JP2022502570A - Wear-resistant steel with excellent hardness and impact toughness and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wear-resistant steel having excellent hardness and impact toughness and a method for producing the same. According to one embodiment of the present invention, in% by weight, carbon (C): 0.33 to 0.42%, silicon (Si): 0.1 to 0.7%, 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), nickel (Ni): 0.55 to 5.0%, copper (Cu): 0.01 to 1.5%, chromium (Cr): 0.01 to 0.8%, molybdenum (excluding 0) Mo): 0.01 to 0.8%, boron (B): 50 ppm or less (excluding 0), cobalt (Co): 0.02% or less (excluding 0), and titanium (Ti) :. 0.02% or less (excluding 0), niobium (Nb): 0.05% or less (excluding 0), vanadium (V): 0.05% or less (excluding 0) and calcium (Ca): 2- Further containing one or more selected from the group consisting of 100 ppm, the balance Fe and other unavoidable impurities, the above C and Ni satisfy the condition of the following relational expression 1, and the microstructure is martensite: 95 area% or more. And baynite: characterized by containing 5% or less (including 0%). [Relational expression 1] [C] × [Ni] ≧ 0.231 [Selection diagram] None

Description

The present invention relates to a wear-resistant steel having excellent hardness and impact toughness and a method for manufacturing the same, and more particularly to a high-hardness wear-resistant steel which can be used for construction machinery and the like and a method for manufacturing the same.

In the case of construction machinery and industrial machinery used in many industrial fields such as construction, civil engineering, mining, and cement industry, it is necessary to apply a material that exhibits wear resistance characteristics because wear occurs severely due to friction during work. ..
In general, the wear resistance and hardness of thick steel sheets are related to each other, and it is necessary to increase the hardness of thick steel sheets where wear is a concern. In order to secure more stable wear resistance, the hardness is uniform from the surface of the thick steel sheet to the inside of the plate thickness (near t / 2, t = thickness) (that is, the surface and the inside of the thick steel plate). It is required to have the same degree of hardness.

Usually, in order to obtain high hardness in a thick steel sheet, a method of rolling _{, reheating at a temperature of Ac 3} or higher, and then quenching is widely used. As an example, Patent Documents 1 and 2 disclose a method of increasing the surface hardness by increasing the C content and adding a large amount of curable ability improving elements such as Cr and Mo. However, in the production of extra-thick steel sheets, it is required to add more curable elements in order to secure the curability at the center of the steel sheet, and a large amount of C and the curable alloy will be added. There is a problem that the manufacturing cost increases and the weldability and low temperature toughness decrease.
Therefore, in a situation where it is unavoidable to add a curable alloy in order to secure the curable ability, a measure that can secure high hardness, excellent wear resistance, high strength and high impact toughness. Is required.

Japanese Publication No. 1996-411535 Gazette Japanese Publication No. 1986-166954

An object of the present invention is to provide a high hardness wear resistant steel having excellent wear resistance, high strength and high impact toughness, and a method for producing the same.

The wear-resistant steel having excellent hardness and impact toughness of the present invention is, in weight%, carbon (C): 0.33 to 0.42%, silicon (Si): 0.1 to 0.7%, 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), nickel (Ni): 0.55 to 5.0%, copper (Cu): 0.01 to 1.5%, chromium (Cr): 0.01 to 0.8 %, Molybdenum (Mo): 0.01-0.8%, Boron (B): 50 ppm or less (excluding 0), Cobalt (Co): 0.02% or less (excluding 0), and titanium (Ti): 0.02% or less (excluding 0), niobium (Nb): 0.05% or less (excluding 0), vanadium (V): 0.05% or less (excluding 0), and calcium ( Ca): Further contains one or more selected from the group consisting of 2 to 100 ppm, and consists of the balance Fe and other unavoidable impurities. The above C and Ni satisfy the condition of the following relational expression 1, and the microstructure is martensite. : 95 area% or more and baynite: 5% or less (including 0%).
[Relational expression 1] [C] × [Ni] ≧ 0.231

