JP2008297571A - Abrasion resistant steel sheet having excellent workability, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasion resistant steel sheet having excellent bending workability and suitable for a member in contact with earth and sand such as a power shovel, and to provide its production method. <P>SOLUTION: The steel sheet has a composition comprising, by mass, 0.05 to 0.35% C, 0.05 to 1.0% Si, 0.1 to 2.0% Mn and ≤0.1% Al, and further comprising one or more kinds selected from 0.1 to 1.0% Nb and 0.1 to 1.0% V, and one or more kinds selected from 0.1 to 1.0% Cu, 0.1 to 2.0% Ni, 0.1 to 1.0% Cr, 0.05 to 1.0% Mo, 0.05 to 1.0% W, 0.0003 to 0.0030% B and 0.005 to <0.1% Ti, satisfying DI*<60, and the balance Fe with inevitable impurities: DI*=33.85×(0.1×C*)<SP>0.5</SP>×(0.7×Si+1)×(3.33×Mn+1)×(0.35×Cu+1)×(0.36×Ni+1)×(2.16×Cr+1)×(3×Mo+1)×(1.5×W+1)...(1); wherein C*=C-(12/93×Nb+12/51×V). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a member used in the fields of construction, civil engineering, mining, etc., for example, an industrial machine such as a power shovel, a bulldozer, a hopper, a bucket, or a transportation device, etc., where wear due to contact with earth and sand becomes a problem. The present invention relates to a wear-resistant steel plate suitable for use and a method for producing the same, and particularly to a material excellent in bending workability.

  Steel members having excellent wear resistance are used for members subjected to wear due to soil, sand, and the like in order to extend the life. It is known that the wear resistance of steel materials is improved by increasing the hardness, and for members that require wear resistance, steel materials to which a large amount of alloy elements such as Cr and Mo are added are hardened. Steel materials that have been heat-treated and hardened have been used.

  For example, Patent Document 1 includes C: 0.10 to 0.19%, steel containing appropriate amounts of Si and Mn, and Ceq limited to 0.35 to 0.44%, after hot rolling. There has been proposed a method for producing a wear-resistant steel sheet which is directly quenched or reheated to 900 to 950 ° C. and then quenched, tempered at 300 to 500 ° C., and having a steel sheet surface hardness of 300 HV or higher.

  Patent Document 2 includes C: 0.10 to 0.20%, and Si, Mn, P, S, N, and Al are adjusted to appropriate amounts, or 1 of Cu, Ni, Cr, Mo, and B is further added. A method of manufacturing a wear-resistant thick steel sheet is proposed in which steel containing more than seeds is directly quenched after hot rolling, or cooled after rolling, and then reheated and quenched to give a hardness of 340 HB or more. ing.

  Patent Document 3 includes C: 0.07 to 0.17%, and Si, Mn, P, S, N, and Al are adjusted to appropriate amounts, or 1 of Cu, Ni, Cr, Mo, and B is further added. Production of wear-resistant steel sheets that are hardened immediately after hot rolling, or once air-cooled into steels containing more than seeds, and then reheated and quenched to have a surface hardness of 321 HB or more and excellent in bending workability A method has been proposed.

  The technologies described in Patent Documents 1 to 3 improve the wear resistance characteristics by adding a large amount of alloy elements and utilizing solid solution hardening, transformation hardening, precipitation hardening, etc. to increase the hardness. Yes. However, when a large amount of alloy elements are added and solid solution hardening, transformation hardening, precipitation hardening, etc. are utilized to increase the hardness, the weldability and workability will decrease, and the manufacturing cost will be further reduced. Soaring.

  By the way, in the case of a member that requires wear resistance, depending on use conditions, only the vicinity of the surface may be increased in hardness, and the wear resistance may be improved. There is no need to add a large amount of an alloying element such as Cr or Mo, and it is conceivable that a heat treatment such as a quenching process is performed to make only the vicinity of the surface a quenched structure.

  However, in order to increase the hardness of the hardened structure, it is generally necessary to increase the solid solution C amount of the steel material. However, the increase in the solid solution C amount causes a decrease in weldability, a decrease in bending workability, and the like. Particularly, the decrease in bending workability restricts the bending work necessary as a member and restricts the use conditions.

