KR20230157920A - High strength black plate and method for manufacturing of the same - Google Patents

Abstract

The present invention relates to a high-strength stone plate and a method of manufacturing the same.
One embodiment of the present invention is carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, silicon (Si): 0.05% by weight or less (0 weight%), based on 100% by weight of the total stone plate. % excluded), phosphorus (P): 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, nitrogen (N): 0.0005 to 0.004% by weight, chromium (Cr): 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, the balance Fe and other inevitable impurities, and providing a high-strength stone plate that satisfies the following relational equation 1. do.
[Relationship 1]
0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035
However, [Nb], [Cr], and [C] refer to the weight percent of each component.

Description

High-strength stone plate and manufacturing method thereof {HIGH STRENGTH BLACK PLATE AND METHOD FOR MANUFACTURING OF THE SAME}

One embodiment of the present invention relates to a high-strength stone plate and a method of manufacturing the same.

One embodiment of the present invention relates to a high-strength stone plate and a method of manufacturing the same.

BP (Blackplate), a steel material conventionally used as a material for cans, is mostly thin, so the material is graded according to the tempering degree indicated by Hr30T, the Rockwell surface hardness. there is. In order to make a can for storing contents using a stone plate, tin, etc. is plated on the surface of the stone plate (this is called a stone plate) to provide corrosion resistance, and then cut to a certain size and processed into a circular or square shape.

Methods for processing containers can be roughly divided into two methods: processing without welding, such as a two-piece can in which the container consists of two parts, a lid and a body, and a method in which the can consists of a body, an upper lid, and a lower lid. It is divided into a method of fastening the body by welding or joining, such as a 3-piece can made of 3 parts.

In addition, depending on the manufacturing process of the stone plate, there is a single-rolled stone plate (SR-BP, Single Reduced Blackplate) that undergoes cold rolling once in the cold rolling process and a double-rolled stone plate (DR-BP, which undergoes two cold rollings). It can also be classified as Double Reduced Blackplate.

Among can materials manufactured by the single rolling method, soft stone plates with a quality of T3 or lower are mainly used for applications that require processability, while hard stone plates with a quality of T4 to T6 are used for use in can bodies, lids, etc., due to their nature of use. It is preferentially used in areas that require the ability to withstand the internal pressure caused by the contents rather than processability.

Secondary rolled steel sheet refers to a steel sheet in which the strength of the material is increased by applying secondary cold rolling at a relatively high reduction rate to the material that has been cold rolled (primary) and heat treated in the cold rolling process. Secondary rolled stone plate, a representative example of secondary rolled steel plate, is an ultra-thin material and is classified into grades according to the yield strength of the material due to the nature of the application that requires pressure resistance characteristics, etc. Typically, ultra-thin, high-strength stone plates are manufactured using this secondary rolling stone plate manufacturing method, so the yield strength increases due to work hardening, but as a reaction, ductility decreases sharply, making it necessary to use neck-in for fastening the end of the can. in) There was a problem that processability was deteriorated.

In addition, when manufacturing secondary rolled stone plates and continuous annealing using medium or low carbon steel as the original plate, a tin-melting step is required to alloy the tin layer to ensure surface gloss during the plating process. In the canning process, strain aging occurs due to elements dissolved in the steel during the baking step of heat treatment at around 200°C for several tens of minutes to dry organic substances such as surface lacquer. This aging phenomenon not only reduces the ductility of the secondary rolled stone plate, but also causes fluting, in which the material is bent into a square shape during the can processing stage, or stretcher-strain, in which stripe-shaped defects appear on the surface of the steel plate. As it acts as a factor causing processing defects such as stretcher strain, its application to applications requiring great processing properties has been limited.

In order to suppress the occurrence of deformation aging of secondary rolled stone plate by tin-melting or baking, a process of top-annealing the plate has been proposed. However, in the case of top-annealed material, the time required for annealing is as long as 3 to 4 days, resulting in low productivity. Not only is the material used in the width and length directions of the product non-uniform, but there are also many surface defects, which has a fundamental problem of poor workability.

In order to solve various problems of secondary rolled stone plates, plans to manufacture high-strength stone plates through continuous annealing, which has excellent productivity and excellent material uniformity, flatness, and surface characteristics, are being actively considered.