The method for producing an abrasion-resistant steel having excellent hardness and impact toughness of the present invention is, in% by weight, carbon (C): 0.33 to 0.42%, silicon (Si): 0.1 to 0.7%. , Manganese (Mn): 0.6 to 1.6%, Lin (P): 0.05% or less (excluding 0), Sulfur (S): 0.02% or less (excluding 0), Aluminum (Al) ): 0.07% or less (excluding 0), nickel (Ni): 0.55 to 5.0%, copper (Cu): 0.01 to 1.5%, chromium (Cr): 0.01 to 0.8%, molybdenum (Mo): 0.01 to 0.8%, boron (B): 50 ppm or less (excluding 0), cobalt (Co): 0.02% or less (excluding 0), Furthermore, titanium (Ti): 0.02% or less (excluding 0), niobium (Nb): 0.05% or less (excluding 0), vanadium (V): 0.05% or less (excluding 0). Calcium (Ca): Further containing one or more selected from the group consisting of 2 to 100 ppm, consisting of the balance Fe and other unavoidable impurities, and the above C and Ni are 1050 steel slabs satisfying the condition of the following relational expression 1. A step of heating in a temperature range of ~ 1250 ° C., a step of rough-rolling the reheated steel slab in a temperature range of 950 to 950 ° C. to obtain a rough-rolled bar, and a step of rough-rolling the rough-rolled bar in a temperature range of 850 to 950 ° C. At the stage of obtaining a hot-rolled steel sheet by hot rolling, the hot-rolled steel sheet is air-cooled to room temperature, and then the furnace time is 1.3t + 10 minutes to 1.3t + 60 minutes (t: plate thickness) in the temperature range of 860 to 950 ° C. It is characterized by including a step of reheating during the above period and a step of water-cooling the reheated hot-rolled steel sheet to 150 ° C. or lower.
[Relational expression 1] [C] × [Ni] ≧ 0.231

According to the present invention, the method for producing a wear-resistant steel having excellent hardness and impact toughness of the present invention can provide a wear-resistant steel having high hardness and excellent low-temperature toughness while having a thickness of 60 mm or less. ..

Hereinafter, the present invention will be described in detail. First, the alloy composition of the present invention will be described. The content of the alloy composition described below is% by weight.

Carbon (C): 0.33 to 0.42%
Carbon (C) is an element that is effective in increasing the strength and hardness of steel having a martensite structure and is effective for improving the curability. In order to sufficiently secure the above-mentioned effects, it is preferable to add 0.33% or more, but if the content exceeds 0.42%, weldability and toughness may be impaired, and tempering may occur. Additional heat treatment work such as is inevitable. Therefore, in the present invention, it is preferable to control the C content to 0.33 to 0.42%. The lower limit of the C content is more preferably 0.34%, further preferably 0.35%, and most preferably 0.36%. The upper limit of the C content is more preferably 0.40%, further preferably 0.39%, and most preferably 0.38%.

Silicon (Si): 0.1 to 0.7%
Silicon (Si) is an element effective for improving strength by deoxidizing and strengthening solid solution. In order to effectively obtain the above effects, it is preferable to add 0.1% or more, but if the content exceeds 0.7%, the weldability deteriorates, which is not preferable. Therefore, in the present invention, it is preferable to control the Si content to 0.1 to 0.7%. The lower limit of the Si content is more preferably 0.12%, further preferably 0.15%, and most preferably 0.2%. The upper limit of the Si content is more preferably 0.5%, further preferably 0.45%, and most preferably 0.4%.

Manganese (Mn): 0.6-1.6%
Manganese (Mn) is an element that suppresses the formation of ferrite _{and effectively increases the hardenability by lowering the Ar 3} temperature to improve the strength and toughness of steel. In the present invention, in order to secure the hardness of the thick material, it is preferable to contain the above Mn in an amount of 0.6% or more, but if the content exceeds 1.6%, the weldability may be deteriorated. be. Therefore, in the present invention, it is preferable to control the Mn content to 0.6 to 1.6%. The lower limit of the Mn content is more preferably 0.65%, further preferably 0.70%, and most preferably 0.75%. The upper limit of the Mn content is more preferably 1.55%, further preferably 1.50%, and most preferably 1.45%.

