JP5017937B2 - Wear-resistant steel plate with excellent bending workability - Google Patents

Description

  The present invention is used in the fields of construction, civil engineering, mining, etc., for example, in industrial machines and transporting equipment such as excavators, bulldozers, hoppers, buckets, etc., wear due to contact with earth and sand becomes a problem. The present invention relates to a wear-resistant steel plate suitable for a member, and particularly relates to improvement of bending workability. The “steel plate” here includes a steel plate and a steel strip.

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. Conventionally, it is known that the wear resistance of a steel material is improved by increasing the hardness. For this reason, steel members that have been hardened by heat treatment such as quenching have been used for members that require a large amount of alloy elements such as Cr and Mo have been required for wear resistance.
For example, Patent Document 1 includes C: 0.10 to 0.19%, a proper amount of Si and Mn, and steel with Ceq limited to 0.35 to 0.44, which is directly quenched after hot rolling, or 900 to 950 ° C. A method of manufacturing a wear-resistant steel sheet is proposed in which the steel sheet is reheated and then quenched, tempered at 300 to 500 ° C., and the steel sheet surface hardness is 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 one of Cu, Ni, Cr, Mo, and B. A steel containing more than seeds is directly quenched after hot rolling, or allowed to cool after rolling, and then reheated and quenched to obtain a wear resistant thick steel plate having a hardness of 340 HB or more. Manufacturing methods have been proposed.
Patent Document 3 includes C: 0.07 to 0.17%, contains an appropriate amount of Si, Mn, V, B, and Al, or further contains one or more of Cu, Ni, Cr, and Mo. A method of manufacturing a wear-resistant steel sheet is proposed in which steel is quenched immediately after hot rolling, or once air-cooled and then re-heated and quenched, with a surface hardness of 321 HB or more and excellent bending workability. ing.

  The techniques described in Patent Documents 1 to 3 improve wear resistance 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 alloying elements are added in large quantities to increase the hardness by using solid solution hardening, transformation hardening, precipitation hardening, etc., the weldability and workability are reduced as a result. Therefore, there is a problem that the manufacturing cost increases.

  Further, depending on the use conditions, there may be a case where only the vicinity of the surface is increased in hardness to improve the wear resistance. In such a case, it is not necessary to add a large amount of alloy elements such as Cr and Mo, and it is conceivable that a heat treatment such as a quenching process is performed so that only the vicinity of the steel material surface becomes a quenched structure. However, in order to increase the hardness of the quenched structure, it is generally necessary to increase the solid solution C amount of the steel material. However, an increase in the solid solution C amount causes a decrease in weldability, a decrease in bending workability, and the like. There is a problem. In particular, with respect to bending workability, an increase in the amount of dissolved C causes an increase in deformation resistance at the time of bending, resulting in problems such as inability to perform bending.

For this reason, there has been a demand for a wear-resistant steel sheet capable of improving the wear resistance without excessively increasing the hardness.
In response to such a request, for example, Patent Document 4 includes C: 0.10 to 0.45%, Si, Mn, P, S, and N are adjusted to appropriate amounts, and further Ti: 0.10 to 1.0%, A wear-resistant steel with excellent surface properties that contains TiC precipitates of 0.5 μm or more or composite precipitates of TiC and TiN, TiS of 400 pieces / mm ² or more, and Ti * of 0.05% or more and less than 0.4%. Has been proposed. According to the technique described in Patent Document 4, precipitates mainly composed of coarse TiC are generated during solidification, and wear resistance can be improved at low cost without excessively increasing the hardness.
JP-A-62-142726 JP 63-169359 A Japanese Patent Laid-Open No. 1-142023 Japanese Patent No. 3089882

However, in the technique described in Patent Document 4, a quenching process is performed and the structure is a martensite structure. As a result, the Brinell hardness is increased to HB296 or higher, and it is difficult to say that bending is easy. There was a problem with bending workability.
The present invention has been made in view of the problems of the prior art, and is capable of improving wear resistance and dramatically improving bending workability, and having excellent bending workability. An object is to provide a steel sheet.

  In order to achieve the above-described object, the inventors have conducted intensive research on various factors that affect wear resistance and bending workability. As a result, with the component system containing Ti and C, the solid solution C content is 0.03% by mass or less, so that the matrix phase becomes a soft ferrite phase and the matrix has a hard second phase (hard Phase: TiC) was dispersed, and it was found that the wear resistance was remarkably improved without excessively increasing the hardness. Further, it has been found that by using such a composition and structure, the wear resistance is improved, the plastic deformability is remarkably improved, and the bending workability is remarkably improved.

