JP2003286542A - Steel plate for steel belt showing excellent resistance to crack propagation and its manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a resistance to crack propagation in a steel plate for steel belts. <P>SOLUTION: The steel plate for steel belts comprises, by mass, 0.30-0.60% C, ≤1.0% Si, 0.10-1.0% Mn, ≤0.020% P, ≤0.010% S, 0 (no addition)-1.0%, preferably 0.1-1.0% Cr, 0 (no addition)-0.5% V, 0 (no addition)-0.1% Ti, 0 (no addition)-0.1% Nb, 0 (no addition)-0.01% B and the balance being Fe and unavoidable impurities. The steel plate is manufactured by performing hot rolling under a condition employing a finish hot-rolling temperature of 800-900°C, an average cooling rate after finish hot rolling to winding of ≥20°C/sec and a winding temperature of 450-650°C, skipping heat treatment, performing cold rolling e.g. with a rolling rate of 30-80%, subsequently performing aging treatment by holding it at 200-500°C for 0.5-30 hours and, if required, performing temper rolling with a rolling rate of ≤10%. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel belt steel sheet made of carbon steel, and more particularly to a steel belt steel sheet having improved crack propagation resistance and a method for producing the same.

[0002]

2. Description of the Related Art Steel belts include "stainless steel belts" made of stainless steel and "carbon steel belts" made of carbon steel. The present invention is directed to the latter carbon steel belt.
A typical application of the carbon steel belt is a belt conveyor of an oven for baking cookies and the like. Hereinafter, in the present specification, the steel belt means “carbon steel belt”.

The steel belt is required to have the following characteristics. (a) "Strength (hardness) -ductility / toughness" Balanced steel belts are used by applying appropriate tension depending on the application of the conveyor, so strength that does not deform under the applied tension is required. Is. In addition, the surface hardness is required to prevent "handling flaws" during use. On the other hand, at the time of manufacturing the steel belt, the shape is corrected by applying tensile deformation to the steel material. At that time, if the strength is too high, the ductility (plastic deformability) is insufficient and the shape cannot be corrected. Also,
Appropriate ductility is also necessary to secure toughness during use. (b) Fatigue strength Since the belt conveyor is repeatedly subjected to bending stress during use, it must have high fatigue strength. (c) Weldability When a steel sheet is made into an endless belt shape, it is welded. Further, welding may be performed during repair of the steel belt. Therefore, it is necessary to have good weldability.

Regarding the method of acquiring such characteristics,
Various studies have hitherto been made, for example, a method of applying quenching / tempering treatment and temper rolling to medium carbon steel, and JP-A-47-
As disclosed in Japanese Patent No. 38616 or JP-A-57-101615, patenting originally used in the field of steel wire,
Methods such as applying treatments such as bluing to steel sheets have been developed. And today, most of them are manufactured by one of the following methods. i) (Hot or cold rolled steel of about 0.65% C steel) → Quenching
Tempering ii) (Hot or cold rolled steel of about 0.65% C steel) → Patenting → Cold rolling → Blueing

[0005]

The steel belts currently used have the basic performances of practically no problem with regard to the above characteristics (a) to (c). However, recently, there is an increasing demand for improvement in durability (lifetime).

Fatigue failure is one of the factors that deteriorate the durability of the steel belt. Fatigue fracture occurs when a microcrack formed from a flaw existing on the end surface (edge surface) of the belt or a flaw generated during use propagates to the surroundings by repeated stress. A material with a property that cracks easily propagate, that is, a material with a small "crack propagation resistance",
By receiving repeated stress, a microcrack easily develops into a so-called fatigue crack. When a fatigue crack grows to a certain size, the material suddenly breaks under cyclic stress. This is fatigue destruction. Therefore, in order to improve the durability and reliability of the steel belt, it is important to increase the crack propagation resistance.

It is believed that crack propagation resistance is greatly affected by the metallic structure of the material. However, in the steel sheet for steel belts, although the structure control utilizing heat treatment such as patenting has been put into practical use as described above,
There is no disclosure of a method of improving crack resistance by focusing on crack propagation resistance. It is difficult to significantly and stably improve the crack propagation resistance simply by refining the metal structure, and this is one of the factors that hinder the progress of steel belt durability improvement technology. Conceivable.
Therefore, the first object of the present invention is to clarify the metal structure effective for the stable improvement of the crack propagation resistance and to significantly improve the crack propagation resistance of the steel sheet for steel belt.