For this reason, there is a demand for a wear-resistant steel sheet that can improve the wear resistance without excessively increasing the hardness. Patent Document 4 includes C: 0.10 to 0.45%, Si , Mn, P, S, N are adjusted to appropriate amounts, and Ti: 0.10 to 1.0% is contained, and an average particle size of 0.5 μm or more TiC precipitate or composite precipitation of TiC and TiN, TiS There has been proposed a wear-resistant steel having excellent surface properties including 400 / mm ² or more and Ti * of 0.05% or more and less than 0.4%.

According to the technique described in Patent Document 4, it is possible to generate precipitates mainly composed of coarse TiC during solidification and improve wear resistance at low cost without excessively increasing the hardness.
Japanese Patent Laid-Open No. 62-142726 JP-A 63-169359 Japanese Patent Laid-Open No. 1-142023 Japanese Patent No. 3089882

  However, in the technique described in Patent Document 4, since quenching heat treatment is performed and the structure is a martensitic structure as it is quenched, the strength is high and, as a result, the deformation resistance during bending is increased. However, it was difficult to say that it was easy, and left a problem in bending workability.

  Moreover, it is indispensable to implement heat treatment even in the wear-resistant steel described in any one of Patent Documents 1 to 4, and problems remain in terms of manufacturing period and manufacturing cost.

  Therefore, an object of the present invention is to provide a wear-resistant steel plate that can be produced without being subjected to heat treatment while being hot-rolled, and that has excellent wear resistance and bending workability, and a method for producing the same.

  In order to achieve the above-mentioned object, the inventors have conducted intensive research on various factors affecting wear resistance and bending workability, and have a component system containing Nb or V and C. By using a composite structure of an as-rolled ferrite-pearlite structure as a base phase and dispersing a hard second phase (hard phase: Nb carbide or V carbide) in the matrix, while maintaining wear resistance, It has been found that the processing load during bending can be reduced, that is, the bending workability can be improved.

The present invention has been made based on the obtained knowledge and further studies, that is, the present invention,
1. In mass%, C: 0.05 to 0.35%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, Al: 0.1% or less, and Nb: 0 0.1-1.0%, V: 0.1-1.0%, or more, Cu: 0.1-1.0%, Ni: 0.1-2.0%, Cr : 0.1-1.0%, Mo: 0.05-1.0%, W: 0.05-1.0%, B: 0.0003-0.0030%, Ti: 0.005-0 A wear-resistant steel plate having excellent workability, comprising one or more than 1%, or DI * <60, the balance Fe and inevitable impurities.
DI * = 33.85 × (0.1 × C *) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0.35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.5 × W + 1) (1)
Here, C * = C− (12/93 × Nb + 12/51 × V)
2. 2. The wear-resistant steel sheet according to 1, wherein the metal structure has a ferrite-pearlite phase as a base phase, and a hard phase is dispersed in the base phase.
3. Further, the wear-resistant steel sheet according to 2, wherein the hard phase has a dispersion density of 400 pieces / mm ² or more.
A method for producing a wear-resistant steel sheet having excellent workability, wherein the steel slab having the composition described in 4.1 is hot-rolled and then cooled to 400 ° C. or less at a cooling rate of 2 ° C./s or less.

According to the present invention, a wear-resistant steel sheet having improved bending workability without deteriorating the wear resistance can be obtained without performing heat treatment after hot rolling, and rational production such as heat treatment cost reduction and manufacturing lead time shortening, etc. It is possible and has a remarkable industrial effect.

The reason why the component composition and the metal structure are defined in the wear-resistant steel sheet according to the present invention will be described.
[Ingredient composition] In the following%, all are mass%.

C: 0.05 to 0.35%
C improves the matrix hardness in the metal structure to improve the wear resistance, and forms carbide as a hard second phase (hereinafter also referred to as a hard phase), which is effective for improving the wear resistance. It is an element, and in order to obtain such an effect, a content of 0.05% or more is required.

  On the other hand, if the content exceeds 0.35%, the carbide as the hard phase becomes coarse, and cracks are generated starting from the carbide during bending. For this reason, C was specified in the range of 0.05 to 0.35%. In addition, Preferably it is 0.15-0.30%.

Si: 0.05-1.0%
Si is an effective element as a deoxidizing element, and in order to obtain such an effect, the content of 0.05% or more is required. Si is an effective element that contributes to high hardness by solid solution strengthening by solid solution in steel. However, if the content exceeds 1.0%, ductility and toughness are reduced, and the amount of inclusions is further increased. Cause problems. For this reason, it is preferable to limit Si to 0.05 to 1.0% of range. In addition, More preferably, it is 0.05 to 0.40%.

