KR20200062439A - Non-quenched and tempered wire rod having excellent drawability and impact toughness and method of manufacturing the same - Google Patents

Abstract

Disclosed in the present invention are a non-heat-treated wire rod with excellent drawing properties and impact toughness which is adequate to be used as a material for a vehicle or a material for a machine part and a manufacturing method thereof. To this end, the non-heat-treated wire rod according to an embodiment of the present invention comprises, based on wt%, 0.05-0.35% of C, 0.05-0.5% of Si, 0.5-2.0% of Mn, 1.0% or less of Cr, 0.03% or less of P, 0.03% or less of S, 0.01-0.07% of sol. Al, 0.01% or less of N, at least one kind among 0.1% or less of Nb, 0.5% or less of V and 0.1% or less of Ti, and the balance being Fe and other inevitable impurities. In addition, the present invention further comprises a micro-structure of a ferrite-pearlite layered structure in a rolling direction.

Description

Non-quenched and tempered wire rod having excellent drawability and impact toughness and method of manufacturing the same}

The present invention relates to an unstructured wire material and a method for manufacturing the same, and more particularly, to an unstructured wire material excellent in fresh workability and impact toughness suitable for use as a material for automobiles or mechanical parts, and a method for manufacturing the same.

Structural steels used for machine structural or automotive parts are mostly used as quenching and tempering steel (인), which have been subjected to reheating, quenching, and tempering processes after hot working to increase strength and toughness.

On the other hand, non-heat treated steel (Non-Heat Treated Steel) refers to a steel that can obtain similar strength to the heat treated tempered steel without heat treatment after hot working. The non-finished wire rod is excellent in economic efficiency by lowering the manufacturing cost by omitting the heat treatment process involved in the manufacture of the existing rough wire rod. It has been tried to apply to many products.

In particular, ferrite-perlite-based non-woven wire rods have the advantage of being able to design components at low cost and stably obtain a homogeneous structure in the manufacturing process of the Stelmor cooling band, but the strength of the product increases as the amount of fresh processing increases. While rising, there is a problem that ductility and toughness drop sharply.

As a method for solving the above problems, a technique for securing a bainite-based microstructure using expensive quenchable alloy elements such as molybdenum (Mo) and boron (B) has been proposed. However, there are limitations in commercial production due to variations in physical properties due to non-uniform texture of bainite due to cooling variations in the Stellamore cooling zone during wire production.

Special Publication No. 10-2018-0082553 (Public Date: July 18, 2018)

In order to solve the above-mentioned problems, the present invention is to provide an uncoated wire material and a method for manufacturing the same, which can secure excellent workability and impact toughness without additional heat treatment.

The non-woven wire having excellent workability and impact toughness according to an embodiment of the present invention is weight%, C: 0.05 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.5 to 2.0%, Cr: 1.0% or less, P : 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.07%, N: 0.01% or less, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less It contains, the balance of Fe and the inevitable impurities, and includes a microstructure, a ferrite-pearlite layered structure in the rolling direction.

In addition, the average thickness of the ferrite layer in the L section, which is a parallel section in the rolling direction, may be 5 to 30 μm.

In addition, the average particle diameter of the ferrite in the C cross section, which is a right-angle cross section in the rolling direction, may be 3 to 20 μm.

In addition, the fraction of the ferrite may be 30 to 90%.

In addition, the average lamellar spacing of the pearlite may be 0.03 to 0.3 μm or less.

In addition, the carbon equivalent represented by the following formula (Ceq) may be 0.4 to 0.6.

Ceq = [C] + [Si]/9 + [Mn]/5 + [Cr]/12

(Here, [C], [Si], [Mn], [Cr] each means the content (%) of the corresponding element.)

In addition, the difference between the maximum hardness value and the minimum hardness value in the cross-section C, which is a right-angle cross section in the rolling direction, may be 30 Hv or less.

In addition, when 30 to 60% of the wire rod is freshly processed, the average value of impact toughness at room temperature may be 100 J or more.

In addition, when 30 to 60% of the wire rod is freshly processed, the following formula (1) may be satisfied.

(1) Imax-Imin ≤ 40J

(Here, Imax: maximum value of average room temperature impact toughness after fresh processing, Imin: minimum value of average room temperature impact toughness after fresh processing.)

A method of manufacturing a non-hard wire having excellent workability and impact toughness according to an embodiment of the present invention is weight%, C: 0.05~0.35%, Si: 0.05~0.5%, Mn: 0.5~2.0%, Cr: 1.0% Or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.07%, N: 0.01% or less, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less A step of manufacturing a steel piece containing at least one kind and containing residual Fe and unavoidable impurities, reheating the steel piece to a reheating temperature (Tr) satisfying the following formula (2), and rolling the reheated steel piece into a wire rod And winding and cooling the rolled wire rod.

