WO2019132372A1 - Cold rolled steel sheet having excellent aging resistance and workability, and manufacturing method therefor - Google Patents

Abstract

A cold rolled steel sheet having excellent aging resistance and workability, according to one embodiment of the present invention, comprises, by wt%, 0.1% or less of C, 0.5% or less of Si, 0.1-0.5% of Mn, 0.015-0.1% of Al, 0.01% or less of P, 0.01% or less of S, 0.01% or less of N, 0.005% or less of Nb, 0.005% or less of Ti, 0.005% or less of V, and the balance of Fe and other inevitable impurities, wherein the total amounts of C and N in grains can meet the following relation 1, and the amounts of solid-solute C and N in the grains can meet the following relation 2. [Relation 1] ([C]/12.01 + [N]/14.01) x 10⁵ ≥ 10 [Relation 2] ([C]/12.01 + [N]/14.01) x 10⁵ ≤ 5 In relation 1 and relation 2, [C] and [N] are respectively the amounts of C and N and mean wt%.

Description

Cold rolled steel sheet excellent in durability and workability and method for manufacturing the same

The present invention relates to a cold-rolled steel sheet and a method of manufacturing the same, and more particularly to a cold-rolled steel sheet for processing which is particularly suitable for materials such as automobiles, household appliances, and the like, and has excellent endurance and workability.

Generally, a cold-rolled steel sheet for use as a material for automobiles, home appliances and the like is required to have good endurance properties in order to ensure moldability. Aging is a phenomenon in which carbon (C) and nitrogen (N), which are interstitial elements, adhere to the dislocations in the crystal grains as time elapses, so that the movable potential is decreased and the material is hardened. When strain aging occurs, it causes stressor strain defects, which causes the workability of the material to deteriorate. Therefore, it is important to appropriately suppress the aging in terms of securing processability of the processable cold-rolled steel sheet.

As a typical technique for securing the endurance of the cold-rolled steel sheet, there is a method using batch annealing. In the case of using the calcined body, the material is held at a high temperature for a long time (generally, for 5 hours or more), so that the solidified carbon C in the crystal grains precipitates and is fixed with a carbide having a strong bonding force. However, it takes a long time due to the nature of the process, so the productivity is low, and there is a disadvantage that the material variation occurs severely in each part of the material.

Interstitial Free Steel has emerged as a result of research to overcome these shortcomings. IF steel is a type of steel which ensures the endurance by precipitating solid carbon (C) and nitrogen (N) by adding carbonitride forming elements such as titanium (Ti), niobium (Nb) and vanadium (V) into steel. Therefore, the IF steel can be produced by continuous annealing in which productivity and material uniformity are ensured, instead of prolonged annealing. However, alloying elements such as titanium (Ti), niobium (Nb), and vanadium (V) are expensive and are not desirable from the economical point of view. Raising the recrystallization temperature due to the precipitation of these alloying elements may be a problem. In addition, as the recrystallization temperature rises, high-temperature annealing must be accompanied, and defects such as surface flaws are caused by high-temperature annealing.

(Patent Document 1) Korean Published Patent Application No. 10-2010-0047503 (Published May 10, 2010)

The present invention provides a cold-rolled steel sheet having improved endurance and workability effectively by optimizing steel composition and manufacturing process conditions, and a method of manufacturing the same.

The object of the present invention is not limited to the above description. Those of ordinary skill in the art will have no difficulty understanding the further subject of the present invention from the general context of this specification.

A cold rolled steel sheet excellent in endurance and workability according to one aspect of the present invention is characterized by containing 0.1% or less of C, 0.5% or less of Si, 0.1 to 0.5% of Mn, 0.015 to 0.1% of Al, 0.01 to 0.1% % Or less of S, not more than 0.01% of S, not more than 0.01% of N, not more than 0.005% of Nb, not more than 0.005% of Ti, not more than 0.005% of V and the balance of Fe and other unavoidable impurities, Satisfies the following relational expression (1), and the solid solution C and N content in the crystal grains satisfy the following relational expression (2).

[Relation 1] ([C] /12.01 + [N] /14.01) x 10 ⁵ ? 10

[Relation 2] ([C] /12.01 + [N] /14.01) x 10 ⁵ 5

[C] and [N] in the relational expression 1 and the relational expression 2 refer to the content of C and N, respectively, by weight.

Nb, Ti and V may be included in an amount of 0.001% or less, respectively.

The aging index of the cold-rolled steel sheet may be 10 MPa or less.

The yield point elongation of the cold-rolled steel sheet may be 0.5% or less.

The yield strength of the cold-rolled steel sheet may be 350 MPa or less.

A cold rolled steel sheet excellent in endurance and workability according to one aspect of the present invention is characterized by containing 0.1% or less of C, 0.5% or less of Si, 0.1 to 0.5% of Mn, 0.015 to 0.1% of Al, 0.01 to 0.1% %, S: not more than 0.01%, N: not more than 0.01%, Nb: not more than 0.005%, Ti: not more than 0.005%, V: not more than 0.005%, and other Fe and other unavoidable impurities; Hot-rolling the reheated slab to provide a hot-rolled steel sheet; Cold-rolling the hot-rolled steel sheet to provide a cold-rolled steel sheet; Continuously annealing the cold-rolled steel sheet; Subjecting the continuously annealed cold rolled steel sheet to first-precision rolling at a first reduction rate of 1 to 3%; Rolling the primary-precision rolled cold-rolled steel sheet at a temperature in the range of 200 to 400 ° C for 10 minutes or less; The cold-rolled steel sheet subjected to the dislocation-fixing annealing can be subjected to secondary-precision rolling at a second reduction ratio of 0.8 to 3%.

