JP4307329B2 - Piston ring wire and piston ring - Google Patents

Description

  The present invention relates to a wire for a piston ring used in an internal combustion engine, a compressor, etc., a method for manufacturing the same, and a piston ring, particularly when ion plating is performed to improve sliding characteristics such as wear resistance. The present invention relates to a piston ring wire and a piston ring which are suitable and have excellent heat resistance.

  Previously, the main material for piston rings used in internal combustion engines was cast iron, but Si-Cr steel and martensite, which can provide higher strength than cast iron for higher output and higher rotation of internal combustion engines. Site-based stainless steel has come to be used. However, since these piston ring materials are not sufficient in wear resistance, seizure resistance, and the like, the outer peripheral surface is subjected to surface treatment. Normally, Si-Cr steel is hard Cr plated, martensitic stainless steel is nitrided, and for internal combustion engines that require sliding properties, the outer peripheral surface is hard ceramic coated by ion plating. Piston rings to which (chromium nitride or the like) has been applied have come to be used.

  During the ion plating process, the material is heated to 200 to 600 ° C. And since it is so that adhesiveness and productivity are so good that it coats at high temperature, it is preferable to coat as high temperature as possible. However, steel materials with low high-temperature strength and temper softening resistance are softened by the ion plating process and cause heat settling, so that a piston ring having a predetermined tension cannot be obtained.

  Therefore, Patent Document 1 proposes a piston ring for improving heat sag that becomes a problem when ion plating is performed. Patent Document 1 adds an appropriate amount of Mo or Cr that is effective in improving heat resistance as a composition of the piston ring, and prevents the effect of improving the heat resistance of Mo and Cr from being reduced by the formation of carbides. Compared to conventional martensitic stainless steel for piston rings, it is reduced to 0.35 to 0.45%.

Patent Document 2 proposes a steel for a piston ring having a C—Si—Mn—Cr—Mo—V-based composition as steel for improving the heat sagability.
Japanese Patent Laid-Open No. 11-294584 JP 2002-348639 A

  However, in the invention disclosed in Patent Document 1, in order to improve heat sagability, C content is reduced to other martensite for piston rings in order to suppress the formation of carbides of Mo and Cr which are heat resistance improving elements. Compared to stainless steel. Therefore, as a natural result, there is a problem that there are few carbides in the steel and the wear resistance after nitriding is not sufficient.

  In general, when the ion plating process is performed, the temperature rises to about 600 ° C. during the process, and the softening of the material proceeds, which appears as a heat sink. Therefore, evaluation of heat settling is performed by measuring how much the hardness of the material changes by holding at a temperature of 600 ° C., which is comparable to the maximum temperature rising during the ion plating process, for 1 hour. ing. It can be said that the smaller the amount of change in hardness due to heating, the better the heat resistance. Usually, since the hardness often decreases due to heating, it can be determined that the higher the hardness after heating to 600 ° C., the better the heat sagability. However, the piston ring manufactured with the steel disclosed in Patent Document 2 has a hardness (HV) after heat treatment at 600 ° C. × 1 hour of about 401 to 439 and has sufficient hardness. It cannot be said, and it is not a satisfactory level with respect to heat resistance. This is because it is preferable that the piston ring for an internal combustion engine has a Vickers hardness of about 500 or more in order to sufficiently withstand practical use. It is not practical.

The present invention has been made in view of such problems of the prior art, and its purpose is to have sufficient strength and hardness, and greatly improve the heat sag during ion plating treatment. The object is to provide an improved wire for a piston ring. Moreover, the objective of this invention is providing the piston ring using such a wire .

  In order to achieve the above object, the piston ring wire of the present invention has C of 0.10% by weight or less, Si of 0.50% by weight or less, Mn of 5.00 to 7.00% by weight, and P of 0. 0.045% by weight or less, S is 0.010% by weight or less, Ni is 9.00 to 11.00% by weight, Cr is 21.00 to 25.00% by weight, and N is 0.40 to 0.55% by weight. , Mo is 1.75 to 2.25 wt%, Cu is 0.75 wt% or less, and the balance is composed of Fe and inevitable impurities.