Phosphorus (P): 0.05% or less (excluding 0)
Phosphorus (P) is an element inevitably contained in steel and is an element that inhibits the toughness of steel. Therefore, it is preferable to reduce the P content as much as possible to control it to 0.05% or less. However, 0% is excluded in consideration of the fact that it is inevitably contained. The P content is more preferably 0.03% or less, further preferably 0.02% or less, and most preferably 0.01% or less.

Sulfur (S): 0.02% or less (excluding 0)
Sulfur (S) is an element that forms MnS inclusions in steel and inhibits the toughness of steel. Therefore, it is preferable to reduce the S content as much as possible to control it to 0.02% or less. However, 0% is excluded in consideration of the fact that it is inevitably contained. The S content is more preferably 0.01% or less, further preferably 0.005% or less, and most preferably 0.003% or less.

Aluminum (Al): 0.07% or less (excluding 0)
Aluminum (Al) is an element effective as a deoxidizing agent for steel in reducing the oxygen content in molten steel. If the Al content exceeds 0.07%, the cleanliness of the steel may be impaired, which is not preferable. Therefore, in the present invention, it is preferable to control the Al content to 0.07% or less, but 0% is excluded in consideration of the load during the steelmaking process, the increase in manufacturing cost, and the like. The Al content is more preferably 0.05% or less, further preferably 0.04% or less, and most preferably 0.03% or less.

Nickel (Ni): 0.55-5.0%
Nickel (Ni) is an element that is generally effective in improving toughness in addition to the strength of steel. For the above-mentioned effects, it is preferable to add 0.55% or more of Ni, but if the content exceeds 5.0%, it is an expensive element and causes an increase in manufacturing cost. Therefore, in the present invention, it is preferable to control the Ni content to 0.55 to 5.0%. The lower limit of the Ni content is more preferably 0.6%, further preferably 0.7%, and most preferably 0.8%. The upper limit of the Ni content is more preferably 4.5%, further preferably 4.0%, and most preferably 3.5%.

Copper (Cu): 0.01-1.5%
Copper (Cu), like Ni, is an element that can also improve the strength and toughness of steel. In order to obtain the above effect, it is preferable to add 0.01% or more of Cu, but if the Cu content exceeds 1.5%, not only the possibility of causing defects on the surface increases, but also heat There is a risk of impairing workability. Therefore, in the present invention, it is preferable to control the Cu content to 0.01 to 1.5%. The lower limit of the Cu content is more preferably 0.05%, further preferably 0.10%, and most preferably 0.15%. The upper limit of the Cu content is more preferably 1.2%, further preferably 1.0%, and most preferably 0.8%.

Chromium (Cr): 0.01-0.8%
Chromium (Cr) is an element that improves the effect of quenching, increases the strength of steel, and is also advantageous for ensuring hardness. For the above-mentioned effects, it is preferable to add 0.01% or more of Cr, but if the content exceeds 0.8%, the weldability becomes inferior and the manufacturing cost increases. .. Therefore, in the present invention, it is preferable to control the Cr content to 0.01 to 0.8%. The lower limit of the Cr content is more preferably 0.1%, further preferably 0.15%, and most preferably 0.2%. The upper limit of the Cr content is more preferably 0.75%, further preferably 0.70%, and most preferably 0.65%.

Molybdenum (Mo): 0.01-0.8%
Molybdenum (Mo) is an element that improves the hardenability of steel and is particularly effective in improving the hardness of thick materials. In order to sufficiently obtain the above-mentioned effects, it is preferable to add 0.01% or more of Mo, but the above-mentioned Mo is also an expensive element, and if the content exceeds 0.8%, the production cost increases. Not only will it rise, but there is a risk that the weldability will be inferior. Therefore, in the present invention, it is preferable to control the Mo content to 0.01 to 0.8%. The lower limit of the Mo content is more preferably 0.1%, further preferably 0.12%, and most preferably 0.15%. The upper limit of the Mo content is more preferably 0.75%, further preferably 0.72%, and most preferably 0.70%.

