KR20180072965A - Steel wire rod and steel wire having high toughness and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a steel wire rod and a steel wire having high toughness, and a method of manufacturing the same, wherein the steel wire rod and the steel wire having high toughness includes: 0.1 to 0.6 wt% C, 0.2 to 2.0 wt% Si, 0.1 to 1.0 wt% Cr, 0.2 to 2.0 wt% Mn, 0.01 to 0.05 wt% Al, 0.004 to 0.02 wt% N, and the remainder Fe and other unavoidable impurities, and having a microtissue including ferrite and pearlite, wherein the grain of the ferrite is 12μm or less in size, the ferrite including 20 to 50 area % of subgrain and AlN precipitates. According to the present invention, the steel wire rod and the steel wire having high toughness can be provided.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire having excellent toughness,

TECHNICAL FIELD The present invention relates to a wire having excellent toughness, a steel wire and a manufacturing method thereof.

The wire rod products can be classified into QT heat treatment type steels according to the purpose of the end customer and non-heat treatment type steels which ensure the physical properties of the steel only by drawing.

The strength and in / ductility of the QT steel are determined by tempering after the austenitizing heat treatment.

The lower the tempering temperature, the more tendency of the material strength to increase, but at the same time, the lowering of the softness / toughness of the product and the decrease in the hydrogen retarding resistance resistance should be maintained. Furthermore, the austenite grain size (AGS) after QT has a great influence on the physical properties. In general, as the strength of the material increases, the softness / toughness decreases. On the other hand, grain refinement is known as the only method capable of ensuring both strength and softness / toughness.

In general, for the purpose of grain refinement, precipitates such as Nb are utilized, or grain refinement is achieved through non-recrystallization reverse rolling. However, the unrecrystallized unreinforced rolled steel is rolled on the upper side of Ar3, and its temperature range is not wide, and there is a limitation in suppressing rapid grain growth due to cumulative deformation and transformation heat upon cooling after completion of rolling.

Korea Patent Publication No. 2011-0099749

A preferred aspect of the present invention is to provide a high-toughness wire having excellent toughness and a method of manufacturing the same.

Another desirable aspect of the present invention is to provide a high tensile steel wire having excellent toughness and a method of manufacturing the same.

According to a preferred aspect of the present invention, there is provided a steel sheet comprising 0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, 0.2 to 2.0% of Mn, 0.01 to 0.05% of Al and 0.004 to 0.02% of N, the balance Fe and other unavoidable impurities, and has a microstructure including ferrite and pearlite, and the ferrite has a grain size of 12 Mu m or less, and 20 to 50 area% And a wire having excellent toughness including AlN precipitates is provided.

The wire may further contain 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, ≪ / RTI >

The wire rod may further include at least one precipitate of Nb-based carbonitride, Ti-based carbonitride, V-based carbonitride and Mo-based carbonitride.

The microstructure of the wire may be composed of 20 to 80% by area of ferrite and the remaining pearlite.

The wire rod may have a grain size (AGS: old austenite grain size) of not more than 5 탆 after QT heat treatment.

According to another aspect of the present invention, there is provided a steel sheet comprising 0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, 0.2 to 2.0% Mn, 0.01 to 0.05% Al and 0.004 to 0.02% N, the balance Fe and other unavoidable impurities at 900 to 1100 캜;

The billet heated as above was rolled at a finishing mill (FM) inlet temperature of 820 to 780 ° C and an inlet temperature condition of 760 to 730 ° C (RSM) to obtain a wire rod having a subgrain grain fraction of 20 to 50% A hot rolling step of obtaining a hot rolled steel sheet; And

There is provided a method of manufacturing a wire rod excellent in toughness including winding the wire rod and cooling the wire rod.

The billet may further contain at least one of Nb: 0.001-0.03%, Ti: 0.01-0.05%, V: 0.2-0.5%, Mo: 0.15-0.50% and B: 0.005-0.02%.

The finish rolling process and the precision rolling process in the hot rolling are preferably carried out in a two-phase region of ferrite and austenite.

