JP2020509211A - Austenitic steel with excellent surface properties and method for producing the same - Google Patents

Abstract

The present invention relates to an austenitic wear-resistant steel material having excellent surface properties and a method for producing the same. According to the present invention, carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22%, copper (Cu): 5% or less (excluding 0%), chromium (% by weight) Cr): 5% or less (excluding 0%), silicon (Si): 1.0% or less (excluding 0%), aluminum (Al): 0.5% or less (excluding 0%), phosphorus (P ): 0.1% or less (including 0%), sulfur (S): 0.02% or less (including 0%), and the balance consists of iron (Fe) and other unavoidable impurities. In addition, the present invention provides an austenitic steel material comprising 5% or less of a carbide and a residual austenite structure in which the size of a surface defect is 0.3 mm or less and excellent in surface characteristics, and a method for producing the same. [Selection diagram] Fig. 1

Description

  The present invention relates to abrasion resistance used in mining, transportation, and storage fields in the oil and gas industry (oil and gas industries) such as industrial machines, structural materials, and steel materials for slurry pipes and sour steel materials. The present invention relates to an excellent austenitic steel material and a method for producing the same, and more particularly, to an austenitic steel material having excellent surface properties such as excellent wear resistance, toughness, and corrosion resistance in addition to ductility, and a method for producing the same.

  Austenitic steel materials are used in various applications due to their properties such as work hardening ability and non-magnetism. In particular, carbon steels having a main structure of ferrite or martensite, which have been mainly used in the past, show a limit in their properties, and their application as a substitute material for overcoming those disadvantages tends to increase.

  In particular, with the growth of the mining and oil and gas industries (Oil and Gas Industries), wear of steel materials used in mining, transportation, refining, and storage processes has emerged as a major problem. In particular, due to the recent development of oil sands as a fossil fuel that replaces oil, the wear of steel materials due to slurries containing oil, gravel, sand, etc. increases production costs. It is pointed out as an important cause. As a result, the need for the development and application of steel materials having excellent wear resistance and toughness has greatly increased.

  Therefore, since Hadfield steel has excellent wear resistance, it is widely used as wear-resistant parts in various industries. In order to enhance the wear resistance of steel materials, a high content of carbon is required. Efforts have been steadily made to increase the austenitic structure and wear resistance by including or by including manganese in large amounts.

  However, the high carbon content of Hadfield steel causes the formation of network-like carbides at high temperatures along the austenite grain boundaries, which sharply reduces the properties of the steel, especially the ductility. In order to suppress such network-like carbide precipitation, there has been proposed a method of producing a high manganese steel by heat treatment or solution treatment at a high temperature and quenching to a room temperature after hot working.

  However, Hadfield steel has excellent wear resistance in general mechanical wear environments, but it is difficult to exhibit excellent wear resistance in environments with corrosive wear, and severe harshness in which complex wear occurs There is no way to apply it to an unusual environment.

  Recently, austenitic wear-resistant steels that also ensure corrosion resistance have been developed in consideration of such points. However, in austenitic wear-resistant steels having a very high carbon content, toughness degradation due to carbide precipitation has always been a problem. Incidentally, segregation due to alloy elements such as manganese and carbon is inevitably generated in the ingot or slab of high manganese steel during solidification. This worsens during post-processing such as hot rolling, and as a result, in the final product, partial precipitation of carbides occurs in a network along the segregation zone, eventually promoting non-uniform microstructure. Results in deterioration of physical properties. Therefore, studies have been conducted on austenitic wear-resistant steels mainly to prevent physical property deterioration due to carbide precipitation.

  Another problem is uneven oxidation occurring on the surface. Such non-uniform oxidation particularly occurs along grain boundaries, induces cracks in a slab reheating process, causes cracks to grow in a rolling process in which stress is generated, and deteriorates surface properties of a final product. Cracks generated on the surface may act as a cause of premature fracture during product bending or tensile processing, and may reduce wear resistance performance.

Korean Published Patent Application No. 2010-0106649

  An object of the present invention is to provide an austenitic steel material which suppresses non-uniform oxidation and has improved surface quality and excellent surface characteristics.

  Another object of the present invention is to provide a method for producing an austenitic steel material having excellent surface characteristics, which suppresses uneven oxidation and improves surface quality.

  According to a preferred aspect of the present invention, by weight%, carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22%, copper (Cu): 5% or less (excluding 0%) ), Chromium (Cr): 5% or less (excluding 0%), silicon (Si): 1.0% or less (excluding 0%), aluminum (Al): 0.5% or less (excluding 0%) , Phosphorus (P): 0.1% or less (including 0%), Sulfur (S): 0.02% or less (including 0%), the balance being iron (Fe) and other unavoidable impurities. Provided is an austenitic steel material having a surface area of 5% or less of carbide and a residual austenite structure, and having a surface defect size of 0.3 mm or less and excellent in surface properties.

