High-hardness wear-resistant steel with excellent low-temperature impact toughness and manufacturing method thereof

Abstract

The purpose of the present invention is to provide a wear-resistant steel having wear resistance, high impact toughness at low temperature, and high hardness, and a method for manufacturing the same.

Description

[0001] This application is a divisional application of the application with the filing date of December 1, 2020, application number 202080081443.1, and invention title "High-hardness wear-resistant steel with excellent low-temperature impact toughness and its manufacturing method" (PCT / KR2020 / 017372, the date of entry into the national phase is May 24, 2022). Technical Field

[0002] The present invention relates to a material applicable to construction machinery and the like. More specifically, the present invention relates to a wear-resistant steel having excellent low-temperature impact toughness and high hardness, and a manufacturing method thereof. Background Art

[0003] Industrial machinery such as bulldozers and power shovels, mining equipment such as crushers or chutes, and large dump trucks require light weight and high performance, so wear-resistant steel is used in easily worn parts.

[0004] In particular, in order to extend the service life of these parts, the wear-resistant steel used gradually shows a trend of high hardness. Due to concerns about defects such as cracks caused by high hardness, high toughness is also required.

[0005] On the other hand, high-hardness wear-resistant steel with excellent toughness is also widely used as bulletproof steel.

[0006] Currently, the following technologies have been proposed for wear-resistant steel used in industrial machinery or construction machinery.

[0007] Patent Document 1 discloses the manufacture of a steel containing C, Si, Mn, and a certain amount of Ti, B, etc. For a steel plate with restricted H content, the cooling end temperature during reheat quenching is restricted to 300°C or lower, thereby having excellent soundness and a Brinell hardness of 450 or lower.

[0008] Patent Document 2 discloses the reheat quenching of a steel plate to manufacture a steel of Brinell hardness grade 500. In addition to C, Si, and Mn, the steel plate contains Cr, Mo, and B.

[0009] In addition, Patent Document 3 discloses a steel of Brinell hardness grade 500 with excellent low-temperature toughness, which can be manufactured by the following process: restricting the contents of C, Si, Mn, Cr, Mo, Ti, Nb, B, etc. in the steel, adding Cu, Ni, V, Ca, etc. as needed, cooling to 100°C or lower after hot rolling, and performing continuous tempering treatment.

[0010] In addition, Patent Document 4 discloses a special steel with high elasticity and high strength. Quenching and tempering treatment is performed on a steel appropriately containing a low content of C, a high content of Si, and other elements, thereby ensuring impact resistance and wear resistance.

[0011] However, Patent Document 1 cannot meet the hardness level required by the actual environment. Although Patent Document 2 meets the hardness level, it has poor toughness. Patent Document 3 contains a large amount of expensive elements, which is economically disadvantageous and its application is restricted. In the case of Patent Document 4, it is difficult to ensure low-temperature toughness and the manufacturing cost is still high.

[0012] Therefore, it is necessary to develop wear-resistant steel with excellent low-temperature toughness and wear resistance through an economical method that does not contain a large amount of expensive elements.

[0013] Patent Document 1: Japanese Patent Publication Gazette 1989-010564B2

[0014] Patent Document 2: Japanese Patent Publication Gazette 1989-021846B2

[0015] Patent Document 3: Japanese Patent Publication Gazette 1996-041535

[0016] Patent Document 4: Korean Patent Authorization Gazette 10-0619841 Summary of the Invention

[0017] Technical Problem

[0018] One aspect of the present invention aims to provide wear-resistant steel with wear resistance, high impact toughness at low temperature, and high hardness, and a manufacturing method thereof.

[0019] The technical problems to be solved by the present invention are not limited to the above. The technical problems to be solved by the present invention can be understood based on the overall content of this specification. For those of ordinary skill in the technical field to which the present invention pertains, it will not be difficult to understand the additional technical problems of the present invention.

