DE60122164T2 - PISTON RING WITH EXCELLENT RESISTANCE TO FRICTION, CRACKING AND TEMPERING AND MANUFACTURING METHOD AND COMBINATION OF PISTON RING AND CYLINDER BLOCK - Google Patents

Description

GENERAL STATE OF THE ART

Technical area

The The present invention relates to a piston ring used in an internal combustion engine is used, in particular a piston ring made of stainless, martensitic, chromium-rich steel with nitriding exists and improved abrasion resistance (Galling resistance), tear resistance (Defect resistance) and fatigue resistance having. The present invention also relates to a method of manufacturing the piston ring.

Technique of State of the art

accompanying with the youngest Requirements for low fuel consumption, weight reduction and high performance of internal combustion engines become the piston rings thinner manufactured to reduce weight and high speed of the Motors to follow. Material properties of the piston rings such as wear resistance, abrasion resistance and fatigue resistance and the like must be improved to the thinner ones To allow production of the piston ring. The conventional ones Cast iron rings were therefore replaced by steel piston rings, in particular from the standpoint of fatigue resistance and the heat resistance ago. Because the abrasion resistance the steel piston ring but lower than that of the cast piston ring is, becomes common any surface treatment on the sliding surface applied to the steel piston ring. Piston ring steels are coarse in carbon steel, Silicon-chromium steel and martensitic stainless steel divided. These subdivisions correspond to the different types of surface treatment, which is applied to the respective steels. Mainly becomes the chrome plating applied to carbon steels and silicon-chromium steels. Gas nitriding is applied to stainless martensitic steels. The chrome plating was earlier the most frequent surface treatment of the steel piston ring, but today is mostly due to nitriding replaced because the abrasion resistance the chrome plating under high load is poor and also the liquid waste The chrome plating must be treated so that no environmental problems caused.

Stainless, martensitic, chromium-rich steel, presently mostly for the nitrided piston ring is JIS SUS440B, equivalent Composition of C: 0.80 to 0.95%; Cr: 17.0 to 18.0%; Si 0.25 to 0.50%; Mn: 0.25 to 0.40%; Mo: 0.70 to 1.25%; V: 0.07 up to 0.15% and Fe in compensation. If the steel with this composition is subjected to nitration, nitrogen atoms penetrate and diffuse from the surface into the steel and form a nitriding layer. The nitrides are mainly Compounds of Cr, V and Mo, which may contain the solute Fe. Chrome, which is the main component of this steel is in the iron matrix solved and also in the form of Cr carbides.

There the affinity from Cr to nitrogen higher when it is too carbon, it comes when nitrogen from the surface through nitriding diffuses in to the reaction between the nitrogen and Cr carbides to form the Cr nitrides. Because the CR content from SUS 440B equivalent Material is 17.0 to 18.0%, Hard cr-nitrides in the nitriding layer become adequate Area percentage dispersed. The nitriding layer is therefore relatively hard and improved the wear and abrasion resistance.

The recently unchecked published Patent publication No. 11 (1999) -80907 stainless martensitic steel with nitration with improved abrasion resistance before, the Si: 0.25% or less, Mn: 0.30% or less, one or more of Mo, W, V and Nb: 0.3 to 2.5% or Cu: 4.0% or less, Ni: 2.0% or less and Al: 1.5% or less.

Japanese Unexamined Patent Publication 11 (1999) -106874 discloses that when the amount of M ₁ C ₃ carbide in the microstructure is suppressed to 4.0% or less in area percent, not only the abrasion resistance but also the processability of the Piston ring steel material is improved.

Even though the resistance to fouling and abrasion resistance are improved by the proposals described above exists the risk of abrasion when the piston rings are in modern internal combustion engines are used, which are under high RPM and high performance conditions.

For this Bushes were forced into the cylinder block of diesel engines. These engines became cast iron monoblocks with close bore spacing modified without sockets, to achieve weight reduction and cost savings. It exists a tendency that the combustion pressure from the point of view of exhaust gas purification and increased performance ago becomes. In the microstructure of the cast iron monoblock is from the relative huge Cooling rate difference the graphite dispersion is not uniform and the soft ferrite phase unevenly distributed as an attrition cause.