  According to another preferable aspect of the present invention, carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22%, and copper (Cu): 5% or less (0%) ), Chromium (Cr): 5% or less (excluding 0%), silicon (Si): 1.0% or less (excluding 0%), aluminum (Al): 0.5% or less (0% Excluding), phosphorus (P): 0.1% or less (including 0%), sulfur (S): 0.02% or less (including 0%), and the balance consists of iron (Fe) and other unavoidable impurities A slab reheating step of reheating the steel slab at 1000 ° C. or more and 1150 ° C. or less, and a hot rolling step of hot rolling the reheated slab at 850 to 950 ° C. to obtain a hot rolled steel material And a cooling step of cooling the hot-rolled steel material to 600 ° C. or less at a cooling rate of 5 ° C./s or more. Excellent production method for austenitic steel material is provided.

  According to the present invention, it is possible to provide an austenitic steel material having excellent surface properties.

  As a result, it has excellent abrasion resistance, so it can be applied to areas where abrasion resistance is required in the mining, transport, storage or industrial machinery fields where a large amount of abrasion occurs in the oil and gas industry. In particular, the application range is expanded to fields requiring beautiful surface quality, and the need for repairing the product surface is reduced in terms of steel material production, so that productivity and efficiency are expected to be improved.

It is the photograph which image | photographed the structure of invention steel 3 and comparative steel 5.

  The present inventors have studied steel materials having superior strength and wear resistance as compared with conventional steel materials used in the technical field where wear resistance is required. In addition to ensuring excellent strength and elongation peculiar to steel materials, when the work hardening rate is improved, the hardness of the material itself becomes higher due to work hardening of the material itself in a wear resistant environment, ensuring excellent wear resistance And found that the present invention was completed based on this.

  In addition, in order to improve the inferior surface characteristics, which is a problem of conventional austenitic wear-resistant steel materials, by deriving conditions for reheating the slab before hot rolling to suppress non-uniform oxidation, wear resistance is improved. In addition, it was confirmed that a wear-resistant steel having excellent surface characteristics can be manufactured.

  Hereinafter, an austenitic steel material having excellent surface characteristics according to a preferred aspect of the present invention will be described.

  An austenitic steel material having excellent surface properties according to a preferred aspect of the present invention is, by weight%, carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22%, and copper (Cu): 5% or less (except 0%), chromium (Cr): 5% or less (except 0%), silicon (Si): 1.0% or less (except 0%), aluminum (Al): 0.5 % (Excluding 0%), phosphorus (P): 0.1% or less (including 0%), sulfur (S): 0.02% or less (including 0%), and the balance is iron (Fe). It consists of other unavoidable impurities, the fine structure is 5% or less in area% of carbides and the rest is an austenitic structure, and the size of surface defects is 0.3 mm or less.

  First, steel components and component ranges will be described.

C: 0.6 to 1.3% by weight (hereinafter referred to as "%")
Carbon (C), while being an austenite stabilizing element, not only plays a role of improving uniform elongation, but is also an extremely advantageous element for improving strength and increasing the work hardening rate. When the carbon content is less than 0.6%, it is difficult to form stable austenite at room temperature, and it is difficult to secure sufficient strength and work hardening rate. On the other hand, if the content of C exceeds 1.3%, a large amount of carbides precipitate and reduce uniform elongation, which may make it difficult to secure excellent elongation, resulting in a decrease in wear resistance. And premature rupture. In order to improve the wear resistance, it is advantageous to increase the carbon content as much as possible. However, since there is a limit in the solid solution of carbon and the physical properties may be deteriorated, the upper limit of C is set to 1.3%. It is preferred to limit to Therefore, it is preferable to limit the content of C to 0.6 to 1.3%. A more preferred C content is 0.6 to 1.25%.

Mn: 14-22%
Manganese (Mn) is a very important element that plays a role in stabilizing austenite, and improves uniform elongation. In the present invention, in order to obtain austenite as a main structure, it is preferable that Mn is contained by 14% or more. If the Mn content is less than 14%, the austenite stability may decrease, and a martensite structure may be formed. Therefore, when the austenite structure cannot be sufficiently secured, it is difficult to secure sufficient uniform elongation. On the other hand, if the Mn content exceeds 22%, not only does the production cost rise, but also problems such as a decrease in corrosion resistance due to the addition of manganese and difficulty in the production process arise. Therefore, it is preferable to limit the content of Mn to 14 to 22%.

