JP4389726B2 - Thin steel strip for metal belt ring of continuously variable transmission belt - Google Patents

Description

  The present invention relates to a thin steel strip for a metal strip ring in a continuously variable transmission belt, and more particularly to a thin steel strip having high corrosion resistance, high strength, and high fatigue characteristics.

  In a belt type continuously variable transmission (CVT) of an automobile, as shown in FIG. 2, a plurality of steel and plate-like elements (pieces) 202 are provided on a plurality of metal band rings 200 forming an endless ring (only a part of which is shown). A steel belt (continuously variable transmission belt) 204, which is mounted side by side, is wound around an endless ring between a pair of pulleys (primary pulley 206 and secondary pulley 208) having a variable groove width shown in FIG. Power is transmitted from the primary pulley 206 to the secondary pulley 208 via

Specifically, the input from the engine enters one pulley (primary pulley 206), is transmitted to the other pulley (secondary pulley 208), and then output.
At that time, the effective diameter of each pulley is changed by changing the groove width of each pulley, and the gear shift is continuously performed in a stepless manner.

Conventionally, 18Ni maraging steel known as high-strength steel has been widely used as a metal band ring in such a continuously variable transmission belt.
For example, the following Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 disclose the use of such 18Ni maraging steel as a metal band ring material in a continuously variable transmission belt of an automobile.
This 18Ni maraging steel is almost martensite single phase in the solution heat treatment state, and is used by increasing the hardness by precipitation hardening by aging treatment.

  When this 18Ni maraging steel is used as a metal band ring in a continuously variable transmission belt, it is further subjected to nitriding treatment to increase the surface hardness, thereby improving wear resistance and fatigue characteristics.

  The metal band ring 200 of the continuously variable transmission belt 204 causes relative frictional sliding between the element 202 and the metal band ring 200 in the movement of power transmission in the continuously variable transmission. 200 requires high wear resistance.

  On the other hand, these metal band rings 200 are repeatedly deformed such as a straight shape between the pulleys and a curved shape at the portion wound around each pulley. Therefore, high fatigue strength and toughness are also required.

  Therefore, when 18Ni maraging steel is used as a metal belt ring for a continuously variable transmission belt, the surface layer is nitrided to prevent the center from becoming excessively hard and toughen the surface. Both wear resistance and wear resistance are ensured.

  This 18Ni maraging steel is one of high-strength steels and has been conventionally applied as a suitable material for parts subjected to high tensile stress such as a metal belt ring of a continuously variable transmission belt.

However, in the case of this 18Ni maraging steel, the addition of Ti and Al is indispensable because high tension is obtained by fine precipitation of intermetallic compounds such as Ni ₃ Ti and Ni ₃ Al by age hardening. Ti-based inclusions and Al-based inclusions, which are harmful to the properties, are likely to be generated, and inherent problems such as deterioration of fatigue properties are included.

In general, when fatigue failure occurs in a low cycle region, it is known that fatigue failure occurs due to crack initiation and propagation starting from the surface.
For such fatigue failure, fatigue failure starting from the surface can be prevented by subjecting the surface layer to nitriding treatment and applying compressive stress to the surface layer.
On the other hand the conventional, in the ultra high cycle range exceeding 10 ⁷ times that are believed to fatigue limit is believed to fatigue fracture occurs as a starting point inside the inclusions not starting from the surface.

Therefore, when 18Ni maraging steel is applied to applications where fatigue characteristics are particularly important, such as metal belt rings for continuously variable transmission belts, the raw materials are selected by high-vacuum melting or secondary refining. It is necessary to reduce impurities as much as possible. Therefore, the manufacturing cost has been extremely high.
Furthermore, since Ni and Co, which are expensive elements, are added in a large amount, the material cost among steel materials is high.

