JPH04263046A - Alloy steel for piston ring - Google Patents

Abstract

PURPOSE:To obtain an alloy steel sheet for a piston ring capable of securing wear resistance equivalent to that of an SWOSC-V hard Cr plating treated material to be a conventional steel without executing Cr plating treatment and, furthermore, excellent in heat resistance and scuffing resistance. CONSTITUTION:This is an alloy steel for a piston ring having the feature of contg., by weight, 0.50 to 0.80% C, 1.50 to 2.50% Si and 0.50 to 1.50% Mn, furthermore contg. one or >= two kinds among 0.05 to 0.50% V, 0.05 to 0.5% Nb and 0.05 to 0.50% Mo and contg., as necessary, 0.20 to 1.50% Cr and the balance Fe with inevitable impurities.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy steel for piston rings, which has excellent wear resistance without being subjected to hard Cr plating and exhibits little tension loss at high temperatures, and is particularly suitable for second rings.

0002

[Prior Art] A piston ring for an internal combustion engine consists of a pressure ring to prevent a decrease in output due to leakage of combustion gas to the outside of the combustion chamber, a second ring that plays an auxiliary role to the pressure ring, and a second ring to carry lubricating oil into the combustion chamber. It consists of an oil ring to prevent the inflow of water.

[0003] In recent years, efforts have been made to make internal combustion engines lighter, higher in output, and higher in rotation. Materials have been developed to make piston rings, which are a component of internal combustion engines, lighter by making them thinner. is being actively carried out. Cast iron has traditionally been used as a material for piston rings, but due to its low strength and heavy weight, it has been replaced by steel, and spring steel, tool steel, stainless steel, etc. are now being used. .

[0004] Pressure rings in particular are used under the most severe conditions, so their required properties are extremely strict.Recently, martensitic stainless steel, which has the highest strength and wear resistance among the above-mentioned steels, has been used. JP-A-1-201441 utilizes the effect of Al to obtain high wear resistance.
Cr-based stainless steel as shown in the above publication has also been proposed.

On the other hand, the second ring plays an auxiliary role to the pressure ring, and although its required properties are not as strict as the pressure ring, there is also a strong need for weight reduction, and recently cast iron is being used to improve strength. Although it has inferior wear resistance compared to the stainless steel mentioned above, it is cheaper.
Si-Cr spring steel SWOSC-V (0.55%C
-1.4%Si-0.7%Mn-0.7%Cr steel) and is used with hard Cr plating to improve wear resistance. In addition, as a steel that can improve the wear resistance of SWOSC-V and omit hard Cr plating treatment, we have developed JP-A-60-1, which contains about 5% Cr.
Steel shown in Japanese Patent No. 14553 has also been proposed.

[0006]

[Problems to be Solved by the Invention] SWOSC-V used as a material for the second ring has the following problems. That is, since the material alone does not have sufficient wear resistance, it is essential to perform hard Cr plating treatment. As a result, the manufacturing process becomes complicated, and the cost increases due to the plating process and subsequent waste liquid treatment. Furthermore, since the heat resistance is insufficient, the tension decreases over time, deteriorating the performance and causing a decrease in the output of the internal combustion engine.

[0007] Furthermore, an alloy described in JP-A-60-114553, which was proposed for the purpose of improving the wear resistance of SWOSC-V and making it possible to omit the hard Cr plating process, has a 5% Cr, a little over 1% Mo, 0.3
Since it contains ~2.1% of V and W, the cost is significantly higher than that of SWOSC-V when comparing only the raw materials.

The present invention has less decrease in tension than SWOSC-V, has excellent wear resistance that makes it possible to omit the hard Cr plating process, and has
The purpose of this invention is to provide an alloy steel for piston rings that is cheaper than the steel described in Publication No. 3.

[0009]

[Means for Solving the Problems] As a result of intensive research to solve the above problems, the present inventors have found that the inclusion of a large amount of Si has a close relationship with the rate of decrease in tension due to heat, and that it is effective for improving heat resistance. I found that it was effective. That is, Si is 1.5
It was confirmed that by containing 0% or more, a large amount of Ni is dissolved in solid solution in the ferrite, and a decrease in tension can be prevented by solid solution strengthening.

