KR101676187B1 - Wire-shaped or rod-shaped steel having excellent cold workability and method for manufacturing same - Google Patents

Wire-shaped or rod-shaped steel having excellent cold workability and method for manufacturing same Download PDF

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KR101676187B1
KR101676187B1 KR1020150125341A KR20150125341A KR101676187B1 KR 101676187 B1 KR101676187 B1 KR 101676187B1 KR 1020150125341 A KR1020150125341 A KR 1020150125341A KR 20150125341 A KR20150125341 A KR 20150125341A KR 101676187 B1 KR101676187 B1 KR 101676187B1
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steel
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문동준
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주식회사 포스코
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.05 to 0.4% of C, 0.05 to 0.5% of Si, 0.1 to 2.0% of Mn, 0.03% or less of P, 0.007 to 0.015% of S, 0.0056 to 0.015% of B, %, Remainder Fe, and unavoidable impurities, and comprising a single or complex precipitate of BN and MnS, and having a P C of 60% or more, defined by the following formula 1, and a method for producing the same.
[Formula 1]
P C (%) = {N c / (N s + N c )} x 100
Where N s is the number of BN-alone precipitates per 1 mm 2 present in the cross-section cut in a direction perpendicular to the longitudinal direction of the linear or bar-shaped steel, and N c is the length of the linear or bar-shaped steel cut in a direction perpendicular to the longitudinal direction Means the number of complex precipitates of BN and MnS per 1 mm 2 present in one cross section)

Description

TECHNICAL FIELD [0001] The present invention relates to a linear or rod-shaped steel having excellent cold workability, and a method of manufacturing the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to a linear or bar-shaped steel excellent in cold workability and a method of manufacturing the same. More particularly, the present invention relates to a linear or bar-shaped steel excellent in cold workability which can be preferably applied to the production of mechanical parts such as bolts and nuts, .

The cold working method is widely used for manufacturing mechanical parts such as bolts and nuts because it has excellent productivity and has a large effect of reducing the heat treatment cost as compared with the hot working method or the mechanical cutting working method.

However, in order to manufacture the mechanical parts using the cold working method as described above, it is required that the cold workability of the steel is essentially excellent, and more specifically, it is required to have low deformation resistance and excellent ductility in cold working. This is because when the deformation resistance of the steel is high, the life of the tool used in the cold working is reduced, and when the ductility of the steel is low, cracking is likely to occur during cold working, which is a cause of defective products.

As a result, the ordinary steel for cold working is subject to a spheroidizing annealing heat treatment before cold working. This is because the steel is softened during the annealing for spheroidizing annealing, the deformation resistance is decreased, the ductility is improved, and the cold workability is improved.

However, since the above-described spheroidizing annealing requires a long heat treatment for about 10 to 20 hours, it is possible to omit the spheroidizing annealing heat treatment in order to improve the productivity and save energy, It is required to develop a linear or bar-shaped steel in which deformation resistance is suppressed.

In this connection, in Patent Documents 1 and 2, the content of ferrite grain refinement elements such as Ti, Nb and V is suppressed in order to prevent the increase of the strength and the simple composition of the cooling due to the miniaturization of the ferrite grains, Discloses a technique for improving the cold workability of a linear or bar-shaped steel by adding a small amount of B or Zr in order to fix the solid solution nitrogen which adversely affects the steel.

Japanese Patent Application Laid-Open No. 2001-303189 Japanese Patent Application Laid-Open No. 2001-342544

One aspect of the present invention is to provide a linear or bar-shaped steel capable of securing excellent cold workability without performing a spheroidizing annealing heat treatment and a method of manufacturing the same.

In order to attain the above object, according to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 0.05 to 0.4% of C, 0.05 to 0.5% of Si, 0.1 to 2.0% of Mn, 0.015%, B: 0.0056 ~ 0.015 %, N: 0.003 ~ 0.015%, the balance Fe and unavoidable containing impurities and, BN, and includes a single or composite precipitates of MnS, to a 60% P C, which is defined by the formula 1 or more Provide linear or bar-type steel.

