KR102507276B1 - Steel and its manufacturing method - Google Patents

Abstract

A steel material and its manufacturing method are provided. In mass%, C: 0.10% or more and 2.50% or less, Mn: 8.0% or more and 45.0% or less, P: 0.300% or less, S: 0.1000% or less, Ti: 0.10% or more and 5.00% or less, Al: 0.001% or more 5.000% Hereinafter, N: 0.5000% or less and O: 0.1000% or less, and C, Ti, and Mn are 25 ([C] -12.01 [Ti] / 47.87) + [Mn] ≥ 25 (where [ C], [Ti], [Mn]: the content (mass%) of each element is contained so as to satisfy the balance, and the balance is Fe and unavoidable impurities in the component composition, in area ratio, an austenite phase of 90% or more, Ti A steel material having a structure containing 0.2% or more of carbide. Such a structure is obtained by heating steel materials having the above-described component composition to a temperature of 950°C or higher and then cooling the temperature range between 900°C and 500°C at a cooling rate of more than 1°C/s. Thereby, it becomes a steel material excellent in wear resistance. In addition, by adjusting the hardness of the austenite phase to 200 HV or more, the impact wear resistance is remarkably improved.

Description

Steel and its manufacturing method

[0001] The present invention relates to a steel material and a method for manufacturing the same, and more particularly to improving the wear resistance of an austenitic steel material.

Industrial machinery and conveying equipment such as power shovels, bulldozers, hoppers, bucket conveyors, and rock crushers used in the fields of construction, civil engineering, and mining, for example, slide wear caused by rocks, sand, ore, etc. , is exposed to abrasion such as impact abrasion. Therefore, members of industrial machinery, transportation equipment, etc. are required to have excellent wear resistance from the viewpoint of improving the life of machinery, equipment, etc.

It is known that the wear resistance of steel materials improves with an increase in steel material hardness. Among the steel structures, the austenite phase has a high amount of hardening upon strain, that is, high work hardenability. Therefore, hardening proceeds in the vicinity of the wear surface during use in an impact wear environment in which an impact force such as a rock collision is applied to the austenitic steel material, and exhibits very excellent wear resistance. Further, the austenite phase has better ductility and toughness than structures such as ferrite phase and martensite phase. Therefore, for example, austenitic steel materials in which an austenite structure is obtained by high manganese content, such as Hadfield steel, have been widely used as inexpensive wear-resistant steel materials.

For example, Patent Literature 1 describes "a wear-resistant austenitic steel and a method for producing the same." The technology described in Patent Literature 1, in weight%, manganese (Mn): 15 to 25%, carbon (C): 0.8 to 1.8%, copper (Cu) that satisfies 0.7C-0.56(%)≤Cu≤5% ), the balance being Fe and other unavoidable impurities, and having a Charpy impact value of 100 J or more at -40 ° C. According to the technology disclosed in Patent Literature 1, the high manganese content stably obtains an austenite structure, and further suppresses the formation of carbides in the heat-affected zone after welding, thereby preventing the decrease in toughness of the heat-affected zone. has been

In addition, Patent Literature 2 describes "a wear-resistant austenitic steel material and a manufacturing method thereof". The wear-resistant austenitic steel described in Patent Literature 2 contains, in weight%, manganese (Mn) of 8 to 15%, carbon (C) satisfying the relationship of 23% < 33.5C-Mn ≤ 37%, 1.6C- A wear-resistant austenitic steel material with excellent ductility, containing copper (Cu) satisfying 1.4 (%) ≤ Cu ≤ 5%, the balance being composed of Fe and other unavoidable impurities, and having an area fraction of carbides of 10% or less. . According to the technique described in Patent Literature 2, it is said that high manganese content stably obtains an austenite structure, and suppresses the formation of carbides inside steel materials, thereby preventing a decrease in toughness of steel materials.

Japanese Patent No. 5879448 Japanese Patent No. 6014682

However, in the austenitic steel materials described in Patent Literatures 1 and 2, in the form of wear in which no impact force is applied to the steel material, for example, as sand rubs the surface of the steel material, that is, in the form of wear such as sliding wear, on the surface of the steel material Since a large hardened layer is not formed, significant improvement in wear resistance is not obtained.

In view of these problems of the prior art, an object of the present invention is to provide an austenitic steel material having excellent wear resistance and a method for producing the same. "Excellent wear resistance" as used herein refers to having both excellent sliding wear resistance and excellent impact wear resistance, and "steel materials" include plate-shaped steel plates (plates), rod-shaped steel bars (bars), wire-shaped wires, It shall contain section steel of various cross-sectional shapes.

In order to achieve the above object, the present inventors first intensively studied various factors affecting the sliding wear resistance of austenitic steel materials. As a result, in order to improve the sliding wear resistance of austenitic steel materials, it is effective to include hard grains in the matrix phase (austenite phase), and in particular, the grains that can be contained in the matrix phase (austenite phase). Among them, Ti carbide having a very high hardness was found to be effective. In sliding wear, wear progresses as the outermost layer of steel materials is continuously shaved, so when hard particles are included in the matrix phase (austenite phase), wear progresses and hard particles appear in the outermost layer of steel materials, It becomes resistance against the progress of abrasion, improves abrasion resistance, and lengthens the abrasion life.

On the other hand, in order to improve the impact wear resistance of austenitic steel materials, it is important to maintain a stable austenite structure, and in addition, in order to obtain a stable austenite structure at low cost even at room temperature, a high amount of C and Mn, which are austenite stabilizing elements, is important. need to do a lot of However, as described above, if a large amount of Ti carbide is included in the matrix phase to improve the slip wear resistance, the amount of C effective for maintaining a stable austenite structure is reduced. Therefore, the present inventors considered the difference between the high capacity of C and Mn, which are austenite stabilizing elements, and the austenite stabilizing ability of C and Mn, and the following equation (1)

25([C]-12.01[Ti]/47.87)+[Mn]≥　25　　... … (One)

(Here, [C], [Ti], [Mn]: content of each element (mass%))

It was newly discovered that adjusting the amounts of C and Mn to satisfy the relational expression of is effective for achieving both excellent slip wear resistance and excellent impact wear resistance.

