KR100770949B1 - Thin steel sheet having high strength, for pressed-gas vessel and manufacturing process thereof - Google Patents

Abstract

A high strength thin steel sheet for a compressed gas container and a manufacturing method for the same are provided to improve yield, workability and stability of the thin steel sheet by providing the thin steel sheet having a stable quality. A manufacturing method for a high strength thin steel sheet for a compressed gas container includes the steps of performing a first cool rolling for a body part, a dome part and a bottom part. The body part is made of Al-killed coil including 0.04~0.06% of carbon and 0.2~0.3% of manganese. The dome part and bottom part are made of the Al-killed coil including 0.06~0.08% of the carbon and 0.3~0.4% of manganese, performing a continuous or batch annealing for a cool-rolled steel sheet in a temperature above a re-crystallization temperature, and performing a second cool rolling in a proper rolling rate for obtaining target yield strength.

Description

Steel plate for high strength pressure gas container and its manufacturing method {Thin steel sheet having high strength, for pressed-gas vessel and manufacturing process}

1 is an explanatory view showing an embodiment of a container when manufacturing a container with a steel sheet for pressure gas container according to the present invention;

2 is a graph showing the theoretical correlation between the length, diameter and thickness of the first door vessel body and the buckling limit pressure

Figure 3 is a graph showing the correlation between the appropriate yield strength (YP) and the internal pressure of the dome member (Dome) and the bottom member (Bottom) in the present invention

4 is a graph showing the correlation between the appropriate yield strength (YP) and the secondary pressure reduction rate in the present invention;

Figure 5 is a micrograph for comparing the crystal structure of the cold rolled steel sheet of the present invention steel and comparative steel

The present invention relates to a steel sheet for high-strength pressure gas container and a method of manufacturing the same.

The present invention is a high-strength ultra-thin tin excellent in workability and internal and external pressure resistance, which is used in a gas container having a deformation resistance of 13kg / cm ² or more and a bursting pressure of 15kg / cm ² or more consisting of three parts, a body part, a dome member and a bottom member. It relates to a method for producing a plated disc.

In particular, the present invention relates to a method for manufacturing a high strength ultra-thin tin plated disc having a thinner thickness and a high strength and sufficient processability in a tin plated steel sheet used as a portable butane gas container material as shown in FIG. 1. will be.

In general, pressure vessels or pressure vessels, such as portable butane containers, are generally divided into three parts: a body, a dome, and a bottom, and have sufficient internal and external pressures for the safe use of consumers. Sex is required. Therefore, tin-plated steel sheets used in pressure vessels have been required to have sufficient strength and thickness. Usually, 0.15 ~ 0.3mm thickness and T3CA (57 ± 3, HR30T) were applied to the body of the gas container, and 0.3 ~ 0.4mm thickness, 0.25 ~ 0.35mm, and quality were applied to the dome and bottom of the container, respectively. T3BA (57 ± 3, HR30T) and T4CA (60 ± 3, HR30T) have been used. Recently, gas container manufacturers are demanding the productivity of manufacturing more containers with the same weight of material for cost reduction, and for this purpose, the thickness reduction of materials is required.

However, when the thickness of the material is adjusted downward, the external pressure that the material withstands falls as shown in FIG. 2, and thus a material of a stronger material is required as the thickness is lowered. For reference, Figure 2 is a theoretical calculation of the buckling limit pressure of a cylindrical vessel of thickness t subjected to external pressure. The external pressure in Figure 2 means the vacuum pressure before filling the gas into the container. As can be seen in Figure 2, for example, if the thickness of the conventional 0.20mm was changed to 0.18mm, the material of the existing roughness (T4CA) buckling the container body portion does not withstand the external pressure (typically 0.8 bar vacuum pressure) This happens, in which case YP should be applied to the material with at least 500MPa. In addition, in the internal pressure, the strength and thickness of the dome part and the bottom part supporting most of the pressure in the container have a large influence. As the strength of the material increases as shown in FIG. 3, the limit pressure withstanding the internal pressure increases.