  An example of the results of experiments conducted by the inventors is the relationship between the amount of solute C and Brinell hardness HB when the amounts of Ti and C are changed in a Ti-C system, the amount of solute C and the wear resistance ratio. FIG. 1 and FIG. It can be seen that by setting the solid solution C amount to 0.03% by mass or less, the hardness is about HB200 or less, but the wear resistance ratio is 6 or more, and the wear resistance is remarkably improved. The wear resistance ratio represents the ratio between the wear amount of mild steel (SS400) and the wear amount of each steel plate in a rubber wheel wear test in accordance with ASTM G65. It shows that it is excellent in abrasion resistance, so that an abrasion resistance ratio is large.

The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) A composition containing, in mass%, C: 0.05 to 0.30%, Ti: 0.1 to 1.2%, the balance being Fe and inevitable impurities, and having a solid solution C content of 0.03% or less, and a ferrite phase A wear-resistant steel sheet having excellent bending workability, characterized in that the base phase has a structure in which a hard phase is dispersed in the base phase, and has a Brinell hardness of 200 HB or less .

( 2 ) The wear-resistant steel sheet according to ( 1 ), wherein the hard phase has a dispersion density of 400 / mm ² or more.
( 3 ) In (1) or (2) , in addition to the above composition, the composition further contains one or two kinds selected from Nb: 0.005 to 1.0% and V: 0.005 to 1.0% by mass%. A wear-resistant steel sheet characterized by having a composition.

( 4 ) In any one of (1) to ( 3 ), in addition to the above composition, in addition to mass, one or two selected from Mo: 0.05 to 1.0% and W: 0.05 to 1.0% A wear-resistant steel sheet characterized by having a composition containing
( 5 ) In any one of (1) to ( 4 ), in addition to the above composition, it is further selected by mass% from Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, Cu: 0.1 to 1.0% A wear-resistant steel sheet characterized by having a composition containing one or more kinds.

( 6 ) In any one of (1) to ( 5 ), in addition to the above composition, one or two selected from Ni: 0.1 to 2.0% and B: 0.0003 to 0.0030% in mass% A wear-resistant steel sheet characterized by having a composition containing
( 7 ) In any one of (1) to ( 6 ), in addition to the above composition, a wear-resistant steel plate characterized by having a composition containing Cr: 0.1 to 1.0% by mass%.

( 8 ) A wear-resistant steel sheet according to any one of (1) to ( 7 ), wherein in addition to the above composition, the composition further contains, by mass%, Al: 0.1% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the abrasion-resistant steel plate in which abrasion resistance and bending workability were improved significantly without accompanying excessively high hardness can be manufactured at low cost, and there is a remarkable industrial effect. In addition, according to the present invention, in particular, there is an effect that the wear resistance against wear due to contact with earth and sand is drastically improved.

First, the reason for defining the composition of the steel sheet of the present invention will be described. In addition, all the following% display represents mass%.
C: 0.05 to 0.30%
C is an effective element for forming a carbide as a hard second phase (hereinafter also referred to as a hard phase) and improving wear resistance. To obtain such an effect, 0.05% The above content is required. On the other hand, if the content exceeds 0.30%, the carbide as the hard phase becomes coarse, and cracks occur starting from the carbide during bending. For this reason, C was specified in the range of 0.05 to 0.30%. In addition, Preferably it is 0.05 to 0.20%.

Solid solution C amount: 0.03% or less The solid solution C amount is specified to be 0.03% or less in the present invention. As a result, the hardness decreases, the matrix (matrix) becomes a soft ferrite-based structure, and a hard second phase (hard phase: Ti carbide) is dispersed in a large amount in the matrix phase. Thereby, as shown in FIG. 1, FIG. 2, although hardness falls, abrasion resistance improves remarkably. This is a result of the synergistic effect of improving wear resistance by dispersing the hard second phase and improving wear resistance by improving plastic deformability by making the base phase (matrix) soft ferrite. It is believed that there is. In addition, the amount of solid solution C is calculated by extracting the carbide by electrolytic extraction method from the test piece collected from the steel sheet, measuring the amount of C that is carbide, and subtracting the amount of C that is carbide from the total C amount. It shall be.

