KR100415676B1 - A nonaging steel sheet for tube with superior formability and a method for manufacturing it - Google Patents

Abstract

The present invention relates to a method for manufacturing a conventional steel sheet, by adjusting the steel composition and appropriately controlling the cold-rolled sheet annealing conditions after cold rolling, to provide a conventional steel sheet having excellent workability and pressure resistance characteristics and its manufacturing method have.

In the present invention, carbon: 0.0015 to 0.010%, manganese: 0.50 to 1.20%, phosphorus: 0.030 to 0.080%, sulfur: 0.015% or less, aluminum: 0.03 to 0.06%, nitrogen: 0.003% or less, titanium: 0.025 ~ 0.040%, chromium: 0.040 to 0.06%, Mn / S atomic ratio: 30 to 45, balance Fe and other unavoidable impurities, and the workability of 1.2 to 1.8 atomic ratio of effective titanium and carbon defined by the following relation 1 An excellent non-aging tolerance steel sheet and its manufacturing method are made into the technical summary.

[Relationship 1]

Ti * = Ti- (48/32) S- (48/14) N

Description

Non-ageing tolerance steel sheet with excellent workability and manufacturing method thereof {A NONAGING STEEL SHEET FOR TUBE WITH SUPERIOR FORMABILITY AND A METHOD FOR MANUFACTURING IT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial miscellaneous pipe which requires excellent expandability after welding and a steel sheet for butane gas pipe (pressure vessel) requiring excellent pressure resistance and anisotropy, and more specifically, by controlling steel components and cold rolled annealing conditions after cold rolling. The present invention relates to a steel sheet and a method of manufacturing the same, which can obtain excellent workability and pressure resistance characteristics.

The conventional steel sheet is usually coated before being processed into a tube. At this time, if a large amount of solid solution carbon is present in the steel sheet, the solid solution carbon fixes the transfer transition.

Because of this phenomenon, when drawing steel sheet is used, stretcher strain occurs, which causes appearance defects and elongation decreases, and yield points increase, resulting in shape defects. . In addition, wrinkles, etc., occur even when the bending process is light.

In order to solve such a problem, development of the steel plate which has a good aging property with inferiority has progressed.

For example, there is a method of reducing the solid solution carbon in the steel by low temperature annealing of low carbon aluminum (Al Killed) steel by the slow annealing. However, this method not only decreases manufacturing efficiency but also causes defects such as surface and shape defects due to an increase in manufacturing process. In addition, the average Rankford value (hereinafter average r value) of the steel sheet manufactured by this method is usually about 1.3 to 1.4, and in order to cope with the recent thinning demand of conventional steel sheet, the average r value of this degree is sufficient in workability. Cannot be secured.

On the other hand, attempts have been made to produce a non-aging steel sheet having good workability by continuous annealing based on ultra low carbon steel.

For example, Japanese Special Public Works 50-31531 (Method for producing a non-aging superhard steel sheet by continuous annealing) generates a large amount of nitrides such as titanium, niobium or zirconium, tantalum, etc., which are stoichiometrically higher than the total amount of carbon and nitrogen in steel. A method of stabilizing by adding components to fix carbon and nitrogen in solid solution as a compound is proposed. However, among the components, titanium, zirconium, and tantalum are chemically very active components, and therefore, they are not suitable for conventional steel sheets requiring a great deterioration in the state of the steel sheet surface and requiring corrosion resistance and beautifulness. In addition, the addition of a large amount of niobium causes material deviations in the width and length directions in the final product, and the recrystallization temperature increases significantly, resulting in deterioration of workability during annealing. Moreover, such components are generally expensive, and a large amount of addition is a factor of the cost increase of the alloy component itself.

The material of the steel sheet is evaluated as Temper Grade by Rockwell Surface Hardness (HR30T), T-1 (HR30T: 49 ± 3), T-2 (HR30T: 53 ± 3). , T-2.5 (HR30T: 55 ± 3), T-3 (HR30T: 57 ± 3), soft steel sheet and quality T-4 (HR30T: 61 ± 3), T-5 (HR30T: 65 ± 3 ), T-6 (HR30T: 70 ± 3), can be divided into hard steel sheets.

