Hot-rolled steel sheets, steel pipes, and methods for manufacturing these materials with excellent wear resistance.

Abstract

The present invention provides a high-manganese hot-rolled steel sheet with excellent wear resistance, a steel pipe manufactured using the above-mentioned hot-rolled steel sheet, and a method for manufacturing these. [Solution] A hot-rolled steel sheet containing, by weight percent, manganese (Mn): 10-20%, carbon (C): 0.6-2.0%, chromium (Cr): 5.0% or less, aluminum (Al): 0.5% or less, silicon (Si): 1.0% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, with the remainder being iron (Fe) and other unavoidable impurities, having a microstructure with austenite as the main phase, and containing film-like precipitates formed along the austenite grain boundaries.

Description

Technical Field

[0001] The present invention relates to hot-rolled steel sheets, steel pipes, and manufacturing methods thereof, and more particularly, to high-manganese hot-rolled steel sheets having excellent wear resistance, steel pipes manufactured using the above hot-rolled steel sheets, and manufacturing methods thereof.

Background Art

[0002] When dredging a navigation channel for ensuring the water depth and water area of a marine vessel or during dredging and landfill for backland formation, the steel pipes used for this dredging are required to have excellent wear resistance against gravel, sand, etc. Also, in the case of steel pipes used for resource extraction and transfer of minerals, etc. in the mining industry, wear resistance is closely related to production costs, and thus excellent wear resistance is required for efficient production costs.

[0003] In the case of carbon steel having ferrite or martensite as the main structure and used as a wear-resistant steel pipe, recently, as the limit to wear resistance has emerged, an alternative material that can overcome these drawbacks is required.

[0004] On the other hand, austenitic steel materials have excellent wear resistance due to the characteristics of work hardening ability and are used as wear-resistant parts in various industries. In order to enhance wear resistance, efforts have been made to increase the content of carbon to a high level and include a large amount of manganese in high-manganese steel to increase the austenite structure and resistance.

[0005] Also, in the case of steel pipes for dredging and mineral extraction / transfer, and small and medium-sized steel pipes, ERW steel pipes are manufactured and used using hot-rolled materials. In the case of large-diameter steel pipes, spiral steel pipes and ​​​​​​​​​​We manufacture SAW (Submerged Arc Welding) steel pipes using thick plate materials. It is in use. In the case of high-manganese steel, much development has been made regarding steel pipes using thick plate material. However, development is needed for hot-rolled high-manganese steel materials and steel pipes made from them. [Overview of the project] [Problems that the invention aims to solve]

[0006] According to one aspect of the present invention, hot-rolled steel sheets, steel pipes, and methods for manufacturing them that have excellent wear resistance are provided. It is intended to be used for that purpose.

[0007] The problems that the present invention will address are not limited to those described above. A person of ordinary skill would be able to understand the entirety of this specification. There is no difficulty in understanding further issues of the present invention from the substantive content. [Means for solving the problem]

[0008] One aspect of the present invention is that, in weight percent, manganese (Mn): 10-20%, carbon (C): 0.6% ~2.0%, chromium (Cr): 5.0% or less, aluminum (Al): 0.5% or less, Recon (Si): 1.0% or less, Phosphorus (P): 0.1% or less, Sulfur (S): 0.02% or less The remainder contains iron (Fe) and other unavoidable impurities. It has a microstructure with austenite as the main phase, and is formed along the austenite grain boundaries. It contains a film-like precipitate, This provides a hot-rolled steel sheet whose hardness increases by 1.1 times or more due to work hardening after pipe formation. .

[0009] The thickness of the above precipitate can be 0.1 to 2.0 μm.

[0010] The above steel plate has a tensile strength of 800 MPa or more and an elongation of 30% or more. to cut.

[0011] The above steel plate can have a Vickers hardness of 220 Hv or more.

[0012] The above steel plate can have a thickness of 4 to 20 mm.

[0013] Another aspect of the present invention is, by weight%, manganese (Mn): 10 to 20%, carbon (C): 0 .6 to 2.0%, chromium (Cr): 5.0% or less, aluminum (Al): 0.5% or less , silicon (Si): 1.0% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02 % or less, the balance being iron (Fe) and other inevitable impurities, having a microstructure with austenite as the main phase, and including film-like precipitates formed along the austenite grain boundaries, and being able to provide a steel pipe having a hardness 1.1 times or more that of the steel plate. The above steel pipe can have a Vickers hardness of 250 Hv or more.

