JP2005314744A - Material for piston ring and piston ring obtained by using the material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material for a piston ring which has sufficient wear resistance without comprising large quantities of expensive metals, further does not wear a piston ring groove, and has excellent cold workability. <P>SOLUTION: The material for a piston ring has a composition comprising, by weight, 0.4 to 0.5% C, ≤0.7% Si, ≤0.8% Mn, 3.0 to 4.0% Cr, 0.8 to 1.3% Mo, 0.2 to 0.7% V, and the balance Fe with inevitable impurities. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a material for a piston ring used for an internal combustion engine, a compressor, and the like, and in particular, has a heat resistance sag suitable for an ion plating process performed for improving sliding characteristics such as wear resistance. In addition, the present invention relates to a piston ring material excellent in wear resistance and a piston ring using the material.

  The present invention relates to a material for a piston ring and a piston ring using the material, and in order to deepen the understanding of the present invention, the current manufacturing process of the piston ring will be described.

  A material having a predetermined composition (for example, high carbon steel or martensitic stainless steel composition) is melted, ingot-formed, rolled, heat-treated at a predetermined temperature, and then cold-drawn to a predetermined wire diameter. Get the wire. Next, after the wire is rolled into a rectangular cross-sectional shape, it is quenched and tempered under predetermined conditions to ensure the straightness and hardness of the wire. The wire having a rectangular cross section is coiled so as to match the outer diameter of the piston ring. However, since distortion occurs with the coiling, heat treatment for removing distortion is performed.

  Conventionally, the main material for piston rings used in internal combustion engines has been cast iron, but in order to increase the output and rotation of internal combustion engines, piston rings must be made thinner and lighter. Therefore, Si-Cr steel, martensitic stainless steel, etc., which can obtain higher strength than cast iron, have come to be used. However, these piston ring materials do not have sufficient wear resistance and seizure resistance, so that the outer peripheral surface is subjected to surface treatment. Normally, hard chromium plating 2 as shown in FIG. 15 is applied to Si—Cr steel, and nitriding treatment 3 is applied to martensitic stainless steel as shown in FIG. As shown in FIG. 17, the internal combustion engine uses a piston ring in which a hard ceramic coating 4 (chromium nitride, titanium nitride, etc.) is applied to the outer peripheral surface of the nitride layer 3 by ion plating.

  In order to improve wear resistance, a piston ring material containing 7.0 to 11.0% of Cr has been proposed (for example, Patent Document 1).

Furthermore, what uses SKD61 which is a raw material for hot molds as a material for piston rings is proposed (for example, refer patent document 2, patent document 3, patent document 4).
JP 2002-348639 A JP-A-5-223172 Japanese Patent Laid-Open No. 6-293554 Japanese Patent No. 2711962

  By the way, in the case of Si—Cr steel, the hardness of the base material 5 of about 530 HV shown in FIG. 15 becomes about 500 HV by heat treatment for removing distortion accompanying coiling in the manufacturing process of the piston ring (held at 450 ° C. for 1 hour). The hardness of the Cr plating layer 2 applied to the outer peripheral surface in contact with the cylinder wall is about 1000 HV. In order to improve the sliding characteristics of this Si-Cr steel, when the hard ceramic coating by ion plating is applied to the outer peripheral surface, the higher the coating temperature, the better the adhesion of the coating film. For example, at 550 ° C for about 4 hours Ion plating is performed under the high temperature conditions. However, there is an inconvenience that the hardness of the base material 5 of about 500 HV is reduced to 380 HV due to heat sag accompanying the ion plating. With this degree of hardness, the wear resistance is insufficient and it cannot be used as a piston ring.

  Moreover, in the case of low Cr (8-13% Cr) martensitic stainless steel, which does not have a very high high-temperature strength, heat treatment (retained at 600 ° C. for 1 hour) to remove strain associated with coiling in the manufacturing process of the piston ring, Although the hardness of the base material 6 of about 400 HV shown in FIG. 16 is about 360 HV, a large amount of CrN is precipitated by the nitriding treatment 3 performed over the entire circumference, so that the surface hardness increases to about 1200 HV. The hardness of 1200 HV is about the same as the hardness of the ceramic coating obtained by ion plating. However, since the nitriding treatment is performed over the entire circumference, the high hardness nitrided layer forms the piston ring groove 7 (see FIG. 16). It may be worn out.

  In this regard, high Cr (for example, 17% Cr) martensitic stainless steel has excellent high-temperature strength, and is suitable for heat treatment for removing strain as described above (held at 600 ° C. for 1 hour) and ion plating treatment. However, as shown in FIG. 16, when the nitriding treatment 3 is performed prior to the hard ceramic coating 4 by ion plating, as described above, a large amount of CrN is generated along with the nitriding treatment. Since it is deposited over the entire circumference, there is a concern that the surface hardness becomes excessively high and the piston ring groove is worn accordingly.