Boron (B): 50 ppm or less (excluding 0)
Boron (B) is an element that is effective in effectively improving the hardenability of steel and improving its strength even when added in a small amount. However, if the content becomes excessive, the toughness and weldability of the steel may be impaired. Therefore, it is preferable to control the content to 50 ppm or less. The lower limit of the B content is more preferably 2 ppm, further preferably 3 ppm, and most preferably 5 ppm. The upper limit of the B content is more preferably 40 ppm, further preferably 35 ppm, and most preferably 30 ppm.

Cobalt (Co): 0.02% or less (excluding 0)
Cobalt (Co) is an element that is advantageous for ensuring hardness in addition to the strength of steel by improving the hardenability of steel. However, if the content exceeds 0.02%, the hardenability of the steel may decrease, which is an expensive element and causes an increase in the manufacturing cost. Therefore, in the present invention, it is preferable to add 0.02% or less of Co. The lower limit of the Co content is more preferably 0.001%, further preferably 0.002% or less, and most preferably 0.003% or less. The upper limit of the Co content is more preferably 0.018%, further preferably 0.015%, and most preferably 0.013%.

In addition to the alloy composition described above, the wear-resistant steel of the present invention may further contain elements advantageous for ensuring physical properties, which is the object of the present invention. For example, titanium (Ti): 0.02% or less (excluding 0), niobium (Nb): 0.05% or less (excluding 0), vanadium (V): 0.05% or less (excluding 0), And calcium (Ca): can further comprise one or more selected from the group consisting of 2-100 ppm.

Titanium (Ti): 0.02% or less (excluding 0)
Titanium (Ti) is an element that maximizes the effect of B, which is an element effective in improving the hardenability of steel. Specifically, the Ti can be combined with nitrogen (N) to form a TiN precipitate to suppress the formation of BN, thereby increasing the solid solution B and maximizing the improvement of hardenability. However, if the Ti content exceeds 0.02%, coarse TiN precipitates may be formed and the toughness of the steel may be inferior. Therefore, in the present invention, it is preferable to add 0.02% or less of the above Ti. The lower limit of the Ti content is more preferably 0.005%, further preferably 0.007%, and most preferably 0.010%. The upper limit of the Ti content is more preferably 0.019%, further preferably 0.017%, and most preferably 0.015%.

Niobium (Nb): 0.05% or less (excluding 0)
Niobium (Nb) is dissolved in austenite to increase the curing ability of austenite and forms carbonitrides such as Nb (C, N) to improve the strength of steel and suppress the growth of austenite crystal grains. It is valid. However, if the Nb content exceeds 0.05%, coarse precipitates are formed, which may become a starting point for brittle fracture and impair toughness. Therefore, in the present invention, it is preferable to add 0.05% or less of the above Nb. The lower limit of the Nb content is more preferably 0.002%, further preferably 0.003%, and most preferably 0.005%. The upper limit of the Nb content is more preferably 0.040%, further preferably 0.035%, and most preferably 0.030%.

Vanadium (V): 0.05% or less (excluding 0)
Vanadium (V) is an element that is advantageous in suppressing the growth of austenite crystal grains, improving the hardenability of steel, and ensuring strength and toughness by forming VC carbides during reheating after hot rolling. Is. However, the above V is an expensive element, and if its content exceeds 0.05%, it becomes a factor that increases the manufacturing cost. Therefore, in the present invention, it is preferable to control the content of V to 0.05% or less when it is added. The lower limit of the V content is more preferably 0.002%, further preferably 0.003%, and most preferably 0.005%. The upper limit of the V content is more preferably 0.045%, further preferably 0.042%, and most preferably 0.040%.

Calcium (Ca): 2-100ppm
Calcium (Ca) has a good bondability with S, and has an effect of suppressing the formation of MnS segregated in the central portion of the steel material thickness by forming CaS. In addition, CaS produced by the addition of Ca has the effect of increasing corrosion resistance in a humid external environment. For the above-mentioned effect, it is preferable to add 2 ppm or more of the above Ca, but if the content exceeds 100 ppm, clogging of the nozzle or the like may be induced during the steelmaking operation, which is not preferable. Therefore, in the present invention, it is preferable to control the content of Ca to 2 to 100 ppm when it is added. The lower limit of the Ca content is more preferably 3 ppm, further preferably 4 ppm, and most preferably 5 ppm. The upper limit of the Ca content is more preferably 80 ppm, further preferably 60 ppm, and most preferably 40 ppm.

