KR102329386B1 - High-carbon cold-rolled steel sheet and its manufacturing method, and high-carbon steel machine parts - Google Patents

Abstract

After a short time solution heat treatment, quenching (quenching) treatment and low temperature tempering treatment (quenching tempering treatment), it is possible to have good impact properties and hardness properties, furthermore, excellent wear resistance, and also before quenching tempering treatment Provided is a high-carbon cold-rolled steel sheet having a sheet thickness of less than 1.0 mm with little decrease in secondary workability.
In terms of mass%, C: 0.85 to 1.10%, Mn: less than 0.60%, Si: 0.10 to 0.35%, P: 0.030% or less, S: 0.030% or less, Cr: less than 0.60%, and Mn + Cr A high-carbon cold-rolled steel sheet having a steel sheet chemical composition that satisfies less than 1.0%, further contains Nb: 0.005 to 0.020 mass%, and the balance consists of Fe and unavoidable impurities. Thereby, compared with conventional steel materials, there is little fall of secondary workability before quenching and tempering. In addition, since the average particle diameter of the carbide is 0.2 to 0.7 (㎛) and a steel sheet structure having a spheroidization ratio of 90% or more, the impact value is 9 J/cm 2 or more even by a short quenching tempering treatment of 3 to 15 min. It becomes possible to set it as the mechanical component which has the outstanding impact characteristic, sufficient hardness characteristic of the range of 600-750 HV, and the outstanding wear resistance.

Description

High-carbon cold-rolled steel sheet and its manufacturing method, and high-carbon steel machine parts

The present invention relates to a high-carbon cold-rolled steel sheet used as a raw material for various mechanical parts manufactured by quenching and tempering, and a manufacturing method therefor, particularly to a high-carbon cold-rolled steel sheet having a sheet thickness of less than 1.0 mm applied to a Meriyasu needle and the like. will be.

Generally, carbon steel steel materials for machine structures (SxxC) and carbon tool steel steel materials (SK) prescribed|regulated to JIS are used for large and small various machine parts. When used as a wrought material, predetermined hardness and toughness (impact characteristics) are imparted by performing a quenching and tempering treatment after forming into a part shape through punching processing or various plastic processing. Among them, since the needle for knitting knitted paper pulls the yarn while repeating a reciprocating motion at high speed to weave the yarn, it has sufficient strength and abrasion resistance for the bat portion of the needle body in contact with the rotational drive unit, and sufficient for the hook portion that rubs against the yarn. In addition to abrasion resistance, it is required to have excellent impact properties of the tip part accompanying the reciprocating motion.

The high-carbon cold-rolled steel sheet used as a material for a meriyasu needle is used for a meriyasu needle for a flat knitting machine when the plate thickness is 1.0 mm or more, and is used for a meriyasu needle for a circular knitting machine or a longitudinal knitting machine when the plate thickness is less than 1.0 mm. In order to weave a thin-diameter thread at high speed with the latter needle, the plate thickness of the material used is often 0.4 to 0.7 mm. Further, in addition to excellent cold workability (also referred to as secondary workability), the raw material is required to have sufficient hardness and sufficient toughness at the needle tip when quenched and quenched after secondary processing into a needle shape.

In addition, so-called high-carbon steel sheets such as carbon steel for machine structure (S×C) and carbon tool steel (SK) prescribed in JIS are finely classified according to the amount of C. In the region where the amount of C is less than 0.8 mass%, that is, in a steel sheet having a sub-eutectoid composition, cold workability is excellent because the fraction of ferrite phase is high, but it is difficult to obtain sufficient quenching hardness, and wear resistance of the hook part and durability of the needle body are required. It is not suitable for applications such as Meriyasu needles. On the other hand, a high-carbon steel sheet having a C content of more than 1.1 mass% even in a hypereutectic composition of 0.8 mass% or more has excellent hardenability, but has extremely poor cold workability due to carbide (cementite) contained in a large amount, resulting in grooving, etc. It is not suitable for use with needles, where precise and fine processing is performed.

Conventionally, a raw material having a steel composition to which a third element is added based on carbon tool steel or alloy tool steel having a C of 0.8 to 1.1 mass%, or a steel composition thereof, is widely used for the Meriyasu needle. In the manufacturing process of this meriyasu needle, the raw material is subjected to a wide variety of plastic processing such as punching (shear processing), cutting, wire drawing, joint fixing, and bending. Therefore, this material for manufacturing needles has sufficient workability (secondary workability) during material processing in the needle manufacturing process, and hardness characteristics and impact characteristics ( toughness) is required.

In the manufacture of a Meriyasu needle, a quenching and tempering treatment is performed on a raw material in order to ensure a predetermined hardness characteristic. As for the temperature of this tempering process, it is common to set it as the low temperature of 200-350 degreeC. However, when the content of Mn or Cr effective for hardening property is increased with emphasis on hardness characteristics, or a large amount of other third elements are contained, in the above-described low-temperature tempering treatment in the temperature range of 200 to 350°C, Tempering of the martensite phase was not sufficiently performed, and the improvement in impact properties (toughness) was insufficient, or there were cases where the toughness value was varied.

On the other hand, for the purpose of improving the impact properties of the Meriyasu needle, the impurity element P or S in the chemical composition of the material is reduced, the grain boundary segregation of P and the generation of inclusions (MnS) are suppressed, and the adverse effects of these elements are reduced. Aiming for mitigation is also an effective countermeasure. However, there is a limit in improving the impact properties of the Meriyasu needle by reducing P or S from the viewpoint of steelmaking technology and economic feasibility.

Moreover, it is conventionally known that the refinement|miniaturization of a metal structure is effective as a means of improving an impact characteristic.

For example, Patent Document 1 describes "a high-carbon steel sheet excellent in quenching properties, fatigue properties, and toughness, and a manufacturing method therefor". The high carbon steel sheet described in Patent Document 1 is, in mass%, C: 0.5 to 0.7%, Si: 0.5% or less, Mn: 1.0 to 2.0%, P: 0.02% or less, S: 0.02% or less, Al: 0.001 to A component composition containing 0.10%, further containing one or more of V: 0.05 to 0.50%, Ti: 0.02 to 0.20%, and Nb: 0.01 to 0.50%, the balance being Fe and unavoidable impurities; , a high-carbon steel sheet having a structure in which carbides having a spheroidization ratio of 95% or more and a maximum particle diameter of 2.5 µm or less are dispersed. In the technique described in Patent Document 1, sub-eutectoid steel is added, carbonitride-forming elements V, Ti, and Nb are added to form fine carbonitrides, and old austenite grains are used by utilizing the peening effect of these fine carbonitrides. It is said that (粒) is made fine and toughness is improved.