By the primary correction rolling, a movable potential can be generated in the cold-rolled steel sheet.

The movable potential generated by the primary corrective rolling by the potential fixing annealing can be fixed to the potential by diffusion.

The movable potential can be regenerated to the cold-rolled steel sheet by the secondary corrective rolling.

The reheating temperature of the slab may be 1200 ° C or higher.

The finish rolling temperature of the hot rolling may be higher than Ar3.

The reduction ratio of the cold rolling may be 50 to 95%.

The temperature of the continuous annealing may be 600 to 900 占 폚.

The hot-rolled steel sheet may be rolled at 550 to 750 ° C to be provided for the cold rolling.

Nb, Ti and V may be included in an amount of 0.001% or less, respectively.

According to an aspect of the present invention, it is possible to provide a cold-rolled steel sheet in which endurance and workability are effectively improved by optimizing steel composition and manufacturing process conditions, and a manufacturing method thereof.

According to an aspect of the present invention, it is possible to provide a cold-rolled steel sheet in which economical efficiency is effectively ensured by minimizing the addition amount of expensive alloying elements and a method of manufacturing the same.

According to an aspect of the present invention, it is possible to provide a cold rolled steel sheet in which productivity can be effectively ensured without being subjected to a prolonged tempering step and a manufacturing method thereof.

The present invention relates to a cold-rolled steel sheet excellent in endurance and workability and a method of manufacturing the same, and the preferred embodiments of the present invention will be described below. The embodiments of the present invention can be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments are provided to explain the present invention to a person having ordinary skill in the art to which the present invention belongs.

The cold rolled steel sheet excellent in endurance and workability according to one aspect of the present invention is characterized by containing 0.1% or less of carbon (C), 0.5% or less of silicon (Si), 0.1 to 0.5% of manganese (Mn) (N): 0.005% or less, Ti (Ti): 0.005% or less, and the content of titanium (Ti) 0.005% or less, vanadium (V): 0.005% or less, the balance Fe and other unavoidable impurities.

Hereinafter, the steel composition of the present invention will be described in more detail. Hereinafter, unless otherwise indicated, the percentages representing the content of each element are by weight.

Carbon (C): Not more than 0.1%

When carbon (C) is added excessively, ductility and strength are excessively increased, and workability is significantly lowered, so that the present invention can limit the upper limit of the carbon (C) content to 0.1%.

Silicon (Si): not more than 0.5%

Silicon (Si) is an element used as a deoxidizing agent and is an element that improves strength by solid solution strengthening. However, when the content is excessive, not only the strength increases more than necessary, but also a plating defect may be caused by the Si-based oxide generated on the surface of the steel sheet during annealing. Therefore, the present invention can limit the upper limit of the silicon (Si) content to 0.5%, and the upper limit of the more preferable silicon (Si) content can be 0.3%.

Manganese (Mn): 0.1 to 0.5%

Manganese (Mn) binds with solid sulfur (S) in the steel and precipitates as MnS, thereby preventing hot shortness due to solid sulfur (S). For the purpose of preventing red embrittlement, the lower limit of the manganese (Mn) content of the present invention may be limited to 0.1%. However, when manganese (Mn) is added excessively, the material is hardened and the ductility is significantly lowered, so that the upper limit of manganese (Mn) content can be limited to 0.5% in order to ensure workability. Accordingly, the manganese (Mn) content of the present invention may be in the range of 0.1 to 0.5%. The preferred manganese (Mn) content may range from 0.1 to 0.4%, more preferably the manganese (Mn) content may range from 0.15 to 0.3%.

Aluminum (Al): 0.015 to 0.1%

Aluminum (Al) is an element having a great deoxidation effect and is an element that prevents the degradation of the formability due to solid nitrogen N by causing AlN to precipitate by reacting with nitrogen (N) in the steel. Therefore, the present invention can limit the lower limit of the aluminum (Al) content to 0.015% in order to achieve this effect. However, if aluminum (Al) is added in excess, the ductility may be drastically lowered and the workability may be lowered. The present invention can limit the upper limit of the aluminum (Al) content to 0.1%. Therefore, the aluminum (Al) content of the present invention may be in the range of 0.015 to 0.1%. The preferred aluminum (Al) content may range from 0.015 to 0.07%, and more preferably the aluminum (Al) content may range from 0.02 to 0.05%.

Phosphorus (P): not more than 0.01%

Phosphorus (P) is an element capable of improving the strength without significantly reducing the ductility of the steel. However, when the content of phosphorus (P) is excessively added, there may arise a problem of segregating the grain boundaries to harden the steel. Therefore, the present invention can limit the upper limit of the phosphorus (P) content to 0.01%.

Sulfur (S): not more than 0.01%

Sulfur (S) is an element that is inevitably contained in the steel, or an element that causes red-hot brittleness when it is in an employment state. Addition of manganese (Mn) can induce precipitation of MnS, but excessive MnS precipitation is not preferable because it hardens the steel. Therefore, the present invention can limit the upper limit of the sulfur (S) content to 0.01%.

Nitrogen (N): not more than 0.01%

Nitrogen (N) is an element that is inevitably contained in the steel. Nitrogen (N) present in the state of employment lowers ductility, deteriorates endurance, and can degrade processability. Therefore, the present invention can limit the upper limit of the nitrogen (N) content to 0.01%.

