KR20210076658A - Wear resistant steel havinh high hardness and excellent low-temperature impact toughness and method for manufacturing thereof - Google Patents

Abstract

The present invention provides wear-resistant steel with high hardness and high impact toughness at low temperatures along with wear-resistance, and a manufacturing method thereof. The present invention comprises: 0.25-0.5 wt% of carbon (C); 1.0-1.6 wt% of silicon (Si); 0.6-1.6 wt% of manganese (Mn), 0.05 wt% or less (excluding 0) of phosphorus (P); 0.02 wt% or less (excluding 0) of sulfur (S); 0.07 wt% or less (excluding 0) of aluminum (Al); 0.5-1.5 wt% of chromium (Cr); 0.0005-0.004 wt% of calcium (Ca); 0.006 wt% or less of nitrogen (N); and the balance Fe and other avoidable impurities.

Description

High hardness wear-resistant steel with excellent low-temperature impact toughness and manufacturing method thereof {WEAR RESISTANT STEEL HAVINH HIGH HARDNESS AND EXCELLENT LOW-TEMPERATURE IMPACT TOUGHNESS AND METHOD FOR MANUFACTURING THEREOF}

The present invention relates to a material suitable for construction machinery, and more particularly, to abrasion-resistant steel having excellent low-temperature impact toughness and high hardness, and a method for manufacturing the same.

Abrasion-resistant steel is used in areas subject to wear as high performance is required along with weight reduction for industrial machines such as bulldozers and power shovels, mining facilities such as crushers and chutes, and large dump trucks.

In particular, in order to extend the service life of these parts, the wear-resistant steel used here shows a tendency to gradually increase in hardness, and high toughness is required together with the concern of defects such as cracks due to the increase in hardness.

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

Currently, the following technologies have been proposed for wear-resistant steel used in industrial machines or construction machines.

Patent Document 1 discloses that steel having a Brinell hardness of 500 or less can be produced by directly quenching a steel sheet containing C, Mn, and Si in addition to a certain amount or more of Cr, Ti, B, etc. in the steel after rolling.

Patent Document 2 contains a certain amount of Ti, B, etc. in addition to C, Si, and Mn in steel, and limits the cooling termination temperature to 300° C. or less when reheating and quenching for a steel sheet with a limited H content, thus providing excellent soundness Brinell hardness It is disclosed to manufacture steels of 450 or less.

Patent Document 3 discloses that a steel sheet containing Cr, Mo, and B in addition to C, Si, and Mn is reheated and quenched to produce a steel having a Brinell hardness of 500.

In addition, Patent Document 4, while limiting the content of Cr, Mo, Ti, Nb, B, etc. in addition to C, Si, Mn in the steel, if necessary, a steel containing additional Cu, Ni, V, Ca, etc. It is disclosed that, after rolling, it is cooled to 100° C. or less, and through a process of continuously tempering, it is possible to manufacture a 500 grade steel with excellent low-temperature toughness.

In addition, Patent Document 5 discloses a special-purpose steel with high elasticity and high strength in which impact resistance and wear resistance are secured together by tempering steel appropriately containing a relatively low content of C and a high content of Si and other elements.

However, Patent Documents 1 and 2 do not satisfy the hardness level required in the real environment, Patent Document 3 satisfies the hardness level but has a disadvantage in terms of poor toughness, and Patent Document 4 contains a large amount of expensive elements, which is economical. Therefore, there is a limit to its application. In the case of Patent Document 5, it is difficult to secure low-temperature toughness, and there is a disadvantage that the manufacturing cost is still high.

Accordingly, there is a demand for the development of wear-resistant steel having excellent low-temperature toughness as well as wear resistance through an economical method without containing a large amount of expensive elements.

Japanese Laid-Open Patent Publication No. 1988-083225 B2 Japanese Laid-Open Patent Publication No. 1989-010564 B2 Japanese Laid-Open Patent Publication No. 1989-021846 B2 Japanese Laid-Open Patent Publication No. 1996-041535 Republic of Korea Registration Publication 10-0619841

One aspect of the present invention is to provide a wear-resistant steel having high hardness and high impact toughness at a low temperature along with abrasion resistance and a method for manufacturing the same.