Moreover, "a high-carbon steel member excellent in impact characteristics" is described in patent document 2. The high carbon steel member described in Patent Document 2 is, in mass%, C: 0.60 to 1.30%, Si: 1.0% or less, Mn: 0.2 to 1.5%, P: 0.02% or less, S: 0.02% or less, Fe: substantially With the composition of the remainder, in the matrix after quenching and tempering, the following formula

8.5 < 15.3 × C % - Vf < 10.0

Volume rate (Vf) to beauty by (% by volume) carbides remains, and the particle diameter that satisfies: 1.0 ㎛ or more undissolved carbide is observed area: high carbon steel member, characterized in that it is regulated to less than 100 ㎛ ^{2 2} per dog am. In the high carbon steel member described in Patent Document 2, in addition to the above composition, in mass%, Ni: 1.8% or less, Cr: 2.0% or less, V: 0.5% or less, Mo: 0.5% or less, Nb: 0.3% Hereinafter, Ti: 0.3 % or less, B: 0.01 % or less, Ca: 0.01 % or less 1 type, or 2 or more types may be contained. In the technique described in Patent Document 2, steels with a wide range of carbon content from hypoeutectoid to hypereutectoid are targeted, but high carbon steel exhibiting excellent impact properties with an impact value of 25 J/cm 2 or more while maintaining a target hardness: 600 to 900 HV. Absence is said to be obtained.

Moreover, "a high carbon cold-rolled steel sheet and its manufacturing method" is described in patent document 3. The high-carbon cold-rolled steel sheet described in Patent Document 3 is, in mass%, C: 0.85 to 1.10%, Mn: 0.50 to 1.0%, Si: 0.10 to 0.35%, P: 0.030% or less, S: 0.030% or less, Cr: _{The average particle size (d av} ) and the spheroidization ratio (N _SC /N _TC ) × 100% of the carbide containing 0.35 to 0.45%, Nb: 0.005 to 0.020%, the remainder being Fe and unavoidable impurities, and dispersed in the steel sheet , respectively, the following (1) formula

0.2 ≤ d _av ≤ 0.7 (μm) … (One)

and the following (2) expression

(N _SC /N _TC ) × 100 ≥ 90% … (2)

is a cold-rolled steel sheet with a sheet thickness of less than 1.0 mm. Moreover, in the technique described in patent document 3, in addition to the above-mentioned composition, it is further containing 1 type or 2 types selected from Mo and V, and it is said that it is said that it is preferable that each content is all 0.001 % or more and less than 0.05 %. And in the technique described in patent document 3, it is said that containing of 0.005-0.020% of Nb: 0.005-0.020% is effective for the hardening property and impact characteristic (toughness) improvement after a short-time solution treatment and a low-temperature tempering process.

Moreover, "abrasion-resistant steel sheet excellent in toughness" is described in patent document 4. The wear-resistant steel sheet described in Patent Document 4 is, in mass%, C: 0.60 to 1.25%, Si: 0.50% or less, Mn: 0.30 to 1.20%, P: 0.030% or less, S: 0.030% or less, Cr: 0.30 to 1.50 %, Nb: 0.10 to 0.50%, Ti: 0 to 0.50%, Mo: 0 to 0.50%, V: 0 to 0.50%, Ni: 0 to 2.00%, the balance having a chemical composition consisting of Fe and unavoidable impurities, and ferrite It has a metal structure in which cementite particles and carbide particles containing one or more of Nb and Ti are dispersed in the metal matrix of the phase, and has a circular equivalent diameter in a cross section parallel to the rolling direction and the plate thickness direction (L cross section) It is a steel sheet in which the number density of Nb·Ti-based carbide particles of 0.5 μm or more is 3000 to 9000 pieces/mm 2 and the number density of voids of 1.0 μm or more of equivalent circle diameter is 1250 pieces/mm 2 or less. The wear-resistant steel sheet described in Patent Document 4 is said to be a steel sheet having excellent wear resistance and toughness.

Japanese Patent Laid-Open No. 2009-24233 Japanese Laid-Open Patent Publication No. 2006-63384 Japanese Patent Laid-Open No. 2017-36492 Japanese Laid-Open Patent Publication No. 2017-190494

The high-carbon cold-rolled steel sheet used as a raw material for meriyasu needles is required to have sufficient hardness and sufficient impact properties (toughness) after quenching and tempering treatment. In recent years, in order to improve productivity, additional speed up of the knitting machine is required, and accordingly, the load applied to the meriyasu needle increases, and the meriyasu needle breaks or the lifespan is frequently shortened in a shorter time than in the prior art, which is a problem. For this reason, the meriyasu needle which improved impact characteristics and abrasion resistance compared with the prior art has come to be calculated|required. Although it is thought that such a meriyasu needle can be realized by adding a third element or increasing the amount of alloy elements such as Cr, Mn, and Mo, there is a concern that the secondary workability in the needle manufacturing process is impaired. From this point of view, there is a demand for a material for meriyasu needles capable of improving abrasion resistance and impact properties (toughness) after quenching and tempering without lowering secondary workability compared to the prior art.

However, it is difficult for the technique described in patent document 1 to apply to the machine part which high hardness is calculated|required. The technique described in Patent Document 1 is limited to the composition of sub-eutectoid steel, and by adding carbonitride forming elements such as V, Ti, and Nb as a third element, the old austenite grains are refined by their fine carbonitrides, and toughness It is a technology that is expected to have an improvement effect. Moreover, since the technique described in patent document 1 has a subeutectoid composition with a carbon level, it is also a technique which improved the moldability of a ferrite matrix phase.

Moreover, in Patent Document 2, addition of Mo, V, Ti, Nb, and B, which are the third elements, only shows examples of steel having a carbon content in the range of 0.67 to 0.81 mass%. In the technique described in patent document 2, it is guessed that 3rd elements, such as Mo, V, Ti, Nb, and B, are added with the intention of improving the characteristic of a sub-eutectoid steel. In addition, in Patent Document 2, there is no description of the action and optimization of third elements such as Mo, V, Ti, Nb, and B on steel having a carbon content exceeding 0.81 mass%.

Moreover, in patent document 1 and patent document 2, with respect to a high carbon cold-rolled steel sheet, after a short-time solution treatment, such as 3 to 15 min, quenching and low-temperature tempering of 200-350 degreeC are performed, and desired impact characteristic and predetermined|prescribed There is no description of a technique for advantageously enhancing hardness.

In addition, in the technique described in Patent Document 3, Nb: 0.005 to 0.020% of containing is effective for quenching after a short period of solution holding and for improving quenching properties and impact properties (toughness) after a low temperature tempering treatment, Patent Document 3 does not specifically mention the secondary workability of the high-carbon cold-rolled steel sheet before quenching (quick cooling) and low-temperature tempering treatment (hereinafter also referred to as quenching tempering treatment) after short-time solution heat retention. Patent Document 3 describes a high-carbon cold-rolled steel sheet capable of having both excellent toughness and excellent wear resistance after quenching tempering treatment. However, in this high-carbon cold-rolled steel sheet, secondary workability before quenching tempering treatment is described. It was insufficient, and there existed a problem that it could not respond to the recent productivity improvement request|requirement.

Moreover, in the technique described in Patent Document 4, it is said that it is possible to increase both the wear resistance and toughness after quenching tempering in a high-carbon cold-rolled steel sheet. Document 4 does not mention that the wear resistance and toughness after quenching tempering can be improved without a decrease in secondary workability before quenching and tempering.