[0010] Also, one or two of Nb, V, Mo
0.05-0.50% with little impact on cost for seeds or more
When added within the range of We discovered that this material has the same wear resistance as the hard Cr-plated material of SWOSC-V even if the hard Cr plating treatment is omitted, and succeeded in ensuring excellent heat resistance. .

That is, the first invention of the present invention has a weight ratio of C: 0.50 to 0.80% and Si: 1.50 to 2.
．． 50%, Mn: 0.50 to 1.50%, further V: 0.05 to 0.50%, Nb: 0.05
~0.50%, Mo:0.05~0.50%, and the remainder is Fe and impurity elements. In the second invention, 0.20 to 1.50% Cr is added to the first invention steel in order to improve hardenability and prevent decarburization.
It contains.

Next, the reasons for limiting the composition of the alloy steel for piston rings of the present invention will be explained.

C: 0.50-0.80% C is an essential element in order to obtain sufficient strength and wear resistance, and must be contained in an amount of at least 0.50%. However, 0.8
Even if it is contained in an amount exceeding 0%, the above effects will not be improved much;
The upper limit was set at 0.80% because the steel becomes hypereutectoid and the toughness decreases significantly.

[0014] Si: 1.50 to 2.50% Si dissolves in ferrite to increase the strength of the base material, and also strengthens the resistance to temper softening, thereby suppressing the phenomenon of tension reduction at high temperatures that progresses over time. It is an element necessary for slowing down and ensuring stable performance over a long period of time, and in order to obtain the above effect, it is necessary to contain it in an amount of 1.50% or more. However, if it is contained in a large amount, decarburization tends to occur and wear resistance decreases, so the upper limit was set at 2.50%.

[0015] Mn: 0.50 to 1.50% Mn is
Like C, it is an element necessary to improve strength and ensure hardenability, and must be contained in an amount of 0.50% or more. However, if it is contained in a large amount, the toughness decreases, so
The upper limit was set at 1.50%.

[0016] V: 0.05-0.50%, Nb: 0.
05 ~ 0.50%, Mo: 0.05 ~ 0.50%
One or more of these, V 2 , Nb, and Mo, precipitate as fine, hard carbonitrides after quenching and tempering, and are uniformly distributed. Therefore, wear resistance is significantly improved compared to SWOSC-V, which does not contain carbonitrides. Furthermore, the presence of carbonitrides has the function of stopping the movement of dislocations and slowing down the tension reduction phenomenon that gradually progresses over a long period of time. In order to obtain the above effects, it is necessary to contain 0.05% or more of each of V, Nb, and Mo. Moreover, combined addition is more effective than single addition. However, if they are contained in large amounts, the effect will be saturated and the cost will increase, so the upper limit was set at 0.50% for each.

Cr: 0.20 to 1.50% Cr is an element that has the effect of preventing decarburization due to heating and adjusting the hardenability to facilitate heat treatment by adding an appropriate amount as necessary. 0.20 to get the effect
% or more. However, if it is contained in a large amount, the hardenability will improve too much and the cost will increase, so the upper limit was set at 1.50%.

[0018]

[Example] Next, the characteristics of the present invention will be clarified by comparing it with comparative steel and conventional steel. Table 1 shows the chemical composition of the test steel.

[0019]

[Table 1]

In Table 1, Steels 1 to 12 are steels of the present invention, Steels 1 to 6 are steels of the first invention, and Steels 7 to 12 are steels of the second invention. Further, Steels 13 to 17 are comparison steels, and Steel 18 is SWOSC-V, which is a conventional steel.

[0021] Using steel with the composition shown in Table 1, after quenching and tempering, it was made into a 10 x 15.7 x 6.3 mm
A wear test piece and a 30 x 30 x 5 mm scuff test piece were prepared. After that, a wear test was performed by the method shown below.
A scuff test was conducted to evaluate suitability as steel for piston rings. In addition, a tension decay test was also conducted to evaluate heat resistance. Regarding the conventional steel No. 18 steel, both those subjected to hard Cr plating treatment and those not subjected to hard Cr plating treatment were evaluated for performance comparison.