The subject of this invention is not limited to the above-mentioned content. The subject of the present invention will be understood from the overall content of the present specification, and those of ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional subject of the present invention.

One aspect of the present invention, by weight, carbon (C): 0.25 to 0.50%, silicon (Si): 1.0 to 1.6%, manganese (Mn): 0.6 to 1.6%, phosphorus (P): 0.05% or less ( Except for 0%), Sulfur (S): 0.02% or less (excluding 0%), Aluminum (Al): 0.07% or less (excluding 0%), Chromium (Cr): 0.5 to 1.5%, Calcium (Ca) : 0.0005 ~ 0.004%, nitrogen (N): 0.006% or less, the remainder contains Fe and other unavoidable impurities, and contains martensite and bainite complex structures as microstructures and retained austenite phases with an area fraction of 2.5 to 10%. Provides high hardness wear-resistant steel with excellent low-temperature impact toughness.

Another aspect of the present invention comprises the steps of preparing a steel slab having the above-described alloy composition; heating the steel slab in a temperature range of 1050 to 1250 °C; rough rolling the heated steel slab in a temperature range of 950 to 1150 °C; manufacturing a hot-rolled steel sheet by finishing hot rolling in a temperature range of 850 to 950° C. after the rough rolling; and cooling the hot-rolled steel sheet to 200 to 400° C. at a cooling rate of 25° C./s or more, followed by air cooling.

ADVANTAGE OF THE INVENTION According to this invention, the wear-resistant steel excellent in low-temperature toughness while having high hardness can be provided.

In particular, the present invention can provide a wear-resistant steel having a target level of physical properties without additional heat treatment from the optimization of the alloy composition and manufacturing conditions, and thus has an economically advantageous effect.

1 shows a photograph of the microstructure of the invention steel according to an embodiment of the present invention observed with an optical microscope.
2 is a photograph showing the microstructure of the inventive steel according to an embodiment of the present invention measured with a scanning electron microscope (a) and EBSD (b).
3 shows a photograph of the microstructure of a comparative steel according to an embodiment of the present invention observed with an optical microscope.
4 is a photograph showing the microstructure of the comparative steel according to an embodiment of the present invention measured with a scanning electron microscope (a) and EBSD (b).

The present inventors have studied deeply in order to provide a steel material that is suitable for construction machinery and the like, and has excellent physical properties such as strength and toughness, while ensuring abrasion resistance, which is a core required physical property.

In particular, it was intended to improve the abrasion resistance of steel materials through an economically advantageous method, and thus the present invention was provided.

Hereinafter, the present invention will be described in detail.

High hardness wear-resistant steel according to an aspect of the present invention, by weight%, carbon (C): 0.25 to 0.50%, silicon (Si): 1.0 to 1.6%, manganese (Mn): 0.6 to 1.6%, phosphorus (P) ): 0.05% or less (excluding 0%), Sulfur (S): 0.02% or less (excluding 0%), Aluminum (Al): 0.07% or less (excluding 0%), Chromium (Cr): 0.5 to 1.5 %, calcium (Ca): 0.0005 to 0.004%, nitrogen (N): 0.006% or less.

Hereinafter, the reason for limiting the alloy composition of the wear-resistant steel provided in the present invention as above will be described in detail.

Meanwhile, unless otherwise specified in the present invention, the content of each element is based on the weight, and the ratio of the tissue is based on the area.

Carbon (C): 0.25 to 0.50%

Carbon (C) is effective for improving strength and hardness in steel having a low-temperature transformation phase such as martensite or bainite phase, and is an effective element for improving hardenability. In order to sufficiently obtain the above-described effect, C may be included in an amount of 0.25% or more, but when the content exceeds 0.50%, there is a problem of inhibiting weldability and toughness of steel.

Accordingly, the C may be included in an amount of 0.25 to 0.50%.