Mn: 0.1 to 2.0%
Mn is an effective element that contributes to high hardness by solid solution strengthening, and in order to obtain such an effect, it needs to be contained in an amount of 0.1% or more. On the other hand, the content exceeding 2.0% reduces weldability. For this reason, it is preferable to limit Mn to the range of 0.1 to 2.0%. In addition, More preferably, it is 0.1 to 1.60%.

Al: 0.1% or less Al acts as a deoxidizer, and such an effect is recognized with a content of 0.0020% or more, but a large content exceeding 0.1% is the cleanliness of steel. Reduce. For this reason, it is preferable to limit Al to 0.1% or less.

One or two of Nb: 0.1 to 1.0% and V: 0.1 to 1.0% Nb and V are important elements in the present invention together with C, and contribute to improvement of wear resistance. It is an essential element that forms a hard second phase (Nb carbide, V carbide). In order to obtain such an effect, the content of 0.1% or more is required. On the other hand, if the content exceeds 1.0%, the hard second phase (Nb carbide, V carbide) becomes coarse, and cracks are generated starting from the coarse second phase during bending. For this reason, Nb and V were limited to the range of 0.1 to 1.0%. In addition, Preferably, all are 0.1 to 0.8%.

  Note that when Nb and V are added in combination, the hard second phase is merely (NbV) C, which has the effect of improving the wear resistance. When N is contained, carbonitride may be formed in addition to carbide, but the same effect can be obtained.

  FIG. 1 shows the effect of Nb or V addition amount on the wear resistance of Nb or V addition steel, and FIG. 2 shows the effect of Nb or V addition amount on tensile strength (YS, TS). In FIG. 1, the vertical axis shows the wear resistance ratio in which the wear amount in the rubber wheel wear test is compared with the wear amount of the conventional steel (SS400).

  When the Nb or V addition amount is 0.1% or more, the wear resistance is as high as that of a general wear-resistant steel, and YS and TS are lowered. That is, it is possible to improve workability while having wear characteristics equivalent to those of a conventional wear-resistant steel plate subjected to quenching heat treatment.

  The test steel in the rubber wheel wear test is a steel slab containing 0.34% C-0.35% Si-1.05% Mn-0.02-0.5% (Nb or V) in mass%. , Rolled to 20 mmt and then air-cooled at a cooling rate of 0.5 ° C./s.

  About the obtained steel plate, the tensile characteristic and the abrasion test were implemented. In the tensile test, a JIS No. 5 test piece was taken and a tensile test was performed in accordance with the provisions of JISZ2201, and tensile properties (tensile strength: TS, yield strength: YS) were obtained.

  The abrasion test was carried out by a rubber wheel abrasion test in accordance with ASTM G65, and the test results were arranged as a wear resistance ratio in which the ratio of the amount of wear of mild steel (SS400) and the amount of abrasion of each test steel sheet. The larger the wear resistance ratio, the better the wear characteristics.

  As a comparative test, a similar test was performed on a wear-resistant steel plate manufactured by a general heat treatment. The general wear-resistant steel plate mentioned here is a material containing 0.15% C and subjected to quenching heat treatment, and refers to a steel plate having a Brinell hardness of about 400 HB.

Cu: 0.1-1.0%, Ni: 0.1-2.0%, Cr: 0.1-1.0%, Mo: 0.05-1.0%, W: 0.05- 1.0%, B: 0.0003 to 0.0030%, Ti: 0.005 to less than 0.1%, or one or more Cu: 0.1 to 1.0%
Cu is an element that improves the hardenability by dissolving in a solid solution, and the content of 0.1% or more is necessary to obtain this effect. On the other hand, the content exceeding 1.0% decreases the hot workability. For this reason, it is preferable to limit Cu to 0.1 to 1.0% of range. In addition, More preferably, it is 0.1 to 0.5%.

Ni: 0.1 to 2.0%
Ni is an element that improves hardenability by solid solution, and such an effect becomes remarkable when the content is 0.1% or more. On the other hand, the content exceeding 2.0% significantly increases the material cost. For this reason, it is preferable to limit Ni to 0.1 to 2.0% of range. In addition, More preferably, it is 0.1 to 1.0%.

Cr: 0.1 to 1.0%
Cr has the effect of improving hardenability, and in order to obtain such an effect, the content of 0.1% or more is required, but the content exceeding 0.1% lowers the weldability. . For this reason, it is preferable to limit Cr to 0.1 to 1.0% of range. In addition, More preferably, it is 0.1 to 0.40%.