However, if only the strength of the material is adjusted upward, the elongation of the material decreases, so that the workability of the dome and the bottom part which is press-molded decreases, and the flanging formability that bends the end of each part to fasten the body part, the bottom part and the dome part. Problems such as deterioration may occur. Properties of the steel sheet, such as strength and elongation, are greatly influenced by the annealing conditions and the reduction ratios. Thus, in order to control the strength and workability of the material, the steel composition, the annealing conditions, and the reduction conditions are controlled.

Usually, the reinforcing method of the steel sheet includes solid solution strengthening, grain refinement, precipitation strengthening, work hardening and the like. For example, a conventional butane gas container material has been applied with a strengthening method such as solid solution strengthening and precipitation strengthening, and the more C and Mn elements in the steel, the greater the strengthening effect. However, the amount of reinforcing elements such as C, Mn, etc. in steel is limited in the amount of addition in consideration of workability. Therefore, it is difficult to secure sufficient strength (YP 50 MPa or more, DR8CA) and workability as the thickness of steel sheet is lowered. Hard.

Accordingly, the present invention, in order to produce a steel plate for high-pressure pressure gas vessels having a higher strength and sufficient workability even if the thickness is reduced as described above, the optimum C and Mn components, crack temperature optimization of continuous annealing and phase annealing In addition to solid solution hardening and aging hardening, the work hardening effect is applied by applying the appropriate pressure reduction in the second stage, so that the strength is increased so that the hardness of the body member is as high as 76 ± 3 HR30T, elongation 1 ~ 2%, in the case of the dome and the bottom member It maintains the hardness of 70 ± 3 HR30T and elongation more than 10 ~ 20% and derives the pressure resistance of the applied gas container by deriving the proper pressure reduction rate in the first and second cold rolling to measure the target yield strength (YP). Steel plate for ultra-high strength high pressure gas container with excellent processability and internal and external pressure resistance to improve the gas container safety by securing more than 13kg / cm ² strain pressure and 15kg / cm ² burst pressure. Its purpose is to provide a method of action.

More specifically, the present invention will be applied separately by separating the body portion and the dome portion and the bottom portion of the pressure gas container, and C: 0.03 to 0.10% by weight of the body (body) (the following chemical components are all by weight) , Mn: 0.15 ~ 0.50%, Al: killed hot rolled coil added with C: 0.04 ~ 0.12%, Mn: 0.25 ~ 0.60% as the material of the dome part and bottom part (for example, the body part) : Cold rolled to 88 ~ 90%, dome and bottom part: 82 ~ 84%), continuous annealing (eg body part, 660 ~ 700 ℃) or normal annealing (eg dome part and bottom part, 550 ~) 570 ° C.), followed by secondary rolling, for example, a body part: 20 to 35%, a dome part and a bottom part: 12 to 25% rolling pressure, and a steel sheet for manufacturing a high-pressure gas resistant vessel having excellent internal pressure resistance and workability. Get

The reason for limiting the chemical composition range in the present invention is as follows. In general, the hardness of the tin-plated disc can be secured only when C: 0.03% or more is added, and increases as C increases. This is because C is dissolved in Fe to induce solid solution, or precipitation strengthening and grain fineness and effects due to carbide precipitation. For this reason, in the present invention, cold rolling should be performed under high pressure in order to manufacture ultrathin high strength tin plate discs having a high pressure resistance as an example, so that the content of carbon cannot be too high to exceed the upper limit.

Therefore, the lower limit of the amount of carbon that secures the target strength of the body portion (76 ± 3 HR30T, elongation 1 ~ 2%), the dome and the bottom portion (70 ± 3 HR30T, elongation 10 ~ 20%) is 0.03% ( Body), 0.04% (dome, bottom) and the upper limit of carbon amount (C) was set to 0.10% (body) and 0.12% (dome, bottom), respectively, in order to secure the target processability. In the case of aluminum-killed steel, there are Mn components in addition to the C component, which affects the strength. The upper and lower limits of the Mn component are 0.15, respectively, to secure the strength of the steel and the upper limit of the Al-killed steel to ensure the processability. It set in the range of -0.50% (body part) and 0.25-0.60% (dome part, bottom part). In particular, the range is C: 0.04 to 0.06% (body), 0.06 to 0.08% (dome and bottom), Mn: 0.20 to 0.30% (body), 0.30 to 0.40% (dome and bottom). It is preferable to set it for more reliable physical properties.