If the cylinder surface with the above-mentioned microstructure with the martensitic stainless steel piston ring combined with nitration, there is a risk that from the following establish a rubdown in the initial Operating period occurs.

If the cylindrical surface finished by honing, the abrasives cause a Constipation due to the ferrite phase, and there is a risk that the cylinder surface roughened after honing. The graphite is made by the plastic brimmed Covered with ferrite. As a result, lubrication and oil reservation effects are of graphite, since the area percentage of graphite decreases. In case of high combustion pressure, the pressure on the piston ring high counterpressure. Rubbing is often the result of cracks the outer peripheral surface of a Piston ring, which are in a direction perpendicular to the sliding direction Extend direction. When examining the nitriding layer Cracks detected along the lamellar joints. The connections are relatively coarse and present in grain boundaries along the iron matrix, what as seagull phase in the Japanese piston ring industry. The Connecting lamellae are distributed parallel to the surface of the piston ring.

Around To solve the problems of piston rings, the training of TiN, CrN and the like are carried out by ion plating. The Ion plating can reduce the wear resistance and the abrasion resistance improve, but the production costs are high. The ion plating enjoy currently not a good reputation among users in terms of cost.

It It is therefore an object of the present invention to provide a piston ring Made of stainless, martensitic, chromium-rich steel with nitration and to provide its manufacturing method, wherein the piston ring inexpensive is and is neither wear, Abrasion, tearing still fatigue fractures, even if it is used in a diesel engine running at high speed and high combustion pressure, in particular a cast iron monoblock diesel engine, its increasing use in the future due to weight reduction is to be expected.

Summary the invention

According to the explanation "Automotive Piston Ring ", edited by Editing Committee of Automotive Piston Ring, Sankaido Publisher, Page 188, 1997, the temperature rises when a load on the convex shapes (especially of soft phases) of microscopic Bumps on a sliding surface are concentrated, due to the friction heat, and abnormal softening and melting occurs. This phenomenon leads to abrasion of the piston ring.

at stainless, martensitic, chromium-rich steel with nitration generally shows the microstructure of the nitriding layer in general hard nitrides dispersed in the tempered martensite matrix are. The abrasion mechanism hangs strongly from the microscopic unevenness of the sliding surface. In the nitriding layer, hard particles disperse in the relative soft matrix. The microscopic unevenness is therefore due to the size and the Defined dispersion state of the hard particles. If you have the cross section the surface layer With such a structure, the following is apparent. The convex, hard particles are opposite sliding surface while in contact the relatively soft matrix is relatively concave. The lubricating oil, which in the concave sections back is held, is subjected to sliding pressure. The frequency the entire direct contact of the steel with nitration and the opposite member is low because the nitrided steel is the microstructure described above having. As a result, the contact pressure between both sliding members reduced. In addition, the oil supplied to the above-mentioned convex portions. The abrasion can therefore be prevented.

The hard convex particles can Achieve the effects described above, provided they show a size of submicroscopic up to a few microns and are in an amount of 5 area percent or more dispersed. If the hard particles are extremely small and if present in a small amount, the above Mechanism according to function and effect of the convex hard particles can not be expected.

however the effects are due to the circumstances of the sliding surface of the opposite Affected. Especially in the case of the above-described Cast iron cylinder monobloc with patchy structure exists the risk of grinding through grinding. Frequently, the ferrite phase flows plastically and covers the graphite.

The sliding surface also of such cast iron is modified by suitable sliding, as called in-service or compatibility by professionals becomes. That is, it is the following phenomenon occurs. If the rough inner surface of a Smoothed cylinder when sliding the ferrite is removed and the covered graphite is exposed. Until the run-in performed there is a risk that an oil film on the sliding surface is missing. When the oil film lacking, the frictional force is amplified on the outer peripheral surface of a Piston ring exercised is. The size Frictional force is repeated on the outer peripheral surface of a Piston ring exercised. The nitriding layer is therefore repeatedly exposed to high stress, those for the initiation and expansion of Tears in one direction, which is perpendicular to the sliding direction. Along with the progress the adaptation phenomenon on the inner surface of a cylinder becomes the practiced Stress decreases while the cracks spread over time. As a result, can the nitriding layer peel off in places, and the inner surface of a Cylinder can be damaged become. There is therefore a risk that rubbing in the initial Sliding period occurs. Because the grain boundary compounds in the nitriding layer very brittle are, promotes their presence the initiation and spread of cracks.