Soft materials of less than T-3 are mainly processed for severe processing and require inaging, deep workability and weldability. Hard materials of more than T-4 are applied to areas requiring excellent pressure resistance, high workability and high strength. It is becoming.

In Japanese Patent Application No. 40-3020 and Special Application No. 36-10052, soft materials of the following T-4 and T-5 grades with high hardness cannot be manufactured. Japanese Patent Application Laid-Open No. 61-207520 discloses a method in which annealing temperature is extremely high, such as 720 to 850 ° C., to increase the crystal grain size, and the temper rolling rate to 5 to 10%. It is a method that becomes a big obstacle to practical use.

Korean Patent Laid-Open Publication No. 1999-010558 is a T-2 grade soft tin-plated disc manufactured with an annealing temperature of 690 to 740 ° C by adding special elements (Ti, B) to ultra low carbon steel, and is stable against internal pressure of butane gas pipes. In order to improve the internal pressure of the pipe (15kg / ㎠ or more), and less than the anisotropy in the dome (Dome) is weak in anisotropy, there is a problem in the workability in applying as a pressure vessel. In addition, there is a problem that the welded portion of the T-3 grade steel sheet applied as an industrial miscellaneous pipe ruptures during expansion after welding. In addition, the production rate of T-3 soft materials and T-4 hard materials is roughly 40% and 45%, respectively, in the producers of steel sheets, which occupy more than 80% of all steel sheets. The method for producing soft and T-4 hard materials in one steel grade has not been proposed yet.

Accordingly, the present inventors have repeatedly conducted research and experiments to solve the above problems, and propose the present invention based on the results. The present invention adjusts the steel components and appropriately controls the cold rolling annealing conditions after cold rolling. By doing so, it is an object of the present invention to provide a conventional steel sheet having excellent workability and pressure resistance characteristics and its manufacturing method.

In the present invention, carbon: 0.0015 to 0.0040%, manganese: 0.50 to 1.20%, phosphorus: 0.030 to 0.080%, sulfur: 0.015% or less, aluminum: 0.03 to 0.06%, nitrogen: 0.003% or less, titanium: 0.025 ~ 0.040%, chromium: 0.040 to 0.06%, Mn / S atomic ratio: 30 to 45, balance Fe and other unavoidable impurities, and the workability of 1.2 to 1.8 atomic ratio of effective titanium and carbon defined by the following relation 1 It relates to an excellent non-aging tolerance steel sheet.

[Relationship 1]

Ti * = Ti- (48/32) S- (48/14) N

In addition, the present invention is a method of manufacturing a conventional steel sheet,

By weight% Carbon: 0.0015 ~ 0.0040%, Manganese: 0.50 ~ 1.20%, Phosphorus: 0.030 ~ 0.080%, Sulfur: 0.015% or less, Aluminum: 0.03 ~ 0.06%, Nitrogen: 0.003% or less, Titanium: 0.025 ~ 0.040%, Chromium: 0.040 to 0.06%, manganese and sulfur atomic ratios: 30 to 45, effective titanium and carbon atomic ratios: 1.2 to 1.8, residual steel and other unavoidable impurities. The present invention relates to a method for producing a non-aging conventional steel sheet having excellent workability, which is wound at a temperature range of 700 ° C., cold rolled at a reduction ratio of 80% or more, and then annealed at a temperature of 710 ° C. or more in a continuous annealing furnace.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The lower the carbon (C) of the present invention from the viewpoint of stretching and improving the average r value.

However, when the amount of carbon in the slab stage is less than 0.0015%, the particle size is significantly coarse, and there is a high risk that an orange peel phenomenon occurs in the state of the final stage product after processing. In addition, the transformation point during hot rolling is greatly influenced by the amount of carbon in the steel, but if the content is small, the transformation point is very high, so that it is not possible to finish the finish rolling in the austenitic single-phase zone, so that it is required to have a uniform and excellent workability. Inappropriate

On the other hand, in the case where the carbon content exceeds 0.0040%, the decarburization reaction cannot proceed sufficiently by a short time annealing after cold rolling, and the target non-aging cannot be obtained. In addition, in actual industrial production, the length of the line is limited, and the amount of carbon is also limited because the annealing time cannot be extended indefinitely.