Further, the current steel plate for steel belt is manufactured through the time-consuming heat treatment as described above. Particularly, since patenting is a constant temperature transformation process, it causes an increase in manufacturing cost. Therefore, the second object of the present invention is to manufacture a steel sheet having a high crack propagation resistance in the simplest possible process.

[0009]

[Means for Solving the Problems] As a metal structure exhibiting a high level of "strength-ductility / toughness" balance suitable for a steel belt, a structure mainly composed of pearlite is considered to be most practical. Therefore, the inventors have conducted various studies on what kind of microstructure state is effective for improving crack propagation resistance in a steel sheet having a pearlite-based microstructure. In particular, the ferrite lamella and the cementite lamella composing pearlite were microscopically observed and examined in detail. As a result, the following findings have been obtained.

[0010]. When a steel sheet having a structure of pro-eutectoid ferrite + pearlite is processed, the pearlite structure has a larger crack propagation resistance between the work-hardened pro-eutectoid ferrite phase and the work-hardened pearlite structure. To obtain a durable steel belt, the pearlite structure is 50% by volume in the steel plate.
The above is necessary. ． In the cold rolling process, micro cracks are introduced into the pearlite structure, which can be the starting point of fatigue cracks. The micro-cracks occur in cementite lamella. ． The thinner the cementite lamella in the pearlite structure, the less likely microcracking occurs during cold rolling. In particular, the relative thickness ratio of cementite lamella and ferrite lamella is important, and when the ratio is 1: 9 or less (that is, the volume ratio of cementite in the pearlite structure is 10% or less), the cementite・ Rammera becomes hard to break suddenly, and the crack propagation resistance of the steel plate is greatly improved. ． In a steel sheet used as a steel belt, high crack propagation resistance is obtained when the thickness of the pro-eutectoid ferrite phase in the thickness direction is 5 μm or less. The present invention has been completed based on these findings.

That is, the above-mentioned object is C: 0.
30 to 0.60%, Si: 1.0% or less, Mn: 0.10 to 1.0%, P:
A steel plate made of carbon steel having a content of 0.020% or less and S: 0.010% or less, in which the volume ratio of the pearlite structure in the metal structure is
For steel belts with a crack propagation resistance of 50% or more, a volume ratio of cementite lamella in the pearlite structure of 10% or less, and a thickness of proeutectoid ferrite phase in the plate thickness direction of 5 μm or less. Achieved by steel plate.

In the steel sheet, the chemical composition is, particularly in mass%, C: 0.30 to 0.60%, Si: 1.0% or less, Mn: 0.10.
~ 1.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0
(No addition) to 1.0%, preferably 0.1 to 1.0%, V: 0 (no addition) to 0.5%, Ti: 0 (no addition) to 0.1%, Nb: 0 (no addition) to 0.1%, B: 0 (No addition) ~ 0.01%, balance Fe
And steel consisting of inevitable impurities. Here, the lower limit of Cr, V, Ti, Nb, and B is set to 0% (no addition) because these elements are different from Si, etc., and the content is zero (0) unless added in a normal steelmaking process. This is for clarifying the points including the case of no addition.

Further, the above steel sheet has a tensile strength at room temperature in the rolling direction of 1000 MPa or more, a total elongation of 6% or more, and a crack propagation resistance as defined in the following [A] of 600 MPa or more. . [A] Tensile speed at room temperature in the longitudinal direction of the test piece shown in FIG.
A 0.3 mm / min tensile test is performed, the maximum load is determined from the load-elongation curve, and the value (unit: MPa) obtained by dividing the maximum load by the initial cross-sectional area (45 mm x plate thickness) is taken as the crack propagation resistance.

Here, FIG. 1 (a) is a plan view showing the overall shape of the test piece. FIG. 1 (b) is an enlarged view of the hole portion shown in the center of FIG. 1 (a), showing the shape and dimensions of the hole and the notches and fatigue pre-cracks formed around it. Notches with a width of about 2.5 mm are formed on both sides of the 4.0 mm diameter hole in the center of the test piece in the plate width direction, and a fatigue precrack with a length of 3.5 ± 0.1 mm is formed at the tip of the notch. . The fatigue pre-crack can be formed by forming notches on both sides of the hole and then performing a partial swing fatigue test in which cyclic stress is repeatedly applied in the longitudinal direction of the test piece.

