KR100238012B1 - The manufacturing method for extruding container cold rolling steel sheet with excellent weldability and formative - Google Patents

Abstract

The present invention relates to a method for manufacturing a cold rolled steel sheet for expansion vessels having excellent weldability and formability, wherein cracks do not occur in the welded portion after expansion of the steel pipe as a material for expansion vessel processing, and the carbon ratio is 0.005% or less. , Manganese: 0.1 to 0.4%, phosphorus: 0.03% or less, sulfur: 0.015%, aluminum: 0.06% or less, nitrogen: 0.004% or less, titanium: 0.03 to 0.05%, solid boron: 0.0005 to 0.0015% When “[Ti]-1.5 [S] ≥ 3.43” Boron (B): (0.77 ｛[N]-([Ti]-1.5 [S]) / 3.43) = 0.0005) ≤ [B] ≤ (0.77 ｛ [N]-([Ti]-1.5 [S]) / 3.43｝ = 0.0015), and the aluminum-kilted steel, which is composed of residual iron and inevitably contained impurities, is homogenized at a temperature range of 1200 to 1250 ° C. After that, finish rolling at 910 DEG C, wound at 600 to 750 DEG C, cold rolling at a reduction ratio of 80% or higher, and continuous annealing at 720 DEG C or higher Thereafter, a method for producing a cold rolled steel sheet for expansion vessel having excellent weldability and formability, which is produced by temper rolling, is provided.

Description

Manufacturing method of cold rolled steel sheet for expansion vessel having excellent weldability and formability

1 is an enlarged micrograph of a welded portion of a comparative steel.

2 is an enlarged photomicrograph of a welded portion of the inventive steel according to the present invention.

The present invention relates to a zero method of a cold rolled steel sheet for expansion vessels having excellent weldability and formability, and in particular, cracks do not occur in the welded portion when expanding after pipe-welding as a material for a pail can. It is related with the manufacturing method of the cold rolled sheet steel for expansion container which is excellent in weldability and forming property.

In general, cans processed in a circle using a container material are subjected to secondary processing by a processing process called expanding. In the case of commonly used small beverage cans, they are rounded and then welded, but containers for storing edible oil, paint, and the like are expanded in the circumferential direction after welding to facilitate storage and transportation.

In this case, when a defect occurs in the welded part, cracks are generated in the welded part during expansion, and when the aging occurs, a stretcher strain occurs to deteriorate the appearance.

Therefore, the material for expansion vessel should have no aging and excellent weldability. To remove aging, there should be no stretcher strain by stabilizing carbon (C), nitrogen (N), and sulfur (S) as solid solution elements. To do this, it is necessary to create a uniform structure with no difference between the tissues in the heat affected zone (HAZ) and the base metal.

That is, when aging occurs, workability is poor due to poor formability, and when weldability is poor, cracks occur due to a decrease in strength due to coarse grains in the welded HAZ portion relative to the base material portion when expanding. For reference, FIG. 1, which is an enlarged micrograph of a comparative steel, is a structure photograph of a welded portion of a material in which cracks occur in a welded HAZ portion at the time of expansion, and the grain abnormal coarse grains of the welded HAZ portion are developed.

On the other hand, according to the known conventional technology, low carbon aluminum-kilted steel using batch annealing is a steel grade without aging phenomenon, and is applied as a material for expansion vessels, but annealing time is 2-3 days by applying batch annealing. Too long, there is a problem that the material is non-uniform, there is a concern that the crack occurs due to the coarse generation of the welding HAZ portion.

Accordingly, the present invention is to improve the defect of the formability due to aging in order to solve the above-mentioned conventional problems, the method of manufacturing cold rolled steel sheet for expansion vessel excellent in weldability and formability that can suppress the development of abnormal coarse grains of the weld HAZ portion To provide.

In order to achieve the above object, the present invention is a weight ratio of carbon (C): 0.005% or less, manganese (Mn): 0.1 to 0.4%, phosphorus (P): 0.03% or less, sulfur (S): 0.015%, aluminum (Sol-Al): 0.06% or less, nitrogen (N): 0.004% or less, titanium (Ti): 0.03 to 0.05%, solid solution boron (B): 0.0005 to 0.0015%, “[Ti]-1.5 μS] ≥ 3.43 ”Boron (B): (0.77 ｛[N]-([Ti]-1.5 [S]) / 3.43｝ = 0.0005) ≤ [B] ≤ (0.77 ｛[N]-([Ti] -1.5 [S]) / 3.43｝ = 0.0015) and provide Al-Killed steel which is composed of residual iron (Fe) and inevitably contained impurities.

