxygen concentration of the molten steel in the tundish exceeds 20 ppm, and the amount of inclusions rather increases. In addition, the residual A in the molten steel in the tundish
The l-concentration tends to be low, so that the inclusions generated during solidification become hard inclusions with a high SiO ₂ concentration,
It was not deformed during hot rolling and was present in the wire rod after hot rolling in a size of 1 μm or more.

Further, as a method for reducing the oxygen content of molten steel,
KAISHO No. 60-184617 discloses "The total amount of Al in molten steel is
10 g or less per ton of molten steel, slag assembly for refining outside the furnace
Composition of CaO-SiO₂ -Al₂ O_Three System, (CaO / S
iO₂ ) ≧ 1.5, (FeO + MnO) ≦ 3%
In both cases, from the viewpoint of adjusting the composition of inclusions, Al in the slag ₂ 
O_Three The upper limit of the amount is 3.0 ≧ (CaO / SiO₂ ) ≧
When 1.5, Al₂ O _Three ≤16% -4 (CaO / Si
O₂ )%, (CaO / SiO₂ )> 3.0, Al
₂ O_Three ≦ 4%, and the total amount of Al in the molten steel after refining is 10
It is disclosed that the content is set to g / ton (molten steel) or less. This
According to the method of slag, slag (CaO / SiO₂ ) ≧ 1.
5 of slag a_SiO2Is low, the oxygen content of the molten steel is reduced,
In addition, Al in the slag₂ O_Three CaO / SiO₂ upon
As the upper limit is lowered with the rise,
The increase of Al concentration in the₂ O_Three High concentration
The formation of inclusions can be prevented.

However, since the amount of CaO in the slag is high and the amounts of SiO ₂ and Al ₂ O ₃ are low, the melting point of the slag increases and the slagification property is poor, and the reaction between the slag and the molten steel during refining is sufficient. Does not progress. Further, when the slag is caught in the molten steel during refining and cannot be floated and remains in the slab to become inclusions, the inclusions have a high CaO content and become non-ductile and hard. In order to improve the slag-forming property of this slag, CaF
It is possible to mix fluorides such as _2, but when fluorides are mixed, there is a problem that the melting loss of the refractory increases and the refractory enters the steel as a non-ductile and hard inclusion. Further, although the total amount of Al in the molten steel after refining is set to 10 g / ton (molten steel) or less, the residual Al concentration in the molten steel is high with respect to the oxygen concentration in the molten steel in the tundish, and
There was a risk that inclusions having a high concentration of l ₂ O ₃ would be formed.

[0013]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention reduces the total oxygen content in the steel material as compared with the prior art to reduce non-ductile inclusions, and has a high strength, but also a work elongation and aging resistance. An object of the present invention is to provide a high carbon steel material having excellent properties and a method for producing the same.

[0014]

In order to achieve the above-mentioned object, the inventor has conducted diligent research based on the above-mentioned prior art, in order to prevent generation of hard Al ₂ O ₃ inclusions as deoxidation products. However, I realized that it is not enough to reduce the Al concentration in the steel, and it is always necessary to consider the balance with the amount of dissolved oxygen. Moreover, regarding oxygen, if you do not consider oxygen picked up from the atmosphere after deoxidation,
In particular, it has been confirmed that it is difficult to control the morphology of the deoxidized product that precipitates during solidification in continuous casting, and the present invention has been completed. That is, in the present invention, C: 0.5 to 1.0 wt.
%, Si: 0.15 to 0.50 wt%, Mn: 0.3 to
0.9 wt%, P: <0.020 wt%, S: <0.0
A carbon steel wire rod composed of the balance iron and unavoidable impurities at 20 wt%, characterized in that the total oxygen concentration in the wire rod is 20 ppm or less, the residual Al concentration is 0.4 ppm or more and 2.0 ppm or less, and nitrogen is 40 ppm or less. It is a carbon steel wire rod having excellent wire drawing workability and aging resistance. Also,
According to the present invention, when the pre-treated hot metal containing phosphorus and sulfur reduced to 0.020 wt% or less is decarburized and blown in a converter and tapped into a ladle, an F content of 0.01 wt% or less in Al content is obtained.
While deoxidizing with e-Si and / or Fe-Mn, Ca
O-SiO ₂ -Al ₂ O ₃ based flux to be added to受鋼the SiO ₂ activity of slag as 0.10, characterized in that the blow stirred refining inert gas into solution steel degassing facility The method for producing a carbon steel wire rod having excellent wire drawing workability and aging resistance, further comprising: continuously stirring the above-described inert gas by blowing until oxygen in molten steel is 10 ppm or less. It is also a method for producing a carbon steel wire rod having excellent wire workability and aging resistance.

[0015]

In the present invention, C: 0.5-1.0 wt%, S
i: 0.15 to 0.50 wt%, Mn: 0.3 to 0.9
wt%, P: <0.020 wt%, S: <0.020w
In the carbon steel wire rod composed of the balance iron and unavoidable impurities at t%, the total oxygen concentration in the wire rod was 20 ppm or less, the residual Al concentration was 0.4 ppm or more and 2.0 ppm or less, and the nitrogen was 40 ppm or less. In addition, there is no hard Al ₂ O ₃ inclusions or SiO ₂ inclusions having a size of 1 μm or more in the wire, and the wire is a high-strength, high-carbon steel wire with markedly improved drawability and aging resistance. As a result, it became possible to stably manufacture an ultrafine wire using this wire without breaking even in the wire drawing process.