Therefore, it is preferable to limit the carbon to 0.0015% to 0.0040%, especially from the viewpoint of improving the average r value.

The manganese (Mn) is an element added to prevent the heat brittleness of the steel, and serves to reduce the transformation point to relax the regulation of the rolling conditions in hot rolling. In other words, by optimizing the content of manganese, it is possible to suppress the solid solution strengthening amount of the steel sheet and to make the steel sheet structure uniform and fine.

The content of such manganese is preferably set in parallel with sulfur (S), it is preferably set to 0.50 ~ 1.20%. As such, if the content is 0.50% or more, even if boron is not added, the Ar ₃ transformation temperature is lowered during cooling and ferrite transformation is suppressed in austenite, thereby causing a mesh transformation at low temperature, thereby welding heat during cooling. It shows the effect of suppressing abnormal grain growth of the affected part. In addition, the hardness drop phenomenon of the weld heat affected zone is similar to the conventional boron-added steel, and the recrystallization temperature is lowered by about 20 ~ 30 ℃ improves the annealing workability.

However, if the content exceeds 1.2%, the hardness value after recrystallization increases, but rather, the hardness decreases, and since the decarburization reaction is delayed during continuous annealing, the component range is preferably set to 0.5 to 1.2%.

Since the sulfur (S) is preferably reduced as much as possible for the decarburization reaction in the continuous annealing process, the content thereof is preferably 0.015% or less. The detailed mechanism for this is unclear, but by reducing sulfur, it is possible to reduce precipitates in the steel to improve workability.

On the other hand, the atomic ratio of manganese and sulfur not only influences the size and distribution of the manganese compound-based precipitates, but also causes cracking defects in the reproducing process, so control of this is important in terms of securing a stable material. In other words, if the atomic ratio of manganese and sulfur is less than 30, the thermal brittleness is induced. If the atomic ratio of manganese and sulfur exceeds 45, the amount of dissolved manganese is increased, so that the target quality and processability cannot be secured. Therefore, the atomic ratio of sulfur to manganese is set to 30 to 45. It is desirable to.

The aluminum (Al) is an important component for fixing and stabilizing nitrogen in the steel, the content is preferably 0.030% or more from the viewpoint of non-aging. However, if the content exceeds 0.060%, not only the component cost increases but also the risk of surface defects increases, and the risk of cracking in the slab stage also increases. Therefore, the component range is preferably set to 0.030 to 0.060%.

The phosphorus (P) is an element having a solid solution strengthening and grain refining effect due to temper strengthening, and it is preferable to use a large amount as much as possible when manufacturing a hard conventional steel sheet.

The increase in phosphorus in steel affects recrystallization during annealing after cold rolling to inhibit nucleation and grain growth of recrystallization. That is, the FeTiP-based precipitates are precipitated at the grain boundary, and the density of the TiC-based precipitates, which are mainly finely precipitated in the mouth, is reduced. Therefore, the precipitation of fine TiC-based precipitates is suppressed, so that the ferrite grain growth of the annealing plate is promoted, and the average r value is improved. Therefore, P is contained in an amount of 0.03% or more, preferably 0.041% or more in order to obtain the above-mentioned addition effect. It is.

However, if the content exceeds 0.080%, not only problems such as deterioration of corrosion resistance and embrittlement of the material, but also increase recrystallization temperature, it is preferable to set the upper limit to 0.080%. In other words, the phosphorus content is preferably 0.08% or less in order to obtain good corrosion resistance and high workability. The upper limit of the nitrogen (N) is preferably set to 0.003% or less from the viewpoint of non-aging resistance reduction. That is, when a large amount of nitrogen is contained in the steel, the fixing and stabilizing effect of nitrogen by the aluminum to be added does not sufficiently work, and solid nitrogen above a critical amount remains in the final product stage. For this reason, side effects, such as fluting during piping and stretcher strain at the time of light processing, generate | occur | produce. In addition, when the nitrogen content in steel is high, it is advantageous for the non-aging property to increase the balanced addition amount of aluminum, but when the nitrogen content exceeds 0.003%, ductility deterioration is remarkable, and cracking occurs in the slab manufacturing stage. The risk is increased. In addition, when the amount of nitrogen exceeds 0.003%, the amount of titanium corresponding to the amount of nitrogen also increases, resulting in an increase in alloy cost and deterioration of workability.