  Moreover, the high Cr martensitic stainless steel has the disadvantage that the cold workability is inferior due to the presence of a large amount of Cr.

  Cr is an element effective in improving wear resistance, and when used for a sliding member such as a piston ring, it is preferable to contain a certain amount of Cr, but on the other hand, Cr has the disadvantages described above. Have Furthermore, since Cr is an expensive element, it is preferable that the amount of addition is limited to a range necessary for ensuring wear resistance.

  In this respect, the piston ring material described in Patent Document 1 has a smaller amount of Cr added than high Cr martensitic stainless steel, but the amount of Cr added is still 7.0 to 11.0%. It's still not low enough.

  Furthermore, although SKD-61 is a material having excellent heat resistance, the contents of expensive Cr, Mo, and V are 4.5 to 5.5%, 1.0 to 1.5%, and 0, respectively. .8-1.2%.

  The present invention has been made in view of such problems of the prior art, and the object thereof is to have sufficient wear resistance without containing a large amount of expensive metal, and to provide a piston ring. An object of the present invention is to provide a piston ring material excellent in cold workability that does not wear a groove and a piston ring using the material.

  In order to achieve the above object, the piston ring material of the present invention has C of 0.4 to 0.5% by weight, Si of 0.7% by weight or less, Mn of 0.8% by weight or less, and Cr of 3%. 0.0 to 4.0% by weight, Mo is 0.8 to 1.3% by weight, V is 0.2 to 0.7% by weight, and the balance is composed of Fe and inevitable impurities. .

  That is, since an appropriate amount of the alloy element is contained, sufficient wear resistance is provided without lowering the cold workability, and the piston ring groove is not worn.

Since this invention is comprised as mentioned above, there exist the following effects.
(1) Since the content of expensive metals such as Cr, Mo, and V is appropriate, the wear resistance is excellent while the cost is low. Moreover, there is no heat sag due to the ion plating process, and there is almost no decrease in hardness due to the heat treatment. Accordingly, the current value during the ion plating process can be increased, and the film formation rate can be improved.
(2) Since the content of Cr, Mo and V is moderately suppressed, the cold workability is excellent.
(3) Since the Cr content is not large, the amount of CrN deposited by nitriding is less than that of martensitic stainless steel, and the hardness of the nitrided layer is about 700 to 800 HV. Therefore, the nitride layer does not wear the piston ring groove.

The reasons for limiting the numerical values of each element constituting the piston ring material of the present invention are as follows.
(1) C is 0.4 to 0.5% by weight.

C is an interstitial solid solution element that contributes to improvement in hardness and strength. In addition, carbide is generated to increase wear resistance. In order to enjoy these effects, C is preferably contained in an amount of 0.4% by weight or more. However, if added in a large amount, fatigue strength is reduced by generating coarse carbides, so the upper limit is preferably 0.5% by weight.
(2) Si is 0.7% by weight or less.

Si is added as a deoxidizer during the melting of steel, and dissolves in the matrix, contributing to the improvement of hardness and strength. However, adding a large amount reduces the cold workability, so its upper limit value. Is preferably 0.7% by weight.
(3) Mn is 0.8% by weight or less.

Mn is added for deoxidation at the time of melting steel and fixing S in the steel, but if added in a large amount, the cold workability is lowered, so the upper limit is 0.8% by weight. It is preferable to do this. In order to compensate for the decrease in hardenability due to the reduction in the amount of alloy elements, it is preferable to add 0.6% by weight or more of Mn.
(4) Cr is 3.0 to 4.0% by weight.

Cr is an element that is combined with C to form carbides and nitrides, and is therefore an indispensable element for improving wear resistance. In order to enjoy these effects, Cr is preferably contained in an amount of 3.0% by weight or more. However, if added in a large amount, the cold workability is lowered, so the upper limit is preferably 4.0% by weight.
(5) Mo is 0.8 to 1.3% by weight.

Mo has the effect of improving the temper softening resistance, and is effective in improving heat sag during the ion plating process. Moreover, carbide is formed similarly to Cr, and wear resistance is improved. In order to enjoy these effects, Mo is preferably contained in an amount of 0.8% by weight or more. However, if added in a large amount, the cold workability is lowered, so the upper limit is preferably 1.3% by weight.
(6) V is 0.2 to 0.7% by weight.

  V, like Mo, has the effect of improving the temper softening resistance, and is effective in improving heat sag during ion plating. Moreover, carbide is formed like Cr and Mo, and wear resistance is improved. In order to enjoy these effects, V is preferably contained in an amount of 0.2% by weight or more. However, if added in a large amount, the cold workability is lowered, so the upper limit is preferably 0.7% by weight.

  To provide a material for a piston ring that has sufficient wear resistance and does not wear the piston ring groove and is excellent in cold workability by subjecting the material having the above composition to the following treatment. Can do.