[Formula 1]

P C (%) = {N c / (N s + N c )} x 100

Where N s is the number of BN-alone precipitates per 1 mm 2 present in the cross-section cut in a direction perpendicular to the longitudinal direction of the linear or bar-shaped steel, and N c is the length of the linear or bar-shaped steel cut in a direction perpendicular to the longitudinal direction Means the number of complex precipitates of BN and MnS per 1 mm 2 present in one cross section)

Another aspect of the present invention is to provide a method of manufacturing a semiconductor device, comprising: 0.05 to 0.4% of C, 0.05 to 0.5% of Si, 0.1 to 2.0% of Mn, 0.03 or less of P, 0.007 to 0.015% of S, 0.015%, N: 0.003-0.015%, the balance Fe and unavoidable impurities, heating a bloom satisfying the following relational equations (1) and (2) to 1150 - 1300 캜, rolling the billet to obtain a billet ; Reheating the billet to 1000 to 1150 占 폚 and then subjecting the billet to wire rolling to obtain a linear or bar-shaped steel; And cooling the linear or bar-shaped steel at a rate of 1 DEG C / sec or less.

 [Relation 1]

[S] ≥ [B] + [N] -0.002

 [Relation 2]

-0.0040? [N] - [B]? 0.0020

(Where each of [S], [N] and [B] means the content (weight%) of the element concerned)

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages and effects of the present invention will become more fully understood with reference to the following specific embodiments.

According to the present invention, even if the annealing for spheroidizing annealing is omitted, it is possible to provide a linear or bar-shaped steel in which the deformation resistance is suppressed in the temperature rising region caused by the processing heat generation during cold working.

Hereinafter, a linear or bar type steel excellent in cold workability which is one aspect of the present invention will be described in detail. First, the alloy composition and the range of the composition of the linear or bar-shaped steel will be described in detail.

Carbon (C): 0.05 to 0.4 wt%

Carbon improves the strength of the steel. In order to exhibit such an effect in the present invention, the content is preferably 0.05% by weight or more, more preferably 0.08% by weight or more, and even more preferably 0.1% by weight or more. However, when the content is excessive, the pearlite structure is excessively formed, so that the deformation resistance of the steel is rapidly increased, thereby deteriorating the cold workability. Therefore, the upper limit of the carbon content is preferably 0.4 wt%, more preferably 0.38 wt%, and even more preferably 0.35 wt%.

Silicon (Si): 0.05 to 0.5 wt%

Silicon is a useful element as a deoxidizer. In order to exhibit such an effect in the present invention, the content is preferably 0.05% by weight or more, more preferably 0.08% by weight or more, and even more preferably 0.1% by weight or more. However, if the content is excessive, resistance to steel deformation increases rapidly due to reinforcement of the solid solution, which results in deterioration of cold workability. Accordingly, the upper limit of the silicon content is preferably 0.5 wt%, more preferably 0.4 wt%, and even more preferably 0.3 wt%.

Manganese (Mn): 0.1 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, the content is preferably 0.1 wt% or more, more preferably 0.25 wt% or more, and even more preferably 0.5 wt% or more. However, if the content is excessive, the strength of the steel itself becomes excessively high, so that the deformation resistance of the steel increases rapidly, thereby deteriorating the cold workability. Accordingly, the upper limit of the manganese content is preferably 2.0 wt%, more preferably 1.5 wt%, and even more preferably 0.8 wt%.

Phosphorus (P): 0.03% by weight or less

Phosphorus is an impurity which is inevitably contained and is an element which segregates in the grain boundaries to decrease the toughness of the steel and reduce the delayed fracture resistance. Therefore, it is desirable to control the content as low as possible. Theoretically, it is preferable to control the phosphorus content to 0 wt%, but it is inevitably contained inevitably 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 controlled to 0.03% by weight.