Further, in the present invention, when the pretreated hot metal having a phosphorus content and a sulfur content each reduced to 0.020 wt% or less is decarburized and blown in a converter and tapped into a ladle, the Al content is 0. Fe-Si and / or Fe-Mn of 01 wt% or less
In addition to _{deoxidation, CaO-SiO 2 -Al 2 O} 3 based flux to be added to受鋼the SiO ₂ activity of slag as 0.10, blowing an inert gas into solution steel degassing facility Since the refining by stirring and the stirring by blowing of the above-mentioned inert gas are continued until the oxygen in the molten steel is 10 ppm or less, the oxygen concentration in the molten steel can be easily reduced, and the ductility It becomes possible to supply high carbon steel materials for extra fine wires with reduced inclusions.

The reasons for limiting the chemical composition of the wire according to the present invention will be described below. C: C is required to be at least 0.50 wt% or more in order to secure the strength of the wire rod after wire drawing, while 1.0 w
If it exceeds t%, coarse pro-eutectoid cementite is precipitated and becomes brittle, so the content was made 0.5 to 1.0 wt%. Si: Si is an element effective for deoxidation, and 0.15 wt% or more is required to exert its effect. On the other hand, excessive addition increases SiO ₂ inclusions and wire drawing workability. Therefore, it is set to 0.50 wt% or less. Mn: S is also effective for deoxidation and promotes deterioration of ductility.
Was fixed as MnS, and the lower limit was set to 0.30 wt% from the viewpoint of securing hardenability and producing strength. But,
If it is added in excess, quenching becomes excessive, and micro martensite occurs in the wire structure, which deteriorates the wire drawing workability, so the upper limit is 0.9 wt%. P, S: P, S is preferable if they are high, so wire drawing workability deteriorates.
It was suppressed to S <0.020 wt%. Al: One of the important points of the present invention is to set the upper and lower limits on the Al concentration in the wire. In order to reduce Al ₂ O ₃ inclusions, the total amount of Al in molten steel has been conventionally regulated, but in the present invention, the residual Al concentration is particularly small and is limited to 0.4 ppm or more and 2.0 ppm or less. . The reason is that a wire rod having various amounts of dissolved Al is hot-rolled using the trace amount dissolved Al amount analysis technique developed by the inventors, and
Based on the results obtained by investigating the presence of inclusions having a width of μm or more.
That is, as is clear from FIG. 2, the residual Al is 0.4
This is because the presence of the above inclusions increased when the concentration was outside the range of ppm to 2.0 ppm. It is estimated that the result of FIG. 2 was obtained, but when the residual Al is less than 0.4 ppm,
The SiO ₂ concentration in the inclusions increased and the residual Al remained 2.0p.
When it exceeds pm, the Al ₂ O ₃ concentration in the inclusions increases,
In all cases, it is considered that the deformability of the inclusions during hot rolling decreased.

In order to keep the Al concentration in steel at a low level,
Fe-Si and Fe-M, which are deoxidizing materials, as a source for mixing Al
As the alloy such as n, it is preferable to use a high-purity (Al <0.01%) alloy, and it is desirable to avoid a refractory alloy of Al ₂ O ₃ quality. O: O is also one of the important points of the present invention, and the residual oxygen concentration in the wire is set to 20 ppm or less, preferably 15 ppm. The grounds for this are the results of the inventors' investigation of the number of wire breaks by wire-drawing a carbon steel wire containing a small amount of O under certain conditions. As is clear from FIG. 1, when O exceeds 20 ppm, the disconnection number index tends to increase, and the index also exceeds 5 which is usually allowable.

It is also an important point of the present invention to cast a wire rod having the above-mentioned limited amount of oxygen, and the molten steel after the steel is discharged from the converter is subjected to secondary refining so that the oxygen concentration of the molten steel is increased in the casting tundish. It should be maintained below 10 ppm. This is a measure considering that the molten steel picks up oxygen during casting. For that purpose, a method of lowering a _SiO2 in the slag by deoxidizing Si to reduce the amount of oxygen in the steel by a slag-molten steel reaction is preferable. In the present invention, in the secondary refining to perform agitation of the inert gas, CaO-SiO ₂ -A
using l ₂ O ₃ slag, lowered a _SiO2 by increasing the CaO / SiO _2, it could be reduced to 10ppm or less in the tundish molten steel a dissolved oxygen concentration. N: N is 40 ppm or less, because if the concentration is high, the elongation after aging due to the heat treatment after wire drawing decreases. The basis is shown in Fig. 4, but a 5.5 mm material is 0.15 m long.
The relationship between the elongation (RA, unit%) after aging and the N concentration after heat treatment at 150 ° C. for 30 minutes after processing into mφ wire rod is because the elongation after aging greatly decreases when N is 40 ppm or more. .