  In the present invention, since a larger amount of nitrogen is added than usual, the strength is improved by precipitation hardening with nitride (for example, Cr nitride) or strain aging with solid solution nitrogen.

  That is, when a material having this composition is subjected to a solution heat treatment, the solute element in the Fe matrix is in a supersaturated solid solution state. Next, when a precipitation hardening heat treatment is performed at an appropriate temperature after cold working, precipitates are generated. As the precipitate is finely dispersed in the matrix, the strength is improved. The method of finely dispersing precipitates is to increase the number of precipitation sites. However, when lattice defects are increased by cold working, the defects can become precipitation sites. In the present invention, since a larger amount of nitrogen is added than usual, after performing cold working, a precipitation hardening heat treatment is performed, so that fine nitrides (for example, N and bonding force of N and bonding strength) are formed in the grain boundaries and grains. It is considered that a large number of strong Cr nitrides, etc. are precipitated. The strength is greatly improved by precipitation hardening by nitride and strain aging by solute nitrogen. As a result, the heat settling property is remarkably improved.

  Since the strength of the piston ring wire and piston ring of the present invention is greatly improved as described above, the hardness does not decrease even when exposed to high temperatures during the ion plating process, and the heat sagability is greatly improved. To be improved.

  The reasons for limiting the numerical value of each element constituting the piston ring wire of the present invention are as follows.

  (1) C is 0.10% by weight or less.

    C is an interstitial solid solution element that contributes to the improvement of strength and has the effect of improving the heat resistance by combining with Cr and Mo described later to produce carbides. In order to obtain such an effect, addition of 0.001% by weight or more is preferable. More preferably, it is 0.005% by weight or more. On the other hand, adding a large amount not only reduces the solid solution amount of N, but also produces coarse primary carbides, reduces cold workability after solution heat treatment, and fatigue after cold work and precipitation hardening heat treatment. Reduce strength. Therefore, the upper limit is 0.10% by weight, preferably 0.05% by weight or less.

  (2) Si is 0.50% by weight or less.

    Si is an element added as a deoxidizer during the melting of steel. In order to obtain such an effect, addition of 0.01% by weight or more is preferable. More preferably, it is 0.05 weight% or more. On the other hand, when added in a large amount, not only the cold workability is lowered, but also the toughness and ductility are remarkably lowered and it is harmful to the hot workability. Therefore, the upper limit is 0.50% by weight, preferably 0.40% by weight or less.

  (3) Mn is 5.00 to 7.00% by weight.

  Mn is an austenite-forming element and an element that remarkably increases the solid solution amount of nitrogen, and thus is an important element contributing to strength improvement. Furthermore, it is also effective as a deoxidizing and desulfurizing element when melting steel. In order to obtain such an effect, it is necessary to add 5.00% by weight or more. Preferably it is 5.50% by weight or more. On the other hand, adding a large amount not only lowers hot workability but also degrades corrosion resistance. Therefore, the upper limit is 7.00% by weight, preferably 6.50% by weight or less.

  (4) P is 0.045% by weight or less.

      P is preferably as low as possible since it lowers impact resistance, and its upper limit is set to 0.045% by weight. Note that a reduction more than necessary causes an increase in cost.

  (5) S is not more than 0.010% by weight.

      S lowers corrosion resistance, cold workability, and hot workability, so it is preferably as low as possible, and its upper limit is set to 0.010% by weight. Note that a reduction more than necessary causes an increase in cost.

  (6) Ni is 9.00 to 11.00% by weight.

  Ni contributes to stabilization of the austenite phase and to improvement of high temperature strength. In order to obtain such an effect, it is necessary to add 9.00% by weight or more. Preferably, the content is 9.20% by weight or more. On the other hand, adding a large amount not only causes an increase in cost, but also reduces the amount of solid solution nitrogen, and at the same time, increases the solid solution temperature of Cr nitride, so that undissolved Cr nitride at the time of solution treatment is added. Since it increases, high temperature strength, cold workability, and toughness are significantly reduced. Therefore, the upper limit is 11.00% by weight, preferably 10.80% by weight or less.