It was found that it is most ideal that the hot rolled steel sheet satisfying the above-described component range is firstly cold rolled to a predetermined thickness in the range of cold reduction ratio of 88 to 90% (body part) and 82 to 84% (dome part, bottom part). The reason is that when the set range is lower than the set cold reduction rate, it causes a problem of strength reduction, and when it is above the set range, it is difficult to secure the flowability of the cold rolling mill as the reduction force and tension increase as the reduction rate increases.

The steel sheet rolled as described above is continuously annealed or phase annealed at a temperature above the recrystallization temperature and the usual annealing temperature. The body member has a continuous annealing type in order to minimize the material deviation which greatly affects the weldability in the steel making process. The relatively soft annealing type is applied to secure processability. In the present invention, the annealing temperature range of 660 ~ 700 ℃ for continuous annealing (body member), 550 ~ 570 ℃ for annealing (dome, bottom), and the appropriate rolling rate of the produced annealing steel sheet (body: 28 ~ 31%, dome and bottom part: 14 ~ 18%) to the secondary rolling to produce a ultra-thin tin plated disc with high strength and workability through the work hardening.

Continuous annealing or annealing at a temperature above the recrystallization temperature may lead to the recovery or recrystallization of the steel crystal structure to change small crystals into large crystals, to diffuse and homogenize component elements without strain, and to generate cracks during hot working. This is to prevent segregation.

The steel plate manufactured in this way has hardness 76 ± 3 HR30T, yield strength, elongation 1 ~ 2% in case of body member, hardness 70 ± 3 HR30T, yield strength, elongation 10 ~ 15% in dome and bottom member. at the same time and in the vacuum pressure at the time of gas charging hwakbodoem 0.8bar withstand an external force, to ensure the deformation of the pressure gas container 13kg / cm ^2, at least within the burst pressure 15kg / cm ^2, so excellent in safety of use of the vessel butane gases Suitable for pressure gas vessels.

Figure 1 shows the structure of a portable butane gas container as an embodiment of the present invention in three basic parts of the dome, the body, and the bottom. In the internal vacuum state before gas filling, the body part receives external pressure, and when used after gas filling, the dome part and the bottom part receive internal pressure.

2 is a graph for calculating the appropriate strength and thickness of the body member in the internal vacuum state before gas filling with reference to FIG. Since the relationship between the length (L) and the thickness (t) diameter (D) of a thin cylindrical tube such as a butane gas container is related to the critical buckling limit pressure of the container, the length L of the butane gas container is generally 150 mm and the diameter D Is made of 34.13mm and the material thickness is often 0.15 ~ 0.23mm, in which case the formula i) is used. In the graph, the appropriate thickness and strength of the body part were determined according to the vacuum pressure condition (typically 0.8 bar) according to the following i) formula, and applied to the material design of the present invention steel.

The research results are calculated using the following formula. That is, in a thin cylindrical tube such as a butane gas container, the relation between the length L, the diameter D, and the thickness t of the container body and the buckling limit pressure Pcr is as follows.

From the above formula, the buckling limit pressure (Pcr) for each thickness of the container is expressed as yield strength (YP), and the thickness of the pressure resistant container disc is calculated according to the relationship between the buckling limit pressure and the length, radius, and thickness of the container. An example is shown in FIG. FIG. 2 shows that the present invention material withstands a thinner material than the conventional one in the buckling area and does not buckle even at a stronger yield strength.

3 is a graph showing the results of the deformation and burst pressure changes according to the strength of the dome and the bottom material, and the strain pressure of 13 kg / cm ² or more and the burst pressure of 15 kg / cm ² or more, respectively, as industry standards. In order to ensure stable, the yield strength (YP) of the steel sheet is a graph indicating that more than 450MPa (45kgf / mm ² ).

