WO2018117678A1 - Austenite steel material having superb surface characteristic, and method for producing same - Google Patents

Abstract

The present invention relates to abrasion-resistant austenite steel material having superb surface characteristic, and a method for producing the abrasion-resistant austenite steel material. Provided are austenite steel material having superb surface characteristic, and a method for producing same, the austenite steel material according to the present invention comprising, in weight %: 0.6-1.3% carbon (C); 14-22% manganese (Mn); 5% or lower (excluding 0%) copper (Cu); 5% or lower (excluding 0%) chromium (Cr); 1.0% or lower (excluding 0%) silicon (Si); 0.5% or lower (excluding 0%) aluminum (Al); 0.1% or lower (including 0%) phosphorous (P); 0.02% or lower (including 0%) sulfur (S); and remainder in iron (Fe) and other unavoidable impurities, and having the microstructure comprising, by surface area %, 5% or lower carbide and the rest in austenite structure, and surface flaw size of 0.3mm or lower.

Description

Austenitic steels with excellent surface properties and manufacturing method

INDUSTRIAL APPLICABILITY The present invention provides an austenitic steel having excellent abrasion resistance for use in mining, transportation, and storage in oil and gas industries, such as industrial machinery, structural materials, steel for slurry pipes, and sour steels. In more detail, the present invention relates to an austenitic steel having excellent surface properties having excellent wear resistance, toughness, corrosion resistance, and the like, and a manufacturing method thereof.

Austenitic steels are used for various purposes due to their properties such as work hardening and nonmagnetic properties. Particularly, as carbon steel mainly composed of ferrite or martensite, which is mainly used, exhibits limitations in its characteristics, its application is increasing as an alternative material to overcome these disadvantages.

In particular, with the growth of the mining industry, oil and gas industries (Oil and Gas Industries), wear of the steel used in the mining, transportation, refining and storage process is a major problem. In particular, with the recent development of oil sands as a fossil fuel to replace petroleum, steel wear caused by slurries containing oil, gravel, sand, etc. has been pointed out as an important cause of an increase in production costs. Accordingly, the demand for the development and application of steel with excellent wear resistance and toughness is greatly increased.

Hadfield steel has been widely used as a wear-resistant component in various industries for its excellent wear resistance, and efforts to increase austenite structure and abrasion resistance by containing a high amount of carbon and containing a large amount of manganese have been made to increase wear resistance of steel materials. It has been a steady progress.

However, the high carbon content of the headfield steel produces network-shaped carbides along the austenite grain boundaries at high temperatures, which drastically lowers the properties, particularly ductility, of the steels. In order to suppress such precipitation of carbides in the network type, a method of manufacturing high manganese steel by quenching heat treatment or solution treatment at high temperature and quenching to room temperature after hot working has been proposed.

However, the hard field steel has excellent wear resistance in general mechanical wear environments, but it is difficult to show excellent wear resistance in environments accompanied with corrosion wear, and thus it is difficult to apply to harsh environments where complex wear occurs.

Recently, in view of this point, austenitic wear resistant steels have been developed to secure corrosion resistance. However, toughness deterioration due to carbide precipitation is always a problem in austenitic wear resistant steels having a very high carbon content, and ingot or cast steel of high manganese steel inevitably segregates due to alloying elements such as manganese and carbon during solidification. This is further worsened during post-processing such as hot rolling, which eventually results in partial precipitation of carbides along the segregation zone in the final product in the form of a network, which in turn promotes non-uniformity of microstructure and deteriorates physical properties. Therefore, in the austenitic wear-resistant steel, research has been mainly made to prevent physical deterioration due to carbide precipitation.

Another problem is the non-uniform oxidation that occurs on the surface, and this non-uniform oxidation occurs especially along the grain boundaries, causing cracks in the slab reheating process, growing cracks in the stress rolling process, and improving the surface characteristics of the final product. Makes you inferior Cracks on the surface can cause premature fractures during product bending or tensioning, and can reduce wear resistance.