(2) T1 ≤ Tr ≤ 1200℃

(Here, T1 = 757 + 606[C] + 80[Nb]/[C] + 1023√[Nb] + 330[V], each of [C], [Nb] is the content (%) of the element. it means.)

In addition, the step of rolling the wire may include rolling to a finish rolling temperature (Tf) that satisfies Expression (3) below.

(3) T2 ≤ Tf ≤ T3

(Where, T2 = 955-396 [C] + 24.6 [Si]-68.1 [Mn]-24.8 [Cr]-36.1 [Nb]-20.7 [V], T3 = 734 + 465 [C]-355 [Si] + 360[Al] + 891[Ti] + 6800[Nb]-650√[Nb] + 730[V]-232√[V], [C], [Si], [Mn], [Cr], Each of [Al], [Ti], [Nb], and [V] means the content (%) of the corresponding element.)

In addition, the cooling may include cooling at an average rate of 0.1 to 2°C/s.

According to an example of the present invention, by controlling the alloy composition and manufacturing conditions, it is possible to provide an excellent wire-processing and impact toughness of the non-crystalline wire and its manufacturing method without additional heat treatment.

1 is a photograph of a ferrite-pearlite layered structure of an amorphous wire according to an example of the present invention.

Hereinafter, preferred embodiments of the present invention will be described. However, embodiments of the present invention may be modified in various other forms, and the technical idea of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Terms used in the present application are only used to describe specific examples. Thus, for example, a singular expression includes a plural expression unless the context clearly indicates that it should be singular. In addition, terms such as “comprise” or “include” as used in the present application are used to clearly indicate the existence of features, steps, functions, elements, or combinations thereof described in the specification, and other features. It should be noted that it is not used to preliminarily exclude the presence of a field or step, function, component, or combination thereof.

On the other hand, unless defined otherwise, all terms used in this specification should be regarded as having the same meaning as generally understood by a person having ordinary skill in the art to which the present invention pertains. Accordingly, unless specifically defined herein, certain terms should not be construed in excessively ideal or formal sense. For example, in this specification, a singular expression includes a plural expression unless the context clearly has an exception.

In addition, "about", "substantially", and the like in the present specification are used in the sense of or close to the value when manufacturing and substance tolerances unique to the stated meaning are presented, and are used to help understand the present invention. Or, an absolute value is used to prevent unscrupulous use of the disclosed content by unscrupulous intruders.

Non-Heat Treated Steel refers to steel that can obtain similar strength to heat-treated tempered steel without heat treatment after hot working, and non-heated wire is made of material by omitting the heat treatment process involved in manufacturing the existing tempered wire. It is a product with excellent economic efficiency by lowering the unit price, and since it does not perform final quenching and quenching, it has been attempted to be applied to many products because defects due to heat treatment, that is, straightness due to heat treatment bending is secured.

In particular, ferrite-perlite-based non-woven wire rods have the advantage of being able to design components at low cost and stably obtain a homogeneous structure in the manufacturing process of the Stelmor cooling band, but the strength of the product increases as the amount of fresh processing increases. On the other hand, there is a problem that ductility and toughness drop sharply.

The present inventors reviewed from various angles in order to provide an unstructured wire that can secure excellent workability and impact toughness after drawing, and as a result, by appropriately controlling the alloy composition and microstructure of the unstructured wire without additional heat treatment. It has been discovered that excellent impact toughness can be secured together with an increase in strength during fresh processing, and the present invention has been completed.

In accordance with an aspect of the present invention, the unprocessed wire having excellent workability and impact toughness is in weight%, C: 0.05 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.5 to 2.0%, Cr: 1.0% or less, P : 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.07%, N: 0.01% or less, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less It contains, and the balance of Fe and inevitable impurities.

Hereinafter, the reason for limiting the composition of the components of the non-woven wire will be described in detail.

Carbon (C): 0.05 to 0.35% by weight

Carbon serves to improve the strength of the wire rod. In order to exhibit such an effect in the present invention, it is preferable that 0.05% by weight or more is included. However, when the content is excessive, the deformation resistance of the steel increases rapidly, and there is a problem that the cold workability deteriorates. Therefore, the upper limit of the carbon content is preferably 0.35% by weight.

Silicon (Si): 0.05 to 0.5% by weight

Silicone is a useful element as a deoxidizer. In order to exhibit such an effect in the present invention, it is preferable that 0.05% by weight or more is included. However, when the content is excessive, the deformation resistance of the steel increases rapidly due to solid solution strengthening, and there is a problem in that cold workability deteriorates. Therefore, the upper limit of the silicon content is preferably 0.5% by weight, and more preferably 0.25% by weight.