The diameter of the wire may be 18 mm or less.

After the winding, the cooling rate may be 5 DEG C / sec or more.

The wire rod manufactured as described above can be subjected to QT heat treatment as it is.

The grain size (AGS: old austenite grain size) of the wire after the QT heat treatment may be 5 탆 or less.

According to another aspect of the present invention, there is provided a steel sheet comprising 0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, Wherein the microstructure comprises tempered martensite, comprising AlN precipitates, and having a grain size (AGS) of from 0.2 to 2.0% Mn, from 0.01 to 0.05% Al and from 0.004 to 0.02% N and balance Fe and other inevitable impurities, (Old austenite grain size) of 5 탆 or less is provided.

The steel wire may further contain 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, ≪ / RTI >

The steel wire may further include at least one of Nb-based carbonitride, Ti-based carbonitride, V-based carbonitride and Mo-based carbonitride.

According to another aspect of the present invention, there is provided a steel sheet comprising 0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, Heating a billet comprising 0.2 to 2.0% of Mn, 0.01 to 0.05% of Al, and 0.004 to 0.02% of N, the balance Fe and other unavoidable impurities at 900 to 1100 占 폚;

The billet heated as above was rolled at a finishing mill (FM) inlet temperature of 820 to 780 ° C and an inlet temperature condition of 760 to 730 ° C (RSM) to obtain a wire rod having a subgrain grain fraction of 20 to 50% A hot rolling step of obtaining a hot rolled steel sheet;

Winding the wire rod and cooling it;

Preparing a steel wire by drawing the wire material at a shrinking rate of 5 to 40%; And

And a step of subjecting the steel wire to QT heat treatment.

The billet further contains 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, ≪ / RTI >

The finish rolling process and the precision rolling process in the hot rolling are preferably carried out in a two-phase region of ferrite and austenite.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to provide a wire rod and a steel wire excellent in toughness.

Fig. 1 is a photograph showing the SEM-EBSD structure of the wire after rolling in Inventive Example 1 and Comparative Example 1
2 is a graph showing Misorientation angle values of 15 DEG or less in Inventive Example 1 and Comparative Example 1
3 is a graph showing the grain size (AGS) after QT heat treatment in Inventive Example 1 and Comparative Example 1
4 is a microstructure photograph showing microstructure after QT heat treatment in Inventive Example 1 and Comparative Example 1

Hereinafter, the present invention will be described.

Minimization of initial austenite grain size and short heating time before QT heat treatment are important to ensure fine AGS (austenite grain size) during QT heat treatment of steel.

The present invention aims at achieving the miniaturization of the initial austenite grains before the QT heat treatment.

For this purpose, the steel and the wire side are controlled along with the composition of the microstructure and the precipitate.

1) In terms of microstructure, ferrite and pearlite are included, and the fraction of subgrain in ferrite is increased to enable the formation of austenite nuclei even in the ferrite grain, thereby achieving miniaturization of the initial austenite grains.

2) On the side of the precipitate, a carbon / nitride formation element such as Al, Ti, Nb, V, and Mo is added to form a carbon / nitride precipitate. When the steel is heated for austenizing in the QT heat treatment, It is possible to suppress the growth of the austenite and achieve the fineness of the initial austenite grains.

3) The precipitates inhibit the growth of ferrite and pearlite in the production of wire rods, thereby making the ferrite and pearlite fine. Such fine ferrite and pearlite structure can contribute to the miniaturization of the initial austenite grains by increasing the fraction of the grain boundaries effective as nucleation sites have.

In the present invention, in order to increase the subgrain fraction in the ferrite, the steel composition and the production conditions are controlled. In particular, the hot rolling process, in particular the finish rolling process and the precision rolling process, is controlled

The finish rolling mill controls the inlet temperature of the finishing mill (FM) and the precision milling (RSM) inlet temperature in the precision milling process.

Preferably, the finish rolling process and the precision rolling process in hot rolling are preferably carried out in a two-phase region of ferrite and austenite.

As described above, by finely grinding the initial austenite grains before the QT heat treatment of the steel material, it is possible to secure fine crystal grains during the final QT heat treatment, thereby improving the toughness of the steel.