The present invention solves the problems of the prior art described above, suppresses a decrease in secondary workability before quenching (quick cooling) and low temperature tempering treatment (quenching tempering treatment) after a short time solution treatment, and also reduces After quenching (quick cooling) and low-temperature tempering treatment (quenching tempering treatment) after solution heat treatment, evaluated by an impact test in the vicinity of the plate thickness actually used, the impact value is 9 J/cm 2 or more, and the hardness is 600 An object of the present invention is to provide a high-carbon cold-rolled steel sheet having a sheet thickness of less than 1.0 mm which satisfies the range of to 750 HV and is excellent in wear resistance.

In order to achieve the above object, the present inventors intensively studied the relationship between the composition of the high-carbon cold rolled steel sheet, secondary workability before quenching tempering treatment, hardness after quenching tempering treatment, impact characteristics, and wear resistance. As a result, from the viewpoints of quenching properties, quenching, hardness after low temperature tempering, impact properties, etc., C, which is preferable for a Meriyasu needle, is limited to a range of 0.85 to 1.10 mass%, and Nb is contained in an amount of 0.005 to 0.020 mass%. It was discovered that specifying the range and implementing a predetermined manufacturing method is effective in being able to adjust the average particle diameter of carbide and the degree of spheroidization, and securing the desired properties after quenching and tempering treatment. Further, by making Mn less than 0.60 mass% and adjusting (Mn+Cr) to less than 1.0%, a decrease in secondary workability before quenching tempering treatment is suppressed, and hardness after quenching tempering treatment , impact properties (toughness), and abrasion resistance were found to satisfy the desired properties.

The present invention has been completed by further investigation based on the above findings. That is, the gist of the present invention is as follows.

(1) In mass%, C: 0.85% or more and 1.10% or less, Mn: less than 0.60%, Si: 0.10% or more and 0.35% or less, P: 0.030% or less, S: 0.030% or less, Cr: less than 0.60%, Nb : It contains 0.005% or more and 0.020% or less, and the sum of Mn content and Cr content (Mn+Cr) satisfies less than 1.0%, has a steel plate composition consisting of remainder Fe and unavoidable impurities, and a steel plate thickness of less than 1.0 mm High carbon cold rolled steel sheet, characterized in that.

_{(2) In (1), the average particle diameter (d av} ) and the spheroidization ratio (N _SC /N _TC ) × 100% of carbides having the composition of the steel sheet and further dispersed in the steel sheet are, respectively, by the following formula (1)

0.2 ≤ d _av ≤ 0.7 (μm) … (One)

and the following (2) expression

(N _SC /N _TC ) × 100 ≥ 90% … (2)

(here, d _av : average value of equivalent circular diameters of carbides (average particle diameter μm), N _TC : total number of carbides per 100 μm ² _{observation area, N SC} : per 100 μm ² observation area, (major diameter d _L )/(minor diameter) d _S ) is the number of carbides that satisfy the condition of 1.4 or less)

A high-carbon cold-rolled steel sheet, characterized in that it has a steel sheet structure that satisfies

(3) In (1) or (2), instead of the composition of the steel sheet, in mass%, C: 0.85% or more and 1.10% or less, Mn: less than 0.60%, Si: 0.10% or more and 0.35% or less, P: 0.030 % or less, S: 0.030% or less, Cr: less than 0.50%, Nb: 0.005% or more and 0.020% or less, and the sum of Mn content and Cr content (Mn+Cr) satisfies less than 0.90%, and the remainder Fe and a steel sheet composition comprising unavoidable impurities.

(4) The steel sheet composition according to any one of (1) to (3), wherein, in mass%, Mo: 0.001% or more and less than 0.05%, V: One or two selected from 0.001% or more and less than 0.05% A high-carbon cold-rolled steel sheet having a steel sheet composition containing species.

(5) A method for manufacturing a high-carbon cold-rolled steel sheet, wherein the hot-rolled steel sheet having the composition according to any one of (1) to (4) is repeatedly subjected to cold rolling and spheroidizing annealing to produce a high-carbon cold-rolled steel sheet, the method comprising: _{The average particle diameter (d av} ) and the spheroidization ratio (N _SC /N _TC ) of the carbides dispersed in the high-carbon cold-rolled steel sheet are expressed by the following formulas (1) and (2), respectively.

0.2 ≤ d _av ≤ 0.7 (μm) … (One)

(N _SC /N _TC ) × 100 ≥ 90% … (2)

(here, d _av : average value of equivalent circular diameters of carbides (average particle diameter μm), N _TC : total number of carbides per 100 μm ² _{observation area, N SC} : per 100 μm ² observation area, (major diameter d _L )/(minor diameter) d _S ) is the number of carbides that satisfy the condition of 1.4 or less.)

is satisfied, and the high-carbon cold-rolled steel sheet has a sheet thickness of less than 1.0 mm.

(6) The method for manufacturing a high-carbon cold-rolled steel sheet according to (5), wherein the number of times of repeatedly performing the cold rolling and spheroidizing annealing is 2 to 5 times.

(7) The method for producing a high-carbon cold rolled steel sheet according to (5) or (6), wherein the rolling reduction of the cold rolling is 25 to 65%, and the temperature of the spheroidizing annealing is 640 to 720°C.

(8) Using the high-carbon cold-rolled steel sheet according to any one of (1) to (4) as a raw material, secondary processing is performed on the raw material to obtain a machine part having a predetermined shape, and then forming the machine part into a solution for a short time A method for manufacturing a machine part in which quenching treatment and tempering treatment are performed after treatment, wherein the quenching treatment after the short-time solution heat treatment is performed at a temperature in the range of 760 to 820°C and for a time in the range of 3 to 15 min. A method of manufacturing a high-carbon steel machine part, characterized in that, in the case of a rapid cooling treatment, and the tempering treatment is a treatment in which the tempering is performed at a temperature in the range of 200 to 350°C, a machine part having excellent wear resistance and excellent toughness is obtained. .

(9) High carbon steel machine parts manufactured by the manufacturing method of high carbon steel machine parts as described in (8).

The high-carbon cold-rolled steel sheet of the present invention suppresses a decrease in secondary workability such as machinability, and the life of tools used for punching, swaging, bending, secondary processing, etc. is about the same as that of a conventional high-carbon cold-rolled steel sheet, and , a short-time solution treatment, followed by a quenching treatment and a low temperature tempering treatment (quenching tempering treatment), compared to a conventional high-carbon steel sheet, a mechanical part that has high hardness properties, excellent impact properties and excellent wear resistance in a balanced way It exhibits a special effect in the industry that it can be manufactured. In addition, the high-carbon cold-rolled steel sheet of the present invention is excellent in impact properties (toughness), abrasion resistance, and further fatigue resistance after quenching and tempering treatment, and in particular, mechanical parts requiring excellent durability under harsh use environments such as Meriyasu needles. There is also an effect that it is preferable as a material for use.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows the outline of an end mill working test (secondary workability evaluation test) typically.
It is explanatory drawing which shows the outline of a wear test apparatus typically.
3 : is explanatory drawing which shows typically the outline of the wear condition of (a) the shape of a wear test piece, and (b) abrasion test piece.
4 : is explanatory drawing which shows typically the outline of the shape of the Charpy impact test piece used by this invention.
5 : is explanatory drawing which shows typically the installation condition of the test piece with respect to the Charpy impact tester used by this invention.