In addition to this, the wear-resistant steel of the present invention additionally has arsenic (As): 0.05% or less (excluding 0) and tin (Sn): 0.05% or less (in addition to the above-mentioned alloying elements). One or more selected from the group consisting of (excluding 0) and tungsten (W): 0.05% or less (excluding 0) can be further included.

The As is effective for improving the toughness of steel, and the Sn is effective for improving the strength and corrosion resistance of steel. Further, W is an element effective for improving hardness at high temperature in addition to increasing hardenability and improving strength. However, if the contents of As, Sn, and W each exceed 0.05%, not only the manufacturing cost increases, but also the physical characteristics of the steel may be impaired. Therefore, in the present invention, when the above As, Sn, and W are further contained, it is preferable to control the content to 0.05% or less, respectively. The lower limit of the contents of As, Sn, and W is more preferably 0.001%, further preferably 0.002%, and most preferably 0.003%, respectively. The upper limit of the contents of As, Sn, and W is more preferably 0.04%, more preferably 0.03%, and most preferably 0.02%, respectively.

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

On the other hand, in the wear-resistant steel of the present invention, it is preferable that C and Ni in the above-mentioned alloy composition satisfy the following relational expression 1. The present invention is characterized in that it secures not only ultra-high hardness but also excellent low-temperature toughness, and for this purpose, it is preferable to satisfy the following relational expression 1. If the following relational expression 1 is not satisfied, it may be difficult to improve the hardness and low temperature toughness to excellent levels. Therefore, the value of [C] × [Ni] is preferably 0.231 or more. The value of [C] × [Ni] is more preferably 0.396 or more, further preferably 0.792 or more, and most preferably 1 or more. On the other hand, the higher the value of [C] × [Ni] is, the more advantageous effect is realized. Therefore, in the present invention, the upper limit of the value of [C] × [Ni] is not particularly limited.
[Relational expression 1] [C] × [Ni] ≧ 0.231

The microstructure of the wear-resistant steel of the present invention preferably contains martensite as a matrix structure. More specifically, the wear-resistant steel of the present invention preferably contains martensite having an area fraction of 95% or more (including 100%). If the martensite fraction is less than 95%, it may be difficult to secure the target level of strength and hardness. On the other hand, the microstructure of the wear-resistant steel of the present invention can further contain bainite of 5 area% or less, whereby the low temperature impact toughness can be further improved. The martensite fraction is more preferably 96% or more, further preferably 97% or more. The bainite fraction is more preferably 4% or less, and even more preferably 3% or less.

The wear-resistant steel of the present invention provided as described above has the effect of ensuring a surface hardness of 550 to 650 HB and having an impact absorption energy of 21 J or more at a low temperature of −40 ° C. However, the above HB indicates the surface hardness of steel measured by a Brinell hardness tester.

Further, it is preferable that the hardness (HB) and the impact absorption energy (J) of the wear-resistant steel of the present invention satisfy the following relational expression 2. The present invention is characterized in that it improves the characteristics of low temperature toughness in addition to high hardness, and for this purpose, it is preferable to satisfy the following relational expression 2. That is, when the surface hardness is only high and the impact toughness is inferior and the relational expression 2 is not satisfied, or the impact toughness is excellent but the surface hardness cannot reach the target value and the relational expression 2 is not satisfied. In some cases, it becomes impossible to guarantee the properties of high hardness and low temperature toughness that are ultimately targeted.
[Relational formula 2] HB ÷ J ≦ 31.0 (However, the above HB indicates the surface hardness of steel measured by a Brinell hardness meter, and J indicates the impact absorption energy value at −40 ° C.).