Hereinafter, the preferred wire and wire having excellent toughness of the present invention will be described.

The preferred toughness of the present invention is 0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, 0.2 to 2.0% of Mn, 0.01 to 0.05% of Al and 0.004 to 0.02% of N, the balance Fe and other unavoidable impurities, and has a microstructure including ferrite and pearlite, and the ferrite has a grain size of 12 Mu m or less, and 20 to 50 area% , And includes AlN precipitates.

0.1 to 0.6% by weight of C (hereinafter also referred to as "%"),

When the content of C exceeds 0.6%, almost all the structure is composed of pearlite, and it is difficult to secure the aimed ferrite crystal grains. When the content of C is less than 0.1%, the ferrite fraction is excessively increased and the pearlite micro- And it is difficult to secure sufficient strength even in a martensite structure.

Therefore, the content of C is preferably limited to 0.1 to 0.6%, more preferably 0.2 to 0.5%.

Si: 0.2 to 2.0%

Si is a representative substitutional element and has a great influence on securing strength of steel. When the content of Si is less than 0.2%, it is difficult to secure the strength of the steel and secure sufficient ingotability. When the content of Si exceeds 2.0%, the formation of decarburized structure during rolling is promoted and additional removal cost is required.

Therefore, the content of Si is preferably limited to 0.2 to 2.0%.

Cr (Cr): 0.1 to 1.0%

Chromium promotes ferrite and pearlite transformation during hot rolling.

In addition, without increasing the strength of the steel itself more than necessary, it precipitates carbides in the steel to reduce the amount of solid carbon, which contributes to reduction of dynamic strain aging due to solid carbon. In order to exhibit such an effect in the present invention, it is preferable that the content is 0.1% or more. However, when the content is excessive, the strength of the steel itself becomes excessively high, so that the deformation resistance of the steel rapidly increases, thereby deteriorating the cooling simple composition. Therefore, the upper limit of the chromium content is preferably 1.0%.

Mn: 0.2 to 2.0%

The manganese (Mn) forms a substitutional solid solution in the matrix and lowers the A1 transformation point, thereby reducing the spacing between the pearlite layers and increasing the crystal grains in the ferrite structure.

When the manganese is added in an amount exceeding 2.0%, the harmful influence is exerted by the tissue heterogeneity due to the manganese grains. It is easy to cause macro segregation and micro segregation according to the segregation mechanism when the steel is solidified. The seismic segregation is promoted by the relatively low diffusion coefficient compared to the other elements, and the hardening ability due to this is promoted by the core martensite It becomes the main cause of generation. On the other hand, when manganese is added in an amount of less than 0.2%, sufficient entrapment property for securing martensite structure after QT is difficult to secure.

Therefore, the content of Mn is preferably limited to 0.2 to 2.0%.

Al: 0.01 to 0.05%

Al is added as a de-oxidizing material, and as a component for forming a precipitate such as AlN, when the content is less than 0.01%, sufficient deoxidizing power is secured and precipitate formation is difficult. When the content is more than 0.05%, Al ₂ O ₃ The inclusion of the inclusions may be increased. In particular, clogging of the nozzle due to inclusions during performance may occur.

The AlN precipitate effectively suppresses crystal grain growth and contributes to the refinement of austenite grain through strain organic precipitation during rolling.

Therefore, the content of Al is preferably limited to 0.01 to 0.05%.

N: 0.004 to 0.02%

When the content of N is less than 0.004%, it is difficult to secure sufficient nitride, and the precipitation amount of Ti, Nb and V can be decreased. When the content of N exceeds 0.02%, the nitrogen / Degradation may occur.

Therefore, the content of N is preferably limited to 0.004 to 0.02%.

Precipitates such as Ti, Nb, V and AlN are firstly produced in a nitride form at a high temperature. Subsequently, the undecomposed precipitates are deficient in C and precipitate in a carbide form at a low temperature or grow together with a nitride formed at a high temperature. Therefore, the amount of nitrogen has a great influence on the distribution of precipitates, and the content thereof needs to be controlled.