  In addition, 18Ni maraging steel does not contain Cr, which is an element that improves corrosion resistance compared to stainless steel, so it is inferior in corrosion resistance. Corrosion occurs during use, and fatigue failure occurs at an early stage starting from the corrosion location. There is also a problem that may occur.

JP 2002-275585 A JP 2001-240944 A JP 2001-240943 A JP 2000-345302 A

  The present invention is based on the above circumstances, and has high strength for a metal belt ring of a continuously variable transmission belt having low material and manufacturing cost, high fatigue strength, good corrosion resistance and good nitriding characteristics. It was made for the purpose of providing a thin steel strip.

Thus, in the first aspect, C: 0.10 to 0.25%, Si: ≤0.25%, Mn: ≤0.40%, Ni: 5.0 to 8.5%, Cr: 0.30 to 2.50%, Mo + 1 / 2W: 1.20 to 2.50%, Cu: ≤0.20%, V: 0.05 to 0.15%, Co: 1.00 to 6.00%, N: ≤0.010%, O: ≤0.0050%, Al: ≤0.10%, Ti: ≤0.10%, P : ≦ 0.05%, S: ≦ 0.03%, and having a composition consisting of the remaining portion Fe and unavoidable impurities.

  According to a second aspect of the present invention, in the first aspect, the composition further contains Zr: 0.01 to 0.50% by mass%.

  Claim 3 further contains one or more of B: 0.0010 to 0.010%, Ca: 0.0010 to 0.010%, Mg: 0.0010 to 0.010% by mass% in any of claims 1 and 2. It is characterized by doing.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the amount of nonmetallic inclusions is 0.05% or less in terms of cleanliness d.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the surface layer is nitrided, the nitrided layer depth according to JIS G 0562 is 20 μm or more, and the surface hardness according to JIS G 0563 Is 800 HV or more.

  According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the 0.2% yield strength in a tensile test based on JIS Z 2241 is 1250 MPa or more.

Effects and effects of the invention

The thin steel strip for the metal belt ring of the continuously variable transmission belt of the present invention has Ni, Co, and Mo of Ni of 8.50% or less, Co of 6.00% or less, and Mo of (Mo + 1 / Mo) compared to 18Ni maraging steel. (With 2W) Less than 2.50%, and the structure is different because C is added. The alloy of the present invention has a bainite structure, high tensile strength can be obtained by quenching and tempering treatment, and good fatigue characteristics can be obtained by hardening the surface layer by nitriding treatment.
For this reason, the tensile strength is slightly inferior to that of the conventional 18Ni maraging steel, but sufficient strength is obtained and the fatigue strength is good.
On the other hand, since the amount of expensive elements Ni, Co, and Mo is small, the cost of the material can be suppressed at a low cost.

Another feature of the present invention is that the impurity components O, Ti, and Al are restricted to a low level.
Ti and Al react with O to form oxide inclusions, which cause the fatigue life to decrease with the origin of fracture.
Therefore, in the present invention, these Ti and Al are regulated to be low together with O to suppress the formation of oxides of Ti and Al as inclusions, which can further improve the fatigue life.

  Also, the conventional 18Ni maraging steel does not contain Cr, so it has insufficient corrosion resistance. Therefore, when it is used for a thin steel strip for a metal strip ring of a continuously variable transmission belt, the corrosion point is the starting point. Although cracks are generated and progress and contain problems that cause fatigue failure, the steel of the present invention is excellent in corrosion resistance because it contains a predetermined amount of Cr, and therefore fatigue failure due to corrosion. It is possible to suppress fatigue and increase the fatigue life.

This Cr has a function of improving the corrosion resistance by forming an oxide film (passive film). On the other hand, when such an oxide is formed, the nitriding characteristics during the nitriding treatment are hindered. That is, Cr content was thought to increase the corrosion resistance while inhibiting the nitriding properties.
However, as long as the addition amount of Cr can be suppressed to a small amount, the inventors have found that addition of Cr improves the nitriding characteristics instead.
That is, in the present invention, Cr is added in an amount of 0.30% or more, but the addition amount is suppressed to 2.50% or less. As a result, the corrosion resistance can be improved and the nitriding characteristics can also be improved.