Cu: 5% or less (excluding 0%)
Since copper (Cu) has a very low solid solubility in carbides and a slow diffusion in austenite, it is concentrated at the interface between austenite and nucleated carbides, thereby suppressing the diffusion of carbon. Effectively retards carbide growth. As a result, an effect of suppressing generation of carbides is exerted. Copper also helps improve corrosion resistance. However, if the content of Cu exceeds 5%, there is a problem that the hot workability of the steel material is reduced. Therefore, it is preferable to limit the upper limit of C to 5%. The content of copper for obtaining the above-described effect of suppressing carbide is more preferably 0.05% or more. A more preferred Cu content is 0.05 to 3.0%.

Cr: 5% or less (excluding 0%)
Chromium plays a role of increasing the strength of the steel material by being solid-dissolved in austenite up to a proper addition amount range. Chromium is also an element that improves the corrosion resistance of steel materials. However, chromium is a carbide element, and in particular, is an element that forms carbide at the austenite grain boundary to lower the toughness. Therefore, the content of chromium added in the present invention is preferably determined by paying attention to the relationship between carbon and other elements added together, and in order to prevent the formation of carbides, the content of Cr is preferably determined. Preferably, the upper limit of the amount is limited to 5%. If the Cr content exceeds 5%, it is difficult to effectively suppress the formation of chromium carbides at austenite grain boundaries, and as a result, there is a problem that impact toughness is reduced. Therefore, it is preferable to limit the chromium content to 5% or less.

Silicon (Si): 1.0% or less (excluding 0%) and Aluminum (Al): 0.5% or less (excluding 0%)
Aluminum (Al) and silicon (Si) are components included as a deoxidizing agent in a steelmaking process. In the present invention, the steel material may include aluminum (Al) and silicon (Si) within the above-mentioned limited component range.

Phosphorus (P): 0.1% or less (including 0%) and Sulfur (S): 0.02% or less (including 0%)
Phosphorus (P) and sulfur (S) are typical impurities, and may cause quality deterioration when added in a large amount. Therefore, phosphorus (P) and sulfur (S) are 0.1% or less and 0.1%, respectively. Preferably, it is limited to 02% or less.

  The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintended impurities are unavoidably mixed from the raw material or the surrounding environment, and thus cannot be excluded. Since these impurities are easily understood by those skilled in the art, those contents are not specifically mentioned in this specification.

The austenitic steel material according to a preferred aspect of the present invention has a microstructure of 5% or less in area% of carbide and a balance of austenite structure. The size of the surface defect is 0.3 mm or less. More preferably, the size of the surface defect is 0.2 mm or less.
If the content of the carbide exceeds 5%, the carbide will surround the crystal grain boundaries. As a result, the elongation and the impact toughness may be rapidly reduced.
If the size of the surface defects exceeds 0.3 mm, the generated surface cracks propagate during additional processing, causing early fracture, or hindering guaranteeing the target thickness of the final product. There's a problem.
Here, the size of the surface defect can be defined as, for example, a length from a point when cracks start to occur to a point where the crack stops.

  Hereinafter, a method for producing an austenitic steel material having excellent surface properties according to another preferred aspect of the present invention will be described.

  According to another preferred aspect of the present invention, a method for producing an austenitic steel material having excellent surface properties is as follows: carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22% by weight. Copper (Cu): 5% or less (excluding 0%), Chromium (Cr): 5% or less (excluding 0%), Silicon (Si): 1.0% or less (excluding 0%), Aluminum (Al ): 0.5% or less (excluding 0%), phosphorus (P): 0.1% or less (including 0%), sulfur (S): 0.02% or less (including 0%), with the balance being A slab reheating step of reheating a steel slab composed of iron (Fe) and other unavoidable impurities at a temperature of 1000 ° C. or more and 1150 ° C. or less, and a finishing rolling temperature of the reheated slab of 850 to 950 ° C. Hot rolling to obtain a hot rolled steel by hot rolling so that the hot rolled steel is 5 ° C./s or less. In a cooling rate up to 600 ° C. or less; and a cooling step of cooling.

Slab Reheating Step Before performing hot rolling, the slab is reheated at a temperature of 1000 ° C. or more and 1150 ° C. or less. At the time of hot rolling, reheating at 1000 ° C. or higher is required to secure a sufficient temperature, and it is essential to reheat at 1150 ° C. or lower to suppress uneven surface oxidation of the high Mn steel slab. .