The present invention was completed by further examination based on the above recognition, and the gist of the present invention is as follows.

(1) in mass%,

C: 0.10% or more and 2.50% or less;

Mn: 8.0% or more and 45.0% or less;

P: 0.300% or less;

S: 0.1000% or less;

Ti: 0.10% or more and 5.00% or less;

Al: 0.001% or more and 5.000% or less;

N: 0.5000% or less;

O (oxygen): 0.1000% or less

and contains C, Ti, and Mn within a range that satisfies the following formula (1), the balance being Fe and unavoidable impurities, and an area ratio of 90% or more of austenite phase and Ti A steel material having a structure containing 0.2% or more of carbides.

energy

25([C]-12.01[Ti]/47.87)+[Mn]≥　25　　... … (One)

Here, [C], [Ti], [Mn]: content of each element (mass%)

(2) The steel materials according to the above (1), wherein the austenite phase has a Vickers hardness of 200 HV or more.

(3) In addition to the above component composition, in mass%,

Si: 0.01% or more and 5.00% or less;

Cu: 0.1% or more and 10.0% or less;

Ni: 0.1% or more and 25.0% or less;

Cr: 0.1% or more and 30.0% or less;

Mo: 0.1% or more and 10.0% or less;

Nb: 0.005% or more and 2.000% or less;

V: 0.01% or more and 2.00% or less;

W: 0.01% or more and 2.00% or less;

B: 0.0003% or more and 0.1000% or less;

Ca: 0.0003% or more and 0.1000% or less;

Mg: 0.0001% or more and 0.1000% or less;

REM: 0.0005% or more and 0.1000% or less

The steel materials described in said (1) or said (2) containing 1 type(s) or 2 or more types selected from among.

(4) A casting step of melting molten steel into a cast steel, a heating step of heating the cast steel, a hot rolling step of hot rolling the heated cast steel into a steel material, and a cooling step of cooling the steel material in sequence. As a method for manufacturing steel materials to be carried out,

The cast steel, in mass%,

C: 0.10% or more and 2.50% or less;

Mn: 8.0% or more and 45.0% or less;

P: 0.300% or less;

S: 0.1000% or less;

Ti: 0.10% or more and 5.00% or less;

Al: 0.001% or more and 5.000% or less;

N: 0.5000% or less;

O (oxygen): 0.1000% or less

In addition, C, Ti, and Mn are contained within a range satisfying the following formula (1), the balance being Fe and unavoidable impurities,

The heating temperature in the heating step is 950 ° C. or more and 1300 ° C. or less,

The manufacturing method of steel materials which makes cooling in the said cooling process an average cooling rate in the temperature range of 900-500 degreeC, more than 1 degreeC/s.

energy

25([C]-12.01[Ti]/47.87)+[Mn]≥　25　　... … (One)

Here, [C], [Ti], [Mn]: content of each element (% by mass)

(5) The cast steel, in addition to the above component composition, in mass%,

Si: 0.01% or more and 5.00% or less;

Cu: 0.1% or more and 10.0% or less;

Ni: 0.1% or more and 25.0% or less;

Cr: 0.1% or more and 30.0% or less;

Mo: 0.1% or more and 10.0% or less;

Nb: 0.005% or more and 2.000% or less;

V: 0.01% or more and 2.00% or less;

W: 0.01% or more and 2.00% or less;

B: 0.0003% or more and 0.1000% or less;

Ca: 0.0003% or more and 0.1000% or less;

Mg: 0.0001% or more and 0.1000% or less;

REM: 0.0005% or more and 0.1000% or less

The manufacturing method of the steel materials as described in said (4) containing 1 type(s) or 2 or more types selected from among.

(6) The method for producing steel materials according to the above (4) or (5), wherein the hot rolling has a total reduction ratio of 25% or more in a temperature range of 950°C or lower.

ADVANTAGE OF THE INVENTION According to this invention, the austenitic steel material excellent in wear resistance, which has both excellent sliding wear resistance and excellent impact wear resistance, can be provided, and it brings about a special industrial effect. In addition, according to the present invention, there is also an effect that the life of industrial machines, transportation machines, etc. operating under various abrasion environments can be improved.

1 is an explanatory view schematically showing the outline of an abrasion test apparatus used in Examples.
Fig. 2 is an explanatory view schematically showing the outline of an abrasion test apparatus used in Examples.

(Mode for implementing the invention)

In the austenitic steel material of the present invention, in mass%, C: 0.10% or more and 2.50% or less, Mn: 8.0% or more and 45.0% or less, P: 0.300% or less, S: 0.1000% or less, Ti: 0.10% or more 5.00% Hereinafter, Al: 0.001% or more and 5.000% or less, N: 0.5000% or less, and O (oxygen): 0.1000% or less, and C, Ti, and Mn are included in the following formula (1)

25([C]-12.01[Ti]/47.87)+[Mn]≥　25　　... … (One)

(Here, [C], [Ti], [Mn]: content of each element (mass%))

is contained within a range that satisfies the relational expression of , and has a component composition of Fe and unavoidable impurities as the balance.

First, the reason for limiting the component composition of steel materials is explained. In addition, below, "mass %" regarding a component composition is simply described as "%" unless otherwise indicated.

C: 0.10% or more and 2.50% or less

C is an element that stabilizes the austenite phase and is an important element for obtaining an austenite structure at room temperature. In order to obtain such an effect, 0.10% or more of C content is required. If C is less than 0.10%, the stability of the austenite phase is insufficient, and a sufficient austenite structure cannot be obtained at normal temperature. On the other hand, when it exceeds 2.50%, the hardness increases and the toughness of the welded part decreases. Therefore, in the present invention, C is limited to a range of 0.10% or more and 2.50% or less. Moreover, it is preferably 0.12% or more and 2.00% or less.

