KR100244630B1 - The manufacturing method for steel strip and same product with coil unity - Google Patents

Abstract

The present invention relates to a coil for binding a coil having excellent toughness and a method for manufacturing the same, wherein the steel component and the manufacturing conditions in the manufacturing process are appropriately controlled to produce a coil for binding a high toughness coil having a tensile strength of 90 kgf / mm 2 or more and an elongation of 9.0% or more. The purpose is to provide a method.

The object of the present invention described above is by weight, C: 0.05-0.13%, Mn: 0.5-1.5%, Ni: 0.1-0.3%, Si: 0.03% or less, P: 0.02% or less, S: 0.02% or less, Soluble Al: 0.02-0.08%, N: 0.006% or less, Ti: 0.12-0.18%, remainder: After homogenizing the slab of steel composed of Fe and inevitably contained impurities in the temperature range of 1200-1250 ° C, Ar Finishing hot rolling in the temperature range of 900-950 ° C. above ₃ temperatures, winding in the temperature range of 550-650 ° C., and then cold rolling to the final thickness at a rolling reduction rate of 45-65%, in the temperature range of 540-600 ° C. The gist of the present invention relates to a method for producing a high toughness coil binding steel by recovering annealing in an annealing furnace and bluing in a temperature range of 430-470 ° C.

Description

High toughness coil binding steel and manufacturing method

1 is a comparative graph of tensile strength-elongation obtained by tensile test after bluing the inventive steel and the comparative steel according to the present invention.

The present invention relates to a coil binding steel having excellent toughness and a method for manufacturing the same, and more particularly, to a cold-rolled steel sheet manufactured from a steel in which a small amount of Ti and Ni are added to a low carbon Al-killed steel containing Mn. The present invention relates to a method for manufacturing a high toughness coil binding steel having an elongation of 9.0% or more of tensile strength of 90 kgf / mm 2 or more by performing recovery annealing by an annealing method before bluing treatment.

Packaging steel used for bonding cold rolled steel, hot rolled steel, and wire rod may be deformed or damaged by a large load or external impact applied to the coil, and thus a sufficient combination of tensile strength and ductility, that is, high toughness, is required. Such packing steels are usually slitting cold rolled steel sheets containing 0.1-0.5% C, 0.5-1.5% Mn (SAE 1527, SAE 1022, etc.) to the desired width and then maintained at a temperature of 430-470 ° C. It is prepared by blueing in the lead bath (lead bath). In the bluing process, an oxide film having a desired color is formed to impart anti-corrosion properties required for roughing, and at the same time, appropriate strength and ductility required for roughing are obtained.

In this case, when the steel is a high carbon or high manganese steel with high carbon content or Mn content, such as SAE 1527, an austempering heat treatment before bluing can further improve the strength and elongation. However, in this case, the installation of expensive induction heating furnace for ostempering treatment is required, and as a result, the price of the product rises significantly, and thus there is a problem in that the demand for the coil coil acts as a cost burden.

In addition to the above problems, when the steel grade contains high carbon and high Mn, such as SAE 1527 steel, it is difficult to apply a high productivity tandem cold rolling mill during cold rolling, and thus, a reversible cold rolling mill has to be applied. This is because the butchering point should be used for continuous operation in the sanserin which passes to remove the scale formed on the surface during hot rolling. If the carbon and Mn content are high, the welding property is deteriorated and welding is difficult.

Therefore, when manufacturing high carbon and high Mn steel such as SAE 1527 steel for binding the coil, it is essential to install expensive equipment such as pickling lines, reversible cold rolling mills and induction furnaces.

In addition, in case of steel grade such as SAE 1022 steel, which is not high carbon and high Mn steel such as SAE 1527 steel, cold rolled steel sheet is directly blued without undergoing an ostampering process to produce coil binding steel. Is 6-8% and there is a limit to the increase.

Accordingly, the present inventors conducted the research and experiment to solve the above problems to produce a high toughness coil binding steel with a tensile strength of 90kgf / ㎜ or more, elongation of 9.0% or more, based on the results, to propose the present invention It is an object of the present invention to provide a method for manufacturing a high toughness coil binding steel having a tensile strength of 90 kgf / mm 2 or more and an elongation of 9.0% or more by appropriately controlling the composition of steel and the conditions of the manufacturing process.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, by weight, C: 0.05-0.13%, Mn: 0.5-1.5%, Ni: 0.1-0.3%, Si: 0.03% or less, P: 0.02% or less, S: 0.02% or less, Soluble The present invention relates to a high toughness coil binding composition composed of Al: 0.02-0.08%, N: 0.006% or less, Ti: 0.12-0.18%, remaining: Fe, and inevitably contained impurities.