The Inventors found the following essentials. A big number hard particles, mainly Cr nitrides, in appropriate Size in the Nitriding layer should be uniformly dispersed in the matrix, the probability of contacts between matrix and cylinder to mitigate and prevent abrading the initial stage. Especially the grain boundary compounds formed during nitriding should be fine about the initiation of cracks related to these Suppress connections. Even if cracks start to appear, their development can this fine microstructure can be suppressed.

As the melt of stainless martensitic chromium-rich steel solidifies, the eutectic Cr carbide (η-phase: (Cr, Fe) - (C ₃ ) crystallizes in the grain boundaries of primary austenite (γ phase).) Cr carbides, which are larger than 20 μm in diameter, are present in the stainless martensitic chromium-rich steel which is solidified as above and then hot rolled, annealed, and finally quenched and tempered.For refining the coarse primary eutectic Cr carbides, Tetsu and Hagane (Journal of Japanese Institute of Iron & Steel), Vol. 82, No. 4, pp. 309-31 (1996), refine carbides by adding 0.25% or more N. According to this report, this disappears eutectic Cr carbide in the primary γ boundaries and instead lamellated M ₂₃ C ₆ and M ₂ N (M: Cr, Fe) precipitate around the primary γ grain boundaries These lamellar precipitates are finely divided during hot rolling Soft annealing again precipitates fine M ₂₃ C ₆ at sites other than M ₂ N. The Cr carbides as a whole thus become fine.

Netsushori Vol. 36, No. 4, pp. 234 to 238 (1996) shows the mechanical properties of 16.5% Cr-0.65 % C stainless martensitic steel with the addition of 0.25% N on. That the quenching temperature at which the greatest hardness is achieved is, with the increase of the N content to lower temperature reduced. The elongation As the N-content increases, it also increases. It explains that the amount of the solution of N increases in the austenite phase and the austenite phase with the increase the quenching temperature is stabilized.

The unchecked published Japanese Patent Publications Nos. 9-289053 and 9-287058 disclose the roller bearing in which the Fresh from Cr carbides due to the addition of N is used.

The Inventors have the abovementioned abrasion mechanism and influence relatively large Laminated grain boundary compounds on the tearing of the sliding surface of Piston rings examined and the Cr-Carbid fresh technology using the addition of N. As a result became found out that wanted is that a big one Number of nitrides uniformly dispersed in the nitriding layer and in particular grain boundary compounds are of fine size. This fine microstructure represents a piston ring made of stainless, martensitic, chromium-rich steel with nitration with improved Abrasion, tear and fatigue resistance even if it is used in internal combustion engines, the below operated at high speed and high performance conditions, in particular modern weight-reduced cast iron monobloc diesel engines, etc.

The stainless steel martensitic chromium-rich nitrided nitriding ring of the present invention is characterized in that it surrounds the stainless martensitic chromium-rich steel which is in weight percent of C: 0.3 to 1.0%, Cr: 14.0 to 21.0%, N: 0.05 to 0.50%, at least one of Mo, V, W and Nb: 0.03 to 3.0% in total, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P: 0.05% or less, S: 0.05% or less where Fe and unavoidable impurities are the balance; and that the stainless martensitic chromium-rich steel has a sliding nitriding layer comprising hard particles consisting of carbide, nitride and carbonitride, mainly nitride, and the hard particles in the surface of the nitriding layer are in a range of 0.5 to 2 , 0 μm in average diameter, where 7 μm or less is the largest diameter, and from 5 to 30% in area percent. The grain boundary compounds noted in the longitudinal section of the nitriding layer have a size (length) of 20 μm or less. The nitriding surface layer having the above-mentioned microstructural feature has a hardness in the range of Hv 900 to 1400 and a sufficient depth from the surface.