Mo: 0.05-1.0%
Mo is an element that improves hardenability. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, if it exceeds 1.0%, weldability is lowered. Therefore, Mo is preferably limited to a range of 0.05 to 1.0%. In addition, More preferably, it is 0.05 to 0.40%.

W: 0.05-1.0%
W is an element that improves hardenability. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, if it exceeds 1.0%, weldability is lowered. Therefore, W is preferably limited to a range of 0.05 to 1.0%. In addition, More preferably, it is 0.05 to 0.40%. In addition, since Mo and W are dissolved in TiC, they also have an effect of increasing the amount of hard phase.

B: 0.0003 to 0.0030%
B is an element that segregates at the grain boundary, strengthens the grain boundary, and contributes effectively to improvement of toughness. In order to obtain such an effect, the content of 0.0003% or more is necessary. On the other hand, the content exceeding 0.0030% lowers the weldability. For this reason, it is preferable to limit B to 0.0003 to 0.0030% of range. In addition, More preferably, it is 0.0003 to 0.0015%.

Ti: 0.005 to less than 0.1% Ti fixes N and effectively acts the effect of improving the hardenability of B. In order to obtain the effect, 0.005% or more is necessary. Even if 0.1% or more is added, this effect does not change. Therefore, the content is made 0.005 to less than 0.1%.

DI * <60
In the present invention, DI * (hardenability index value) is DI * = 33.85 × (0.1 × C *) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0 .35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.5 × W + 1), where C * = C− (12/93 × Nb + 12 / 51 * V) and DI * <60.

  FIG. 3 shows the influence of DI * on wear resistance, and FIG. 4 shows the influence of DI * on tensile strength (YS, TS). In FIG. 3, the vertical axis represents the wear resistance ratio in which the wear amount in the rubber wheel wear test is compared with the wear amount of the conventional steel (SS400). The larger the wear resistance ratio, the better the wear characteristics.

  3 and 4, it can be seen that when DI * is less than 60, the wear amount is comparable to that of general wear-resistant steel, although the tensile strength is as low as 800 MPa or less. On the other hand, when DI * is 60 or more, the wear resistance is excellent, but the tensile strength is 800 MPa or more and the workability is poor. This is because when DI * is 60 or more, a ferrite-bainite structure is formed.

  The test steel in the rubber wheel wear test is 0.33% C-0.28% Si-1.12% Mn-0.44% Nb in mass%, and further Cu, Ni, Cr, Mo, W, B, A steel piece containing one or more of Ti and having a DI * of 40 to 120 was rolled to 12 mmt and then air-cooled (cooling rate: 1.0 ° C./s).

  About the obtained steel plate, the tensile characteristic and the abrasion test were implemented. In the tensile test, a JIS No. 5 test piece was sampled and a tensile test was performed in accordance with the provisions of JISZ2201, and tensile properties (tensile strength TS, yield strength YS) were obtained.

The rubber wheel wear test was conducted in accordance with ASTM G65, and the test results were arranged as a wear resistance ratio by the ratio of the wear amount of mild steel (SS400) and the wear amount of each steel plate.
[Metal structure]
The wear-resistant steel sheet of the present invention has the above-described composition, and has a structure in which a ferrite-pearlite phase is a base phase (matrix) and a hard phase (hard second phase) is dispersed in the matrix. The base phase means 90% or more by volume ratio, and in the steel sheet according to the present invention, two phases of ferrite and pearlite occupy 90% or more of the whole. In consideration of workability, it is preferable that the base phase has a Brinell hardness of 300 HB or less.

The hard phase is preferably Nb carbide such as NbC or V carbide such as VC. The size of the hard phase is not particularly limited, but is preferably about 0.5 μm or more and 50 μm or less from the viewpoint of wear resistance. Moreover, it is preferable that the dispersion density of a hard phase shall be 400 pieces / mm < ² > or more from a viewpoint of abrasion resistance.

The size of the hard phase is determined by measuring the area of each hard phase, calculating the equivalent circle diameter from the same area, and arithmetically averaging the obtained equivalent circle diameters to obtain an average value of the size of the hard phase in the steel sheet. (Average particle diameter). Next, a manufacturing method will be described.
[Production method]
The wear-resistant steel sheet of the present invention is preferably prepared by melting the molten steel having the above composition by a known melting method and using a continuous casting method or an ingot-decomposition rolling method as a steel material such as a slab having a predetermined size. .