The high-carbon cold-rolled steel sheet of the present invention, in mass%, C: 0.85% or more and 1.10% or less, Mn: 0.60% or less, Si: 0.10% or more and 0.35% or less, P: 0.030% or less, S: 0.030% or less, Cr: It contains less than 0.60%, Nb: 0.005% or more and 0.020% or less, and the sum of Mn content and Cr content (Mn+Cr) satisfies less than 1.0%, has a steel plate composition consisting of remainder Fe and unavoidable impurities, and has a plate thickness It is a high carbon cold rolled steel sheet less than 1.0 mm. First, the reason for limiting the composition of the steel sheet will be described. In addition, hereafter, the mass % related to a composition is simply described in %.

C: 0.85% or more and 1.10% or less

C is an essential element in order to obtain sufficient hardness (600 to 750 HV) in precision parts such as meriyasu needles after heat treatment (quenching and tempering treatment). In order to stably secure a hardness of 600 HV or more after heat treatment (quenching and tempering treatment), the content of C is required to be 0.85% or more. On the other hand, as the amount of C increases, the amount of carbides increases, the cold workability deteriorates, and plastic working (cold working) in various fields such as punching, swaging, bending, and secondary working cannot be tolerated. By repeating cold rolling and spheroidizing annealing and performing a spheroidizing process of a carbide|carbide, cold workability is improved, but when C is contained exceeding 1.10 %, the rolling load in a hot rolling process and a cold rolling process will become high, and a coil end part Problems in the manufacturing process, such as a remarkably high frequency of cracks, become present. From this point of view, C was limited to 0.85% or more and 1.10% or less. Moreover, Preferably it is 0.95 to 1.05 %.

Mn: less than 0.60%

Mn is an element which acts effectively on deoxidation of steel, and can improve the hardenability of steel and ensure predetermined hardness stably. However, the content of 0.60% or more increases the MnS inclusion and adversely affects secondary workability before quenching and tempering treatment. When the cleanliness, particularly dA, is 0.10% or more, the probability that the inclusions will hit the cutting edge increases, the cutting resistance increases, and the deterioration of secondary workability becomes remarkable. For this reason, in this invention, Mn is the range from which dA becomes less than 0.10 %, and was limited to less than 0.60 %. Moreover, Preferably it is 0.50 % or less. Cleanliness shall be measured based on JISG0555. Here, in particular, the A-type interference|inclusion was targeted and attention was paid to dA.

Si: 0.10% or more and 0.35% or less

Si acts as a deoxidizer of molten steel and is an effective element in melting clean steel. Moreover, Si is an element contributing to the tempering softening resistance of martensite. In order to acquire such an effect, 0.10 % or more of containing is required. On the other hand, a large amount of Si content exceeding 0.35 % makes the tempering of martensite insufficient at the time of a low temperature tempering process, and deteriorates an impact characteristic. From this point of view, Si was limited to 0.10% or more and 0.35% or less.

P: 0.030% or less, S: 0.030% or less

Both P and S are elements that are unavoidably present in steel and adversely affect impact properties, and it is desirable to reduce them as much as possible. From this point of view, P was limited to 0.030% or less, and S was limited to 0.030% or less. In addition, it is preferable to adjust P to 0.020 % or less and S to 0.020 % or less from a viewpoint of maintaining the outstanding impact characteristic.

Cr: less than 0.60%

Cr is an element contributing to the improvement of abrasion resistance by improving the hardenability of steel and by being dissolved in carbide (cementite) to harden the carbide. In order to acquire such an effect, it is preferable to contain 0.10% or more. Since Cr is dissolved in carbide (cementite) to retard re-dissolution of the carbide in the heating step, the residual carbide after quenching and tempering increases with an increase in the amount of Cr. Here, the residual carbide refers to a carbide remaining in the matrix after quenching for martensite transformation of the carbide that could not be completely dissolved in the matrix during heating and holding during quenching treatment. Abrasion resistance is improved when residual carbide is increased. However, when Cr is contained in a large amount (0.60% or more), in addition to an increase in residual carbide, the effect of retarding the dissolution of the carbide during quenching heating and holding is increased, and quenching property is inhibited and toughness is reduced. From this point of view, Cr was limited to less than 0.60%. Moreover, Preferably it is 0.10 % or more and less than 0.50 %.

Nb: 0.005% or more and 0.020% or less

It is conventionally known that Nb is an element that mainly expands the non-recrystallization temperature range of steel at the time of hot rolling in low-carbon steel, precipitates as NbC, and contributes to refinement of austenite grains. Also in high carbon steel, it may be added in anticipation of the microstructure-refining effect in after a cold rolling process. In this invention, 0.005 % or more and 0.020 % or less of Nb is made to contain for the main purpose of toughness recovery by low-temperature tempering after quenching. If it is a trace amount of Nb, NbC to the extent that it contributes to the refinement of the structure is not formed, and Nb is in a lean solid solution state. It is thought that diffusion of C in the ferrite phase and martensite phase which are BCC structures is accelerated|stimulated by Nb being in a lean solid solution state. That is, the diffusion and precipitation of C dissolved in the ferrite phase from the carbide to the austenite phase during heating in the quenching treatment and the supersaturated solid solution C in the martensite phase during heating in the tempering treatment are promoted. , As a result, it is thought that the improvement of the hardenability by short-time heating and the recovery of the toughness by a low-temperature tempering process can be made compatible. Such an effect becomes remarkable when the content of Nb is 0.005% or more, but when the content of Nb exceeds 0.020%, the precipitation of NbC becomes remarkable, the lean solid solution state of Nb cannot be ensured, and it is caused by the lean solid solution state of Nb The accelerating effect of the C diffusion is not confirmed. For this reason, Nb was limited to 0.005 % or more and 0.020 % or less. Moreover, Preferably it is 0.015 % or less.

(Mn + Cr): less than 1.0%

In the present invention, in order to improve the toughness and wear resistance after quenching tempering while suppressing a decrease in secondary workability before quenching tempering treatment, the sum of Mn content and Cr content (Mn+Cr) is set to less than 1.0%. Adjust. According to the studies of the present inventors, since both Mn and Cr are easily dissolved in carbide, as the sum of the Mn content and Cr content (Mn + Cr) increases, re-dissolution of the carbide in the heating step during quenching heating The effect of retarding is greater than that of Mn alone or Cr alone, and the residual carbide also increases, and the wear resistance also increases. However, when (Mn+Cr) increases to 1.0% or more, the residual carbide becomes 6% or more in terms of area ratio, the influence of quenching property fall becomes large, and the impact value (toughness) after quenching and tempering also falls. When (Mn+Cr) is less than 1%, the residual carbide is less than 6% in terms of area ratio, and excellent wear resistance and toughness can be achieved. On the other hand, when there is too little (Mn+Cr), residual carbide will decrease and it will become impossible to ensure desired wear resistance. For this reason, it is preferable to make the residual carbide|carbonized_material into 3 % or more in area ratio. In addition, it is preferable that (Mn+Cr) for realizing 3% or more of residual carbide content in area ratio shall be 0.15 % or more. On the other hand, secondary workability before quenching and tempering treatment increases (Mn+Cr), in particular MnS inclusions that adversely affect secondary workability increase with an increase in Mn. Therefore, the decrease in secondary workability is suppressed. In the present invention, (Mn+Cr) was limited to less than 1.0% in order to improve both wear resistance and toughness. Further, it is preferably less than 0.90%.