Mn: 8.0% or more and 45.0% or less

Mn is an element that stabilizes the austenite phase and is an important element for obtaining an austenite structure at room temperature. In order to obtain such an effect, Mn content of 8.0% or more is required. If Mn is less than 8.0%, the stability of the austenite phase is insufficient, and a sufficient austenite structure cannot be obtained. On the other hand, when it exceeds 45.0%, the effect of stabilizing the austenite phase is saturated and becomes economically unfavorable. Therefore, in the present invention, Mn is limited to a range of 8.0% or more and 45.0% or less. Moreover, it is preferably 10.0% or more and 40.0% or less.

P: 0.300% or less

P is an element having an effect of segregating at the grain boundaries to embrittle the grain boundaries and reducing the toughness of steel materials. In the present invention, it is desirable to reduce P as much as possible, but it is permissible if it is 0.300% or less. Preferably it is 0.250% or less. Further, P is an element that is unavoidably contained in steel as an impurity, and the smaller it is, the better. However, since excessively low P causes an increase in refining time and an increase in refining cost, P is set to 0.001% or more. desirable.

S: 0.1000% or less

S is an element that is mainly dispersed in steel as a sulfide-based inclusion and reduces the ductility and toughness of steel. Therefore, in this invention, it is desirable to reduce as much as possible, but if it is 0.1000% or less, it is permissible. Moreover, Preferably it is 0.0800 % or less. The smaller the S is, the better it is, but since an excessive reduction in S causes an increase in the refining time and an increase in the refining cost, S is preferably set to 0.0001% or more.

Ti: 0.10% or more and 5.00% or less

Ti is an important element in the present invention, and is an element that has an effect of forming hard carbides and improving the slip wear resistance of the austenite structure. In order to obtain such an effect, 0.10% or more of containing is required. On the other hand, containing exceeding 5.00% reduces ductility and toughness. Therefore, Ti was limited to the range of 0.10% or more and 5.00% or less. Moreover, it is 0.60 % or more and 4.50 % or less preferably.

Al: 0.001% or more and 5.000% or less

Al is an element that effectively acts as a deoxidizer, and requires 0.001% or more of Al to obtain the effect. On the other hand, when it contains more than 5.000%, the cleanliness of steel will fall and ductility and toughness will fall. Therefore, Al is 0.001% or more and 5.000% or less. Moreover, it is 0.003% or more and 4.500% or less preferably.

N: 0.5000% or less

N is an element that is unavoidably contained in steel as an impurity and reduces the ductility and toughness of a welded part. It is desirable to reduce it as much as possible, but it is permissible if it is 0.5000% or less. Preferably it is 0.3000% or less. A smaller N is preferable, but excessively low N causes an increase in refining time and an increase in refining cost. For this reason, it is preferable to make N into 0.0005% or more.

O (oxygen): 0.1000% or less

O is an element that is unavoidably contained in steel as an impurity, exists in steel as an inclusion such as oxide, and reduces ductility and toughness. Preferably it is 0.0500% or less. The smaller the amount of O, the better. However, since excessive hypoxia causes an increase in the refining time and an increase in the refining cost, the amount of O is preferably 0.0005% or more.

In the present invention, C, Ti, and Mn are added within the above ranges, and the following formula (1)

25([C]-12.01[Ti]/47.87)+[Mn]≥　25　　... … (One)

(Here, [C], [Ti], [Mn]: content of each element (mass%))

It contains so as to satisfy the relational expression of

The left side of the equation (1) represents the degree of stabilization of the austenite phase, and the larger the value on the left side, the higher the degree of stability of the austenite phase. The left side of equation (1) is the sum of the content of C, which is an element contributing to the stabilization of the austenite phase, and the content of Mn, and the austenite stabilization ability of each element is taken into account and multiplied by a coefficient according to the austenite stabilization ability. In addition, the effective content of C is obtained by subtracting the amount that precipitates as Ti carbide and does not contribute to the stabilization of the austenite phase.

In addition, when the content of C, Ti, and Mn does not satisfy the formula (1), the austenite stability is insufficient, and a desired austenite structure cannot be obtained at room temperature.

Further, from the viewpoint of the degree of stabilization of the austenite phase, the value on the left side of the formula (1) is preferably 30 or more.

In the present invention, the above-described components are basic components, but in addition to these basic components, as necessary, Si: 0.01% or more and 5.00% or less, Cu: 0.1% or more and 10.0% or less, Ni: 0.1% or more, 25.0% or less, Cr: 0.1% or more, 30.0% or less, Mo: 0.1% or more, 10.0% or less, Nb: 0.005% or more, 2.000% or less, V: 0.01% or more, 2.00% or less, W: 0.01% or more 2.00% Hereinafter, B: 0.0003% or more and 0.1000% or less, Ca: 0.0003% or more and 0.1000% or less, Mg: 0.0001% or more and 0.1000% or less, REM: 0.0005% or more and 0.1000% or less. there is.

Si, Cu, Ni, Cr, Mo, Nb, V, W, B, Ca, Mg, and REM are all elements that improve the strength of steel materials (strength of the base material or welded part), and are selected as needed and selected as one type. Or it may contain 2 or more types.

Si: 0.01% or more and 5.00% or less

Si is an element that works effectively as a deoxidizer and also contributes to high hardness of steel materials by solid solution. In order to acquire such an effect, 0.01% or more of containing is required. If Si is less than 0.01%, the above effects cannot be sufficiently obtained. On the other hand, containing exceeding 5.00% causes problems such as an increase in the amount of inclusions in addition to lowering ductility and toughness. From these points, when it is contained, it is preferable to set Si as the range of 0.01% or more and 5.00% or less. More preferably, it is 0.05% or more and 4.50% or less.