After the homogenization treatment of the aluminum-kilted steel at a temperature range of 1200 to 1250 ° C, the final rolling is carried out at 910 ° C, followed by winding at a temperature of 600 to 750 ° C, and then cold rolled to a rolling reduction of 80%. After continuous annealing at 720 ° C. or higher, tempering rolling is performed to provide a production method.

The present invention will be described in detail below.

The present invention relates to a method for producing a cold rolled steel sheet for expansion vessel having excellent weldability and formability, the chemical composition of which is by weight ratio of carbon (C): 0.005% or less, manganese (Mn): 0.1 to 0.4%, phosphorus (P) : 0.03% or less, sulfur (S): 0.015%, aluminum (Sol-Al): 0.06% or less, nitrogen (N): 0.004% or less, titanium (Ti): 0.03-0.05%, solid boron (B): 0.0005 -0.0015%, “In case of [Ti]-1.5 ｛S] ≥ 3.43｝ Boron (B): (0.77 ｛[N]-([Ti]-1.5 [S]) / 3.43｝ = 0.0005) ≤ [B] ≤ (0.77 kPa [N]-([Ti]-1.5 [S]) /3.43 kPa = 0.0015) and it is composed of the balance iron (Fe) and inevitably contained impurities.

After homogenizing treatment of the steel composition as described above in the temperature range of 1200-1250 ° C, finish finishing rolling at 910 ° C and winding up at 600-750 ° C, then cold rolling at a reduction ratio of 80%, After continuous annealing at 720 ° C. or higher, it is produced by temper rolling.

Steel produced by the composition and production method as described above is characterized in that the excellent formability and weldability.

On the other hand, the reason for limiting the concentration of the chemical component in the present invention as described above is as follows.

First, when the content of carbon (C) is more than 0.004% by weight (hereinafter referred to as%), the yield strength is increased to cause a defect in forming, and also to increase the yield point after the final annealing due to the increase of solid solution carbon. It is preferable to limit the carbon content to 0.005% or less, since it causes a stretcher strain, and the lower the carbon content, the better.

When the content of manganese (Mn) is 0.4% or more, the material hardens or deteriorates formability due to solid solution strengthening of manganese, and when the content is 0.10% or less, sulfur (S), a hot brittle element, is not sufficiently fixed. Since it is impossible, it is preferable to limit it to 0.10 to 0.40%.

The phosphorus (P) is a substitutional alloy element having the largest solid solution hardening effect, and thus, when added in an amount of 0.03% or more, the material hardening and moldability deteriorate. Therefore, the content of phosphorous (P) is preferably limited to 0.03% or less.

The sulfur (S) is a fragile element that causes hot brittleness is better to manage the lower the range, and also to precipitate the manganese sulfide, so to reduce the manganese it is preferable to limit the content to 0.015% or less.

The aluminum (Al) is a component added for deoxidation of steel, and if the amount is 0.06% or more, it causes hardening of the material, and therefore the content is preferably limited to 0.06% or less.

Nitrogen (N) is an invasive element, which inhibits the [1,1,1] texture, impairs the processability, impairs particle growth, and manages the lower the better. It is preferable to limit to.

The titanium (Ti) precipitates solid solution elements (carbon, nitrogen, sulfur) with titanium carbide (TiC), titanium nitride (TiN), and titanium sulfide (TiS) to lower the yield strength and remove the yield point elongation. It plays a role in suppressing occurrence. In general, the yield strength after annealing and the stretcher strain generated during molding increase in proportion to the amount of solid solution present in the steel. Therefore, the addition of titanium in the present invention is to completely precipitate the solid solution element compared to the addition of niobium (Nb) to lower the yield strength and to remove the stretcher strain.

Therefore, if the content is less than 0.03%, it is not possible to effectively precipitate the solid solution element, and if it is more than 0.05%, it is preferable to limit the content range to 0.03 to 0.05%, since there is a possibility that a large amount of precipitates may cause the increase in strength. Do.

The boron (B) can be seen by adding 0.0005 ~ 0.0015% of boron in solid solution as a grain boundary strengthening element.

When the boron in solid solution is added at 0.0005% or less, the effect of grain boundary strengthening is insignificant, and when it is added at 0.0015% or more, it is desirable to limit the amount of boron in solid solution state to 0.0005 to 0.0015% because of poor processing properties such as El and r values. .