Although the above-mentioned component is a basic component, in addition to the basic component, it may contain 1 type or 2 types selected from Mo: 0.001 % or more and less than 0.05 %, and V: 0.001 % or more and less than 0.05 % as an additional element.

Mo: 0.001% or more and less than 0.05%, V: 1 or 2 types selected from 0.001% or more and less than 0.05%

Mo and V are both elements contributing to the improvement of the quenching properties of steel and the improvement of the impact properties (toughness) after quenching and tempering treatment, and one or two types are unavoidably selected as needed. (0.001%) It can contain more.

Mo is an element effective for improving the hardenability of steel, but when the content is increased to 0.05% or more, the effect of slowing the dissolution of carbides is increased, rather, the quenching property is lowered, and in addition to that sufficient hardness is not obtained, Nb effect is lost, and the impact properties after low-temperature tempering are lowered. For this reason, when containing, it is preferable to limit Mo to 0.001 % or more and less than 0.05 % which is more than the level to contain unavoidably. Moreover, more preferably, it is 0.01 % or more and 0.03 % or less.

V is an element that contributes to the improvement of impact properties through refining the steel structure, but when it is contained in a large amount at 0.05% or more, the effect of slowing the dissolution of carbides increases, rather, the quenching property decreases, and sufficient hardness In addition to not being obtained, the effect of Nb is lost, and the impact properties after low-temperature tempering treatment are lowered. From such a point, when containing, it is preferable to limit V to 0.001 % or more and less than 0.05 % which is more than the level to contain unavoidably. Moreover, more preferably, it is 0.01 % or more and 0.03 % or less.

The remainder other than the above components consists of Fe and unavoidable impurities.

The high-carbon cold-rolled steel sheet of the present invention has the composition described above, and the following formula (1)

0.2 ≤ d _av ≤ 0.7 (μm) … (One)

The average particle diameter (d _av ) (㎛) that satisfies

(N _SC /N _TC ) × 100 ≥ 90% … (2)

A carbide having a spheroidization ratio (N _SC /N _TC ) that satisfies has a dispersed structure.

Here, the average particle diameter (d _av ) in the formula (1) is an average value of the diameters (equivalent diameters) of individual circles assuming a circle having an area equivalent to that of individual carbides observed in the cross section of the steel sheet. When the average particle diameter (d _av ) of the dispersed carbide is in the range satisfying the formula (1), the impact properties are excellent, and even in a treatment in which a quenching (quenching) is performed after a short time solution treatment, desired quenching There is an effect that hardness can be easily secured. When the average particle diameter (d _av ) of the dispersed carbides is less than 0.2 µm, the carbides become finer and the number of dispersed carbides increases, so that the load of secondary processing on the needle shape increases. Moreover, when the average particle diameter (d _av ) exceeds 0.7 µm, it becomes difficult to ensure desired quenching hardness in the treatment to be quenched after the solution treatment for a short time.

In addition, in this invention, the spheroidization ratio was defined as _{(N SC} /N _{TC ) of Formula (2).} Here, N _TC is the total number of carbides per 100 μm ^{2 of} _{observation area, N SC} is the number of carbides that can be considered to be spheroidized in the same observation field, and d _L /d _S ≤ 1.4. It was set as the number of carbides. Here, the major axis of the carbide is d _L , and the minor axis is d _S .

The carbide cannot be said to be completely spherical, and since it is often observed as an ellipse depending on the observation surface, the degree of spheroidization is defined by _{the ratio of the major axis to the minor axis (d L} /d _{S ).} . In the present invention, _{a carbide satisfying the condition of (d L} /d _S ): 1.4 or less was defined as a spheroidized carbide (spheroidized carbide), and the number of carbides was N _SC . Moreover, in order to maintain the secondary workability of a steel plate favorably from empirical knowledge, _{it is necessary for the spheroidization ratio (N SC} /N _TC )x100 to be 90 % or more.

In addition, calculation of the average particle diameter and spheroidization ratio of said carbide was performed by observing a secondary electron image (magnification: 2000 times) using a scanning electron microscope, and setting it as image analysis.

A test piece for carbide observation is taken from the steel sheet (plate thickness central part) after cold rolling, embedded in resin, polished, etched with a etchant, and carbide is observed using a scanning electron microscope, and observation near the plate thickness central part In the range of 100 μm ² in area, the equivalent circle diameter of the carbide, the major axis (d _L ) / minor diameter (d _S ) The ratio, N _TC , and N _SC were measured. Five such measurements were performed, and the average value of each was computed. For these measurements and calculations, commercially available image analysis software winroof was used.

The high-carbon cold-rolled steel sheet of the present invention has the above-described composition and structure of the steel sheet, and while maintaining secondary workability such as machinability, the life of tools used for punching, swaging, bending, secondary processing, etc. It is about the same as that of a steel sheet, and after a short-time solution treatment followed by a quenching treatment and a low-temperature tempering treatment (quenching tempering treatment), higher hardness properties, superior impact properties and excellent wear resistance compared to conventional high-carbon steel sheets It is a high-carbon cold-rolled steel sheet that can manufacture machine parts with a balanced combination of

The term "excellent in secondary workability" as used herein means, as shown in Fig. 1, when a cutting (endmill machining) test is performed and the force applied to the tool (endmill) is less than 40 N (tool rotation) Let the number be low speed (1300 rpm)) or the case where it is less than 35 N (when the tool rotation speed is high speed (2300 rpm)).

In the present invention, paying attention to general end milling, as shown in Fig. 1 , cutting (end milling) is performed on a steel plate (workpiece) using an end mill, and at that time, a cutting dynamometer mounted on a tool (not shown), as the cutting resistance force applied to the tool (end mill: Φ6 mm diameter), the X-direction component force, the Y-direction component force, and the Z-direction component force were measured, and then their resultant force was calculated as an evaluation index of secondary workability. . In addition, the conditions of the end mill machining test were: cutting speed: 25 m/min (low speed), 45 m/min (high speed), feed per tooth: 0.016 mm/tooth, depth of cut: 0.2 mm, tool protrusion length: 25 mm, cutting distance: 30 mm, and cutting oil was not used.

By employing such an end mill machining test, secondary workability can be evaluated in a state closer to the actual use environment. If the cutting resistance applied to the tool is less than 40 N (or less than 35 N), it means that it has excellent secondary workability equivalent to or higher than that of the conventional high-carbon cold-rolled steel sheet.

In addition, the "excellent abrasion resistance" as used herein shall mean the case where the wear depth obtained by performing the wear test using the wear test apparatus shown in FIG. 2 is less than 485 micrometers.