  (7) Cr is 21.0 to 25.00% by weight.

  Cr significantly increases the amount of N solid solution and contributes to improvement in strength. Moreover, it contributes to the improvement of corrosion resistance and oxidation resistance, and contributes greatly to the improvement of high temperature strength and fatigue strength by combining with C and N by precipitation hardening heat treatment after cold working. In order to obtain such an effect, it is necessary to add 21.00% by weight or more. Preferably, it is 22.00% by weight or more. On the other hand, when added in a large amount, since it is a ferrite-forming element, not only the austenite phase becomes unstable, but also the precipitation of the σ phase that causes a decrease in toughness is promoted. Therefore, the upper limit is set to 25.00% by weight, and preferably 24.00% by weight or less.

  (8) N is 0.40 to 0.55% by weight.

  N is an interstitial solid solution element and is an important element effective for improving strength, stabilizing austenite phase, improving corrosion resistance, and further improving high-temperature strength by precipitation hardening heat treatment after cold working. . In order to obtain such an effect, addition of 0.40% by weight or more is necessary. Preferably it is 0.42 weight% or more. On the other hand, the addition of a large amount induces the formation of nitrogen blow. In addition, cold workability and toughness are significantly reduced due to the remaining of the insoluble Cr nitride in the steel during the solution treatment. Therefore, the upper limit is 0.55% by weight.

  (9) Mo is 1.75 to 2.25% by weight.

  Mo is an element that increases the solid solution amount of nitrogen and contributes to the improvement of corrosion resistance, and further improves the high-temperature strength as a solid solution strengthening element. In addition, similarly to Cr, it combines with C to form a carbide, and improves heat resistance. In order to obtain such an effect, it is necessary to add 1.75% by weight or more. Preferably, it is 1.85% by weight or more. On the other hand, if added in a large amount, cold workability and toughness are remarkably reduced due to the formation of coarse primary carbides. It also degrades oxidation resistance and is harmful during hot working. Therefore, the upper limit value is 2.25% by weight, preferably 2.15% by weight or less.

 (10) Cu is 0.75 wt% or less.

  Cu is an austenite-forming element and contributes to the stabilization of the austenite phase and to the improvement of corrosion resistance. It also contributes to improved toughness during cold working. In order to obtain such an effect, addition of 0.01% by weight or more is preferable. More preferably, the content is 0.02% by weight or more. On the other hand, adding a large amount not only reduces the amount of dissolved nitrogen but also degrades hot workability. Further, since the solid solution temperature of Cr nitride is increased, undissolved Cr nitride remains in the steel during the solution treatment, and the high temperature strength, cold workability and toughness are significantly reduced. Therefore, the upper limit is 0.75 weight, preferably 0.65 weight% or less.

  In addition, although Al is effective as a deoxidizing element, it is characterized by the maximum solid solution of N. Therefore, excessive addition significantly reduces the high-temperature strength and toughness due to the formation of AlN. Is preferred.

  Further, as a solid solution strengthening element, W may be contained at 1.0% by weight or less and Co may be contained at 1.0% by weight or less.

  In addition, Ti, Nb, or V can be contained in an amount of 0.50% by weight or less in order to combine with C or N to improve high-temperature strength or refine crystal grains.

  Further, in order to improve the high-temperature strength or the grain boundary strength, B may be contained in an amount of 0.010% by weight or less and Zr in an amount of 0.10% by weight or less.

  Furthermore, in order to improve the hot workability, Mg or Ca may be contained in an amount of 0.010% by weight or less.

  In the present invention, since a larger amount of nitrogen is added than usual, the strength is improved by precipitation hardening with nitride (such as Cr nitride) or strain aging with solute nitrogen, as will be described below.

  That is, when the material having the above composition is subjected to a solution heat treatment, the solute element in the Fe matrix is in a supersaturated solid solution state. The solution heat treatment temperature is not particularly limited as long as the solution is completely dissolved at a temperature equal to or higher than the solubility curve, and is maintained at a temperature of 1000 to 1200 ° C. for a predetermined time (about 30 minutes), and then water-cooled. be able to.