Cu: 0.1% or more 10.0%

Cu is an element that is dissolved or precipitated and contributes to improving the strength of steel materials. In order to acquire such an effect, 0.1% or more of containing is required. On the other hand, even if it contains more than 10.0%, the effect is saturated and economically unfavorable. Therefore, when it contains, it is preferable to set Cu as the range of 0.1% or more and 10.0% or less. More preferably, it is 0.5% or more and 8.0% or less.

Ni: 0.1% or more and 25.0% or less

Ni is an element that has an effect of improving toughness while contributing to improvement of strength of steel materials. In order to acquire such an effect, 0.1% or more of containing is required. On the other hand, even if it contains more than 25.0%, the effect is saturated and economically unfavorable. Therefore, when containing, it is preferable to make Ni into the range of 0.1% or more and 25.0% or less. More preferably, it is 0.5% or more and 20.0% or less.

Cr: 0.1% or more and 30.0% or less

Cr is an element that contributes to improving the strength of steel. In order to acquire such an effect, 0.1% or more of containing is required. On the other hand, when it contains more than 30.0%, the effect is saturated and economically unfavorable. Therefore, when it contains, it is preferable to make Cr into the range of 0.1% or more and 30.0% or less. More preferably, it is 0.5% or more and 28.0% or less.

Mo: 0.1% or more and 10.0% or less

Mo is an element that contributes to improving the strength of steel. In order to acquire such an effect, 0.1% or more of containing is required. On the other hand, when it contains more than 10.0%, the effect is saturated and economically unfavorable. Therefore, when it contains, it is preferable to make Mo into the range of 0.1% or more and 10.0% or less. More preferably, it is 0.5% or more and 8.0% or less.

Nb: 0.005% or more and 2.000% or less

Nb is an element that contributes to the strength improvement of steel by precipitating as a carbonitride. In order to obtain such an effect, 0.005% or more of containing is required. On the other hand, containing exceeding 2.000% lowers toughness. Therefore, when it contains, it is preferable to make Nb into the range of 0.005% or more and 2.000% or less. More preferably, it is 0.007% or more and 1.700% or less.

V: 0.01% or more and 2.00% or less

V is an element that precipitates as a carbonitride and contributes to improving the strength of steel. In order to acquire such an effect, 0.01% or more of containing is required. On the other hand, containing exceeding 2.00% lowers toughness. Therefore, when it contains, it is preferable to set V as 0.01% or more and 2.00% or less of range. More preferably, it is 0.02% or more and 1.80% or less.

W: 0.01% or more and 2.00% or less

W is an element that contributes to improving the strength of steel. In order to acquire such an effect, 0.01% or more of containing is required. On the other hand, containing exceeding 2.00% lowers toughness. Therefore, when it contains, it is preferable to make W into the range of 0.01% or more and 2.00% or less. More preferably, it is 0.02% or more and 1.80% or less.

B: 0.0003% or more and 0.1000% or less

B is an element that is segregated at grain boundaries and contributes to improvement of grain boundary strength. In order to obtain such an effect, 0.0003% or more of containing is required. On the other hand, when it contains exceeding 0.1000%, toughness will fall by grain boundary precipitation of carbonitride. Therefore, when it contains, it is preferable to make B into the range of 0.0003% or more and 0.1000%. More preferably, it is 0.0005% or more and 0.0800% or less.

Ca: 0.0003% or more and 0.1000% or less

Ca forms an oxysulfide with high stability at high temperature, pinning grain boundaries, suppressing coarsening of crystal grains in weld zones and keeping them fine, and improving the strength and toughness of welded joints. is an element that contributes to In order to obtain such an effect, 0.0003% or more of containing is required. On the other hand, when it contains more than 0.1000%, cleanliness will fall and toughness of steel will fall. Therefore, when it contains, it is preferable to set Ca as 0.0003% or more and 0.1000% or less of range. More preferably, it is 0.0005% or more and 0.0800% or less.

Mg: 0.0001% or more and 0.1000% or less

Mg forms oxysulfides with high stability at high temperatures, pinning grain boundaries, suppressing coarsening of grains in weld zones and keeping grains fine, particularly for improving strength and toughness of welded joints. element that contributes In order to obtain such an effect, 0.0001% or more of containing is required. On the other hand, when it contains more than 0.1000%, cleanliness will fall and the toughness of steel materials will fall. Therefore, when it contains, it is preferable to make Mg into the range of 0.0001% or more and 0.1000% or less. More preferably, it is 0.0005% or more and 0.0800% or less.

REM: 0.0005% or more and 0.1000% or less

REM (rare earth metal) forms oxysulfide with high stability at high temperature, pinning the grain boundaries, suppressing the coarsening of the grains in the weld zone in particular, keeping the grains fine, and improving the strength and toughness of the welded joint. It is an element that contributes to improvement. In order to obtain such an effect, 0.0005% or more of containing is required. On the other hand, when it contains more than 0.1000%, cleanliness will fall and the toughness of steel materials will fall. Therefore, when containing, it is preferable to make REM into the range of 0.0005% or more and 0.1000% or less. More preferably, it is the range of 0.0010% or more and 0.0800% or less.

Remainder other than the above components is Fe and unavoidable impurities.

The austenitic steel material of the present invention has the above-described component composition, and further has a structure containing an austenite phase of 90% or more and Ti carbide of 0.2% or more in area ratio.