The present invention also regulates P and S as impurity components to a predetermined low value, thereby ensuring good toughness.
In the present invention, the thickness of the thin steel plate can be 0.5 mm or less.

  In the present invention, in addition to the above components, Zr can be added in the above-mentioned predetermined amount as necessary, and one or more of B, Ca, Mg can be added in the above-mentioned predetermined amount. (Claim 2, Claim 3).

In the present invention, the amount of non-metallic inclusions is preferably 0.05% or less in terms of cleanliness d (Claim 4), and the surface hardness after nitriding is 800 HV or more and the nitrided layer depth is 20 μm or more. it can.
The metal band ring that is always in contact with the elements in the continuously variable transmission belt is a member that requires wear resistance. Therefore, the thin steel band plate of the present invention having a surface hardness of 800 HV or more is provided with such a metal band ring. The present invention can be preferably applied as (claim 5).

  INDUSTRIAL APPLICABILITY The present invention can achieve a strength of 1250 MPa or more as the strength (0.2% yield strength) of a thin steel strip, and is suitable as a metal strip of a continuously variable transmission belt subjected to a strong tensile stress. (Claim 6).

Next, the reasons for limiting each chemical component in the present invention will be described in detail.
C: 0.10-0.25%
C is a strong solid solution strengthening element and an important element for obtaining a bainite structure. Further, it is an essential element for obtaining high strength by precipitating fine carbides and carbonitrides by tempering after quenching, and the effect cannot be obtained unless 0.10% or more is added.
However, when added in a large amount, coarse carbides are formed at the grain boundary portion, thereby reducing the corrosion resistance and notch toughness of the steel, and for the same reason, reducing the strength of the weld.
Since the fatigue strength decreases as a result of the above effects, the upper limit of the C content is 0.25%.

Si: ≤0.25%
Si is added as a deoxidizer during the melting of steel. Excess Si increases the strength of the steel at room temperature, but it reduces the cold workability and reduces the fatigue properties as the Si oxide generated in the steel becomes the starting point of fracture, so it is necessary to reduce the content as much as possible. is there.
Further, since the addition of a large amount of Si causes an oxide film to be formed during heat treatment (for example, tempering treatment) immediately before the nitriding treatment and deteriorates the nitriding property, the upper limit is made 0.25%.

Mn: ≤0.40%
Mn is added as a deoxidizer, but if it is contained excessively, the hardenability increases and it becomes difficult to form a bainite structure, so the upper limit is made 0.40%.

Ni: 5.00-8.50%
Ni is an effective element together with Cr, Mo and W for adjusting the bainite structure.
However, if it is less than 5.00%, the strength toughness is low, and conversely if it exceeds 8.50%, retained austenite is formed and the increase in strength is reduced. On the other hand, the tempering hardness is increased and the cold workability is deteriorated. And

Cr: 0.30-2.50%
Appropriate addition of Cr improves the nitriding properties because it promotes the diffusion of nitrogen. It is also effective in improving corrosion resistance. Therefore, add 0.30% or more where the effect appears.
However, if Cr is added more than necessary, the oxide film (passive film) formed on the surface prevents the diffusion of nitrogen during the nitriding process and makes the nitride layer depth shallow.
For this reason, the range of Cr content is set to 0.30 to 2.50% as a condition for improving both corrosion resistance and nitriding characteristics.

Mo + 1 / 2W: 1.20-2.50%
Mo and W are necessary for adjusting the bainite structure, and in order to improve the temper softening resistance, it is necessary to contain 1.20% or more, but if added over 2.50%, the hardenability increases and the balance of the bainite structure. Therefore, the content range is set to 1.20 to 2.50%.