  Next, when a precipitation hardening heat treatment is performed at an appropriate temperature after cold working, precipitates are generated. As the precipitate is finely dispersed in the matrix, the strength is improved. The method of finely dispersing precipitates is to increase the number of precipitation sites. However, when lattice defects are increased by cold working, the defects can become precipitation sites. In the present invention, since a larger amount of nitrogen is added than usual, after performing cold working, a precipitation hardening heat treatment is performed, so that fine nitrides (for example, N and bonding force of N and bonding strength) are formed in the grain boundaries and grains. It is considered that a large number of strong Cr nitrides, etc. are precipitated. The strength is greatly improved by the precipitation hardening by the nitride and the strain aging by the solute nitrogen, so that the heat settling property is remarkably improved. As precipitation hardening heat processing, the heat processing process hold | maintained for 10 to 30 minutes at 500-675 degreeC is preferable. A heat treatment of less than 500 ° C. and / or less than 10 minutes is insufficient for precipitation hardening, and a heat treatment exceeding 675 ° C. and / or more than 30 minutes is not preferable because the strength decreases.

  Examples of the present invention will be described below in the order of production steps, but the present invention is not limited to the following examples, and can be appropriately changed and modified without departing from the technical scope of the present invention.

(1) Dissolution and Solution Heat Treatment A material having a composition (% by weight) as shown in Table 1 below was melted, hot forged, hot rolled, and rolled to a wire diameter of 5.2 mm.

  Next, the material was held at 1050 ° C. for 10 minutes (hydrogen gas atmosphere), then cooled with water, and then drawn into a wire having a wire diameter of 2.0 mm.

(2) Rolling of rectangular cross section The wire was rolled into a rectangular cross section having a width of 2.3 mm and a height of 1.0 mm (cross-sectional reduction rate of 73%).

(3) Heat treatment conditions and mechanical property values The above-described rectangular cross-section rolled material was subjected to the following heat treatments.
(a) The rolled rectangular section material was heated to a temperature in the range of 550 to 800 ° C., held at each temperature for 10 minutes, and then cooled to room temperature (hydrogen gas atmosphere).

  The relationship between the heat treatment temperature and the tensile strength at this time is shown in FIG. 1, the relationship between the heat treatment temperature and the surface layer hardness (HV10) is shown in FIG. 2, and the relationship between the heat treatment temperature and the cross-sectional hardness (HV0.5) is shown in FIG. .

  In addition, Table 2 shows the actual tensile strength, surface layer hardness, and cross-sectional hardness values of the points shown in FIGS. In addition, surface layer hardness means the average value which measured the hardness in the surface (the code | symbol x reference of FIG. 4, the space | interval of the longitudinal direction of an adjacent x mark is 2 cm) in five places of the longitudinal direction of a rectangular cross-section material, Cross-sectional hardness means the average value which measured the hardness in the surface and center part (5 places, the code | symbol x reference of FIG. 5) in five places of the longitudinal direction of a rectangular cross-section material.

As is apparent from FIGS. 1 to 3 and Table 2, by performing a heat treatment held at 500 to 675 ° C. for 10 minutes, the Vickers hardness (HV 0.5 and HV 10) is 500 HV or more and the tensile strength is more than 1800 MPa or more. It can be seen that a material with high hardness and ultra-high strength can be obtained.
(b) The rolled material having a rectangular cross section was heated to various temperatures described below and then cooled to room temperature (hydrogen gas atmosphere).

Heat treatment A = raised to 550 ° C and held for 10 minutes, then raised to 675 ° C and held for 10 minutes Heat treatment B = raised to 550 ° C and held for 5 minutes, then raised to 675 ° C and held for 5 minutes Heat treatment C = Temperature rise to 650 ° C. and hold for 20 minutes Heat treatment D = Temperature rise to 675 ° C., hold for 10 minutes, then drop to 550 ° C. and hold for 10 minutes Heat treatment E = Temperature rise to 675 ° C. and hold for 5 minutes, then 550 ° C. The temperature is lowered to 5 minutes and the heat treatment is heated to F = 550 ° C., held for 10 minutes, then heated to 800 ° C. and held for 5 minutes. The heat treatment G is raised to 550 ° C. and held for 10 minutes, and then heated to 800 ° C. And held for 10 minutes Table 3 shows the values of tensile strength, surface layer hardness, and cross-sectional hardness after each of the above heat treatments.