Titanium (Ti), niobium (Nb), vanadium (V): not more than 0.005%

Titanium (Ti), niobium (Nb) and vanadium (V) are elements that easily form carbonitride by bonding with carbon (C) or nitrogen (N) at high temperatures. In addition, these elements are not only expensive but also cause an increase in the recrystallization temperature, and they are also an element causing a problem of excessively increasing the strength when added excessively. In addition, since the effect of ensuring the endurance of the present invention is not expressed by the addition of titanium (Ti), niobium (Nb) and vanadium (V), the content of titanium (Ti), niobium (Nb) and vanadium (C) and nitrogen (N), even when the amount of carbon (C) is positively suppressed. Therefore, in the present invention, it is preferable to positively suppress the contents of titanium (Ti), niobium (Nb) and vanadium (V). That is, in the present invention, titanium (Ti), niobium ) Are contained inevitably, they are preferably contained in an amount of 0.005% or less, respectively. More preferably, the content of titanium (Ti), niobium (Nb) and vanadium (V) may be 0.002% or less and the content of titanium (Ti), niobium (Nb) and vanadium (V) have.

The present invention may be Fe and unavoidable impurities in addition to the above-mentioned steel composition. Unavoidable impurities can be intentionally incorporated in a conventional steel manufacturing process, and can not be entirely excluded, and the meaning of ordinary steel manufacturing industry can be understood easily. Further, the present invention does not exclude the addition of other compositions other than the above-mentioned steel composition in the whole.

The cold rolled steel sheet excellent in endurance and workability according to one aspect of the present invention is characterized in that the total carbon (C) and nitrogen (N) contents in the crystal grains satisfies the following relational expression 1 and the solid carbon (C) The content can satisfy the following relational expression (2).

[Relation 1] ([C] /12.01 + [N] /14.01) x 10 ⁵ ? 10

[Relation 2] ([C] /12.01 + [N] /14.01) x 10 ⁵ 5

However, [C] and [N] in the relational expression 1 and the relational expression 2 refer to the content of carbon (C) and nitrogen (N), respectively, by weight.

Hereinafter, the relational expression of the present invention will be described in more detail.

Relation

In the steel composition of the present invention, carbon (C) and nitrogen (N) can be limited to satisfy the following relational expressions 1 and 2. Relation 1 is a condition for limiting the total carbon (C) and nitrogen (N) contents in the crystal grains, and Relation 2 is a condition for limiting the content of the solid carbon (C) and nitrogen (N) in the crystal grains.

[Relation 1] ([C] /12.01 + [N] /14.01) x 10 ⁵ ? 10

[Relation 2] ([C] /12.01 + [N] /14.01) x 10 ⁵ 5

However, [C] and [N] in the relational expression 1 and the relational expression 2 refer to carbon (C) and nitrogen (N) content, respectively, by weight%.

Relation 1 means that carbon (C) and nitrogen (N) should be contained at a certain level or higher. In the formula (2), the content of the solid carbon (C) and the nitrogen (N) in the crystal grains is lowered to a certain level or less through a series of steps as described later. ) Content is lower than a certain level. Therefore, the present invention can effectively ensure the endurance and workability of the final product through the limitation of the steel composition and the limitation of the carbon (C) and nitrogen (N) contents according to the relational expression.

The cold rolled steel sheet satisfying the steel composition and the relational expression of the present invention has an aging index of 10 MPa or less and a yield point elongation of 0.5% or less So that the anti-hypersensitivity can be effectively ensured. In addition, since the cold-rolled steel sheet satisfying the steel composition and the relational expression of the present invention has a yield strength of 350 MPa or less, workability can be effectively ensured while assuring anti-aging properties.

Hereinafter, the production method of the present invention will be described in more detail.

The cold rolled steel sheet excellent in endurance and workability according to one aspect of the present invention is characterized by containing 0.1% or less of carbon (C), 0.5% or less of silicon (Si), 0.1 to 0.5% of manganese (Mn) (N): 0.005% or less, Ti (Ti): 0.005% or less, and the content of titanium (Ti) 0.005% or less, vanadium (V): 0.005% or less, the balance Fe and other unavoidable impurities; Hot-rolling the reheated slab to provide a hot-rolled steel sheet; Cold-rolling the hot-rolled steel sheet to provide a cold-rolled steel sheet; Continuously annealing the cold-rolled steel sheet; Subjecting the continuously annealed cold rolled steel sheet to first-precision rolling at a first reduction rate of 1 to 3%; Rolling the primary-precision rolled cold-rolled steel sheet at a temperature in the range of 200 to 400 ° C for 10 minutes or less; The cold-rolled steel sheet subjected to the dislocation-fixing annealing can be subjected to secondary-precision rolling at a second reduction ratio of 0.8 to 3%.

The slab alloy composition of the present invention corresponds to the alloy composition of the cold-rolled steel sheet described above, and the description of the slab alloy composition of the present invention is replaced with the description of the alloy composition of the cold-rolled steel sheet described above.

Reheating slabs

The slab having the above-mentioned steel composition can be reheated to a temperature higher than a predetermined temperature. Most of the precipitates present in the steel should be recycled, and the present invention can limit the lower limit of the reheating temperature to 1200 ° C. The lower limit of the preferable reheating temperature for further increasing the solubility of the precipitate may be 1250 캜.

