JPH11159581A - Steel laminated hoop for continuously variable speed change belt and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wear and abrasion resistance without damaging durability or seizure resistance by forming a nitrosulphurized layer on at least a part of a steel hoop. SOLUTION: A hoop 4 is desirable to manufacture by nitrosulphurizing at least a part of the surface of a steel hoop in a gas atmosphere where sulfurization end nitriding progress simultaneously. In addition, the hoop 4 may be formed of one member, but may be manufactured by laminating an endless band steel. In this case, a nitrosulphurized lay may be formed in every hoop, but may be formed only on an outside in a laminated state. The hoop laminated in about ten layers is frequently used for a continuous variable speed change belt of an automobile to require a large driving power. In addition, a nitrosulphurizing processing is desirable to substantially carry out using NH3 gas, N2 gas and H2 S gas at 450-550 deg.C within 5-30 minutes, and moreover to virtually progress nitriding and sulfurization under a condition where concentration is 5-50% in NH3 and 50-1000 pp in H2 S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel hoop incorporated in a power transmission belt of a continuously variable transmission and a method of manufacturing the same.

[0002]

2. Description of the Related Art A belt having an endless hoop made of steel laminated on a belt for transmitting power of a continuously variable transmission of an automobile, a printer, a plotter or the like has begun to be used. Such endless hoops are required to be able to be processed thinly, to have high material strength and high fatigue strength, and also to have good seizure resistance and wear resistance.

[0003] In response to such demands, materials are difficult to process,
Precipitation hardening stainless steels such as 18% Ni maraging steel and SUS630 (17-4PH) which are excellent in material strength and fatigue strength have been conventionally used and are being put to practical use. In a continuously variable transmission of a car, for example,
As shown in FIG. 1 and FIG.
A block 5 for transmitting torque by frictional contact with the block 2 is arranged, and the hoop 4 and the block 5 constitute a power transmission belt 3. Hoop 4
Is in contact with the block, and sometimes the end faces of the hoop come into contact with the pulleys 1 and 2, and it is necessary not only to have excellent fatigue strength, but also to have excellent seizure resistance and wear resistance It is.

Many proposals have been made for a hoop for a continuously variable speed belt, but there are few proposals for improvement from the above viewpoint. Japanese Patent Application Laid-Open No. SHO 59-197,642 discloses only a laminate of a maraging steel hoop subjected to nitriding treatment and a metal block, and at least one surface of the hoops in contact with each other and the innermost surface on the block side are sulfurized. There has been proposed a transmission belt in which the friction due to slip between hoops and between a hoop and a block is reduced by forming a transmission belt having a layer. This proposal is excellent in reducing friction due to slip.

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No.
The continuously variable transmission belt disclosed in Japanese Patent No. 197642 is advantageous in that it reduces friction caused by slip between hoops and between a hoop and a block, and improves seizure resistance (scuffing resistance), but is not practical. There are many problems.
The biggest problem is poor wear resistance. The method of sulfurizing the hoop to form an FeS layer on the surface has a large lubricating effect, but since the hardness of the layer is as low as 500 HV at the maximum, excessive torque and compressive stress generated at the start of the continuously variable transmission can be reduced. In other words, it is easily worn away and does not have a sufficient effect on abrasion between the hoop and the block or between the hoop and the pulley.

Further, in the method of nitriding and then sulfurizing as disclosed in Japanese Patent Application Laid-Open No. 197,762 / 1979, the nitriding treatment and the sulfurizing treatment are separately performed twice, which is economically expensive. There is also. SUMMARY OF THE INVENTION An object of the present invention is to provide a steel hoop for a continuously variable transmission belt, which has improved wear resistance and also has durability and seizure resistance, and a method of manufacturing the same.

[0007]

The inventor of the present invention has investigated the wear of a hoop incorporated in a discarded continuously variable speed belt, and found that the inferior wear resistance is due to the structure and hardness of the hoop surface. In light of this, we have conducted extensive research. As a result, instead of performing nitriding and sulfurizing separately,
By proceeding the nitriding and the sulfurizing at the same time, it is possible to form a sulfuritrided layer in which iron sulfide and iron nitride are mixed on the surface of the hoop, without impairing the durability and seizure resistance by the sulfuritrided layer, The present inventors have found that improvement in wear resistance can be achieved, and have reached the present invention.

That is, the present invention relates to a steel hoop for a continuously variable transmission belt in which steel blocks are arranged, wherein the steel hoop has a sulfided nitrided layer formed on at least a part of the steel hoop. It is a hoop made.