Hot Rolling Step The slab reheated as described above is hot rolled so that the finish rolling temperature is 850 to 950 ° C. to obtain a hot rolled steel material.
If the finish rolling temperature is lower than 850 ° C., carbides may precipitate and uniform elongation may be reduced, and the microstructure may be pancaked to cause non-uniform stretching due to structural anisotropy. On the other hand, when the finish rolling temperature exceeds 950 ° C., there is a problem that it is difficult to accurately determine the target temperature in the actual process because the rolling finish temperature is too high.

Cooling Step The hot-rolled steel material obtained through the hot rolling is cooled at a rate of 5 ° C./s or more to 600 ° C. or less.
If the above cooling rate is less than 5 ° C./s or if the cooling stop temperature exceeds 600 ° C., a problem may occur that carbide is precipitated and elongation is reduced. The rapid cooling step also helps to ensure high solid solubility of the C and N elements in the matrix. Therefore, the cooling is preferably performed at a temperature of 5 ° C./s or more and 600 ° C. or less. The cooling rate preferably has a rate of 10 ° C./s or more, and more preferably has a rate of 15 ° C./s or more.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, it should be noted that the following examples are for illustrating the present invention in more detail and not for limiting the scope of the present invention. This is because the scope of rights of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

(Example)
A slab satisfying the component system and composition range as shown in Table 1 below was used to produce a hot-rolled steel sheet having a thickness of 12 mm under the reheating and rolling conditions shown in Table 2 below.
Then, the microstructure, yield strength, uniform elongation, and impact toughness of each of the manufactured hot-rolled steel sheets were measured, and the results are shown in Table 3 below. In addition, the size of the surface defect on the hot-rolled steel sheet was measured and is shown in Table 3 below.
The structures of Inventive Steel 3 and Comparative Steel 5 were observed, and the results are shown in FIG.

As shown in Tables 1 to 3, in the case of the invention steel (1-4), all the component ranges and production conditions were satisfied, and all exhibited good surface characteristics.
On the other hand, in the comparative steel (1), since C was very low, sufficient strength could not be ensured. In the comparative steel (2), carbide was increased due to the addition of a large amount of C to increase elongation and In the comparative steel (3), a stable austenite phase was not formed due to insufficient Mn content, martensite was formed, and the impact toughness was rapidly reduced. In steel (4), if the content of Cr is exceeded, carbides are excessively formed, and the elongation and impact toughness are sharply reduced. In comparative steel (5), the reheating temperature exceeds the reference value and the product surface In the comparative steel (6-8), carbides were excessively precipitated due to the conditions such as the rolling finish temperature, cooling rate, and cooling stop temperature falling outside the range of the present invention. Indicates a sharp drop in toughness
On the other hand, as shown in FIG. 1, in the case of the comparative steel (5) having a high reheating temperature, large cracks were formed on the surface, whereas in the case of the invention steel (3) to which the low reheating temperature was applied, the surface layer was large. Is uniform and no large cracks are generated.

Claims (5)

  By weight%, carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22%, copper (Cu): 5% or less (excluding 0%), chromium (Cr): 5% Or less (excluding 0%), silicon (Si): 1.0% or less (excluding 0%), aluminum (Al): 0.5% or less (excluding 0%), phosphorus (P): 0.1 % (Including 0%), sulfur (S): 0.02% or less (including 0%), and the balance is composed of iron (Fe) and other unavoidable impurities, and the fine structure is 5% in area%. An austenitic steel material comprising the following carbides and a balance of austenite and having a surface defect size of 0.3 mm or less, and having excellent surface characteristics.   The austenitic steel material having excellent surface characteristics according to claim 1, wherein the size of the surface defect is 0.2 mm or less. By weight%, carbon (C): 0.6 to 1.3%, manganese (Mn): 14 to 22%, copper (Cu): 5% or less (excluding 0%), chromium (Cr): 5% Or less (excluding 0%), silicon (Si): 1.0% or less (excluding 0%), aluminum (Al): 0.5% or less (excluding 0%), phosphorus (P): 0.1 % (Including 0%), sulfur (S): 0.02% or less (including 0%), and a balance of iron (Fe) and other unavoidable impurities. A slab reheating stage for heating;
A hot rolling step of hot rolling the reheated slab at a finish rolling temperature of 850 to 950 ° C. to obtain a hot rolled steel;
A cooling step of cooling the hot-rolled steel material to 600 ° C. or less at a cooling rate of 5 ° C./s or more, a method for producing an austenitic steel material having excellent surface characteristics.   4. The method of claim 3, wherein a cooling rate at the time of cooling is 15 ° C./s or more in the cooling step. 5. 4. The surface characteristic according to claim 3, wherein the steel material has a microstructure of 5% or less in area% of a carbide and a residual austenite structure, and a size of a surface defect is 0.3 mm or less. 5. Excellent austenitic steel manufacturing method.