Cu: ≤0.20%
Cu is mixed as an impurity element, but if it exceeds 0.20%, delayed fracture characteristics and hot workability are impaired, so the upper limit of Cu content is set to 0.20%.

V: 0.05-0.15%
V increases the hardenability and refines the crystal grains, so 0.05% or more is necessary. However, if over 0.15%, the effect is saturated, so the content range is 0.05 to 0.15%.

Co: 1.00-6.00%
Co is added in an amount of 1.00% or more in order to obtain high strength without improving the annealing hardness. The effect of Co on the transformation temperature of bainite martensite is smaller than that of Ni, Cr, Mo, and W, and works effectively for the stable formation of bainite. However, excessive addition exceeding 6.00% leads to a decrease in notch toughness and a decrease in fatigue strength, so the Co content range is set to 1.00 to 6.00%.

N: ≤0.010%
N is a powerful solid-solution strengthening element and is an essential element for obtaining high strength by precipitating fine nitrides and carbonitrides by tempering after quenching. It is necessary to reduce as much as possible in order to form a system inclusion and an Al system inclusion. In the present invention, the upper limit of the N content is set to 0.010%.

O: ≦ 0.0050%
O generates oxides such as SiO ₂ and Al ₂ O ₃ and lowers fatigue characteristics such as fatigue strength. Therefore, it is desirable that O be as low as possible. However, an extreme decrease leads to an increase in manufacturing costs, so the upper limit is regulated to 0.0050%.

Al: ≤0.10%
Al is an element that can be expected to improve strength by forming Ni ₃ Al or the like by tempering after quenching, but it is easy to bond with N, O, etc., and forms Al-based nonmetallic inclusions like Ti, On the other hand, in order to deteriorate the fatigue characteristics, it is desirable to reduce it as much as possible like Ti.
In addition, the increase in Al reduces the nitrided layer depth in the same way as Cr, so the upper limit was made 0.10%.

Ti: ≤0.10%
Ti is an element that can be expected to improve strength by forming Ni ₃ Ti, etc. by tempering after quenching, but it is easy to bond with C, N, O, etc. and forms Ti-based non-metallic inclusions. It is desirable to reduce as much as possible in order to deteriorate the characteristics. Therefore, the upper limit was made 0.10%.

P: ≦ 0.05%
P is segregated at the grain boundaries to increase the intergranular corrosion susceptibility and cause a decrease in toughness. However, the lower effect is preferable, but the improvement effect is almost saturated at 0.05% or less, so the upper limit is made 0.05%.

S: ≤0.03%
S degrades hot workability and significantly reduces fatigue properties and corrosion resistance. It is desirable to reduce it as much as possible. However, if 0.03% or less, sufficient fatigue properties and corrosion resistance can be obtained, so the upper limit is 0.03%. did.

Zr: 0.01-0.50%
Zr has the effect of refining crystal grains after heat treatment. If the crystal grains are refined, the critical compressibility of the steel increases, so that strong cold working can be applied. The effect starts to appear at a content rate of 0.01%, but even if the content rate exceeds 0.50%, the effect is saturated, so the range of the content rate is set to 0.01 to 0.50%.

B, Ca, Mg: 0.0010 to 0.010%
B, Ca, and Mg may be added because they are effective elements for improving hot workability. The effect begins to appear at a content of 0.0010%, but excessive addition forms low-boiling borides at the grain boundaries or forms oxides, degrading the cleanliness of the steel, In order to reduce the cold workability and fatigue strength, the content range of these elements is set to 0.0010 to 0.010%.