High-strength stone plates that currently require machinability are mainly produced by top annealing, and then apply a relatively high reduction rate in the secondary rolling stage to secure the target quality and ultra-low carbon steel. A method has been proposed to secure processability by suppressing aging by adding carbonitride forming elements such as Ti or Nb. However, these materials also have process problems that not only deteriorate operability but also increase production costs as additional rolling processes are required due to the use of soft stone plates as secondary rolling materials, so they are not suitable for efficient processing. It was difficult to regard it as a manufacturing method for high-strength stone plates.

In other words, the secondary rolled stone plate, which secures high strength characteristics through work hardening, is manufactured by going through the process of hot rolling, primary cold rolling, annealing, and secondary cold rolling of the tapped material, making it a normal primary rolling process. As additional rolling is required in the heat treatment process compared to the process of producing the final product, such as stone plate, manufacturing costs increase and neck-in processability deteriorates, so countermeasures are being actively considered.

In the case of pressure-resistant pipes applied to such applications, it is necessary to manage the hole expansion rate, including yield strength and elongation, as the stability of the can by securing pressure resistance characteristics, neck-in processability, and weight reduction are simultaneously pursued. Reflecting the characteristics of the application, a multifaceted review is underway on ways to secure a yield strength of 580 to 670 MPa, a total elongation of 5% or more, and a hole expansion rate of 10% or more.

For example, Japanese Patent Publication No. 1997-104919 describes a method for manufacturing container steel plates with excellent deep drawing properties, by adding Nb, Ti, etc. to an ultra-low carbon steel base to create a soft material with excellent processability and aging properties. A method of manufacturing a original plate is disclosed. In addition, a method of manufacturing secondary rolled stone plates with excellent workability was proposed by using these steel sheets to perform primary rolling of 80 to 98% and secondary reduction of 30% or less after recrystallization heat treatment. However, in this case, in order to secure processability, special elements such as Nb are added and recrystallized annealed, so the annealing temperature is fundamentally higher than that of commonly produced low-carbon or medium-low carbon-based materials, so as to secure the annealing temperature when combining work with general materials. Not only does it have to be used, but there is a problem of fundamentally deteriorating the passability of ultra-thin materials due to high-temperature annealing. Additionally, in order to achieve high strength, an additional secondary rolling process is required, which is a factor in increasing the cost.

As another example, Japanese Patent Laid-Open No. 1999-189841 describes manufacturing a high-strength ultra-thin material by secondary rolling at a reduction ratio of 5 to 30% in steel containing 0.01 to 0.03% of C, 0.02 to 0.15% of Al, and 0.0035% or less of N. A method has been disclosed, but even in this case, it was difficult to secure the target processability due to the low elongation, and the strength characteristics were also secured through the secondary rolling process.

In addition, Japanese Patent Publication Hei 8-269568 discloses that steel to which rare earth elements are added is finished at a hot rolling temperature of Ar ₃ transformation point or lower, cold rolling is performed at a reduction ratio of 85% or lower, and heat treatment is performed at a temperature of 200 to 500 ° C. for more than 10 minutes. By doing so, a method of manufacturing a steel plate with a yield strength of 640 MPa or more is disclosed. However, although it is said that cold-rolled sheets are annealed at 200 to 500°C to recover the deformation, in order to heat-treat them in a heat treatment furnace for more than 10 minutes, they must be rolled at a very slow line speed that is not commercially applicable, which significantly reduces productivity and also increases the operating temperature. Because it is too low, there is a problem with compatibility with general work materials, making practical application difficult.

The purpose is to provide a high-strength stone plate and a manufacturing method thereof.

The high-strength stone plate, which is an embodiment of the present invention, contains carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, and silicon (Si): 0.05% by weight, based on 100% by weight of the total stone plate. or less (excluding 0% by weight), phosphorus (P): 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, nitrogen ( N): 0.0005 to 0.004% by weight, chromium (Cr): 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, the balance Fe and other unavoidable impurities, and satisfying the equation 1 below. Stone plates can also be provided.

[Relationship 1]

0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035

However, [Nb], [Cr], and [C] refer to the weight percent of each component.

With respect to the total microstructure of the stone plate, the fraction of strained ferrite may be 96 area% or more. The yield strength of the stone disk may be 580 to 670 MPa, and the elongation of the stone disk may be 5% or more. In addition, the hole expansion rate of the stone plate may be 10% or more.

