JP5328331B2 - Steel materials for wear-resistant quenched and tempered parts and manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel which has compatibility between wear resistance and toughness at high levels, and is suitable for a saw blade or the like. <P>SOLUTION: The steel for a quenched-tempered component (such as a saw blade) having excellent wear resistance has a chemical composition containing, by mass, 0.6 to 1.0% C, &le;0.5% Si, 0.1 to 1.5% Mn, &le;0.02% P, &le;0.02% S, 0.1 to 1.5% Cr and 0.1 to 0.5% Nb, and, if required, further one or more selected from &le;0.5% Mo, &le;0.5% V, &le;2% Ni, &le;0.25% Ti and &le;0.005% B, and the balance Fe with inevitable impurities, wherein ideal critical diameter D<SB>1</SB>as the index of hardenability is &ge;50, and carbides with a grain size of &ge;2 &mu;m and containing one or more selected from Nb and Ti are present in the matrix, having the density of 300 to 1,000 pieces/mm<SP>2</SP>. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a steel material for quenched and tempered parts having excellent wear resistance, and a method for producing the same.

  Circular saws and band saws used for cutting wood, mowing, etc. are required to have improved “abrasion resistance” for the purpose of extending the life. Conventional steel plates used for such blades usually ensure wear resistance by tempering at a lower temperature after quenching to maintain a high hardness level. In order to obtain higher hardness, steel with an increased carbon content may be used. Hardness and wear resistance of steel materials are closely related, and increasing the hardness of the matrix leads to improvement of wear resistance, so conventionally increasing the hardness as a method of imparting wear resistance to steel materials It is common to adopt a technique.

On the other hand, for safety reasons, it is important that the blade does not break during use. In order to prevent breakage of the blade, it is necessary to sufficiently ensure the “toughness” of the steel material used for the blade. Generally, to improve the toughness of steel materials, it is considered effective to keep the tempering hardness low. However, when the tempering hardness is suppressed, the wear resistance is usually lowered at the same time. That is, “wear resistance” and “toughness” have a trade-off relationship in steel.
Until now, various attempts have been made to improve wear resistance without impairing toughness as much as possible (Patent Documents 1 to 6).

Japanese Patent No. 3962143 Japanese Patent Publication No. 5-37202 JP 2003-27181 A JP 2003-328078 A JP 2005-146321 A Japanese Patent No. 3946369

  The methods for improving the wear resistance of steel materials that have been studied in the past are to impart “wear resistance” by means of increasing the “hardness” and to suppress the decrease in “toughness” by refining crystal grains. Those based on thought were mainstream. Under such circumstances, the present applicant has disclosed a technique for improving the wear resistance of stainless steel by dispersing hard carbides such as Ti, Nb, Zr, V, and W in a matrix (Patent Document 6). .

  Abrasion mode in which the material surface is scraped off by the surface roughness of the mating friction surface and foreign matter present on the friction surface is called abrasive wear. Abrasive wear occurs when the wear counterpart material has a large surface roughness and is hard, or when a foreign object harder than the member is present on the friction surface. This type of wear is mainly used for wear of blade members such as circular saws and band saws. Depending on the type of wear partner material and the usage environment, foreign matter that is much harder than the hardness of a member such as alumina or silicon carbide may be present on the friction surface. In order to impart resistance to abrasive wear, it is effective to disperse a certain amount or more of Nb or Ti carbide having a particle diameter of several μm in the steel matrix constituting the blade member. The hardness of Nb or Ti carbide is equivalent to 2000 HV or more, which is almost the same level as that of alumina or silicon carbide. The hard particles dispersed in the steel matrix work as a resistance to wear, so that the amount of wear of the steel due to abrasive wear is greatly reduced. If a hard carbide is used, it is not necessary to harden the matrix more than necessary to improve wear resistance, which is advantageous for improving toughness. In Patent Document 6, this technique is used to improve the wear resistance of stainless steel.

  However, it is usually difficult to employ expensive stainless steel for cutting blade applications such as circular saws and band saws. In the case of general medium and high carbon steels, it is difficult to achieve a high level of wear resistance and toughness by simply dispersing hard carbide, and such a technology has not yet been established. .

  In the future, in order to support the improvement of the blade movement speed and the increased hardness of the material to be cut in blades such as saw blades, the appearance of inexpensive steel materials that combine high levels of wear resistance and toughness is desired. It is. The present invention intends to provide such a steel material.