Next, embodiments of the present invention will be described below.
150 kg of steel having the chemical composition shown in Table 1 is melted and cast, homogenized at 1200 ° C. × 6 hr, hot-worked at a temperature of 1200 ° C. or lower to a thickness of 3 mm, and then cooled. A thin steel strip of about 0.4 mm was obtained by hot rolling.
This material is heat treated in the order of quenching, tempering, nitriding treatment, mechanical properties (tensile strength, 0.2% proof stress, elongation, drawing), base material hardness, surface layer hardness, corrosion resistance under the following conditions: The fatigue properties were investigated.
Quenching is performed at 700 to 1100 ° C./˜1 hr. Here, the results under conditions of 850 ° C./10 min / air cooling are shown.
Moreover, tempering is implemented at 300-600 degreeC / -100hr. Assuming the short-time processing of this step, in the examples, the holding time is 2 hr / air cooling, and the results under the temperature conditions in Table 2 are shown.
The nitriding treatment is performed at 300 to 600 ° C./-10 hr in a mixed gas stream of ammonia and nitrogen. Here, it was set to 500 ° C./1 hr / air cooling.
Further, depending on the alloy component, if the temperature conditions of the tempering treatment and the nitriding treatment are uniform, the nitriding treatment can also serve as the tempering treatment.

(1) Cleanliness Cleanliness was measured according to JIS G 0555, a microscopic test method for nonmetallic inclusions in steel.
The test piece had a shape of 0.4 mm × 5 mm × 10 mm, and five of these were embedded, mirror polished, and etched.

(2) Tensile test A tensile test was performed according to the metal tensile test method of JIS Z 2241.
The test piece was a JIS Z 22015 test piece.

(3) T / 2 hardness A test was performed according to the Vickers hardness test method of JIS Z 2244.
The test piece had a shape of 0.4 mm × 5 mm × 10 mm, and the hardness was measured with a load of 0.5 N for the sample that was embedded and mirror-polished. The average value of 10-point measurement was adopted as the measurement value.
The measurement site was a hardness measurement at a position (T / 2) half the sample thickness from the surface in the cross section.

(4) Surface hardness The surface hardness was measured in accordance with JIS G 0563, a method for measuring the surface hardness of a nitrided steel layer. The measurement load was 0.1N.

(5) Nitriding characteristics The nitrided layer depth was measured according to the method for measuring the nitrided layer depth of steel according to JIS G 0562.

(6) Fatigue properties Fatigue properties were investigated in accordance with JIS Z 2273 general rules for fatigue testing of metallic materials.
Specifically, as shown in FIG. 1, for a test piece 10 having dimensions of about 0.4 mm × 10 mm × 60 mm, conditions of maximum stress 1450 N / mm ² , minimum stress 0 N / mm ² and excitation speed 1000 rpm. The test piece 10 was repeatedly bent and deformed under vibration, and the number of repeated vibrations (deformation) until the fracture was reached was measured. An SN diagram was created by measuring the number of repetitions until breakage by changing the maximum value of the vertical stress applied to the sticking portion of the plate at any time.
For the evaluation of fatigue characteristics, when the maximum stress value is 1000 N / mm ² and the same test is performed 5 times, and the number of times of repeated vibration (deformation) until breakage is 10 ⁷ times or more. Was evaluated as ◯ when 4 times, Δ as 2 to 3 times, and × when 0 times.

(7) Corrosion resistance The test piece had a shape of φ15 mm × 50 mm, the surface was finished with ▽▽▽ G, and three similar alloys were prepared. In a wet test (50 ° C., 95% RH or more), the presence or absence of rusting was confirmed after holding for 168 hours.
These results are shown in Table 3.

  In Table 3, the difference (Δ) between T / 2 of the hardness HV and the surface represents the difference in hardness between the core and the surface, and this difference in hardness represents the nitriding characteristics along with the nitrided layer depth. Expresses good or bad.

  In Table 3, Comparative Example S having a C content of 0.31% and more than the upper limit of 0.25% of the present invention produces coarse carbides at the crystal grain boundaries, resulting in poor mechanical properties and sufficient fatigue. Characteristics cannot be obtained.