Sulfur (S): 0.007 to 0.015 wt%

Sulfur is generally classified as an impurity inevitably contained in the steel, but in the present invention, it is an element intentionally added to form a MnS precipitate and serve as a nucleation site of a BN precipitate. In order to exhibit such an effect in the present invention, the content is preferably 0.007% by weight or more, more preferably 0.008% by weight or more. However, when the content thereof exceeds an appropriate level, there is a possibility that the toughness is lowered due to the formation of a large number of MnS. Therefore, the upper limit of the sulfur content is preferably limited to 0.015 wt%.

Boron (B): 0.0056-0.015 wt%

Boron is an element that plays a role in fixing solid nitrogen by BN formation. Particularly, in the present invention, by using MnS precipitates as nuclei for BN precipitation, it is a technical feature that the content of boron which can be used as a fixed element of dissolved nitrogen is greatly increased. Particularly, in view of the fact that the content of N contained in the steel is generally about 0.004% by weight, in the present invention, the content of boron for minimizing the content of solid N is preferably 0.0056% by weight or more, more preferably 0.0060% . However, if the content is excessive, BN precipitates may form at the grain boundaries, which may adversely affect the ductility of the steel. Therefore, the upper limit of the boron content is preferably 0.015 wt%, more preferably 0.010 wt%.

Nitrogen (N): 0.003 to 0.015 wt%

Nitrogen is an impurity inevitably contained. When the content is excessive, the amount of solid solution nitrogen is increased, so that the deformation resistance of the steel is rapidly increased, thereby deteriorating the cold workability. In theory, it is preferable to control the content of nitrogen to 0 wt%, but it is inevitably contained in the manufacturing process normally, and is usually contained in an amount of 0.003 wt% or more. Therefore, it is important to manage the upper limit. In the present invention, the upper limit of the nitrogen content is preferably controlled to 0.015 wt%, more preferably 0.01 wt%, and more preferably 0.007 wt% desirable.

The balance other than the alloy composition is iron (Fe). In addition, the linear or bar-shaped steels of the present invention may include other impurities that may normally be included in the industrial production of steel. These impurities can be known to anyone with ordinary knowledge in the art to which the present invention belongs, so that the kind and content of the impurities are not specifically limited in the present invention.

However, since Ti, Nb and V correspond to representative impurities whose content should be suppressed as much as possible in order to obtain the effect of the present invention, a brief description thereof will be given below.

Titanium (Ti): 0.01 wt% or less

Titanium is a carbonitride-forming element that forms carbonitride at temperatures higher than B. Therefore, if titanium is included in the steel, it may be advantageous to fix C and N, but Ti (C, N) may precipitate at a high temperature to deteriorate the cold toughness. Therefore, it is important to manage the upper limit. In the present invention, the upper limit of the titanium content is preferably controlled to 0.01 wt%, and more preferably 0.008 wt%.

Niobium (Nb) and vanadium (V): Not more than 0.05% in total

Niobium and vanadium also form a carbonitride-forming element, but carbonitride is formed at a temperature lower than B. In the present invention, the fixing effect of N is insufficient even when these elements are added. However, if these contents are excessive, the precipitation strengthening or fine grain refinement due to the formation of fine carbonitride during cooling may increase the strength of the steel more than necessary, thereby deteriorating the cold-rolled steel composition. Therefore, it is important to manage the upper limit, and in the present invention, it is preferable that the upper limit of the sum of the contents of niobium and vanadium is controlled to 0.05 wt%.

According to one embodiment of the present invention, when designing an alloy of a steel material having the above-described composition range, it is preferable to control the content of S, B and N so as to satisfy the following relational expression (1).

[Relation 1]

[S] ≥ [B] + [N] -0.002

(Where each of [S], [B] and [N] means the content (weight%) of the element concerned)

The inventors of the present invention have found out that, in the present invention in which B and N are added in excess of the usual levels, when a proper amount of MnS precipitate is formed by appropriately controlling the contents of Mn and S, most of the BN precipitates are composed of MnS precipitates as nuclei Precipitates to form BN and MnS complex precipitates, and the complex precipitates as described above are formed in the mouth instead of in the grain boundary, and thus it is possible to secure a good cold step composition. If the value of [S] is too low, sufficient MnS precipitates can not be secured, and a large amount of BN precipitates are formed in the grain boundaries, thereby reducing the ductility. According to this study, it was confirmed that sufficient MnS was formed at the nucleation sites of the BN precipitates when the [S] value satisfied the relationship (1).