0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, May be contained.

Nb: 0.001 to 0.03%

The Nb forms carbonitride such as Nb (C, N), which is useful for micronization of ferrite / pearlite wire during proper rolling. In addition, prior to precipitation, the solute drag effect affects the fineness of the austenite grain during rolling.

However, when the content is less than 0.001%, the precipitation effect is not sufficient. When the content exceeds 0.03%, the precipitation effect may be deteriorated due to precipitate coarsening.

Therefore, the content of Nb is preferably limited to 0.001 to 0.03%.

Ti: 0.01 to 0.05%

The Ti is the most powerful carbonitride-forming element and helps to refine the grain in the furnace. However, if the Ti content is less than 0.01%, the precipitation amount is small and the effect decreases. When the Ti content exceeds 0.05%, the Ti content may act as a crack initiation site which deteriorates phosphorus / ductility due to precipitate coarsening.

Therefore, the content of Ti is preferably limited to 0.01 to 0.05%.

V: 0.2 to 0.5%

V forms VC, VN, V (C, N) and the like, and accompanied by appropriate rolling induces ferrite / pearlite wire microfabrication. If the content is less than 0.2%, the effect on the toughness is insignificant because the distribution of the vanadium precipitates in the base material is decreased and the ferritic grain boundary is not fixed, and if the content exceeds 0.5%, the carbon and nitrogen In the range, coarse vanadium carbonitride is formed and adversely affects toughness.

Therefore, the content of V is preferably limited to 0.2 to 0.5%.

Mo: 0.15 to 0.50%

The Mo forms deposits of Mo2C upon tempering during the QT heat treatment, and is effective in suppressing the strength decrease (temper softening) during tempering. However, if the content is less than 0.15%, it is difficult to obtain a sufficient temper softening effect. If the content is more than 0.50%, a low-temperature structure may be generated in the wire rod state, and additional heat treatment cost for removing the cold structure may be required.

Mo-based carbide is a secondary precipitation strengthening element and mainly precipitates during tempering during QT heat treatment. Particularly, in order to improve hydrogen delay fracture resistance, material softening does not occur during high temperature tempering, and the strength is rather increased. At this time, if the content of Mo is less than 0.15%, the secondary precipitation strengthening effect hardly occurs, so it is preferable to limit the content as described above.

Therefore, the Mo content is preferably limited to 0.15 to 0.50%.

B: 0.005 to 0.02%

B is a component that serves to densify the rust formed on the surface and increase the strength of the grain boundaries by enhancing the corrosion resistance and improving the hardenability. If the content is less than 0.005%, the ingot is not ensured and the strength required for the high-strength wire can not be secured. If the content exceeds 0.02%, the carbonitride-based precipitates are coarsened and adversely affect the tensile and fatigue properties . Therefore, the content of B is preferably limited to 0.005 to 0.02%.

The preferred high-tenacity wire of the present invention has a microstructure comprising ferrite and pearlite, wherein the ferrite has a grain size of 12 탆 or less and 20 to 50 area% , And includes Al-based precipitates.

The wire rod may further include at least one precipitate of Nb-based carbonitride, Ti-based carbonitride, V-based carbonitride and Mo-based carbonitride.

The microstructure of the wire may be composed of 20 to 80% by area of ferrite and the remaining pearlite.

Precipitates are used to maximize the effect of inhibiting grain growth during rolling and cooling. For the pinning effect of such a precipitate, it is preferable that the size of the precipitate is reduced to 10 to 500 nm, and if the coarsening is performed beyond this, the pinning effect may be drastically reduced.

In addition, grain boundary growth inhibition is effective when the distribution of precipitates is 2 to 10 / um ² . When the precipitate density is less than ² particles / um ² , it is difficult to inhibit the growth of crystal grains. When the particle size exceeds 10 particles / um ² , the effect is saturated.

The wire may be subjected to QT heat treatment, wherein the microstructure of the wire after QT heat treatment is tempered martensite and the grain size (AGS; old austenite grain size) may be 5 탆 or less.