Hereinafter, the method for manufacturing the wear-resistant steel of the present invention will be described in detail.
First, the steel slab is heated in the temperature range of 1050 to 1250 ° C. If the slab heating temperature is less than 1050 ° C, the resolidification of Nb and the like becomes insufficient, while if the temperature exceeds 1250 ° C, the austenite crystal grains may be coarsened and a non-uniform structure may be formed. There is. Therefore, in the present invention, it is preferable that the heating temperature of the steel slab is in the range of 1050 to 1250 ° C. The lower limit of the heating temperature of the steel slab is more preferably 1060 ° C, further preferably 1070 ° C, and most preferably 1080 ° C. The upper limit of the heating temperature of the steel slab is more preferably 1230 ° C, further preferably 1200 ° C, and most preferably 1180 ° C.

The reheated steel slab is roughly rolled in a temperature range of 950 to 1050 ° C. to obtain a rough rolled bar. If the temperature is less than 950 ° C. during the rough rolling, the rolling load increases and the rolling load is relatively weakly reduced, so that the deformation cannot be sufficiently transmitted to the center in the thickness direction of the slab, and it looks like a void. Defects may not be removed. On the other hand, if the temperature exceeds 1050 ° C., the particles will grow after recrystallization occurs at the same time as rolling, and the initial austenite particles may become excessively coarse. Therefore, in the present invention, the temperature of the rough rolling is preferably 950 to 1050 ° C. The lower limit of the rough rolling temperature is more preferably 960 ° C, further preferably 970 ° C, and most preferably 980 ° C. The upper limit of the rough rolling temperature is more preferably 1040 ° C, further preferably 1020 ° C, and most preferably 1000 ° C.

The rough-rolled bar is finished and hot-rolled in a temperature range of 850 to 950 ° C. to obtain a hot-rolled steel sheet. If the temperature of the finish hot-rolling is less than 850 ° C, the two-phase region rolling may occur and ferrite may be generated in the fine structure. On the other hand, if the temperature exceeds 950 ° C, the grain size of the final structure becomes small. There is a risk that it will become coarse and the low temperature toughness will be inferior. Therefore, in the present invention, the finish hot rolling temperature is preferably 850 to 950 ° C. The lower limit of the finish hot rolling temperature is more preferably 860 ° C, further preferably 870 ° C, and most preferably 880 ° C. The upper limit of the finish hot rolling temperature is more preferably 940 ° C, further preferably 930 ° C, and most preferably 920 ° C.

After that, the hot-rolled steel sheet is air-cooled to room temperature and then reheated in a temperature range of 860 to 950 ° C. for a furnace time of 1.3 t + 10 minutes to 1.3 t + 60 minutes (t: plate thickness). The reheating is for reverse-transforming a hot-rolled steel sheet composed of ferrite and pearlite with austenite single phase. There is a risk that the hardness of the final product will decrease due to the mixture of soft ferrite. On the other hand, when the temperature exceeds 950 ° C., the austenite crystal grains become coarse and have the effect of increasing the hardenability, but the low temperature toughness of the steel may be inferior. Therefore, in the present invention, the reheating temperature is preferably 860 to 950 ° C. The lower limit of the reheating temperature is more preferably 870 ° C, further preferably 880 ° C, and most preferably 890 ° C. The upper limit of the reheating temperature is more preferably 940 ° C, further preferably 930 ° C, and most preferably 920 ° C.

On the other hand, if the furnace time at the time of reheating is less than 1.3 t + 10 minutes (t: plate thickness), austenitization does not occur sufficiently, and the subsequent phase transformation due to rapid cooling, that is, the martensite structure is sufficient. You will not be able to get it. On the other hand, if the furnace time at the time of reheating exceeds 1.3 t + 60 minutes (t: plate thickness), the austenite crystal grains become coarse and have the effect of increasing the hardenability, which results in low temperature toughness. There is a risk of being inferior. Therefore, in the present invention, the furnace time at the time of reheating is preferably 1.3 t + 10 minutes to 1.3 t + 60 minutes (t: plate thickness). The lower limit of the furnace time at the time of reheating is more preferably 1.3t + 12 minutes, further preferably 1.3t + 15 minutes, and most preferably 1.3t + 20 minutes. The upper limit of the furnace time at the time of reheating is more preferably 1.3t + 50 minutes, further preferably 1.3t + 45 minutes, and most preferably 1.3t + 40 minutes.