Therefore, in order to prevent the above-mentioned problem and to further improve the workability represented by the average r value and the like, it is preferable to set the content to 0.003% or less.

The chromium (Cr) is an element added for reinforcement in the steel, when the content is less than 0.04%, it is difficult to obtain a reinforcing effect corresponding to T-3 and T-4 materials, and when exceeding 0.06%, tin plating Although the reinforcing effect of the original plate is increased, the production cost is increased due to the increase in the amount of chromium. Therefore, it is preferable to limit the component range to 0.04 to 0.06%.

The titanium (Ti) is an effective ingredient for inaging, the content is preferably set to 0.025 ~ 0.040%, the reason is that when the content is less than 0.025% fluting and strainer strain in the processing process When defects such as (Stretcher Strain) occur, on the other hand, when exceeding 0.040%, the recrystallization temperature becomes high, and the solid-state titanium delays the recovery and recrystallization of the ferrite phase during continuous annealing, thereby increasing the annealing temperature during continuous annealing. Because it makes you bad.

On the other hand, in the present invention, in order to secure the material and workability, it is preferable to control the addition amount of titanium by combination with the addition amount of carbon, nitrogen, and sulfur present in the steel. That is, the atomic ratio (Ti * / C) of the effective titanium and carbon defined by the following relational formula 1 is preferably set to 1.2 to 1.8. The reason is as follows.

As described above, when the atomic ratio of effective titanium to carbon is set to 1.2 to 1.8, titanium added as a carbonitride-forming element is precipitated in the steel as a coarse precipitate, unlike niobium nitride, which is finely formed, and has a ferrite phase. It is possible to suppress the aging phenomenon caused by the solid solution by fixing carbon and nitrogen which are employed without suppressing the recrystallization phenomenon. In other words, excellent non-aging characteristics cannot be obtained by simply reducing carbon to less than 0.0015%. In addition, due to the refinement of the crystal grains there is an effect that can prevent the surface roughness during molding. In particular, in the present invention, since the carbon level of the raw material is low, it has an extremely excellent effect in terms of coarsening of crystal grain size and preventing surface roughness of the final product in each manufacturing process.

[Relationship 1]

* Ti = Ti- (48/32) S- (48/14) N When the atomic ratio (Ti * / C) is less than 1.2, the fluting resistance and weldability are lowered, and when it exceeds 1.8, the additive effect is Is saturated.

The steel slab formed as described above is reheated, hot rolled and hot rolled, and then cold rolled and cold rolled to form a steel sheet through a process of annealing. a is preferably set to Ar ₃ transformation point ~ 950 ℃ to be improved. The reason is that when the temperature exceeds 950 ° C, the structure of the steel sheet tends to coarsen and exhibits a tendency to deteriorate in workability.

Since it is advantageous for the refinement of the steel sheet structure to start cooling as soon as possible after the end of the hot rolling as described above, it is preferable to start cooling within about 0.3 seconds. After the start of cooling, cooling at a cooling rate of 30 ° C./s or more until the start of winding is preferable. In this way, since the structure of a steel plate can be refined | miniaturized, the workability of the obtained final product becomes favorable.

After that, it is preferable to wind up at a temperature range of 620 ° C to 700 ° C. If the temperature is less than 620 ° C, it causes defects in the plate shape due to uneven cooling, which hinders pickling and cold rolling in the next step. This is because when the temperature exceeds 700 ° C, not only does the scale thickness increase and the pickling takes time, but also the structure of the hot coil becomes coarse, thereby deteriorating the final workability of the steel sheet. In addition, the winding temperature exceeding 700 ° C. is not preferable because a material variation occurs in the steel plate width direction due to a difference in cooling rate after winding.

On the other hand, in the present invention, in order to obtain sufficient deep workability, it is preferable to perform cold rolling after the winding at a reduction ratio of 80% or more, and more preferably 85% or more. Although the detailed mechanism for this is unclear, when the cold rolling reduction is 85% or more, the decarburization reaction during continuous annealing tends to be promoted.