Further, according to one embodiment of the present invention, it is preferable to control the content of N and B to satisfy the following relational expression 2 when designing an alloy of a steel material having the above-mentioned composition range.

[Relation 2]

-0.0040? [N] - [B]? 0.0020

(Where each of [N] and [B] represents the content (weight%) of the corresponding element)

If, when the nitrogen content of the steel than the boron content is too excessive, there is a danger of the remaining boron after forming BN precipitates degrade the mechanical properties by forming a precipitate 6 Fe 23 (C, B) in the grain boundary. Therefore, the lower limit of the value of [N] - [B] is preferably -0.0040, more preferably -0.0030, even more preferably -0.0025. On the other hand, if the nitrogen content in the steel is too high compared to the boron content in the steel, the nitrogen fixation effect by boron is insufficient, which may result in deterioration of the cold simple composition. Therefore, the upper limit of the value of [N] - [B] is preferably 0.0020, more preferably 0.0010.

The steel may contain a single or complex precipitate of BN and MnS, and the P C defined by the following formula 1 may be 60% or more. If the P C is less than 60%, the ductility of the steel may be deteriorated due to the grain boundary formation of the excessive BN precipitates. On the other hand, the larger P is advantageous for obtaining the effect of the present invention, the upper limit of P C is not particularly limited.

[Formula 1]

P C (%) = {N c / (N s + N c )} x 100

Where N s is the number of BN-alone precipitates per 1 mm 2 present in the cross-section cut in a direction perpendicular to the longitudinal direction of the linear or bar-shaped steel, and N c is the length of the linear or bar-shaped steel cut in a direction perpendicular to the longitudinal direction Means the number of complex precipitates of BN and MnS per 1 mm < 2 >

In the present invention, the method of measuring the number of BN or MnS alone or the number of complex precipitates is not particularly limited, but the following method can be used, for example. That is, the linear or bar-shaped steel is cut in the direction perpendicular to the longitudinal direction, and then the R / 2 position (here, R means the radius of the linear or bar-shaped steel) by means of a scanning electron microscope (FE-SEM, Field Emission Scanning Electron Microscope) , And the number of total precipitates can be calculated by analyzing the cross-sectional photographs at a magnification of 1,000 at a magnification of 1,000, and the composition of each precipitate is analyzed by using an electron probe micro-analyzer (EPMA) It is possible to distinguish kinds.

According to one embodiment of the present invention, the linear or bar-shaped steel of the present invention may include ferrite and pearlite as its microstructure, more preferably at least 30% (100% ) And 70% or less (excluding 0%) of pearlite. When such a structure as described above is secured, excellent cold workability can be ensured and strength after proper drawing processing can be secured.

Also, according to an embodiment of the present invention, the average particle size of the ferrite may be 10 to 30 탆, and more preferably 15 to 25 탆. If the mean particle size of the ferrite is less than 10 탆, the strength of the steel may increase due to grain refinement, and the cold-rolled steel may decrease. On the other hand, if the average grain size exceeds 30 탆, the strength may decrease. On the other hand, the average particle diameter of the pearlite formed together is not particularly limited because it is influenced by the average particle diameter of the ferrite. Here, the average particle diameter means an equivalent circular diameter of the particles detected by observing one end face of the steel sheet.

The above-described linear or bar-shaped steel of the present invention can be produced by various methods, and the production method thereof is not particularly limited. However, as an embodiment, it can be produced by the following method.

Hereinafter, a method of manufacturing a linear or bar-shaped steel of the present invention, which is another aspect of the present invention, will be described in detail.

First, a bloom satisfying the above-mentioned component system is heated, followed by rolling a billet to obtain a billet. This step is a step for finely reducing the size of MnS coarsened in the performance process by rolling a piece of MnS by heating and then rolling the steel piece.