Silicon (Si): 1.0~1.6%

Silicon (Si) is effective for strength improvement due to solid solution strengthening along with deoxidation effect, and is an element that promotes the formation of retained austenite by suppressing the formation of carbides such as cementite in high carbon steel containing a certain amount of C or more.

In particular, since the retained austenite homogeneously distributed in steel having a low-temperature transformation phase such as martensite and bainite contributes to the improvement of impact toughness without lowering strength, Si is an element advantageous for securing low-temperature toughness in the present invention.

In order to sufficiently obtain the above-described effect, Si may be included in an amount of 1.0% or more, but when the content exceeds 1.6%, there is a problem in that weldability is rapidly deteriorated.

Therefore, the Si may be included in an amount of 1.0 to 1.6%, and more advantageously, it may be included in an amount of 1.2% or more.

Manganese (Mn): 0.6~1.6%

Manganese (Mn) is an advantageous element for suppressing the formation of ferrite and improving the hardenability of steel by lowering the Ar3 temperature to increase strength and toughness.

In the present invention, in order to obtain a target level of hardness, Mn may be contained in an amount of 0.6% or more, but when the content exceeds 1.6%, weldability is deteriorated, and central segregation is promoted, so that there is a problem in that the properties of the steel core are reduced. .

Accordingly, the Mn may be included in an amount of 0.6 to 1.6%.

Phosphorus (P): 0.05% or less (excluding 0%)

Phosphorus (P) is an element that is unavoidably contained in steel and inhibits the toughness of steel. Accordingly, the P content is preferably as low as possible.

In the present invention, even if the content of P is up to 0.05%, there is no significant effect on the physical properties of the steel, so the content of P can be limited to 0.05% or less. More advantageously, it may be limited to 0.03% or less, but 0% may be excluded in consideration of the unavoidable content level.

Sulfur (S): 0.02% or less (excluding 0%)

Sulfur (S) is an element that inhibits the toughness of steel by bonding with Mn in steel to form MnS inclusions. Accordingly, it is preferable to lower the content of S as much as possible.

In the present invention, even if the S content is at most 0.02%, there is no significant effect on the physical properties of the steel, so the S content can be limited to 0.02% or less. More advantageously, it may be limited to 0.01% or less, but 0% may be excluded in consideration of the unavoidably contained level.

Aluminum (Al): 0.07% or less (excluding 0%)

Aluminum (Al) is an effective element for lowering the oxygen content in molten steel as a deoxidizer of steel. When the content of Al exceeds 0.07%, there is a problem that the cleanliness of the steel is impaired.

Accordingly, the Al may be included in an amount of 0.07% or less. However, when the content of Al is excessively lowered, a load is generated during the steelmaking process and the manufacturing cost is increased. Considering this, 0% may be excluded.

Chromium (Cr): 0.5~1.5%

Chromium (Cr) improves the strength by increasing the hardenability of the steel, and is advantageous for securing the hardness of the surface and the center of the steel. Since Cr is a relatively inexpensive element, Cr may be included in an amount of 0.5% or more in order to secure high hardness and high toughness of steel by using Cr. However, when the content exceeds 1.5%, there is a problem in that the weldability of the steel is inferior.

Accordingly, the Cr may be contained in an amount of 0.5 to 1.5%, and more advantageously may be contained in an amount of 0.65% or more.

Calcium (Ca): 0.0005~0.004%

Calcium (Ca) has good bonding strength with sulfur (S), so it is advantageous in improving toughness in a direction perpendicular to the rolling direction by inhibiting elongation of MnS by generating CaS around (perimeter) MnS. In addition, CaS generated by the addition of Ca has an effect of increasing corrosion resistance under a humid external environment.

In order to sufficiently obtain the above-described effect, Ca may be included in an amount of 0.0005% or more, but when the content exceeds 0.004%, there is a problem of causing defects such as nozzle clogging during steelmaking.

Accordingly, the Ca may be included in an amount of 0.0005 to 0.004%.

Nitrogen (N): 0.006% or less

Nitrogen (N) is advantageous for improving the strength of steel by forming precipitates in the steel, but when the content exceeds 0.006%, there is a problem in that the toughness of the steel is rather reduced.

