KR101461713B1 - Wire rod having high toughness and method for manufacturing the same - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a method of manufacturing a wire rod capable of ensuring high human strength and a high-tenacity wire rod.
In order to accomplish the above object, the present invention provides a method for manufacturing a steel sheet, comprising: controlling a composition and a content of the alloy in a steel strip and controlling conditions of a manufacturing process to form a coarse precipitate; increasing the content of ferrite in the microstructure through the coarse precipitate; So that the toughness of the steel can be improved.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-toughness wire and a method of manufacturing the same. BACKGROUND ART [0002]

TECHNICAL FIELD The present invention relates to a method of manufacturing a wire rod capable of ensuring high human strength and a high-tenacity wire rod.

Generally, in the case of heavy carbon wire, most of the structure is composed of pearlite and a little ferrite. In the case of non-welded wire of medium carbon wire, the fraction of ferrite in the microstructure is inferior to that of steel. It is well known as an influencing factor.

On the other hand, a well known method for improving the toughness of the non-tempered steel wire is to add a carbon / nitride forming element capable of fixing the ferrite grain boundaries such as Ti, Nb and V and controlling the rolling process, Non-patent document 1 discloses a method for improving toughness through ferrite microfabrication by forming ferrite in an austenitic grain boundary while suppressing conversation. However, the above method is required to precisely control precipitates formed of Ti, Nb, V, and the like. Since the bloom is used, the heating temperature must be set to 1200 ° C or higher in the heating furnace.

As another method for producing a tough, noncondensed steel, a steel containing 0.2% by weight of carbon (C) as proposed in Non-Patent Document 2 is subjected to a Bauschinger effect to separate the microstructure into ferrite + pearlite Layered structure. Such microstructure can maximize impact toughness and has the advantage of using ordinary carbon steel. However, since the material itself has a directionality due to the layered structure, it has a limited disadvantage in use.

 F.B.Pickering; Physical Metall. and the Design of Steel (1978) pp. 98 ~ 99  Kobe Tech. Report (1997)

An aspect of the present invention is to provide a wire having high toughness and a method of manufacturing the wire without performing the low temperature annealing heat treatment and the spheroidizing heat treatment which are processes after the wire material is manufactured.

An aspect of the present invention is a method of manufacturing a semiconductor device, comprising: 0.2 to 0.6% carbon, 0.001 to 0.50% silicon, 0.8 to 2.0% manganese (Mn), 0.03 to 0.20% vanadium (V) , Titanium (Ti): 0.005 (inclusive), and phosphorus (P): 0.03% or less (including 0%), sulfur (S): 0.1% To 0.040% of boron (B) and 0.0001 to 0.0030% of boron (B), wherein the remainder is Fe and inevitable impurities; Hot rolling the heated slab to a wire rod at a finishing rolling temperature of 780 to 900 占 폚; And cooling the hot-rolled wire material, wherein at least one precipitate of titanium oxide, titanium nitride, and boron nitride is contained in the cooled wire, And the average particle diameter of the precipitate is 0.4 占 퐉 or more.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, the method comprising the steps of: forming the wire in a composition range as described above, wherein at least one precipitate of titanium oxide, titanium nitride and boron nitride is contained in the wire; The average particle diameter of the precipitate is 0.4 μm or more, and the microstructure of the wire includes 15 to 30% of ferrite and the remaining pearlite in an area fraction.

According to the present invention, it is possible to produce a wire having excellent toughness without controlling additional processes such as spheroidizing annealing by controlling the composition and content of the steel strip and controlling the conditions of the manufacturing process.

Fig. 1 shows the results of observing the microstructure of Invention Material 1 and Comparative Material 1. Fig.
FIG. 2 is a graph showing the results of measurement of impact toughness of an inventive material and a comparative material.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the high-toughness wire and the method of manufacturing the high-toughness wire according to the present invention will be described in detail, but the present invention is not limited to the following embodiments. Therefore, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Hereinafter, the present invention will be described in detail.

The method for producing a wire having high toughness according to the present invention is characterized in that it comprises 0.2 to 0.6% of carbon (C), 0.001 to 0.50% of silicon (Si), 0.8 to 2.0% of manganese (Mn) ): 0.03 to 0.20%, phosphorus (P): 0.03% or less (including 0%), sulfur (S): 0.1% The steel strip further comprises at least one of titanium (Ti): 0.005 to 0.040% and boron (B): 0.0001 to 0.0030%, the balance consisting of Fe and inevitable impurities, The hot-rolled steel strip is heated and then cooled.

At this time, the wire preferably contains at least one precipitate of titanium oxide, titanium nitride, and boron nitride, and the average particle size of the precipitate is preferably 0.4 μm or more .