[0014] One aspect of the present invention is, by weight%, manganese (Mn): 10 to 20%, carbon (C): 0.6

[0015] ~2.0%, chromium (Cr): 5.0% or less, aluminum (Al): 0.5% or less, silicon (Si): 1.0% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, reheating a steel slab containing residual iron (Fe) and other inevitable impurities; hot rolling the reheated steel slab to obtain a hot-rolled steel plate; and cooling the hot-rolled steel plate to a temperature range of less than 500°C and then winding it up, including a manufacturing method of a hot-rolled steel plate having a winding start temperature of 500°C or less and a winding average temperature of less than 300°C. can be included.

[0016] The reheating is performed within a temperature range of 1000 to 1250 °C, the hot rolling is performed at a finishing rolling temperature of 800 °C or higher, during the cooling, the cooling rate can be 5 °C / s or higher.

[0017] The thickness of the steel plate after the hot rolling can be 4 to 20 mm.

[0018] Another aspect of the present invention includes a method for manufacturing a steel pipe including a step of forming the hot-rolled steel plate into a steel pipe to obtain a steel pipe which can be provided.

Effects of the Invention

[0019] According to one aspect of the present invention, a hot-rolled steel plate, a steel pipe, and a manufacturing method thereof with excellent wear resistance can be provided which can be provided.

Brief Description of the Drawings

[0020] [Figure 1] It is a photograph obtained by observing the microstructure of Invention Example 1 according to one aspect of the present invention with an optical microscope (200 times magnification).

Modes for Carrying Out the Invention

[0021] Hereinafter, preferred embodiments of the present invention will be described. The embodiments of the present invention can be variously modified and should not be construed as limiting the scope of the present invention to the embodiments described below. This embodiment is provided to explain the present invention in more detail to those having ordinary knowledge in the technical field to which the invention pertains. Hereinafter, the present invention will be described in detail. Hereinafter, the steel composition of the present invention will be described in detail.

[0022] Hereinafter, the present invention will be described in detail.

[0023] Hereinafter, the steel composition of the present invention will be described in detail.

[0024] Unless otherwise specified in this invention, the percentages representing the content of each element are based on weight.

[0025] In weight percent, manganese (Mn): 10-20%, carbon (C): 0.6-2.0%, chromium (Cr): 5.0% or less, Aluminum (Al): 0.5% or less, Silicon (Si): 1% .0% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, balance iron (Fe) It may also contain other unavoidable impurities.

[0026] Manganese (Mn): 10-20% Manganese (Mn) is a very important element that plays a role in stabilizing austenite. This improves the uniform elongation rate. The above manganese (Mn) is austenite. It is preferable that it be contained at a concentration of 10% or more in order to ensure that it is the main component. If the content is less than 10%, the austenite stability decreases, and during the rolling process in the manufacturing stage... A martensite structure can be formed, thereby allowing the austenite structure to be fully formed. It may be difficult to secure a sufficient uniform elongation rate. On the other hand, its content If it exceeds 20%, manufacturing costs will rise significantly, and excessive addition will reduce corrosion resistance and manufacturing costs. During the heating process, severe internal oxidation can occur, which can lead to a decrease in surface quality. Problems can arise. A more preferable lower limit for manganese (Mn) content is 11. It can be 5%, and a more preferable upper limit can be 19.5%.

[0027] Carbon (C): 0.6~2.0% Carbon (C) is an austenite-stabilizing element and plays a role in improving uniform elongation. Furthermore, it is an element that is extremely advantageous for improving strength and increasing work hardening rate. Carbon (C If the content of ) is less than 0.6%, it is difficult to form stable austenite at room temperature. Because it is difficult, there is a problem in that it is difficult to ensure sufficient strength and work hardening rate. On the other hand, When the content exceeds 2.0%, a large amount of carbides precipitate, reducing the uniform elongation rate and thus improving the elongation rate. It is difficult to ensure this, which can lead to premature fracture. In order to maximize the carbon (C) content, it is advantageous, but heat treatment causes carbide precipitation. Even if carbon (C) solid solution is suppressed, there are limits to its potential, and there are concerns about the deterioration of the steel's physical properties. The upper limit is preferably restricted to 2.0%. A more preferable lower limit is 0.75%. This is possible, and a more preferable upper limit can be 1.85%.

