WO2002006546A1

WO2002006546A1 - Piston ring excellent in resistance to scuffing, cracking and fatigue and method for producing the same, and combination of piston ring and cylinder block

Info

Publication number: WO2002006546A1
Application number: PCT/JP2001/006127
Authority: WO
Inventors: Junya Takahashi; Toru Onuki; Shigeo Inoue; Mitsutaka Sasakura
Original assignee: Kabushiki Kaisha Riken; Tokusen Kogyo Company Limited
Priority date: 2000-07-17
Filing date: 2001-07-16
Publication date: 2002-01-24
Also published as: US20070187002A1; BR0112573A; US20040040631A1; EP1304393A4; DE60122164T2; JP2002030394A; KR20030025275A; EP1304393B1; JP4724275B2; BR0112573B1; DE60122164D1; EP1304393A1; TW521093B; AR029730A1; KR100507424B1; CN1210427C; CN1458983A

Abstract

A piston ring comprised of a high chromium martensitic stainless steel having a nitrided layer on the surface thereof, characterized in that the stainless steel has a chemical composition, in wt %: C: 0.3 to 1.0 %, Cr: 14.0 to 21.0, N: 0.05 to 0.50, the total of one or more of Mo, V, W and Nb: 0.03 to 3.0, Si: 0.1 to 1.0 %, Mn: 0.1 to 1.0 %, P: 0.05 % or less, S: 0.05 % or less, and balance: Fe and inevitable impurities, and the sliding nitrided layer has hard particles mainly comprising nitrides which have an average diameter of 0.2 to 2 µm and a maximum diameter of 7 µm or less and are dispersed on the surface thereof with an area percentage of 5 to 30 %. The high chromium martensitic stainless steel exhibits improved resistance to scuffing, cracking and fatigue.

Description

Description: A stainless steel ring having excellent anti-scratching, cracking and fatigue resistance and a method of manufacturing the same, and a combination of a steel ring and a cylinder block. Matching

Technical field

The present invention relates to a bis-ring used in an internal combustion engine, and particularly to a scuffing resistance (seizure resistance), a cracking resistance (breakage resistance) and a fatigue resistance. The present invention relates to an excellent high chrome martensitic stainless steel-made bis-nitride ring and a method for producing the same. Background art

In recent years, internal combustion engines have been required to have low fuel consumption, light weight, and high performance. Therefore, even in the case of the bis-ring, it has been required to withstand the thinning of the bis-ring due to the weight reduction and high rotation. Improvements in properties such as abrasion resistance, scuffing resistance, and fatigue resistance are required.In particular, from the viewpoint of fatigue resistance and heat resistance, the conventional steel-made steel ring is replaced with a steel-made steel ring. Has been replaced by Since the steel piston ring is inferior to the anti-scratching property compared to the steel piston ring, the sliding surface is usually provided with some surface treatment. Depending on the type of surface treatment to be combined, steel materials for piston rings are broadly classified into carbon steel, silicon chrome steel, and martensitic stainless steel. Chromium is applied to steel and silicon chromium steel, while gas nitriding is applied to martensite stainless steel. In conventional steel piston rings, chrome plating was almost the only force applied.S, problems with scuffing of the plating layer under high load, and wastewater treatment Due to environmental issues, bis-nitride rings have become the mainstream in recent years. In high chromium manure stainless steel, C: 0.80-0.95%, Cr: 17.0-18.0%, Si: 0.25-0.50%, Mn: 0.25-0.40%, Mo: 0.70-1.25% , V: 0.07-0.15%, Fe: Remaining composition, JIS SUS440B equivalent material is the main steel type used for bis-nitride ring. When nitriding is performed on steel having this composition, nitrogen atoms penetrate into the steel from the surface and diffuse to form a nitrided layer. The nitride in the nitride layer is mainly a compound with Cr, V, and Mo, or a compound thereof with Fe as a solid solution. In particular, Cr, which is contained abundantly in steel, dissolves in the matrix and exists as Cr carbide.However, it has a greater affinity for nitrogen than carbon, so it can be used for nitriding. Nitrogen diffused from the surface and the Cr carbide react to form Cr nitride. Since SUS440B has a high Cr content of 17.0-18.0%, a relatively hard nitrided layer in which hard Cr nitrides are dispersed at an appropriate area ratio is obtained for the above-mentioned reasons, and excellent wear resistance is obtained. Shows resistance and anti-scratching properties.