The heating temperature of the bloom is preferably 1150 to 1300 ° C, and more preferably 1200 to 1250 ° C. If the heating temperature of the bloom is less than 1150 ° C, the coarse MnS produced during the casting process may not decompose and may not be sufficient to serve as a nucleation site for a large number of BNs, The toughness may deteriorate due to coarsening of the austenite.

When rolling a billet of a heated bloom, the finish rolling temperature may be 1000 to 1200 캜, and preferably 1050 to 1150 캜. If the finish rolling temperature is less than 1000 ° C, there is a fear that the thermal deformation resistance is increased and the productivity is lowered. On the other hand, when the finish rolling temperature is higher than 1200 ° C, the ductility may decrease due to the coarsening of the ferrite grains.

Next, after the billet is reheated, the billet is subjected to wire rolling to obtain a linear or bar-shaped steel. This step is carried out to inhibit the decomposition of BN formed with MnS as nuclei in a billet manufacturing process.

The reheating temperature of the billet is preferably 1000 to 1150 캜, and more preferably 1050 to 1100 캜. If the reheating temperature of the billet is less than 1000 ° C, there is a fear that the resistance to hot deformation increases. On the other hand, if the billet temperature exceeds 1150 ° C, the BN produced using MnS as nuclei may be decomposed.

In billet rolling, the finishing rolling temperature may be 900 to 1000 캜, preferably 920 to 980 캜.

The present invention is characterized in that the finishing rolling temperature is controlled to be somewhat higher at the time of rolling the wire, in order to overcome the deterioration of the hot rolling property due to the formation of a large amount of MnS. For this purpose, it is necessary to control the finishing rolling temperature to 900 DEG C or higher. However, if the finishing rolling temperature is too high, the ferrite grains may become excessively coarse and the ductility may deteriorate. The finishing rolling temperature needs to be controlled to 1000 캜 or lower.

Thereafter, the linear or bar-shaped steel is wound and cooled.

The winding temperature of the linear or bar-shaped steel may be 750 to 950 캜, more preferably 780 to 900 캜, and even more preferably 780 to 850 캜. If the coiling temperature is less than 750 占 폚, the martensite at the surface layer during cooling may not be recovered by the double refraction, and burnt martensite may be generated to form a hard and soft steel, which may lower the cold workability. On the other hand, when the coiling temperature exceeds 950 deg. C, a thick scale is formed on the surface of the coiling, so that troubles on descaling may easily occur, and the cooling time may be prolonged, thereby lowering the productivity.

The cooling rate during cooling of the linear or bar-shaped steel may be 1 ° C / sec or less, preferably 0.8 ° C / sec or less, and more preferably 0.5 ° C / sec or less. In order to stably form ferrite and pearlite composite structure, if the cooling rate exceeds 1 캜 / sec, a low-temperature structure may be formed to deteriorate the cold-rolled steel composition. On the other hand, in the present invention, the lower limit of the cooling rate during the cooling is not particularly limited. However, considering productivity, it may be limited to 0.1 占 폚 / sec or more.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the description of these embodiments is intended only to illustrate the practice of the present invention, but the present invention is not limited thereto. And the scope of the present invention is determined by the matters described in the claims and the matters reasonably deduced therefrom.

( Example )

A bloom having an alloy composition as shown in Table 1 below was heated at 1200 DEG C for 4 hours and then subjected to rolling at a finishing rolling temperature of 1050 DEG C to obtain a billet. Thereafter, the billet was reheated at 1100 ° C for 3 hours, and then subjected to wire rolling at a wire diameter of 20 mm to obtain a linear or bar-shaped steel. At this time, the finish rolling temperature was 950 占 폚. Thereafter, the linear or bar-shaped steel was wound at a temperature of 850 캜 and then cooled at a rate of 0.5 캜 / sec.

Then, types and fractions of microstructures, types and numbers of precipitates were analyzed and measured using an electron microscope, and the results are shown in Table 2 below.