The steel hoop of the present invention is not a single-layer hoop, but may be formed by laminating, for example, an endless strip in order to have sufficient strength. In addition, the hoop of the present invention can be expected to have an effect of improving abrasion resistance if at least a part of the oxynitrided layer is formed.
It is most desirable to form a oxynitrided layer on the side of the contact surface with the steel block, which has the highest contact frequency. Also,
The end face of the hoop of the present invention may come into contact with a pulley or the like, and it is desirable that this portion is also subjected to sulfurizing treatment. As a matter of course, the entire surface may be subjected to the sulfur-nitriding treatment. Preferably, the surface hardness is adjusted to Vickers hardness of 700 to 1000 HV.

A preferred method of obtaining the above-mentioned steel hoop for a continuously variable transmission belt according to the present invention is to perform sulphinitriding at least a part of the surface of the steel hoop in a gas atmosphere in which sulfuration and nitridation proceed simultaneously. . In particular, this method is preferable when the steel hoop in a state where the steel strips are laminated in layers is subjected to the nitrosulphurizing treatment.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an important feature of the present invention is that a nitrosulfurized layer is formed on a steel hoop.
As described above, in the conventional simple sulfurizing treatment or the sulfurizing treatment after the nitriding treatment, a single sulfide layer is formed, so that the abrasion resistance is poor. The oxynitridation layer applied by the present invention is a layer in which iron nitride and iron sulfide are dispersed. By forming this composite structure, the wear resistance is remarkably improved as compared with a hoop formed of iron sulfide as a single layer.

The first reason is the difference in surface texture. When iron sulfide is formed in a single layer, Vickers hardness is 50
Only about 0 HV can be obtained, and seizure resistance can be secured if iron sulfide is not worn, but iron sulfide is soft and is worn away, impairing wear resistance. On the other hand, in the structure of the present invention in which iron nitride and iron sulfide are mixed, the softness in the case of a single layer of iron sulfide is relaxed, and a high hardness of 700 to 1000 HV is obtained. Seizure is ensured, and it is possible to also have wear resistance.

FIG. 3 shows an example of a specific oxynitrided layer of the hoop of the present invention. FIG. 3 is an example of a 5000 times cross-sectional metallographic photograph of the present invention. The base material is a maraging steel shown in Table 1. In the structure shown in FIG. 3, the outermost surface forms a fine mixed layer of particulate iron sulfide and black iron nitride shown in white. Further, a nitrided layer is formed at a deep portion of the fine mixed layer, and has a sound structure without cracks or the like.

The hoop of the present invention is preferably manufactured by subjecting at least a part of the surface of a steel hoop to a nitrosulphurizing treatment in a gas atmosphere in which sulfuration and nitridation proceed simultaneously. In the present invention, the hoop 4 may be a single member, but may be a laminate of endless strip steel as shown in FIG. In this case, the oxynitrided layer may be formed for each hoop, or the oxynitrided layer may be formed only on the outer surface of the laminated state. Especially,
For a continuously variable speed change belt such as an automobile that requires a large driving force, a hoop having about 10 layers stacked is often used.

In this case, the nitrosulphurizing treatment in a gas atmosphere has the advantage that, even if the treatment is performed in a stacked state, the gas can be diffused into the laminated portion to form a sulphonitrided layer between the layers. is there. The use of gas also has the advantage of not discharging toxic waste such as harmful cyanide. Specifically, the hoop of the present invention can be manufactured, for example, by the process shown in FIG. In particular, when imparting compressive residual stress to prevent crack propagation and improve fatigue strength, after performing a known shot peening method or the like after aging treatment, laminating hoops, and then also performing sulfonitriding treatment Good.

The nitrosulphurizing treatment is carried out at 450 to 550 ° C. for 5 hours.
In about 300 minutes, NH ₃ gas and N ₂ gas and H ₂ gas
Depending on the S gas, the NH ₃ concentration is 5 to 50% and the H ₂ S concentration is 5%.
It is desirable that nitriding and sulfurizing proceed simultaneously at a concentration of 0 to 1000 ppm. The outermost surface layer of the hoop has a mixed layer of iron sulfide and iron nitride, and a processing method that does not form a nitrided embrittlement layer is desirable. If the treatment temperature is 450 ° C. or lower, the decomposition of NH ₃ becomes insufficient, and it is difficult to obtain a nitrided layer having the required surface hardness and hardness. Conversely, if the temperature is 550 ° C. or more, a nitride embrittlement layer may be formed, and the fatigue strength and seizure resistance may be reduced. Therefore, 450-550 ° C is desirable.