  The inventors have so far obtained a large number of blade members damaged during use and steel materials after a durability test, and have investigated in detail the damaged portion from a microscopic viewpoint. As a result, we found that the main factors that lead to breakage of blade members made of medium- and high-carbon steel are “carbide” and “incompletely quenched portion”. When the density of carbide increases, it becomes a starting point of fracture and a path of crack propagation, so that the toughness is lowered. An incompletely hardened portion similarly reduces toughness and, in addition, reduces wear resistance. In other words, in order to maintain the high toughness of medium and high carbon steels that are not stainless steel, it has become clear that it is extremely important to pay attention to the form of carbides and not to form incompletely quenched parts as much as possible. It was.

  On the other hand, hard carbide exhibits the effect of improving wear resistance as described above. As a result of detailed studies, the inventors have steadily improved the "wear resistance" and "toughness" at a high level in medium and carbon steels by strictly controlling the composition of components and the distribution form of hard carbides. As a result, the present invention has been completed.

That is, in the present invention, by mass, C: 0.6 to 1.0%, Si: 0.5% or less, Mn: 0.1 to 1.5%, P: 0.02% or less, S: 0 0.02% or less, Cr: 0.1-1.5%, Nb: 0.1-0.5%, and Mo: 0.5% or less, V: 0.5% or less, if necessary. Ni: not more than 2%, Ti: not more than 0.25%, B: not more than 0.005%, the balance consisting of Fe and inevitable impurities, depending on the B content, the following formula (1) or (2) 300-1000 carbides having a chemical composition having an ideal critical diameter D _I defined by the formula of 50 or more and containing one or more of Nb and Ti and having a particle diameter of 2 μm or more in cross section observation of the steel material There is provided a steel material for a quenched and tempered part (for example, a saw blade) having a density of mm ² and having excellent wear resistance existing in a matrix.
When B content is less than 0.0005% (including 0%): D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1 −0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) (1)
When B content is 0.0005% or more: D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1−0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) × {1 + 1.5 × (0.9−C)} (2)
However, the content value of the element expressed in mass% is substituted for the element symbol on the right side of the formula (1) or (2), and 0 (zero) is substituted for elements not contained.

In addition, as a method for producing such a steel for quenching and tempering parts, a step of precipitating coarse carbide containing one or more of Nb and Ti by casting the steel whose component is adjusted to the above chemical composition and then allowing to cool. ,
A step of adjusting the density of carbides having a particle diameter of 2 μm or more containing one or more of Nb and Ti to 300 to 1000 pieces / mm ² by heating and holding the steel containing the coarse carbides at 1200 to 1350 ° C .;
A manufacturing method is provided.

After passing through the step of adjusting the density of the carbides to 300 to 1000 pieces / mm ² , hot rolling is performed under conditions of a heating extraction temperature of 1100 to 1300 ° C, a finish rolling temperature of 800 to 900 ° C, and a winding temperature of 750 ° C or less, It can be subjected to a heating and holding step in a temperature range of 600 ° C. or higher and less than Ac ₁ point. Further, if necessary, it can be cold-rolled and subjected to a step of heating and holding in a temperature range of 600 ° C. or higher and less than Ac ₁ point.

  According to the present invention, it is possible to provide a steel material in which “abrasion resistance” and “toughness” are compatible at a high level without any particular increase in cost. This steel material is suitable for blades such as saw blades because of its high durability against abrasive wear and good hardenability. In addition to oil quenching, it can also be used for gas quenching, and there is a wide selection of manufacturing conditions at parts manufacturers. If the material of the present invention is applied to a blade application, safety can be improved, and the speed of the saw blade and the hardness of the material to be cut can be increased.

[Chemical composition]
The chemical composition of the steel material of the present invention will be described. Hereinafter, “%” regarding the constituent elements of steel means “% by mass” unless otherwise specified.
C is an important element for securing tempered hardness, strength, and wear resistance, and in the present invention, a content of 0.6% or more, preferably more than 0.6% is required. However, when the C content is increased, coarse undissolved carbides increase after quenching and tempering, which becomes a starting point of fracture and a crack propagation path and inhibits toughness and ductility. As a result of various studies, the C content is limited to 1.0% or less in order to stably obtain good toughness.