Hereinafter, the reason why the composition of the wire is limited in the method of manufacturing the high-toughness wire of the present invention will be described. At this time, the content of the component elements means all the weight percentages.

C: 0.2 to 0.6%

Carbon (C) is an essential element added for securing strength of steel.

If the content of C exceeds 0.6%, the microstructure of the steel is largely composed of pearlite, which is not effective in the present invention aiming at ferrite production. On the other hand, when the content of C is less than 0.2%, the ferrite fraction is sufficient, Ferrite contributing to improving impact toughness is very small. Therefore, in the present invention, the content of C is preferably limited to 0.2 to 0.6%.

Si: 0.001 to 0.50%

Silicon (Si) is a typical substitutional element and has a great influence on the work hardening of steel. Especially, in non - tempered steel which is subjected to cold pressing directly after drawing without softening heat treatment process, the work hardening is increased as the content of Si is increased, resulting in deterioration of die life.

Therefore, when the content of Si exceeds 0.50%, the amount of work hardening is increased to lower the ductility of the steel, thereby lowering impact toughness. Therefore, it is necessary to control the content to a low level. It is preferable to limit the lower limit to 0.001%.

Mn: 0.8 to 2.0%

Manganese (Mn) is an element that increases the soundness of a tissue by forming a substitute solid solution in the matrix and lowering the A ₁ temperature to refine the interval between the pearlite layers.

It is preferable that an appropriate amount of Mn is contained in order to obtain the above-mentioned effect. However, if the content exceeds 2.0%, there is a problem that the structure heterogeneity due to the mesoscopic gypsum is more harmful to the non-tempered steel than the effect of refining the interval between pearlite layers. It is easy to cause macro segregation and micro segregation depending on the segregation mechanism at the time of solidification of the steel. The net segregation segregation promotes the segregation zone due to the relatively low diffusion coefficient compared to other elements, martensite). On the other hand, when the content of Mn is less than 0.8%, the effect of segregation due to manganese grains is relatively small, but the pearlite interlayer spacing is increased, which may adversely affect the toughness impact resistance of noncondensed steel. Therefore, in the present invention, the content of Mn is preferably limited to 0.8 to 2.0%.

V: 0.03 to 0.20%

Vanadium (V) forms elements such as VC, VN, and V (C, N) in the steel and improves the toughness of the non-tempered steel by refining the ferrite by applying appropriate rolling.

If the content of V is less than 0.03%, the distribution of vanadium precipitates in the base material is decreased, and the effect on the toughness is insufficient because the ferrite grain boundary is not fixed. On the other hand, when the content of V is more than 0.20% The formation of coarse vanadium carbonitrides in the range of carbon and nitrogen suggested in the present invention has an adverse effect on toughness. Therefore, in the present invention, the content of V is preferably limited to 0.03 to 0.20%.

N: 0.01% or less (excluding 0%)

Nitrogen (N) is an element that reacts with titanium (Ti) or boron (B) to form TiN or BN nitride. These nitrides can act as ferrite nucleation sites above a certain size (about 0.4 μm in diameter) and are actively added to promote ferrite formation. However, when the content of N exceeds 0.01%, coarse nitrides may be formed to lower the impact toughness of the steel. Therefore, it is preferable that the N content be 0.01% or less (excluding 0%).

P and S: 0.03% or less (including 0%) and 0.1% or less (excluding 0%), respectively

Phosphorus (P) is segregated in grain boundaries to decrease toughness and decrease the delayed fracture resistance. Therefore, it is preferable to limit the content to 0.03% or less (including 0%).

Sulfur (S) is segregated at the grain boundary with a low melting point element to lower the toughness and form an emulsion, thereby detrimentally affecting the delayed fracture resistance and stress relaxation characteristics, and therefore, it is desirable to suppress the content thereof to the maximum. However, it is preferable to induce MnS precipitation by adding an appropriate amount of S for cutting property. Therefore, in view of the above, it is preferable in the present invention to limit the content of S to 0.1% or less (excluding 0%).

Ti and B: 0.005 to 0.040% and 0.0001 to 0.0030%

In the present invention, titanium (Ti) and boron (B), which are additionally added in addition to the above components, form coarse precipitates through high-temperature heating, thereby acting as sites of ferrite nucleation during the ferrite transformation of austenite, .

When the content of Ti or B is less than 0.005% or less than 0.0001%, it is difficult to form a proper amount of precipitates and does not affect the increase of the ferrite content. On the other hand, when the content of Ti or B is more than 0.040% or 0.0030% The coarse precipitate is excessively generated, which may become a main crack generation site of the inclusion rupture.