Next, cold-rolled annealing is carried out. If the temperature is set to 710 ° C. or more, which is the minimum temperature at which recrystallization is completed, the structure can be refined at a high cold reduction rate to improve strength. In addition, the upper limit of the annealing temperature is not particularly specified, but the upper limit temperature of the operation that does not cause breakage of the steel strip and defects such as heat buckles at the time of continuous annealing is equivalent to this. The upper limit of the temperature at which austenite appears is the upper limit. In view of this, the upper limit of the preferable annealing temperature is preferably set to 728 DEG C. On the other hand, the annealing time is set to 18 seconds or more in order to improve the stability of the material. It is desirable to. By setting it in this way, the recrystallization of the steel plate which is an essential requirement of this invention can fully be achieved.

Thereafter, the thickness of the conventional steel sheet manufactured as described above is preferably 0.40 mm or less.

(Example)

After continuous casting of molten steel as shown in Table 1, the slab was reheated to 1,250 ° C., and manufactured as a cold rolled thin steel sheet having a plate thickness of 0.25 mm under the manufacturing conditions of Table 2 below.

At this time, the annealing time was 30 seconds, the atmosphere in the furnace was a mixed gas atmosphere of H ₂ 4% + N ₂ 96%, the dew point was -15 ℃. The cooling rate after such annealing was made constant as 25 degree-C / s.

Then, after the tempered rolling was made constant at a rolling reduction rate of 1.0% on the manufactured steel sheet, various tests were performed by tin plating # 25 in a ferrostan type electro tin plating process, and the test results were obtained. It is shown in Table 2 below.

At this time, the tensile characteristic was measured using the normal JIS 5 test piece.

In addition, the average r value was measured by a three-point method using a JIS No. 5 test piece, and the r value in each of 0 °, 45 °, and 90 ° directions with respect to the rolling direction was r ₀ , r ₄₅ , and r ₉₀ , respectively. r ₀ + r was calculated as _{90 + 2r 45) / 4,} △ r value = (r ₀ + 2r ₉₀ + r ₄₅₎ / 2.

The aging index (Al) was evaluated as an increase in stress after the deformation was applied in advance, and the load was lowered and aged at 100 ° C. for 30 minutes.

Flute resistance and weldability were visually evaluated by processing specimens manufactured by a pipe mill. The internal pressure was obtained by performing a pressure resistance test on a butane gas pipe.

division Chemical composition (% by weight) C Mn P S Sol-Al N Ti Cr Ti * / C atomic ratio Mn / S atomic cost Inventive Steel A 0.0028 0.91 0.064 0.012 0.052 0.0025 0.030 0.05 1.22 44.3 Inventive Steel B 0.0034 1.12 0.038 0.015 0.044 0.0023 0.035 0.04 1.35 43.6 Invention Steel C 0.0035 0.76 0.077 0.012 0.049 0.0029 0.033 0.05 1.44 37.0 Inventive Steel D 0.0030 0.64 0.051 0.011 0.034 0.0019 0.028 0.06 1.66 34.0 Conventional Steel E 0.0036 1.01 0.056 0.014 0.040 0.0027 0.032 0.04 0.48 42.1 Conventional Steel F 0.0034 0.95 0.062 0.008 0.045 0.0025 0.034 0.05 3.95 69.3 Conventional Steel G 0.0025 0.34 0.041 0.012 0.052 0.0023 0.035 0.05 3.64 16.5 Conventional Steel H 0.0030 0.86 0.018 0.013 0.045 0.0027 0.028 0.04 -0.25 38.6 Conventional Steel I 0.0051 0.79 0.056 0.013 0.056 0.0026 0.040 0.05 2.27 35.5 Conventional Steel J 0.0034 0.91 0.049 0.008 0.033 0.0038 0.025 0.04 -0.01 66.4 Conventional Steel K 0.0035 1.03 0.061 0.020 0.051 0.0025 0.035 0.04 -1.02 30.1 Conventional Steel L 0.0023 0.66 0.045 0.014 0.069 0.0027 0.036 0.06 2.49 27.5 * Ti = Ti- (48/32) S- (48/14) N