[0020] Technical Solution

[0021] One aspect of the present invention provides high-hardness wear-resistant steel with excellent low-temperature impact toughness. In terms of weight percentage, the wear-resistant steel contains carbon (C): 0.25 - 0.50%, silicon (Si): 1.0 - 1.6%, manganese (Mn): 0.6 - 1.6%, phosphorus (P): less than 0.05% and excluding 0%, sulfur (S): less than 0.02% and excluding 0%, aluminum (Al): less than 0.07% and excluding 0%, chromium (Cr): 0.5 - 1.5%, calcium (Ca): 0.0005 - 0.004%, nitrogen (N): less than 0.006%, and the balance is Fe and other inevitable impurities. The fine microstructure contains a martensite and bainite composite structure and a retained austenite phase with an area fraction of 2.5 - 10%.

[0022] On the other hand, the present invention provides a method for manufacturing a high-hardness wear-resistant steel with excellent low-temperature impact toughness, which includes: a step of preparing a steel billet having the above alloy components; a step of heating the steel billet in a temperature range of 1050 to 1250 °C; a step of rough rolling the heated steel billet in a temperature range of 950 to 1150 °C; a step of hot finish rolling the steel billet after rough rolling in a temperature range of 850 to 950 °C to manufacture a hot-rolled steel sheet; and a step of cooling the hot-rolled steel sheet to 200 to 400 °C at a cooling rate of 25 °C / second or more and then performing air cooling.

[0023] Advantages of the Invention

[0024] According to the present invention, a wear-resistant steel with high hardness and excellent low-temperature toughness can be provided.

[0025] In particular, by optimizing the alloy components and manufacturing conditions, the present invention can provide a wear-resistant steel with physical properties at a target level without additional heat treatment, thus having an economically advantageous effect. Brief Description of the Drawings

[0026] Figure 1 A picture showing the microstructure of the inventive steel according to an embodiment of the present invention observed with an optical microscope.

[0027] Figure 2 A picture showing the microstructure of the inventive steel according to an embodiment of the present invention detected with an electron scanning microscope (a) and EBSD (b).

[0028] Figure 3 A picture showing the microstructure of the comparative steel according to an embodiment of the present invention observed with an optical microscope.

[0029] Figure 4 A picture showing the microstructure of the comparative steel according to an embodiment of the present invention detected with an electron scanning microscope (a) and EBSD (b). Detailed Description of the Invention

[0030] The present inventors have conducted in-depth research to provide a material applicable to construction machinery, etc., which has excellent physical properties such as strength and toughness, and at the same time can ensure wear resistance, which is a key physical property requirement.

[0031] In particular, the present inventors aim to improve the wear resistance of steel by an economically advantageous method, and thus the present invention is provided.

[0032] Hereinafter, the present invention will be described in detail.

[0033] The high-hardness wear-resistant steel according to one aspect of the present invention, by weight %, the wear-resistant steel may include carbon (C): 0.25 to 0.50%, silicon (Si): 1.0 to 1.6%, manganese (Mn): 0.6 to 1.6%, phosphorus (P): less than 0.05% and excluding 0%, sulfur (S): less than 0.02% and excluding 0%, aluminum (Al): less than 0.07% and excluding 0%, chromium (Cr): 0.5 to 1.5%, calcium (Ca): 0.0005 to 0.004%, nitrogen (N): less than 0.006%.

[0034] Hereinafter, the reasons for restricting the alloy components of the wear-resistant steel provided by the present invention as described above will be described in detail.

[0035] On the other hand, unless otherwise specified in the present invention, the content of each element is based on weight, and the proportion of the structure is based on area.

[0036] Carbon (C): 0.25 to 0.50%

[0037] Carbon (C) effectively improves strength and hardness in steels with low-temperature transformation phases such as martensite or bainite, and is an effective element for improving hardenability. In order to fully obtain the above effects, C may include 0.25% or more, but when the C content is greater than 0.50%, there are problems of impairing the weldability and toughness of the steel.

[0038] Therefore, the C may include 0.25 to 0.50%.

[0039] Silicon (Si): 1.0 to 1.6%

[0040] Silicon (Si) has a deoxidizing effect and effectively improves strength based on solid solution strengthening. In high-carbon steels with a certain amount or more of C content, it inhibits the formation of carbides such as cementite, thereby promoting the formation of retained austenite.