Hot rolling

The hot-rolled steel sheet can be provided by hot-rolling the reheated slab. In order to perform hot rolling in the austenite single phase region, the present invention can limit the lower limit of the hot rolling finishing temperature to the Ar3 temperature.

Hot-rolled steel sheet coiling

The hot-rolled steel sheet can be wound within a predetermined temperature range. When the hot-rolled steel sheet is rolled in a temperature range of 550 占 폚 or more, nitrogen (N) remaining in the solid state can be additionally precipitated with AlN, thereby ensuring excellent endurance. On the other hand, when the hot-rolled steel sheet is rolled at less than 550 ° C, the workability can be damped by the dissolved nitrogen (N) remaining without being precipitated as AlN. In the present invention, the lower limit of the hot- . Further, when the hot-rolled steel sheet is rolled in a temperature range exceeding 750 占 폚, there may arise a problem that the crystal grains are coarse and the cold rolling property is deteriorated. Therefore, the present invention can limit the upper limit of the hot-rolled sheet coiling temperature to 750 캜. Therefore, the hot rolled steel sheet coiling temperature of the present invention may be in a temperature range of 550 to 750 占 폚.

Cold rolling

The rolled hot-rolled steel sheet can be cold-rolled at a reduction ratio of 50 to 95% to produce a cold-rolled steel sheet. The thickness of the final cold-rolled steel sheet is determined by the reduction rate of the cold-rolling, and it is difficult to achieve the final target thickness when the reduction rate of the cold-rolling is less than 50%. In addition, when the reduction rate exceeds 95%, the load of the rolling equipment becomes excessive, which may cause a problem in the process. Therefore, the cold rolling reduction ratio of the present invention may be in the range of 50 to 95%.

Continuous annealing

Continuous annealing of the cold-rolled steel sheet can be carried out at a constant annealing temperature for recrystallization of the elongated crystal grains during cold rolling. If the continuous annealing temperature is lower than 600 ° C, recrystallization does not sufficiently occur, and therefore, dislocations generated during cold rolling can not be sufficiently removed, resulting in a problem of deterioration in ductility. Therefore, the present invention can limit the lower limit of the continuous annealing temperature to 600 占 폚. However, when the continuous annealing temperature exceeds 900 ° C, there is a problem that the crystal grains are coarse, the strength is lowered and the workability is lowered. In this invention, the upper limit of the continuous annealing temperature can be limited to 900 ° C. Therefore, the continuous annealing temperature of the present invention may be in the range of 600 to 900 占 폚. In addition, the continuous annealing of the present invention can be performed within 10 minutes to ensure economical efficiency and productivity.

Primary corrective rolling

It is possible to provide a steel sheet in which a continuously-annealed steel sheet is primary-precision rolled at a reduction ratio of 1 to 3% to generate a movable potential. The movable potential generated by the primary corrective rolling is a position where the solid carbon (C) and the nitrogen (N) can be easily adhered via potential fixing annealing to be performed later. When the reduction ratio of the primary corrective rolling is less than 1%, sufficient dislocation is not generated enough to mostly adhere the solid carbon (C) and the nitrogen (N), and the present invention is characterized in that the lower limit of the reduction ratio of the primary corrective rolling 1%. In addition, when the reduction ratio of the primary corrective rolling is excessive, a large amount of the movable potential is generated more than necessary, and the material is hardened, so that the workability may be deteriorated. Therefore, in the present invention, the upper limit of the reduction ratio of the primary corrective rolling can be limited to 3%. In order to prevent the hardening of the material, the upper limit of the reduction ratio of the preferred first-order rolling may be 2%.

Dislocation anchoring

The steel sheet in which the movable potential is generated by the primary corrective rolling is heat-treated at 200 DEG C or more for 30 seconds or more to produce a steel sheet to which the movable potential is fixed. The movable potential generated immediately after the first electrostatic rolling is fixed to the electric potential by the diffusion during the dislocation annealing, and the higher the dislocation annealing temperature is, the more the time required for dislocation fixing is reduced. It takes about 30 seconds at the dislocation annealing temperature of 200 ° C, but it takes longer time at the lower temperature. Therefore, the present invention can limit the lower limit of the dislocation-annealing temperature to 200 占 폚 in terms of productivity. However, when the dislocation-fixing annealing temperature exceeds 400 ° C, the fixed carbon (C) may be re-used. In this invention, the upper limit of the dislocation annealing temperature may be limited to 400 ° C. In consideration of sufficient dislocation fixing and productivity, the potential fixing annealing time of the present invention may be 20 seconds or more and less than 10 minutes. In terms of productivity, the potential fixing annealing time may be one minute or less.

Second order rolling

The steel sheet to which the dislocations are fixed in the dislocation-fixed annealing can be subjected to secondary-precision rolling at a reduction ratio of 0.8 to 3% to provide a steel sheet having the movable dislocations again. After the potential fixing annealing, most of the potentials are fixed and the movable property is in a deteriorated state, but the movable potential is generated again through the secondary correction rolling, and the workability can be restored. Therefore, the present invention can limit the lower limit of the secondary corrective rolling reduction to 0.8% for the workability recovery effect. On the other hand, when the reduction amount of the secondary correction rolling is excessive, the material may be hardened and the workability may be lowered, so that the present invention can limit the upper limit of the reduction ratio of the secondary correction rolling to 3%. More preferably, the upper limit of the reduction ratio of the secondary corrective rolling to prevent the hardening of the material may be 2%.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the embodiments described below are for the purpose of further illustrating the present invention and are not for limiting the scope of the present invention.