In the present invention, C: 0.05-0.13%, Mn: 0.5-1.5%, Ni: 0.1-0.3%, Si: 0.03% or less, P: 0.02% or less by weight% (hereinafter referred to simply as '%'), S: 0.02% or less, Soluble Al: 0.02-0.08%, N: 0.006% or less, Ti: 0.12-0.18%, remainder: A sleeve of steel composed of Fe and an unavoidable impurity in the temperature range of 1200-1250 ° C. After homogenization, finish hot rolling in the temperature range of 900-950 ° C above the Ar ₃ temperature, winding in the temperature range of 550-650 ° C, and cold rolling to the final thickness at a rolling reduction of 45-65%, 540-600 The present invention relates to a method for producing a high toughness coil binding steel by recovering annealing in an ordinary annealing furnace in a temperature range of ℃ and bluing in a temperature range of 430-470 ℃.

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

In order to manufacture the above-mentioned object of the present invention, that is, a coil binding steel having a tensile strength of 90 kgf / mm 2 or more and an elongation of 9.0% or more, it is preferable to first prepare the steel as described above, for the following reasons.

Since the present invention steel contains a large amount of Mn in addition to carbon, when the carbon content is 0.13% or more, the weldability deteriorates and welding in pickling lines becomes difficult, and there is a fear of breakage during continuous cold rolling, and the carbon content If it is less than 0.05%, the strength is insufficient, so the carbon content is limited to 0.05-0.13%.

Manganese is added to the steel to make the structure of the hot rolled sheet into a mixed structure of ferrite and perlite. At this time, it is added to 0.5% or more because it is dissolved in cementite constituting the layer of perlite to harden the material. When added, the reinforcing effect is slowed down and the ductility is deteriorated, and also, it is difficult to apply to pickling lines and continuous cold rolling mill due to deterioration of weldability.

Ni is added in the steel to make the distribution of precipitates finer, which makes the grains finer. Therefore, it is preferable to add Ni more than 0.1%, but adding more than 0.3% delays the blueing recovery process, so that effective soft recovery during the blueing process is achieved. Not only is it difficult, but it also raises the price.

Phosphorus is the substitution type alloy element with the largest hardening effect, so adding more than 0.02% will harden the steel and worsen the ductility after bluing treatment. In addition, silicon is limited to less than 0.03% because it serves to deteriorate the weldability and surface properties. On the other hand, since sulfur acts as a factor to inhibit the toughness of the steel to form a sulfide-based inclusions it is preferably limited to 0.02% or less.

Aluminum is added for the purpose of deoxidation of steel, but when it is less than 0.02%, the deoxidation effect is small and when excessively added to more than 0.08%, it becomes a factor of material hardening.

When nitrogen is added at least 0.006%, the tensile strength after bluing is increased or the ductility is deteriorated due to the increase in the amount of AIN or the amount of solid solution nitrogen. Therefore, the upper limit is preferably limited to 0.006%.

On the other hand, Ti plays a role of widening the temperature at which recovery annealing is performed in the recovery annealing process for cold annealing and increasing the strength by forming fine precipitates such as TiC on the hot rolled plate. It is preferable to add more than that. However, when Ti is added in an amount of 0.18% or more, excessive Ti-based oxides are formed and workability deterioration, such as clogging of nozzles, occurs in the steelmaking-casting process.

In the present invention, after the steel is formed as described above, the slab that is continuously cast after melting using a converter is heated in the range of 1200-1250 ° C., which is a temperature where the austenitic structure before hot rolling can be sufficiently homogenized, and is directly above the Ar ₃ temperature. It is preferable to finish the hot rolling in the temperature range of 900-950 ° C, which is as follows.

When the hot rolling finish temperature is below 900 ℃, the top, tail and edges of the hot rolled coil become less than Ar ₃ , which causes non-uniformity of material. This is because the combination of strength and ductility after bluing is spoiled.