[0028] Chromium (Cr): 5.0% or less Chromium (Cr) plays a role in increasing the strength of steel by dissolving in austenite. It can be done. Also, although it is an element that improves the corrosion resistance of steel, carbon forms at austenite grain boundaries. It may form chromium compounds and reduce toughness. Therefore, the chromium added in this invention The content is preferably determined considering the relationship with C and other elements added together. Furthermore, to prevent carbide formation, it is preferable to include 5% or less of chromium (Cr). It is more preferable to include 4% or less. If the content exceeds 5%, austenite It is difficult to effectively suppress the formation of chromium-based carbides at grain boundaries, which affects impact toughness. It may decrease. In this invention, the chromium (Cr) content is controlled as needed. It is possible to include 0%.

[0029] Aluminum (Al): 0.5% or less Aluminum (Al) is an ingredient included as a deoxidizing agent in the steelmaking process, and in this invention... It can be contained in an amount of 0.5% or less. In this invention, the aluminum (Al) content is 0%. It can be removed.

[0030] Silicon (Si): 1.0% or less Silicon (Si), along with Al, is an ingredient included as a deoxidizing agent in the steelmaking process, and this development In the Ming Dynasty, it can be included at a rate of 1.0% or less, and 0% can be excluded.

[0031] Phosphorus (P): 0.1% or less Phosphorus (P) is a typical impurity that is inevitably added to steel, and excessive addition can damage the quality. Because it could cause degradation, its upper limit can be restricted to 0.1%.

[0032] Sulfur (S): 0.02% or less Sulfur (S), along with phosphorus (P), is an unavoidable impurity added to steel, and its upper limit is 0.02%. It can be limited to a percentage.

[0033] The steel of the present invention, in addition to the composition described above, may also contain the remaining iron (Fe) and unavoidable impurities. Yes, it is possible. Unavoidable impurities can be introduced unintentionally during the normal manufacturing process. It is impossible to eliminate such impurities. Even engineers in the field of ordinary steelmaking can identify them. Since this is something everyone understands, we will not specifically mention all of its contents in this specification.

[0034] The steel microstructure of the present invention will be described in detail below.

[0035] In this invention, unless otherwise specified, the percentages indicating the fraction of microstructure are based on area. .

[0036] One aspect of the present invention is that a hot-rolled steel sheet has a microstructure in which austenite is the main phase. It is possible.

[0037] In this invention, the hardness of the material itself is increased due to excellent work hardening in a wear environment, thereby improving wear resistance. To ensure this, it is possible to have a microstructure with austenite as the main phase. More preferably It can contain 97% or more austenite by area.

[0038] According to one aspect of the present invention, the steel is a film-like structure formed along the austenite grain boundaries. It may contain precipitates, the thickness of which may be 0.1 to 2.0 μm.

[0039] In this invention, by forming a film-like precipitate at the austenite grain boundary, the strength The aim is to ensure sufficient degree of abrasion resistance. The precipitate according to the present invention contains carbides. This can be formed, and it can include carbides in which Cr is formed together with C. If the thickness is less than 0.1 μm, sufficient strength cannot be ensured, resulting in a problem of reduced wear resistance. However, there is a problem in that its ductility and toughness decrease when its thickness exceeds 2.0 μm.

[0040] A steel pipe formed by manufacturing a hot-rolled steel sheet according to one aspect of the present invention has austenite as its main phase. It can have a fine structure, and contains film-like precipitates at the grain boundaries, and the precipitates The thickness can be between 0.1 and 2.0 μm.

[0041] The steel manufacturing method of the present invention will be described in detail below.

[0042] One aspect of the present invention involves reheating and hot-rolling a steel slab that satisfies the above-mentioned alloy composition. It can be manufactured by cooling and winding.

[0043] reheating The steel slab satisfying the alloy composition of the present invention is reheated in a temperature range of 1000 to 1250°C. It is possible.

[0044] The slab can be reheated before hot rolling. In the slab stage described above, the slab The casting structure can be reheated to address segregation and the solid solution and homogenization of the secondary phase. If the temperature is below 1000°C, it is difficult to ensure the above reheating effect, and heating furnace There is a problem that if the temperature is too low, the deformation resistance becomes large during hot rolling. On the other hand, the temperature If the temperature exceeds 1250°C, partial melting occurs in segregation zones within the cast structure, and surface quality deteriorates. It is possible.

[0045] Hot rolling The above reheated slab is hot-rolled at a finishing rolling temperature of 800°C or higher to a thickness of 4 to 20 mm. A hot-rolled steel sheet of mm thickness can be obtained.