Recently, as a martensitic stainless nitrided steel for piston rings, Japanese Patent Application Laid-Open No. H11-80907 discloses that although Cr is slightly lower than 5.0 and less than 12.0%, Si: 0.25% and Mn: Excellent by containing 0.30% or less, one or more of Mo, W, V, Nb: 0.3-2.5%, or Cu: 4.0% or less, Ni: 2.0% or less, ΑΙ: 1.5% or less and this the anti ska Zuph fin grayed resistance is obtained, by the this to the Japanese Patent Laid-Open No. 11-106874, to 4.0% and the content of M ₇ C ₃ type carbide that exists in the tissue area% It is disclosed that a bistable ring material having excellent workability in addition to squatting resistance can be obtained.

However, bis-nitride rings exhibiting such excellent wear resistance and anti-scratching properties are also required for high-speed, high-output, high-load internal combustion engines. Raising is causing problems. In particular, in recent diesel engines, the conventional liner has been changed from the press-fitting method to the cylinder opening to the iron monoblock method with a narrow pore space from the viewpoint of weight reduction and cost reduction. In the direction There is also a trend to increase the combustion pressure from the viewpoint of exhaust gas purification and high output.では In the iron monoblock, the microstructure of the sliding surface with the biston ring has a large variation in the dispersion state of graphite due to the non-uniform cooling rate, and causes the scattering. The soft ferrite phase is unevenly distributed. When one side of the cylinder having such a microstructure is combined with a martensite stainless steel bis-nitride ring, scuffing is performed at the beginning of operation. I get up. The cause is as follows. In other words, honing the cylinder surface tends to cause clogging of the grindstone due to unevenly distributed ferrite, which tends to increase the roughness of the cylinder surface after honing, and that the graphite plastically flows. As a result, the area ratio of graphite is reduced and the lubrication and oil reservoir functions of graphite are reduced, and when the combustion pressure is high, the back pressure applied to the bis-ring is reduced. Will also increase. This scattering is often caused by the occurrence of a crack perpendicular to the sliding direction of the outer periphery of the piston ring. It is observed along a relatively coarse layered grain boundary compound (also referred to by those skilled in the art as a seagull phase) which is almost parallel to the surface formed at the crystal grain boundary of the nitride layer on the ring sliding surface. .

These problems have been addressed by surface treatment of TiN, CrN, etc. by ion plating, which is more excellent in abrasion resistance and scuffing resistance. The cost of production is higher than the cost. In fact, users are not satisfied with the performance.

Therefore, the purpose of the present invention is to use an internal combustion engine with a high rotation speed and a high combustion pressure and a high load, especially a diesel engine employing a lightweight steel monoblock that is expected to increase in the future. Bi-stone ring made of high chrome martensitic stainless steel, which does not cause abrasion, scuffing, cracking, and fatigue breakage, and has excellent cost performance. Its purpose is to provide a manufacturing method thereof. Disclosure of the invention

"Piston Rings for Automobiles" According to the Editorial Committee for Automobile Piston Rings, Sankaido, p. 188, 1997, the scuffing of piston rings is based on sliding surfaces. It is explained that concentrated loads are applied to the microscopic projections and projections (particularly the projections of the soft phase), and the temperature rises due to frictional heat, causing abnormal softening and melting.

The structure of the nitrided layer in the high chrome martensite stainless steel is generally tempered and has a form in which hard nitrides are mainly dispersed in the matrix of the martensite. Scuffing is based on its mechanical force, microscopic irregularities on the sliding surface, that is, the size of the hard particles dispersed in the relatively soft matrix. Strongly related to dispersion. When observing the cross section of the surface layer having such a structure, the convex hard particles come into contact with the sliding surface of the mating member, and the relatively soft matrix becomes relatively concave. I have. Therefore, the probability of the nitrided steel coming into direct contact with the counterpart material is reduced, and a lubricating oil film is formed in the recess, and pressure is generated in the oil film during sliding, thereby reducing the contact pressure. The lubrication of the convex contact portion can be prevented to prevent the occurrence of scuffing. In order to achieve the effect as convex hard particles by such a mechanism, a particle size of submicron to several micron size is required, and the dispersion amount is 5% in area ratio. % Is desirable. If the hard particles are extremely small or the amount of dispersion is small, the mechanism due to the effect of the convex hard particles cannot be expected.