division Manufacture conditions Quality characteristics Finish rolling temperature (℃) Winding temperature (℃) Cold rolling rate (%) Annealing Temperature (℃) Average r value Δr (±) Al (Kg / mm2) YP-EL (%) Internal pressure (kg / ㎠) Fluting Resistance Weldability HR30T Quality Rating secure Invention 1 Inventive Steel A 913 670 87 725 1.8 0.03 0 0 13.6 0 0 58.1 T3 0 Invention 2 915 670 89 715 1.8 0.05 0 0 15.5 0 0 61.9 T4 0 Comparative Material 3 914 718 89 721 1.2 0.25 0.3 0 13.9 0 0 56.3 T4 x Comparative Material 4 913 670 86 702 1.5 0.34 0.1 0 13.7 △ 0 54.8 T3 x Comparative Material 5 915 670 87 698 1.3 0.38 0.3 0 13.5 0 △ 58.3 T3 x Comparative Material 6 912 670 89 702 1.2 0.35 0.2 0 15.6 0 0 62.4 T4 x Invention 7 Inventive Steel B 915 670 87 724 1.8 0.08 0 0 13.8 0 0 57.8 T3 0 Comparative Material 8 915 670 89 704 1.3 0.41 0.5 0 15.5 0 0 62.7 T4 x Invention Material 9 Invention Steel C 915 670 87 721 1.9 0.06 0 0 13.8 0 0 56.8 T3 0 Comparative Material 10 913 670 89 705 1.2 0.31 0.5 0 15.9 0 0 64.9 T5 x Invention 11 Inventive Steel D 925 670 87 721 1.9 0.06 0 0 13.7 0 0 57.4 T3 0 Comparative Material 12 920 670 87 706 1.3 0.29 0.3 0 15.5 0 0 59.5 T4 x Conventional Materials 13 Conventional Steel E 913 670 87 718 0.9 0.41 2.5 4.2 13.2 x x 54.8 T2.5 x Conventional Material14 Conventional Steel F 915 670 89 720 1.0 0.38 4.5 4.6 13.5 x △ 56.6 T3 x Conventional Material15 Conventional Steel G 916 670 87 721 0.9 0.45 3.8 5.1 13.2 x x 54.2 T2.5 x Conventional Materials 16 Conventional Steel H 915 670 89 730 0.8 0.36 3.9 4.5 13.4 x x 56.7 T3 x Conventional Materials 17 Conventional Steel I 914 670 87 718 1.0 0.40 4.0 5.2 12.9 △ △ 54.0 T2.5 x Conventional Materials 18 Conventional Steel J 915 670 89 723 0.9 0.42 3.8 4.3 13.4 x x 56.5 T3 x Conventional materials 19 Conventional Steel K 920 670 87 712 0.8 0.40 5.0 3.2 13.0 x x 53.4 T2.5 x Conventional 20 Conventional Steel L 917 670 89 715 0.9 0.43 4.2 4.7 13.5 x △ 56.4 T3 x Note: 0: good, △: bad, x: very bad

As shown in Tables 1 and 2, the inventive steels (A) to (D) are all atomic ratios of carbon to effective titanium in the scope of the present invention, and completely fixed and precipitated solid solution elements in the steel to yield yield elongation (YP -EL) represents zero. In addition, all manganese is added at least 0.60% to lower the Ar ₃ transformation temperature during cooling without adding boron, and to suppress the ferrite transformation in austenite, thereby causing the transformation at low temperature. The negative grain growth was suppressed and the material was excellent in the weld state.

On the other hand, in the conventional steel outside the scope of the present invention, T-2, 5 and T-3 grade steel sheets having low quality were obtained even under the same manufacturing conditions as those of the same invention steel.

All invention materials produced using the inventive steel under the manufacturing conditions within the scope of the present invention had a high average r value and a low Δr value (that is, less ear generation). In addition, both the fluting resistance and the weldability were excellent. In particular, both Al (aging index) and YP-EL (yielding point elongation) exhibited a non-aging property of 0, resulting in a marked improvement. Such a steel sheet having a high average r value and a small Δr value is suitable for dome production, which requires workability and good ear free characteristics. In addition, it was confirmed that the steel sheet within the invention range having excellent ductility due to non-aging was excellent in formability even after high processing or after aging treatment was performed thereafter.