Ti: 0.1-1.2%
Ti is an important element in the present invention together with C, and is an essential element for forming a hard second phase (Ti carbide) that contributes to improvement in wear resistance. In order to obtain such an effect, the content of 0.1% or more is required. On the other hand, if the content exceeds 1.2%, the hard second phase (Ti carbide) becomes coarse, and cracks occur starting from the coarse second phase during bending. For this reason, Ti was limited to the range of 0.1 to 1.2%. In addition, Preferably it is 0.1 to 0.5%.

  The above-described components are basic components, but in the present invention, a selective element can be contained as necessary. As selective elements, Nb: 0.005 to 1.0%, V: one or two selected from 0.005 to 1.0%, and / or Mo: 0.05 to 1.0%, W: 0.05 to 1.0% 1 type or 2 types selected and / or Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, Cu: 0.1 to 1.0%, and / or Ni: 0.1 to 2.0%, B: One or two selected from 0.0003 to 0.0030%, and / or Cr: 0.1 to 1.0%, and / or Al: 0.1% or less Can do.

One or two selected from Nb: 0.005-1.0%, V: 0.005-1.0%
Nb and V are elements that form a hard second phase and contribute to the improvement of wear resistance, and can be selected and contained as necessary.
Nb is an element that, when added in combination with Ti, forms a composite carbide of Ti and Nb ((NbTi) C), disperses as a hard second phase, and contributes effectively to improved wear resistance. . In order to obtain such an effect of improving wear resistance, a content of 0.005% or more is required. On the other hand, if the content exceeds 1.0%, the hard second phase (carbide) is coarsened, and cracks are generated starting from the hard second phase (carbide) during bending. For this reason, it is preferable to limit Nb to 0.005 to 1.0% of range. In addition, More preferably, it is 0.1 to 0.5%.

  V is added in combination with Ti to form Ti and V composite carbide ((VTi) C), which is dispersed as a hard second phase, and is effective in improving wear resistance. It is a contributing element. In order to obtain such an effect of improving wear resistance, a content of 0.005% or more is required. On the other hand, if the content exceeds 1.0%, the hard second phase (carbide) is coarsened, and cracks are generated starting from the hard second phase (carbide) during bending. For this reason, V is preferably limited to a range of 0.005 to 1.0%. In addition, More preferably, it is 0.1 to 0.5%.

When Nb and V are added in combination, the hard second phase is only (NbVTi) C, which has the same effect of improving wear resistance. When N is contained, carbonitride may be formed in addition to carbide, but the same effect can be obtained.
One or two selected from Mo: 0.05-1.0%, W: 0.05-1.0%
Both Mo and W are elements that have the effect of increasing the amount of the hard second phase that contributes to improving wear resistance by dissolving in Ti carbide (TiC), and can be selected and contained as necessary. .

  Mo is an element having an effect of increasing the amount of hard second phase by dissolving in Ti carbide (TiC). In order to acquire such an effect, 0.05% or more of content is required. On the other hand, if the content exceeds 1.0%, the effect is saturated, and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, it is preferable to limit Mo to the range of 0.05 to 1.0%. In addition, More preferably, it is 0.05 to 0.40%.

  W, like Mo, is an element that has an effect of increasing the amount of hard second phase by dissolving in Ti carbide (TiC). In order to acquire such an effect, 0.05% or more of content is required. On the other hand, if the content exceeds 1.0%, the effect is saturated, and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, it is preferable to limit W to 0.05 to 1.0% of range. In addition, More preferably, it is 0.05 to 0.40%.

One or more selected from Si: 0.05-1.0%, Mn: 0.1-2.0%, Cu: 0.1-1.0%
Si, Mn, and Cu are all elements that contribute to increasing the hardness of steel, and can be selected and contained as necessary.
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. In addition, Si is an effective element that contributes to high hardness by solid solution strengthening by solid solution strengthening. However, inclusion exceeding 1.0% decreases ductility and toughness, and further increases the amount of inclusions. Cause problems. For this reason, it is preferable to limit Si to the range of 0.05 to 1.0%. In addition, More preferably, it is 0.05 to 0.40%. In the case of unavoidable impurities, Si is less than 0.05%.