  Si is effective in deoxidizing molten steel and has the effect of increasing temper softening resistance. In order to sufficiently obtain these functions, it is more effective to secure a Si content of 0.1% or more. However, excessive Si content makes the hot-rolled sheet and cold-rolled sheet hard, and becomes a factor that hinders manufacturability. For this reason, Si content shall be 0.5% or less of range.

  Mn is an element that improves hardenability, and a content of 0.1% or more is ensured in order to obtain its effect. However, since excessive Mn content may significantly reduce toughness, the Mn content is limited to 1.5% or less.

  P segregates at the austenite grain boundaries during quenching, lowers the grain boundary strength, and causes fatigue characteristics and toughness. As a result of the study, the P content is acceptable up to 0.02%.

  S forms MnS which is the starting point of impact fracture and fatigue fracture in steel, and becomes a factor of reducing fatigue characteristics and toughness. As a result of the study, the S content is acceptable up to 0.02%.

  Cr is effective for improving the hardenability like Mn, and ensures a content of 0.1% or more. However, if a large amount of Cr is added, the amount of undissolved carbide generated increases and the toughness may be significantly reduced, so the Cr content is limited to 1.5% or less.

  Nb forms a very hard Nb-containing carbide in the steel after casting, and contributes to improvement in wear resistance. Further, Nb re-dissolved after casting refines the crystal grains during quenching and contributes to improvement of toughness. In order to sufficiently bring out these effects, it is necessary to secure an Nb content of 0.1% or more, and more preferably 0.15% or more. On the other hand, when a large amount of Nb is added, Nb-containing carbides are excessively generated, which become a starting point of fracture and a crack propagation path, leading to a decrease in toughness. Further, according to the study by the inventors, the effect of improving durability against abrasive wear due to the addition of Nb tends to saturate when the Nb content is about 0.5%. Therefore, Nb is contained in the range of 0.5% or less.

  Mo and V are both effective elements for improving toughness, and can be added as necessary. In the case of Mo, it is more effective to secure a content of 0.1% or more. In the case of V, it is more effective to secure a content of 0.1% or more. However, Mo and V are expensive elements, and excessive addition causes an increase in cost. When adding 1 type or 2 types of Mo and V, let Mo and V be 0.5% or less of content range.

  Ni is effective for improving hardenability and can be added as necessary. In that case, it is more effective to secure a Ni content of 0.1% or more. However, excessive addition of Ni is a factor that impairs economic efficiency. Therefore, when Ni is added, it is performed within a range of 2% or less.

  Ti, like Nb, forms a very hard Ti-containing carbide in the steel after casting, contributing to the improvement of wear resistance, and Ti that has been re-dissolved after casting has fine grains during quenching. To contribute to improved toughness. Further, Ti has a strong bonding force with N. Therefore, when B is added, formation of BN is prevented, and it is advantageous in extracting the effect of improving the hardenability of B. In order to sufficiently obtain these effects, it is more effective to secure a Ti content of 0.01% or more. However, excessive Ti content causes a decrease in toughness. When adding Ti, it is performed within a range of 0.25% or less.

  B is an element effective for improving the hardenability, and can be added as necessary. In order to sufficiently exhibit the hardenability improving effect, it is more effective to secure a B content of 0.0005% or more. However, since the action is saturated at about 0.005%, when B is added, it is performed within the range of 0.005% or less.

The ideal critical diameter D _I is an index indicating the diameter (mm) of a bar that is completely quenched when it is assumed that quenching is performed at an infinite cooling rate. As a function of the alloy component content, (1) It can represent with Formula or (2) Formula. Since hardenability is greatly influenced by the presence or absence of B, either (1) or (2) is properly used depending on the B content. D more hardenability _I value is larger means that it is good. We study results (1) or (2) becomes smaller than D _I value 50 of the formula, in a quenching step being performed in the factory to produce a tool member such as a saw blade, compared It has been found that an incompletely quenched structure is likely to occur when a quenching process (for example, gas quenching) with a low static cooling rate is applied. The incompletely quenched structure was found to function as a starting point of crack generation and a crack propagation path, as in the case where carbides exist excessively. Incompletely quenched parts are also inferior in wear resistance. Therefore, in order to stably and significantly improve the wear resistance and toughness, it is important to adjust the component composition so that sufficient hardenability can be ensured so that an incompletely hardened portion does not occur. Therefore, the present invention defines strict component composition such that D _I value more than 50, which is defined by equation (1) or (2) below. D _I value is more preferably 55 or more.