Manganese (Mn): 0.5 to 2.0 wt%

Manganese is a useful element as a deoxidizer and desulfurizer. In order to exhibit such an effect in the present invention, it is preferably contained at 0.5% by weight or more, and more preferably at least 0.8% by weight. However, when the content is excessive, the strength of the steel itself becomes too high, so that the deformation resistance of the steel increases rapidly, and there is a problem that the cold workability deteriorates. Therefore, the upper limit of the manganese content is preferably 2.0% by weight, more preferably 1.8% by weight.

Chromium (Cr): 1.0% by weight or less

Chromium serves to promote ferrite and pearlite transformation during hot rolling. Further, without increasing the strength of the steel itself more than necessary, carbides in the steel are precipitated to reduce the amount of dissolved carbon, thereby contributing to the reduction of the aging aging effect by the dissolved carbon. However, when the content is excessive, the strength of the steel itself becomes too high, so that the deformation resistance of the steel increases rapidly, and there is a problem that the cold workability deteriorates. Therefore, the upper limit of the chromium content is preferably 1.0% by weight, and more preferably 0.5% by weight.

Phosphorus (P): 0.03% by weight or less

Phosphorus is an inevitably contained impurity and is segregated at the grain boundaries, thereby reducing the toughness of the steel, and is a major factor in reducing delayed fracture resistance, so it is desirable to control its content as low as possible. Theoretically, it is advantageous to control the content of phosphorus to 0% by weight, but inevitably, it must be contained in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the phosphorus content is managed at 0.03% by weight.

Sulfur (S): 0.03% by weight or less

Sulfur is an inevitably contained impurity that segregates at the grain boundaries, greatly reducing the ductility of the steel, and forming an emulsion in the steel, which is a major factor in deteriorating the delayed fracture resistance and stress relaxation properties, so controlling its content as low as possible desirable. Theoretically, the content of sulfur is advantageously controlled at 0% by weight, but inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the sulfur content is managed at 0.03% by weight.

Soluble aluminum (sol.Al): 0.01~0.07% by weight

Soluble aluminum is an element that acts usefully as a deoxidizer. In order to exhibit this effect in the present invention, it is preferable to include 0.01% by weight or more. More preferably, it is 0.015% by weight or more, and even more preferably, it is 0.02% by weight or more. However, if the content is excessive, the effect of miniaturizing the austenite particle size due to AlN formation is increased, and thus cold forging may be deteriorated. Therefore, the upper limit of the soluble aluminum content is preferably 0.07% by weight.

Nitrogen (N): 0.01% by weight or less

Nitrogen is an imperatively contained impurity, and when its content is excessive, the amount of dissolved nitrogen increases, so that the deformation resistance of the steel increases rapidly, and thus, the cold workability deteriorates. Theoretically, the nitrogen content is advantageously controlled to 0% by weight, but inevitably contained in the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, the upper limit of the nitrogen content is preferably managed at 0.01% by weight, more preferably 0.008% by weight, and even more preferably 0.007% by weight.

In addition, the present invention may include one or more of the above-described component system and niobium (Nb), vanadium (V) and titanium (Ti).

Niobium (Nb): 0.1% by weight or less

Niobium is an element that forms carbides and carbonitrides to limit grain boundary movement of austenite and ferrite. However, when the content is excessive, the carbonitride may act as a starting point for destruction, thereby reducing impact toughness, and there is a problem of forming coarse precipitates, so it is preferable to add niobium by keeping a solubility limit. Do. Therefore, the upper limit of the niobium content is preferably 0.1% by weight or less.

Vanadium (V): 0.5% by weight or less

Vanadium, like niobium, is an element that forms carbides and carbonitrides to limit grain boundary movement of austenite and ferrite. However, when the content is excessive, the carbonitride may act as a starting point for destruction, thereby deteriorating impact toughness, and there is a problem of forming coarse precipitates, so it is preferable to add vanadium to keep the solubility limit. Therefore, the upper limit of the vanadium content is preferably 0.5% by weight or less.

Titanium (Ti): 0.1% by weight or less

Titanium also has the effect of limiting the grain size of austenite by combining with carbon and nitrogen to produce carbonitrides. However, if the content is excessive, there is a problem that a coarse precipitate is formed, which increases the possibility of acting as a major crack generating place for inclusion fracture. Therefore, the upper limit of the titanium content is preferably 0.1% by weight or less.

The balance other than the alloy composition is Fe. In addition, the wire rod for drawing of the present invention may contain other impurities that may be included in the industrial production process of steel. These impurities are contents that can be understood by anyone having ordinary knowledge in the technical field to which the present invention belongs, and thus do not particularly limit the type and content of the present invention.

The carbonaceous material (Ceq) represented by the following formula may be 0.4 to 0.6 of the non-woven wire according to an example of the present invention. If the carbon equivalent (Ceq) is less than 0.4, it may be difficult to secure the target strength, and when the carbon equivalent exceeds 0.6, the deformation resistance of the steel increases rapidly, and cold workability may deteriorate.