[0041] In particular, in steels with low-temperature transformation phases such as martensite and bainite, uniformly distributed retained austenite helps to improve impact toughness without reducing strength. Therefore, in the present invention, the Si is an element beneficial to ensuring low-temperature toughness.

[0042] In order to fully obtain the above effects, Si may include 1.0% or more, but when the Si content is greater than 1.6%, there is a problem of rapid deterioration of weldability.

[0043] Therefore, the Si may include 1.0 to 1.6%, and more preferably may include 1.2% or more.

[0044] Manganese (Mn): 0.6 to 1.6%

[0045] Manganese (Mn) inhibits the formation of ferrite and reduces the Ar3 temperature, thereby improving the hardenability of steel and is an element beneficial to improving strength and toughness.

[0046] In the present invention, in order to obtain the target hardness, the Mn may contain 0.6% or more. However, when the Mn content is greater than 1.6%, there are problems such as a decrease in weldability and an increase in center segregation, resulting in a decrease in the properties of the center part of the steel.

[0047] Therefore, the Mn may contain 0.6 to 1.6%.

[0048] Phosphorus (P): 0.05% or less, excluding 0%

[0049] Phosphorus (P) is an element inevitably contained in steel and is an element that impairs the toughness of steel. Therefore, it is preferable to reduce the content of the P as much as possible.

[0050] In the present invention, even if the P contains up to 0.05%, it will not have a great impact on the properties of the steel, and the content of the P can be limited to 0.05% or less. More preferably, it can be limited to 0.03% or less. However, considering the inevitable content, 0% can be excluded.

[0051] Sulfur (S): 0.02% or less, excluding 0%

[0052] Sulfur (S) combines with Mn in steel to form MnS inclusions and is an element that impairs the toughness of steel. Therefore, it is preferable to reduce the content of the S as much as possible.

[0053] In the present invention, even if the S contains up to 0.02%, it will not have a great impact on the properties of the steel, and the content of the S can be limited to 0.02% or less. More preferably, it can be limited to 0.01% or less. However, considering the inevitable content, 0% can be excluded.

[0054] Aluminum (Al): 0.07% or less, excluding 0%

[0055] Aluminum (Al), as a deoxidizer for steel, is an element that effectively reduces the oxygen content in molten steel. When the content of Al is greater than 0.07%, there is a problem of impairing the cleanliness of the steel.

[0056] Therefore, the Al may contain 0.07% or less. However, if the content of the Al is too low, a load will be generated in the steelmaking process and the manufacturing cost will increase. Considering this, 0% can be excluded.

[0057] Chromium (Cr): 0.5 to 1.5%

[0058] Chromium (Cr) increases the hardenability of steel and thus enhances its strength, which is beneficial for ensuring the hardness of both the surface and the core of the steel. Such Cr is a relatively inexpensive element. To utilize Cr to ensure high hardness and high toughness of the steel, Cr can be contained in an amount of 0.5% or more. However, when the Cr content is greater than 1.5%, there is a problem of deteriorated weldability of the steel.

[0059] Therefore, the Cr can be contained in an amount of 0.5 - 1.5%, and more preferably in an amount of 0.65% or more.

[0060] Calcium (Ca): 0.0005 - 0.004%

[0061] Calcium (Ca) has a good binding force with sulfur (S). Therefore, CaS is formed around MnS, thereby inhibiting the extension of MnS, which is beneficial for improving the toughness in the direction perpendicular to the rolling direction. In addition, CaS formed by adding the above-mentioned Ca has the effect of improving corrosion resistance in a humid external environment.

[0062] To fully obtain the above effects, Ca can be contained in an amount of 0.0005% or more. However, when the Ca content is greater than 0.004%, there is a problem of defects such as nozzle clogging during steelmaking operations.

[0063] Therefore, the Ca can be contained in an amount of 0.0005 - 0.004%.

[0064] Nitrogen (N): 0.006% or less

[0065] Nitrogen (N) forms precipitates in the steel, which is beneficial for increasing the strength of the steel. However, when the nitrogen content is greater than 0.006%, there is instead a problem of decreased toughness of the steel.