A method of manufacturing a high-strength stone plate, which is another embodiment of the present invention, includes carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, and silicon (Si): 0.05%, based on the total 100% by weight. Weight% or less (excluding 0% by weight), phosphorus (P): 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, Preparing a slab containing nitrogen (N): 0.0005 to 0.004% by weight, chromium (Cr): 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, the balance Fe and other inevitable impurities; Manufacturing a hot-rolled sheet by hot-rolling the slab; Finish rolling the hot rolled sheet; manufacturing a coil by winding the finish rolled sheet; manufacturing a cold-rolled sheet by cold-rolling the coil; and continuously annealing the cold-rolled plate to obtain a final stone plate.

At this time, the slab may satisfy the following relational expression 1.

[Relationship 1]

0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035

However, [Nb], [Cr], and [C] refer to the weight percent of each component.

The step of finishing rolling the hot rolled sheet may be performed at a temperature range of 880 to 950°C.

The step of manufacturing a coil by winding the finish rolled sheet may be performed at a temperature range of 550 to 650°C.

manufacturing a coil by winding the finish rolled sheet; Afterwards, the step of pickling the coil may be further included.

In the step of manufacturing a cold-rolled sheet by cold rolling the coil, the cold rolling reduction rate may be 80 to 94%.

The step of continuously annealing the cold-rolled plate to obtain a final stone plate may be continuously annealed at a temperature range of 640 to 700°C.

With respect to 100 percent area percent of the total microstructure of the stone plate manufactured by the above step, the fraction of deformed ferrite may be 96 area percent or more. Additionally, the yield strength of the stone plate may be 580 to 670 MPa. In addition, the elongation of the stone plate may be 5% or more. The hole expansion rate of the stone plate may be 10% or more.

According to one embodiment of the present invention, it is possible to provide a stone plate in which niobium (Nb), chromium (Cr), etc. are added to low-carbon steel-based steel and the ratio of the alloy elements is controlled. In addition, according to another embodiment of the present invention, it is possible to provide a method of manufacturing a high-strength stone plate through a highly productive continuous annealing process and optimizing the rolling and heat treatment processes. From this, it is possible to provide a stone plate with excellent neck-in processability and pressure resistance characteristics that can maintain high strength in a more economical manner, and a method for manufacturing the same.

The advantages and features of the present invention and methods for achieving them will become clear by referring to the embodiments described in detail below along with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. The present embodiments are merely provided to ensure that the disclosure of the present invention is complete and to provide a general understanding of the technical field to which the present invention pertains. It is provided to fully inform those with knowledge of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Accordingly, in some embodiments, well-known techniques are not specifically described in order to avoid ambiguous interpretation of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with meanings that can be commonly understood by those skilled in the art in the technical field to which the present invention pertains. When a part in the entire specification is said to “include” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary. The singular also includes the plural, unless specifically stated in the phrase.

The high-strength stone plate, which is an embodiment of the present invention, contains carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, and silicon (Si): 0.05% by weight or less ( 0% by weight excluded), phosphorus (P): 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, nitrogen (N) : 0.0005 to 0.004% by weight, chromium (Cr): 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, a high-strength stone plate containing the balance Fe and other inevitable impurities can be provided.

Below, the reason for limiting the components and composition range of the stone plate will be explained.

First, carbon may be included in an amount of 0.001 to 0.003% by weight.

Typically, carbon plays a role in improving the strength of steel sheets. More specifically, it is a representative element that can cause aging when included in steel as a solid solution element. However, if added in excess of 0.003% by weight, the material may harden due to dissolved carbon, which may reduce rollability and ductility. On the other hand, if it is less than 0.001% by weight, it may be difficult to obtain the desired strength and hardness values of the steel sheet due to coarsening of the ferrite structure.

Manganese (Mn) may be included in an amount of 0.4 to 0.7% by weight.

Manganese (Mn) is a solid solution strengthening element that can increase the strength of steel and improve hot workability. However, when added in excessive amounts, excessive manganese-sulfide (MnS) precipitates are formed, which may impair the ductility and workability of the steel. Therefore, when added in excess of 0.7% by weight, ductility may decrease. In addition, adding a large amount of alloy elements can increase costs and cause central segregation. On the other hand, if it is added in less than 0.4% by weight, processability may be improved, but it may cause red heat embrittlement and it may be difficult to secure the target strength.

Silicon (Si) may be included in an amount of 0.05% by weight or less (excluding 0% by weight).

Silicon (Si) combines with oxygen and other substances to form an oxide layer on the surface of the steel sheet. Since this may act as a factor that worsens the plating properties of tin and reduces corrosion resistance, the silicon element can be appropriately controlled and added within the above range.

Phosphorus (P) may be included in an amount of 0.01 to 0.04% by weight.