FIG. 4 is a graph obtained through simulations of the correlation between the reduction ratio of the secondary rolling and the yield strength. FIG. 4 shows the conditions of secondary reduction ratio in the laboratory for the steel sheet annealed under the condition of Table 3 of the steel components of the present invention. Yield strength obtained by changing is shown. In other words, it refers to the cold rolling reduction condition for obtaining the target yield strength (YP). To obtain a predetermined strength, yield strength is defined by using the dome part and the bottom part 47-50kg / mm ² and the body part 58- by using FIG. This is to derive the corresponding appropriate secondary reduction ratio when obtaining 60 kg / mm ² . Accordingly, it can be derived that the proper reduction ratio is 28 to 31% for the body part and 14 to 18% for the dome part and the bottom part, respectively.

Figure 5 compares the microscopic structure of the tin-plated disc prepared by the present invention (steel of the present invention) and the conventional tin-plated disc (comparative steel). As can be seen from this photograph, it can be seen that the structure of the product produced by the present invention has a more stable and uniform crystal structure than that of the conventional one.

Example

As shown in Fig. 1, the high strength ultra-thin tin-plated disc for portable butane gas container, which consists of three parts, a dome part, a body part, and a bottom part, has a high strength and sufficient strength while lowering the thickness of the technical task, namely, the material to be achieved. In order to manufacture a high strength ultrathin tin plated disc having workability, tin plated discs were manufactured through primary cold rolling, annealing, secondary cold rolling, heat treatment, and the like. The annealing conditions were applied under the conditions shown in Table 3 in the continuous annealing line to obtain relatively uniform properties of the material of the body of the container to prevent welding defects due to material deviation. This particularly required material of the bottom and upper dome portions of the vessel is relatively easy to obtain workability. A heat treatment was performed at based line.

After the heat treatment, in order to have a thin thickness and a strong strength, a second pressing was performed to prepare a predetermined tin plated disc.

As described above, the high-strength ultra-thin tin-plated disc for manufacturing a portable butane gas container is manufactured by dividing the disc for the container body part, the disc for the container dome part, and the disc for the container bottom part, respectively. In addition, in order to contrast with the ultra-thin tin plated disc of the present invention, the conventional disc is used as a comparative steel, and the body part, the dome part, and the bottom part are respectively distinguished as "la", "hem" and "bar", and their chemical composition is measured. Annealing was performed under the same conditions as in Table 3.

As described above, the invention steels "A", "I", and "C" of the steels shown in Table 1 satisfy the composition of the present invention, and the comparative steels "D", "H", and "Bar" are conventionally used steel grades. . Comparative steels, unlike the invention steel, are steels produced by only temper rolling after annealing. In the present invention, "me," "many" shows the chemical composition of the dome (bottom) and bottom (bottom).

Figure 1 shows the structure of a portable butane gas container, which is the object of the present invention, which is composed of three basic parts: a body, a dome, and a bottom. In the internal vacuum state before gas filling, the body part receives external pressure, and when used after gas filling, the dome part and the bottom part receive internal pressure.

2 is a graph for calculating the appropriate strength and thickness of the body member in the internal vacuum state before gas filling with reference to FIG. Generally, the length L of the butane gas container is 150 mm and the diameter D is 34.13 mm, and when the material thickness is 0.15-0.23 mm, the formula i) is used. In the graph, the proper thickness and strength of the body were obtained according to the formula of i) according to the vacuum pressure condition (typically 0.8 bar) and applied to the material design of the present invention steel.

3 is a graph showing the results of the deformation and rupture pressure change according to the strength of the dome and the bottom material, the yield strength of the steel sheet in order to secure the strain and burst pressure more than 13, 15kg / cm ² , respectively (YP) should be secured over 450MPa (45kgf / mm ² ).