In the present invention, even if the N is not contained, there is no difficulty in securing strength, and the N may be contained in an amount of 0.006% or less. However, 0% may be excluded in consideration of the unavoidably contained level.

In addition to the alloy composition described above, the wear-resistant steel of the present invention may further include the following elements for the purpose of advantageously securing target physical properties.

Specifically, the wear-resistant steel may further include one or more of nickel (Ni), molybdenum (Mo), titanium (Ti), boron (B), and vanadium (V).

Nickel (Ni): 0.01 to 0.5%

Nickel (Ni) is an element advantageous for simultaneously improving the strength and toughness of steel, and for this purpose, Ni may be contained in an amount of 0.01% or more. However, since it is an expensive element, when its content exceeds 0.5%, there is a problem in that the manufacturing cost is greatly increased.

Therefore, when the Ni is contained, it may be included in an amount of 0.01 to 0.5%.

Molybdenum (Mo): 0.01~0.3%

Molybdenum (Mo) is an element advantageous for increasing the hardenability of steel and, in particular, improving the hardness of a thick material having a thickness greater than or equal to a certain level. In order to sufficiently obtain the above-described effect, it may be included in an amount of 0.01% or more, but when the content exceeds 0.3%, there is a problem that not only the manufacturing cost increases, but also the weldability is inferior.

Therefore, when the Mo is contained, it may be contained in an amount of 0.01 to 0.3%.

Titanium (Ti): 0.005 to 0.025%

Titanium (Ti) is an element advantageous for maximizing the effect of B, which is an element advantageous for improving hardenability of steel. That is, the Ti is combined with N in the steel to precipitate TiN to reduce the content of solid solution N, and from this, the BN formation of B is suppressed to increase the solid solution B, thereby maximizing the hardenability improvement.

In order to sufficiently obtain the above-described effect, Ti may be contained in an amount of 0.005% or more, but when the content exceeds 0.025%, coarse TiN precipitates are formed, and there is a problem in that the toughness of the steel is lowered.

Therefore, when the Ti is contained, it may be contained in an amount of 0.005 to 0.025%.

Boron (B): 0.0002~0.005%

Boron (B) is an effective element for increasing the strength by effectively increasing the hardenability of steel even with a small amount of addition. In order to sufficiently obtain such an effect, B may be contained in an amount of 0.0002% or more. However, if the content is excessive, there is a problem in that the toughness and weldability of the steel are rather impaired, so the content may be limited to 0.005% or less.

Therefore, when the B is contained, it may be included in an amount of 0.0002 to 0.005%. More advantageously, the B content may be 0.0040% or less, even more advantageously 0.0035% or less, and further 0.0030% or less.

Vanadium (V): 0.2% or less

Vanadium (V) forms VC carbide during reheating after hot rolling, thereby suppressing the growth of austenite grains and improving the hardenability of steel to secure strength and toughness. Since V is a relatively expensive element, when its content exceeds 0.2%, there is a problem in that the manufacturing cost is greatly increased.

Therefore, when V is added, it may be contained in an amount of 0.2% or less.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since these impurities are known to anyone skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

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

Specifically, the wear-resistant steel of the present invention may include a composite structure of martensite and bainite phases in an area fraction of 90% or more, and if these phase fractions are less than 90%, it becomes difficult to secure the target level of strength and hardness. Here, it is noted that the martensite and bainite phases may include tempered martensite and tempered bainite phases, respectively.

The wear-resistant steel of the present invention preferably has an average lath size of 0.3 μm or less of the above-described composite structure. When the average lath size of the composite structure exceeds 0.3 μm, there is a problem in that the toughness of the steel is reduced.

The wear-resistant steel of the present invention may include a retained austenite phase in addition to the composite structure, and in this case, it may be contained in an area fraction of 2.5 to 10%. When the fraction of the retained austenite phase is less than 2.5%, low-temperature impact toughness is deteriorated, whereas when it exceeds 10%, there is a problem in that hardness is deteriorated.

On the other hand, it is revealed that the wear-resistant steel of the present invention has the above-described structure over the entire thickness.