The wire may be manufactured as a steel wire by a drawing process and then subjected to a QT heat treatment. The microstructure of the steel wire after the QT heat treatment may be tempered martensite, and the grain size (AGS; old austenite grain size) .

Hereinafter, a preferable example of the method for manufacturing a wire rod and a steel wire according to the present invention will be described.

According to another preferred embodiment of the present invention, there is provided a method for producing a wire having excellent toughness, which comprises 0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, 0.2 to 2.0% Mn, 0.01 to 0.05% Al and 0.004 to 0.02% N, the balance Fe and other unavoidable impurities at 900 to 1100 캜; The billet heated as above was rolled at a finishing mill (FM) inlet temperature of 820 to 780 ° C and an inlet temperature condition of 760 to 730 ° C (RSM) to obtain a wire rod having a subgrain grain fraction of 20 to 50% A hot rolling step of obtaining a hot rolled steel sheet; And cooling the wire after winding the wire.

The billet further contains 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, ≪ / RTI >

Billet  Heating step

The billet is heated at 900 to 1100 占 폚.

It is preferred that the billet is heated to 900 to 1100 DEG C and maintained at this temperature, for example, for 10 to 30 minutes.

The total time for heating and holding the billet to 900 to 1100 占 폚 is preferably 90 to 120 minutes, for example.

If the heating temperature is less than 900 ° C, the rolling load is rapidly increased, which may cause problems such as roll breakage, cobblestone and surface scratches during rolling. When the temperature exceeds 1100 ° C, the billet surface decarburization There is a fear that the reaction rapidly increases and the deteriorated surface structure is increased.

Therefore, the heating temperature of the billet is preferably limited to 900 to 1100 占 폚.

If the holding time is less than 10 minutes at 900 to 1100 ° C, there is a possibility that the target temperature is not sufficiently reached to the center of the material, There is a fear that the surface deteriorated structure is increased due to an increase in scale, surface decarburization and the like.

Hot rolling step

The rolling method preferably applied to the present invention is a rolling method Rough rolling of the heated billets, finishing rolling and precision rolling.

The heated billet is hot-rolled to obtain a wire rod.

The finish rolling process and the precision rolling process are preferably carried out in a two-phase region of ferrite and austenite.

The hot rolling is preferably carried out under the conditions of an inlet temperature of the finishing mill (FM) of 820 to 780 ° C and an inlet temperature of the precision mill (RSM) of 760 to 730 ° C.

When the inlet temperature of the finishing mill (FM) is less than 780 DEG C, there is a fear that the decarburized structure and surface flaws such as ferrite on the surface portion increase rapidly due to overcooling / quenching during rolling. When the temperature exceeds 820 DEG C, Ferrite) is decreased and a target crystal grain size can not be ensured.

Therefore, the inlet temperature of the finish mill (FM) is preferably limited to 820 to 780 ° C.

When the inlet temperature of the precision mill (RSM) is less than 730 캜, it may be subcooled below the Ar 1 transformation point to increase the roll load and secure the microstructure composed of ferrite / pearlite. When the inlet temperature exceeds 760 캜, The target crystal grain size may not be ensured.

The hot rolling is carried out under the condition that the sub-grain fraction of the ferrite phase of the wire rod obtained by rolling is 20 to 50% by area.

If the area is less than 20% by area, the effect of grain refinement may not be secured in the QT heat treatment. If it exceeds 50% by area, the strength of the wire rod may be increased There is a possibility that the linearity of the wire rod is not ensured.

Therefore, it is preferable that the grain fraction of the sub grain in the ferrite phase of the wire is limited to 20 to 50 area%.

The diameter of the wire is preferably limited to, for example, 18 mm or less.

Coiling  And cooling step

The wire rod obtained by hot rolling as described above is wound and cooled.

The cooling rate during cooling is preferably limited to, for example, 5 DEG C / sec or more

When the cooling rate is less than 5 ° C / sec, crystal grain coarsening may occur due to deformation and transformation heat, so that the temperature is preferably limited to 5 ° C / sec or more, more preferably 5 to 20 ° C / sec will be.