Hot-rolled steel sheet is preferably wound in the temperature range of 550-650 ℃, because the reason is that when the coiling temperature is 650 ℃ or more, the grains of the hot rolled sheet is coarse to damage the combination of strength and ductility after bluing The lower the winding temperature of the plate is, the better, but if it becomes too low below 550 ° C, the hit ratio of the hot rolled winding temperature is lowered, which is a factor of material variation.

The hot rolled plate subjected to pickling after winding is preferably cold rolled in a continuous cold rolling mill having good productivity by applying a cold reduction rate of 45-65%. Of course, cold rolling is also possible to apply a reversible rolling mill. In this case, the cold reduction rate is applied according to the thickness of the desired product, but the lower the cold reduction rate, the better the ductility after blueing. However, if the cold reduction rate is too low below 45%, not only the thickness of the hot rolled sheet should be lowered, but also the heat recovery temperature of the tissue is increased and the bluing temperature is moved to the high temperature to increase the heat energy required for bluing, as well as the color of the oxide film. It will also cause deterioration. On the other hand, if the cold reduction rate is 65% or more, the rolling load is caused during cold rolling, and since the ductility deteriorates after bluing, the cold reduction rate is preferably limited to the range of 45-65%.

The cold rolled steel sheet is preferably annealed in a temperature range of 430-470 ° C after recovery and annealing in an ordinary annealing furnace in a temperature range of 540-600 ° C, for the following reasons.

The purpose of the annealing is to recover the necessary ductility by restoring the tissue from the cold rolled material to the state of recovery tissue immediately before recrystallization. Therefore, if the recovery annealing temperature is too low below 540 ℃, recovery does not occur and the material in the cold rolled state remains. If the recovery annealing temperature is over 600 ℃, the recrystallization proceeds after recovery, the ductility increases but the strength decreases rapidly. Therefore, it is desirable to limit the recovery annealing temperature to 540 ° C-600 ° C. In this case, the continuous annealing may be used for recovery annealing instead of the annealing, but in this case, the annealing temperature may be lowered than the normal working temperature.

In general, the main purpose of the bluing process is to improve the ductility through the formation of blue oxide film and tissue recovery process to secure the rust resistance, but in the present invention, the former is mainly the purpose and the latter does not play a large role. This is because, in the case of the present invention, the ductility is sufficiently recovered in the recovery annealing process. In terms of oxide film formation to ensure rust resistance, the bluing temperature is in the range of 430-470 ° C.

When the steel is formed as described above and the manufacturing conditions are controlled to manufacture the steel coil binding steel, it is possible to manufacture the steel coil binding steel having a high tensile strength of 90 kgf / mm 2 and an elongation of 9.0% or more.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Steel was formed as shown in Table 1 below. In Table 1, if steel (1-3) is steel to which recovery annealing is applied before blueing treatment as invention steel, steel (4-15) is comparative steel (4-6) steel after recovery annealing Steels treated (7-15) correspond to steels directly blued without recovery annealing. Steel (4) is steel with Mn content lower than 0.5% and Ti is added 0.2% or more. (5) Steel is added with 0.5% Si and 0.2% Ti instead of reducing Mn content to 0.5% or less. It is the steel added above. In the (4-5) steel, all of Ni was not added. On the other hand, steel (6) is a steel with a small amount of Nb added to SAE 1022 equivalent steel (7-9), steel with a small amount of Ni in SAE 1022 steel, and steel (10-11) is an existing SAE 1022 steel. Corresponds to Steel (12-15) is a steel in which a small amount of Ti, V, Mo and Nb are added to SAE 1022 steel.

Tensile strength and elongation were measured in the state of bluing the steel formed as shown in Table 1 according to the manufacturing process as shown in Table 2 below, and the results are shown in Tables 2 and 1 below. Shown in

* SRT: Slab reheating temperature, FT: Hot rolled finishing temperature, CT: Winding temperature

As can be seen from Table 2 and Figure 1, the steel component is C: 0.05-0.13%, Mn: 0.5-1.5%, Ni: 0.1-0.3%, Si: 0.03% or less, P: 0.02% or less, S The temperature of Ar ₃ after homogenization treatment of (1-3) steels of (1-3) controlled to: 0.02% or less, soluble Al: 0.02-0.8%, N: 0.006% or less, Ti: 0.12-0.18% Finished hot rolling at above 910-930 ° C, wound at 600-630 ° C, cold rolled to final thickness at a reduction ratio of about 52-61%, and then recovered and annealed in an annealing furnace at 540-600 ° C to 450-460 ° C. Inventive material (a ~ i) bluing in the exhibits a very good material with a tensile strength of 90kgf / mm2 or more, elongation of 9.0% or more.