Phosphorus (P) is a representative element that exists as a solid solution element in steel and improves the strength and hardness characteristics of steel by causing solid solution strengthening. To ensure the above properties, the composition may be added within the above composition range. However, if added in excess of 0.04% by weight, center segregation may occur during casting, which may reduce the processability of the final product.

Sulfur (S) may be included in an amount of 0.02% by weight or less (excluding 0% by weight).

Sulfur (S) can combine with manganese (Mn) in steel to form non-metallic inclusions that serve as corrosion initiation points. In addition, since it is a factor in red shortness, it is better to reduce its content as much as possible. In addition, if sulfur is added in excess, the size of the manganese-sulfide-based precipitates may become coarse, making it difficult to secure the desired roughness, so it can be added in an amount of 0.02% by weight or less.

Aluminum (Al) may be included in an amount of 0.01 to 0.07% by weight.

Aluminum (Al) is an element added to aluminum killed steel for the purpose of preventing material deterioration due to deoxidizing agents and aging. Therefore, to obtain the above effect, addition of at least 0.01% by weight or more may be necessary. However, if added excessively, the deoxidation effect may become saturated and surface inclusions such as aluminum-oxide (Al ₂ O ₃ ) may rapidly increase. Because of this, the problem of deteriorating the surface properties of the hot rolled material and deteriorating workability may occur, so the addition can be controlled within the above range.

Nitrogen (N) may be included in an amount of 0.0005 to 0.004% by weight.

Nitrogen (N) is an element that exists in a solid state inside steel and is effective in strengthening materials. Therefore, in order to secure the desired strength, it can be added in an amount of 0.0005% by weight or more. However, if added in excessive amounts, the aging property rapidly deteriorates, increasing the burden of denitrification in the steel manufacturing stage, which may worsen steelmaking workability.

Chromium (Cr) may be included in an amount of 0.05 to 0.40% by weight.

Chromium (Cr) is an element that increases the recrystallization temperature of steel, and is an element added to ensure annealing plateability and to improve steel strengthening and aging resistance. Therefore, in order to ensure the above effect, 0.05% by weight or more can be added. More specifically, when added in the above range, fruiting resistance, etc. can be improved. However, if it exceeds 0.4% by weight, the manufacturing cost increases due to an increase in the amount of expensive chrome and the hard phase fraction increases, which may reduce rolling workability.

Niobium (Nb) may be included in an amount of 0.03 to 0.10% by weight.

Niobium (Nb) plays a role in securing annealed plateability of ultra-thin materials by fixing dissolved carbon in the steel to suppress strain aging and forming fine precipitates to delay recrystallization of strained grains. In addition, it also plays a role in improving the characteristics of the weld zone by suppressing grain growth in the heat affected zone (HAZ) during welding.

To ensure the above effect, more than 0.03% by weight can be added. However, when added in excessive amounts, the strain aging suppression effect shows a saturation value, while the manufacturing cost may increase due to the addition of a large amount of expensive alloy elements. In addition, when added in large amounts, recrystallization in the austenite region is greatly suppressed during the hot rolling process, which increases the hot rolling load and may reduce workability.

In addition, a high-strength stone plate that satisfies the above components and composition ranges can satisfy the following relational equation 1.

[Relationship 1]

0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035

However, [Nb], [Cr], and [C] refer to the weight percent of each component.

More specifically, in order to secure the surface and processing characteristics of the stone plate, it is necessary to properly manage the fraction of precipitates and solid solution. Therefore, in order to secure the neck-in processing characteristics desired in the present invention, it is necessary to control the relationship between the above components and carbon (C), an element forming a compound with niobium and chromium, by equation.

More specifically, it is necessary to maintain the value of relational equation 1 between 0.005 and 0.035. More specifically, if the value of relational equation 1 is less than 0.005, the amount of solid elements remaining in the steel increases, which may cause processing defects such as fluting during processing. In addition, the effect of suppressing the growth of crystal grains in high-temperature treatment processes such as welding is insufficient, and recrystallization of deformed grains progresses rapidly during the heat treatment process, so the desired yield strength may not be secured.

On the other hand, if the value of relational equation 1 exceeds 0.035, ductility may decrease and neck-in processability may deteriorate.

Therefore, the relationship between niobium, chromium, and carbon components can be controlled by the value according to equation 1 above.

With respect to the total microstructure of the stone plate, the fraction of strained ferrite may be 96 area% or more.