The abrasion testing apparatus 10 shown in FIG. 2 includes a yarn unwinding means 11 for unwinding a yarn, a tension adjusting means 12 for applying a desired tension to the unwound yarn 2, and passing the tensioned yarn. It has an abrasion test piece 1 having holes 1a to 1d to make it, and a yarn winding means 13 for winding a yarn, so that the abrasion of the needle by the knitting yarn can be reproduced in a situation close to the actual machine. It is a device that can In addition, the wear test apparatus 10 has a structure in which the tension becomes zero (zero) when the yarn breaks, and the apparatus automatically stops at that point.

The abrasion test piece 1 to be used is a wear test piece having the shape shown in FIG. After being given an appropriate tension by is wound up Holes were formed at four points (1a to 1d) in one specimen. In addition, the conditions of the abrasion test used a knitted yarn polyester glue (standard 110T48), a yarn feeding speed: 160 m/s, and a tension: 10 ± 2 N/cm, and the length of the yarn in one hole. It carried out until 100,000 m unwinding, and the abrasion depth in the said hole was measured. Such abrasion test was performed in each of the holes 1a to 1d at four points formed in one wear test piece, the wear depth of each hole was measured, and the average value was taken as the wear depth (average) of the wear test piece.

As a result of performing the wear test under the above conditions, if the wear depth is less than 485 μm, it means that it has excellent wear resistance equivalent to or higher than that of the conventional high-carbon cold-rolled steel sheet. By employing such an abrasion test, the abrasion resistance can be evaluated in a state close to the abrasion caused by the thread of the hook part of the Meriyasu needle. Further, by evaluating the abrasion resistance in a state close to the abrasion caused by the thread of the hook portion of the needle hook, it was found that the presence of residual carbide greatly affects the abrasion resistance. The abrasion resistance is proportional to the area ratio of the residual carbide, and when the residual carbide is less than 3% in the area ratio, the desired wear resistance cannot be ensured. The residual carbide is preferably 3% or more in terms of area ratio.

In addition, "excellent impact properties" as used herein refers to an impact test piece shown in FIG. 4 (a U-notch test piece with a notch width of 0.2 mm (notch depth 2.5 mm, notch radius 0.1 mm)), rated capacity based on JIS K 7077 : As shown in FIG. 5 with a 1 J Charpy impact tester (Toyo Seiki Seisakusho Co., Ltd., model DG-GB), the impact value when tested at room temperature with a distance between supports set to 40 mm was 9 J/ It is assumed that the case is more than cm2.

By using such a Charpy impact tester, even if a test piece having a plate thickness of less than 1.0 mm is used, it can be tested under conditions close to JIS Z 2242, which is a Charpy impact test method for metal materials, and also use such an impact test piece By doing so, the stress concentration coefficient becomes high, the curvature at the time of an impact test is minimized, and a stable impact value is obtained. By employing such an impact test method and impact test piece, the impact characteristics in a state close to the actual use environment can be evaluated. In addition, the impact value tends to be higher when the amount of residual carbide is small, but when the amount of residual carbide exceeds 6% by area ratio, the impact value decreases significantly. The present inventors found out that it was set as less than 6 % in area ratio.

In this way, by introducing a new wear test method for evaluating wear resistance and also introducing an end mill machining test method for evaluating secondary workability, an appropriate chemical composition range can be defined based on the evaluation in an environment close to the actual machine. became possible

Next, the manufacturing method of this invention high carbon cold rolled steel sheet is demonstrated.

The high-carbon cold-rolled steel sheet of the present invention is manufactured by subjecting a hot-rolled steel sheet to softening annealing as necessary, followed by repeated cold rolling and spheroidizing annealing.

The hot-rolled steel sheet used in the present invention may be obtained under normal manufacturing conditions, for example, a steel piece (slab) having the above composition is heated to 1050 to 1250° C., and hot rolled at a finishing temperature of 800 to 950° C. , it can manufacture by setting it as a coil at the winding temperature of 600-750 degreeC. In addition, the plate thickness of a hot-rolled steel plate may be suitably set so that it may become a preferable cold-rolling-reduction|draft ratio from the plate|board thickness of a desired cold-rolled steel plate.

The hot-rolled steel sheet is subjected to repeated cold rolling and spheroidizing annealing several times to obtain a high-carbon cold-rolled steel sheet having a sheet thickness of less than 1.0 mm. It is preferable to repeat cold rolling and spheroidizing annealing 2 to 5 times, respectively.

It is preferable that the rolling-reduction|draft ratio of cold rolling sets it as 25 to 65 % of range. When spheroidizing annealing is performed to the steel plate (cold-rolled steel plate) whose rolling-reduction|draft ratio of cold rolling is less than 25 %, carbide|carbonized_material will coarsen. On the other hand, when the rolling reduction of cold rolling exceeds 65 %, the load of a cold rolling operation may be too large. For this reason, the rolling-reduction|draft ratio of cold rolling was limited to 25 to 65 % of range. In addition, about the last cold rolling which does not perform spheroidizing annealing after cold rolling, the minimum in particular of a rolling reduction is not limited.

Moreover, it is preferable to perform spheroidizing annealing at the temperature of the range of 640-720 degreeC. If the spheroidizing annealing temperature is less than 640°C, the spheroidizing tends to be insufficient, while at a higher temperature than 720°C, the carbide tends to coarsen. For this reason, spheroidizing annealing was performed at the temperature of the range of 640-720 degreeC. In addition, it is preferable to select and implement the holding time of spheroidizing annealing suitably in the range of 9-30 hr.

In addition, the reason for repeating cold rolling (25-65%) and spheroidizing annealing (640-720 degreeC) multiple times is that the average particle diameter (d _av ) of a carbide and a spheroidization ratio (N _SC /N _TC ) x 100 are respectively This is for controlling to satisfy the above (1) and (2) expressions.

First, cracks are introduced into the carbide by cold rolling, and the carbide that has started to break by the spheroidizing annealing is spheroidized, but it is difficult to increase the spheroidization rate of the carbide to 90% or more by only one spheroidizing annealing, and it is difficult to Carbide remains. In such a case, the quenching property is also adversely affected, and the cold workability of the precision part is deteriorated. Therefore, in order to make the spheroidization ratio (N _SC /N _TC ) x 100 of the carbide to 90% or more, it is optimal to alternately repeat cold rolling and spheroidization annealing, and as a result, fine carbide in the steel sheet and a high spheroidization ratio distribution is obtained. Especially preferably, they are 2-5 times of cold rolling and 2-5 times of spheroidizing annealing. Moreover, the same temperature range is preferable also about the softening annealing aiming at softening of the hot-rolled steel sheet before cold rolling.

Although the above is the manufacturing method of the high carbon cold rolled steel sheet of this invention, in order to make this steel sheet into the final objective, mechanical parts, such as a meriyasu needle, it is preferable to perform the following heat processing after processing into a predetermined shape.

A high-carbon cold-rolled steel sheet in which 90% or more of spheroidized carbide is distributed is processed into various mechanical parts, and then subjected to a treatment of quenching (quenching) after a solution treatment, followed by a tempering treatment. Solution heat treatment makes heating temperature 760-820 degreeC, and makes holding time into 3-15 min which is short time. It is preferable to use oil for quenching (quick cooling). In a tempering process, it is preferable to make tempering temperature into 200-350 degreeC of low temperature. Moreover, More preferably, it is 250-300 degreeC. Thereby, it can be set as various mechanical parts which have a hardness of 600-750 HV.