The cooling end temperature is preferably limited to, for example, 200 to 600 ° C.

The reason for limiting the cooling end temperature to 200 to 600 ° C is to terminate the transformation at the cooling zone and secure the desired microstructure.

QT heat treatment ( Submission  And Heat treatment )

The wire rod produced as described above can be directly quenched and subjected to a heat treatment (QT heat treatment).

The heating temperature during the quenching heat treatment is preferably 800 to 1000 占 폚, and the cooling rate is preferably 20 占 폚 / sec or more.

If the quenching temperature is less than 800 ° C., austenite structure can not be secured at a low heat treatment temperature, and it may be difficult to obtain sufficient strength after heat treatment. If the temperature is more than 1000 ° C., There is a concern. When the cooling rate is less than 20 캜 / sec, the complete martensite structure may not be obtained.

The heating temperature during the baking heat treatment is preferably 300 to 600 ° C.

When the annealing temperature is less than 300 ° C, a film-like plate-like cementite is formed along the grain boundary, which may cause problems such as hydrogen embrittlement. When the annealing temperature exceeds 600 ° C, sufficient strength is secured It can be difficult.

The microstructure of the wire after the QT heat treatment is tempered martensite and the grain size (AGS) may be, for example, 5 탆 or less.

Freshness and QT heat treatment

The wire rod manufactured as described above may be subjected to quenching and quenching heat treatment (QT) after drawing.

It is preferable that the freshness rate is limited to, for example, 5 to 40%.

When the shrinkage ratio is less than 5%, the sufficient deformation structure does not develop to the center of the material, so it may be difficult to austenize for a short time during the QT heat treatment. Therefore, there is a fear of crystal grain coarsening at the time of heat treatment for a long time, and if it exceeds 40%, 1 pass drawing can not be performed, and the manufacturing process may become long and complicated.

The microstructure of the steel wire after the QT heat treatment is tempered martensite, and the grain size (AGS) may be, for example, 5 占 퐉 or less.

Hereinafter, the present invention will be described in more detail by way of examples.

(Example)

A billet having the composition shown in Table 1 below was heated and hot-rolled under the conditions shown in Table 2 below to produce a wire having a diameter of 13 mm.

The wire thus prepared was subjected to QT heat treatment and AGS (old austenite grain size) was measured. The results are shown in Table 2 below. In this case, the QT heat treatment was performed by IQT (Induction Queching & tempering Treatment) with a short heating time in order to minimize the AGS deviation by heating temperature, and the heating temperature was 850 to 950 ° C.

In Table 2 below, FM represents the finishing mill inlet temperature, RSM represents the precision mill inlet temperature, FGS represents the ferrite grain size, and AGS represents the old austenite grain size.

The SEM-EBSD texture photographs of the rolled wire of Inventive Example 1 and Comparative Example 1 in the following Table 2 are shown in FIG. 1 and the misorientation angle values of 15 ° or less are examined. The results are shown in FIG. 2 .

The AGS (old austenite grain size) of the wire rod after the QT heat treatment in Inventive Example 1 and Comparative Example 1 was measured, and the results are shown in Fig. 3. The microstructure of the wire rod after the QT heat treatment was observed, Respectively.

Steel grade C Si Cr Mn Al N Nb Ti V Mo B Inventive Steel 1 0.25 0.30 0.35 1.30 0.042 0.015 0.015 - - - Invention river 2 0.35 1.20 0.20 1.30 0.010 0.004 0.015 0.02 - - Invention steel 3 0.40 0.80 0.30 1.20 0.042 0.013 0.020 0.02 - 0.2 Comparative River 1 0.72 0.30 0.15 0.80 0.035 0.010 - - - - Inventive Steel 4 0.35 0.20 0.50 0.70 0.035 0.010 - - - - Invention steel 5 0.20 0.25 0.35 0.80 0.030 0.015 0.015 - 0.3 0.2 Invention steel 6 0.25 0.30 0.45 1.20 0.040 0.020 0.015 - - -  Invention steel 7 0.45 0.18 0.25 1.20 0.036 0.016 - 0.03 - 0.3 Inventive Steel 8 0.50 0.15 0.20 1.50 0.032 0.012 - 0.02 0.3 0.2 Invention river 9 0.45 0.18 0.65 1.20 0.036 0.016 - 0.03 - 0.3 0.01