On the other hand, in the cold rolling reduction rate 86%, T-3 grade and 88% T-4 grade strength can be secured.

On the other hand, the comparative materials and the conventional materials outside the scope of the present invention were very poor compared to the present invention steel, the average r value, Δr value, pressure resistance, fluting resistance and weldability representing the processing characteristics.

Conventional materials (13), (16), (18), and (19) using comparative steels (E), (H), (J), and (K) whose atomic ratio of carbon to effective titanium is lower than the limiting conditions of the present invention. ) Recrystallization was completed at annealing temperature above 710 ℃, but due to lack of atomic ratio for effective titanium, fluting phenomenon occurred during can processing, and the welding condition was poor. This is due to the presence of elements in the steel, which causes deformation aging by these solid elements in the reflow process of the tin plating line and the baking process of the steel making line. ) And stretching strain (Stretcher Strain) phenomenon caused poor pipe workability.

Although the inventive steel is used, the comparative materials (4), (5), (6), (8), (10), and (12) whose annealing temperature is lower than the range of the present invention are not recrystallized. Not only could the target material not be secured, but as the variation of the material increased, the average r and Δr values were 0.9 ~ 1.3 and 0.29 ~ 0.43, respectively, and the workability such as anisotropy was significantly decreased.

In addition, the comparative material (3) wound at a temperature higher than the winding temperature of 620 ~ 700 ℃ proposed in the present invention because the coil structure of the hot coil is coarse and the material variation in the width direction of the steel sheet occurs in the difference in cooling rate after winding Workability, such as an average r value and (triangle | delta) r value, fell.

Elemental ratio of sulfur to manganese (Mn / S ratio) is outside the scope of the present invention prior art material (14), (15), (18) using conventional steels (F), (G), (J), (L) , (20) was very low in hardness and internal pressure compared to the invention steel at the same cold reduction rate, the average r value and △ r value was poor.

In other words, if the atomic ratio of manganese and sulfur is less than 30, it acts as a cause of redness, and if it exceeds 45, the amount of dissolved manganese increases, and thus the target quality and processability cannot be secured.

As described above, the present invention is added to the manganese and phosphorus upwards, by appropriately controlling the annealing conditions after cold rolling, to secure the non-aging, weldability and material reinforcement, and to strengthen the anisotropic effect, the steel sheet for T-3 grade flexible pipe It has excellent weldability, pipe workability, and excellent pressure resistance and anisotropy of T-4 grade hard tin plated disc, and both types have the effect of efficiently manufacturing non-aging steel sheets.

Claims (3)

By weight% Carbon: 0.0015 ~ 0.0040%, Manganese: 0.50 ~ 1.20%, Phosphorus: 0.041 ~ 0.080%, Sulfur: 0.015% or less, Aluminum: 0.03 ~ 0.06%, Nitrogen: 0.003% or less, Titanium: 0.025 ~ 0.040%, Chromium: 0.040 to 0.06%, atomic ratio of Mn / S: 30 to 45, balance of Fe and other unavoidable impurities, and excellent in workability with a processability of 1.2 to 1.8, which is an atomic ratio of effective titanium and carbon defined by Equation 1 below. Steel plate [Relationship 1] Ti * = Ti- (48/32) S- (48/14) N In the method of manufacturing a conventional steel sheet, By weight% Carbon: 0.0015 ~ 0.0040%, Manganese: 0.50 ~ 1.20%, Phosphorus: 0.041 ~ 0.080%, Sulfur: 0.015% or less, Aluminum: 0.03 ~ 0.06%, Nitrogen: 0.003% or less, Titanium: 0.025 ~ 0.040%, Chromium: 0.040 to 0.06%, manganese and sulfur atomic ratios: 30 to 45, effective titanium and carbon atomic ratios: 1.2 to 1.8, residual steel and other unavoidable impurities. A method for producing a non-aging conventional steel sheet having excellent workability, which is wound at a temperature range of 700 ° C., cold rolled at a reduction ratio of 80% or more, and then annealed at a temperature of 710 to 728 ° C. in a continuous annealing furnace. The method of manufacturing a non-ageing tolerant steel sheet excellent in workability according to claim 2, wherein the cold rolling reduction rate is 85% or more.