Ceq = [C] + [Si]/9 + [Mn]/5 + [Cr]/12

Here, each of [C], [Si], [Mn], and [Cr] means the content (%) of the corresponding element.

Hereinafter, the microstructure of the unstructured wire according to the present invention will be described.

The non-woven wire according to an example of the present invention includes ferrite and pearlite as a microstructure. Referring to FIG. 1, the ferrite and pearlite may form a ferrite-perlite band structure. Further, the layered structure may be a ferrite-pearlite layered structure in a rolling direction according to an example.

At this time, the ferrite-perlite layer structure in the rolling direction means that the length and width of each ferrite and pearlite layer are formed in a direction parallel to the rolling direction and a direction perpendicular to each other.

The ferrite-pearlite layered structure in the rolling direction has excellent fresh workability because the initial structure before drawing is arranged in a direction favorable to the fresh working, and the ferrite-pearlite layered structure stretched in the rolling direction through the fresh working has a thickness upon impact It is difficult to propagate the impact in the direction, and the impact toughness is improved because the propagation of the impact along the ferrite-pearlite interface, which is the weakest part.

Further, according to an example, the non-finished wire may include ferrite of 30 to 90% in an area fraction. In the case of securing the above-described structure, it is possible to secure excellent freshness and impact toughness while securing strength.

The ferrite structure of the present invention may have an average thickness of 5 to 30 μm of a ferrite band in an L section that is a parallel cross section in the rolling direction. In addition, the average particle diameter of ferrite in the cross-section C, which is a right-angle cross section in the rolling direction, may be 3 to 20 μm.

The thickness of the ferrite layer refers to the thickness of the ferrite layer in the L section, which is a parallel cross-section in the rolling direction, and when the average thickness of the ferrite layer is less than 5 μm, strength may increase and cold workability may deteriorate, whereas 30 μm is used. If exceeded, it may be difficult to secure the target strength.

The particle diameter of the ferrite means a ferrite particle diameter in the cross section C, which is a right-angled cross section in the rolling direction, and if the average particle diameter of the ferrite is less than 3 μm, strength may increase due to grain boundary refinement, and cold forging may decrease. If it exceeds 20㎛, it may be difficult to secure the target strength. At this time, the average particle diameter refers to the average circular equivalent diameter of particles detected by observing one section of the steel sheet, and the average particle diameter of pearlite formed together is particularly limited because it is affected by the average particle diameter of the ferrite I never do that.

The pearlite structure of the present invention may have an average lamellar spacing of 0.03 to 0.3 μm. The finer the lamellar spacing of the pearlite structure, the higher the strength of the wire rod, but if it is less than 0.03 μm, there is a fear that cold workability deteriorates, and if the lamellar spacing exceeds 0.3 μm, it may be difficult to secure the target strength.

Hereinafter, the unfinished wire rod of the present invention having excellent workability and impact toughness including the above-described composition range and microstructure will be described.

According to an example, the difference between the maximum hardness value and the minimum hardness value in the C section, which is a right-angled cross section in the rolling direction, is 30 Hv or less.

According to another example, the non-coated wire has an average value of impact toughness at room temperature of 100J or more when 30 to 60% of fresh processing is performed.

According to another example, the non-coated wire material satisfies the following formula (1) during 30-60% fresh processing.

(1) Imax-Imin ≤ 40J

(Here, Imax: the maximum value of average room temperature impact toughness after fresh processing, Imin: the minimum value of average room temperature impact toughness after fresh processing).

Here, the impact toughness at room temperature is evaluated as a Charpy impact energy value obtained by performing a Charpy impact test on a specimen having a U-notch (U-notch standard sample standard, 10x10x55mm) at 25°C.

Hereinafter, a method of manufacturing a wire rod according to an aspect of the present invention will be described in detail.

The present invention has been discovered through a number of experiments that it is possible to secure excellent fresh workability and impact toughness at the same time when securing a well-developed ferrite-pearlite layered structure (FP band structure) in the rolling direction, and has come to propose the present invention. .

A method of manufacturing an unstructured wire according to an embodiment of the present invention includes a step of manufacturing a steel piece, reheating the steel piece to a reheating temperature, rolling the reheated steel piece into a wire, and winding the rolled wire to cool it. do.

Steel pieces manufactured according to an example of the present invention are weight %, C: 0.05 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.5 to 2.0%, Cr: 1.0% or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.07%, N: 0.01% or less, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less, and at least one of them. And unavoidable impurities.

Hereinafter, each manufacturing step will be described in more detail.

Steps to reheat the piece

In the step of reheating the steel piece, the steel piece having the composition range may be reheated to a reheating temperature (Tr) satisfying the following formula (2).