[0066] In the present invention, even if the above-mentioned N is not contained, it will not affect the ensuring of strength. Therefore, the N can be contained in an amount of 0.006% or less. However, considering the inevitable content, 0% can be excluded.

[0067] In addition to the above alloy components, the wear-resistant steel of the present invention may further contain the following elements to be beneficial for ensuring the target performance.

[0068] Specifically, the wear-resistant steel may further contain one or more elements selected from nickel (Ni), molybdenum (Mo), titanium (Ti), boron (B), and vanadium (V).

[0069] Nickel (Ni): 0.01 - 0.5%

[0070] Nickel (Ni) is an element that is beneficial for simultaneously increasing the strength and toughness of the steel. For this purpose, Ni can be contained in an amount of 0.01% or more. However, since Ni is an expensive element, when the Ni content is greater than 0.5%, there is a problem of a significant increase in manufacturing cost.

[0071] Therefore, when containing the said Ni, it may contain 0.01 - 0.5%.

[0072] Molybdenum (Mo): 0.01 - 0.3%

[0073] Molybdenum (Mo) is an element that increases the hardenability of steel, especially an element that is beneficial to improving the hardness of thick steel with a thickness of a certain amount or more. In order to fully obtain the above effects, Mo may contain 0.01% or more. However, when the Mo content is greater than 0.3%, not only does the manufacturing cost increase, but the weldability also deteriorates.

[0074] Therefore, when containing the said Mo, it may contain 0.01 - 0.3% of Mo.

[0075] Titanium (Ti): 0.005 - 0.025%

[0076] Titanium (Ti) is an element that is beneficial to maximizing the effect of B. B is an element that is beneficial to improving the hardenability of steel. That is to say, the said Ti combines with N in the steel to precipitate TiN, reducing the content of dissolved N, thereby inhibiting the formation of BN by B, and further increasing the dissolved B, which can maximize the hardenability.

[0077] In order to fully obtain the above effects, Ti may contain 0.005% or more. However, when the Ti content is greater than 0.025%, coarse TiN precipitates will be formed, so there is a problem of a decrease in the toughness of the steel.

[0078] Therefore, when containing the said Ti, it may contain 0.005 - 0.025% of Ti.

[0079] Boron (B): 0.0002 - 0.005%

[0080] Boron (B) is an effective element that can effectively improve the hardenability of steel and increase the strength even when added in a small amount. In order to fully obtain such an effect, B may contain 0.0002% or more. However, when the B content is too high, there is instead a problem of damaging the toughness and weldability of the steel. Therefore, the B content can be limited to 0.005% or less.

[0081] Therefore, when containing the said B, it may contain 0.0002 - 0.005% of B. More preferably, the B content may be 0.0040% or less, even more preferably 0.0035% or less, and still more preferably 0.0030% or less.

[0082] Vanadium (V): 0.2% or less

[0083] Vanadium (V) forms VC carbides when reheated after hot rolling, thereby inhibiting the growth of austenite grains and improving the hardenability of steel, which is an element beneficial to ensuring strength and toughness. This V is a relatively expensive element. Therefore, when the V content is greater than 0.2%, there is a problem of a significant increase in manufacturing cost.

[0084] Therefore, when adding the said V, V of 0.2% or less can be included.

[0085] The balance component of the present invention is iron (Fe). However, during the conventional manufacturing process, unexpected impurities from raw materials or the surrounding environment will inevitably be mixed in, so it is impossible to exclude the mixed-in impurities. These impurities are known to anyone skilled in the art of the conventional manufacturing process, so all related content will not be elaborated in this specification.

[0086] The wear-resistant steel of the present invention having the above alloy components may have a microstructure composed of a composite structure of martensite and bainite phases.

[0087] Specifically, the wear-resistant steel of the present invention may include a composite structure of martensite and bainite phases with an area fraction of 90% or more. If their phase fractions are less than 90%, it is difficult to ensure the target strength and hardness. The martensite and bainite phases may respectively include tempered martensite and tempered bainite phases, which are described first here.

[0088] The average lath size of the above composite structure of the wear-resistant steel of the present invention is preferably 0.3 μm or less. When the average lath size of the composite structure exceeds 0.3 μm, there is a problem of a decrease in the toughness of the steel.