When the holding time of the solution treatment is longer than 15 min, the carbide is dissolved too much and the austenite grains are coarsened, so that the martensite phase after quenching becomes rough and the impact properties are lowered. On the other hand, when the holding time is shorter than 3 min, dissolution of the carbide is insufficient, and it becomes difficult to obtain a desired high hardness after rapid cooling. For this reason, it is preferable that the holding time of a solution treatment shall be 3 min or more and 15 min or less. More preferably, it is 5-10 min.

Moreover, when the tempering temperature is less than 200 degreeC, the toughness recovery of a martensite phase becomes inadequate. On the other hand, when a tempering temperature exceeds 350 degreeC, although hardness is less than 600 HV and an impact value becomes high, durability and abrasion resistance fall, and it becomes a problem. For this reason, it is preferable to make tempering temperature into the temperature in the range of 200-350 degreeC. Moreover, More preferably, it is 250-300 degreeC. It is preferable to select and implement the holding time of a tempering process suitably in the range of 30 min - 3 hr.

Hereinafter, based on an Example, this invention is further demonstrated.

Example

Molten steel having the chemical composition shown in Table 1 was melted in a vacuum melting furnace and then poured into a mold to obtain a small steel ingot (50 kgf). After ingot-rolling these small-sized steel ingots to make a steel piece, it hot-rolled on the conditions of heating temperature: 1150 degreeC and rolling finishing temperature: 870 degreeC, and it was set as the hot-rolled steel plate (plate|board thickness: 4 mm). Next, the obtained hot-rolled steel sheet was subjected to cold rolling and spheroidizing annealing under the conditions shown in Table 2 to obtain a cold-rolled steel sheet having a sheet thickness of 0.4 mm or more and less than 1.0 mm.

First, a test piece for tissue observation is taken from the obtained cold-rolled steel sheet, embedded in a resin, polished and corroded, and the structure is observed with a secondary electron image (magnification: 2000 times) of a scanning electron microscope, imaged, and imaged By analysis, the average particle diameter (d _av ) and the spheroidization ratio (N _SC /N _TC ) of the carbide were calculated. ^{In the range of an observation area of 100 µm 2} near the center of the plate thickness, the ratio _{of the major diameter (d L} )/minor diameter (d _S ) of each carbide to the equivalent circular diameter of each carbide is calculated, and the carbide per ^{100 µm 2 of} the observation area is obtained. Total number (N _TC ), d _L /d _S : The total number of carbides satisfying the conditions of 1.4 or less (N _SC ) was measured. Such a measurement was implemented in 5 visual fields, and those average values were computed, respectively. For these measurements and calculations, commercially available image analysis software winroof was used. Moreover, about the test piece for tissue observation, based on JISG0555, the cleanliness (dA) was measured for A type inclusion target. In addition, the measurement visual field was made into 60 visual fields.

In addition, a test piece is taken from the obtained cold-rolled steel sheet, and a machinability test (end mill machining test) is performed as shown in FIG. 1 under the conditions shown in Table 3, and applied to a tool (end mill: 6 mm diameter). After measuring the forces in the X-direction, Y-direction, and Z-direction, the resultant force was calculated and used as the cutting resistance force. In addition, the rotation speed of the tool was made into two types: low speed (1300 rpm) and high speed (2300 rpm).

Next, the obtained cold-rolled steel sheet is charged into a heating furnace under the conditions shown in Table 4, subjected to a solution treatment for a short time, then subjected to a treatment to be quenched (oil quenched), and further subjected to a low-temperature tempering treatment. was carried out. A test piece was taken from the heat-treated steel sheet and subjected to residual carbide irradiation, hardness test, impact test, and wear test. The test method was as follows.

(1) Residual carbide investigation

A test piece for tissue observation is taken from the heat-treated steel sheet, embedded in resin, polished and corroded, and the structure is observed with a secondary electron image (magnification: 2000 times) of a scanning electron microscope, imaged, and image analysis , the area ratio (%) of residual carbides was calculated for residual carbides having a size of 0.1 µm or more in equivalent circle diameter. In addition, the measurement area was 100 micrometers<^2> .

(2) Hardness test

A hardness test piece was cut out from the heat-treated steel sheet in a direction perpendicular to the rolling direction, this was embedded in resin, the cross section was polished, and hardness was measured at the center of the sheet thickness. The hardness measurement was carried out at each of 5 points using a Vickers hardness tester (test force: 49.0 N) in accordance with the regulations of JIS Z 2244, and the average value thereof was taken as the hardness of the steel sheet.

(3) Impact test

An impact test piece (U-notch test piece with a notch width of 0.2 mm (notch depth 2.5 mm, notch radius 0.1 mm)) shown in FIG. 4 is taken from the heat-treated steel sheet so as to be parallel to the rolling direction, and a rating based on JIS K 7077 In a capacity: 1 J Charpy impact tester (Model DG-GB manufactured by Toyo Seiki Seisakusho Co., Ltd.), as shown in FIG. 5 , a Charpy impact test was performed at room temperature with a distance between supports set to 40 mm, and the impact value (J) was obtained. The test piece was made into 5 pieces each, and the average of each obtained impact value was made into the impact value of the said steel plate.

(4) Wear test

From the heat-treated steel sheet, a wear test piece having a shape shown in Fig. 3 was taken, and a wear test using the wear test apparatus shown in Fig. 2 was performed. The conditions of the abrasion test were that a knitted yarn made of polyester paste (standard 110T48) was used, and the yarn feeding speed: 160 m/s and the tension: 10 ± 2 N/cm were used. After feeding 100,000 m of yarn through one hole, the testing apparatus was stopped, and the depth of wear formed in the hole (here, 1a) of the wear test piece 1 as shown in FIG. 3(b) was measured with an optical microscope. Such abrasion test was performed in each hole 1a to 1d, respectively, the wear depth of each hole (four points) was measured, the average value thereof was calculated|required, and it was set as the wear depth of the said wear test piece.

The obtained result is shown in Table 5.

In all of the examples of the present invention, the force (cutting resistance) applied to the tool is less than 40 N in low-speed machining and less than 35 N in high-speed machining, and secondary workability is a high-carbon cold-rolled steel sheet equivalent to that of a conventional high-carbon cold-rolled steel sheet. After solution heat treatment, rapid cooling (oil quenching) treatment and low temperature tempering treatment, the hardness has high hardness characteristics satisfying the range of 600 to 750 HV, the impact value satisfies 9 J/cm2 or more, and impact properties The high carbon cold-rolled steel sheet was excellent, and the abrasion depth was less than 485 µm, and the high carbon cold-rolled steel sheet was excellent in abrasion resistance, and it was evaluated as "double-circle". On the other hand, in the comparative example out of the scope of the present invention, the force (cutting resistance) applied to the tool becomes 40 N or more in low-speed machining and 35 N or more in high-speed machining, and the secondary workability is inferior, or after a short time solution treatment After heat treatment in which rapid cooling (oil quenching) treatment is performed and additional low-temperature tempering treatment is performed, the impact value is less than 9 J/cm 2 , and the impact property is lowered, or the abrasion resistance is lowered when the abrasion depth is 485 µm or more It is a high-carbon cold-rolled steel sheet rated as "x".