The Manufacturing process of the piston ring of stainless, martensitic, Chromium-rich steel with nitration according to the present invention comprising: melting the steel with the above composition followed from adding nitrogen; Pouring the molten steel in a block; Hot rolling; Glow; Wire cold drawing; Cold rolling to form an approximate cross-sectional shape the piston ring; Scare off; Starting to provide the wire material; Bending the wire material into the shape of the piston ring; Zugentlastungsglühen; roughing the side surfaces; nitriding; Removing the surface compound layer; Grinding the end pieces; Polishing the side surfaces; and fine grinding the outer peripheral surfaces. In front the bending in the piston ring shape is a quenching with a Temperature of 850 º to 1000 º performed, the relatively low as the quenching temperature of the stainless, martensitic, chromium-rich steel is. As a result, the microstructure is fine and contains a maximum amount the dispersed carbides. Nitriding can be gas nitriding, ion nitriding or radical nitriding. The nitriding becomes in one area from 450 º to 600 ºC for 1 to 20 hours running.

The The present invention will be described in detail below.

It become the components of the stainless, martensitic, chromium-rich Steel according to the present Invention described.

C is an interstitial solved element in Fe and increases the matrix hardness. C is easily combinable with Cr, Mo, V, W and Nb to form carbides. The carbides are mainly converted into nitrides during nitriding. In other words, the nitrides promote wear resistance and abrasion resistance of the sliding surface of a piston ring. When the C content is less than 0.3%, the hardening and formation of carbides is insufficient. On the other hand, when the C content is over 1%, coarse eutectic Cr carbide (η phase: M ₇ C ₃ carbide) crystallizes in a large amount during the solidification of the molten steel. This carbide drastically affects the processability of the material in the subsequent manufacturing processes of wires. The carbon content is therefore in a range of 0.3 to 1.0%, preferably in a range of 0.4 to 0.9%.

Cr is a solved one Substituting element in Fe. Cr not only improves corrosion resistance, but induces as well the solution strengthening and thus improving the thermal setting resistance. Here, the thermal setting is a phenomenon in which the Sealing property due to voltage drop due to slip deteriorated during operation of a piston ring at high temperature. Cr reacts with C in steel and forms Cr carbides. These Cr carbides react easily with N, which penetrates from the surface during nitriding, and are converted to Cr nitrides. The Cr nitrides are used in the Nitriding layer dispersed as hard particles. The hard particles promote in the nitriding layer the wear resistance and the abrasion resistance the sliding surface a piston ring to a high degree. When the Cr content is less than 14%, the formation of Cr carbides is not enough. On the other hand, when the Cr content exceeds 21%, the δ-ferrite becomes formed and the toughness thus reduced. In addition, the Cr concentration in the matrix so high that the Ms (the starting temperature of the martensitic transformation) is reduced such that no satisfactory quenching temperature is achieved. The Cr content is therefore in a range of 14 to 21%, preferably in a range of 16 to 19%.

N is like C an interstitial element in Fe. Ternary Fe-Cr-C phase diagram may be expressed by a pseudo-binary phase diagram by cutting on, for example, the 17% Cr line. A eutectic reaction takes place between Fe and C, the concentration of which is given by the left end of the eutectic line. Meanwhile, molten steel remains around the grain boundaries of primary crystals before solidification. As the temperature continues to drop, the molten steel undergoes the eutectic reaction. When nitrogen is added according to the present invention, the C concentration on the above-mentioned left side is higher than that of the molten steel without nitrogen. Therefore, the eutectic Reaction and thus the formation of η-carbide suppressed. When the temperature falls below the eutectic temperature, the supersaturated C and N precipitate around the primary γ grains in the form of laminated M ₂₃ C ₆ and M ₂ N precipitates. When the N content is less than 0.05%, the η phase crystallizes. On the other hand, when the content of N is more than 0.05%, the amount of M ₂ N precipitates in a rod shape, so that the toughness is lowered. The N content is therefore in the range of 0.05 to 0.50%, preferably in a range of 0.10 to 0.30%. The dissolved N in the matrix prevents the diffusion of C and also contributes to the refining of the grain boundary compounds. This is first Fe ₃ C after casting and is finally converted to Fe ₃ N after the nitriding treatment. Nitrogen up to 0.2% can be added under normal pressure. A nitrogen content above 0.2% requires melting under N ₂ gas pressure atmosphere. The nitrogen content in a range of 0.05 to 0.20% is therefore preferred from the viewpoint of N addition.

any Mo, V, W and Nb is a carbide image and promotes wear and abrasion resistance. moreover Mo prevents softening while tempering and nitriding treatments and plays an important role in achieving the dimensional stability of a piston ring. V promotes that Nitriding, and therefore the hardness of a Nitriding layer high, containing V. Any of these elements is for enhancing the properties of a piston ring effective. When the total content of at least one of Mo, V, W and Nb is less than 0.03%, their effects are virtually negligible. On the other hand, if the Total content of these elements / this element is over 3%, is the processability seriously impaired and the toughness reduced. The total content of Mo, V, W and Nb is therefore from 0.03 to 3.00%.