  In Comparative Example T, the Si amount is 0.98%, which is larger than the upper limit of 0.25% of the present invention, and the drawing value, which is an index for toughness evaluation, is slightly low, 44%. The hardness difference Δ, which is an index, is low, and the nitride layer depth is also shallow. For this reason, the corrosion resistance and fatigue characteristics are both poor and poor.

  In Comparative Example U where the Mn amount is 0.88%, which is higher than the upper limit of 0.40% of the present invention, the formation of MnS or the like deteriorates the cleanliness. For this reason, in Comparative Example U, although corrosion resistance can be secured without any problem with respect to nitriding characteristics, fatigue characteristics are insufficient.

Comparative Example V with a Cr content of 0.12%, which is less than 0.30%, which is the lower limit of the present invention, can obtain a nitrided layer depth of 20 μm or more, but has insufficient corrosion resistance. Further, since the surface hardness is low, the fatigue characteristics are x.
In Comparative Example W, which is 3.09%, which is higher than the upper limit of 2.50% of the present invention, although sufficient tensile strength and 0.2% proof stress can be obtained by the formation of Cr carbide, the effect of promoting nitrogen diffusion of Cr during nitriding treatment And the latter is superior in the balance of the effect of suppressing the nitrogen diffusion due to the formation of the oxide film (passive film), so that the nitrided layer depth is shallow and the fatigue characteristics are as bad as Δ.
FIG. 4 shows the relationship between the Cr content and the nitrided layer depth, surface hardness, corrosion resistance, and fatigue characteristics when the Cr content is changed based on the components of Invention Steel J.
FIG. 4 shows that the nitride layer depth and surface hardness can be improved by adding a small amount of Cr.
Since the material surface is nitrided, the corrosion resistance is also good, and the fatigue properties satisfy the target with 0.30% Cr addition that can provide sufficient nitrided layer depth and surface hardness.
However, excessive addition of Cr forms an oxide film on the surface layer and inhibits the diffusion of nitrogen into the material, so that sufficient nitriding characteristics are not obtained.

Since Comparative Example X with Mo content of 2.89% and Comparative Example Z with W content of 6.52% are higher than 2.50% which is the upper limit value of the Mo + 1 / 2W amount of the present invention, it is mechanical due to coarsening of Mo and W carbides. Properties, particularly strength properties, are degraded. In Comparative Example Z, the aperture value, which is an indicator of toughness, is slightly improved, which is considered to be an effect of W addition.
As described above, Comparative Examples X and Z have poor results in both nitriding characteristics and fatigue characteristics because sufficient base material strength cannot be obtained.
In addition, since W addition amount is 1.52% and Mo + 1 / 2W is 0.76%, Comparative Example Y, which is less than the lower limit value 1.20% of Mo + 1 / 2W amount of the present invention, lacks reinforcing elements, so tensile strength is 0.2%. The yield strength and T / 2 hardness are insufficient, and sufficient fatigue characteristics are not obtained.

  In Comparative Example 2A, in which P and S contents exceed the upper limits of 0.05 and 0.03% of the present invention and are contained in a large amount, the cold workability, corrosion resistance and fatigue characteristics are poor, and the Cu content is 0.44%. Comparative Example 2B, which is greater than the upper limit of 0.20%, has poor hot workability and fatigue properties.

  In the case of Comparative Example 2C in which the amount of O is 0.0087%, which is higher than 0.0050%, which is the upper limit of the present invention, the cleanliness deteriorates due to the formation of oxides, so the fatigue characteristics deteriorate. Further, in Comparative Example 2D in which the N amount is 0.028% and the Al amount is 0.46%, which is higher than the upper limit values of 0.010% and 0.10% of the present invention, respectively, the cleanliness is deteriorated due to the formation of Al nitride, and also during nitriding Since the formation of the nitride is promoted, the depth of the nitrided layer is shallow and non-uniform, resulting in poor corrosion resistance and fatigue characteristics.