[0089] In addition to the above composite structure, the wear-resistant steel of the present invention may include a retained austenite phase. At this time, a retained austenite phase with an area fraction of 2.5 - 10% can be included. When the fraction of the retained austenite phase is less than 2.5%, the low-temperature impact toughness will deteriorate. On the contrary, when the fraction of the retained austenite phase is greater than 10%, there is a problem of hardness deterioration.

[0090] On the other hand, the wear-resistant steel of the present invention has the above-described tissue composition throughout the entire thickness, which is described first here.

[0091] The wear-resistant steel of the present invention having the above alloy components and the proposed microstructure may have a thickness of 5 - 40 mm. The surface hardness of this wear-resistant steel is 460 - 540 HB, having high hardness, and the impact energy absorption at -40 °C is 17 J or more, having the excellent effect of excellent low-temperature toughness.

[0092] In this article, the surface hardness refers to the hardness value detected at 2 mm - 5 mm in the thickness direction from the surface of the wear-resistant steel.

[0093] In the following, a method for manufacturing a high-hardness wear-resistant steel according to another aspect of the present invention will be described in detail.

[0094] Briefly, after preparing a steel billet that meets the aforementioned alloy components, the steel billet can be processed through the [heating - rolling - cooling] process to manufacture wear-resistant steel. The process conditions for each process will be described in detail below.

[0095] [Steel billet heating process]

[0096] First, after preparing a steel billet with the alloy components proposed in the present invention, it can be heated in the temperature range of 1050 - 1250°C.

[0097] If the temperature during the heating is lower than 1050°C, the deformation resistance of the steel will increase, and the subsequent rolling process cannot be effectively carried out. On the contrary, if the temperature is higher than 1250°C, the austenite grains will become coarse, and there may be a formation of non-uniform structures.

[0098] Therefore, the heating of the steel billet can be carried out in the temperature range of 1050 - 1250°C.

[0099] [Rolling process]

[0100] The steel billet heated as above can be rolled. At this time, a hot-rolled steel plate can be manufactured through the processes of rough rolling and hot finish rolling.

[0101] First, the heated steel billet is rough-rolled in the temperature range of 950 - 1150°C to form a rough-rolled billet (bar), and then hot finish rolling can be carried out in the temperature range of 850 - 950°C.

[0102] If the temperature during the rough rolling is lower than 950°C, the rolling load increases, and the reduction force is relatively weak. Therefore, the deformation cannot be fully transmitted to the center of the steel billet thickness direction, and as a result, defects such as voids may not be removed. On the contrary, if the temperature is higher than 1150°C, the recrystallized grain size will become too coarse, which may be unfavorable for toughness.

[0103] If the temperature during the hot finish rolling is lower than 850°C, ferrite may be generated in the fine structure due to two-phase zone rolling. On the contrary, if the temperature is higher than 950°C, the grain size of the final structure becomes coarse, and there is a problem of poor low-temperature toughness.

[0104] [Cooling process]

[0105] The hot-rolled steel plate manufactured through the above rolling process can be water-cooled to a certain temperature and then air-cooled.

[0106] Specifically, in the present invention, when the hot-rolled steel plate is cooled, it is water-cooled to a temperature range of 200 - 400°C at a cooling rate of 25°C / second or more on average, and then can be air-cooled to below 150°C, and has the effect of self-tempering during the air-cooling. That is to say, during air-cooling, tempering of martensite and bainite phases occurs, and due to the formation of a certain fraction of retained austenite phase, the toughness of the steel can be improved.

[0107] The air-cooling can be carried out to room temperature.

[0108] On the other hand, the cooling can start at a temperature above Ar3. Ar3 depends on the alloy composition system, which is known to any person skilled in the art.

[0109] If the cooling rate during the water-cooling is less than 25°C / second, a ferrite phase or the average lath size of the hard phase (martensite + bainite) will become larger during the cooling process, making it difficult to ensure high hardness. There is no particular limitation on the upper limit of the cooling rate during the water-cooling, but considering the cooling equipment, the cooling can be carried out at a maximum cooling rate of 100°C / second.