This anti-scratch mechanism depends on the condition of the sliding surface of the mating material. In a steel iron monobloc with an inhomogeneous structure as described above, the surface roughness of the entire surface of the cylinder is likely to be roughened by grinding, and the plastic flow of the ferrite phase Is often blocked by graphite. Such iron is also suitable for sliding It is also “familiar” among traders. ) Causes the following phenomena. Immediately, the rough inner surface of the cylinder is smoothed and the graphite that has been blocked by the ferrite phase is opened. Until the break-in is completed, the oil film on the sliding surface tends to break, and a large frictional force is repeatedly applied to the outer peripheral surface of the piston ring. For this reason, cracks are generated in the nitride layer on the outer peripheral surface of the piston ring in the direction perpendicular to the sliding direction due to the repetitive stress caused by frictional force, and expand. The stress applied along with the progress of the inner circumferential surface of the cylinder is reduced, but the cracks develop over time and local surface peeling or chipping, and furthermore, The inner surface of the underlayer is damaged and causes scuffing. The grain boundary compounds present in the nitrided layer are very brittle and promote the generation and propagation of cracks. Therefore, in order to prevent such initial scattering, hard particles composed of Cr nitride as the main part of the nitrided layer are dispersed in an appropriate size and uniformity, and a large number of particles are dispersed. This reduces the contact probability between the matrix and the cylinder, and in particular reduces the size of the grain boundary compounds generated by the nitriding treatment to reduce the The present inventors have found that it is indispensable to suppress the generation of cracks and to prevent the spread of cracks even if they occur.

In high chrome martensitic stainless steel, eutectic Cr carbide (phase: (Cr, Fe) ₇ C ₃ ) becomes primary austenite (γ phase) when the molten steel solidifies. Crystallizes at grain boundaries. Even after hot rolling, spheroidizing heat treatment, and final quenching and tempering heat treatment, Cr carbides with a maximum diameter exceeding 20 μπι are observed. The refinement of this coarse primary eutectic carbide is achieved by adding at least 0.25% of nitrogen (N) to iron and steel, Vol. 82, No. 4, pp. 309-314 (1996). Thus, it has been reported that a fine Cr carbide structure can be obtained. According to the report, the eutectic Cr carbides at the primary y grain boundaries disappeared, and instead, lamellar M ₂₃ C ₆ and M ₂ N (M: Cr, Fe) were replaced by primary _γ grain boundaries. Around the surface and these lamellar forms M ₂₃ C ₆ and M ₂ N is divided into fine fine hot rolling, order to newly deposited in different sites fine M ₂₃ C ₆ is an M ₂ N in the subsequent spheroidizing annealing, and overall It is described that a fine Cr carbide structure results. Heat treatment, Vol. 36, No. 4, p. 234-238 (1996) also shows that the mechanical properties of 16.5% Cr-0.65% C martensitic stainless steel with 0.25% Ν added It has been reported that as the amount of N added increases, the temperature at which the maximum quench hardness increases shifts to the lower temperature side and the ductility increases.The reason is that the higher the quench temperature, the higher the quench temperature. It is explained that the amount of N dissolved in the austenite phase increases and the austenite phase stabilizes.

Japanese Patent Application Laid-Open Nos. 9-289053 and 9-287058 disclose rolling bearings utilizing the technique of refining Cr carbide by adding N.

The present inventors have considered the mechanism of the above-mentioned scuffing, and found that the crack formed on the surface formed at the crystal grain boundary of the nitrided layer on the piston ring sliding surface is observed. As a result of intensive research on the refinement technology of Cr carbide by adding N for the substantially parallel and relatively coarse layered grain boundary compound, there is a large number of fine nitrides in the nitride layer. By making the microstructure such that the layered grain boundary compound in the inside becomes fine, high-speed, high-output, high-combustion-pressure internal combustion engines, especially recent lightweight steel monobloc diesel engines Even when used in such applications as high-chromium martensitic stainless steel bis-nitride rings, which are excellent in wear resistance, scuffing resistance, cracking resistance, and fatigue resistance. What you can get And found.

That is, the nitrided piston ring made of high chrome martensitic stainless steel according to the present invention has a weight of ⁰ / chrome martensitic stainless steel. C: 0.3-1.0%, Cr: 14.0-21.0%, N: 0.05-0.50%, Mo-, V-, W-, Nb-0.03-3.0%, total of at least one or more types, Si: 0.1-1.0 %, Mn: 0.1-1.0%, P: 0.05% or less, S: 0.05% or less, with the balance Fe and Hard particles of nitrides, carbides, and carbonitrides mainly consisting of nitrides on the surface of the sliding nitride layer consist of unavoidable impurities and have an average diameter of 0.5-2 m and a maximum diameter of 7 mm. It is characterized in that it is less than μπι and the area ratio is in the range of 5-30%. Further, the size (length) of the grain boundary compound observed at the cross section of the nitride layer in the longitudinal direction of the piston ring is at most 20 or less. Further, the hardness of the nitrided sliding surface having the above-mentioned structural characteristics is such that the Vickers hardness is in the range of 900-1400, and the depth of the nitrided layer is sufficient from the surface subjected to the nitriding treatment. It is characterized by having a thickness.