The dissolved Al concentration of the wire was determined by iron separation-electric heating atomic absorption spectrometry.

[0021]

EXAMPLE First, P: <0.0 by hot metal pretreatment.
20 wt%, S: <0.020 wt% reduced hot metal 1
80 tons of C content 0.7wt% in the composite blowing converter
It was blown with oxygen. When tapping steel, Al content (0.01
% Fe or less of Fe-Si, and Fe-
1000 kg of Mn was added to deoxidize, and other components were adjusted.

Next, the molten steel was received in a ladle lined with a refractory containing no Al ₂ O ₃ . Also, when steel is received, C
aO-SiO ₂ -Al 2000k a ₂ O ₃ based flux
g was added and the SiO ₂ activity of the slag was adjusted to 0.10. As the refractory material, magnesia carbon brick was used for the slag line, and zircon pouring material was used for other walls and floors.

Thereafter, the ladle was placed in a VOD facility, Ar gas was blown into the molten steel to perform stirring and refining treatment, and the molten steel after the treatment was cast in a continuous casting facility. At that time, when a sample was taken from the molten steel in the tundish and analyzed for oxygen, oxygen was 8 ppm. This slab is rolled by hot rolling to 5.5 mmφ, the number of non-metallic inclusions having a width of 1 μm or more in the wire is measured by a known JIS method, and then wire drawing is performed to obtain a final product of 0.15 mmφ. did.

[0024]

[Table 1]

Table 1 shows the results of investigating inclusions, wire breakage index and RA (elongation) after aging for the wire rods of the present invention and comparative examples. In the wire rod according to the present invention, 5.5 mm
The index of the number of inclusions of 1 μm or more in the φ wire material was 5 or less, which was a very low level. As a result, disconnection in the drawing process up to the ultrafine wire of 0.15 mmφ is greatly reduced. It is also found that the aging resistance is also excellent.

Finally, the relationship between the residual Al concentration in the wire and the index of the number of wire breakages is summarized from these data and shown in FIG. From Fig. 3, the residual Al concentration of the wire rod is 2.0 ppm.
If it is larger, the width in the 5.5 mmφ wire rod after hot rolling is 1
It is clear that the number of inclusions having a size of μm or more greatly increases and the disconnection number index increases. Desirably, Al is 1.
If it is set to 0 ppm or less, the disconnection index seems to be lower. On the other hand, when the residual Al concentration in the wire rod was less than 0.4 ppm, the number of inclusions having a width of 1 μm or more in the 5.5 mmφ wire rod after hot rolling significantly increased, and the wire breakage index increased.

[0027]

As described above, according to the present invention, the oxygen content is 20 ppm or less, and 1 μm in the wire rod after hot rolling.
High carbon steel materials with a small amount of inclusions of m width or more came to be manufactured, and high carbon steel wire materials with excellent cold drawing workability (drawing workability) and aging resistance can be obtained. It was

[Brief description of drawings]

FIG. 1 shows the total oxygen concentration and 5.5 mmφ wire rod as 0.
It is the relationship of the number of wire breakage indexes when the wire is drawn up to a 15 mmφ ultrafine wire.

FIG. 2 is a relationship between the residual Al concentration of a 5.5 mmφ wire after hot rolling and the number of inclusions having a width of 1 μm or more in the wire.

FIG. 3 is a relationship between the residual Al concentration of a 5.5 mmφ wire and the index of the number of wire breakages in the step of drawing the wire to an ultrafine wire of 0.15 mmφ.

[Fig. 4] 30m at 150 ° C in 0.15mmφ wire
It is a relationship between elongation (RA) after aging by heat treatment of in and N concentration.

Claims (3)

[Claims] 1. C: 0.5 to 1.0 wt%, Si: 0.15 to 0.50 wt%, Mn: 0.3 to 0.9 wt%, P: <0.020 wt%, S: <0. In a carbon steel wire rod containing 0.020 wt% of the balance iron and inevitable impurities, the total oxygen concentration in the wire rod is 20 ppm or less, the residual Al concentration is 0.4 ppm or more and 2.0 ppm or less, and the nitrogen content is 40 p
A carbon steel wire rod excellent in wire drawing workability and aging resistance, which is characterized by being pm or less. 2. A phosphorus content and a sulfur content each are 0.020 wt.
% Of the pre-treated hot metal reduced to less than or equal to 0.1% when decarburizing and blowing in a converter and tapping in a ladle, deoxidizing with Fe-Si and / or Fe-Mn with an Al content of 0.01 wt% or less. , CaO-SiO ₂ -A
l ₂ O ₃ -based flux is added to the slag so that the SiO ₂ activity of the slag is 0.10 or less and steel is received, and an inert gas is blown into the molten steel in a degassing facility to perform stirring refining. Of carbon steel wire with excellent heat resistance and aging resistance. 3. The carbon steel wire rod excellent in wire drawing workability and aging resistance as set forth in claim 2, characterized in that the stirring and blowing of the inert gas is continued until oxygen in the molten steel is 10 ppm or less. Production method.