In the case of the high-tenacity wire satisfying the above-mentioned composition, coarse precipitates are present in the wire. More specifically, it contains at least one precipitate of titanium oxide, titanium nitride and boron nitride, and the average particle size of the precipitate is 0.4 μm or more, more preferably 0.5 To 0.7 mu m.

These coarse precipitates act as heterogeneous nucleation sites during the austenite-ferrite transformation, and the resulting wire rod can contain 15 to 30% of ferrite. As a result, the toughness of the wire rod can be improved by increasing the ferrite fraction.

The most preferable method derived by the present inventors for producing the high-toughness wire satisfying the above-mentioned conditions will be specifically described below.

On the other hand, the above-produced steel strip is reheated according to the present invention, and then subjected to hot rolling and cooling to produce a wire rod. The wire produced by this method can be cold-drawn after cold-drawing through a conventional non-tempered steel manufacturing process and then processed into a product.

The present invention is characterized in controlling the reheating, rolling and cooling conditions in such a manufacturing process.

Hereinafter, detailed conditions for each step will be described.

Reheating step: heating at 1200 ~ 1250 ℃ for over 100 minutes

The steel strip thus formed is reheated at a high temperature of 1200 DEG C or more for 100 minutes or more to generate coarse precipitates through high-temperature heating. That is, when the micro-precipitates are re-dissolved through reheating, coarse precipitates are formed. The resulting coarse precipitates act as sites of ferrite nucleation when the austenite is transformed into ferrite in the subsequent rolling process, Can be increased.

However, if the heat treatment is performed at a temperature exceeding 1250 占 폚 for a long time, coarse austenite grains are generated as TiN is dissolved in the steel. Therefore, the reheating temperature is preferably limited to 1200 to 1250 占 폚.

Hot rolling step: Finishing hot rolling temperature 780 to 900 ° C

The reheated steel strip is hot-rolled, and at this time, the temperature of the finish hot-rolling is preferably set to 780 to 900 ° C.

Normally, hot rolling is carried out for the purpose of controlling the size of the slab, wherein the rolling temperature may vary depending on the component, but is carried out at a temperature of 900 ° C or higher at which the austenite structure is formed. On the other hand, in the case of controlled rolling, it is carried out at a lower temperature, namely Tnr (austenite non-recrystallization temperature) to Ac3, and in some recent researches, it is also carried out in the Ac3 sub- . It is intended to miniaturize the size of ferrite nucleated at the austenite grain boundaries by forming a pan cake by applying a process to the austenite grains.

The hot rolling step of the present invention follows the form of controlled rolling. By setting the finish hot rolling temperature at 780 to 900 ° C, the ferrite particles can be miniaturized and the fraction of ferrite can be maximized.

In the present invention, by performing the hot rolling as described above, at least one precipitate of titanium oxide, titanium nitride and boron nitride formed in the reheated steel strip before hot rolling can be obtained. And used as a ferrite nucleation site. That is, nucleation occurs on the surface of the precipitates during the rolling process, and they act as heterogeneous nucleation sites during transformation from austenite to ferrite, so that they can have a higher ferrite fraction than conventional heavy carbon wires.

Cooling step: cooling rate 0.5 ℃ / s or less

After hot rolling under the above conditions, cooling is started. At this time, it is preferable to set the cooling rate to 0.5 DEG C / s or less so that the cooling is performed.

Since non-tempered steel is not subjected to a separate heat treatment process in the process of manufacturing the product, the bainite or martensite structure is badly affected by the formation of the low-temperature structure, that is, bainite or martensite. Therefore, when the cooling rate exceeds 0.5 占 폚 / s during cooling, low-temperature structure may be generated. Therefore, it is preferable that the cooling rate is 0.5 占 폚 / s or less.

Hereinafter, the high-toughness wire, which is another aspect of the present invention, will be described in detail.

It is preferable that the high-strength wire rod provided according to the present invention satisfies the above-described composition and contains 15 to 30% of ferrite and the remaining pearlite in a microstructure. If the fraction of ferrite is less than 15%, there is a problem that the toughness is largely lowered. On the other hand, if the ferrite fraction exceeds 30%, it is difficult to secure the aimed tensile strength in the present invention.

It is also preferable that the high-strength wire of the present invention contains at least one precipitate of titanium oxide, titanium nitride and boron nitride. The average particle diameter of the precipitate is preferably 0.4 占 퐉 or more, and more preferably 0.5 to 0.7 占 퐉.

Hereinafter, the present invention will be described in more detail with reference to examples.

( Example )

The steel sheets having the composition shown in the following Table 1 were prepared and cast into an ingot of 50 kg in size, and then subjected to homogenization heat treatment for 20 hours at the respective heating temperatures shown in Table 1, followed by hot rolling to obtain a wire rod having a diameter of about 26 mm . At this time, the finish hot rolling temperature is shown in the following Table 1, followed by cooling at a cooling rate of 0.5 ° C / s to produce a wire rod.