Regarding the time of the nitrosulphurizing treatment, in order to obtain a sulphinitrided layer having a sufficient thickness for abrasion resistance, the treatment is preferably carried out for 5 minutes or more under the above conditions. Since the total nitrosulphurized layer becomes thick and the toughness of the hoop may be reduced, it is preferable to set the time to 5 to 300 minutes.

Control of the gas concentration is effective in forming a mixed layer. When the NH ₃ concentration is 5% or less, a necessary nitrided layer is difficult to obtain, and when the NH ₃ concentration is 50% or more, a nitride embrittlement layer is easily formed. The H ₂ S concentration is 5
At 0 ppm or less, iron sulfide is not easily formed and may be a single layer of a nitride layer. At 1000 ppm or more, the outermost surface becomes a single layer of iron sulfide and an improvement in wear resistance may not be ensured. It is desirable to do.

The H ₂ S gas can be produced using, for example, a 0.5-2% H ₂ S cylinder gas diluted with N ₂ or an H ₂ S gas decomposed from an ammonium sulfide solution. The H ₂ S gas can also be generated by, for example, reacting a dilute inorganic acid and metal S with each other.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. Example 1 A hoop having the composition shown in Table 1 was produced. Table 1
Is a 250 ksi grade 18% Ni maraging. First, after vacuum induction melting of steel, vacuum arc remelting was performed to form a lump of 1000 kg. Thereafter, the steel ingot was subjected to hot working, and finally solution treatment and cold rolling were repeated to produce a cold-rolled thin strip having a thickness of 0.19 mm. The obtained cold-rolled ribbon was cut out and 820 ° C. × 1 in vacuum.
After performing the solution treatment for a time, aging treatment was performed at 480 ° C. for 3 hours in a vacuum. When the residual stress is applied by shot peening after the aging treatment, 5 to 10 μm alumina using water as a medium is mixed and dispersed, and a spray pressure is applied.
It was sprayed at 3.5 atm for 30 seconds.

Thereafter, a surface treatment was performed under the conditions shown in Table 2. The structure evaluation of the obtained treated layer, the surface hardness measurement of the hoop, the depth measurement of the treated layer, the measurement of the compressive residual stress, and the fatigue test were performed. Table 3 shows the results. In addition, the surface hardness of the hoop is a result measured at a position 10 μm deep from the surface with a micro Vickers load of 100 g. Also,
The depth of the processing layer is a depth including the nitride layer.

The measurement of the compressive residual stress was performed using the measured value of the X-ray residual stress on the outer surface of the hoop. Fatigue strength was measured using a swing-bending tester, and S-N indicating stress and frequency was used.
Draw the curve was determined as the fatigue strength at 10 ⁷ times.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

As shown in Table 3, the hoop having the nitrosulphurized layer of the present invention had higher surface hardness and higher fatigue than the comparative example in which the nitrided layer alone or the sulfided monolayer was formed on the nitrided layer. Has both strength. The sample 4 of the comparative example is
Because the crack was confirmed early in the fatigue test, fatigue test of up to 10 ⁷ times it is not implemented. Samples 9 and 11 of the present invention to which shot peening treatment was applied
In the test, the residual compressive stress was increased, and improvement in fatigue strength was observed.

Example 2 In order to evaluate seizure resistance and wear resistance, a 15 mm thick cold-rolled strip having the composition shown in Table 1 was subjected to an aging treatment after a solution treatment. A surface treatment was performed under the conditions shown in Table 2 to produce a baked test piece having a diameter of 8 mm × length 20 mm and a wear test piece having a thickness of 10 mm × width 20 mm × length 50 mm. Table 2 shows the sample Nos. Shown in Example 2.
Sample No. shown in FIG. This corresponds to the condition (1). Block materials and pulley materials having the compositions shown in Table 4 were selected as counterpart materials for evaluation of seizure resistance and wear resistance.

[0028]

[Table 4]

The block material used was alloy tool steel SK
S95. In the present example, the ingot was ingoted in a 1000 kg arc melting furnace, finished into a 30 mm thick hot rolled plate by hot working, cut out from the hot rolled plate, quenched at 800 ° C., quenched at 180 ° C., and tempered at 60 ° C. After tempering to a hardness of, a seizure test piece having a size of 20 mm in diameter and 180 mm in length and a wear test piece having a diameter of 30 mm and a thickness of 3 mm were prepared.