Austenite phase in the structure: 90% or more

The structure of the steel of the present invention mainly contains an austenite phase from the viewpoint of improving impact wear resistance. In order to obtain such an effect, the austenite phase is set to 90% or more in area ratio. If the austenite phase is less than 90% in area ratio, the impact wear resistance is lowered, and the ductility, toughness, workability, and toughness of the weld zone (weld heat affected zone) are also lowered. Therefore, the area ratio of the austenite phase in the structure is 90% or more, and may be 100%. The ratio of the "austenite phase in the structure" referred to herein represents the ratio (area ratio) of the austenite phase to the total amount of the structure excluding inclusions and precipitates. In addition, the structure other than the austenite phase may be at least one of a ferrite phase, a bainite structure, a martensite structure, and a pearlite structure with an area ratio of less than 10% in total.

The area ratio of the austenite phase in the structure was determined by backscattering electron diffraction (EBSP) analysis, and from the obtained Inverse Pole Figure map, the structure excluding inclusions and precipitates (ferrite phase, bainite structure, martensite structure, Pearlite structure, austenite phase) It is determined by calculating the ratio of the austenite phase to the total amount. In addition, "the ratio of austenite phase" here shall use the value measured at the position of 1 mm depth below the surface of steel materials.

Further, in order to further improve wear resistance, particularly impact wear resistance, it is desirable to keep the hardness of the matrix (austenite phase), that is, the hardness of the austenite phase itself high. By setting the hardness of the austenite phase to 200 HV or more, particularly in terms of Vickers hardness, significant improvement in impact wear resistance is confirmed. When the austenitic phase hardness is less than 200 HV, the improvement in impact wear resistance is small. For this reason, from the viewpoint of improving impact wear resistance, it is preferable to set the hardness of the austenite phase to 200 HV or more. More preferably, it is 250 HV or more. Moreover, in order to ensure ductility, it is preferably 400 HV or less, more preferably 380 HV or less.

Ti carbide: 0.2% or more

In the present invention, Ti carbide, which is a particle harder than sand or rock components such as Al ₂ O ₃ and SiO ₂ , is included in the structure. Ti carbide contained in the structure is a hard particle, and has an action of improving the sliding wear resistance by being resistant to sliding wear caused by sand or rock components. In order to obtain such an effect, it is necessary to include Ti carbide in an area ratio of 0.2% or more in the structure. For this reason, the content of Ti carbide was limited to 0.2% or more in terms of area ratio. Preferably it is 0.5% or more. In addition, the upper limit of the content of Ti carbide is not particularly limited, but it is preferably 10% or less in terms of area ratio from the viewpoint of ductility and toughness of steel materials. More preferably, it is 8.0% or less.

Further, in the present invention, Ti carbide is identified using energy dispersive X-ray spectroscopy (EDS) of a scanning electron microscope (SEM), and the total area of the Ti carbide is measured using image analysis software. Then, the area ratio of Ti carbide was calculated. In the measurement of EDS, precipitates containing 10 at% or more of Ti and 30 at% or more of C in atomic fraction were counted as Ti carbides. In addition, "content of Ti carbide" mentioned here shall use the value measured at the position of 1 mm depth below the surface of steel materials.

Next, a preferable manufacturing method for steel materials having the above-described component composition and structure will be described.

In a preferred method for producing steel of the present invention, first, molten steel is melted with a commercially available solvent such as an electric furnace or a vacuum melting furnace, and then a casting step of obtaining a cast steel by casting and a heating step of heating the cast steel are performed in this order. carried out with Then, a hot rolling process of hot rolling (hot working) the heated cast steel to obtain steel materials, and a cooling process of cooling the obtained steel materials following the hot rolling process are performed. Examples of steel materials obtained by this step include plate-shaped steel plates, rod-shaped steel bars, linear wire rods, and shaped steels having various cross-sectional shapes such as H-shaped and the like.

In the preferred production method of the present invention, first, molten steel melted with a commercially available solvent such as an electric furnace or a vacuum melting furnace is cast, and a casting step of forming a cast steel having the above-described predetermined component composition is performed.

Usually, since the cooling rate during casting is very slow, the contained C may precipitate as carbides other than Ti carbides during casting. When the contained C precipitates as carbides other than Ti carbides, the stability of the austenite phase decreases. Therefore, after cooling to normal temperature, it becomes difficult to stably form an austenite phase.

So, in this invention, the heating process of heating the cast steel which has the above-mentioned component composition is performed.

The "heating" temperature, that is, the "heating temperature" referred to herein is a temperature range of 950°C or more and 1300°C or less, which is a temperature range in which carbides other than Ti carbides form solid solution. Ti carbide is generated during cooling after solidification of molten steel, and its solid solution temperature is very high, close to the melting point of steel. Therefore, in the step of heating in the above temperature range, Ti carbide remains without solid solution, and carbides other than Ti carbide form solid solution.

When the heating temperature is less than 950°C, the carbides precipitated during casting do not dissolve into solid solution. For this reason, the amount of solid solution C is insufficient, the degree of stabilization of the austenite phase is low, and after cooling to room temperature, the austenite phase is not obtained. On the other hand, when the heating temperature exceeds 1300°C, the heating temperature becomes excessively high, and the cost for heating increases, which becomes economically unfavorable. Therefore, the heating temperature was limited to a temperature in the range of 950°C or more and 1300°C or less. Preferably, it is 980 degreeC or more and 1270 degreeC or less. In addition, said temperature is the temperature at the position of 1 mm below the surface of steel materials.

Next, a hot rolling step is performed to obtain a steel material having a predetermined shape by subjecting the heated cast steel to hot rolling (hot working).

Further, in the present invention, as long as it is possible to roll (process) a steel material having a desired size and shape, there is no need to specifically limit the rolling (processing) conditions such as temperature and reduction ratio. In addition, when it is desired to further improve the wear resistance of steel materials, particularly the impact wear resistance, it is necessary to increase the hardness of the austenite phase as a base. In this case, it is preferable to perform hot rolling under conditions where the total reduction ratio in a temperature range of 950°C or lower is 25% or more.