Table 2 is an example comparing the physical properties of the various types of steel sheets produced by the company to obtain the strength of the material derived from Figures 2 and 3. First, when the thickness of the body portion is 0.18mm, the yield strength (YP) of the steel sheet is 500MPa (50kgf / mm ² ) or more to ensure the buckling stability of the container, so select the "ga" and "ra" steel in Table 2 It is done. However, considering the error, the "la" steel is located at the buckling limit line, so the "a" steel is applied in consideration of stability. When the dome and the bottom part are manufactured to a thickness of 0.33 mm and 0.30 mm, respectively, steel plates having a strength of 450 MPa (45 kgf / mm ² ) or more must be secured.

Table 3 shows the production conditions for manufacturing the steel sheet of the material selected in Table 2. Annealing conditions of Table 3 were applied to the normal working conditions of steel grade "A", "B", "C" selected in Table 2. FIG. 4 is a graph obtained by simulating the correlation between the secondary reduction ratio and the strength, and obtained by changing the secondary reduction ratio conditions in a laboratory in which a steel sheet of the component used in the present invention is annealed under the conditions shown in Table 3. Yield strength is shown. In order to obtain a predetermined strength, the appropriate secondary reduction ratio was set to 30% (28 to 31%) for the body member and 16% (14 to 18%) for the dome and bottom members using FIG. 4.

Table 4 finally shows the physical properties of the tin-plated disc prepared by the present invention. The targeted strength of the body, dome and bottom members were obtained, respectively, and at the same time, a minimum elongation for processing was secured.

Table 5 shows the inspection results of the butane gas container to which the steel of the present invention is applied, and shows suitable results in all standards including the internal and external pressure resistance, and the pressure resistance is improved compared to the conventional steel, so that the deformation resistance is 14.9 kg / cm ² and the bursting pressure. Showed 18.9 kg / cm ² . Here, a deformation pressure and burst pressure within the criterion of 13kg / cm ² or more respective specifications of the Korea Gas Safety Corporation, 15kg / cm ² represents the pressure resistance, the yiraya the figure above.

In this embodiment, the cutting step, the welding process, each reference value seaming (seaming) got a good standard, etc. All the working process, in which the transformation overwhelmed average 14.94kg / cm ^2, the average burst pressure also 18.95kg / cm ² 13kg / cm ² It was found to be much better than 15 kg / mm ² .

According to the present invention, since it is possible to supply a steel plate of stable quality according to the high strength pressure gas container having excellent workability and pressure resistance, it is possible to reduce the manufacturing cost and to improve the stability, workability and error rate of the container. .

Claims (3)

In the manufacturing method of the steel plate for pressure gas container, the body part of the container and the dome part and the bottom part are separately applied, but the material of the body part (C) is 0.04 to 0.06%, Mn: 0.20 to 0.30%, the dome part Cold-rolled aluminum-killed hot rolled coil added with (dome) and bottom material (C: 0.06 ~ 0.08%, Mn: 0.30 ~ 0.40%) and continuously at temperatures above recrystallization temperature After annealing or annealing, secondary cold rolling is carried out at an appropriate reduction ratio to obtain a target yield strength. The vessel has a deformation resistance of 13 kg / cm ² or more, a burst pressure of 15 kg / cm ² , and a yield strength of YP 450 Mpa or more. High strength ultra-thin tin plated disc with excellent internal pressure resistance and processability In order to manufacture the tin-plated disc of claim 1, the cold rolling rate in the cold rolling to obtain the yield strength body portion 58 ~ 60kg / mm ² , dome portion bottom 47 ~ 50kg / mm ² is the primary cold rolling 88 ~ 90% (body part), 82 ~ 84% (dome part, bottom part) respectively, and the appropriate reduction ratio during the second cold rolling after annealing is 28 ~ 31% for the body part, 14 for each of the dome part and the bottom part. Manufacturing Method of High Strength Ultrathin Tin Plated Disc of ~ 18% The method of claim 1, The thickness (t) of the pressure resistant container is derived from the correlation between the buckling limit pressure (Pcr) expressed by the yield strength (YP) and the length and radius of the container according to the following equation. Manufacturing method

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