[0046] This invention allows for the production of hot-rolled steel sheets with a thickness of 4 to 20 mm by hot rolling. The top rolling temperature is preferably limited to 800°C or higher for productivity, and more preferably... It can be hot-rolled at a finish rolling temperature below the pre-recrystallization temperature (Tnr).

[0047] Cooling and winding The hot-rolled steel sheet described above is cooled to a temperature range of 500°C or less at a cooling rate of 5°C / s or more. It can be wound up afterwards, the winding start temperature is 500°C or less, and the average winding temperature The temperature can be 300°C or lower.

[0048] In this invention, cooling to a temperature range of less than 500°C is performed to prevent the formation of coarse carbides. This is possible. If the cooling end temperature exceeds 500°C, it takes time to cool to room temperature after winding. Coarse carbides are formed, reducing uniform elongation and making it difficult to ensure excellent elongation. There is a possibility that premature breakage may occur. The lower limit of the winding temperature mentioned above is not particularly limited. It is not necessary, and it can be done at room temperature without any problems.

[0049] If the cooling rate is less than 5°C / s, coarse carbides are formed, resulting in a decrease in strength and elongation. There is a problem in that this can occur. The upper limit of the average cooling rate is not particularly limited, but the equipment You can choose as appropriate depending on the situation.

[0050] Furthermore, in this invention, by controlling the winding start temperature and the winding average temperature, This prevents the formation of carbides and ensures the excellent strength and elongation characteristic of austenitic steel. This allows for improved work hardening and ensures excellent wear resistance.

[0051] In this invention, the winding start temperature is the temperature at which winding is started using the winding equipment. This indicates the temperature of the steel plate, and the winding average temperature is the winding temperature over the entire length of the coil. This refers to the average value. This occurs when the winding start temperature exceeds 500°C, or when the winding average temperature is 30°C. A problem arises when temperatures exceed 0°C, as excessive carbide formation occurs, leading to a decrease in ductility and toughness. .

[0052] One aspect of the present invention relates to a steel pipe that satisfies the alloy composition and manufacturing method described above, and is made from a hot-rolled steel sheet. It can be manufactured using a pipe.

[0053] Pipe making A steel pipe can be obtained by forming a steel plate according to one aspect of the present invention.

[0054] In this invention, the method for manufacturing welded steel pipes is not particularly limited, and a conventional method for manufacturing ERW steel pipes is also applicable. It can be used. However, if the Mn content is high, the steel material will melt and solidify during ERW welding. In this process, oxides are generated that can cause penetration defects. To prevent this, To completely remove the molten metal and oxides in the narrow gap before they enter the welding point, Additional devices can be installed to prevent exposure to air and cooling water.

[0055] The steel plate manufactured in this manner according to the present invention has a thickness of 4 to 20 mm and a tensile strength of 800. The strength is MPa or higher, the elongation is 30% or higher, and the hardness after pipe formation is greater than that of hot-rolled steel sheet. It can have a ratio of 1.1 or more, and possess excellent work hardening rate and wear resistance properties.

[0056] Furthermore, the steel plate of the present invention can have a hardness of 220 Hv or higher, and the steel pipe can have a hardness of 250 Hv. It can be greater than or equal to v. [Examples]

[0057] The present invention will be described more specifically below with reference to examples. However, the following examples are based on the present invention. This is merely illustrative and for the purpose of providing a more detailed explanation, and is not intended to limit the scope of the rights of the present invention. It's important to note that this is not a product.

[0058] A steel slab having the alloy composition shown in Table 1 below is used to produce a hot-rolled steel sheet according to the conditions shown in Table 2 below. Steel plates were manufactured with the thicknesses shown in Table 3 below. The reheating temperature was the same, at 1150°C.

[0059] [Table 1]

[0060] [Table 2]

[0061] Table 3 below shows the microstructure and mechanical properties measured for the steel sheets manufactured as described above. The steel plates are used to manufacture ERW welded steel pipes, and the physical properties of these steel pipes are also shown. The microstructure is shown by observing a quarter of the thickness of the steel plate with a 200x optical microscope, and the tensile strength is also shown. The elongation rate was determined by taking a test specimen conforming to API 5L standards from 1 / 4 of the steel plate thickness and performing a tensile test. Here are the results. At this time, the microstructure contains more than 97% austenite. In such cases, it is indicated by ○. Also, precipitates with a thickness of 0.1 to 2.0 μm at the austenite grain boundaries. If a defect was formed, a circle (○) was indicated. Regarding mechanical properties, the Vickers hardness test was performed on the steel. The hardness of the board was measured, and the hardness after pipe formation was also measured. The ratio of these values ​​was then calculated and shown.