The slabs having the composition shown in the following Table 1 were produced. The slabs were reheated to 1250 占 폚, hot rolled, rolled at 620 占 폚 and then cold rolled at a reduction ratio of 70% to obtain cold-rolled steel sheets of 1.2 mm in thickness.

The obtained cold-rolled steel sheet was subjected to continuous annealing (or unsupervised placing), primary corrective rolling, dislocation-fixed annealing, and secondary correction rolling under the conditions shown in Table 2 below to obtain final steel plate specimens. The continuous annealing was carried out at a temperature of 750 ° C. for 30 seconds and then maintained at 400 ° C. for 60 seconds. The temperature of the continuous annealing was maintained at 700 ° C. for 60 minutes and then maintained at 400 ° C. for 300 minutes.

The carbon (C) and nitrogen (N) contents in the grain and the carbon (C) and nitrogen (N) contents in the grain were measured for each specimen. The tensile strength of each specimen was measured and the yield strength was measured. The aging index and elongation at break were measured to investigate the aging characteristics. The measurement results for each specimen are shown in Table 3 below.

The contents of carbon (C) and nitrogen (N) in the crystal grains were measured by wet element analysis of the inorganic element for the parts excluding the grain boundaries. Internal carbon content (C) and nitrogen (N) Respectively. However, the inorganic element wet component analysis and the internal friction test are merely examples for measuring the content of carbon (C) and nitrogen (N) in the crystal grains, the amount of the solid carbon (C) and the nitrogen (N) in the crystal grains, Is not necessarily bound to these measurement methods.

The aging index refers to the difference in yield strength before and after the artificial aging, and the specimen is held at a temperature of 100 ° C for 1 hour so that carbon (C) and nitrogen (N) The specimens before and after the accelerating aging were subjected to tensile tests and measured.

division	Component (% by weight)
	C	Si	Mn	Al	P	S	N	Nb	Ti	V
River 1	0.003	0.20	0.20	0.03	0.009	0.008	0.002	-	-	-
River 2	0.003	0.20	0.20	0.03	0.008	0.008	0.003	-	-	-
River 3	0.003	0.20	0.21	0.03	0.008	0.008	0.005	-	-	-
River 4	0.003	0.19	0.20	0.04	0.008	0.009	0.010	-	-	-
River 5	0.020	0.21	0.21	0.04	0.008	0.009	0.003	-	-	-
River 6	0.030	0.21	0.21	0.04	0.008	0.009	0.003	-	-	-
River 7	0.031	0.21	0.19	0.04	0.009	0.009	0.005	-	-	-
River 8	0.030	0.19	0.20	0.04	0.009	0.008	0.010	-	-	-
River 9	0.062	0.19	0.20	0.04	0.009	0.009	0.002	-	-	-
River 10	0.062	0.20	0.20	0.03	0.008	0.008	0.003	-	-	-
River 11	0.061	0.19	0.20	0.04	0.009	0.008	0.005	-	-	-
River 12	0.060	0.19	0.20	0.04	0.009	0.008	0.010	-	-	-
River 13	0.090	0.20	0.20	0.04	0.008	0.008	0.002	-	-	-
River 14	0.091	0.19	0.21	0.03	0.008	0.009	0.003	-	-	-
River 15	0.090	0.20	0.19	0.04	0.008	0.008	0.005	-	-	-
River 16	0.092	0.19	0.20	0.04	0.008	0.008	0.010	-	-	-
River 17	0.113	0.20	0.21	0.03	0.008	0.008	0.015	-	-	-
River 18	0.003	0.20	0.21	0.03	0.009	0.009	0.002	-	-	-
River 19	0.032	0.20	0.21	0.04	0.009	0.009	0.003	-	-	-
River 20	0.021	0.20	0.19	0.03	0.009	0.008	0.003	-	-	-
River 21	0.095	0.21	0.21	0.03	0.009	0.008	0.002	-	-	-
River 22	0.056	0.20	0.20	0.03	0.008	0.008	0.005	-	-	-
River 23	0.012	0.21	0.21	0.03	0.008	0.009	0.007	-	-	-
River 24	0.071	0.19	0.20	0.04	0.009	0.009	0.010	-	-	-
River 25	0.056	0.20	0.21	0.04	0.008	0.008	0.005	-	-	-
River 26	0.020	0.21	0.21	0.03	0.009	0.008	0.003	-	-	-
River 27	0.021	0.21	0.21	0.03	0.008	0.008	0.003	-	-	-
River 28	0.019	0.19	0.20	0.04	0.009	0.008	0.003	-	-	-
River 29	0.020	0.20	0.20	0.03	0.008	0.008	0.003	-	-	-
River 30	0.019	0.19	0.20	0.04	0.009	0.008	0.003	-	-	-
River 31	0.021	0.20	0.19	0.03	0.008	0.008	0.003	-	-	-
River 32	0.020	0.20	0.20	0.04	0.009	0.008	0.003	-	-	-
River 33	0.020	0.21	0.20	0.04	0.008	0.008	0.003	-	-	-
River 34	0.020	0.21	0.21	0.04	0.008	0.008	0.003	-	-	-
River 35	0.020	0.20	0.20	0.03	0.008	0.008	0.003	-	-	-
River 36	0.019	0.21	0.19	0.04	0.009	0.008	0.003	-	-	-
River 37	0.050	0.21	0.20	0.03	0.008	0.008	0.003	-	-	-
River 38	0.003	0.20	0.21	0.03	0.009	0.009	0.002	0.015	0.015	-
River 39	0.050	0.21	0.21	0.03	0.009	0.008	0.003	-	-	-