In the method for producing a high-chromium martensitic stainless steel-made bis-nitride ring according to the present invention, first, a steel having a predetermined composition is melted, nitrogen is added, and the ingot is manufactured. Then, hot rolling, annealing, cold drawing, and cold rolling are performed to approximate the predetermined cross section of the steel ring, and quenching and tempering are performed to obtain a wire. The wire is bent into a ring shape and subjected to strain relief heat treatment, side surface rough grinding, nitriding, removal of the surface compound layer, grinding between the abutment, side finish grinding, outer wrapping, etc. However, in the quenching process before bending the steel into the stainless steel ring, a relatively high chrome martensitic stainless steel temperature of 850-1000 ° C is relatively low. By quenching from a low temperature, a fine, microstructured material with as much carbide as possible is obtained. Gas nitriding, ion nitriding, or radical nitriding can be used for nitriding, and all are performed at 450-600 ° C for 1-20 hours.

Hereinafter, the present invention will be described in detail. To explain the components of the high-chrome martensitic stainless steel of the present invention, first, C forms a solid solution in Fe to increase the hardness of the matrix, It easily combines with Cr, Mo, V, W, and Nb to form carbides. Carbides by connexion nitride layer during nitriding treatment changes to nitride as a main, improving the wear resistance and ska Tsu off I ring of the sliding surface of the bis tons Li in g _c

When C is less than 0.3%, the increase in hardness and generation of carbides are small, and exceeds 1.0%. As a result, coarse and large amounts of eutectic Cr carbide (η phase: M ₇ C ₃ ) crystallize out during solidification of the molten steel, and workability in the subsequent wire rod production is extremely reduced. And It is preferably in the range of 0.4-0.9%.

Since Cr dissolves in Fe in a substitutional form, it improves not only corrosion resistance but also heat resistance by strengthening solid solution. Here, the term “heat loss” refers to a phenomenon in which the sealing property deteriorates due to a decrease in tension due to the cleaving phenomenon during use of the biston ring at a high temperature. In addition, it reacts with C in steel to form Cr carbide. This Cr carbide easily reacts with N invading from the surface by nitriding, and becomes CrN in the nitrided layer and is dispersed as hard particles. These hard particles in the nitrided layer significantly improve the wear resistance and scuffing resistance of the piston ring sliding surface. If the Cr content is less than 14%, the formation of Oehic compounds is small, and if it exceeds 21%, the toughness is reduced due to the formation of δ ferrite and the Cr concentration in the matrix becomes too high. Since the Ms (martensite transformation start temperature) may be lowered and sufficient quenching hardness may not be obtained, the Cr content should be in the range of 14-21%. Preferably it is in the range of 16-19%.

N forms an interstitial solid solution with Fe as does C. Due to the addition of N, for example, the C concentration at the left end of the eutectic line in the 17% Cr isoconcentration cross section of the Fe-Cr-C phase diagram changes the C concentration of the Shifting to a higher concentration side suppresses the eutectic reaction, thereby suppressing the crystallization of the η phase. C subsequent supersaturated during cooling, New precipitates around as a lame error like M ₂₃ C ₆ and Micromax ₂ New precipitates primary crystal γ grain boundaries. New is out η phase crystallizes is less than 0.05%, and if it exceeds 0.50% increases the amount of precipitation of Micromax ₂ New rod-shaped, since the toughness is lowered, New is in the range of 0.05-0.50%. It is preferably in the range of 0.10-0.30%. Further, the solid solution of Ν to Conclusions click scan during inhibit the diffusion of C in the Conclusions click scan, the grain boundary compounds (eventually changed to Fe ₃ N Fe ₃ C It also contributes to the miniaturization of). If the addition of N is 0.2% or less, it can be added at normal pressure, and if it exceeds 0.2%, melting in a pressurized] ^ ₂ atmosphere is required. Yo Therefore, from the viewpoint of the N addition force Q, the range of 0.05 to 0.20% is preferable.

Mo, V, W, and Nb are all carbide-forming elements that improve wear resistance and anti-scratching properties. In addition, Mo has an effect of preventing softening during tempering and nitriding, and plays an important role in the dimensional stability of the bis-ring. V is an element that promotes nitriding and has the effect of increasing the hardness of the nitrided layer. Therefore, any of the elements is useful because it improves various performances required for piston ring, but if the total of at least one of Mo, V, W, and Nb is less than 0.03%, The effect is negligible, and if it exceeds 3%, the workability is significantly impaired and the toughness is reduced, so that the total of at least one of Mo, V, W and Nb is 0.03-3.0 % Range.