Example
No. Steel grade Heating conditions [heating temperature (占 폚)
/ Total heating time (minute)] FM
(° C) RSM
(° C) Microstructure FGS (um) Artificial lip
Fraction
(area%) AGS after QT
(um) Comparative Example 1 Inventive Steel 1 1000 ° C / 90 min 900 850 F (70) + P (30) 20 15 12 Comparative Example 2 Invention river 2 1050 ° C / 90 min 850 760 F (65) + P (35) 25 16 14 Comparative Example 3 Invention steel 3 1020 DEG C / 100 min 815 780 F (50) + P (50) 15 8 13 Comparative Example 4 Comparative River 1 1000 ° C / 90 min 800 750 F (5) + P (95) 25 5 15 Inventory 1 Inventive Steel 4 1000 ° C / 90 min 780 760 F (65) + P (35) 10 30 5.0 Inventory 2 Invention steel 5 1000 ° C / 90 min 800 750 F (80) + P (20) 8.8 35 4.8 Inventory 3 Invention steel 6 1000 ° C / 90 min 810 730 F (70) + P (30) 8.5 40 4.2 Honorable 4 Invention steel 7 1000 ° C / 90 min 800 760 F (45) + P (55) 8.3 33 4.1 Inventory 5 Inventive Steel 8 1000 ° C / 90 min 780 750 F (30) + P (70) 9.2 33 3.2 Inventory 6 Invention river 9 1000 ° C / 90 min 800 760 F (45) + P (55) 8.3 33 4.5

(In Table 2, F denotes ferrite and P denotes pearlite)

As shown in Table 2 and FIG. 1-4, it can be seen that the wire material according to the present invention (Examples 1-6) has a grain size (AGS) of 5 μm or less after the QT heat treatment.

It can be seen that the wire rod (Comparative Example 1-4) deviating from the scope of the present invention has a grain size (AGS) exceeding 5 탆 after QT heat treatment.

As can be seen from Table 2 and FIG. 2, it can be seen that, in the case of Inventive Example 1-6, a high subgrain grain (crystal grains having a misorientation angle value of 15 ° or less) of 30% or more was produced, As shown in Table 2, Fig. 3 and Fig. 4, when the QT heat treatment is performed, the ratio of the sublattice grain size is 5 mu m or less Ultrafine grains can be secured. These results show that securing of the subgrain grain ratio more than the optimum in the initial wire rod state has a great influence on the final AGS.

When the Al-based precipitates were observed for the wires conforming to the present invention (Examples 1-6), it was confirmed that the fine Al-based precipitates were distributed.

On the other hand, when the wires prepared according to the inventive example 1 of Tables 1 and 2 were freshly prepared at a shrinking rate of 10 to 30%, and the AGS of the wires was measured after the QT heat treatment as described above, .

Claims (23)