division	Recrystallization annealing	Primary corrective rolling	Dislocation anchoring		Second order rolling
		Reduction rate (%)	Temperature (℃)	Time (min)	Reduction rate (%)
River 1	Continuous annealing	1.0	300	1.0	1.0
River 2	Continuous annealing	1.0	300	1.0	1.0
River 3	Continuous annealing	1.0	300	1.0	1.0
River 4	Continuous annealing	1.0	300	1.0	1.0
River 5	Continuous annealing	1.0	300	1.0	1.0
River 6	Continuous annealing	1.0	300	1.0	1.0
River 7	Continuous annealing	1.0	300	1.0	1.0
River 8	Continuous annealing	1.0	300	1.0	1.0
River 9	Continuous annealing	1.0	300	1.0	1.0
River 10	Continuous annealing	1.0	300	1.0	1.0
River 11	Continuous annealing	1.0	300	1.0	1.0
River 12	Continuous annealing	1.0	300	1.0	1.0
River 13	Continuous annealing	1.0	300	1.0	1.0
River 14	Continuous annealing	1.0	300	1.0	1.0
River 15	Continuous annealing	1.0	300	1.0	1.0
River 16	Continuous annealing	1.0	300	1.0	1.0
River 17	Continuous annealing	1.0	300	1.0	1.0
River 18	Continuous annealing	1.0	100	10.0	1.0
River 19	Continuous annealing	1.0	100	50.0	1.0
River 20	Continuous annealing	1.0	140	1.0	1.0
River 21	Continuous annealing	1.0	170	0.5	1.0
River 22	Continuous annealing	1.0	200	0.5	1.0
River 23	Continuous annealing	1.0	300	0.3	1.0
River 24	Continuous annealing	1.0	400	0.2	1.0
River 25	Continuous annealing	1.0	450	0.5	1.0
River 26	Continuous annealing	0.2	300	1.0	1.0
River 27	Continuous annealing	0.5	300	1.0	1.0
River 28	Continuous annealing	1.5	300	1.0	1.0
River 29	Continuous annealing	2.0	300	1.0	1.0
River 30	Continuous annealing	3.0	300	1.0	1.0
River 31	Continuous annealing	3.5	300	1.0	1.0
River 32	Continuous annealing	1.0	300	1.0	0.6
River 33	Continuous annealing	1.0	300	1.0	0.8
River 34	Continuous annealing	1.0	300	1.0	2.0
River 35	Continuous annealing	1.0	300	1.0	3.0
River 36	Continuous annealing	1.0	300	1.0	3.5
River 37	Continuous annealing	1.0	-	-	-
River 38	Continuous annealing	1.0	-	-	-
River 39	Appeal	1.0	-	-	-

division	(C / 12.01 + N / 14.01) X 10 5		Aging Index (MPa)	Yield point elongation (%)	Yield strength (MPa)	Remarks
	Whole in crystal grain	In-grain employment
River 1	12.5	1.9	2.7	0.0	186	Inventory 1
River 2	19.5	0.3	0.5	0.0	188	Inventory 2
River 3	16.6	5.0	8.3	0.0	205	Inventory 3
River 4	10.8	3.7	5.9	0.0	212	Honorable 4
River 5	19.9	3.9	6.3	0.0	235	Inventory 5
River 6	10.3	3.6	6.2	0.0	265	Inventory 6
River 7	19.6	4.7	7.5	0.0	270	Honorable 7
River 8	16.4	3.1	5.5	0.0	275	Honors 8
River 9	10.7	0.6	1.0	0.0	295	Proposition 9
River 10	18.9	4.7	8.7	0.0	298	Inventory 10
River 11	12.1	0.6	1.0	0.0	305	Exhibit 11
River 12	17.8	2.6	4.7	0.0	310	Inventory 12
River 13	12.7	1.0	1.8	0.0	332	Inventory 13
River 14	14.6	0.8	1.6	0.0	342	Inventory 14
River 15	19.5	4.0	6.6	0.0	346	Honorable Mention 15
River 16	15.9	3.9	6.6	0.0	342	Inventory 16
River 17	19.1	4.1	6.2	0.0	385	Comparative Example 1
River 18	17.1	15.6	29.2	0.6	182	Comparative Example 2
River 19	16.9	10.1	14.7	0.5	265	Comparative Example 3
River 20	18.6	10.4	20.4	0.2	241	Comparative Example 4
River 21	13.7	7.3	13.6	0.1	349	Comparative Example 5
River 22	14.1	3.6	6.5	0.0	302	Inventory 17
River 23	12.0	1.1	1.7	0.0	206	Inventory 18
River 24	15.1	4.5	9.0	0.0	329	Evidence 19
River 25	20.5	19.1	37.6	0.8	300	Comparative Example 6
River 26	16.5	10.4	17.4	0.6	213	Comparative Example 7
River 27	16.9	7.1	12.4	0.4	221	Comparative Example 8
River 28	19.3	1.7	2.7	0.0	235	Inventory 20
River 29	15.3	0.8	1.5	0.0	238	Inventory 21
River 30	18.1	0.6	1.0	0.0	250	Inventory 22
River 31	16.1	0.6	1.2	0.0	358	Inventory 23
River 32	14.5	2.1	3.5	0.6	275	Honors 24
River 33	13.3	1.9	3.6	0.0	240	Honors 25
River 34	14.2	3.7	5.6	0.0	245	Evidence 26
River 35	14.0	2.0	3.9	0.0	255	Honors 27
River 36	16.0	1.7	3.1	0.0	360	Evidence 28
River 37	17.3	16.4	31.8	0.6	253	Comparative Example 9
River 38	10.1	0.2	0.3	0.0	210	Comparative Example 10
River 39	0.7	0.6	1.3	0.0	203	Comparative Example 11