Si is a deoxidation additive. Si is also dissolved in Fe and promotes the Softening resistance during Tempering. The so-called thermal setting resistance can therefore be improved. If the Si content is less than 0.1% is, its effect is weak. On the other hand, if the Si content is more is 1.00%, is the tenacity impaired. The Si content is therefore in a range of 0.1 to 1.0%.

Mn is also a deoxidation additive. If the Mn content less than 0.1%, its effect is weak. On the other hand, if the Mn content is more is 1.0%, the processability is impaired. The Mn content is therefore from 0.1 to 1.0%.

P forms inclusions with Mn and the like, and sets the fatigue strength and corrosion resistance down. P is a steel impurity. The less P, the better. Of the P content is from a practical point of view thus 0.05% or less. Preferably P is 0.03% or less.

S sets like P the fatigue strength and corrosion resistance down. S is a steel impurity. The less S, the better. Of the S content is From a practical point of view thus 0.05% or less. Preferably S is 0.03% or less.

Of the Steel made from the composition ranges described above is a training of a microstructure with improved abrasion resistance That is, a number of fine nitride particles are in the nitriding layer available. In particular, the hard particles should be made of nitrides exist, i. mostly Cr-nitride, carbides and carbonitrides, the in the surface the nitriding layer are present: an average diameter in a range of 0.2 to 2 μm, being the largest diameter 7 μm or less, and an area percentage in a range of 5 to 30%. If the average particle diameter less than 0.2 μm is, are the convex shapes of the hard particles to prevent one Rubbing off not effective. On the other hand, if the average particle diameter more than 2 μm is, There is a risk that rubbing occurs when the strain is high. When the biggest diameter more than 7 μm is, the microstructure of the nitriding layer becomes uneven, so that There is a risk that abrasion occurs under high load. If the area percentage less than 5% the danger that rubbing will occur. On the other hand, if the nitride area percentage is more than 30%, will wire drawing and bending in piston ring shape after melting difficult. A preferred area percentage is 10 to 25%.

The Microstructure of the nitriding layer with improved tear resistance is such that the grain boundary compounds, in longitudinal section of the piston ring are 20 μm or less in size (length). If the longest Length more than 20 μm is, arises the problem that there is a risk that the tearing under high load occurs.

The microstructure of the nitriding layer as described above according to the present invention is attributable to the microstructure of stainless steel. First, no coarse eutectic carbide (η-phase: (Cr, Fe) -C ₃ carbide) is present in the steel, which is then hot rolled, annealed, wire drawn, deburred was scared and tempered. This is achieved by the addition of nitrogen.

Second, a number of the fine secondary carbide (ε phase, (Cr, Fe) ₂₃ C ₆ carbide) precipitates when it keeps at quenching temperature prior to nitriding. The Fe - Cr - C phase diagram shows that more and finer carbide precipitates as the quenching temperature is lower in the (γ + ε) region. When quenching is carried out from as low a temperature as possible in the (γ + ε) region, γ carbides can precipitate in the largest possible amount. In addition, the growth of γ crystal grains is suppressed, so that the quenched steel has a fine grain structure. When this steel is subjected to nitriding, the grain boundary compounds also become fine. A preferred quenching temperature is therefore in the range of 850 to 1000 ° C from the viewpoint described above. if the quenching temperature is less than 850 ° C, no curing takes place and the desired hardness is not achieved due to α phase precipitation. When the quenching temperature is over 1000 ° C, the carbides in the holding step grow together at the quenching temperature, and the γ crystal grains become coarse. As a result, the coarse carbides are converted to coarse nitrides. The grain boundary compounds formed along the coarsened γ crystal grains in the subsequent nitriding treatment become coarse.

at The present invention has a high hardness of Hv900 to 1400 to to a satisfactory depth from the surface the nitriding treatment for achieved a relatively short period of time. This feature is the relative one fine γ-crystal grains, the be formed at low quenching temperature, and thus attributable to the increase in grain boundaries, which are the main ones Diffusion passages from N while of the nitriding treatment.