The deformation temperature was measured at room temperature (25 ℃) and maximum 200 ℃. The deformation rate and deformation rate were ε = 1, ε '= 5 / s. After the bolt cold forging simulation, the change in the deformation strength was measured. At this time, the increase (+) or the decrease (-) was measured based on the strength value of the comparative material having the same level of C content. More specifically, the strength values of the invention steel 1 and the comparative steel 1 are based on the strength value of the comparative member 1, the strength values of the inventive steels 2 to 4 and the comparative steels 2 to 5 are based on the strength value of the comparative member 2, The strength values of Inventive Steel 5 and Comparative Steel 6 are based on the strength value of the comparative material 3, and the inventive steel 6 and the comparative steel 7 are measured for the increase (+) or decrease (-) based on the strength value of the comparative material 4 Respectively. The results are shown in the following Table 2, and the occurrence of cracks was observed and is shown in Table 2 below.

Steel grade Alloy composition (% by weight) ① ② C Si Mn P S Ti B N Comparison 1 0.10 0.21 0.71 0.009 0.010 0.003 - 0.0045 0.0025 0.0045 Comparative material 2 0.16 0.19 0.72 0.01 0.012 0.004 - 0.0052 0.0032 0.0052 Comparative material 3 0.25 0.18 0.68 0.01 0.013 0.003 - 0.0055 0.0035 0.0055 Comparison 4 0.36 0.17 0.69 0.009 0.009 0.005 - 0.0060 0.0040 0.0060 Inventive Steel 1 0.09 0.18 0.73 0.01 0.013 0.004 0.0062 0.0054 0.0096 -0.0008 Invention river 2 0.14 0.18 0.73 0.01 0.014 0.002 0.0075 0.0048 0.0103 -0.0027 Invention steel 3 0.16 0.19 0.70 0.009 0.012 0.003 0.0069 0.0055 0.0104 -0.0014 Inventive Steel 4 0.15 0.20 0.69 0.009 0.008 0.004 0.0063 0.0042 0.0078 -0.0022 Invention steel 5 0.24 0.17 0.71 0.01 0.013 0.005 0.0062 0.0066 0.0108 0.0004 Invention steel 6 0.33 0.18 0.68 0.01 0.012 0.003 0.0070 0.0065 0.0115 -0.0005 Comparative River 1 0.11 0.20 0.69 0.009 0.002 0.003 0.0064 0.0043 0.0087 -0.0021 Comparative River 2 0.16 0.21 0.68 0.01 0.004 0.004 0.0022 0.0026 0.0028 0.0004 Comparative Steel 3 0.17 0.18 0.71 0.011 0.005 0.003 0.0019 0.0048 0.0047 0.0029 Comparative Steel 4 0.17 0.19 0.73 0.010 0.006 0.005 0.0020 0.0065 0.0065 0.0045 Comparative Steel 5 0.15 0.19 0.70 0.009 0.004 0.003 0.0064 0.0068 0.0112 0.0004 Comparative Steel 6 0.24 0.21 0.67 0.011 0.003 0.004 0.0072 0.0067 0.0119 -0.0005 Comparative Steel 7 0.34 0.17 0.66 0.009 0.003 0.002 0.0063 0.0058 0.0101 -0.0005 [N] and [B] each represent the content (% by weight) of the corresponding element,

Steel grade Microstructure type and fraction
(area%) Ferrite average particle diameter (占 퐉) P C (%) Deformation Resistance Strength (MPa) Crack occurrence 25 ℃ 200 ℃ Comparison 1 F80.2 + P19.8 20.4 - 618 645 X Comparative material 2 F75.3 + P24.7 19.2 - 658 680 X Comparative material 3 F61.5 + P38.5 17.4 - 695 714 X Comparison 4 F36.7 + P63.3 14.3 - 763 781 X Inventive Steel 1 F79.1 + P20.9 19.6 83 -14 -45 X Invention river 2 F76.4 + P23.6 20.3 74 -26 -60 X Invention steel 3 F75.5 + P24.5 18.6 67 -18 -48 X Inventive Steel 4 F76.2 + P23.8 17.4 70 -22 -56 X Invention steel 5 F60.3 + P39.7 16.5 68 -10 -36 X Invention steel 6 F35.6 + P64.4 13.7 62 -12 -40 X Comparative River 1 F78.4 + P21.6 21.3 11 - - O Comparative River 2 F75.1 + P24.9 19.8 12 -17 -50 X Comparative Steel 3 F75.5 + P24.5 17.1 27 -8 -24 X Comparative Steel 4 F75.7 + P24.3 18.5 33 +2 +5 X Comparative Steel 5 F74.8 + P25.2 17.6 10 - - O Comparative Steel 6 F58.8 + P41.2 15.8 8 - - O Comparative Steel 7 F37.3 + P62.7 13.5 7 - - O Of the microstructures, F means ferrite and P means pearlite.