  In order to adjust the hard phase to a predetermined size and number, for example, when a continuous casting method is used, a cooling rate of 0.2 to 10 ° C. in a temperature range of 1500 to 1200 ° C. of a slab having a thickness of 200 to 400 mm. It is preferable to adjust the cooling so as to be in the range of / s.

  Even when the ingot-making method is used, it goes without saying that the size of the ingot and the cooling conditions need to be adjusted so that the desired size and number of hard phases can be obtained.

  Next, the steel material is immediately cooled without cooling, or cooled and reheated to 950 to 1250 ° C., and then hot-rolled to obtain a steel plate having a desired plate thickness (wall thickness). At this time, the average cooling rate needs to be 2 ° C./s or less.

  When cooling at a cooling rate exceeding 2 ° C./s, since a ferrite-pearlite structure cannot be obtained, the tensile strength becomes 800 MPa or more, the working load at the time of steel plate bending increases, and the workability deteriorates. Therefore, it shall be 2 degrees C / s or less.

  The hot rolling conditions are not particularly limited as long as the steel sheet can have a desired size and shape. The wear-resistant steel plate according to the present invention does not need to be heat-treated, and can be used for various applications that require bending while being rolled.

Molten steel having the composition shown in Table 1 is melted in a vacuum melting furnace to form a small steel ingot (50 kg) (steel material), and then heated to 1050 to 1250 ° C. and hot-rolled to obtain a thickness of 6 to 100 mm. This was a test steel plate. Microstructure observation, tensile test, and wear test were performed on each test steel sheet.
Tissue observation The specimen for structure observation was subjected to nital corrosion after polishing, and the structure was identified and the size and number of hard phases were measured using an optical microscope (magnification: 400 times) at a position 1 mm below the surface layer. . In the observation field of view, the structure occupying 90% or more was defined as the base phase, and the size of the hard phase was the average particle diameter determined by the method described above.
Tensile test In accordance with JISZ2201, the JIS No. 5 test piece was sampled and subjected to a tensile test in accordance with JISZ2241 to determine tensile properties (yield strength: YS, tensile strength: TS).
Abrasion test The test piece was t (plate thickness) × 20 × 75 (mm), and a rubber wheel abrasion test was performed using abrasion sand in accordance with the provisions of ASTM G65. After the test, the wear amount of the test piece was measured.

  The test results were evaluated by the wear resistance ratio = (abrasion amount of mild steel plate) / (abrasion amount of each steel plate) with the wear amount of the mild steel (SS400) plate as a reference (1.0). The larger the wear resistance ratio, the better the wear resistance, and the scope of the present invention is the wear resistance ratio: 4.0 or more.

  Table 2 shows the results of the structure observation, tensile test, and wear test. Examples of the present invention (steel plates Nos. 1 to 6, steel plates Nos. 8 and 9) are steel plates with extremely excellent wear resistance. On the other hand, the comparative example is inferior in wear resistance as compared with the inventive example.

The figure which shows the influence of Nb and V addition amount which has on wear resistance. The figure which shows the influence of Nb and V addition amount which has on tensile strength (YS, TS). The figure which shows the influence of DI * which has on wear resistance. The figure which shows the influence of DI * which acts on tensile strength (YS, TS).

Claims (4)

In mass%, C: 0.05 to 0.35%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, Al: 0.1% or less, and Nb: 0 0.1-1.0%, V: 0.1-1.0%, or more, Cu: 0.1-1.0%, Ni: 0.1-2.0%, Cr : 0.1-1.0%, Mo: 0.05-1.0%, W: 0.05-1.0%, B: 0.0003-0.0030%, Ti: 0.005-0 A wear-resistant steel plate having excellent workability, containing one or more than 1%, or DI * <60, the balance Fe and inevitable impurities.
DI * = 33.85 × (0.1 × C *) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0.35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.5 × W + 1) (1)
Here, C * = C− (12/93 × Nb + 12/51 × V)   The wear-resistant steel sheet according to claim 1, wherein the metal structure has a ferrite-pearlite phase as a base phase, and a hard phase is dispersed in the base phase. The wear resistant steel sheet according to claim 2, wherein the dispersion density of the hard phase is 400 pieces / mm ² or more.   A method for producing a wear-resistant steel sheet having excellent workability, wherein the steel slab having the composition according to claim 1 is hot-rolled and then cooled to 400 ° C or lower at a cooling rate of 2 ° C / s or lower.

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