Mn is an effective element that contributes to higher 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, if the content exceeds 2.0%, weldability decreases. For this reason, it is preferable to limit Mn to the range of 0.1 to 2.0%. More preferably, it is 0.1 to 1.60%. In the case of unavoidable impurities, Mn is less than 0.1%.
Cu is an effective element that contributes to high hardness through aging precipitation hardening. In order to obtain this effect, it is necessary to contain 0.1% or more. On the other hand, the content exceeding 1.0% decreases the hot workability. For this reason, it is preferable to limit Cu to the range of 0.1 to 1.0%. In addition, More preferably, it is 0.1 to 0.5%.

One or two selected from Ni: 0.1-2.0%, B: 0.0003-0.0030%
Ni and B are both elements that contribute to toughness improvement, and can be selected and contained as necessary.
Ni is an element that improves toughness, 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. More preferably, it is 0.1 to 1.0%.

B is an element that segregates at the grain boundary, strengthens the grain boundary, and effectively contributes to the improvement of toughness. In order to obtain such an effect, the content of 0.0003% or more is required. On the other hand, the content exceeding 0.0030% reduces weldability. For this reason, it is preferable to limit B to the range of 0.0003 to 0.0030%. In addition, More preferably, it is 0.0003 to 0.0015%.
Cr: 0.1-1.0%
Cr dissolves in ferrite and has the effect of softening the ferrite, improving the plastic deformability and further improving the wear resistance. In order to acquire such an effect, 0.1% or more of content is required, but the content exceeding 1.0% reduces weldability. For this reason, Cr is preferably limited to a range of 0.1 to 1.0%. In addition, More preferably, it is 0.1 to 0.40%.

Al: 0.1% or less
Al is an element that acts as a deoxidizing agent and combines with N to contribute to refinement of crystal grains, and can be contained as necessary. Such an effect is recognized at a content of 0.0020% or more, but a large content exceeding 0.1% lowers the cleanliness of the steel. For this reason, it is preferable to limit Al to 0.1% or less. When not contained, Al is an inevitable impurity, and less than 0.0020% is acceptable.

  The balance other than the above components is Fe and inevitable impurities. Inevitable impurities include P: 0.040% or less, S: 0.040% or less, and N: 0.040% or less. If P is contained in a large amount, it causes a decrease in toughness, so it is desirable to make it 0.040% or less. Further, S forms MnS in the steel, acts as a starting point of fracture occurrence, and causes a decrease in toughness. Therefore, S is preferably made 0.040% or less. Further, if N is contained in a large amount, the weldability is deteriorated. Therefore, N is preferably 0.040% or less. Si and Mn are less than 0.05% and less than 0.1%, respectively, when they are inevitable impurities.

  The wear-resistant steel sheet of the present invention has the above-described composition, and has a structure in which a ferrite phase is a base phase (matrix) and a hard phase (hard second phase) is dispersed in the matrix, preferably with Brinell hardness It has a surface hardness of 200HB or less. The hard phase is preferably a Ti-based carbide such as TiC. Examples of Ti carbides include TiC, (NbTi) C, (VTi) C, or TiC in which Mo and W are dissolved.

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. The dispersion density of the hard phase is preferably 400 / mm ² or more from the viewpoint of wear resistance.
Below, the preferable manufacturing method of the abrasion-resistant steel plate of this invention is demonstrated.
The wear-resistant steel sheet of the present invention may be prepared by melting the molten steel having the above-described composition by a known melting method, and forming a steel material such as a slab having a desired size by a continuous casting method or an ingot-bundling rolling method. preferable. In order to adjust the hard phase to a desired 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 is used. 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 cooled directly or cooled and reheated to 950 to 1250 ° C., and then hot-rolled to obtain a steel plate having a desired thickness (wall thickness). The hot rolling conditions are not particularly limited as long as the steel sheet can have a desired size and shape. After hot rolling, the steel sheet is air cooled to near room temperature. After cooling, in order to improve performance other than wear resistance and bending workability such as toughness of the base material, reheating quenching treatment or further tempering treatment will not impair the effects of the present invention. . Moreover, you may perform the direct quenching process which quenches immediately after a hot rolling, or also a tempering process.

  Molten steel having the composition shown in Table 1 was melted in a vacuum melting furnace to obtain a small steel ingot (50 kg) (steel material). These steel materials were heated to 1050 to 1250 ° C. and then hot-rolled to form steel plates with a thickness of 20 mm and air-cooled. For some steel plates, direct quenching treatment (DQ), which is water-cooled immediately after hot rolling is completed, direct quenching-tempering treatment (DQT), which is tempered after direct quenching treatment, air cooling after hot rolling, and 900 ° C Reheating and quenching (RQ), reheating and quenching, reheating and quenching after reheating and quenching, reheating and quenching-tempering (RQT), or normalizing (Nor) reheating to 900 ° C and air cooling Was given. Note that the amount of solute C is obtained by taking a test piece from the obtained steel sheet, extracting the carbide by electrolytic extraction, measuring the amount of C that is carbide, and subtracting the amount of C that is carbide from the total C amount. Asked.