(Prior art document)

(Patent Document 1) Korean Patent Publication No. 2010-0106649

One preferred aspect of the present invention is to provide an austenitic steel having excellent surface properties by suppressing heterogeneous oxidation to improve surface quality.

Another preferred aspect of the present invention is to provide a method for producing an austenitic steel having excellent surface properties by improving the surface quality by inhibiting heterogeneous oxidation.

According to a preferred aspect of the present invention, in weight%, carbon (C): 0.6-1.3%, manganese (Mn): 14-22%, 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 (0% ), Sulfur (S): less than 0.02% (including 0%), containing the remaining iron (Fe) and other unavoidable impurities; the microstructure consists of% by area, less than 5% of carbide and residual austenite tissue Austenitic steels having excellent surface properties having a surface defect size of 0.3 mm or less are provided.

According to another preferred aspect of the present invention, in weight%, carbon (C): 0.6-1.3%, manganese (Mn): 14-22%, 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 (0 %), Sulfur (S): 0.02% or less (including 0%), the slab reheating step of reheating the steel slab containing the remaining iron (Fe) and other unavoidable impurities at 1000 ℃ to 1150 ℃;

A hot rolling step of hot rolling the heated slab under a finish rolling temperature of 850 to 950 ° C. to obtain a hot rolled steel; And

Provided is a method for producing an austenitic steel having excellent surface properties including a cooling step of cooling the hot rolled steel to 600 ° C or lower at a cooling rate of 5 ° C / s or more.

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

Through this, it can be applied to the fields where mining, transportation, storage, or general industrial machinery needs abrasion resistance in the oil and gas industry where abrasion occurs due to its excellent abrasion resistance. In terms of steel production, it is expected to increase productivity and efficiency by reducing product surface maintenance.

1 is a photograph of the tissue of invention steel 3 and comparative steel 5 .

The inventors of the present invention while studying the steel having excellent strength and wear resistance compared to the existing steel used in the technical field requiring wear resistance, in the case of high manganese steel can not only secure the excellent strength and elongation peculiar to the austenitic steel, In the case of improving the work hardening rate, the work hardening of the material itself in the abrasion environment, the hardness is rather high, thereby recognizing that excellent wear resistance can be obtained, and thus, the present invention has been completed.

In addition, in order to improve the thermal surface properties, which is a problem of the conventional austenitic wear-resistant steels, the wear-resistant steel having excellent surface properties as well as wear resistance by deriving the reheating conditions of the slab before hot rolling to suppress heterogeneous oxidation. It has been recognized that can be prepared.

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

Austenitic steels having excellent surface properties according to a preferred aspect of the present invention, in weight%, carbon (C): 0.6-1.3%, manganese (Mn): 14-22%, 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): less than 0.1% (including 0%), sulfur (S): less than 0.02% (including 0%), containing the remaining iron (Fe) and other unavoidable impurities; It is composed of carbide and residual austenite structure, and the surface defect size is less than 0.3mm.

First, the steel component and the component range will be described.

C: 0.6 to 1.3% by weight (hereinafter referred to as "%")

Carbon (C) is an austenite stabilizing element that not only plays a role of improving the uniform elongation, but is also an element that is very advantageous for improving the strength and the work hardening rate. If the carbon content is less than 0.6%, it may be difficult to form stable austenite at room temperature, and it may be difficult to secure sufficient strength and work hardening rate. On the other hand, when the content exceeds 1.3%, carbides are precipitated in large quantities, thereby reducing the uniform elongation, which may make it difficult to obtain excellent elongation, leading to abrasion resistance decline and premature fracture. In order to increase the wear resistance, it is advantageous to increase the carbon content as much as possible, but there is a limit to the solid solution of carbon, and there is a concern about deterioration of the physical properties, so it is preferable to limit the upper limit to 1.3%.

Therefore, the C content is preferably limited to 0.6 to 1.3%.

More preferred content of C may be 0.6 to 1.25%.