According to the present Invention will be the nitriding treatment in the temperature range of 450 up to 600 ºC executed. In the prior art, the treatment temperature is about 590 ° C at which the nitrogen solubility in the α-Fe Lattice is the largest, considered as recommended. Since the present invention, the N-diffusion but mainly about the Grain limits, the treatment temperature is not limited to about 590 ° C. The Treatment at a lower temperature is from the point of view of dimensional stability a piston ring is recommended. From a practical point of view however, nitriding is carried out at 450 to 600 ° C for 1 to 20 hours.

Short description the drawings

1 Fig. 11 is a photograph of a backscattered electron image of the surface of a sliding nitriding layer by a scanning electron microscope.

1 (a) and (b) correspond to Example 1 and Comparative Example 1, respectively.

2 is a photograph through a light microscope of the cross section of a nitriding layer. 2 (a) and (b) correspond to Example 1 and Comparative Example 1, respectively.

3 shows a sample of the abrasion test.

4 shows the movement mechanism of a friction and wear tester.

5 shows the movement mechanism of a fatigue tester of a piston ring.

6 is a graph showing the fatigue limit.

7 Fig. 15 is a photograph showing a crack formed on the sliding surface of Comparative Example 13.

BEST MODE OF PERFORMANCE THE INVENTION

Example 1-11 (J1-J11) and Comparative Example 1-8 (H1-H18)

The stainless martensitic chromium-rich steels having a composition shown in Table 1 were melted in an amount of 10 kg in a vacuum induction melting furnace. However, less than 0.2% N was added to the steel when melting under normal pressure, while 0.2% or more N was added to the steel under N ₂ gas pressure atmosphere. By thermoforming wire material was obtained with 12 mm diameter. After acid pickling, soft annealing was performed at 750 ° C for 10 hours leads. By working a wire with a rectangular cross-section of 3.5 mm × 5.0 mm was produced. The wire was passed through a quench oven (Ar guard atmosphere) and a tempering furnace (Ar guard atmosphere). The air quench was carried out at 930 ° C after holding for about 10 minutes at this temperature. The tempering was carried out at 620 ° C for about 25 minutes.

The wires were in about 50 mm long samples for cut the nitriding treatment. Gas nitriding was at 570 ° C for 4 hours executed. However, the quenching temperature of Comparative Example 1 (H1) was 1100 ° C, as with the conventional one Method. The other conditions are the same as for the example and the other comparative examples.

Table 1% by weight

• * Vergleichsbeispiele 2, 4 und 8 (H2, H4 und H8) konnten wegen dürftiger Verarbeitbarkeit nicht zu Drähten ausgebildet werden.
• ** Die Dimension nach dem Nitrieren war in Vergleichsbeispiel 7 (H7) unstabil. Der Ertrag ist daher niedrig.

The above wire samples were further cut into lengths of 10 mm to examine the microscopic structure. The samples were embedded in resin and mirror finished. The examination and quantitative evaluation were carried out using a microsection analyzer. The backscattering electron image of the sliding nitriding surface was examined with respect to Example 1 (J1) and Comparative Example 1 (H1) by a scanning electron microscope. The examined images for Example 1 (J1) and Comparative Example 1 (H1) are in 1 (a) or (b) shown. The cross section of the nitriding layer was examined by a light microscope, and the examined photographs are in 2 (a) or (b) with respect to Example 1 (J1) and Comparative Example 1 (H1). The hard particles appear black in the backscatter electron image and white in the light microscope photo. It is obvious that: the hard particles according to the present invention are extremely small in size; and that the grain boundary compounds investigated in the cross section of the nitriding layer are extremely small in size. The microstructures of Examples 1 to 11 (J1 to J11) and Comparative Examples 1 to 8 (H1 to H8) became quantitative with respect to the average particle diameter, the largest particle diameter, and the area ratio of the hard particles in the sliding nitriding surface and the longest length of the grain boundary compounds in the cross section of the nitriding layer rated. These results are shown in Table 2 together with the hardness of the sliding surface of the nitriding layer. Table 2

• * Comparative Examples 2, 4 and 8 (H2, H4 and H8) could not be formed into wires because of poor workability.
• ** The dimension after nitriding was unstable in Comparative Example 7 (H7). The yield is therefore low.