[0062] [Table 3]

[0063] As shown in Table 3, in the case of an example of the invention that satisfies the alloy composition and manufacturing conditions of the present invention, The microstructural characteristics proposed in the invention are satisfied, and the desired physical properties are ensured in this invention.

[0064] Figure 1 shows the microstructure of Invention Example 1, which relates to one aspect of the present invention, observed with an optical microscope (200x magnification). This is a photograph.

[0065] On the other hand, Comparative Example 1 is a case where the content of C does not reach the range proposed in the present invention, and is an example of the invention. Compared to that, it lacked strength, and the work hardening rate after steel pipe manufacturing was also insufficient.

[0066] Comparative Example 2 is a case where the content of Mn and C falls outside the range proposed in the present invention, and the steel plate Strength deteriorates, austenite stability deteriorates due to insufficient Mn content, and elongation is not maintained. I couldn't.

[0067] Comparative Example 3 is one in which the winding start temperature and average temperature exceed the range of the present invention, and Excessive formation of large carbides resulted in a deterioration of ductility.

[0068] The present invention has been described in detail through the above examples, but other forms of embodiments are also possible. Therefore, the technical idea and scope of the claims described below are not limited to examples. It is not determined.

Claims

1. In weight percent, manganese (Mn): 10-20%, carbon (C): 0.6-2.0%, chromium (Cr): 5.0% or less, Aluminum (Al): 0.5% or less, Silicon (Si): 1% .. 0% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, balance iron (Fe) and other unavoidable impurities, It has a microstructure with austenite as the main phase, and is formed along the austenite grain boundaries. It contains a film-like precipitate, Hot-rolled steel sheet whose hardness increases by more than 1.1 times due to work hardening after pipe formation.

2. The hot-rolled steel sheet according to claim 1, wherein the thickness of the precipitate is 0.1 to 2.0 μm.

3. The steel plate has a tensile strength of 800 MPa or more and an elongation of 30% or more, claim. The hot-rolled steel sheet described in 1.

4. The hot-rolled steel sheet according to claim 1, wherein the steel sheet has a Vickers hardness of 220 Hv or more.

5. The hot-rolled steel sheet according to claim 1, wherein the steel sheet has a thickness of 4 to 20 mm.

6. In weight percent, manganese (Mn): 10-20%, carbon (C): 0.6-2.0%, chromium (Cr): 5.0% or less, Aluminum (Al): 0.5% or less, Silicon (Si): 1% .. 0% or less, phosphorus (P): 0.1% or less, sulfur (S): 0.02% or less, balance iron (Fe) and other unavoidable impurities, It has a microstructure with austenite as the main phase, and is formed along the austenite grain boundaries. It contains a film-like precipitate, A steel pipe with a hardness 1.1 times or more that of a steel plate.

7. The steel pipe according to claim 6, wherein the steel pipe has a Vickers hardness of 250 Hv or more.

8. In weight percent, manganese (Mn): 10-20%, carbon (C): 0.6-2.0%, chromium (Cr): 5.0% or less, Aluminum (Al): 0.5% or less, Silicon (Si): 1% 0% or less, Phosphorus (P): 0.1% or less, Sulfur (S): 0.02% or less, Residual iron (Fe) The step of reheating the steel slab containing and other unavoidable impurities; The step of hot-rolling the reheated steel slab to obtain a hot-rolled steel sheet; and The process includes cooling the hot-rolled steel sheet to a temperature range of less than 500°C, followed by winding it up. The winding start temperature is 500°C or less, and the average winding temperature is less than 300°C. A method for manufacturing rolled steel sheets.

9. The aforementioned reheating is performed in a temperature range of 1000 to 1250°C. The aforementioned hot rolling is carried out at a finish rolling temperature of 800°C or higher. The method for manufacturing a hot-rolled steel sheet according to claim 8, wherein the cooling rate during the cooling process is 5°C / s or more. 。

10. Manufacturing of a hot-rolled steel sheet according to claim 8, wherein the thickness of the steel sheet after hot rolling is 4 to 20 mm. method.

11. The step of forming a pipe from the hot-rolled steel sheet to obtain a steel pipe is included in any one of claims 8 to 10. A method for manufacturing steel pipes.

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