(2) T1 ≤ Tr ≤ 1200℃

Here, T1 = 757 + 606[C] + 80[Nb]/[C] + 1023√[Nb] + 330[V].

The step of reheating the steel piece to a reheating temperature (Tr) that satisfies Eq. (2) is a step for re-using carbonitride formed by Nb, V, or a combination of these in the base material. When the carbonitride formed by Nb, V, or a combination thereof does not dissolve during reheating in the heating furnace and remains, when it is maintained at high temperature, it becomes difficult to refine the ferrite grains in the subsequent wire rod rolling process due to continuous coarsening during high temperature maintenance, and when cooled Mixed tissue can be produced.

In the above formula (2), when the steel reheating temperature is less than T1, coarse carbonitrides formed by Nb, V or a combination thereof are not completely re-used, and when the steel reheating temperature exceeds 1200°C, austenite structure There is a possibility that the ductility decreases due to excessive growth.

Step of rolling reheated steel piece with wire rod

The step of rolling the reheated steel piece into a wire may include hot rolling to a finish rolling temperature (Tf) satisfying the following formula (3).

(3) T2 ≤ Tf ≤ T3

Here, T2 = 955-396 [C] + 24.6 [Si]-68.1 [Mn]-24.8 [Cr]-36.1 [Nb]-20.7 [V], T3 = 734 + 465 [C]-355 [Si] + It is 360[Al] + 891[Ti] + 6800[Nb]-650√[Nb] + 730[V]-232√[V].

Since the finish rolling temperature (Tf) affects the alloy microstructure, it corresponds to a very important process condition for forming a ferrite-pearlite layered structure. When finishing rolling under the condition of the formula (3), a ferrite-pearlite layered structure is well formed.

In the formula (3), when the finishing rolling temperature (Tf) is less than T2, there is a possibility that the cold forging property is deteriorated due to an increase in deformation resistance due to the refinement of ferrite grain boundaries, and when the finishing rolling temperature (Tf) exceeds T3. There is a fear that the ferrite-pearlite layered structure is not well formed.

In addition, the step of rolling to the finishing rolling temperature is preferably a reheating step that satisfies Expression (1), which is a pre-treatment step, and then rolled to a finishing rolling temperature (Tf) that satisfies Expression (2) to form a ferrite-pearlite layered structure. The fineness of the ferrite and the homogeneity of the distribution can be better secured.

Cooling after winding the rolled wire

In the present invention, the step of winding the rolled wire and cooling it corresponds to a step of controlling the lamellar spacing of pearlite in the ferrite-pearlite layered structure formed in the final rolling condition, which is the previous process.

Basically, in the structure composed of ferrite-perlite, pearlite is advantageous in terms of strength, but acts as a main factor that deteriorates toughness. At this time, when the lamellar spacing of pearlite is fine, there is a side that relatively favors toughness.

Therefore, in the cooling step of the present invention, it is necessary to appropriately control the cooling rate in order to refine the pearlite lamella spacing. If the cooling rate is too slow, the lamella interval is widened, which may lead to insufficient ductility. If it is too fast, a low-temperature structure may be generated, which may sharply degrade toughness.

In the present invention, preferably, the average cooling rate during cooling may be 0.1 to 2°C/sec. If the average cooling rate is less than 0.1°C/sec, the lamellar spacing of the pearlite structure may be wide, resulting in insufficient ductility. When the average cooling rate exceeds 2°C/sec, a low-temperature structure is formed, which excessively increases the strength of the steel. And there is a risk of sharply degrading toughness.

When cooling, the average cooling rate may be more preferably 0.3 to 1°C/sec. In the above range, it is possible to obtain an unstructured wire having excellent ductility and toughness while sufficiently securing the strength of the wire.

As described above, the present invention controls the reheating temperature, rolling temperature, and subsequent cooling process of the steel piece to form a ferrite-pearlite layered structure. That is, the present invention is characterized by optimizing the reheating, rolling and cooling conditions in a series of processes consisting of reheating-rolling-cooling a steel piece satisfying the above-mentioned component system.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and reasonably inferred therefrom.

{Example}

After heating the steel piece having the alloy composition as shown in Table 1 at a heating temperature suitable for the component conditions for 3 hours, hot rolling was performed with a wire diameter of 20 mm to prepare a wire rod. At this time, the finish rolling temperature was set and performed according to the component conditions, and after winding, it was cooled at an arbitrary cooling rate.

Thereafter, using an electron microscope, the type and fraction of the microstructure, ferrite layer thickness and pearlite lamellar spacing were analyzed and measured, and the results are shown in Table 2 below.

Thereafter, after 30-60% fresh processing, presence or absence of disconnection, tensile strength at room temperature, and impact toughness at room temperature were measured, and the results are shown in Table 3 below. The expression of fresh workability is indicated by ○ when no disconnection occurred during fresh processing, and X when disconnection occurred more than once.