[0110] When cooling at the above cooling rate, if the cooling end temperature is lower than 200°C, the self-tempering effect is small, and it is difficult to ensure the target toughness. On the contrary, if the cooling end temperature is higher than 400°C, the average lath size of the hard phase (martensite + bainite) will become larger, and due to the decrease in strength or toughness, the target hardness or toughness cannot be ensured.

[0111] The hot-rolled steel plate obtained through the above series of manufacturing processes is a steel material with a thickness of 5 - 40 mm, and can have the characteristics of wear resistance, high hardness, and high toughness.

[0112] In particular, according to the present invention, self-tempering can be achieved in the cooling process, and subsequent tempering processes are not required, so there is an effect of manufacturing wear-resistant steel more economically.

[0113] The present invention will be described in more detail below through examples. However, the following examples are only used to describe the present invention in more detail, and the scope of rights of the present invention is not limited to the following examples. The scope of rights of the present invention is subject to the content of the claims and the content reasonably derived therefrom.

[0114] Modes of implementing the invention

[0115] (Examples)

[0116] After preparing steel billets with the alloy components shown in Table 1 below, [heating - rolling - cooling] is carried out according to the process conditions shown in Table 2 below to manufacture each hot - rolled steel plate. At this time, for the cooling, it is water - cooled to a certain temperature and then air - cooled to below 150 °C.

[0117] Then, the microstructure and mechanical properties of each hot - rolled steel plate are detected, and the results are shown in Table 3 below.

[0118] For the microstructure of each hot - rolled steel plate, the specimen is cut into any size and then polished to a mirror surface, and then etched with nitric acid etchant (Nital), and then the thickness center part at 1 / 2t is observed with an optical microscope and an electron scanning microscope (SEM). At this time, electron back - scattered diffraction (EBSD) analysis is used to detect the lath size of the martensite and bainite composite structure.

[0119] In addition, for the hardness and toughness of the hot - rolled steel plate, a Brinell hardness tester (load: 3000 kgf, 10 - mm tungsten indenter) and a Charpy impact tester are used for detection respectively. At this time, for the surface hardness, after milling 2 mm of the surface of the hot - rolled plate, it is detected 3 times and the average value is taken. For the Charpy impact test, after sampling at 1 / 4t in the thickness direction, it is detected 3 times at - 40 °C and the average value is taken.

[0120]

Table 1

[0121]

[0122]

[0123] In Table 1, P*, S*, Ca*, B*, N* are expressed in ppm.

[0124]

Table 2

[0125]

[0126]

[0127] In Table 2, the cooling start temperature of the inventive example is above Ar3.

[0128]

Table 3

[0129]

[0130] In Table 3, M represents martensite, B represents bainite, F represents ferrite, and r - γ represents the retained austenite phase.

[0131] As shown in Tables 1 to 3 above, in the case of Invention Examples 1 to 10 where the alloy components and manufacturing conditions proposed in the present invention are satisfied, the microstructure contains martensite + bainite and a certain fraction of retained austenite phase. In addition, the lath size of the martensite + bainite is all 0.3 μm or less. Thus, excellent hardness and low-temperature impact toughness can be ensured for Invention Examples 1 to 10.

[0132] In contrast, in Comparative Examples 1 to 8 where the alloy components proposed in the present invention are satisfied but the manufacturing conditions deviate from the present invention, the ferrite phase formed as the microstructure or the lath size of martensite and bainite becomes coarser, or the fraction of the austenite phase is insufficient, making it difficult to ensure excellent high hardness and low-temperature impact toughness simultaneously.

[0133] On the other hand, in Comparative Examples 9 to 11, due to insufficient C content in the steel, the hardenability is low, and too much proeutectoid ferrite phase is generated, resulting in significantly poor hardness and toughness. In addition, in Comparative Examples 12 and 13 where the C content in the steel is too high, due to insufficient fraction of the retained austenite phase, the low-temperature impact toughness is significantly poor.

[0134] In addition, in Comparative Example 14 where the contents of Si and Cr in the steel are insufficient, the formation of the retained austenite phase is insufficient, and the formation of cementite phase that is unfavorable to toughness is promoted. Therefore, although the hardness is high, the toughness is poor.