0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, 0.2 to 2.0% of Mn, 0.01 to 0.05% of Al and 0.004 to 0.02% of N, the balance Fe and other unavoidable impurities, and has a microstructure including ferrite and pearlite, and the ferrite has a grain size of 12 Mu m or less, and 20 to 50 area% And an excellent toughness including Al-based precipitates.
The steel wire rod according to claim 1, wherein the wire rod further contains 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, And at least one of them is contained.
The wire according to claim 2, characterized in that the wire further comprises at least one precipitate of Nb-based carbonitride, Ti-based carbonitride, V-based carbonitride, Mo-based carbonitride and B- Pre-existing.
The wire according to claim 1 or 2, wherein the microstructure of the wire comprises 20 to 80% by area of ferrite and the remaining pearlite.
The wire according to claim 1 or 3, wherein the size of the precipitate is 10 to 500 nm and the precipitate density is 2 to 10 / um ² .
The wire rod according to claim 1, wherein the wire rod has a grain size (AGS) of 5 탆 or less after QT heat treatment.
0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, 0.2 to 2.0% of Mn, 0.01 to 0.05% of Al and 0.004 to 0.02% of N, Heating the billet containing unavoidable impurities at 900 to 1100 占 폚;
The billet heated as above was rolled at a finishing mill (FM) inlet temperature of 820 to 780 ° C and an inlet temperature condition of 760 to 730 ° C (RSM) to obtain a wire rod having a subgrain grain fraction of 20 to 50% A hot rolling step of obtaining a hot rolled steel sheet; And
And winding the wire rod and cooling the wire rod.
The billet according to claim 7, wherein the billet further contains 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, By weight based on the total weight of the raw material.
The method according to claim 7, wherein the hot rolling step and the precision rolling step are performed in a two-phase region of ferrite and austenite.
8. The method according to claim 7, wherein the wire has a diameter of 18 mm or less.
The method according to claim 7, wherein a fraction of the crystal grain fraction in the ferrite phase of the hot rolled wire after hot rolling in the hot rolling step is 20 to 50%.
The method for producing a wire rod excellent in toughness according to claim 7, wherein the cooling rate in the step of cooling after the winding is 5 ° C / sec or more.
The method according to claim 7, wherein the cooling end temperature in the step of cooling after the winding is 200 to 600 占 폚.
8. The method according to claim 7, further comprising the step of subjecting the wire rod to QT heat treatment.
15. The method according to claim 14, wherein the grain size (AGS) of the wire after the QT heat treatment is 5 占 퐉 or less.
0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, Wherein the microstructure comprises tempered martensite, comprising AlN precipitates, and having a grain size (AGS) of from 0.2 to 2.0% Mn, from 0.01 to 0.05% Al and from 0.004 to 0.02% N and balance Fe and other inevitable impurities, ; Old austenite grain size) of 5 탆 or less.
The steel wire according to claim 16, wherein the steel wire further comprises 0.001 to 0.03% of Nb, 0.01 to 0.05% of Ti, 0.2 to 0.5% of V, 0.15 to 0.50% of Mo, and 0.005 to 0.02% of B, By weight based on the total weight of the steel wire.
18. The method of claim 17, wherein the steel wire further comprises at least one precipitate of Nb-based carbonitride, Ti-based carbonitride, V-based carbonitride, Mo-based carbonitride and B- Steel wire.
0.1 to 0.6% of C, 0.2 to 2.0% of Si, 0.1 to 1.0% of Cr, Heating a billet comprising 0.2 to 2.0% of Mn, 0.01 to 0.05% of Al, and 0.004 to 0.02% of N, the balance Fe and other unavoidable impurities at 900 to 1100 占 폚;
The billet heated as above was rolled at a finishing mill (FM) inlet temperature of 820 to 780 ° C and an inlet temperature condition of 760 to 730 ° C (RSM) to obtain a wire rod having a subgrain grain fraction of 20 to 50% A hot rolling step of obtaining a hot rolled steel sheet;
Winding the wire rod and cooling it;
Preparing a steel wire by drawing the wire material at a shrinking rate of 5 to 40%; And
And subjecting the steel wire to QT heat treatment.
The billet according to claim 19, wherein the billet further comprises at least one of Nb: 0.001-0.03%, Ti: 0.01-0.05%, V: 0.2-0.5%, Mo: 0.15-0.50%, and B: 0.005-0.02% By weight based on the total weight of the steel wire.
20. The method of manufacturing a steel wire excellent in toughness according to claim 19, wherein the finish rolling process and the precision rolling process in the hot rolling are performed in a two-phase region of ferrite and austenite.
The steel wire manufacturing method according to claim 19, wherein a fraction of the crystal grain fraction in the ferrite phase of the hot rolled wire after hot rolling in the hot rolling step is 20 to 50%
20. The method of manufacturing a steel wire according to claim 19, wherein the grain size (AGS) of the steel wire after the QT heat treatment is 5 占 퐉 or less.

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