In the wear test, FC25, which is cast iron for cylinder liners, was used as the mating material, and the friction speed was 1 m/sec.
1 engine oil under the condition of surface pressure 100kgf/mm2
．． The testing was carried out by operating the test machine for 8 hours while supplying 5 cc/min. After the test, the amount of wear on the sliding surface was measured and the wear resistance was evaluated. For the scuff test, the surface pressure is 40
The test was carried out by increasing the temperature from kgf/mm2 by 5 kgf/mm2 every 3 minutes. Then, the surface pressure at which the friction coefficient suddenly increased was recorded as the surface pressure at which seizure occurred, and the scuff resistance was evaluated. The tension reduction test was conducted using a 80 mm x 1.
Manufacture 3mm x 3.2mm piston rings, J
The method and conditions (heating temperature: 300°C, heating time: 1 hour) specified in IS B 8032 "Piston Rings" were used. The test results are shown in Table 2.

[0023]

[Table 2]

As is clear from Table 2, when comparative steels and conventional steels 13 to 18 are compared with the steel of the present invention, steel 13 has a
Due to the low C content, the wear amount is 7.8 μm, the surface pressure at which seizure occurs is 80 kgf/mm2, and the degree of tension reduction is 2.8%, and the wear resistance, scuff resistance, and heat resistance are all inferior. 14 steel has a low Si content, so the degree of tension reduction is 2.
．． 3%, and has poor heat resistance.15,16
, 17 steel has a low content of V, Nb, and Mo, which form carbonitrides, so the wear amount is 9.9 to 10.8μ.
m, the surface pressure at which seizure occurs is 80 to 95 kgf/mm, the degree of tension reduction is 2.6 to 2.8%, and the wear resistance, scuff resistance, and heat resistance are poor. In addition, conventional steel SWOS
C-V 18 steel has a lower Si content than the steel of the present invention and does not contain any V, Nb, or Mo, so the wear amount is 12.6 μm without hard Cr plating treatment, and the resistance is low. The abrasion resistance is extremely poor, and the degree of tension reduction is as high as 2.6 to 2.8% regardless of the presence or absence of hard Cr plating treatment, and the heat resistance is poor.

On the other hand, Steels 1 to 12, which are the steels of the present invention, have an increased amount of Si compared to SWOSC-V to further strengthen the solid solution strengthening by Si, and contain V, Nb, and Mo to improve the strength after heat treatment. As a result of uniformly dispersing carbonitrides and aiming for precipitation strengthening, the wear amount was 4.4 to 5.4 μm, the surface pressure at which seizure occurred was 105 to 115 kgf/mm2, and the degree of tension reduction was 0.9 to 1.3%. It has wear resistance equivalent to that of the hard Cr-plated material of SWOSC-V, less loss of tension, and excellent scuff resistance.

In addition, by increasing the amount of inexpensive Si and adding small amounts of V, Nb, and Mo of 0.5% or less, it became possible to omit the hard Cr plating process, and as a result
It is cheaper and SW than the steel described in the 114553 publication.
It has now become possible to manufacture a steel for piston rings that is suitable as a material to replace OSC-V.

[0027]

Effects of the Invention The alloy steel for piston rings of the present invention can be applied to SWOSC, which has been conventionally used for piston rings.
Hard C applied to ensure the wear resistance necessary for V
This material is suitable for piston rings because it allows the omission of r-plating and has excellent heat resistance and scuff resistance. In addition, although only the case where hard Cr plating treatment was not performed was described in the Example of this invention, it is of course possible to obtain even more excellent wear resistance if hard Cr plating treatment is performed. Therefore, it is possible to manufacture piston rings at a lower cost than before, greatly contributing to the realization of lighter weight and higher output of internal combustion engines, and the industrial contribution is extremely large.

Claims (2)

[Claims] [Claim 1] C: 0.50 to 0.80 in terms of weight ratio
%, Si: 1.50 to 2.50%, Mn: 0.5
Contains 0 to 1.50%, and further contains V: 0.05 to 0.
．． 50%, Nb: 0.05 to 0.50%, Mo:
An alloy steel for piston rings, characterized in that it contains one or more of 0.05 to 0.50%, with the remainder consisting of Fe and impurity elements. [Claim 2] C: 0.50 to 0.80 in terms of weight ratio
%, Si: 1.50 to 2.50%, Mn: 0.5
0 ~ 1.50% and Cr: 0.20 ~ 1.50%
Contains V: 0.05-0.50%, Nb:
0.05 to 0.50%, Mo: 0.05 to 0.5
Contains one or more of 0% and the remainder is Fe.
and an impurity element.