[Metal structure]
As described above, in the present invention, a hard carbide containing one or more of Nb and Ti is used to remarkably improve the wear resistance against abrasive wear. However, in order to ensure toughness, it is necessary to consider the dispersion form. As a result of detailed studies, when the steel structure before quenching has a metal structure in which a carbide having a particle diameter of 2 μm or more containing one or more of Nb and Ti is present in the matrix at a density of 300 to 1000 pieces / mm ^2. It has been found that after quenching, the wear resistance is remarkably improved and the adverse effect of impairing toughness is avoided. If the steel is adjusted to the above chemical composition, the distribution state of carbides having a particle diameter of 2 μm or more containing one or more of Nb and Ti after the normal quenching and tempering treatment is almost the same as that before quenching. Maintained.

Here, the carbide containing one or more of Nb and Ti is mainly composed of NbC, TiC, (Nb, Ti) C, and the precipitated particles contained in the steel are “Nb and Ti. It can be confirmed by microscopic analysis by EDX etc. whether it corresponds to the carbide | carbonized_material containing 1 or more types. As the particle diameter of each particle, the equivalent circle diameter of the particle observed on the steel cross section is adopted. That is, the diameter of a perfect circle having the same area is calculated from the area of the particle, and this diameter is taken as the particle diameter of the particle. It is desirable that the maximum particle size of carbides observed in the steel material is adjusted to 30 μm or less. If the number of carbides having a particle diameter of 2 μm or more is less than 300 / mm ² , the effect of improving wear resistance tends to be insufficient. More preferably, it is 400 pieces / mm ² or more. However, if it exceeds 1000 pieces / mm ² , the toughness tends to decrease.

  FIG. 1 shows an SEM photograph of carbide and an EDX analysis example. FIG. 1A shows a steel plate having a low Nb content of about 0.05% by mass (a material corresponding to Comparative Example No. 1 in Table 2 described later), and FIG. 1B shows an Nb content of about 0.2% by mass. %, And a Ti content of about 0.02 mass% (a material corresponding to Invention Example No. 17 in Table 2 described later). In the material (b) having a high Nb content, the density of the precipitated particles is increased as compared with the material (a). FIG.1 (c) observes the material of (b) at high magnification. When the arrow part of FIG.1 (c) is analyzed by EDX, it turns out that precipitation particle | grains are the carbide | carbonized_material containing Nb and Ti (FIG.1 (d)).

〔Production method〕
In order to obtain a steel material having the metal structure as described above, first, coarse carbides containing at least one of Nb and Ti are precipitated using a cooling process after casting. Specifically, it is effective to adopt a cooling pattern in which the residence time in the temperature range of 900 to 1500 ° C. at which carbide containing one or more of Nb and Ti is likely to grow is approximately 30 min or more. All of the examples described later satisfy this cooling pattern. Such a cooling pattern can be realized by a method of cooling the ingot or slab after casting. Cooling means natural cooling without forcibly cooling the ingot or slab. “Coarse carbide” refers to a carbide having a particle size of approximately 2 μm or more.

Next, the density of carbides having a particle diameter of 2 μm or more containing one or more of Nb and Ti is adjusted to 300 to 1000 pieces / mm ² by heating and holding the steel containing the coarse carbides at 1200 to 1350 ° C. When heated to this temperature range, re-dissolution of coarse carbides containing one or more of Nb and Ti proceeds, and the density of carbides with a particle diameter of 2 μm or more can be adjusted to 300 to 1000 / mm ^2. is there. Although the heating and holding time depends on the holding temperature and the size of the steel material used for heating, the optimum holding time can usually be found in the range of 0.5 to 12 h. Actually, the holding temperature and holding time may be set by a preliminary experiment corresponding to the production equipment to be used. In medium- and high-carbon steels that are not stainless steel, it is impossible to perform heat treatment at a high temperature of 1200 to 1350 ° C. at the final stage of the product. Therefore, in the present invention, the distribution density of carbides having a particle diameter of 2 μm or more containing one or more of Nb and Ti is adjusted in an initial manufacturing stage including casting. The distribution density of the carbide is substantially maintained even after each process of normal hot rolling, hot-rolled sheet annealing, cold rolling, finish annealing, and quenching and tempering.