The microstructure can be obtained through an annealing process described later. Additionally, the microstructure can be identified using an optical or electron microscope. In addition, the proportion of deformed ferrite with high dislocation density may be 96 area% or more with respect to 100 percent area percent of the total microstructure of the stone plate.

If the fraction of strained ferrite is less than 96 area%, it may be difficult to secure the withstand pressure characteristics due to a decrease in yield strength. On the other hand, when the fraction of the strained ferrite is 96 area% or more, the variation range of the material is small and the desired strength and ductility can be obtained.

Additionally, the yield strength of the stone plate may be 580 to 670 MPa.

The stone plate according to one embodiment of the present invention can be used as a high-strength material, like a secondary rolled stone plate. Specifically, it can be used in areas where ultra-thin materials are used, such as pressure-resistant tubes or can bodies.

If the yield strength of the steel plate suitable for the above application is less than 580 MPa, defects such as buckling may occur in the body portion of the ultra-thin molded can. On the other hand, if the yield strength exceeds 670 MPa, it is advantageous in terms of securing the pressure resistance characteristics of the can, but it may reduce workability by lowering the rollability due to the increase in strength during the manufacturing process and worsening the tool wear characteristics of the forming press. there is.

Additionally, the elongation of the stone plate may be 5% or more.

Using the stone plate according to one embodiment of the present invention, neck-in processing can be performed to fasten the end of the can body and the lid. At this time, if the total elongation of the material is less than 5%, the neck-in processability of the can may deteriorate and processing cracks may occur. Therefore, in order to secure neck-in processability, an elongation of 5% or more can be secured.

In addition, the hole expansion rate of the stone plate may be 10% or more.

At this time, the Hole Expansion Ratio (HER) refers to the cracking properties of the steel sheet after hole expansion. More specifically, the hole expansion rate is a factor closely related to elongation flangeability, and is defined as [{(hole length of the machined part after forming)-(length of the initial machined hole)}*100/(length of the initial machined hole)]. do.

Currently, the typical hole expansion rate in application areas where high-strength stone disks requiring internal pressure characteristics are applied is around 8%, so the high-strength stone disks, which are an embodiment of the present invention, can secure a hole expansion rate of 10% or more.

A method of manufacturing a high-strength stone plate, which is another embodiment of the present invention, includes carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, and silicon (Si): 0.05%, based on the total 100% by weight. Weight% or less (excluding 0% by weight), phosphorus (P): 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, Preparing a slab containing nitrogen (N): 0.0005 to 0.004% by weight, chromium (Cr): 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, the balance Fe and other inevitable impurities; Manufacturing a hot-rolled sheet by hot-rolling the slab; Finish rolling the hot rolled sheet; manufacturing a coil by winding the finish rolled sheet; manufacturing a cold-rolled sheet by cold-rolling the coil; and continuously annealing the cold-rolled plate to obtain a final stone plate.

At this time, the reason for limiting the components and composition range of the slab is the same as described above, so it is omitted.

More specifically, the slab may satisfy the following relational equation 1.

[Relationship 1]

0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035

However, [Nb], [Cr], and [C] refer to the weight percent of each component.

The reason for limiting the value of relational expression 1 is the same as described above, so it is omitted.

The step of finishing rolling the hot rolled sheet may be performed at a temperature range of 880 to 950°C.

When the finish rolling temperature is less than 880°C, hot rolling may be completed in the ferrite single phase region. As a result, agglomeration of crystal grains may occur, resulting in a decrease in hot rolling properties and processability. On the other hand, if the finish rolling temperature is higher than 950°C, it may be advantageous in terms of hot rolling, but the thickness of the corrosion layer of the material may become thick, which may deteriorate the surface characteristics of the product.

The step of manufacturing a coil by winding the finish rolled sheet may be performed at a temperature range of 550 to 650°C. The previously finished rolled sheet may be cooled in the run-out-table (ROT) step and then wound at a temperature range of 550 to 650°C.

More specifically, when the coiling temperature is less than 550°C, the formation behavior of low-temperature precipitates may differ due to temperature unevenness in the width direction during cooling and maintenance. This may adversely affect machinability by causing material deviation. On the other hand, if the coiling temperature exceeds 650°C, the material may soften and corrosion resistance may deteriorate as the structure of the final product becomes coarse. Accordingly, the finish rolled sheet can be wound at the above temperature range.

In the step of manufacturing a cold-rolled sheet by cold rolling the coil, the cold rolling reduction rate may be 80 to 94%. More specifically, it may be 86 to 92%.