In addition, the total reduction ratio r in the temperature range of 950 ° C. or less is

r(%) = {(ti−tf)/ti}×100

(Here, ti: sheet thickness when the steel sheet temperature reaches 950 ° C. during rolling (mm), tf: sheet thickness at the end of rolling (mm))

can be calculated as

By performing hot rolling under the condition that the total reduction ratio in the temperature range of 950 ° C. or less is 25% or more, the hardness of the austenite phase is increased to 200 HV or more, and wear resistance, particularly impact wear resistance, is improved. When the total reduction ratio in the temperature range of 950°C or lower is less than 25%, the hardness improvement of the austenite phase is insufficient. The total reduction ratio is preferably 30% or more. In addition, considering the rolling efficiency, the total rolling reduction is preferably 80% or less, and more preferably 70% or less. In addition, the dislocation introduced by the reduction in the temperature range exceeding 950°C is consumed by recrystallization of the austenite phase, and the contribution to the improvement of the hardness of the austenite phase is small. From that point of view, the finish rolling temperature is preferably 930°C or lower. In addition, taking operational efficiency into consideration, the finish rolling temperature is preferably 600°C or higher, and more preferably 650°C or higher.

Following the process of performing hot rolling on the heated cast steel, a cooling process in which the average cooling rate in the temperature range of 900 ° C. or less and 500 ° C. or more performs cooling of more than 1 ° C. / s is performed.

In the cooling step, the average cooling rate between 900°C and 500°C is adjusted to more than 1°C/s. When the average cooling rate between 900 ° C and 500 ° C is 1 ° C / s or less, carbides precipitate, the amount of solid solution C decreases, and the austenite stability is insufficient, so that the desired austenite phase cannot be obtained after cooling. Therefore, cooling makes the average cooling rate in the temperature range of 900 degreeC - 500 degreeC exceed 1 degreeC/s. Also, it is preferably 2°C/s or higher. As the cooling method, any commercially available cooling method capable of achieving the above cooling rate can be applied.

In addition, there is no need to particularly limit the upper limit of the average cooling rate, but expensive cooling equipment is required to realize rapid cooling such that the average cooling rate exceeds 300°C/s. Therefore, the average cooling rate between 900°C and 500°C during cooling is preferably 300°C/s or less. More preferably, it is 200 degrees C/s or less. In addition, said temperature is the temperature at the position of 1 mm below the surface of steel materials.

Hereinafter, the present invention will be further described based on examples.

Example

(Example 1)

First, molten steel was melted and cast in a vacuum melting furnace to manufacture cast pieces (thickness: 100 to 200 mm) having the component composition shown in Table 1. Next, a heating step of heating the obtained cast steel to the heating temperature shown in Table 2, and a hot rolling step of hot rolling the heated cast steel under the conditions shown in Table 2 to obtain a steel plate (steel material) having a plate thickness shown in Table 2. Then, the cooling step of cooling the obtained steel sheet at an average cooling rate between 900°C and 500°C as shown in Table 2 was sequentially performed to obtain steel materials (steel sheet). In addition, in some hot rolling, it was set as the hot rolling which adjusted the reduction ratio (cumulative reduction ratio) in the temperature range of 950 degreeC or less.

In the cooling step after the hot rolling step, cooling was performed by water cooling, air cooling, or a combination thereof. In addition, the average cooling rate was calculated based on the temperature measured with a thermocouple attached to a position 1 mm below the surface of the steel sheet. When the cooling start temperature was less than 900°C, the average cooling rate was calculated between the cooling start temperature and 500°C.

The obtained steel sheet was subjected to a hardness measurement test, a structure observation, and an abrasion test to determine the hardness of the austenite phase, the area ratio of the austenite phase, and the area ratio of Ti carbide in a subsurface 1 mm portion, and further, slip resistance Abrasion resistance and impact abrasion resistance were evaluated. The test method was carried out as follows.

(1) Hardness measurement test

A test piece for hardness measurement is taken from a predetermined position of each obtained steel sheet, polished so that the cross section in the thickness direction becomes a measurement surface, and then austenite at a position 1 mm below the surface with a Vickers hardness tester (test force: 10 kgf). The Vickers hardness (HV) of each phase was measured at 10 points, and the average value thereof was made the hardness of the steel sheet concerned. In addition, when the austenite phase did not exist, the hardness was not measured.

(2) Tissue observation

From a predetermined position of each obtained steel plate, a test piece for structure observation was taken so that the observation surface was at a position 1 mm below the surface, and the observation surface was ground and polished (mirror-finished).

(2-1) Area ratio of austenite phase

Backscattered electron diffraction (EBSP) analysis was performed on the mirror-polished observation surface using the collected specimen for tissue observation. EBSP analysis was performed in the range of 1 mm × 1 mm under the conditions of a measurement voltage: 20 kV and a step size: 1 μm, and from the obtained Inverse Pole Figure (reverse pole figure) map, the structure excluding inclusions and precipitates (ferrite phase , bainite structure, martensite structure, pearlite structure, austenite phase) The ratio (area ratio) of the austenite phase to the total amount was calculated.

(2-2) Ti carbide area ratio

With respect to the mirror-polished observation surface using the collected tissue observation test piece, using energy dispersive X-ray spectroscopy (EDS) of a scanning electron microscope (SEM), an acceleration voltage in the range of 1 mm × 1 mm was used. : 15 kV, step size: 1 μm, Ti carbide was identified by analysis, and the total area of the Ti carbide was measured using image analysis software to calculate the area ratio of Ti carbide. In the measurement of EDS, precipitates containing 10 at% or more of Ti and 30 at% or more of C in atomic fraction were counted as Ti carbides.