Mn: 14-22%

Manganese (Mn) is a very important element that plays a role of stabilizing austenite, and improves uniform elongation. In the present invention, in order to obtain austenite as the main tissue, it is preferable that Mn is included in 14% or more.

If the Mn content is less than 14%, the austenite stability may be lowered to form martensite structure, which may make it difficult to secure sufficient uniform elongation if the austenite structure is not sufficiently secured. On the other hand, if the content exceeds 22%, not only the manufacturing cost increases, but also there are problems such as deterioration of corrosion resistance due to manganese addition and difficulty in manufacturing process.

Therefore, the Mn content is preferably limited to 14-22%.

Cu: 5% or less (except 0%)

Cu (copper) is concentrated in the austenite and nucleated carbide interface due to its very low solubility in carbides and slow diffusion in austenite, which effectively slows the growth of carbides by impeding the diffusion of carbon, eventually leading to carbide production. It has a suppressing effect. In addition, copper also helps to improve corrosion resistance. However, when the content of Cu exceeds 5%, there is a problem of lowering the hot workability of the steel, the upper limit is preferably limited to 5%. As for the content of copper for obtaining the above-mentioned carbide suppression effect, it is more preferable that it is 0.05% or more.

Even more preferred content of Cu may be 0.05-3.0%.

Cr: 5% or less (except 0%)

Chromium is dissolved in austenite up to the range of the proper amount of addition, and serves to increase the strength of the steel. Chromium is also an element that improves the corrosion resistance of steels. However, chromium is a carbide element, in particular, an element that reduces the toughness by forming carbide at the austenite grain boundary. Therefore, it is preferable to determine the content of chromium added in the present invention paying attention to the relationship between carbon and other elements added together, and in order to prevent carbide formation, the upper limit of the Cr content is preferably limited to 5%. . When the Cr content exceeds 5%, it is difficult to effectively suppress the formation of chromium carbide at the austenite grain boundary, and thus there is a problem that the impact toughness is reduced. Therefore, the chromium content is preferably limited to 5% or less.

Silicon (Si): 1.0% or less (excluding 0%), Aluminum (Al): 0.5% or less (excluding 0%)

Aluminum (Al), silicon (Si) is a component included as a deoxidizer during the steelmaking process, the steel material of the present invention may include aluminum (Al), silicon (Si) within the above limited component range.

Phosphorus (P): 0.1% or less (including 0%), Sulfur (S): 0.02% or less (including 0%)

Phosphorus (P) and sulfur (S) are representative impurities, and it is preferable to limit the phosphorus (P) to 0.1% or less and sulfur (S) to 0.02% or less because they may cause quality deterioration when excessively added.

The remaining components of the present invention are iron (Fe) and other unavoidable impurities. However, in the conventional steel manufacturing process, impurities that are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded.

Since these impurities are known to those skilled in the art of ordinary steel manufacturing, not all of them are specifically mentioned herein.

The austenitic steel according to one preferred aspect of the present invention has a microstructure consisting of carbide and residual austenite structure of 5% or less in area%, and the size of surface defects is 0.3 mm or less. More preferably, the size of the surface defects is 0.2 mm or less.

When the content of the carbide exceeds 5%, the carbide surrounds the grain boundary, which may cause the elongation and impact toughness to drop sharply.

If the size of the surface defects exceeds 0.3mm, there is a problem in that the generated surface cracks propagate during further processing to cause premature failure or to guarantee a target final product thickness.

The size of the surface defects presented can be defined as, for example, the length from the point where the crack starts to the point where it stops.

Hereinafter, a method for producing an austenitic steel 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 having excellent surface properties 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% or less (except 0%) Phosphorus (P): 0.1% or less (including 0%), Sulfur (S): 0.02% or less (including 0%), steel slab containing the remaining iron (Fe) and other unavoidable impurities Reheating slab in the reheating step;

Hot rolling to obtain a hot rolled steel by hot rolling the heated slab to a finish rolling temperature of 850 to 950 ° C .; And

It comprises a cooling step of cooling the hot rolled steel to 600 ° C or less at a cooling rate of 5 ° C / s or more.