[0135] In Comparative Example 15, the contents of Si and Cr are also insufficient, and the retained austenite phase cannot be sufficiently generated, and the formation of cementite phase is promoted. Therefore, not only is the toughness poor, but also due to the excessive content of Mo, the hardenability increases, resulting in a result that the toughness is significantly lower than the standard.

[0136] Figure 1 and Figure 2 Show the microstructure pictures of Invention Example 5.

[0137] Among them, Figure 1 is a picture observed by an optical microscope, Figure 2 is a picture observed by a scanning electron microscope and EBSD. It can be confirmed that the matrix structure mainly forms martensite phase and bainite phase, and a small amount of retained austenite phase is distributed at the boundaries of the laths of martensite and bainite.

[0138] Figure 3 and Figure 4 Show the microstructure pictures of Comparative Example 6.

[0139] Among them, Figure 3 is a picture observed by an optical microscope, Figure 4 is a picture observed by a scanning electron microscope and EBSD. It can be confirmed that the matrix structure mainly forms martensite phase and bainite phase, but the formation of the retained austenite phase is very insufficient.

[0140] This application also relates to the following aspects:

[0141] 1. A high-hardness wear-resistant steel with excellent low-temperature impact toughness, wherein,

[0142] By weight percentage, the wear-resistant steel contains carbon (C): 0.25 - 0.50%, silicon (Si): 1.0 - 1.6%, manganese (Mn): 0.6 - 1.6%, phosphorus (P): below 0.05% and excluding 0%, sulfur (S): below 0.02% and excluding 0%, aluminum (Al): below 0.07% and excluding 0%, chromium (Cr): 0.5 - 1.5%, calcium (Ca): 0.0005 - 0.004%, nitrogen (N): below 0.006%, and the balance is Fe and other inevitable impurities.

[0143] The fine microstructure contains a martensite and bainite composite structure and a retained austenite phase with an area fraction of 2.5 - 10%.

[0144] 2. The high-hardness wear-resistant steel according to aspect 1, wherein,

[0145] By weight percentage, the wear-resistant steel further contains one or more elements of nickel (Ni): 0.01 - 0.5%, molybdenum (Mo): 0.01 - 0.3%, titanium (Ti): 0.005 - 0.025%, boron (B): 0.0002 - 0.005%, and vanadium (V): below 0.2%.

[0146] 3. The high-hardness wear-resistant steel according to aspect 1, wherein,

[0147] The average lath size of the martensite and bainite composite structure is below 0.3 μm.

[0148] 4. The high-hardness wear-resistant steel according to aspect 1, wherein,

[0149] The wear-resistant steel contains the martensite and bainite composite structure with an area fraction of 90% or more.

[0150] 5. The high-hardness wear-resistant steel according to aspect 1, wherein,

[0151] The surface hardness of the wear-resistant steel is 460 - 540 HB, and the impact absorption energy at -40°C is 17 J or more.

[0152] 6. The high-hardness wear-resistant steel according to aspect 1, wherein,

[0153] The wear-resistant steel has a thickness of 5 - 40 mm.

[0154] 7. A manufacturing method of a high-hardness wear-resistant steel with excellent low-temperature impact toughness, which comprises:

[0155] Steps for preparing a steel billet, by weight %, the steel billet comprising carbon (C): 0.25 - 0.50%, silicon (Si): 1.0 - 1.6%, manganese (Mn): 0.6 - 1.6%, phosphorus (P): less than 0.05% and excluding 0%, sulfur (S): less than 0.02% and excluding 0%, aluminum (Al): less than 0.07% and excluding 0%, chromium (Cr): 0.5 - 1.5%, calcium (Ca): 0.0005 - 0.004%, nitrogen (N): less than 0.006%, and the balance being Fe and other inevitable impurities;

[0156] Steps for heating the steel billet in a temperature range of 1050 - 1250 °C;

[0157] Steps for rough rolling the heated steel billet in a temperature range of 950 - 1150 °C;

[0158] Steps for hot finish rolling in a temperature range of 850 - 950 °C after the rough rolling to manufacture a hot rolled steel sheet; and

[0159] Steps for cooling the hot rolled steel sheet at a cooling rate of 25 °C / second or more to 200 - 400 °C and then performing air cooling.