Further, in the present invention, as a method for producing these steel sheets, the finish hot rolling temperature: 800 to 900 ° C., after the finish hot rolling, the average cooling rate until winding is 20 ° C./sec or more, the winding temperature: 450. ~ 650
After hot-rolling at ℃, cold-rolling (for example, 30-80% cold rolling) without heat treatment, then 200
Provided is a method of performing an aging treatment of holding at ~ 500 ° C for 0.5 to 30 hours. Furthermore, if necessary, a rolling rate of 10% after aging treatment
The following method for performing temper rolling is provided. Here, the finish hot rolling temperature means the steel plate surface temperature on the exit side of the stand of the hot rolling final pass.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The steel sheet for steel belts of the present invention is characterized by constituent elements, a metal structure, and, if necessary, mechanical properties. Hereinafter, matters for specifying the present invention will be described.

[Component element] C is an important element for obtaining a metal structure mainly composed of pearlite. That is, the C content has a great influence on the production amount and morphology of pearlite. When the amount of C is less than 0.3% by mass, the volume ratio of the pearlite structure in the hot-rolled steel sheet decreases, and it becomes difficult to secure a pearlite structure of 50% by volume or more in the steel plate used in the steel belt. Further, since work hardenability in cold rolling decreases due to an increase in proeutectoid ferrite, there is a possibility that the cold rolling rate becomes excessively high to obtain a target strength level. Further, the work strain of the pro-eutectoid ferrite phase becomes excessively large, and since there are few pearlite structures that are advantageous in ductility and toughness, the ductility and toughness are significantly reduced. Therefore, the C content must be 0.3% by mass or more.

On the other hand, when the amount of C is increased, the cementite ratio in the pearlite structure is increased. In particular, if it exceeds 0.6% by mass, it becomes difficult to reduce the volume ratio of cementite lamella in the pearlite structure to 10% or less, and the crack propagation resistance cannot be stably improved. Also, the hardness of the welded portion increases and the toughness decreases. From the above, in the present invention, it is necessary to strictly control the C content within the range of 0.3 to 0.6 mass%.

Si is effective as a deoxidizing element for molten steel. However, if it exceeds 1.0% by mass, both the hot-rolled sheet and the cold-rolled sheet become hard and the manufacturability deteriorates.

Mn refines the lamella spacing in the pearlite structure. When the amount of Mn is less than 0.10% by mass, a layered pearlite structure is not formed, and a pseudo-pearlite structure in which granular cementite is dispersed is likely to be formed. In that case, the original excellent "strength-ductility / toughness" balance cannot be obtained. On the other hand, 1.
If it exceeds 0% by mass, the steel sheet becomes hard and the toughness deteriorates.

P segregates at the austenite grain boundaries and deteriorates the toughness of the steel sheet. In the present invention, a P content of up to 0.02 mass% is allowed as a range that does not substantially cause a problem. S
Causes MnS to form in the steel and tends to be the origin of cracks, leading to deterioration of fatigue properties. In the present invention, S content up to 0.01% by mass is allowed as a range that does not substantially cause a problem.

Since Cr makes the lamella spacing in the pearlite structure fine, it is advantageous to add Cr for the purpose of improving strength. Further, it can be added to control the pearlite transformation property (the position of the nose in the TTT curve). 0.1 is sufficient to obtain the effect of refining the lamella spacing.
It is desirable to add Cr in an amount of% by mass or more. However, if it exceeds 1.0% by mass, cementite becomes hard and crack propagation resistance decreases.

V, Ti and Nb all have the effect of refining the prior austenite grain size and contribute to the improvement of crack propagation resistance, so these can be added alone or in combination. However, even if added in too large an amount, the effect is saturated, so V is preferably 0.5 mass% or less, and Ti and Nb are preferably 0.1 mass% or less.

B contributes to the improvement of crack propagation resistance due to the effect of strengthening the former austenite grain boundary. However, even if added in a too large amount, the effect will be saturated, so when B is added, it is desirable to make it 0.01 mass% or less. It should be noted that 0.001% by mass is required to bring out the above effect remarkably.
The above B addition is preferable.

[Metal Structure] In the present invention, the steel plate in a state of being used as a steel belt is required to have a volume ratio of the pearlite structure in the metal structure of 50% or more. The balance other than pearlite consists essentially of proeutectoid ferrite phase. When a hot-rolled steel sheet having a metallographic structure containing pearlite is cold-rolled, the lamella spacing becomes finer while the lamellae of the pearlite structure are oriented in the cold rolling direction. The pearlite structure is work-hardened by forming fine lamellas aligned in the rolling direction. The fine pearlite structure in which the lamellae are aligned in the rolling direction has a small decrease in toughness despite the high strength. Further, further aging treatment further improves the ductility and toughness while maintaining high strength.