As is apparent from Table 3, by performing heat treatment A, B, C, D or E, a material having an ultra-high hardness and an ultra-high strength having a Vickers hardness of 500 HV or more and a tensile strength of 1800 MPa or more can be obtained. I understand.
(c) Change in hardness before and after heating at 600 ° C. for 1 hour The above-mentioned rolled material having a rectangular cross section was heat-treated under the conditions shown in Table 5 and coiled to an outer diameter of 70 mm, and after coiling, a piston as shown in FIG. Table 5 shows the change in cross-sectional hardness before and after heat treatment at 600 ° C. × 1 hour when the ring 1 was cut, then heated to 600 ° C. and held for 1 hour and then cooled to room temperature (atmosphere in air).

  For comparison, the material having the composition (% by weight) shown in Table 4 was also coiled so that a rolled material having a rectangular cross-section was obtained in the same process and heat treated under the conditions shown in Table 5 to an outer diameter of 70 mm. Then, after coiling, it is cut into the shape of the piston ring 1 as shown in FIG. 6, then heated to 600 ° C., held for 1 hour and then cooled to room temperature (atmosphere in air), 600 ° C. × 1 hour Table 5 also shows changes in cross-sectional hardness before and after heat treatment.

  As is apparent from Table 5, the piston ring of the present invention hardly changes in hardness compared to before heating even when heated to 600 ° C. and held for 1 hour, and the amount of change in hardness due to heating at 600 ° C. It turns out to be small enough to be ignored. Moreover, the minimum value of the hardness after heat treatment at 600 ° C. × 1 hour is 495 HV as Vickers hardness HV (0.5), which shows that the hardness is extremely high. In addition, since the temperature of the material may rise up to about 600 ° C. during the ion plating process, a simple evaluation of heat settling is performed by holding the material at a temperature of 600 ° C. for 1 hour. However, the actual heating conditions during the ion plating process are often performed under more severe conditions of 550 ° C. for 4 hours. Therefore, in Examples 1, 2, and 3 of Table 5, when heat treatment at 550 ° C. × 4 hours is further performed after heat treatment at 600 ° C. × 1 hour, the cross sections of Example 1, Example 2, and Example 3, respectively. The hardness (HV0.5) was 514HV, 497HV, 496HV, and it was found that the amount of change in hardness was negligible even after heat treatment at 550 ° C x 4 hours.

  However, the piston rings of Comparative Examples 1 to 3 having C as the main strength-improving contributing element are significantly reduced in hardness by heat treatment at 600 ° C. × 1 hour, and the hardness before heating to 600 ° C. is sufficiently high. It can not be said.

It is a figure which shows the relationship between heat processing temperature and tensile strength. It is a figure which shows the relationship between heat processing temperature and surface layer hardness. It is a figure which shows the relationship between heat processing temperature and cross-sectional hardness. It is a figure explaining the measurement position of surface layer hardness. It is a figure explaining the measurement position of cross-sectional hardness. It is a perspective view of a piston ring.

Explanation of symbols

    1 Piston ring

Claims (2)

  C is 0.10% by weight or less, Si is 0.50% by weight or less, Mn is 5.00 to 7.00% by weight, P is 0.045% by weight or less, S is 0.010% by weight or less, Ni is 9.00 to 11.00% by weight, Cr 21.00 to 25.00% by weight, N 0.40 to 0.55% by weight, Mo 1.75 to 2.25% by weight, Cu 0.0. A material having a composition of 75% by weight or less and the balance consisting of Fe and inevitable impurities is subjected to a solution heat treatment at 1000 to 1200 ° C., followed by cold working, and then a precipitation hardening heat treatment at 500 to 675 ° C. for 10 to 30 minutes. Piston ring wire obtained by applying A piston ring using the wire according to claim 1 .

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