Si is added as a deoxidizing agent, and forms a solid solution in Fe to increase temper softening resistance and improve so-called heat resistance. If it is less than 0.1%, the effect is small. If it exceeds 1.0%, the toughness is reduced. Therefore, the Si content is in the range of 0.1 to 1.0%.

Mn is also added as a deoxidizing agent like Si. If the content is less than 0.1%, the effect is small, and if it exceeds 1.0%, the workability is reduced. Therefore, Mn is set in the range of 0.1 to 1.0%.

Since P forms inclusions with Mn and the like and lowers the fatigue strength and further lowers the corrosion resistance, it is desirable that the amount of impurities in steel be as low as possible. Therefore, from a practical viewpoint, the content is set to 0.05% or less. Preferably, it is 0.03% or less.

S reduces the fatigue strength like P, and further reduces the corrosion resistance. Therefore, it is better to minimize the impurities in steel as much as possible. Therefore, from a practical viewpoint, the content is set to 0.05% or less. Preferably, it is 0.03% or less.

In order for a steel having a composition in the above range to have an excellent scuffing resistance, it is necessary for the nitride in the nitrided layer to be fine and numerous. In other words, the main surface of the sliding nitride layer is C r Hard particles of nitrides, carbides and carbonitrides consisting of the following nitrides should be in the range of 0.2-2 // m in average diameter, 7 xm or less in maximum diameter, and 5-30% in area ratio. When the average particle size is less than 0.2 m, the effect as a convex hard particle for preventing scuffing cannot be expected, and when it exceeds 2 / _tm, the problem of scuffing when the load is high is high. Remains. On the other hand, when the maximum diameter exceeds 7 m, the uniformity of the tissue is poor, and in the case of a high load, the problem of scuffing remains. If the area ratio is less than 5%, there remains a problem in anti-scratching resistance, and if it exceeds 30%, it becomes difficult to process the wire after melting or to bend the wire into a ring shape. Preferably it is 10-25%. Further, in order to obtain a structure having excellent cracking resistance in the present invention, it is necessary to observe the nitrided layer cross-section in the longitudinal direction of the bis-ring, which is substantially composed of matrix and hard particles. The size (length) of the grain boundary compound to be used is 20 / m or less at maximum. Exceeding the maximum length of 20 causes problems with cracking under heavy loads.

The nitride layer structure of the present invention as described above is caused by the microstructure of stainless steel. In this structure, firstly, after quenching and tempering through processing such as hot rolling, spheroidizing heat treatment, and cold drawing, the η phase ((Cr, Fe) ₇ C ₃ ) does not exist. This can be achieved by adding nitrogen.

Further, the second, secondary carbides _(epsilon _{phase: (Fe, Cr) 23 C} e) precipitated when kept at the quenching temperature prior to nitriding treatment there are many fine. Considering this point based on the Fe-Cr-C phase diagram, in the (γ + _ε ) region, as the temperature is lower, more carbides precipitate in an equilibrium manner, so the ( _γ + ε) region By setting the quenching temperature as low as possible, it is possible to precipitate as many _f carbides as possible. Further, quenching from a low temperature range makes the crystal grains fine in order to suppress the growth of γ crystal grains, and thus makes it possible to make the grain boundary compound phase formed in the subsequent nitriding treatment also fine. From these aspects, the preferred quenching temperature is in the range of 850-1000 ° C. Below 850 ° C, Prescribed hardness cannot be obtained due to lack of cracking and precipitation of α phase.At quenching temperatures exceeding 1000 ° C, coagulation of carbides and coarsening of γ grains occur at the stage where quenching temperature is maintained. As a result, nitrides and grain boundary compound phases formed in the subsequent nitriding process are coarsened. The high hardness of 900-1400 can be obtained to a sufficient depth in a relatively short time in the nitrided layer.However, the relatively small quenching temperature allows relatively fine γ grains to be obtained. This is attributable to an increase in grain boundaries that play a role of the other. In the present invention, the reason for performing the nitriding treatment in the range of 450 to 600 ° C has been considered to be that the solubility of N in the -Fe lattice becomes maximum at about 590 ° C, It is not necessary to limit to this temperature if the grain boundary is the main diffusion path of N. In the perspective of the shape stability of the bis bets Nri ring, arbitrary processing at low as Ru can temperature preferred is 1 in a range of practical point of view from 450- 600 ^D C - it was 20 hours. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a backscattered electron image photograph of the sliding nitride layer surface by a scanning electron microscope. FIG. 1 (a) corresponds to Example 1 and FIG. 2 (b) corresponds to Comparative Example 1.