After that, the reheated hot-rolled steel sheet is water-cooled to 150 ° C. or lower based on the plate surface layer portion (for example, the region from the surface to 1/8 t (t: plate thickness (mm))). If the temperature exceeds 150 ° C., a ferrite phase may be formed or a bainite phase may be excessively formed during cooling. Therefore, the water cooling stop temperature is preferably 150 ° C. or lower. The stop temperature is more preferably 100 ° C. or lower, further preferably 70 ° C. or lower, and most preferably 40 ° C. or lower.

The water cooling rate is preferably 10 ° C./s or higher. If the cooling rate is less than 10 ° C./s, there is a possibility that a ferrite phase is formed or a bainite phase is excessively formed during cooling. The cooling rate during water cooling is more preferably 15 ° C./s or higher, and even more preferably 20 ° C./s or higher. On the other hand, in the present invention, the faster the cooling rate is, the more advantageous it is. Therefore, the upper limit of the cooling rate is not particularly limited, and an ordinary engineer can appropriately set it in consideration of the limit of the equipment. can.

The hot-rolled steel sheet of the present invention that has undergone the above process conditions can be a thick steel sheet having a thickness of 60 mm or less, more preferably 8 to 50 mm, still more preferably 12 to 40 mm. Can be done. On the other hand, in the present invention, it is preferable not to perform the tempering step on the thick steel sheet.

Hereinafter, the present invention will be described in more detail with reference to examples. However, it should be noted that the following examples are merely intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of rights of the present invention. The scope of rights of the present invention is determined by the matters described in the claims and the matters reasonably inferred from them.

(Example)
After preparing the steel slabs having the alloy compositions of Tables 1 and 2 below, the steel slabs are heated-roughly rolled-hot rolled-cooled (normal temperature) -reheated-water-cooled under the conditions shown in Table 3 below. This was done to manufacture a hot-rolled steel sheet. The microstructure and mechanical properties of the hot-rolled steel sheet were measured and shown in Table 4 below.

At this time, the microstructure is made into a mirror surface by cutting a test piece to an arbitrary size, corroded with a Nital etching solution, and then thickened using an optical microscope and an electron scanning microscope. The position of 1 / 2t, which is the center of the
The hardness and toughness were measured using a Brinell hardness tester (load 3000 kgf, 10 mm tungsten pressure inlet) and a Charpy impact tester, respectively. At this time, the surface hardness was measured three times after the surface of the plate was milled by 2 mm, and the average value was shown. The results of the Charpy impact test showed the average value of the test pieces taken at the 1 / 4t position and then measured three times at −40 ° C.

As can be seen from Tables 1 to 4, in the case of the alloy composition and relational expression 1 proposed by the present invention, and the invention examples 1 to 6 satisfying the production conditions, it is needless to satisfy the fraction of the microstructure of the present invention. It can be seen that excellent hardness and low temperature impact toughness are ensured.
On the other hand, in the case of Comparative Examples 1 to 12 which satisfy the production conditions proposed by the present invention but do not satisfy the alloy composition or the relational expression 1, the hardness and the low temperature impact toughness level targeted by the present invention are not reached. I understand.

In the case of Comparative Example 13 which satisfies the alloy composition and the relational expression 1 proposed by the present invention but does not satisfy the reheating temperature among the production conditions, it is possible to secure the type and fraction of the microstructure proposed by the present invention. It can be seen that the surface hardness is also low.
In the case of Comparative Example 14 which satisfies the alloy composition and the relational expression 1 proposed by the present invention but does not satisfy the cooling end temperature among the production conditions, the martensite fraction proposed by the present invention cannot be secured. Retained austenite is formed, which indicates that the surface hardness is at a low level.
In the case of Comparative Example 15 which satisfies the alloy composition and the relational expression 1 proposed by the present invention but does not satisfy the cooling rate among the production conditions, the martensite fraction proposed by the present invention cannot be secured. It can be seen that the surface hardness is at a low level.