Specifically, in the comparative example (steel sheet No. 1) with a low amount of C outside the range of the present invention, the cutting resistance is low, the secondary workability is excellent, the impact value is 9 J/cm 2 or more, and the impact property is excellent, but the residual There were few carbides, and the abrasion resistance was lowered with a wear depth of 485 micrometers or more. In addition, the comparative example (steel No. 12) with a high amount of C out of the range of the present invention had a lot of residual carbide and had an abrasion depth of less than 485 μm and excellent wear resistance, but had an impact value of less than 9 J/cm 2 and had poor impact properties. is lowered. Moreover, (Mn+Cr) exceeds 1.0 %, cleanliness is also bad, the force (cutting resistance) applied to a tool is high, and secondary workability is falling. Moreover, all of the comparative examples (steel sheets No. 9, No. 10, No. 11) in which (Mn+Cr) was 1.0% or more and highly exceeding the range of this invention had many residual carbides, and the abrasion depth was less than 485 micrometers. It is excellent in abrasion resistance, but the impact value is less than 9 J/cm 2 , and the impact properties are lowered. In addition, the cleanliness is poor, the force (cutting resistance) applied to the tool is high, and the secondary workability is lowered. Moreover, the comparative example (steel plate No. 13) in which the amount of V highly deviates from the range of this invention, and the comparative example (steel sheet No. 14) in which the amount of Mo exceeds the range of this invention high, there are many residual carbides and are excellent in wear resistance, but toughness is lowered. Moreover, the comparative example (steel plate No.3, No.15) in which the Nb amount deviates low from the range of this invention, and the comparative example (steel plate No.16) in which the Nb amount deviates high from the range of this invention, the impact value is 9 J/ The impact properties are lowered to less than cm 2 . In addition, the inventive example (steel sheet No. 19) in which (Mn+Cr) was as low as 0.14% showed a tendency for the wear resistance to decrease somewhat, and (Mn+Cr) was as high as 0.90% in the inventive example (steel sheet No. 20). ) indicates a tendency for secondary workability to decrease somewhat. Moreover, in the comparative example (steel plate No. 21) in which (Mn+Cr) exceeds 1.0 %, and the comparative example (steel plate No. 22) in which Cr highly deviates from the range of this invention, the residual carbide is 6% in area ratio. Exceeds, the abrasion resistance is excellent, but the impact value is less than 9 J/cm 2 , and the impact toughness is lowered.

1: abrasion test piece
1a, 1b, 1c, 1d: Hall
2: thread
10: wear test device
11: thread unwinding means (bobbin)
12: tension adjustment means
13: thread winding means

Claims (9)

in mass %,
C: 0.85% or more and 1.10% or less, Mn: 0.49% or less,
Si: 0.10% or more and 0.35% or less, P: 0.030% or less,
S: 0.030% or less, Cr: less than 0.60%,
Nb: 0.005% or more and 0.020% or less,
In addition, the sum of the Mn content and the Cr content (Mn + Cr) satisfies less than 1.0%, has a steel sheet composition comprising the remainder Fe and unavoidable impurities, and the average particle size (d _av ) and spheroidization ratio ( N _SC /N _TC ) × 100% has a steel sheet structure that satisfies the following formulas (1) and (2), respectively, and the steel plate thickness is less than 1.0 mm.
0.2 ≤ d _av ≤ 0.7 (μm) … (One)
(N _SC /N _TC ) × 100 ≥ 90% … (2)
Here, d _av : the average value of the equivalent circle diameter of the carbide (average particle diameter μm),
N _TC : total number of carbides per 100 μm ^{2 of observation area,}
N _SC : The number of carbides that satisfy the condition that (major diameter d _L )/(minor diameter d _S ) per 100 µm ^{2 of observation area is 1.4 or less.} delete The method of claim 1,
Instead of the steel sheet composition, in mass%,
C: 0.85% or more and 1.10% or less, Mn: 0.49% or less,
Si: 0.10% or more and 0.35% or less, P: 0.030% or less,
S: 0.030% or less, Cr: less than 0.50%,
Nb: 0.005% or more and 0.020% or less,
Further, the high-carbon cold-rolled steel sheet having a steel sheet composition in which the sum of the Mn content and the Cr content (Mn+Cr) satisfies less than 0.90%, the remainder being Fe and unavoidable impurities. The method of claim 1,
The high-carbon cold-rolled steel sheet, characterized in that the steel sheet composition further contains, in mass%, one or two selected from Mo: 0.001% or more and less than 0.05%, and V: 0.001% or more and less than 0.05%. 5. A method for manufacturing a high-carbon cold-rolled steel sheet, wherein the hot-rolled steel sheet having the composition according to any one of claims 1, 3, and 4 is repeatedly subjected to cold rolling and spheroidizing annealing to produce a high-carbon cold-rolled steel sheet, , the average particle diameter (d _av ) and the spheroidization ratio (N _SC /N _TC ) of carbides dispersed in the high-carbon cold-rolled steel sheet satisfy the following formulas (1) and (2), respectively, and the high-carbon cold-rolled steel sheet A method for producing a high-carbon cold-rolled steel sheet, comprising a high-carbon cold-rolled steel sheet having a sheet thickness of less than 1.0 mm.
0.2 ≤ d _av ≤ 0.7 (μm) … (One)
(N _SC /N _TC ) × 100 ≥ 90% … (2)
where d _av : average value of equivalent circle diameters of carbides (average particle diameter μm),
N _TC : total number of carbides per 100 μm ^{2 of observation area,}
N _SC : The number of carbides that satisfy the condition that (major diameter d _L )/(minor diameter d _S ) per 100 µm ^{2 of observation area is 1.4 or less.} 6. The method of claim 5,
The method for manufacturing a high-carbon cold-rolled steel sheet, characterized in that the number of times of repeatedly performing the cold rolling and spheroidizing annealing is 2 to 5 times. 6. The method of claim 5,
A method for producing a high-carbon cold-rolled steel sheet, wherein a reduction ratio of the cold rolling is 25 to 65%, and the temperature of the spheroidizing annealing is 640 to 720°C. Using the high-carbon cold-rolled steel sheet according to any one of claims 1, 3 and 4 as a raw material, secondary processing is performed on the raw material to obtain a machine part having a predetermined shape, and then the machine part is used for a short time. A method for manufacturing a machine part in which quenching treatment and tempering treatment are performed after sieving treatment, the method comprising:
The treatment to be quenched after the short-time solution heat treatment is performed at a temperature in the range of 760 to 820°C, and after holding for a time in the range of 3 to 15 min, the quenching treatment is performed, and the tempering treatment is in the range of 200 to 350°C. A method for manufacturing high-carbon steel machine parts, characterized in that by tempering at a temperature of A high carbon steel machine part manufactured by the method for manufacturing a high carbon steel machine part according to claim 8.

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