FIG. 2 is an optical micrograph of a cross section of the nitride layer. FIG. 2 (a) corresponds to Example 1 and FIG. 2 (b) corresponds to Comparative Example 1.

FIG. 3 is a diagram showing a test piece for a scuffing test.

FIG. 4 is a view showing an operation mechanism of the friction and wear tester.

Fig. 5 is a diagram showing the operation mechanism of the Biston ring fatigue tester.

Figure 6 is a graph of the fatigue limit diagram.

FIG. 7 is a photograph of a crack formed on the sliding surface of Comparative Example 13. BEST MODE FOR CARRYING OUT THE INVENTION

The following specific examples (which explain the present invention in further detail) Example 1-11 (Jl-Jll) Comparative Example 1-8 (H1-H8)

High chrome martensite stainless steel with the chemical composition shown in Table 1 was melted using a 10 kg vacuum induction melting furnace. However, steel with less than 0.2% N was added with nitrogen at normal pressure, and steel with 0.2% or more was melted in a pressure ₂ atmosphere. Next, it is made into a linear material with a diameter of 12 mm through hot working, and after pickling, subjected to spheroidizing annealing at 750 ° C for 10 hours.After a predetermined process, a rectangular cross section of 3.5 mm X 5.0 mm is formed. It was processed into a wire rod. Here, quenching and tempering are performed in a quenching furnace (Ar atmosphere) at 930 ° C for about 10 minutes, and after air-cooled quenching, they pass through a tempering furnace (Ar atmosphere) at 620 ° C for about 25 minutes. The test was performed in a continuous manner, and nitriding was performed on a test piece obtained by cutting a wire into a length of 50 mm, and gas nitriding was performed at 570 ° C for 4 hours. However, the quenching temperature of Comparative Example 1 (HI) was performed at iioo ° c, which was conventionally performed conventionally. Other conditions are the same as those of the other examples and comparative examples.

Table 1

C Cr N Mo V W Nb Si Mn P S

J1 0.65 17.5 0.13 1.5 0.25 0.35 0.02 0.01

J2 0.41 17.0 0.19 1.0 0.15 0.25 0.50 0.02 0.02

J3 0.83 17.8 0.23 0.20 0.20 0.30 0.02 0.02

J4 0.59 17.2 0.16 0.05 0.20 0.20 0.02 0.02

J5 0.62 17.5 0.15 0.3 0.20 0.30 0.02 0.02

J6 0.60 14.5 0.15 1.5 0.5 0.1 0.5 0.55 0.65 0.02 0.02

J7 0.60 19.5 0.25 1.0 0.1 0.20 0.30 0.02 0.02

J8 0.35 20.3 0.28 1.0 0.3 0.20 0.30 0.02 0.02

J9 0.95 14.9 0.25 0.5 0.1 0.20 0.30 0.02 0.02

J10 0.55 16.5 0.08 0.5 0.3 0.35 0.55 0.02 0.02

J11 0.48 18.2 0.42 0.1 0.3 0.20 0.20 0.02 0.02

HI 0.81 17.5 0.03 1.0 0.3 0.25 0.25 0.02 0.02

H2 0.45 18.0 0.58 1.5 0.5 0.20 0.20 0.02 0.02

H3 0.25 17.3 0.16 1.0 0.4 0.20 0.30 0.02 0.02

H4 1.12 17.8 0.15 1.2 0.6 0.20 0.30 0.02 0.02

H5 0.69 13.2 0.21) .1 0.5 0.20 0.30 0.02 0.02

H6 0.73 22.1 0.22 1.0 0.2 0.20 0.20 0.02 0.02

H7 0.65 17.8 0.16 0.20 0.20 0.02 0.02

H8 0.68 17.3 0.15 1.5 1.0 0.5 0.5 0.20 0.20 0.02 0.02 Each wire rod specimen was further cut to a length of 10 mm for microscopic structure observation, embedded in resin and polished to the mirror surface, and the structure observation and quantification of the structure were performed using an image analyzer. Fig. 1 and Fig. 2 show the backscattered electron images (Figs. 1 (a) and (b)) of the sliding nitride layer surface of Example 1 (J1) and Comparative Example 1 (HI) by a scanning electron microscope. Optical micrographs (FIGS. 2A and 2B) of the cross section of the layer are shown. The hard particles are black in the backscattered electron image and white in the light micrograph. It can be seen that in the present invention, the size of the hard particles is small, and the size of the grain boundary compound in the cross section of the nitride layer is also extremely small. Table 2 shows the results of quantification of the structures of Example 1-11 (J1-J11) and Comparative Example 1-8 (H1-H8). , The area ratio, the maximum length of the grain boundary compound in the cross section of the nitrided layer, and the hardness of the sliding surface of the nitrided layer are shown.