Claims (8)

By weight%, carbon (C): 0.33 to 0.42%, silicon (Si): 0.1 to 0.7%, 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), nickel (Ni): 0 .55-5.0%, copper (Cu): 0.01-1.5%, chromium (Cr): 0.01-0.8%, molybdenum (Mo): 0.01-0.8%, Boron (B): 50 ppm or less (excluding 0), cobalt (Co): 0.02% or less (excluding 0), and titanium (Ti): 0.02% or less (excluding 0), niobium (Nb): 0.05% or less (excluding 0), vanadium (V): 0.05% or less (excluding 0), and calcium (Ca): one or more selected from the group consisting of 2 to 100 ppm. Containing more, the balance consists of Fe and other unavoidable impurities.
The C and Ni satisfy the condition of the following relational expression 1.
Abrasion resistant steel having excellent hardness and impact toughness, characterized in that the microstructure contains martensite: 95 area% or more and bainite: 5% or less (including 0%).
[Relational expression 1] [C] × [Ni] ≧ 0.231 The wear-resistant steel includes arsenic (As): 0.05% or less (excluding 0), tin (Sn): 0.05% or less (excluding 0), and tungsten (W): 0.05% or less (0). The wear-resistant steel having excellent hardness and impact toughness according to claim 1, further comprising one or more selected from the group consisting of (excluding). The wear-resistant steel according to claim 1, wherein the wear-resistant steel has a hardness of 550 to 650 HB and is 21 J or more at a low temperature of −40 ° C.
(However, the HB indicates the surface hardness of steel measured by a Brinell hardness meter.) The wear-resistant steel according to claim 1, wherein the wear-resistant steel satisfies the following relational expression 2 in hardness (HB) and impact absorption energy (J), and has excellent hardness and impact toughness.
[Relational formula 2] HB ÷ J ≦ 31.0 (However, the HB indicates the surface hardness of the steel measured by the Brinell hardness meter, and J indicates the impact absorption energy value at −40 ° C.). The wear-resistant steel according to claim 1, wherein the wear-resistant steel has a thickness of 60 mm or less and has excellent hardness and impact toughness. By weight%, carbon (C): 0.33 to 0.42%, silicon (Si): 0.1 to 0.7%, 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), nickel (Ni): 0 .55-5.0%, copper (Cu): 0.01-1.5%, chromium (Cr): 0.01-0.8%, molybdenum (Mo): 0.01-0.8%, Boron (B): 50 ppm or less (excluding 0), cobalt (Co): 0.02% or less (excluding 0), and titanium (Ti): 0.02% or less (excluding 0), niobium (Nb): 0.05% or less (excluding 0), vanadium (V): 0.05% or less (excluding 0), and calcium (Ca): 1 or more selected from the group consisting of 2 to 100 ppm. Further containing, the balance Fe and other unavoidable impurities, the C and Ni are the steps of heating a steel slab satisfying the condition of the following relational expression 1 in a temperature range of 1050-1250 ° C.
The step of rough-rolling the reheated steel slab in a temperature range of 950 to 1050 ° C. to obtain a rough-rolled bar.
The stage where the rough-rolled bar is finished and hot-rolled in a temperature range of 850 to 950 ° C. to obtain a hot-rolled steel sheet.
After the hot-rolled steel sheet is air-cooled to room temperature, it is reheated in the temperature range of 860 to 950 ° C. for the furnace time [1.3t + 10 minutes to 1.3t + 60 minutes (t: plate thickness)], and the reheating. A method for producing wear-resistant steel having excellent hardness and impact toughness, which comprises a step of water-cooling a heated hot-rolled steel sheet to 150 ° C. or lower.
[Relational expression 1] [C] × [Ni] ≧ 0.231 The steel slab has arsenic (As): 0.05% or less (excluding 0), tin (Sn): 0.05% or less (excluding 0), and tungsten (W): 0.05% or less (excluding 0). The method for producing a wear-resistant steel having excellent hardness and impact toughness according to claim 6, further comprising one or more selected from the group consisting of). The method for producing wear-resistant steel having excellent hardness and impact toughness according to claim 6, wherein the cooling rate at the time of water cooling is 10 ° C./s or more.