As shown in Tables 1 to 3, Inventive Samples 1 to 22 and Inventive Samples 25 to 27, which satisfy the steel composition and manufacturing conditions of the present invention, have an aging index of 10 MPa or less, yield point elongation does not occur, As shown in Fig. This is explained as a result that the content of carbon (C) and nitrogen (N) in the solid state is lowered by the primary corrective rolling and the potential fixing heat treatment after the recrystallization, . In this case, the contents of the total carbon (C) and nitrogen (N) in the crystal grains satisfy the following relational expression 1 and the carbon (C) and nitrogen N) content satisfies the following relational expression (2).

[Relation 1] ([C] /12.01 + [N] /14.01) x 10 ⁵ ? 10

[Relation 2] ([C] /12.01 + [N] /14.01) x 10 ⁵ 5

However, [C] and [N] in the relational expression 1 and the relational expression 2 refer to the content of carbon (C) and nitrogen (N), respectively, by weight.

Based on the results of relational expressions 1 and 2 and Table 3, the sum of the number of moles of the solid carbon (C) and the nitrogen (N) in the crystal grain with respect to the sum of the total number of moles of carbon (C) and nitrogen It can be derived that the antioxidant property and the processability can be effectively secured.

In Comparative Example 1, the yield point elongation shape does not occur, but the content of carbon (C) and nitrogen (N) in the steel is high and has a yield strength of 385 MPa, which means that the steel has an excessively high strength for use as a working material. It is preferable that the yield strength does not exceed 350 MPa for use as a working material.

From Examples 2 to 6 and Inventive Examples 17 to 19, it is possible to confirm the change of the aging characteristics according to the potential fixing annealing time and the temperature. The higher the temperature, the faster the diffusion rate of carbon (C) and nitrogen (N) contained in the steel. Therefore, the higher the annealing temperature for dislocation annealing, the shorter the annealing time for dislocation annealing.

In the case of Comparative Examples 2 to 5, diffusion and adhesion of sufficient carbon (C) and nitrogen (N) were not formed because the temperature of the heat treatment for dislocation annealing was less than 200 ° C, , It can be confirmed that the relation (2) is not satisfied. As a result, all of the aging index exceeded 10 MPa, and the elongation at the yield point was observed to confirm that the endurance was maintained.

In the case of Comparative Examples 2 and 3, since the heat treatment temperature for the dislocation-fixed annealing does not fall within the heat treatment temperature range of the dislocation-annealing of the present invention, the desired physical properties could not be achieved even though the dislocation annealing was performed for a relatively long time can confirm. That is, if the heat treatment temperature for the dislocation-fixed annealing does not fall within the heat treatment temperature range of the dislocation-annealing of the present invention, the productivity may be lowered.

In the case of Comparative Example 6, as the heat treatment temperature for dislocation-annealing exceeds the heat treatment temperature range for the dislocation-annealing of the present invention, re-use of carbon (C) and nitrogen (N) occurs, It can be confirmed that it is not satisfied. Therefore, it can be confirmed that the aging index exceeds 10 MPa and the yield point elongation phenomenon occurs, so that the endurance is maintained.

On the other hand, in Examples 17 to 19, the heat treatment temperature of the dislocation-fixed annealing satisfies the heat treatment temperature range of the dislocation-annealing of the present invention, and the solid solution carbon and the nitrogen (N) As a result, it can be confirmed that good endurance can be secured.

From the Comparative Examples 7 and 8 and Examples 20 to 23, it is possible to confirm the change in the aging characteristics with the first-round rolling reduction ratio. In order to secure the amount of carbon (C) and nitrogen (N) adhered in the steel during the dislocation-fixing annealing process, a sufficient moving electric potential must be generated in advance, and such a moving electric potential can be generated by the first- .

 In the case of Comparative Examples 7 and 8, the reduction rate of the primary corrective rolling did not reach the reduction rate of the primary corrective rolling of the present invention, so that a sufficient density of dislocations could not be generated. As a result, The carbon (C) and nitrogen (N) of the carbon nanotubes remain in a considerable amount, and therefore, it can be confirmed that the relationship (2) is not satisfied. Therefore, in the case of Comparative Examples 7 and 8, it can be confirmed that the aging index exceeds 10 MPa and the endurance is not ensured.

On the other hand, in Examples 20 to 22, it can be confirmed that the primary corrective rolling reduction ratio satisfies the reduction rate of the primary corrective rolling of the present invention, so that a sufficient potential is formed to secure the endurance. have. However, in the case of Inventive Example 23, since the reduction ratio of the primary corrective rolling exceeds the reduction ratio of the primary corrective rolling of the present invention, the effect of improving the endurance is insufficient, while the yield strength is excessively increased, Can be confirmed.