However, when boron is present as boron nitride (BN) as a precipitate, the grain boundary strengthening effect is ignored. In order for boron to segregate at the grain boundary and exhibit a strengthening effect, the grain boundary must be present in solid solution and diffused from the inside to the grain boundary. If it is precipitated with boron nitride (BN) before the transfer, the grain boundary strengthening effect cannot be obtained because it does not diffuse to the grain boundary. Therefore, the content of boron can be determined by the amount of titanium to fix nitrogen, and since titanium first reacts with sulfur at a high temperature, the amount of boron added is determined by the formula of titanium, nitrogen and sulfur as variables. Can be specified

That is, the relation between titanium, nitrogen, and sulfur is [Ti]-3.43 [N]-1.5 [S] = 0, assuming that there is a minimum amount to fix nitrogen and sulfur of titanium, so that [N] = ([Ti ] -1.5 [S]) / 3.43. Therefore, in order to combine boron and nitrogen at a ratio of 0.77 and to have solid boron present at 0.0005 to 0.0015%, the content of boron is as follows.

First, when “[Ti]-1.5 [S] ≥ 3.43 [N]”, the boron content should be 0.0005 to 0.0015%, and then when “[Ti]-1.5 [S] [3.43 [N]” , The content of boron is in the range of 0.77N [N]-([Ti]-1.5 [S] / 3.43｝ + 0.0005 ≤ B ≤ 0.77 ｛[N]-([Ti] -1.5 [S]) /3.43｝ + 0.0015 Should be managed within.

The slab made by continuously casting the steel produced as described above is homogenized at 1200 to 1250 ° C. so that the austenite structure is sufficiently homogenized before hot rolling. The reason for limiting the homogenization temperature as described above is that if the slab reheating temperature is lower than 1200 ° C, the steel does not become uniform austenite grains and is mixed, and when the temperature exceeds 1250 ° C, excessive scale layers are generated on the surface. Therefore, since the loss of the product is large, it is preferable to limit the temperature to 1200 to 1250 ° C.

After the homogenization treatment, the finish hot rolling is performed directly at the Ar ₃ temperature, that is, at 910 ° C. The reason why the finish hot rolling is performed at the above Ar ₃ temperature network is that if it is less than Ar ₃ (ferrite + pearlite), it is rolled in an abnormal structure, and thus abnormal coarse grains are generated, thereby causing defects in product processing. Becomes Therefore, it is preferable to limit the finishing hot rolling temperature to around 910 ° C which is greater than or equal to the Ar ₃ transformation point.

The hot rolled winding temperature is a problem occurs in the quality of the surface due to the generation of a large amount of scale (Scale) during high-temperature work, and the winding at low temperature may cause a large temperature deviation inside and outside the coil, causing a variation in the material in the coil 600 It is preferable to limit to -750 degreeC.

The cold reduction rate is preferably limited to 80% or more in order to secure high toughness.

When the continuous annealing temperature is annealed below the recrystallization completion temperature, a mixed structure is generated, so that material variation and cracks may occur during processing. desirable.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

To prepare a steel slab (Slab) by dissolving the ultra-low carbon aluminum-kilted steel in the converter so as to have a composition as shown in Table 1 below, after the furnace refining treatment. At this time, the inventive steels 1 to 3 and the comparative steels 4 to 9 shown in the following [Table 1] are all final components after out-of-furnace refining.

TABLE 1

(Where α = 0.77 0.7 [N]-([Ti]-1.5 [S]) / 3.43｝ + 0.0005, β = .77 ([N]-([Ti]-1.5 [S]) / 3.43｝ + 0.0015, γ = ｛Ti]-1.5 [S]-3.43 [N])

Inventive steel 1 has a component composition in which ｛[Ti]-1.5 [S]-3.43 [N] (hereinafter referred to as γ) is greater than or equal to "0", that is, γ ≥ 0, and the composition of boron is 5 to 15. (ppm) was added in the range, and the inventive steels 2 and 3 have a component composition in which γ is less than “0”, that is, γ <0, and the composition of boron is 0.77 ｛[N]-([Ti]-1.5 [S] ) / 3.43 kPa + 0.0005 (hereinafter referred to as α) to 0.77 kPa [N]-([Ti]-1.5 [S] / 3.43 kPa + 0.80015 (hereinafter referred to as β)).