The wear-resistant steel of the present invention having the proposed microstructure in addition to the alloy composition described above may have a thickness of 5 to 40 mm, and the surface hardness of this wear-resistant steel is 460 to 540 HB, which is high hardness, and shock absorption at -40 ° C. With an energy of 17J or more, it has an excellent low-temperature toughness.

Here, the surface hardness means a hardness value measured at a point of 2 mm to 5 mm in the thickness direction from the surface of the wear-resistant steel.

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

Briefly, after preparing a steel slab satisfying the alloy composition described above, the steel slab may be manufactured through a process of [heating-rolling-cooling]. Hereinafter, each process condition will be described in detail.

[steel slab heating process]

First, after preparing a steel slab having an alloy composition proposed in the present invention, it can be heated in a temperature range of 1050 to 1250 °C.

When the heating temperature is less than 1050 ℃, the deformation resistance of the steel becomes large and the subsequent rolling process cannot be effectively performed. On the other hand, when the temperature exceeds 1250 ℃, the austenite grains become coarse and there is a risk of forming a non-uniform structure.

Therefore, the heating of the steel slab can be performed in a temperature range of 1050 ~ 1250 ℃.

[Rolling process]

The heated steel slab can be rolled according to the above, and in this case, it can be manufactured into a hot-rolled steel sheet through the processes of rough rolling and finish hot rolling.

First, the heated steel slab is rough-rolled in a temperature range of 950 to 1150° C. to produce a bar, and then finish hot rolling can be performed in a temperature range of 850 to 950° C.

When the rough rolling temperature is less than 950 ℃, as the rolling load is increased and relatively weak pressure is reduced, the deformation is not sufficiently transmitted to the center of the slab thickness direction, and as a result, there is a fear that defects such as voids may not be removed. On the other hand, when the temperature exceeds 1150° C., the recrystallized grain size becomes too coarse, which may be harmful to toughness.

If the temperature during the finish hot rolling is less than 850 ° C, two-phase rolling is performed and there is a fear that ferrite is generated in the microstructure, whereas when the temperature exceeds 950 ° C, the grain size of the final structure becomes coarse and the low-temperature toughness is inferior there is a problem.

[Cooling process]

The hot-rolled steel sheet manufactured through the above-described rolling process may be water-cooled to a predetermined temperature and then air-cooled.

Specifically, in the present invention, when cooling a hot-rolled steel sheet, water cooling is performed at an average cooling rate of 25°C/s or more to a temperature range of 200 to 400°C, and then air cooling can be performed to 150°C or less. There is an effect that tempering (self-tempering) is expressed. That is, the tempering of the martensite and bainite phases is performed during air cooling, and the retained austenite phase is formed in a certain fraction, thereby improving the toughness of steel.

The air cooling may be performed to room temperature.

Meanwhile, the cooling may be initiated at Ar3 or higher. Here, Ar3 is dependent on the alloy composition system, which is clear to any person skilled in the art.

If the cooling rate during water cooling is less than 25° C./s, a ferrite phase is formed during cooling or the average lath size of the hard phase (martensite + bainite) increases, making it difficult to secure high hardness. The upper limit of the cooling rate during the water cooling is not particularly limited, but it is noted that the cooling rate can be performed at a maximum cooling rate of 100° C./s in consideration of the cooling equipment.

In performing cooling at the above cooling rate, if the cooling end temperature is less than 200 ° C, the self-tempering effect is small and it is difficult to secure the target level of toughness, whereas when the temperature exceeds 400 ° C, the hard phase (martene) The average lath size of site + bainite) increases, so that the target level of hardness or toughness cannot be secured due to a decrease in strength or toughness.

The hot-rolled steel sheet obtained through the above-described series of manufacturing processes is a steel material having a thickness of 5 to 40 mm, and may have characteristics of high hardness and high toughness in addition to wear resistance.

In particular, in the case of the present invention, self-tempering can be realized during the cooling process, and a subsequent tempering process is not required, and it will be said that there is an effect of manufacturing abrasion-resistant steel more economically therefrom.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail 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 matters reasonably inferred therefrom.