The obtained steel sheet was subjected to structure observation, surface hardness measurement, bending test, and wear test. The test method was as follows.
(1) Microstructure observation A specimen for microstructural observation is collected from the obtained steel plate, polished, subjected to nital corrosion, and the type of structure and the position of 1 mm below the surface layer using an optical microscope (magnification: 400 times). The size and number of hard phases were measured. 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, arithmetically averaging the obtained equivalent circle diameter, and calculating the average value obtained from the hard phase in the steel sheet. (Average particle size).

(2) Surface hardness measurement For the obtained steel sheet, the hardness HB10 / 3000 of the steel sheet surface was measured using a Brinell hardness tester (test force: 29.42 kN) in accordance with the provisions of JIS Z 2243. . The measurement positions were 5 points selected at random, and the average value of the 5 points was determined as the surface hardness of the steel sheet.
(3) Bending test A specimen was collected from the obtained steel sheet and subjected to a bending test in accordance with the provisions of JIS Z 2248. The bending radius was set at two levels of 2.0t and 1.0t. After completion of the test, the surface of the test piece was visually observed, and the bending workability was evaluated with ○ when the crack was not generated and × when the crack was generated.

(4) Wear test A test piece (size: t × 20 × 75 mm) was collected from the obtained steel sheet, and a rubber wheel wear test was performed in accordance with ASTM G 65 regulations. Wear sand was used. After the test, the wear amount of the test piece was measured. A mild steel (SS400) plate was also tested in the same manner. The wear resistance of each steel sheet was evaluated by the ratio of wear resistance = (abrasion amount of mild steel sheet) / (abrasion quantity of each steel sheet), with the wear amount of mild steel (SS400) plate as the standard (1.0). The higher the wear resistance ratio, the better the wear resistance. Here, a wear resistance ratio of 5.0 or more is considered excellent in wear resistance.

  The obtained results are shown in Table 2.

  Each of the examples of the present invention is a steel plate having a very excellent wear resistance despite having a low surface hardness and excellent bending workability. Comparative examples outside the scope of the present invention have a low wear resistance ratio and low wear resistance, or cracks are generated during bending and bending workability is reduced. Has also declined.

It is a graph which shows the relationship between solid solution C amount and hardness. It is a graph which shows the relationship between the amount of solute C and an abrasion resistance ratio.

Claims (8)

A composition containing, in mass%, C: 0.05 to 0.30%, Ti: 0.1 to 1.2%, the balance being Fe and inevitable impurities, and having a solid solution C content of 0.03% or less, and a ferrite phase A wear-resistant steel sheet having excellent bending workability, characterized by having a structure in which a hard phase is dispersed in the matrix phase, and having a surface hardness of 200 HB or less in Brinell hardness . The wear-resistant steel sheet according to claim 1 , wherein a dispersion density of the hard phase is 400 pieces / mm ² or more. In addition to the above composition, by mass%, Nb: 0.005 to 1.0%, V: containing one or two species selected from among 0.005 to 1.0%, characterized in that a composition according to claim 1 or 2. A wear-resistant steel sheet according to 2. In addition to the above composition, the composition further comprises one or two kinds selected from Mo: 0.05 to 1.0% and W: 0.05 to 1.0% by mass%. 4. The wear-resistant steel plate according to any one of 3 . In addition to the above composition, the composition further contains one or more selected from Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, and Cu: 0.1 to 1.0% by mass%. The wear-resistant steel plate according to any one of claims 1 to 4 . 2. The composition according to claim 1, wherein the composition further comprises one or two selected from Ni: 0.1 to 2.0% and B: 0.0003 to 0.0030% by mass% in addition to the composition. The wear-resistant steel plate according to any one of 5 . The wear-resistant steel sheet according to any one of claims 1 to 6 , wherein in addition to the composition, the composition further contains Cr: 0.1 to 1.0% by mass. The wear-resistant steel sheet according to any one of claims 1 to 7 , wherein in addition to the composition, the composition further contains, by mass%, Al: 0.1% or less.

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