 From Examples 24 to 28, it is possible to confirm a change in the aging characteristics according to the second-order rolling reduction ratio. Since the movable potential generated in the primary corrective rolling is mostly converted to the nonconductive phase through the potential fixing annealing, it is necessary to regenerate the movable potential through the secondary corrective rolling to secure the processability.

However, in the case of Example 24, the solid carbon (C) and the nitrogen (N) are sufficiently fixed to the potential through the dislocation fixing heat treatment to satisfy the aging index of 10 MPa or less. However, It can be confirmed that the yield point elongation phenomenon remains because the rolling reduction rate is not lowered.

In the case of Inventive Example 28, since the reduction ratio of the secondary corrective rolling exceeds the reduction ratio of the secondary corrective rolling of the present invention, dislocation is generated more than necessary and the yield strength is excessively increased, It can be confirmed that it is dormant.

Comparative Example 9 is a low carbon steel in which the anti-aging property is not ensured. In terms of steel composition, there is no significant difference from the present invention, but the carbon (C) content in the crystal grain is high and the carbon (C) It can be confirmed that the relational expression 2 of the present invention is not satisfied.

Comparative Example 10 is an IF steel in which most of the carbon (C) and nitrogen (N) in the crystal grains exists in the form of carbide or nitride, satisfying the relational expressions 1 and 2, and securing the anti-aging property. However, Comparative Example 10 essentially contains a precipitate-forming element such as titanium (Ti) and niobium (Nb), which is not preferable from the economical point of view, and there is a risk of occurrence of surface defects due to high temperature heating.

In Comparative Example 11, since most of the carbides were precipitated at the grain boundaries through the heat treatment for 5 hours or more at a high temperature, it was confirmed that the productivity did not satisfy the relational expression 1 and the heat treatment was performed for a long time.

Accordingly, the cold-rolled steel sheet according to one aspect of the present invention and the method of manufacturing the same can effectively ensure endurance and workability by optimizing steel composition and manufacturing process conditions, and can effectively secure productivity and economical efficiency in cold- .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, Therefore, the technical idea and scope of the claims set forth below are not limited to the embodiments.

Claims (15)

1. 0.01% or less of S, 0.01% or less of S, 0.01% or less of N, 0.01% or less of N, 0.1% or less of Si, 0.005% or less, Ti: 0.005% or less, V: 0.005% or less, and the balance of Fe and other unavoidable impurities, wherein the total C and N contents in the crystal grains satisfies the following relational expression 1, The cold-rolled steel sheet excellent in endurance and processability satisfying the relationship (2).

   [Relation 1] ([C] /12.01 + [N] /14.01) x 10 ⁵ ? 10

   [Relation 2] ([C] /12.01 + [N] /14.01) x 10 ⁵ 5

   [C] and [N] in the relational expression 1 and the relational expression 2 refer to the content of C and N, respectively, by weight.
2. The method according to claim 1,

   And Nb, Ti and V are each 0.001% or less.
3. The method according to claim 1,

   Wherein the cold-rolled steel sheet has an aging index of 10 MPa or less, and is excellent in endurance and workability.
4. The method according to claim 1,

   The cold-rolled steel sheet has an elongation at break at a yield point of 0.5% or less, and is excellent in endurance and workability.
5. The method according to claim 1,

   The cold-rolled steel sheet has a yield strength of 350 MPa or less, and is excellent in endurance and workability.
6. 0.01% or less of S, 0.01% or less of S, 0.01% or less of N, 0.01% or less of N, 0.1% or less of Si, 0.005% or less, Ti: 0.005% or less, V: 0.005% or less, the balance Fe and other unavoidable impurities;

   Hot-rolling the reheated slab to provide a hot-rolled steel sheet;

   Cold-rolling the hot-rolled steel sheet to provide a cold-rolled steel sheet;

   Continuously annealing the cold-rolled steel sheet;

   Subjecting the continuously annealed cold rolled steel sheet to first-precision rolling at a first reduction rate of 1 to 3%;

   Rolling the primary-precision rolled cold-rolled steel sheet at a temperature in the range of 200 to 400 ° C for 10 minutes or less;

   Wherein the hot-rolled cold-rolled steel sheet is subjected to secondary-precision rolling at a second reduction ratio of 0.8 to 3%.
7. The method according to claim 6,

   And a movable potential is generated in the cold-rolled steel sheet by the primary corrective rolling.
8. The method according to claim 6,

   And the movable potential generated by the primary fixed rolling is fixed to the potential by diffusion by the dislocation-fixed annealing.
9. The method according to claim 6,

   And the movable potential is regenerated to the cold-rolled steel sheet by the secondary corrective rolling.
10. The method according to claim 6,

    Wherein the reheating temperature of the slab is 1200 占 폚 or higher, and the cold-rolled steel sheet is excellent in endurance and workability.
11. The method according to claim 6,

    Wherein the finish rolling temperature of the hot rolling is at least Ar3, and is excellent in endurance and workability.
12. The method according to claim 6,

    Wherein the reduction ratio of the cold rolling is 50 to 95%, and the cold-rolled steel sheet has excellent endurance and workability.
13. The method according to claim 6,

    Wherein the temperature of the continuous annealing is 600 to 900 占 폚.
14. The method according to claim 6,

    Wherein the hot-rolled steel sheet is rolled at 550 to 750 占 폚 and is provided for the cold-rolling, wherein the cold-rolled steel sheet is excellent in endurance and workability.
15. The method according to claim 6,

    And Nb, Ti and V are each 0.001% or less.