Slab reheating stage

Prior to hot rolling, the slabs are reheated at 1000 ° C. to 1150 ° C. It is necessary to reheat above 1000 ℃ to secure sufficient temperature during hot rolling, and to reheat below 1150 ℃ to suppress the surface uneven oxidation of high Mn steel slab.

Hot rolling stage

The slab reheated as above is hot rolled to obtain a finish rolling temperature of 850 to 950 ° C. to obtain a hot rolled steel.

When the finish rolling temperature is less than 850 ℃ the carbide may be precipitated to reduce the uniform elongation, the microstructure is pancake may cause uneven stretching due to the anisotropy of the tissue. Meanwhile, When the finish rolling temperature exceeds 950 ° C., the rolling finish temperature is too high, and it is difficult to hit the target temperature in actual process.

Cooling stage

The hot rolled steel obtained through the hot rolling is cooled to 600 ° C. or less at 5 ° C./s or more.

If the cooling rate is less than 5 ℃ / s, or the cooling stop temperature exceeds 600 ℃ may cause a problem that the carbide is precipitated elongation is lowered. Rapid cooling also helps to ensure high solubility of the C and N elements in the matrix. Therefore, the cooling is preferably carried out to 5 ℃ / s or more to 600 ℃ or less. The cooling rate is more preferably at a rate of 10 ° C / s or more, and even more preferably at a rate of 15 ° C / s or more.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it should be noted that the following embodiments are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

(Example)

The slab satisfying the component system and composition range as shown in Table 1 was prepared as a hot rolled steel sheet having a thickness of 12mm through the reheating and rolling conditions shown in Table 2.

Then, the microstructure, yield strength, uniform elongation, impact toughness of each of the prepared hot-rolled steel sheet was measured, and the results are shown in Table 3 below. In addition, by measuring the size of the surface defects for the hot-rolled steel sheet is shown in Table 3 together.

Tissues were observed for Inventive Steel 3 and Comparative Steel 5, and the results are shown in FIG. 1.

division	Ingredient composition (% by weight)
	C	Mn	Si	Al	Cr	Cu	P	S
Inventive Steel 1	0.64	16.9	0.08	0.057	4.7	1.5	0.022	0.009
Inventive Steel 2	0.81	18.1	0.014	0.119	2.5	1.3	0.023	0.006
Inventive Steel 3	1.09	21.5	0.31	0.041	3.3	0.06	0.016	0.004
Inventive Steel 4	1.22	14.7	0.091	0.262	0.09	0.35	0.012	0.016
Comparative Steel 1	0.33	15.2	0.017	0.08	0.023	0.025	0.013	0.007
Comparative Steel 2	1.35	15.8	0.098	0.044	0.11	0.1	0.017	0.005
Comparative Steel 3	0.65	12.2	0.046	0.041	0.22	0.15	0.013	0.003
Comparative Steel 4	1.11	18.6	0.16	0.076	5.8	0.09	0.018	0.009
Comparative Steel 5	1.23	19.1	0.15	0.08	1.1	0.09	0.015	0.006
Comparative Steel 6	0.64	16.4	0.11	0.041	1.8	0.9	0.017	0.008
Comparative Steel 7	0.61	18.3	0.11	0.045	1.8	0.9	0.014	0.005
Comparative Steel 8	0.75	17.6	0.11	0.041	1.8	0.9	0.017	0.008

division	Reheating and Rolling Conditions
	Furnace temperature (℃)	Finish rolling temperature (℃)	Cooling rate (℃ / s)	Cooling stop temperature (℃)
Inventive Steel 1	1145	940	26	385
Inventive Steel 2	1108	915	16	200
Inventive Steel 3	1056	901	32	475
Inventive Steel 4	1023	869	41	275
Comparative Steel 1	1110	876	22	495
Comparative Steel 2	1125	899	19	425
Comparative Steel 3	1130	920	27	355
Comparative Steel 4	1134	925	19	375
Comparative Steel 5	1231	925	19	375
Comparative Steel 6	1105	825	25	390
Comparative Steel 7	1140	912	3.5	435
Comparative Steel 8	1125	947	23	670