The coiled steel sheet can be cold rolled at a reduction ratio of 80 to 94% after pickling treatment.

More specifically, when the cold rolling reduction ratio is less than 80%, hot rolling sheet thickness must be thinned in order to manufacture ultra-thin products, so hot rolling workability may be reduced. In addition, the cold rolling reduction rate is low, so it may be difficult to secure the target high strength characteristics. On the other hand, if the cold reduction ratio exceeds 94%, it may be advantageous in terms of securing strength characteristics, but the hardness of the material according to the reduction ratio shows a saturation value and increases the roll force of the rolling mill, reducing cold rolling performance. It can be bad. Therefore, the cold rolling reduction rate may be within the above range, and more specifically, may be 86 to 92%.

The step of continuously annealing the cold-rolled plate to obtain a final stone plate may be continuously annealed at a temperature range of 640 to 700°C.

The cold rolled sheet may be continuously annealed at a temperature range of 640 to 700° C. to control microstructure. More specifically, by performing annealing in a state where the strength is increased due to the strain previously generated by cold rolling, the strain can be partially removed. Because of this, the target strength can be obtained and appropriate ductility can also be secured. Therefore, when annealing below 640°C, removal of the strain generated during cold rolling may be insufficient. As a result, a steel sheet with a strength higher than the target can be obtained, but workability may be significantly reduced.

On the other hand, when annealed above 700°C, recrystallization of deformed grains progresses rapidly, and the fraction of deformed ferrite may decrease. Accordingly, the material may be softened and a yield strength of 580 to 670 MPa may not be secured. Therefore, the annealing temperature can be controlled within the above range.

In the high-strength stone plate manufactured by the above manufacturing method, the fraction of deformed ferrite may be 96 area% or more with respect to 100% area% of the total microstructure.

Additionally, the yield strength of the stone plate may be 580 to 670 MPa, and the elongation of the stone plate may be 5% or more. In addition, the hole expansion rate of the stone plate may be 10% or more. Since the effects of the above physical properties are the same as described above, they are omitted.

As described above, the following experiment was conducted to compare the effectiveness of the manufacturing method of a high-strength stone plate with excellent neck-in processability and pressure resistance characteristics.

Example

First, examples and comparative examples containing the compositions shown in Table 1 below were prepared. Afterwards, after reheating in a furnace at 1250°C for 2 hours, a stone plate was manufactured according to the conditions disclosed in Table 2 below. The physical properties and mechanical properties of each steel type manufactured under the conditions in Table 2 below were measured and shown in Table 3.

Steel grade Chemical composition (% by weight) Ratio between elements C Mn Si P S Al N Nb Cr ([Nb]/91)*([Cr]/52) /([C]/12) Real-time lecture 1 0.0014 0.64 0.016 0.018 0.011 0.048 0.0028 0.048 0.31 0.0270 Real-time lecture 2 0.0022 0.56 0.011 0.031 0.009 0.051 0.0015 0.035 0.18 0.0073 Real-time lecture 3 0.0026 0.45 0.018 0.026 0.006 0.038 0.0031 0.061 0.24 0.0143 Comparison lecture 1 0.0023 0.28 0.014 0.006 0.013 0.095 0.0065 - 0.29 0 Comparison lecture 2 0.0056 0.86 0.015 0.021 0.005 0.048 0.0025 0.019 0.15 0.0013 Comparison lecture 3 0.0007 0.52 0.094 0.048 0.011 0.006 0.0016 0.044 0.94 0.1498

division Steel grade Reheating temperature
(℃) Finishing hot rolling temperature (℃) Winding temperature
(℃) Cold reduction rate
(%) Annealing temperature
(℃) Example 1 Real-time lecture 1 1250 910 600 88 650 Example 2 1250 910 600 88 670 Example 3 1250 910 600 88 690 Example 4 Real-time lecture 2 1250 890 580 90 660 Example 5 1250 890 580 90 680 Example 6 Real-time lecture 3 1250 930 620 89 660 Comparative Example 1 Real-time lecture 1 1250 700 600 88 600 Comparative example 2 1250 910 600 68 670 Comparative example 3 Real-time lecture 2 1250 890 500 90 760 Comparative example 4 Comparison lecture 1 1250 910 620 89 660 Comparative Example 5 Comparison lecture 2 1250 910 620 89 660 Comparative Example 6 Comparison lecture 3 1250 910 620 89 660