(3) Abrasion test

The wear resistance of steel materials is mainly determined by the characteristics of the surface. Therefore, a wear test piece 10 (thickness 10 mm × width 25 mm × length 75 mm) was sampled so that the position 1 mm below the surface of the obtained steel sheet became the test position (test surface). In addition, the thickness of the test piece was adjusted to 10 mm in thickness by reducing the thickness when the steel plate thickness exceeded 10 mm. When the steel plate thickness was 10 mm or less, no thickness reduction beyond adjustment of the test position (1 mm below the surface) was performed.

(3-1) Impact abrasion test

Three abrasion test specimens 10 taken from each steel plate were simultaneously attached to the abrasion test apparatus shown in FIG. 1 to conduct an impact abrasion test. In addition, the test piece was mounted in a direction in which the test surface collided with the wear material 2. In addition, the conditions of the abrasion test are,

Drum rotation speed: 45 rpm;

Specimen rotation speed: 600 rpm

made it In addition, the test was performed by replacing the wear material at every 10000 rotations of the test piece, and the test was ended when the total number of rotations of the test piece reached 50000 times. As the wear material 2, a stone containing 90% or more of SiO ₂ (equivalent circle diameter of 5 to 35 mm) was used. In addition, as a comparison, the same abrasion test was performed on the abrasion test piece taken from the soft steel plate (SS400).

After the test, the amount of abrasion (amount of weight change (decrease) before and after the test) of each test piece was measured. The average value of the abrasion amount of each obtained test piece was made into the representative value of the abrasion amount of each steel plate.

Then, from the obtained amount of wear, the ratio of the amount of wear of the mild steel plate and the amount of wear of each steel plate (test steel plate), (amount of wear of the mild steel plate) / (amount of wear of each steel plate (test steel plate)) was calculated as the impact wear resistance ratio. It means that the impact wear resistance of each steel plate is excellent, so that this impact wear resistance ratio is large. Here, steel materials having an impact wear resistance ratio of 1.7 or more were evaluated as having excellent impact wear resistance and evaluated as pass, and others were evaluated as fail.

(3-2) Sliding wear test

A wear test piece 10 taken from each steel plate was attached to the wear test apparatus shown in Fig. 2, and a sliding wear test was conducted in accordance with the provisions of AMTM G-65. The abrasion test was carried out in three pieces for each steel plate. As the wear material, sand containing 90% or more of SiO ₂ (equivalent circle diameter: 210 to 300 μm) was used. In addition, as a comparison, the same abrasion test was performed on the abrasion test piece taken from the mild steel plate (SS400). The test conditions are as follows,

Flow rate of abrasive (sand): 300 g/min,

Rubber wheel speed: 200±10rpm,

Load: 130±3.9N

made it When the number of revolutions of the rubber wheel reached 2000, the test was ended.

After the test, the amount of abrasion (amount of weight change (decrease) before and after the test) of each test piece was measured. The average value of the abrasion amount of each obtained test piece was made into the representative value of the abrasion amount of each steel plate.

And, from the obtained amount of wear, the ratio of the amount of wear of the mild steel plate and the amount of wear of each steel plate (test steel plate), (amount of wear of the mild steel plate) / (amount of wear of each steel plate (test steel plate)) was calculated as a slip wear resistance ratio. It means that the slip wear resistance of each steel plate is excellent, so that this slip wear resistance ratio is large. Here, a steel material having a slip wear resistance ratio of 3.0 or more was evaluated as passing as having excellent slip wear resistance, and other than that was evaluated as disqualified.

The obtained results are shown in Table 2.

In all of the examples of the present invention (steel materials No. 1 to No. 31), the structure has a structure containing 90% or more of austenite phase and 0.2% or more of Ti carbide, and has both excellent slip wear resistance and excellent impact wear resistance. It is made of steel (steel plate). On the other hand, in comparative examples (steel materials No. 32 to No. 45) outside the scope of the present invention, the austenite phase was less than 90% or the Ti carbide content was less than 0.2%, resulting in slip wear resistance and impact wear resistance. Among them, at least one is degraded.

For example, in steel materials No.32 and No.35 with a low C content, the austenite stability is lowered and the impact wear resistance is lowered because the ratio of the austenite phase is low. In steel materials No.33 and No.37 with low Mn content, the austenite stability is low and the ratio of the austenite phase is low, so the impact wear resistance is reduced. (1) In steel materials No. 34 and No. 36 that do not satisfy the formula, since the austenite stability is low and the ratio of the austenite phase is low, the impact wear resistance is lowered. Further, in steel materials No. 38 and No. 39 with low Ti content, since the content of Ti carbide is low, the sliding wear resistance is lowered. In steel materials No. 40, No. 41, No. 44, and No. 45 in which the cooling rate after heating is slow, formation of austenite phase is not confirmed, and impact wear resistance is lowered. Moreover, in steel materials No.42, No.43, and No.46 with low heating temperature, since the ratio of austenite phase is small, impact wear resistance is falling.

(Example 2)

Molten steel was melted and cast in a vacuum melting furnace to manufacture cast steel (thickness: 100 to 200 mm) having the component composition shown in Table 3. Next, a heating step of heating the obtained cast steel to the heating temperature shown in Table 4, and a hot rolling step of hot rolling the heated cast steel under the conditions shown in Table 2 to obtain a steel plate (steel material) having a plate thickness shown in Table 4. And, subsequently, the cooling step of cooling the steel sheet at an average cooling rate between 900°C and 500°C as shown in Table 4 was sequentially performed to obtain a steel material (steel sheet). Further, in the hot rolling process, as shown in Table 4, hot rolling was performed at the finish rolling temperature shown in Table 4 by adjusting the reduction ratio (cumulative reduction ratio) in a temperature range of 950°C or lower.

In the cooling step after the hot rolling step, cooling was performed by water cooling, air cooling, or a combination thereof. In addition, the average cooling rate was calculated based on the temperature measured with a thermocouple attached to a position 1 mm below the surface of the steel sheet. When the cooling start temperature was less than 900°C, the average cooling rate was calculated between the cooling start temperature and 500°C.