When the amount of pearlite structure is small, the strength level required for a steel belt (tensile strength 1000MP
In order to obtain (a) or more), the cold rolling ratio must be increased because there are many proeutectoid ferrite phases with low work hardening ability. Comparing the work-hardened pro-eutectoid ferrite phase with the work-hardened pearlite structure, the latter has a larger crack propagation resistance. Therefore, a small amount of pearlite is extremely disadvantageous in improving the crack propagation resistance of the steel sheet. As a result of various studies, tensile strength of 1000
It was found that the volume ratio of the pearlite structure in the metal structure of the steel sheet should be at least 50% or more in order to significantly improve the crack propagation resistance while maintaining the high strength of MPa or more.

Next, the present invention defines that the volume ratio of cementite lamella in the pearlite structure is 10% or less. According to the inventors' microscopic observation, when the relative thickness of the cementite lamella with respect to the thickness of the ferrite lamella in the pearlite structure becomes large, cracking frequently occurs in the cementite lamella during cold rolling. I found out that Moreover, it was found that the easiness of cracking is promoted as the lamella spacing of the pearlite structure is increased. The cracked portion of the cementite lamella becomes a void and acts as an initial crack. In particular, when an initial crack occurs in a cementite lamella located near the tip of a microcrack caused by an external factor (such as a flaw from the outside), the crack propagation resistance is greatly reduced.

The following means can be considered to make the cementite lamella difficult to break. i) Lower the pearlite transformation temperature to reduce the lamella spacing. ii) Reducing the carbon concentration in the matrix austenite to relatively reduce the thickness of cementite lamella in the pearlite structure. Among these, when the means i) was tried, the hardness of the pearlite structure increased, and the crack propagation resistance could not be effectively increased. It is considered that this is because the hardness of the pearlite structure mainly depends on the thickness of the ferrite lamella.

On the other hand, the means of ii) was very effective. The volume ratio of pearlite structure in the metal structure is 50%
With respect to the steel sheet after cold rolling as described above, as a result of a detailed investigation on the occurrence of cracking of cementite lamella, the relative thickness ratio of cementite lamella and ferrite lamella adjacent to each other in the pearlite structure was 1: It was found that when it was 9 or less, the cementite lamella suddenly became difficult to break. As a result, crack propagation resistance is significantly improved.
That is, the inventors have found that in a steel plate used as a steel belt (usually undergoing a cold rolling process), the volume ratio of cementite lamella in the pearlite structure is 10%.
It has been found that the following is important for exhibiting high crack propagation resistance.

In order to reduce the volume ratio of cementite lamella in the pearlite structure to 10% or less, it is basically necessary to reduce the C content of the steel sheet. However, the C content does not uniquely determine the volume ratio of cementite / lamella. That is, when the hot rolled structure is a proeutectoid ferrite + pearlite structure, a proeutectoid ferrite phase is likely to be generated in a steel sheet having a low C content. If the proeutectoid ferrite phase is increased, the volume fraction of cementite in the pearlite structure will inevitably increase.

As a result of various studies, this problem was solved by increasing the cooling rate after finishing hot rolling in hot rolling. When the cooling rate is increased, the degree of supercooling against the pearlite transformation is increased, and the formation of proeutectoid ferrite phase is suppressed. As a result, the volume ratio of cementite / lamella in the pearlite structure can be reduced to 10% or less.

Further, in the present invention, it is specified that the thickness of the pro-eutectoid ferrite phase in the plate thickness direction of the steel plate used in the steel belt is 5 μm or less. The ferrite phase is a phase rich in ductility, but the "strength-ductility / toughness" balance after strong cold rolling is inferior to that of the pearlite structure.
The pro-eutectoid ferrite phase in the hot-rolled structure is expanded in the rolling direction by cold rolling, but if the thickness of the pro-eutectoid ferrite phase after cold rolling exceeds 5 μm, the elongation and toughness of the pearlite structure The crack propagation resistance is reduced.

[Mechanical Properties] In the present invention, as the preferred mechanical properties of the steel sheet, the tensile strength at room temperature in the rolling direction is 1000 MPa or more, the total elongation is 6% or more, and the mechanical properties are defined in the above [A]. The specified crack propagation resistance is 600 MPa or more. In particular, those having a crack propagation resistance of 600 MPa or more have excellent durability and reliability when the steel belt is used.