division Transparency yield strength
(MPa) elongation
(%) Hole expansion rate (%) Modified ferrite fraction (%) Neck-in machinability Example 1 O 653 (O) 7.8 (O) 14.2 (O) 99.1 Good Example 2 O 641 (O) 8.2 (O) 16.9 (O) 98.5 Good Example 3 O 628 (O) 10.1 (O) 19.2 (O) 98.7 Good Example 4 O 635 (O) 6.9 (O) 15.1 (O) 99.7 Good Example 5 O 604 (O) 8.4 (O) 18.7 (O) 99.2 Good Example 6 O 596 (O) 9.6 (O) 16.4 (O) 98.9 Good Comparative Example 1 X 728 (X) 1.8 (X) 7.5 (X) 100.0 error Comparative example 2 O 509 (X) 7.4 (O) 8.5 (X) 82.8 error Comparative example 3 X 381 (X) 13.8 (O) 9.4 (X) 16.3 error Comparative Example 4 O 275 (X) 28.6 (O) 18.2 (O) 8.2 Good Comparative Example 5 O 494 (X) 3.9 (X) 6.8 (X) 55.6 error Comparative Example 6 O 805 (X) 2.1 (X) 7.6 (X) 98.1 error

The yield strength, elongation rate, and hole expansion rate values disclosed in Table 3 were indicated as "O" if they satisfied a yield strength in the range of 580 to 670 MPa, an elongation rate of 5% or more, and a hole expansion rate of 10% or more, respectively, and those that did not meet the above criteria were In this case, it is marked with “X”.

In addition, machinability was marked as “bad” if a machining defect occurred during neck-in processing, and as “good” if no machining defect occurred.

In addition, passability was marked as "O", meaning pass, if there was no rolling load during cold and hot rolling and no heat buckle occurred during heat treatment, and there was no risk of rolling load occurring or heat buckle during annealing. Cases where it exists are marked with “X”, meaning failure.

In addition, the deformed ferrite phase fraction was determined by applying 200x magnification to the target test specimen at 1/4 thickness of the specimen using an optical microscope, and five tissue images were photographed at different positions. Afterwards, the fractions of deformed ferrite and regular ferrite were calculated using the tissue photo using the point calculation method. In the above case, the sum of the deformed and normalized ferrite fractions is 100%.

Therefore, the experimental results disclosed in Table 3 above are summarized according to the above-mentioned criteria as follows.

Examples 1 to 6 are cases where all process conditions such as steel component control, hot rolling process, and cold rolling process according to the present invention are satisfied. In all examples, the fraction of the strained ferrite phase was 96% or more, and the yield strength of 580 to 670 MPa was satisfied. In addition, the elongation of the material was over 5%, so no bending or cracking occurred during neck-in processing, ensuring excellent processability. In addition, the hole expansion ratio was excellent at over 10%, showing good elongation flange processability, making it possible to manufacture a high-strength stone plate with excellent neck-in processability and pressure resistance characteristics.

On the other hand, Comparative Examples 1 to 3 satisfied the conditions for controlling steel components (invention steel 1, invention steel 2) according to the present invention, but did not satisfy the process range.

More specifically, in Comparative Example 1, the finish rolling temperature and annealing temperature were performed at 700°C and 600°C, which were respectively lower than the management range, and in Comparative Example 2, the cold rolling reduction rate was 68%, which did not fall within the range limited herein. In addition, Comparative Example 3 is a case where the coiling temperature was 500°C, which is lower than the manufacturing management range of the present invention, and the annealing temperature was 760°C, which is higher than the management standard. It can be seen that Comparative Examples 1 to 3 did not satisfy the process management standards of the present invention, and thus the overall yield strength and hole expansion ratio did not satisfy the desired values. Because of this, it can be confirmed that neck-in processability cannot be secured.

In addition, Comparative Examples 4 to 6 are cases where steel types (Comparative Steels 1 to 3) that satisfied the manufacturing conditions for each process according to the present invention but did not satisfy the steel composition conditions were used. Among the above cases, it can be seen that in Comparative Examples 4 and 5, the fraction of modified ferrite was lower than 96% and the yield strength was lower than the level of 580 to 670 MPa that was intended to be obtained in the present invention, making it difficult to secure pressure resistance characteristics. Additionally, in the case of Comparative Examples 5 and 6, it can be seen that the elongation rate and hole expansion rate did not meet the target level. Accordingly, it can be seen that the target properties of a high-strength stone plate with excellent neck-in processability and pressure resistance characteristics, which are ultra-thin and require appropriate pressure resistance and processability, cannot be satisfied.