In addition, Comparative steels 4 and 5 are steels without boron added, Comparative steel 6 is γ <0, boron is outside the range of α to β, and comparative steel 7 is steel with excess boron added. In addition, Comparative Steel 8 is a steel grade in which titanium is insufficient, Comparative Steel 9 is a steel grade in which r <0, boron is outside the α to β range, and titanium is insufficient.

The steel slab having the composition as described in [Table 1] is homogenized at a temperature of 1250 ° C., and then finish hot rolled to a thickness of 2.3 (mm) near 910 ° C., which is directly above Ar ₃ .

Then, it wound up at each hot-rolling winding temperature shown in following Table 2, and pickled by the normal method.

The pickled hot rolled steel sheet was subjected to continuous annealing after cold rolling to obtain a cold rolled steel sheet having a thickness of 0.35 (mm). On the other hand, Table 2 shows the mechanical properties of the inventive steel and the comparative steel and the workability of the expansion vessel.

TABLE 2

As shown in Tables 1 and 2, in the case of Comparative Steel 4, as the titanium-added steel without boron, aging did not occur due to sufficient titanium addition, and the foamability was good during processing of the container, but cracks occurred after welding.

In the case of Comparative Steel 5, the titanium-added steel without boron caused aging due to the undertreatment of titanium. Therefore, the forming property was poor during the processing of the container, and the weldability was also poor due to the occurrence of cracks.

In the case of Comparative Steel 6, the boron, titanium-added steel, or boron were γ <0 and were not added within the range of α to β, so that cracks occurred after welding, resulting in poor weldability.

In the case of the comparative steel 7, boron, titanium and steel or boron were not added within the range of 5 to 15 (ppm) under the condition of γ> 0, so that YP was high and El was decreased, resulting in poor formability.

In the case of Comparative Steel 8, the titanium was insufficiently added to formability due to aging, and in the case of boron, γ <0, but within the range of α-β, no cracks occurred after welding.

In the case of Comparative Steel 9, boring and titanium added steel or titanium were under-added due to aging, resulting in poor foaming. In the case of boron, γ <0, but not within the range of α ~ β. Generated and poor weldability.

However, in the case of invention steel 1, boron and titanium were added, and there was no aging due to the addition of sufficient titanium, so that the forming property was good during processing of the container. There was no crack after welding, and weldability was good.

In the case of invention steels 2 and 3 as well, boron and titanium were added, and there was no aging due to the addition of sufficient titanium. There was no crack after welding, and weldability was good.

When comparing the comparative steel and the invention steel through the attached micrograph, FIG. 1 is a microscopic photographic image of a weld zone microscope of Comparative Steel 4, showing that an abnormal coarse phenomenon occurs due to the growth of the tissue at the center of the heat affected zone. Cracks are generated at these heat affected sites.

FIG. 2 is a microscopic structure photograph of the welded portion of the inventive steel 2, and the structure of the heat affected area shown in the center of the photograph is almost the same and finer as compared with the surrounding base material. There was no crack in the site, and weldability was very good.

As described above, the present invention provides an effect of eliminating the defect in forming due to aging during processing of the container, and preventing the occurrence of cracks in the welded area after welding, thereby improving the weldability during expansion processing.

Claims (1)

By weight ratio, carbon (C): 0.005% or less, manganese (Mn): 0.1-0.4%, phosphorus (P): 0.03% or less, sulfur (S): 0.015%, aluminum (Sol-Al): 0.06% or less, Nitrogen (N): 0.004% or less, Titanium (Ti): 0.03-0.05%, Solid boron (B): 0.0005-0.0015%, When "[Ti]-1.5 ｛S] ≥ 3.43" Boron (B): ( 0.77 ｛[N)-([Ti] -1.5 [S]) / 3.43｝ = 0.0005) ≤ [B] ≤ (0.77 ｛[N]-([Ti]-1.5 [S]) / 3.43｝ = 0.0015) The aluminum-kilted steel, which was managed within the range and composed of the remaining iron (Fe) and inevitably contained impurities, was homogenized at a temperature range of 1200 to 1250 ° C, followed by finishing rolling at 910 ° C and at a temperature of 600 to 750 ° C. After winding, it is cold-rolled to 80% or more of reduction ratio, and after continuous annealing at 720 degreeC or more, and is produced by temper rolling, The manufacturing method of the cold rolled sheet steel for expansion pipe containers excellent in weldability and formability characterized by the above-mentioned.