Here, the tensile strength at room temperature was measured by taking a sample from the center of a non-hardened steel specimen at 25°C, and the room temperature impact toughness was obtained by performing a Charpy impact test on a specimen having a U-notch (U-notch standard sample standard, 10x10x55mm) at 25°C. It was evaluated by the impact energy value.

Steel Alloy composition (% by weight) Ceq C Si Mn Cr P S sol.Al N Nb V Ti Inventive Example 1 0.06 0.25 1.65 0.3 0.012 0.0052 0.034 0.0055 0.050 0.110 0 0.443 Inventive Example 2 0.11 0.21 1.48 0 0.011 0.0043 0.041 0.0046 0.038 0.054 0 0.430 Inventive Example 3 0.18 0.22 1.37 0 0.010 0.0038 0.030 0.0040 0.030 0.050 0 0.478 Inventive Example 4 0.25 0.24 1.28 0.15 0.009 0.0046 0.026 0.0045 0.019 0 0 0.546 Inventive Example 5 0.33 0.23 1.15 0 0.011 0.0050 0.032 0.0052 0.010 0 0.010 0.586 Comparative Example 1 0.07 0.12 1.22 0.24 0.010 0.0062 0.031 0.0048 0.043 0.152 0 0.347 Comparative Example 2 0.15 0.16 1.41 0.15 0.012 0.0055 0.035 0.0042 0.032 0.104 0 0.462 Comparative Example 3 0.26 0.14 1.52 0.11 0.011 0.0043 0.042 0.0058 0.029 0.046 0 0.589 Comparative Example 4 0.32 0.21 1.67 0 0.010 0.0051 0.033 0.0060 0.021 0.038 0 0.677 Comparative Example 5 0.38 0.25 1.02 0 0.009 0.0047 0.024 0.0053 0.017 0 0.015 0.612 Comparative Example 6 0.43 0.27 0.15 0 0.010 0.0056 0.027 0.0047 0.013 0 0 0.690 Where Ceq = [C] + [Si]/9 + [Mn]/5 + [Cr]/12,
Each of the [C], [Si], [Mn], and [Cr] means the content (%) of the corresponding element.

Steel T1
(℃) Reheat
Temperature
Tr(℃) T2
(℃) T3
(℃) Wrap-up
Rolling
Temperature
Tf(℃) Average
Cooling
speed
(℃/s) Organization ferrite
Fraction
(%) L section
ferrite
layer
Average thickness
(㎛) Section C
ferrite
Average
Particle size
(㎛) Pearlite
Average
Lamella
interval
(㎛) Section C
Hardness
Deviation
(Hv) Inventive Example 1 1122 1156 814 880 834 1.6 F+P 84 23 15 0.26 9 Inventive Example 2 1069 1085 813 841 828 1.1 F+P 77 22 12 0.24 15 Inventive Example 3 1073 1097 794 826 815 0.8 F+P 69 17 7 0.25 20 Inventive Example 4 1056 1073 770 813 806 0.4 F+P 56 15 8 0.20 18 Inventive Example 5 1062 1082 751 829 789 1.0 F+P 42 10 11 0.16 26 Comparative Example 1 1111 1135 836 914 812 1.3 F+P 82 32 12 0.30 32 Comparative Example 2 1082 1104 796 862 887 0.9 F+P 71 36 25 0.28 26 Comparative Example 3 1113 1065 747 891 834 0.08 F+P 53 19 14 0.34 19 Comparative Example 4 1117 1087 718 851 856 2.4 F+P 35 31 18 0.21 28 Comparative Example 5 1124 1132 741 875 862 0.05 F+P 28 26 22 0.32 36 Comparative Example 6 1137 1154 713 862 841 1.2 F+P 21 24 16 0.27 41 Where T1 = 757 + 606[C] + 80[Nb]/[C] + 1023√[Nb] + 330[V],
T2 = 955-396[C] + 24.6[Si]-68.1[Mn]-24.8[Cr]-36.1[Nb]-20.7[V],
T3 = 734 + 465[C]-355[Si] + 360[Al] + 891[Ti] + 6800[Nb]-650√[Nb] + 730[V]-232√[V]