As described above, according to the present invention, it is possible to provide a stone plate that is thin in thickness and requires high pressure resistance characteristics even by the primary rolling method. More specifically, when manufacturing the stone plate, neck-in processability is applied to the use. High-strength stone plates can also be provided.

Stone plates with excellent neck-in processability and pressure-resistance characteristics are improved in rollability and annealing through control through appropriate composition and manufacturing process control, as well as elongation and hole that can be applied to pressure-resistance containers without going through secondary rolling. We were able to secure characteristics such as expansion rate.

Therefore, according to the method for manufacturing a high-strength stone plate, which is an embodiment of the present invention, a stone plate with high strength and excellent neck-in processability is provided by only going through the heat treatment process, without going through the secondary rolling process, which is a factor in increasing the process cost. can do. In addition, when used in applications requiring the above characteristics, not only can the occurrence of cracks in the processing stage be reduced, but it is also possible to ensure stable workability of the product and reduce the occurrence of material deviation in the product.

Although the embodiments of the present invention have been described above, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing its technical idea or essential features.

Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. .

Claims (11)

For 100% by weight of the total stone plate, carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, silicon (Si): 0.05% by weight or less (excluding 0% by weight), phosphorus ( P): 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, nitrogen (N): 0.0005 to 0.004% by weight, chromium ( Cr): 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, including the balance Fe and other inevitable impurities,
A high-strength stone plate that satisfies the following relational expression 1.
[Relationship 1]
0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035
(However, [Nb], [Cr], and [C] refer to the weight percent of each component.)
According to paragraph 1,
A high-strength stone plate in which the fraction of deformed ferrite is 96 area% or more with respect to 100 percent area percent of the total microstructure of the stone plate.
According to paragraph 2,
A high-strength stone disk having a yield strength of 580 to 670 MPa.
According to paragraph 3,
A high-strength stone disk having an elongation rate of 5% or more.
According to paragraph 4,
A high-strength stone disk having a hole expansion rate of 10% or more.
For the total 100% by weight, carbon (C): 0.001 to 0.003% by weight, manganese (Mn): 0.4 to 0.7% by weight, silicon (Si): 0.05% by weight or less (excluding 0% by weight), phosphorus (P) : 0.01 to 0.04% by weight, sulfur (S): 0.02% by weight or less (excluding 0% by weight), aluminum (Al): 0.01 to 0.07% by weight, nitrogen (N): 0.0005 to 0.004% by weight, chromium (Cr) Preparing a slab containing: 0.05 to 0.40% by weight, niobium (Nb): 0.03 to 0.10% by weight, the balance Fe and other inevitable impurities;
Manufacturing a hot-rolled sheet by hot-rolling the slab;
Finish rolling the hot rolled sheet;
manufacturing a coil by winding the finish rolled sheet;
manufacturing a cold-rolled sheet by cold-rolling the coil; and
Continuously annealing the cold-rolled plate to obtain a final stone plate,
The step of finishing rolling the hot rolled sheet is performed at a temperature range of 880 to 950°C,
The step of manufacturing a coil by winding the finish rolled sheet is performed at a temperature range of 550 to 650°C,
In the step of manufacturing a cold-rolled sheet by cold rolling the coil, the cold rolling reduction rate is 80 to 94%,
The step of continuously annealing the cold-rolled plate to obtain a final stone plate is continuously annealed at a temperature range of 640 to 700°C,
The slab is a method of manufacturing a high-strength stone plate that satisfies the following relational expression 1.
[Relationship 1]
0.005≤([Nb]/91)*([Cr]/52)/([C]/12)]≤0.035
(However, [Nb], [Cr], and [C] refer to the weight percent of each component.)
According to clause 6,
manufacturing a coil by winding the finish rolled sheet; Since the,
A method of manufacturing a high-strength stone plate further comprising the step of pickling the coil.
According to any one of paragraphs 6 or 7,
A method of manufacturing a high-strength stone plate, wherein the fraction of deformed ferrite is 96 area% or more with respect to the total microstructure of the stone plate.
According to any one of paragraphs 6 or 7,
A method of manufacturing a high-strength stone disk, wherein the yield strength of the stone disk is 580 to 670 MPa.
According to any one of paragraphs 6 or 7,
A method of manufacturing a high-strength stone plate, wherein the elongation of the stone plate is 5% or more.
According to any one of paragraphs 6 or 7,
A method for manufacturing a high-strength stone plate, wherein the hole expansion rate of the stone plate is 10% or more.