In Table 1, comparative materials 1 to 4 are steels to which B is not added and are the standard for measuring the strength of deformation resistance.

Invention steels 1 to 6 were intentionally added with a large amount of sulfur intentionally to form MnS precipitates and to act as nucleation sites of BN precipitates and to treat the boron in a usual manner Is higher than the level.

Comparative steels 1, 5, 6 and 7 show the case where boron and nitrogen are added at a higher level than usual while the sulfur content is maintained at a normal level, and comparative steels 2 are subjected to severe conditions The nitrogen content is intentionally lowered through the process and boron is added in a small amount, and the comparative steel 3 is a case where a small amount of boron is added while controlling the sulfur and nitrogen contents to a normal level. In Comparative Steel 4, the content of nitrogen was controlled to be higher than the normal level and the amount of boron was added in a small amount while the content of sulfur was controlled to a normal level.

Referring to Table 2, in Inventive steels 1 to 6, it was confirmed that P C , which means the ratio of BN and MnS complex precipitates in the total BN precipitates, satisfies the alloy composition and the manufacturing conditions proposed in the present invention and is 60% or more This shows that the strength of deformation resistance at room temperature and 200 ° C is lowered and the strength of deformation resistance at equivalent temperature or lower is lower than that of comparative steel 2 in which the nitrogen content is intentionally lowered through the steelmaking process in harsh conditions . On the other hand, in the comparative steels 2 to 4, when the content of sulfur is added at a normal level and the amount of boron is added in a small amount, the deformation resistance strength is increased as the nitrogen content is increased. In addition, in comparative steels 1, 5, 6 and 7, when the content of sulfur is increased to the normal level and when the content of boron and nitrogen is high, MnS does not sufficiently act as a nucleation site of the BN precipitate and BN precipitates are formed in the austenite grain boundaries As a result, it can be seen that cracks are generated during cold forging.

The change in the strength of deformation resistance of the above steel types does not appear to be much different from those of the comparative materials, but it is a very large difference when a cold stamping process is actually carried out several thousands or tens of thousands times, May have a very large effect on the cold-pressured die life.