Psalter
No. 0%
Fresh processing 35%
Fresh processing 45%
Fresh processing 55%
Fresh processing I _max -I _min
(J) Seal
burglar
(Mpa) Shock
tenacity
(J) Seal
burglar
(Mpa) Shock
tenacity
(J) fresh
Processability Seal
burglar
(Mpa) Shock
tenacity
(J) fresh
Processability Seal
burglar
(Mpa) Shock
tenacity
(J) fresh
Processability Inventive Example 1 546 345 738 253 ○ 781 221 ○ 824 224 ○ 32 Inventive Example 2 574 316 771 219 ○ 813 210 ○ 857 216 ○ 9 Inventive Example 3 621 256 822 209 ○ 870 206 ○ 909 190 ○ 19 Inventive Example 4 613 211 840 188 ○ 887 179 ○ 933 168 ○ 20 Inventive Example 5 642 185 867 164 ○ 908 153 ○ 958 162 ○ 11 Comparative Example 1 617 225 807 168 ○ 845 135 ○ 889 103 ○ 65 Comparative Example 2 625 212 826 151 ○ 873 116 ○ 924 97 ○ 54 Comparative Example 3 689 156 908 102 ○ 953 88 ○ 997 61 X 41 Comparative Example 4 696 143 927 94 ○ 979 74 X 1029 52 X 42 Comparative Example 5 742 133 970 81 ○ 1022 62 X 1063 38 X 43 Comparative Example 6 770 115 996 61 X 1041 43 X 1088 25 X 36 Here, I _max is the maximum value of average room temperature impact toughness after fresh processing, and I _min is the minimum value of average room temperature impact toughness after fresh processing.

Hereinafter, each invention example and a comparative example are comparatively evaluated from Tables 1-3.

From Examples 1 to 5 satisfying the alloy composition and manufacturing conditions of the present invention from Tables 1 to 3, the ferrite-pearlite layered structure developed in the rolling direction secured strength and was excellent in fresh workability and impact toughness.

On the other hand, in the case of Comparative Examples 1 to 6, when the manufacturing conditions suggested by the present invention are not satisfied, the ferrite-pearlite layered structure in the rolling direction proposed by the present invention is not sufficiently formed, so that it is disconnected during the fresh processing compared to the inventive example Has a high incidence rate and low impact toughness.

In Comparative Example 1, the carbon equivalent (Ceq) was 0.347 and less than 0.4, and the finish rolling temperature (Tf) was less than T2. For this reason, the non-woven wire of Comparative Example 1 had an L-section ferrite layer having an average thickness of 32 µm, which was thicker than 30 µm, and the C-section hardness deviation exceeded 30 Hv as 32 Hv, and the average room temperature after 30-60% fresh processing. The difference in impact toughness was 65 J, which was 40 J or more, and the equation (1) of the present invention was not satisfied.

In Comparative Example 2, the finish rolling temperature (Tf) exceeded T3. For this reason, the non-woven wire of Comparative Example 2 had an L-section ferrite layer having an average thickness of 36 µm and was thicker than 30 µm, and a C-section ferrite average particle diameter of 25 µm exceeding 20 µm, and impact after 55% fresh working Toughness was 97J, which was less than 100J, and after 30~60% fresh processing, the difference in average room temperature toughness was 40J or higher, which did not satisfy Eq. (1) of the present invention.

In Comparative Example 3, the reheating temperature (Tr) exceeded T1, and the average cooling rate was 0.08°C/s, which was less than 0.1°C/s. For this reason, in the non-coated wire of Comparative Example 3, the pearlite average lamellar spacing was 0.34 µm, exceeding 0.3 µm, and after 45% and 55% fresh working, the impact toughness was 88J and 61J, respectively, less than 100J, and 55% fresh working. After the disconnection occurred, after 30~60% fresh processing, the difference in average room temperature impact toughness was 41J or more, which did not satisfy Eq. (1) of the present invention.

In Comparative Example 4, the carbon equivalent (Ceq) exceeded 0.6 as 0.677, the reheating temperature (Tr) exceeded T1, the finish rolling temperature (Tf) exceeded T3, and the average cooling rate was 2.4°C/s 2 ℃/s was exceeded. For this reason, the non-woven wire of Comparative Example 4 had an L-section ferrite layer having an average thickness of 31 µm and was thicker than 30 µm, and impact toughness after each of 35%, 45%, and 55% fresh work was 94J, 74J, and 52J. It was smaller than 100J, and after 45%, 55% fresh processing, disconnection occurred, and after 30~60% fresh processing, the difference in average room temperature impact toughness was 42J or more, which did not satisfy Equation (1) of the present invention.

In Comparative Example 5, the content of carbon was 0.38% by weight, which exceeded 0.35% by weight, and the carbon equivalent (Ceq) exceeded 0.6 by 0.612, and the average cooling rate was 0.05°C/s, which was smaller than 0.1°C/s. For this reason, the non-finished wire of Comparative Example 5 had a ferrite fraction of 28% and less than 30%, a C-section ferrite average particle diameter of 22 µm, exceeding 20 µm, and a pearlite average lamella spacing of 0.32 µm, exceeding 0.3 µm. , The C-section hardness deviation exceeded 30Hv as 36Hv, and after 35%, 45, and 55% fresh processing, the impact toughness was less than 100J as 81J, 62J and 38J, and disconnection occurred after 45%, 55% fresh processing, After 30-60% fresh processing, the difference in average room temperature impact toughness was 43J, which is 40J or more, and the formula (1) of the present invention was not satisfied.