The steel belt steel plate having the metal structure described above can be manufactured by the following method. [Hot Rolling] In hot rolling, in order to increase the degree of supercooling of pearlite transformation, it is desirable to increase the cooling rate after finish hot rolling. Specifically, when using the steel having the component composition described above, the finishing hot rolling temperature is set to 800 to 900 ° C, and then the average cooling rate until winding is 20 ° C / sec or more. It is possible to suitably employ a method of rapidly cooling to 450 ° C. and winding at 450 to 650 ° C.

[Cold Rolling] In the present invention, as described above, a metal structure capable of realizing a high level of “strength-ductility / toughness” balance and durability was clarified. As a result of various studies on the manufacturing process, it was confirmed that a steel sheet exhibiting such a metallographic structure can be manufactured by a method of directly cold rolling a hot-rolled steel sheet without performing a conventional isothermal transformation treatment. The cold rolling rate is preferably 30 to 80%. Specifically, the hot-rolled steel sheet subjected to the hot rolling can be pickled and then cold-rolled as it is in a cold rolling line. Also,
In the case of cold rolling using an in-line mill attached to a pickling line or the like, the total cold rolling rate before subjecting to aging treatment may be set within the above range. In either case, it is not necessary to perform heat treatment between hot rolling and cold rolling.

[Aging treatment] 200 to 500 ° C. after cold rolling
It is desirable to apply an aging treatment for 0.5 to 30 hours.

[Temperature Rolling] Temper rolling can be performed as necessary. When temper tempering is applied after aging treatment,
It is desirable to perform the rolling reduction at 10% or less.

[0038]

[Examples] Steels having the chemical compositions shown in Table 1 were melted, and subjected to hot rolling → cold rolling → aging treatment → temper rolling under the following conditions,
A steel plate having a plate thickness of 1.0 mm was manufactured. In the hot rolling, the finish hot rolling temperature is 800 to 900 ° C and the winding temperature is 450 to 650 ° C. The average cooling rate after the finish hot rolling to the winding is No.
Is about 10 ° C / sec, No. 5 and 7 is about 60 ° C / sec, other than 30 ° C / sec
It was set to sec or more. The thickness of hot-rolled steel sheet is 1000MP after the cold rolling, aging treatment and temper rolling in the following steps.
It was adjusted within a range of 2.0 to 5.0 mm so that a strength of a or more could be obtained. For cold rolling, after pickling the hot rolled steel sheet, the sheet thickness is 1.
Rolled to 0 mm. The aging treatment was performed under the condition of 400 ° C. × 20 hours. The temper rolling was performed so that the final plate thickness was 1.0 mm.

[0039]

[Table 1]

The obtained steel plate having a thickness of 1.0 mm was subjected to metallographic observation and mechanical test in the following manner. [Observation of pearlite structure] A sample was prepared by electrolytically polishing a cross section of the steel sheet including the rolling direction and the thickness direction and then etching. The volume ratio of the pearlite structure was determined by an image processing device based on the image of the sample surface photographed using an optical microscope. In addition, using an atomic force microscope, 20 pearlite colonies with lamellas that are almost parallel to the observation direction were photographed at a magnification of 20,000, and based on the photographed image, cementite was used with an image processor. -The volume ratio of the lamella was obtained, and the average value was defined as "volume ratio of cementite in pearlite".

[Observation of pro-eutectoid ferrite phase] Using a scanning electron microscope, the maximum thickness of 10 pro-eutectoid ferrite phases extending in the rolling direction was measured using a scanning electron microscope. The average value was defined as "thickness of proeutectoid ferrite phase in the plate thickness direction".

[Hardness Test] The Vickers hardness of a cross section including the rolling direction and the plate thickness direction of the steel sheet was measured. A steel belt suitable for 310 HV or higher was judged to be good.

[Tensile Test] Using a JIS No. 5 tensile test piece parallel to the rolling direction, a tensile test was performed at room temperature at a tensile speed of 10 mm / min. A tensile strength of 1000 MPa or more and a total elongation of 6% or more were judged to be good.

[Test for Measuring Crack Propagation Resistance] Using the test piece shown in FIG. 1, the crack propagation resistance was determined by the method defined in [A] above. Those having a value of 600 MPa or more were judged to be good. The results are shown in Table 2.

[0045]

[Table 2]

Nos. 2, 3, 11 to 15 exhibiting the composition and metal structure defined in the present invention have high values of hardness, tensile strength and total elongation, and crack propagation resistance of 600 MPa or more. A value was shown, and it was confirmed that the steel belt had extremely excellent durability.