Then, the ferrite fraction of each wire was measured and the impact toughness was measured. The results are shown in Table 1 and Figs. 1 and 2. Fig.

Impact toughness was measured using a U-notch Charpy impact test method, and the average value of the five test results at room temperature was obtained.

division C
(%) Si
(%) Mn
(%) V
(%) P
(%) S
(%) N
(%) Ti
(%) B
(%) Reheating
Temperature Wrap-up
Rolling temperature Ferrite fraction Comparison 1 0.45 0.2 1.3 0.05 0.012 0.01 0.005 - - 1100 ℃ 780 ° C 8% Comparative material 2 0.45 0.2 1.3 0.05 0.012 0.01 0.005 0.05 - 1100 ℃ 950 ℃ 12% Comparative material 3 0.45 0.2 1.3 0.05 0.012 0.01 0.005 - 0.005 1230 DEG C 950 ℃ 11% Inventory 1 0.45 0.2 1.3 0.05 0.012 0.01 0.005 0.01 - 1230 DEG C 800 ° C 19% Inventory 2 0.45 0.2 1.3 0.05 0.012 0.01 0.005 0.02 - 1230 DEG C 830 ° C 24% Inventory 3 0.45 0.2 1.3 0.05 0.012 0.01 0.005 - 0.002 1230 DEG C 900 ℃ 19%

As shown in Table 1, when the reheating temperature and the finishing rolling temperature are controlled in order to appropriately contain Ti or B which reacts with N to form a precipitate and obtain the precipitate effect by the above elements, Can be confirmed. This can be interpreted as a result of the formation of TiN or BN precipitates in a large amount as proposed by the present invention.

As shown in FIG. 1, when the microstructure of the inventive material 1 and the comparative material 1 are observed, it can be seen that the ferrite fraction of the inventive material 1 is significantly higher than that of the comparative material 1.

The results of measuring the impact toughness of the respective wire rods are shown in Fig.

As shown in FIG. 2, the higher the percentage of ferrite in the microstructure, the higher the impact toughness value is increased by about 20%. It can be interpreted that the comparative material is mostly composed of pearlite structure and the impact toughness value is relatively low.

In the medium carbon wire, most of the structure is a mixture of pearlite and a little ferrite. Especially, in noncondensed steel, ferrite fraction is known to affect the impact toughness of steel.

Therefore, in the present invention, precipitates such as TiN, BN, and VN that are capable of generating ferrite nuclei during the course of manufacturing the wire rod are precipitated sufficiently coarsely and then act as a heterogeneous nucleation site during the austenite-ferrite transformation, The toughness of the steel can be improved.

Therefore, according to the present invention, it is possible to directly produce the product by cold forging using the wire material excellent in toughness without further processing after manufacturing the wire material.

Claims (5)

(P): 0.03 to 0.03%, and the phosphorus (P) content is 0.2 to 0.6%, the silicon (Si) is 0.001 to 0.50%, the manganese (Mn) (Ti): 0.005 to 0.040% and boron (B), in addition to 0.1% or less (including 0%), sulfur (S) ): 0.0001 to 0.0030%, further comprising heating the billet consisting of the remainder Fe and unavoidable impurities to a temperature of 1200 ° C or higher in a heating furnace;
Hot rolling the heated slab to a wire rod at a finishing rolling temperature of 780 to 900 占 폚; And
And cooling the hot-rolled wire rod,
Wherein at least one precipitate of titanium oxide, titanium nitride and boron nitride is contained in the cooled wire rod and the average particle diameter of the precipitate is 0.4 μm or more Wherein said method comprises the steps of:
The method according to claim 1,
Wherein the heating step is performed for at least 100 minutes.
The method according to claim 1,
Wherein the cooling step is performed at a cooling rate of 0.5 DEG C / s or less.
(P): 0.03 to 0.03%, and the phosphorus (P) content is 0.2 to 0.6%, the silicon (Si) is 0.001 to 0.50%, the manganese (Mn) , Titanium (Ti): 0.005 to 0.040% and boron (B) in addition to not more than 0.1% (inclusive of 0%), sulfur (S): not more than 0.1% ): 0.0001 to 0.0030%, the balance being Fe and inevitable impurities,
Wherein at least one precipitate of titanium oxide, titanium nitride and boron nitride is contained in the wire, and the average particle size of the precipitate is 0.4 m or more. Toughness wire.
5. The method of claim 4,
Wherein the microstructure of the wire comprises 15 to 30% of ferrite and the remaining pearlite in an area fraction.

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