division	Microstructure (γ: austenite)	Size of surface defects (mm)	Yield strength (MPa)	Elongation (%)	Impact Toughness (J @ -40 ℃)
Inventive Steel 1	γ + Carbide 5% or less	0.24mm or less	453	50	199
Inventive Steel 2	γ + Carbide 5% or less	0.11mm or less	411	60	227
Inventive Steel 3	γ + Carbide 5% or less	0.05mm or less	500	53	208
Inventive Steel 4	γ + Carbide 5% or less	0.13mm or less	523	47	116
Comparative Steel 1	γ + Carbide 5% or less	-	270	48	87
Comparative Steel 2	γ + carbide 9.1%	-	581	19	27
Comparative Steel 3	γ + martensite	-	380	33	19
Comparative Steel 4	γ + carbides 11.8%	-	607	17	22
Comparative Steel 5	γ + Carbide 5% or less	More than 0.3mm	564	31	121
Comparative Steel 6	γ + carbide 6.1%	-	420	36	42
Comparative Steel 7	γ + carbide 6.9%	-	431	53	33
Comparative Steel 8	γ + carbide 7.2%	-	520	43	29

As shown in Tables 1 to 3, the invention steel (1-4) satisfies both the component range and the manufacturing conditions, the invention steel (1-4) all show good surface properties.

On the other hand, the comparative steel (1) shows that C is very low and thus does not secure sufficient strength.

Comparative steel (2) shows that carbides increase due to excessive C addition, and elongation and impact toughness drop sharply.

In the case of the comparative steel (3), due to the lack of Mn content, a stable austenite phase is not formed, and martensite is formed, indicating that the impact toughness drops sharply.

Comparative steel (4) shows that the elongation and impact toughness plummet due to excessive carbide formation when the Cr content is exceeded.

Comparative steel 5 shows that a large defect occurred on the surface of the product because the reheating temperature exceeded the reference value.

Comparative steel 6-8 shows that the toughness of the rolling finish temperature, cooling rate, cooling stop temperature, etc. falls outside the scope of the present invention and the impact toughness drops sharply due to excessive precipitation of carbides.

On the other hand, as shown in Figure 1, the comparative steel (5) having a high reheating temperature has a large crack formed on the surface, in the case of the invention steel (3) to which the low temperature reheating temperature is applied, the surface layer is uniform, there is no large crack can confirm.

Claims (5)

1. By weight, carbon (C): 0.6-1.3%, manganese (Mn): 14-22%, 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 It contains less than% (including 0%), the remaining iron (Fe) and other unavoidable impurities, the microstructure consists of% by area, less than 5% of carbide and residual austenite structure, and the surface defect size is 0.3 mm or less. Austenitic steel with excellent surface properties.
2. The austenitic steel according to claim 1, wherein the austenitic steel having excellent surface properties having a surface defect size of 0.2 mm or less.
3. By weight, carbon (C): 0.6-1.3%, manganese (Mn): 14-22%, 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 A slab reheating step of reheating the steel slab containing% or less (including 0%) and the remaining iron (Fe) and other unavoidable impurities at 1000 ° C or more and 1150 ° C or less;

   A hot rolling step of hot rolling the heated slab under a finish rolling temperature of 850 to 950 ° C. to obtain a hot rolled steel; And

   A method for producing an austenitic steel having excellent surface properties including a cooling step of cooling the hot rolled steel to 600 ° C or lower at a cooling rate of 5 ° C / s or more.
4. The method of claim 3, wherein the cooling rate is 15 ° C./s or more during cooling in the cooling step. 5.
5. The method according to claim 3, wherein the microstructure of the steel is an area%, including 5% or less of carbide and residual austenite structure, and having excellent surface properties with a surface defect size of 0.3 mm or less.

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