With reference to 3 A sample of abrasion in the form of the Japanese katakana "]" of 45 mm overall length was shown The wire material was formed into two-pin integral abrasion test specimens The counterpart material was made of FC250 and in the form of a disc 60 cm in diameter and 12 mm in thickness.

The sliding surface of disc 2 ( 4 ) was adjusted to the roughness (Rz) of 1 to 2 μm. The abrasion test was carried out using a friction and wear tester (product of Riken, trade name "Triborik I") 1 . 4 ) are convex sliding surfaces with 20 mm radius. The front ends were subjected to a gas nitriding treatment. The 5 to 20 μm thick tie layers (white layer) formed at the front ends were removed by grinding. The front ends were then polished by polishing. The roughness (Rz) of the sliding surface of the used FC250 disc ( 4 , Reference number 2 ) is set to 1 to 2 μm. The movement mechanism of the friction wear tester is in 4 shown. The abrasion test conditions were as follows:
Sliding speed (disc): 8 m / s
Compressive load: Gradual increase of 0.2 MPa from the initial 1.0 MPa to the occurrence of attrition
Lubricating oil: engine oil (trade name: Nisseki Motor Oil P No. 12)
Lubricating oil temperature: 80 ºC (near the outlet)
Oil bath temperature: 100 ° C
Lubricating oil supply amount: 40 cc / min

Of the Abreibflächendruck was calculated from the Abreibbelastung and the wear area of the sliding surface. The scoring surface pressure achieved is re Examples 1 to 11 (J1 to J11) and Comparative Examples 1 to 8 (H1 to H8).

Table 3

It It is obvious that the abrasion resistance of Examples 1 to 11 (J1 to J11) opposite that of Comparative Examples 1, 3 5-7 (H1, H3, H5-H7) improved is.

Example 12 to 14 (J12 to J14) and Comparative Examples 9 to 11 (H9 to H11)

• * Die Härte der Nitrierschicht von Vergleichsbeispiel 9 (H9) lag unter Hv890.

The materials having the chemical composition of Example 1 were made into a wire and air quenched from the temperature shown in Table 4. The gas nitriding treatment was carried out by the same method as in Example 1. The microstructure of the nitriding layer was quantitatively analyzed. The results are shown in Table 4. Table 4

• The hardness of the nitriding layer of Comparative Example 9 (H9) was below Hv890.

Example 15 and Comparative Example 12

The steel materials of Example 1 and Comparative Example 1 were subjected to operations for forming a compacting ring having a rectangular cross section. The nominal diameter (d ₁ ) was 95.0 mm, the thickness (a ₁ ) 3.35 mm and the width (h ₁ ) 2.3 mm. Quenching was carried out by passing the quench oven at 930 ° C for 10 minutes followed by air cooling. Annealing was carried out by annealing at 620 ° C for about 25 minutes. The continuous quenching and tempering was carried out. Gas nitriding was carried out at 570 ° C for 4 hours. However, the quenching temperature of Comparative Example 12 was 1100 ° C as in the conventional method. The other conditions are the same as for Comparative Example 15.

The generated piston compression ring was tested in a fatigue tester, whose motion mechanism is in 5 is shown. The end pieces of the piston compression ring were cut at both ends to widen the dimension of the piston ring gap. The thus treated piston ring 3 was through an adjustment device 9 in the tester adjusted so that its diameter was reduced to the nominal diameter. The eccentric cam 4 was then rotated to impart repeated strokes of 40 cycles per second to further reduce the diameter to less than the nominal diameter until the piston ring 3 broke. The load number at break was obtained. This test was repeated by transferring the applied load to the sample of identical specification. The so-called SN diagram and finally the fatigue limit diagram, which in 6 shown was obtained.

With reference to 6 It is apparent that Example 15 is greatly improved over Comparative Example 12.