Claims (12)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.05 to 0.4% of C, 0.05 to 0.5% of Si, 0.1 to 2.0% of Mn, 0.03% or less of P, 0.007 to 0.015% of S, 0.0056 to 0.015% of B, %, Remainder Fe, and unavoidable impurities, including single or complex precipitates of BN and MnS, and having a P C of 60% or more as defined by the following formula (1).
[Formula 1]
P C (%) = {N c / (N s + N c )} x 100
Where N s is the number of BN-alone precipitates per 1 mm 2 present in the cross-section cut in a direction perpendicular to the longitudinal direction of the linear or bar-shaped steel, and N c is the length of the linear or bar-shaped steel cut in a direction perpendicular to the longitudinal direction Means the number of complex precipitates of BN and MnS per 1 mm 2 present in one cross section)
The method according to claim 1,
The content of S, B and N satisfies the following relational expression (1).
[Relation 1]
[S] ≥ [B] + [N] -0.002
(Where each of [S], [B] and [N] means the content (weight%) of the element concerned)
The method according to claim 1,
Wherein the content of N and B satisfies the following relational expression (2).
[Relation 2]
-0.0040? [N] - [B]? 0.0020
(Where each of [N] and [B] represents the content (weight%) of the corresponding element)
The method according to claim 1,
Wherein the inevitable impurities include Ti, Nb and V and are suppressed to 0.01% or less of Ti, 0.05% or less of Nb and V in total by weight%.
The method according to claim 1,
Wherein the microstructure of the steel comprises ferrite and pearlite.
The method according to claim 1,
Wherein the microstructure of the steel comprises an area fraction of 30% or more (excluding 100%) of ferrite and 70% or less (excluding 0%) of pearlite.
The method according to claim 5 or 6,
Wherein said ferrite has an average grain size of 10 to 30 占 퐉.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.05 to 0.4% of C, 0.05 to 0.5% of Si, 0.1 to 2.0% of Mn, 0.03% or less of P, 0.007 to 0.015% of S, 0.0056 to 0.015% of B, %, Remainder Fe and unavoidable impurities, heating a bloom satisfying the following relational equations (1) and (2) to 1150 to 1300 캜, rolling the billet to obtain a billet;
Reheating the billet to 1000 to 1150 占 폚 and then subjecting the billet to wire rolling to obtain a linear or bar-shaped steel; And
Cooling the linear or bar-shaped steel at a rate of 1 占 폚 / sec or less;
Wherein the method comprises the steps of:
[Relation 1]
[S] ≥ [B] + [N] -0.002
[Relation 2]
-0.0040? [N] - [B]? 0.0020
(Where each of [S], [N] and [B] means the content (weight%) of the element concerned)
9. The method of claim 8,
Wherein the inevitable impurities include Ti, Nb and V, and are suppressed to 0.01% or less of Ti, 0.05% or less of Nb and V in total by weight%.
9. The method of claim 8,
Wherein the finish rolling temperature is 1000 to 1200 占 폚 at the time of rolling the steel strip.
9. The method of claim 8,
Wherein the finishing rolling temperature during the wire rolling is 900 to 1000 占 폚.
9. The method of claim 8,
Wherein the coiling temperature is 750 to 950 占 폚 at the time of winding.
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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000336456A (en) * 1999-05-26 2000-12-05 Nippon Steel Corp Hot rolled wire rod-bar steel for machine structure and production thereof
JP2001303189A (en) 2000-02-18 2001-10-31 Kobe Steel Ltd Wire-shaped or bar-shaped steel whose rise in deformation resistance in heat generating region by working as well as at room temperature is suppressed, and machine parts
JP2001342544A (en) 2000-02-18 2001-12-14 Kobe Steel Ltd Wire or rod steel suppressed arising of deformation resistance at room temperature and in area of working heat generation
JP2004176175A (en) * 2002-11-15 2004-06-24 Nippon Steel Corp Steel superior in machinability and manufacturing method therefor
JP2014047356A (en) * 2012-08-29 2014-03-17 Nippon Steel & Sumitomo Metal Bar steel or wire material
KR20140076360A (en) * 2012-12-12 2014-06-20 주식회사 포스코 A wire rod having excellent cold forging and method for manufacturing the same

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000336456A (en) * 1999-05-26 2000-12-05 Nippon Steel Corp Hot rolled wire rod-bar steel for machine structure and production thereof
JP2001303189A (en) 2000-02-18 2001-10-31 Kobe Steel Ltd Wire-shaped or bar-shaped steel whose rise in deformation resistance in heat generating region by working as well as at room temperature is suppressed, and machine parts
JP2001342544A (en) 2000-02-18 2001-12-14 Kobe Steel Ltd Wire or rod steel suppressed arising of deformation resistance at room temperature and in area of working heat generation
JP2004176175A (en) * 2002-11-15 2004-06-24 Nippon Steel Corp Steel superior in machinability and manufacturing method therefor
JP2014047356A (en) * 2012-08-29 2014-03-17 Nippon Steel & Sumitomo Metal Bar steel or wire material
KR20140076360A (en) * 2012-12-12 2014-06-20 주식회사 포스코 A wire rod having excellent cold forging and method for manufacturing the same

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