On the other hand, No. 1 has a small amount of C, so that the amount of pro-eutectoid ferrite phase in the metal structure is large and the cold rolling rate for obtaining a tensile strength of 1000 MPa is excessive (about 80%). And the total growth is low. In Nos. 4 and 8, since the cooling rate after finishing hot rolling was as low as 10 ° C / sec, the volume fraction of the pro-eutectoid ferrite phase increased, and the volume fraction of cementite in the pearlite structure exceeded 10%. This resulted in good tensile strength and elongation, but poor crack propagation resistance. In Nos. 5 and 7, the hot-rolled structure was mainly composed of bainite, so the crack propagation resistance was low. In Nos. 9 and 10, the C content was large and the cementite volume fraction in the pearlite structure was high, so that the crack propagation resistance was deteriorated.

[0048]

As described above, the present invention provides means for remarkably and stably improving the crack propagation resistance of the steel sheet for steel belts. This means is characterized in that the metal structure is adjusted to a specific form, and the metal structure is hot-rolled → cold-rolled → without performing complicated heat treatment such as patenting treatment which has been conventionally performed. It was confirmed that it can be realized by a simple process called aging treatment. Therefore, the present invention makes it possible to significantly improve the durability and reliability of the steel sheet for steel belts and to reduce the manufacturing cost as compared with the conventional one.

[Brief description of drawings]

FIG. 1A is a plan view showing the shape of a test piece for measuring crack propagation resistance, and FIG. 1B is an enlarged view of a central portion thereof.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akifumi Hiramatsu             11-1 Showa-cho, Kure-shi, Hiroshima Nisshin Steel Co., Ltd.             In the company F term (reference) 4K037 EA02 EA06 EA07 EA11 EA15                       EA19 EA23 EA25 EA27 EA31                       EA32 EB06 EB09 FC03 FC04                       FD03 FD04 FE01 FE02 FG00                       FJ04 FM02

Claims (7)

[Claims] 1. C: 0.30 to 0.60% and Si: 1.0 by mass%
% Or less, Mn: 0.10 to 1.0%, P: 0.020% or less, S: 0.0
A steel sheet made of carbon steel of 10% or less, the volume ratio of pearlite structure in the metal structure is 50% or more, and the volume ratio of cementite lamella in the pearlite structure is 10% or less. Steel plate for steel belts with excellent crack propagation resistance in which the thickness of the precipitated ferrite phase in the plate thickness direction is 5 μm or less. 2. C: 0.30 to 0.60% and Si: 1.0 by mass%.
% Or less, Mn: 0.10 to 1.0%, P: 0.020% or less, S: 0.0
10% or less, Cr: 0 (no addition) to 1.0%, V: 0 (no addition)
~ 0.5%, Ti: 0 (no addition) ~ 0.1%, Nb: 0 (no addition)
0.1%, B: 0 (no addition) to 0.01%, with the balance being steel consisting of Fe and unavoidable impurities, and the volume ratio of the pearlite structure in the metal structure is 50% or more, A steel plate for steel belts having excellent crack propagation resistance in which the volume ratio of cementite lamella in the pearlite structure is 10% or less and the thickness of the pro-eutectoid ferrite phase in the plate thickness direction is 5 μm or less. 3. The steel sheet according to claim 2, wherein the Cr content is 0.1 to 1.0 mass%. 4. Tensile strength at room temperature in the rolling direction is 10
The steel sheet according to any one of claims 1 to 3, which has a total elongation of 00 MPa or more, a total elongation of 6% or more, and a crack propagation resistance defined in [A] below of 600 MPa or more. [A] Tensile speed at room temperature in the longitudinal direction of the test piece shown in FIG.
A 0.3 mm / min tensile test is performed, the maximum load is determined from the load-elongation curve, and the value (unit: MPa) obtained by dividing the maximum load by the initial cross-sectional area (45 mm x plate thickness) is taken as the crack propagation resistance. 5. Hot rolling at a finish hot rolling temperature of 800 to 900 ° C., after finishing hot rolling at an average cooling rate of 20 ° C./sec or more until winding, and at a winding temperature of 450 to 650 ° C. Cold rolled without heat treatment, then 0.5 ~ 30 at 200 ~ 500 ℃
The method for manufacturing a steel sheet according to any one of claims 1 to 4, wherein an aging treatment for holding for a time is performed. 6. The manufacturing method according to claim 5, wherein the cold rolling rate is 30 to 80%. 7. The production method according to claim 5, wherein after the aging treatment, temper rolling with a rolling rate of 10% or less is performed.