Example 16 to 19 and Comparative Example 13 to 14

The steel materials of Example 1 (Example 16, 17), Example 7 (Example 18, 19) and Comparative Example 1 (Comparative Example 13, 14) were worked to form a compression ring (Example 16, 18 and Comparative Example 13) and the body of a two-piece oil ring (Example 17, 19 and Comparative Example 14). The compression ring had a rectangular cross-section. Its nominal diameter (d ₁ ) was 99.2 mm, the thickness (a ₁ ) 3.8 mm and the width (h ₁ ) 2.5 mm. The body of the oil ring had a saddle-shaped cross-section. Its nominal diameter (d ₁ ) was 99.2 mm, the thickness (a ₁ ) 2.5 mm and the width (h ₁ ) 3.0 mm.

The Quenching, tempering and gas nitriding in Example 16-19 the same as in Example 15. Quenching, tempering and gas nitriding in Comparative Examples 13 to 14 was the same as in Comparative Example 12th

The generated compression ring and oil ring were mounted in a 4 cylinder diesel engine with 3200 cc displacement. The rings were mounted on a flask and combined with a cast monoblock and run for 100 hours for the endurance test under the following conditions.
Speed: 3600 rpm
Power: 75 kW
Load: full load
Water temperature: 110 ºC
Oil temperature: 130 ºC

Attrition occurred after 2 hours 10 minutes in the case of Comparative Example 13 and after 7 hours 55 minutes in the case of Comparative Example 14. There were no disturbances during the test in the case of Example 16 to 19. Referring to 7 Fig. 3 is a photograph of a crack in the sliding nitriding surface of Comparative Example 13.

industrial applicability

According to the present Invention is a big one Amount of fine nitrides in the nitriding layer of the piston ring, made of stainless, martensitic, chromium-rich steel with nitration is made. The laminated grain boundary compounds are also refined. Such microstructures can by the addition of nitrogen and quenching at low temperature be educated. The wear resistance, Abrasion resistance, tear resistance and fatigue resistance is improved due to the microstructure. The piston ring according to the invention can therefore be advantageous in internal combustion engines with high rotational and high performance conditions, in particular the modern, lightweight monobloc diesel engine. The piston ring according to the present Invention can also used advantageously as a piston ring of a small truck which is likely to be the fatigue problem when using the engine brake occurs. The piston ring of the present Invention may be appropriate as the body of a two-piece oil ring and rail of a three-piece oil ring accomplished be.

Claims (6)

Piston ring with improved abrasion resistance, tear resistance and fatigue resistance, consisting of stainless, martensitic, chromium-rich steel and a sliding nitriding layer formed on the surface of the steel, characterized in that the stainless, martensitic, chromium-rich steel in weight percent of C: 0.3 to 1.0%, Cr: 14.0 to 21.0%, N: 0.05 to 0.50%, at least one of Mo, V, W and Nb: 0.03 to 3.0% in total, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P: 0.05% or less, S: 0.05% or less, Fe and unavoidable impurities being balance; and further that the sliding nitriding layer has on its surface 5 to 30 area percent of hard particles having an average particle size in a range of 0.2 to 2.0 μm, with 7 μm or less being the largest diameter. Piston ring according to claim 1, characterized that the grain boundary nitride, in the longitudinal section of a nitriding layer can be considered, 20 microns or less in size (length). Piston ring according to one of claims 1 or 2, wherein the N content of stainless, martensitic, chromium-rich steel from 0.05 to 0.20%. Piston ring according to one of claims 1 to 3, wherein the Hardness of Sliding nitride layer is located in a range of Hv900 to 1400. Manufacturing method for a piston ring after a the claims 1 to 4, with improved abrasion resistance, tear resistance and fatigue resistance, by subjecting to stainless, martensitic, chromium rich Steel nitriding treatment, characterized in that the stainless, martensitic, chromium-rich steel in weight percent from C: 0.3 to 1.0%, Cr: 14.0 to 21.0%, N: 0.05 to 0.50%, at least one of Mo, V, W and Nb: 0.03 to 3.0% in total, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P: 0.05% or less, S: 0.05% or less, with Fe and unavoidable impurities balancing is; and that quenching of the stainless, martensitic, chromium-rich steel before bending into a ring mold of a temperature in the range of 850 to 1000 ºC accomplished becomes. Combination of the piston ring according to one of claims 1 to 4 with a cast iron monoblock cylinder.