(Example)

After preparing a steel slab having an alloy composition shown in Table 1 below, it was subjected to [heat-rolling-cooling] according to the process conditions shown in Table 2 below to prepare each hot-rolled steel sheet. At this time, the cooling was performed by water cooling to a certain temperature and then air cooling to 150° C. or less.

Thereafter, the microstructure and mechanical properties were measured for each hot-rolled steel sheet, and the results are shown in Table 3 below.

The microstructure of each hot-rolled steel sheet is cut to an arbitrary size to produce a mirror surface, corroded using a nital etchant, and then used an optical microscope and a scanning electron microscope (SEM) to create a 1/ The 2t point was observed. At this time, the lath size of the martensite and bainite composite structures was measured using electron back-scattered diffraction (EBSD) analysis.

In addition, the hardness and toughness of each hot-rolled steel sheet were measured using a Brinell hardness tester (load 3000 kgf, 10 mm tungsten indentation hole) and a Charpy impact tester, respectively. At this time, for the surface hardness, the average value of the values measured three times after milling the surface of the hot-rolled sheet by 2 mm was used. For the Charpy impact test, a specimen was taken at 1/4t in the thickness direction and measured three times at -40°C. The average of the values was used.

steel grade Alloy composition (wt%) C Si Mn P* S* Cr Mo V Al Ca* Ti B* N* A 0.25 1.35 1.01 110 20 0.71 0 0 0.025 13 0 0 34 B 0.30 1.35 1.00 100 20 0.70 0 0 0.020 10 0 0 48 C 0.35 1.35 0.75 100 20 0.69 0 0 0.024 11 0 0 36 D 0.45 1.40 0.68 120 20 0.70 0 0 0.033 15 0 0 43 E 0.45 1.40 0.69 90 20 0.70 0 0.158 0.034 10 0 0 41 F 0.30 1.34 1.00 100 20 0.70 0 0 0.038 10 0.015 0 34 G 0.30 1.35 1.02 110 20 0.70 0 0 0.027 10 0.016 15 37 H 0.21 1.34 1.02 110 20 0.71 0 0 0.024 12 0 0 41 I 0.56 1.41 0.71 110 20 0.70 0 0 0.030 14 0 0 41 J 0.26 0.30 1.20 80 10 0.25 0.25 0 0.030 10 0.020 20 40 K 0.38 0.32 1.10 80 6 0.40 0.50 0 0.030 10 0.019 20 37

(In Table 1, P*, S*, Ca*, B*, and N* are expressed in ppm.)

steel grade thickness
(mm) heating
(℃) rolled cooling (water cooling) remark rough rolling
(℃) finish hot
Rolling (℃) start temperature
(℃) end temperature
(℃) speed
(℃/s) A 12 1200 1150 880 790 360 30 Invention Example 1 B 12 1200 1140 860 760 300 38.4 Invention Example 2 B 12 1200 1135 860 755 360 30.4 Invention example 3 C 14 1200 1100 935 780 350 43 Invention Example 4 D 12 1200 1145 860 760 310 45 Invention Example 5 E 12 1200 1120 860 760 360 50 Invention Example 6 F 12 1200 1130 880 800 270 48 Invention Example 7 F 12 1200 1120 880 800 285 61 Invention Example 8 G 12 1200 1100 880 800 219 58 Invention Example 9 G 12 1200 1130 880 800 293 63 Invention example 10 A 12 1200 1135 880 790 256 23 Comparative Example 1 B 25 1200 1100 870 790 300 13 Comparative Example 2 B 25 1200 1120 870 790 390 20 Comparative Example 3 C 14 1200 1100 830 720 270 52 Comparative Example 4 C 14 1200 1110 930 780 410 41 Comparative Example 5 D 12 1200 1125 860 760 170 60 Comparative Example 6 F 12 1200 1120 880 800 180 68 Comparative Example 7 G 12 1200 1130 880 800 411 52 Comparative Example 8 H 12 1200 1140 880 790 251 40 Comparative Example 9 H 12 1200 1130 880 790 335 35 Comparative Example 10 H 12 1200 1150 880 790 364 40 Comparative Example 11 I 12 1200 1120 870 760 295 52 Comparative Example 12 I 12 1200 1110 870 760 380 38 Comparative Example 13 J 12 1200 1120 880 790 269 48 Comparative Example 14 K 12 1200 1110 880 760 300 38 Comparative Example 15