The pulley material used is carbon steel SCM420H for machine structure. In this thread removal example,
Ingots were formed in a 1000 kg arc melting furnace and finished into a 30 mm thick hot rolled plate by hot working. The hot-rolled material was cut out, quenched at 925 ° C. and tempered. After tempering to a hardness of 44 HRC, abrasion test specimens having a diameter of 20 mm × length of 180 mm and a diameter of 30 mm × thickness of 3 mm were prepared. .

The seizure test was performed using a reciprocating friction wear machine.
A test piece of the hoop material of the present invention was fixed, and a block material and a pulley material were arranged at orthogonal positions, and the room temperature was 30 m / mi at room temperature.
The load was increased by 100 N at a speed of n, and the lubricant oil was applied dropwise to a maximum of 1960 N while dripping, and continued until seizure occurred, and the seizure occurrence load was measured. The abrasion test uses the Ogoshi type abrasion test, fixing the belt material and applying a surface pressure of 2 to the mating material.
A wear test was performed under a load of 0 N / mm ² and a distance of 400 m under two conditions of a wear speed of 0.9 m / sec and 2.4 m / sec, and a specific wear amount was measured to evaluate wear resistance.

Table 5 shows the results. The base itself sample No. While the seizure load of No. 1 is 100N,
Any surface treatment increases the seizure load and improves seizure resistance. In particular, in the hoop having the nitrosulphurized layer of the present invention formed, no seizure occurred up to the maximum load of the tester as compared with the nitride layer alone or the comparative example in which the sulfide monolayer was formed on the nitride layer. Thus, the hoop of the present invention having a mixed layer of iron sulfide particles and iron nitride particles is superior to the comparative example in which the hoop of the present invention having the mixed layer of the iron sulfide particles and the iron nitride particles is formed on the nitride layer alone or on the nitride layer. It can be seen that it is.

In the wear test, 0.9 m / s
The wear rate of ec evaluates the wear of the surface treatment material.
2.4 m / sec was performed for the purpose of evaluating the wear of the surface treatment material including the matrix. While the specific wear amount of the sample 1 of the comparative example of the base itself is 1.6 to 1.9, when the surface treatment is performed, the specific wear amount is reduced and the wear resistance is improved. In particular, in the hoop formed with the oxynitrided layer of the present invention,
Compared to the comparative example in which a nitride layer alone or a sulfide monolayer was formed on the nitride layer, the specific wear rate was lower, and it was confirmed that the seizure resistance was improved. From these results, the role of iron sulfide particles and iron nitride particles in the nitrosulphurized layer in the hoop of the present invention is as follows. It is presumed that they respectively share and exhibit excellent seizure resistance and wear resistance.

[0034]

[Table 5]

[0035]

As described above, the formation of a sulfur-nitrided layer in which iron sulfide and iron nitride are combined makes it possible for a steel laminated hoop for a continuously variable speed belt to achieve both the galling resistance and the wear resistance. The present invention is applied to a belt for transmitting power of a printer, a plotter, or the like, and has a great effect on the durability, reliability, size, and weight of a continuously variable transmission.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a continuously variable transmission.

FIG. 2 is a conceptual sectional view showing an example of a hoop, a block, and a pulley in the continuously variable transmission.

FIG. 3 is a photograph showing a cross-sectional metal microstructure of a hoop of the present invention.

FIG. 4 is a cross-sectional view showing an example of a configuration when the hoops of the present invention are stacked.

FIG. 5 is a process chart showing a hoop material manufacturing process.

[Explanation of symbols]

1 pulley, 2 pulleys, 3 belts, 4 hoops, 5 blocks

Claims (6)

[Claims] 1. A continuously variable transmission belt for a continuously variable transmission belt in which steel blocks are arranged, wherein at least a part of the steel hoop is formed with a sulfided nitrided layer. For steel hoop. 2. The steel hoop according to claim 1, wherein the steel hoop is formed by laminating strips in layers. 3. The steel hoop for a continuously variable transmission belt according to claim 1, wherein a sulfided nitrided layer is formed on a side of the steel hoop in contact with the steel block. 4. The steel hoop for a continuously variable transmission belt according to claim 1, wherein a sulfided nitrided layer is formed on both side surfaces of the steel hoop. 5. A method for producing a steel hoop for a continuously variable transmission belt in which steel blocks are arranged, wherein at least a part of the surface of the steel hoop is subjected to nitrosulphurizing treatment in a gas atmosphere in which sulfuration and nitridation proceed simultaneously. A method for producing a steel hoop for a continuously variable speed belt. 6. The method for producing a steel hoop for a continuously variable transmission belt according to claim 5, wherein the steel hoop in which the strips are laminated in a layered manner is subjected to a nitrosulphurizing treatment.