Conventionally general production methods can be applied to the processes after hot rolling. For example, the hot rolling can employ conditions of a heating extraction temperature of 1100 to 1300 ° C, a finish rolling temperature of 800 to 900 ° C, and a winding temperature of 750 ° C or less. For hot-rolled sheet annealing, for example, a condition of heating and holding in a temperature range of 600 ° C. or higher and less than Ac ₁ point can be employed. Further, if necessary, it may be cold-rolled and subjected to finish annealing that is heated and held in a temperature range of 600 ° C. or higher and less than Ac ₁ point, for example, for 10 to 50 hours. In this way, it is possible to obtain a raw steel material for use in quenching and tempering.

  Steel having the chemical composition shown in Table 1 was melted, and a slab was produced by allowing the cooling process after casting to cool, and the obtained slab was subjected to heating at 1250 ° C. × 1 h. Thereafter, hot rolling was performed under conditions of a finish rolling temperature of 850 ° C. and a winding temperature of 550 ° C. to obtain a hot rolled steel plate having a thickness of 3.5 mm. Next, annealing is performed at 690 ° C. for 15 hours, the steel sheet is 1.5 mm thick by cold rolling, and finish annealing is performed at 670 ° C. for 15 hours to provide a material steel plate for quenching and tempering (sheet thickness of 1.5 mm). Got.

The quenching and tempering treatment was performed by selecting one of the following methods. By adjusting the tempering temperature, tempered materials having tempered hardness corresponding to 42 HRC, 46 HRC, and 50 HRC were obtained. The tempering temperature T (° C.) for each steel type is shown in Table 1.
[Quenching and tempering treatment a]
820 ° C. × 15 min → 60 ° C. oil quenching → T ° C. × 30 min tempering By this treatment, tempered materials with tempered hardness of 42HRC, 46HRC, and 50HRC are produced (quenching and tempering treatment b).
820 ° C. × 15 min → gas quenching → T ° C. × 30 min tempering This process produces a tempered material with a tempered hardness of 50 HRC.

[Investigation of carbide distribution state]
About the raw steel plate before being subjected to quenching treatment, a cross section (L cross section) parallel to the rolling direction and the plate thickness direction is observed with an analytical scanning electron microscope, and “Nb, which exists in the observation area 61 × 61 μm ² × 20 field of view” The number of “carbonized particles having a particle diameter of 2 μm or more containing one or more of Ti” was counted, and the existence density was calculated. The particle diameter was the aforementioned equivalent circle diameter, and particles having a particle diameter of 2 μm or more were picked up by image processing.

[Abrasion resistance test]
A test was performed using a pin-on-disk type wear tester using a 5 mm-diameter disk (obtained by polishing and removing the oxide scale) cut out from the sample after quenching and tempering. While the test piece disk is fixed to the sample holder, the friction surface speed is 0.66 m / min while pressing the test piece surface against a rotating # 400 emery polishing paper (abrasive paper coated with silicon carbide powder) with a test load F = 30 N. The wear test was conducted under the conditions of sec and the friction distance L = 200 m. The volume of the material that disappeared due to wear was calculated from the difference in thickness of the sample plate before and after the test, and this was defined as wear loss W (mm ³ ). Then, the specific wear amount C (mm ³ / N · m) was determined by the following equation (3).
Specific wear amount C = wear loss W / (test load F × friction distance L) (3)
If the specific wear amount C is 1.5 × 10 ⁻⁴ mm ³ / N · m or less in a material with a tempered hardness of 50 HRC, the wear resistance is much superior to the current steel used for cutting tools. It is judged that it has.

[Impact test]
A 2 mm V notch impact test piece (notch tip radius is 0.25 mm) having a rolling direction as a longitudinal direction was prepared from a plate material having a thickness of 1.35 mm obtained by polishing the sample surface after quenching and tempering. A Charpy impact test at room temperature (25 ° C. ± 2 ° C.) was performed using this test piece.
If the impact value in this test is 10 J / cm ² or more in a material having a tempered hardness of 50 HRC, it is judged that the material has sufficient toughness from the viewpoint of safety.

[Observation of quenched and tempered structure]
The structure of the sample that had been quenched and tempered was observed, and the area ratio of the incompletely quenched portion (the portion where the matrix was a phase other than the martensite phase) was measured.