  In Comparative Example 2E in which the N amount is 0.034% and the Ti amount is 0.19%, which is higher than the respective upper limit values of 0.010% and 0.10% of the present invention, the amount of inclusion increases in the same manner as Al due to the formation of Ti nitride. The fatigue characteristics are poor.

  On the other hand, Comparative Example 2F, which is a conventional 18Ni maraging steel, has excellent tensile strength and 0.2% proof stress, so its fatigue characteristics are evaluated as ◯. However, since it does not contain Cr, it has the same corrosion resistance as the alloy of the present invention. It is not done. In addition, there are problems such as a high material cost due to a large amount of addition of Co, Ni, Mo, and the like, and a high manufacturing cost in the melt casting because it contains a large amount of Ti and the like.

On the other hand, in the examples of the present invention, good characteristics are obtained in all the characteristics.
Further, as seen in the results of FIG. 4, the nitriding characteristics are deteriorated in Comparative Examples V and W in which the Cr content does not fall within the scope of the present invention, but the present invention containing Cr within the scope of the present invention. The example has both improved nitriding properties and improved corrosion resistance. Compared to Comparative Example 2F of 18Ni maraging steel containing no Cr, the addition of a predetermined amount of Cr results in excellent nitriding characteristics (nitriding layer depth) that are substantially equal to or greater. I understand.

  Tables 4 and 5 show various characteristics of the steel types B and J shown in Table 1 treated according to Steps 1 to 5 in Table 2, respectively. From the results of these tables, the treatment conditions are shown in Steps 1 to 3. It can be understood that things are good.

Table 6 shows the characteristics of steel types B and J when only nitriding is performed.
In the results of Table 6, since the holding time is insufficient as the tempering time, the tensile properties are slightly lowered and the hardness is also lowered.

  Although the embodiments of the present invention have been described in detail above, these are merely examples, and the present invention can be implemented in variously modified forms without departing from the spirit of the present invention.

It is explanatory drawing explaining the content of a fatigue test. It is a figure which shows a continuously variable transmission belt with a metal belt ring, an element, etc. It is explanatory drawing of a belt-type continuously variable transmission. It is a figure showing the relationship between Cr amount and various characteristics.

Claims (6)

In mass%
C: 0.10-0.25%
Si: ≤0.25%
Mn: ≤0.40%
Ni: 5.0 to 8.5%
Cr: 0.30-2.50%
Mo + 1 / 2W: 1.20-2.50%
Cu: ≤0.20%
V: 0.05-0.15%
Co: 1.00-6.00%
N: ≦ 0.010%
O: ≦ 0.0050%
Al: ≤0.10%
Ti: ≤0.10%
P: ≦ 0.05%
S: ≦ 0.03%
Remaining portion Fe and other CVT metal strip ring for thin steel strip of the belt, characterized in that it has a composition consisting of unavoidable impurities. In mass%
Zr: 0.01-0.50%
The thin steel strip for a metal strip of a continuously variable transmission belt according to claim 1, further comprising: In mass%
B: 0.0010 to 0.010%
Ca: 0.0010 to 0.010%
Mg: 0.0010 to 0.010%
The thin steel strip for a metal strip of a continuously variable transmission belt according to any one of claims 1 and 2, further comprising at least one of the following.   The thin steel strip for a metal strip ring of a continuously variable transmission belt according to any one of claims 1 to 3, wherein the amount of non-metallic inclusions is 0.05% or less in terms of cleanliness d.   The nitriding treatment is applied to the surface layer, the nitrided layer depth in accordance with JIS G 0562 is 20 μm or more, and the surface hardness in accordance with JIS G 0563 is 800 HV or more. A thin steel strip for a metal strip of a continuously variable transmission belt according to claim 1.   The thin steel strip for a metal strip ring of a continuously variable transmission belt according to any one of claims 1 to 5, wherein a 0.2% yield strength in a tensile test based on JIS Z 2241 is 1250 MPa or more.

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