(In Table 2, the cooling start temperature of the invention examples is Ar3 or higher.)

division Microstructure (area fraction %) M+B average
lath size (㎛) surface hardness
(HB) impact toughness
(J,@-40℃) M+B F r-γ Invention Example 1 97.5 0 2.5 0.29 481 22.2 Invention Example 2 97 0 3 0.27 494 30.2 Invention example 3 92.5 0 7.5 0.28 477 29.0 Invention Example 4 94 0 6 0.25 477 22.7 Invention Example 5 97 0 3 0.28 535 26.0 Invention Example 6 97.2 0 2.8 0.26 485 18.0 Invention Example 7 96.8 0 3.2 0.20 496 23.0 Invention Example 8 96.2 0 3.8 0.19 481 25.4 Invention Example 9 96.9 0 3.1 0.16 533 22.1 Invention example 10 92.8 0 7.2 0.29 490 28.4 Comparative Example 1 99 0 One 0.18 492 14.7 Comparative Example 2 85 13.2 1.8 0.38 366 14.5 Comparative Example 3 88 11 One 0.40 444 11.7 Comparative Example 4 86 12 2 0.30 430 10.1 Comparative Example 5 85 13 2 0.48 406 19.5 Comparative Example 6 98.9 0 1.1 0.17 584 4.4 Comparative Example 7 99 0 One 0.17 558 5.9 Comparative Example 8 93 5.5 1.5 0.37 456 27.8 Comparative Example 9 86 12 2 0.28 402 12.7 Comparative Example 10 86 11 3 0.29 409 15.4 Comparative Example 11 81 15 4 0.28 381 16.7 Comparative Example 12 99 0 One 0.14 569 3.9 Comparative Example 13 98.5 0 1.5 0.18 500 8.5 Comparative Example 14 99 0 One 0.19 497 12.9 Comparative Example 15 99 0 One 0.14 616 5.8

(In Table 3, M denotes martensite, B denotes bainite, F denotes ferrite, and r-γ denotes retained austenite phase.)

As shown in Tables 1 to 3, in the case of Inventive Examples 1 to 10, which satisfy both the alloy composition and the manufacturing conditions proposed in the present invention, the microstructure includes the retained austenite phase in a certain fraction along with martensite + bainite. can be checked. In addition, the lath size of the martensite + bainite was formed to be 0.3 μm or less. From this, it was possible to secure excellent hardness and low-temperature impact toughness in Inventive Examples 1 to 10.

On the other hand, while the alloy composition proposed in the present invention is satisfactory, Comparative Examples 1 to 8, in which the manufacturing conditions are outside the present invention, have microstructures of ferrite phases or large martensite and bainite laths, or austenite. It was difficult to secure excellent high hardness and low-temperature impact toughness at the same time because the fraction of the phase was insufficient.

On the other hand, Comparative Examples 9 to 11 were significantly inferior in hardness and toughness due to excessive generation of proeutectoid ferrite phase due to low hardenability due to insufficient C content in the steel. In Comparative Examples 12 and 13, the C content in the steel was excessively high, and the retained austenite phase fraction was insufficient to ensure hardness, but was significantly inferior in low-temperature impact toughness. In Comparative Examples 14 and 15, in which the Si content in the steel was insufficient, hardness could be secured, but the retained austenite phase was not sufficiently formed, so that the low-temperature impact toughness was inferior.

1 and 2 show microstructure photographs of Inventive Example 5.

Of these, FIG. 1 is a photograph observed with an optical microscope, and FIG. 2 is a photograph observed with a scanning electron microscope and EBSD. It can be confirmed that the martensite phase and the bainite phase are formed as the main structures as the matrix structure, and martensite and It can be seen that the retained austenite phase is finely distributed at the lath boundary of bainite.