These results are shown in Table 2. A material having a tempered hardness of 50 HRC and having a specific wear amount C of 1.5 × 10 ⁻⁴ mm ³ / N · m or less and an impact value of 10 J / cm ² or more is referred to as “wear resistance. The material was judged to have a high level of both “strength” and “toughness”, and evaluated as “good” (pass). The other materials were indicated as evaluation x (failed).

  As can be seen from Table 2, the examples of the present invention have a very hard distribution of carbides having a particle diameter of 2 μm or more containing one or more of Nb and Ti which are very hard, thereby providing “abrasion resistance”. And “toughness” were compatible at a high level.

On the other hand, Nos. 1 and 2 as comparative examples were made using steel with insufficient Nb content, and both wear resistance and toughness were inferior. No. 3 uses steel with too much Nb content, and wear resistance is good, but the toughness is inferior due to a large amount of precipitation of hard carbides. No. 4 uses steel with too much C content, and because there were a lot of undissolved carbides after quenching and tempering, they became the starting point of fracture and crack propagation path, and the toughness decreased. No. 5 uses steel with insufficient C content and has good toughness but poor wear resistance. Nos. 6 and 7 used steels having too much Mn and Cr contents, respectively, and the toughness was lowered due to the presence of many undissolved carbides after quenching and tempering treatment. No.8 and 9 is obtained by using a lower steel D _I value out of the present invention defined range, it was subjected to different quenching and tempering treatment of conditions for the same steel sheet. In No. 8, it was possible to achieve both wear resistance and toughness by oil quenching, but in No. 9, the results were inferior in both wear resistance and toughness by gas quenching. Therefore, it is difficult to achieve both a stable and high level "tenacity" and "abrasion resistance" is a steel D _I value is below the present invention defined range. No. 10 uses steel with too much Ti content. Due to the presence of a large amount of Ti-containing carbides, they became the starting point of fracture and crack propagation paths, and reduced toughness.

  Using the steels C, J, and L shown in Table 1, a raw steel plate was prepared in the same manner as in Example 1 except that the temperature and holding time of the slab heat treatment (solution treatment) were varied. The same characteristic investigation as in Example 1 was conducted. However, quenching and tempering were performed by the above-described “quenching and tempering treatment a”, and only a material having a tempered hardness of 50 HCR was produced. The results are shown in Table 3.

  As can be seen from Table 3, the examples of the present invention achieved both high levels of “wear resistance” and “toughness”. On the other hand, Nos. 3, 21, and 22 use steel with too much Nb content, and wear resistance is good, but the conditions of the heat treatment (solution treatment) of the slab are changed. Even toughness could not be improved. No. 3 is a reprint of the data listed in Table 2. In No. 23, the temperature of the heat treatment (solution treatment) of the slab was too low, so the abundance of hard carbides was too large and the toughness was poor. In No. 27, the temperature of the heat treatment (solution treatment) of the slab was too high, and the wear resistance was inferior due to the decrease in the amount of hard carbides.

  FIG. 2 shows a graph in which the relationship between the impact value and the specific wear amount is plotted for the materials (except No. 8) obtained in the above examples. It can be seen that the examples of the present invention suppress the increase of the specific wear amount even when the impact value is high, that is, the “wear resistance” and the “toughness” are compatible at a high level.

The figure which showed the SEM photograph and EDX analysis example of the carbide | carbonized_material. The graph which plotted the relationship between an impact value and specific wear amount about the material (except No. 8) obtained by said each example.

Claims (8)