On the other hand, the steel component is high in the case of the inventive steel (1-3) satisfying the scope of the present invention or the comparative material (1, 2, 4, 5) whose recovery annealing temperature is out of the scope of the present invention or less than 540 ° C. Instead, the lack of recovery during the bluing process, the comparative materials (3,6) of more than 600 ℃ can be seen that the ductility is excellent while the decrease in strength is a significant problem.

Comparative steel (4-5), as shown in comparative steel (7,8), has a lower Mn content and no added Ni compared to invention steel (1-3), so ductility is less than 9% even when blueing after recovery annealing. It was only. The comparative steel (6) is a steel in which a small amount of Nb is added to SAE 1022 steel, and as shown in the comparative material (a), it is recovered and annealed in an annealing furnace after cold rolling, and has a tensile strength of 91-96kgf / mm2. And low elongation of 7.3-8.2%, the high elongation could not be obtained by applying recovery annealing. On the other hand, the comparative steel (7-9) grade steel with a small amount of Ni added to SAE 1022 steel showed excellent tensile strength of 93-99kgf / mm2 while the elongation was less than 9.0%, as shown by the comparative material (10-18). Indicated. Although the comparative steels (7-9) were steels not subjected to recovery annealing, the comparatively excellent ductility close to 9.0% was considered to be an effect of Ni contained in the main steel. On the other hand, in the case of comparative steel (10-11) that does not contain Ni, tensile strength and elongation are 86-95kgf / mm2 and elongation 7.0-7.5% as can be seen in the comparative materials (19, 10). It was less than 9.0%.

On the other hand, if the comparative steel (12-15) steels prepared under similar conditions were added to the SAE 1022 steel with a small amount of Ti, V, Mo, and Nb added instead of Ni, the blue material was found in the comparative material (21-24). As shown, the tensile strength was over 90kgf / mm2 regardless of the steel grade, but the elongation was 4.2-6.2%, showing very small ductility. These results are due to insufficient recovery of tissues because Ti, V, Mo, and Nb are all elements that delay the recovery of tissues during the bluing process by the precipitate or the solute drag effect.

As described above, the present invention can manufacture a high toughness coil binding steel having a tensile strength of 90 kgf / mm2 or more and an elongation of 9.0% or more by appropriately controlling the composition of steel and general manufacturing conditions, especially recovery annealing temperature and bluing temperature. It works.

In addition, the present invention is not high in the content of added elements such as carbon, Mn can be welded in the pickling line of the existing integrated steel mill, it is possible to use a high productivity continuous cold rolling mill, and the existing SAE 1527 steel for coil binding When used as a rough steel, high toughness coil binding objects with a tensile strength of 90kgf / mm2 and elongation of 9.0% or more can be manufactured using only bluing equipment without the need of pickling equipment, heated cold rolling equipment, and induction heating furnace. It has an effect.

Claims (2)

By weight%, C: 0.05-0.13%, Mn: 0.5-1.5%, Ni: 0.1-0.3%, Si: 0.03% or less, P: 0.02% or less, S: 0.02% or less, Soluble Al: 0.02-0.8% , N: 0.006% or less, Ti: 0.12-0.18%, remainder: Fe roughness for binding a high toughness coil composed of Fe and inevitable impurities. By weight%, C: 0.05-0.13%, Mn: 0.5-1.5%, Ni: 0.1-0.3%, Si: 0.03% or less, P: 0.02% or less, S: 0.02% or less, Soluble Al: 0.02-0.08% , N: 0.006% or less, Ti: 0.12-0.18%, remainder: after homogenizing the slab of steel composed of Fe and inevitably contained impurities in the temperature range of 1200-1250 ° C, 900-950 ° C above the Ar ₃ temperature Finished hot rolling in the temperature range of, rolled up in the temperature range of 550-650 ° C, cold-rolled to the final thickness at a rolling rate of 45-65%, and then recovered and annealed in an annealing furnace in the temperature range of 540-600 ° C. After 430-470 ℃ high toughness coil binding method characterized in that it comprises blueing in the temperature range.