Table 2

* Comparative Examples 2, 4, and 8 (H2, H4, H8) could not be made into wires due to the difficulty in processing.

** In Comparative Example 7 (H7), the dimensions after nitriding were unstable and the yield decreased. The scuffing test is a U-shaped 2-pin integrated test piece with a total length of 45 mm as shown in Fig. 3 made from a wire test piece. The test was performed using a friction and wear tester (manufactured by RIKEN: trade name "Tribolic 1"). The sliding surface at the tip of the pin (Fig. 4, reference numeral 1) has a convex shape with a radius of 20mm and grinds a 5-20μm thick compound layer (white layer) formed on the surface by gas nitriding. Removed and polished to a mirror finish. On the other hand, the FC250 disk (Fig. 4, reference numeral 2) was prepared by adjusting the surface roughness (Rz) of the sliding surface to 1-2 m. Fig. 4 shows the operating mechanism of the friction and wear tester, and the fuzzing test conditions are shown below.

Sliding speed (disk): 8 m / sec

Pressing load: Increase from the initial l.OMPa every 0.2MPa, pressure increase until scatting occurs

Lubricating oil: Motor oil (Product name, Nippon Oil Motor Oil P # 20) Lubricating oil temperature: 80 ° C (near the outlet)

Λ • ィレ / レ: 100 ° C

Lubricating oil supply: 40cc / min

The squashing surface pressure was calculated from the load applied when squashing occurred and the wear area of the sliding surface. Table 3 shows the scuffing surface pressure of Example 1-11 (J1-J11) and Comparative Example 1-8 (H1-H8).

Table 3

Example 1-11 (J1-J11) according to the present invention was found to have improved anti-scuffing properties as compared with Comparative Examples 1, 3, and 5-7 (HI, H3, H5-H7). I understand.

Example 12-14 (J12-14) and Comparative Example 9-11 (H9-H11)

A nitride layer obtained by subjecting the material having the chemical composition of Example 1 to air quenching from the quenching temperature shown in Table 4 in the quenching process after wire processing, and performing gas nitriding through the same process as in Example 1 The tissue was quantified ₍ the results are shown in Table 4). Table 4

In Comparative Example 9 (H9), the hardness of the nitrided layer was a low value of 860. Example 12-14 (J12-14) and Comparative Example 9-11 (H9-H11)

In the material having the chemical composition of Example 1, a nitrided layer structure obtained by air-quenching quenching from the quenching temperature shown in Table 7 in the quenching process after wire rod processing and performing gas nitriding through the same predetermined process as in Example 1 Quantified. Table 5 shows the results.

Table 5

In Comparative Example 9 (H9), the hardness of the nitrided layer was a low value of 860.

Example 15 and Comparative Example 12

Through a predetermined process from the steel material of Example 1 and Comparative Example 1, a pressure ring with a rectangular cross section of nominal diameter (95.0 mm), thickness (a,) 3.35 mm, width (h,) 2.3 ram (implemented Example 15 and Comparative Example 12). Here, quenching and tempering are performed in a continuous manner by passing through a quenching furnace at 930 ° C for about 10 minutes, air-quenching and then passing through a tempering furnace at 620 ° C for about 25 minutes. , 570 ° C For 4 hours. However, the quenching temperature of Comparative Example 12 was performed at 1100 ° C., which was conventionally performed conventionally. Other conditions are the same as in Example 15.

A fatigue test was carried out using the fabricated pressure ring with a piston ring fatigue tester having the operating mechanism shown in Fig. 5. In other words, the product 3 with the free opening dimension expanded by cutting both ends of the opening is set on the testing machine with the ring closed to the nominal diameter, and the direction of further closing from this state The eccentric cam 4 repeats the stroke corresponding to the applied stress at a cycle of 40 cycles / second, causing the ring to break. The number of loads was determined. This test was repeated for samples of the same specifications while changing the load stress, so-called SN diagrams were created, and finally fatigue limit diagrams were obtained.

FIG. 6 shows a fatigue limit diagram. It can be seen that the fatigue limit is significantly improved in Example 15 of the present invention as compared with Comparative Example 12.