In mass%, C: 0.6-1.0%, Si: 0.5% or less, Mn: 0.1-1.5%, P: 0.02% or less, S: 0.02% or less, cr: 0.1~1.5%, Nb: 0.1~0.5 %, and a balance of Fe and unavoidable impurities, are the following (1) the ideal critical diameter D _I, which is defined by the formula 50 or A steel material for wear-resistant quenched and tempered parts having a chemical composition and containing Nb and having a particle diameter of 2 μm or more in a matrix at a density of 300 to 1000 pieces / mm ² .
D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1−0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) (1)
However, the content value of the element expressed in mass% is substituted for the element symbol on the right side of the formula (1), and 0 (zero) is substituted for elements not contained. In mass%, C: 0.6-1.0%, Si: 0.5% or less, Mn: 0.1-1.5%, P: 0.02% or less, S: 0.02% or less, Cr: 0.1 to 1.5%, Nb: 0.1 to 0.5%, Mo: 0.5% or less, V: 0.5% or less, Ni: 2% or less, Ti: 0 Ideally defined by the following formula (1) or (2) depending on the B content, containing at least one kind of 0.25% or less and B: 0.005% or less, the balance being Fe and inevitable impurities Abrasion resistance having a chemical composition with a critical diameter D _I of 50 or more and a carbide having a particle diameter of 2 μm or more containing one or more of Nb and Ti in the matrix at a density of 300 to 1000 / mm ² Steel for quenching and tempering parts.
When B content is less than 0.0005% (including 0%): D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1 −0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) (1)
When B content is 0.0005% or more: D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1−0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) × {1 + 1.5 × (0.9−C)} (2)
However, the content value of the element expressed in mass% is substituted for the element symbol on the right side of the formula (1) or (2), and 0 (zero) is substituted for elements not contained.   The steel material according to claim 1 or 2, wherein the wear-resistant quenching and tempering part is a saw blade. In mass%, C: 0.6-1.0%, Si: 0.5% or less, Mn: 0.1-1.5%, P: 0.02% or less, S: 0.02% or less, cr: 0.1~1.5%, Nb: 0.1~0.5 %, and a balance of Fe and unavoidable impurities, are the following (1) the ideal critical diameter D _I, which is defined by the formula 50 or A step of precipitating coarse carbides containing Nb by casting steel whose composition is adjusted to the composition and then allowing to cool;
A step of adjusting the density of carbides having a particle diameter of 2 μm or more containing Nb to 300 to 1000 pieces / mm ² by heating and holding the steel containing the coarse carbides at 1200 to 1350 ° C .;
A method for producing a steel material for wear-resistant quenched and tempered parts.
D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1−0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) (1)
However, the content value of the element expressed in mass% is substituted for the element symbol on the right side of the formula (1), and 0 (zero) is substituted for elements not contained. In mass%, C: 0.6-1.0%, Si: 0.5% or less, Mn: 0.1-1.5%, P: 0.02% or less, S: 0.02% or less, Cr: 0.1 to 1.5%, Nb: 0.1 to 0.5%, Mo: 0.5% or less, V: 0.5% or less, Ni: 2% or less, Ti: 0 Ideally defined by the following formula (1) or (2) depending on the B content, containing at least one kind of 0.25% or less and B: 0.005% or less, the balance being Fe and inevitable impurities step of precipitating coarse carbides containing Nb, one or more Ti by critical diameter D _I is allowed to cool After casting the component adjustment steel the composition is 50 or more,
A step of adjusting the density of carbides having a particle diameter of 2 μm or more containing one or more of Nb and Ti to 300 to 1000 pieces / mm ² by heating and holding the steel containing the coarse carbides at 1200 to 1350 ° C .;
A method for producing a steel material for wear-resistant quenched and tempered parts.
When B content is less than 0.0005% (including 0%): D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1 −0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) (1)
When B content is 0.0005% or more: D _I = 6.0 (C) ^1/2 × (1 + 0.64Si) × (1 + 4.1Mn) × (1 + 2.83P) × (1−0.62S) × (1 + 2.33Cr) × (1 + 1.52Ni) × (1 + 3.14Mo) × {1 + 1.5 × (0.9−C)} (2)
However, the content value of the element expressed in mass% is substituted for the element symbol on the right side of the formula (1) or (2), and 0 (zero) is substituted for elements not contained. After passing through the step of adjusting the density of the carbides to 300 to 1000 pieces / mm ² , hot rolling is performed under conditions of a heating extraction temperature of 1100 to 1300 ° C, a finish rolling temperature of 800 to 900 ° C, and a winding temperature of 750 ° C or less, The method for producing a steel material for wear-resistant quenched and tempered parts according to claim 4 or 5, which is subjected to a step of heating and holding in a temperature range of 600 ° C or higher and less than Ac ₁ point. The method for producing a steel material for wear-resistant quenched and tempered parts according to claim 6, which is further cold-rolled and subjected to a step of heating and holding in a temperature range of 600 ° C or higher and less than Ac ₁ point.   The method for manufacturing a steel material according to any one of claims 4 to 7, wherein the wear-resistant quenched and tempered part is a saw blade.