[0160] 8. The manufacturing method according to aspect 7, wherein,

[0161] By weight %, the steel billet further comprises one or more elements of nickel (Ni): 0.01 - 0.5%, molybdenum (Mo): 0.01 - 0.3%, titanium (Ti): 0.005 - 0.025%, boron (B): 0.0002 - 0.005% and vanadium (V): less than 0.2%.

[0162] 9. The manufacturing method according to aspect 7, wherein,

[0163] Self - tempering occurs during the air cooling.

[0164] 10. The manufacturing method according to aspect 7, wherein,

[0165] The air cooling is carried out to 150 °C or lower.

Claims

1. A high-hardness wear-resistant steel with excellent low-temperature impact toughness, wherein, by weight percentage, the wear-resistant steel contains carbon (C): 0.25 - 0.50%, silicon (Si): 1.0 - 1.6%, manganese (Mn): 0.6 - 1.6%, phosphorus (P): below 0.05% and excluding 0%, sulfur (S): below 0.02% and excluding 0%, aluminum (Al): below 0.07% and excluding 0%, chromium (Cr): 0.5 - 1.5%, calcium (Ca): 0.0005 - 0.004%, nitrogen (N): below 0.006%, and the balance is Fe and other inevitable impurities; the fine microstructure contains a martensite and bainite composite structure and a retained austenite phase with an area fraction of 2.5 - 10%; wherein the average lath size of the martensite and bainite composite structure is 0.16 - 0.3 μm.

2. The high-hardness wear-resistant steel according to claim 1, wherein, by weight percentage, the wear-resistant steel further contains one or more elements of nickel (Ni): 0.01 - 0.5%, molybdenum (Mo): 0.01 - 0.3%, titanium (Ti): 0.005 - 0.025%, boron (B): 0.0002 - 0.005%, and vanadium (V): below 0.2%.

3. The high-hardness wear-resistant steel according to claim 1, wherein, the wear-resistant steel contains the martensite and bainite composite structure with an area fraction of 90% or more.

4. The high-hardness wear-resistant steel according to claim 1, wherein, the surface hardness of the wear-resistant steel is 460 - 540 HB, and the impact energy absorption at -40°C is 17 J or more.

5. The high-hardness wear-resistant steel according to claim 1, wherein, the wear-resistant steel has a thickness of 5 - 40 mm.

6. A manufacturing method of a high-hardness wear-resistant steel with excellent low-temperature impact toughness, which includes: a step of preparing a steel billet, by weight percentage, the steel billet contains carbon (C): 0.25 - 0.50%, silicon (Si): 1.0 - 1.6%, manganese (Mn): 0.6 - 1.6%, phosphorus (P): below 0.05% and excluding 0%, sulfur (S): below 0.02% and excluding 0%, aluminum (Al): below 0.07% and excluding 0%, chromium (Cr): 0.5 - 1.5%, calcium (Ca): 0.0005 - 0.004%, nitrogen (N): below 0.006%, and the balance is Fe and other inevitable impurities; a step of heating the steel billet in a temperature range of 1050 - 1250°C; a step of rough rolling the heated steel billet in a temperature range of 950 - 1150°C; a step of hot finish rolling in a temperature range of 850 - 950°C after the rough rolling to manufacture a hot-rolled steel plate; and a step of cooling the hot-rolled steel plate to 200 - 400°C at a cooling rate of 30°C / second or more and then performing air cooling.

7. The manufacturing method according to claim 6, wherein, By weight percentage, the steel billet further contains one or more of the following elements: nickel (Ni): 0.01 - 0.5%, molybdenum (Mo): 0.01 - 0.3%, titanium (Ti): 0.005 - 0.025%, boron (B): 0.0002 - 0.005%, and vanadium (V): less than 0.2%.

8. The manufacturing method according to claim 6, wherein, self-tempering occurs during the air cooling.

9. The manufacturing method according to claim 6, wherein, the air cooling is carried out to a temperature below 150°C.

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