Example 16-19 and Comparative Example 13-14

From the steel materials of Example 1 (Examples 16 and 17), Example 7 (Examples 18 and 19), and Comparative Example 1 (Comparative Examples 13 and 14), through a predetermined process, a nominal diameter of 99.2 mm and a thickness of 99.2 mm (A,) 3.8mm, width (h,) 2.5mm rectangular section pressure ring (Examples 16, 18 and Comparative Example 13), nominal diameter (d,) 99.2mm, thickness (a,) The two-piece oil bearing body with a saddle-shaped cross section of 2.5 mm and width (h,) 3.0 mm ('Examples 17, 19, Comparative Example 14) was machined. The heat treatment of quenching and tempering and the gas nitriding were performed in the same manner as in Example 15 in Examples 16 to 19 and in Comparative Example 12 in Comparative Examples 13 to 14.

The manufactured pressure ring and oil ring were subjected to a 100-hour durability test under the following conditions using a 4-cylinder 3200 cc ferromagnetic monobloc nozzle diesel engine.

Number of rotations: 3600rpm

Output: 75kW

Load: Full load Water temperature: 110 ° C

Oil temperature: 130 ° C

In Comparative Example 13, scuffing occurred 2 hours and 10 minutes after the start of the test and in Comparative Example 14 7 hours and 55 minutes after the start of the test, whereas in Examples 16 to 19, the test was performed without any problem. finished. Fig. 7 shows a photograph of the crack generated on the sliding surface of Comparative Example 13. Industrial applicability

As described above, the bismuth ring made of high chromium martensite stainless steel according to the present invention is based on the technology of refining Cr carbide by adding nitrogen and the relatively low temperature. Due to the quenching, many nitrides in the nitrided layer are fine and numerous, and especially the layered grain boundary compounds in the nitrided layer have a fine microstructure, and are resistant to wear and scuffing. Because of its excellent resistance, cracking resistance and fatigue resistance, it can be used for high-speed, high-power, high-load internal combustion engines, especially recent lightweight rust-resistant monolithic diesel engines. Is possible. It can also be used effectively against fatigue of the bis-rings when using exhaust brakes on small trucks. Applicable screw rings can be conveniently used in pressure ring as well as 2-piece oil ring main bodies and 3-piece oil ring rails.

Claims

The scope of the claims

1 in the surface nitride layer was formed consisting Ri by high click b Mumarute Nsai preparative steels piston tons Li in g, the high click b Mumarute Nsai preparative system scan Te emission Les scan steel force;., A weight ^_0/0. , C: 0.3-1.0%, Cr: 14.0-21.0%, N: 0.05-0.50%, total of at least one of Mo, V, W, and Nb: 0.03-3.0%, Si: 0.1-1.0 %, Mn: 0.1-1.0%, P: 0.05 ° /. Below, 8: 0.05% or less, with the balance being Fe and unavoidable impurities, and the hard particles consisting mainly of nitride as the main surface of the sliding nitride layer have an average diameter of 0.2-2 m. Pis with excellent anti-scratching, anti-cracking and anti-fatigue properties, characterized by a range of 7 μm or less in maximum diameter and an area ratio of 5-30%. Tong ring.

2. The method according to claim 1, wherein the size (length) of the observed grain boundary compound is at most 20 m or less in the longitudinal section of the piston ring in the nitrided layer. Boston ring.

3. The biston according to claim 1 or 2, wherein the nitrogen content of said high chrome martensite steel is in the range of 0.05 to 0.20% by weight N. Ring.

4. The piston ring according to any one of claims 1 to 3, wherein the nitrided layer on the sliding surface has a Vickers hardness in the range of 900 to 1400. .

5. The method of manufacturing a bis-ring that nitrides the surface of high chrome martensitic steel has a weight of ⁰ /. Where: C: 0.3-1.0%, Cr: 14.0-21.0%, N: 0.05-0.50%, Mo, V, W, Nb At least one or more: 0.03-3.0%, Si: 0.1- 1.0%, Mn: 0.1-1.0%, P: 0.05% or less, S: 0.05% or less, balance is Fe and unavoidable impurities, high chromium martensite stainless steel In the quenching process before bending into a ring shape, quenching is performed from a temperature in the range of 850 to 1000 ° C, which is characterized by its anti-scratching, cracking and fatigue resistance. An excellent method for manufacturing a rubber ring.

6. Combination of the stainless steel ring described in any one of claims 1 to 3 and a stainless steel monobloc mouth cylinder.