3 and 4 show microstructure photographs of Comparative Example 6.

Of these, FIG. 3 is a photograph observed with an optical microscope, and FIG. 4 is a photograph observed with a scanning electron microscope and EBSD. Martensite phase and bainite phase were mainly formed as a matrix structure, but the retained austenite phase was very insignificantly formed. that can be checked

Claims (10)

By weight%, carbon (C): 0.25 to 0.50%, silicon (Si): 1.0 to 1.6%, manganese (Mn): 0.6 to 1.6%, phosphorus (P): 0.05% or less (excluding 0%), sulfur (S): 0.02% or less (excluding 0%), Aluminum (Al): 0.07% or less (excluding 0%), Chromium (Cr): 0.5 to 1.5%, Calcium (Ca): 0.0005 to 0.004%, Nitrogen (N): 0.006% or less, the balance contains Fe and other unavoidable impurities,
High hardness and wear-resistant steel with excellent low-temperature impact toughness, including martensite and bainite composite structures as microstructures, and retained austenite phases with an area fraction of 2.5 to 10%.
The method of claim 1,
The wear-resistant steel is, by weight, nickel (Ni): 0.01 to 0.5%, molybdenum (Mo): 0.01 to 0.3%, titanium (Ti): 0.005 to 0.025%, boron (B): 0.0002 to 0.005% and vanadium (V): High hardness wear-resistant steel excellent in low-temperature impact toughness further comprising at least one of 0.2% or less.
The method of claim 1,
The martensite and bainite composite structure has an average lath size of 0.3 μm or less and high hardness wear-resistant steel with excellent low-temperature impact toughness.
The method of claim 1,
The wear-resistant steel is a high-hardness wear-resistant steel with excellent low-temperature impact toughness comprising the martensite and bainite composite structure in an area fraction of 90% or more.
The method of claim 1,
The wear-resistant steel has a surface hardness of 460 to 540HB, and a high-hardness wear-resistant steel with excellent low-temperature impact toughness with an impact absorption energy of 17J or more at -40°C.
The method of claim 1,
The wear-resistant steel is a high-hardness wear-resistant steel having a thickness of 5-40 mm and excellent low-temperature impact toughness.
By weight%, carbon (C): 0.25 to 0.50%, silicon (Si): 1.0 to 1.6%, manganese (Mn): 0.6 to 1.6%, phosphorus (P): 0.05% or less (excluding 0%), sulfur (S): 0.02% or less (excluding 0%), Aluminum (Al): 0.07% or less (excluding 0%), Chromium (Cr): 0.5 to 1.5%, Calcium (Ca): 0.0005 to 0.004%, Nitrogen (N): preparing a steel slab containing 0.006% or less, the balance Fe and other unavoidable impurities;
heating the steel slab in a temperature range of 1050 to 1250 °C;
rough rolling the heated steel slab in a temperature range of 950 to 1150 °C;
manufacturing a hot-rolled steel sheet by finishing hot rolling in a temperature range of 850 to 950° C. after the rough rolling; and
Cooling the hot-rolled steel sheet to 200-400°C at a cooling rate of 25°C/s or more, followed by air cooling
A method for producing high-hardness wear-resistant steel with excellent low-temperature impact toughness, comprising:
8. The method of claim 7,
The steel slab is in wt%, nickel (Ni): 0.01 to 0.5%, molybdenum (Mo): 0.01 to 0.3%, titanium (Ti): 0.005 to 0.025%, boron (B): 0.0002 to 0.005% and vanadium ( V): A method of manufacturing high-hardness wear-resistant steel having excellent low-temperature impact toughness, further comprising at least one of 0.2% or less.
8. The method of claim 7,
A method of manufacturing high-hardness wear-resistant steel having excellent low-temperature impact toughness, characterized in that self-tempering occurs during the air cooling.
8. The method of claim 7,
The method for producing a high-hardness wear-resistant steel excellent in low-temperature impact toughness that the air cooling is performed at 150° C. or less.

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