The obtained steel sheet was subjected to a hardness measurement test, a structure observation, and an abrasion test in the same manner as in Example 1, and the hardness of the austenite phase, the area ratio of the austenite phase, and the area ratio of Ti carbide in a subsurface 1 mm portion were determined. , and further, the slip wear resistance and impact wear resistance were evaluated in the same manner as in Example 1.

The obtained results are listed together in Table 4.

In all examples of the present invention (steel materials No.51 to No.81), the structure contains 90% or more of austenite phase, and the hardness of the austenite phase (position of 1 mm below the surface) is 200 HV or more, and 0.2% It becomes a structure containing the above Ti carbide, and becomes a steel material (steel plate) having both excellent slip wear resistance and excellent impact wear resistance. Compared with the examples of the present invention (steel materials No. 96 to No. 98) in which the hardness of the austenite phase (position of 1 mm below the surface) is less than 200 HV, the improvement in impact wear resistance is particularly remarkable.

On the other hand, in the comparative examples (steel No. 82 to No. 95) outside the scope of the present invention, the austenite phase is less than 90% or the Ti carbide content is less than 0.2%, resulting in slip wear resistance and impact wear resistance. , at least one of which is degraded.

For example, in steel materials No. 82 and No. 85 having a low C content, the austenite stability is lowered and the impact wear resistance is lowered because the ratio of the austenite phase is low. In steel materials No. 83 and No. 87 with a low Mn content, the austenite stability is low and the ratio of the austenite phase is low, so the impact wear resistance is lowered. (1) In steel materials No. 84 and No. 86 that do not satisfy the formula, the austenite stability is low and the ratio of the austenite phase is low, so the impact wear resistance is lowered. In addition, in steel materials No. 88 and No. 89 with low Ti content, since the content of Ti carbide is low, the sliding wear resistance is lowered. In steel materials No.90, No.91, No.94, and No.95 having a slow cooling rate after heating, formation of an austenite phase was not confirmed, and impact wear resistance was reduced. Moreover, in steel materials No.92 and No.93 with low heating temperature, since the ratio of austenite phase is small, impact wear resistance is falling.

1 : drum
2: abrasive material (stone)
10: Abrasion test piece
21 : rubber wheel
22: weight
23 : Hopper
24: abrasive material (sand)

Claims (6)

in mass percent,
C: 0.10% or more and 2.50% or less;
Mn: 10.8% or more and 45.0% or less;
P: 0.300% or less;
S: 0.1000% or less;
Ti: 0.10% or more and 5.00% or less;
Al: 0.001% or more and 5.000% or less;
N: 0.5000% or less;
O (oxygen): 0.1000% or less
and contains C, Ti, and Mn within a range that satisfies the following formula (1), the balance being Fe and unavoidable impurities, and an area ratio of 90% or more of austenite phase and Ti It has a structure containing 0.2% or more of carbides,
The austenite phase has a Vickers hardness of 200 HV or more, steel.
energy
25([C]-12.01[Ti]/47.87)+[Mn] ≥ 25... … (One)
Here, [C], [Ti], [Mn]: content of each element (mass%) According to claim 1,
In addition to the above component composition, in mass%,
Si: 0.01% or more and 5.00% or less;
Cu: 0.1% or more and 10.0% or less;
Ni: 0.1% or more and 25.0% or less;
Cr: 0.1% or more and 30.0% or less;
Mo: 0.1% or more and 10.0% or less;
Nb: 0.005% or more and 2.000% or less;
V: 0.01% or more and 2.00% or less;
W: 0.01% or more and 2.00% or less;
B: 0.0003% or more and 0.1000% or less;
Ca: 0.0003% or more and 0.1000% or less;
Mg: 0.0001% or more and 0.1000% or less;
REM: 0.0005% or more and 0.1000% or less
Steel materials containing 1 type, or 2 or more types selected from among. A steel material comprising a casting process of melting molten steel into a cast steel, a heating process of heating the cast steel, a hot rolling process of hot rolling the heated cast steel into a steel material, and a cooling process of cooling the steel material. As a manufacturing method of
The cast steel, in mass%,
C: 0.10% or more and 2.50% or less;
Mn: 10.8% or more and 45.0% or less;
P: 0.300% or less;
S: 0.1000% or less;
Ti: 0.10% or more and 5.00% or less;
Al: 0.001% or more and 5.000% or less;
N: 0.5000% or less;
O (oxygen): 0.1000% or less
In addition, C, Ti, and Mn are contained within a range satisfying the following formula (1), the balance being Fe and unavoidable impurities,
The heating temperature in the heating step is 950 ° C. or more and 1300 ° C. or less,
In the hot rolling, the total reduction in the temperature range of 950 ° C. or less is 25% or more,
The manufacturing method of steel materials which makes cooling in the said cooling process an average cooling rate in the temperature range of 900-500 degreeC, more than 1 degreeC/s.
energy
25([C]-12.01[Ti]/47.87)+[Mn] ≥ 25... … (One)
Here, [C], [Ti], [Mn]: content of each element (mass%) According to claim 3,
The cast steel, in addition to the above component composition, in mass%,
Si: 0.01% or more and 5.00% or less;
Cu: 0.1% or more and 10.0% or less;
Ni: 0.1% or more and 25.0% or less;
Cr: 0.1% or more and 30.0% or less;
Mo: 0.1% or more and 10.0% or less;
Nb: 0.005% or more and 2.000% or less;
V: 0.01% or more and 2.00% or less;
W: 0.01% or more and 2.00% or less;
B: 0.0003% or more and 0.1000% or less;
Ca: 0.0003% or more and 0.1000% or less;
Mg: 0.0001% or more and 0.1000% or less;
REM: 0.0005% or more and 0.1000% or less
The manufacturing method of steel materials containing 1 type(s) or 2 or more types selected from among. delete delete

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