In Comparative Example 6, the content of carbon was 0.43% by weight, exceeding 0.35% by weight, and the carbon equivalent (Ceq) was 0.690, which exceeded 0.6. Due to this, the non-hardened wire of Comparative Example 6 had a ferrite fraction of less than 30% as 21%, and a C-section hardness deviation exceeded 30Hv as 41Hv, and impact toughness after fresh processing of 35%, 45%, and 55% of each was 61J. , 43J, 25J, smaller than 100J, and disconnection occurred after 35%, 45%, and 55% fresh processing.

From this, it can be seen that the unstructured wire of the present invention and its manufacturing method can provide an excellent unprocessed wire having excellent workability and impact toughness without additional heat treatment by controlling alloy composition and manufacturing conditions.

As described above, although exemplary embodiments of the present invention have been described, the present invention is not limited thereto, and a person skilled in the art does not depart from the concept and scope of the following claims. It will be understood that various modifications and variations are possible.

Claims (12)

In weight percent, C: 0.05 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.5 to 2.0%, Cr: 1.0% or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.07 %, N: less than or equal to 0.01%, Nb: less than or equal to 0.1%, V: less than or equal to 0.5%, and Ti: less than or equal to 0.1%, including residual Fe and unavoidable impurities,
Microstructure, non-woven wire with excellent workability and impact toughness, including a ferrite-pearlite layered structure in the rolling direction. According to claim 1,
A non-hard wire having excellent workability and impact toughness with an average thickness of 5 to 30 µm of the ferrite layer in the L section, which is a parallel section in the rolling direction. According to claim 1,
A non-hard wire having excellent workability and impact toughness with an average particle diameter of 3 to 20 µm in the C cross section, which is a right-angle cross section in the rolling direction. According to claim 1,
The ferrite has a fraction of 30 to 90%, and is an uncoated wire having excellent workability and impact toughness. According to claim 1,
The pearlite has an average lamellar spacing of 0.03 to 0.3 µm, and is an uncoated wire having excellent workability and impact toughness. According to claim 1,
Uncoated wire having excellent workability and impact toughness with a carbon equivalent of 0.4 to 0.6 represented by the following formula:
Ceq = [C] + [Si]/9 + [Mn]/5 + [Cr]/12
(Here, [C], [Si], [Mn], [Cr] each means the content (%) of the corresponding element). According to claim 1,
An uncoated wire having excellent workability and impact toughness with a difference between a maximum hardness value and a minimum hardness value of 30 Hv or less in the cross-section C, which is a right-angle cross section in the rolling direction. According to claim 1,
When 30 to 60% of the wire rod is freshly processed, an unstructured wire having excellent workability and impact toughness having an average value of 100 J or more at room temperature impact toughness. According to claim 1,
When 30 to 60% of the wire rod is freshly processed, an unstructured wire having excellent fresh workability and impact toughness satisfying the following formula (1):
(1) Imax-Imin ≤ 40J
(Here, Imax: the maximum value of average room temperature impact toughness after fresh processing, Imin: the minimum value of average room temperature impact toughness after fresh processing). In weight percent, C: 0.05 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.5 to 2.0%, Cr: 1.0% or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.07 %, N: 0.01% or less, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less, and at least one of the following steps: preparing a steel piece containing the balance Fe and unavoidable impurities;
Reheating the steel piece to a reheating temperature (Tr) that satisfies Expression (2) below;
Rolling the reheated steel piece into a wire rod; And
Winding the rolled wire rod and then cooling it; A method for manufacturing a non-woven wire rod having excellent workability and impact toughness, including:
(2) T1 ≤ Tr ≤ 1200℃
(Here, T1 = 757 + 606[C] + 80[Nb]/[C] + 1023√[Nb] + 330[V], each of [C], [Nb] is the content (%) of the element. it means). The method of claim 10,
The step of rolling the wire rod,
Method for manufacturing a non-woven wire having excellent workability and impact toughness, including rolling to a finish rolling temperature (Tf) satisfying the following formula (3):
(3) T2 ≤ Tf ≤ T3
(Where, T2 = 955-396 [C] + 24.6 [Si]-68.1 [Mn]-24.8 [Cr]-36.1 [Nb]-20.7 [V],
T3 = 734 + 465[C]-355[Si] + 360[Al] + 891[Ti] + 6800[Nb]-650√[Nb] + 730[V]-232√[V],
Each of [C], [Si], [Mn], [Cr], [Al], [Ti], [Nb], [V] means the content (%) of the corresponding element). The method of claim 10,
The cooling step,
Method of manufacturing a non-woven wire having excellent workability and impact toughness, including cooling at an average rate of 0.1 to 2°C/s.

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