  A material having the above-described composition with appropriate contents of Cr, Mo, and V contributing to improvement in wear resistance is melted, and hot-rolled after hot forging to obtain a wire having a predetermined diameter. Next, the wire is cold-drawn into a wire having a predetermined diameter. Next, the wire is cold-rolled into a predetermined rectangular cross section. By quenching and tempering the rolled material having a rectangular cross section, carbides are precipitated in the crystal grains to improve the strength and improve straightness. Next, the rectangular cross-section rolled material is coiled to a predetermined outer diameter, and after coiling, it is cut into the shape of a piston ring and subjected to nitriding treatment 3 as shown in FIG. After heat treatment for strain relief, an ion plating process 4 as shown in FIG. 17 is performed on the outer peripheral surface of the piston ring.

  The piston ring thus obtained keeps the amount of C low, so it has the necessary fatigue strength and cold work because the contents of Cr, Mo and V contributing to the improvement of wear resistance are appropriate. Since the Cr content is not too much, an appropriate amount of CrN is precipitated by nitriding treatment, and the hardness of the nitrided layer is about 700 to 800 HV. Will not wear the piston ring groove.

Examples of the present invention will be described below. However, 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) Evaluation of high-temperature softening resistance and cold workability 10 kg of each of the steel compositions (wt%) shown in Table 1 below are melted in a vacuum melting furnace and made into an ingot, and then hot forged into a 20 mm diameter round bar Further, spheroidizing annealing was performed, and the cold workability described later was evaluated for this sample.

  The annealed material was kept at 980 ° C. for 30 minutes and then air-cooled and quenched, and further tempered to 580 to 620 ° C., so that the tempered hardness was 480 to 490 HV. About this sample, the high temperature softening resistance mentioned later was evaluated.

  Table 2 shows the evaluation results of cold workability and high temperature softening resistance.

高温軟化抵抗については、硬さを調質した直径２０mmの丸棒を長さ２０mmに切断することにより、直径が２０mmで長さが２０mmの試料を各組成について複数個作製し、各試料に６００℃で１０時間の熱処理を施した後、熱処理前後の断面の硬さを測定することにより評価した。表２の硬さの数値は、３個の試料について、中心から半径方向に５mm離れるとともに円周方向に互いに７２゜づつ等間隔で離れた５点のビッカース硬さ（ＨＶ５）を測定することによって得られた合計１５点の硬さの平均値である。

For high-temperature softening resistance, a 20 mm diameter round bar with a tempered hardness is cut into a length of 20 mm to produce a plurality of samples having a diameter of 20 mm and a length of 20 mm for each composition. After heat treatment at 10 ° C. for 10 hours, evaluation was made by measuring the hardness of the cross section before and after the heat treatment. The hardness values in Table 2 are obtained by measuring the five Vickers hardnesses (HV5) of three specimens that are 5 mm apart from the center in the radial direction and 72 ° apart from each other at equal intervals in the circumferential direction. It is an average value of the hardness of 15 points in total obtained.

  The cold workability was evaluated by a drawing (%) numerical value by machining an annealed round bar having a diameter of 20 mm into a tensile test piece No. 4 of JISZ2201 and conducting a tensile test. The numerical value of the aperture (%) in Table 2 is an average value of three samples.

  From Table 2, the following points are clear.

  Samples Nos. 7 and 8 have a small decrease in hardness after heat treatment because of a small amount of Cr.

  Since sample No. 9 has too much Cr, cold workability is not good.

  Since sample No10 has a small amount of Mo, the hardness reduction after heat treatment is large.

  Since sample Nos. 11, 12, 13, and 14 have a large amount of Mo, V, Si, and Mn, respectively, cold workability is not good.

On the other hand, sample Nos. 1 to 6 have appropriate addition amounts of C, Si, Mn, Cr, Mo, and V, so there is little decrease in hardness after heat treatment (high resistance to high-temperature softening) and good cold workability. It is.
(2) Effects of each element on high-temperature softening resistance and cold workability Based on the numerical values in Tables 1 and 2, the effects of each element on high-temperature softening resistance and cold workability are shown in FIG. 10.
a. Effect of Cr (Figs. 1 and 2)
As shown in FIG. 1, ΔHV decreases as the amount of Cr increases, but it can be seen that when Cr exceeds 3% by weight, the decrease in ΔHV decreases.

As shown in FIG. 2, it can be seen that the numerical value of the aperture (%) decreases almost linearly as the Cr amount increases.
b. Effect of Mo (Figs. 3 and 4)
As shown in FIG. 3, it can be seen that ΔHV decreases substantially linearly as the Mo amount increases.

As shown in FIG. 4, it can be seen that the numerical value of the aperture (%) decreases almost linearly as the amount of Mo increases.
c. Effect of V (FIGS. 5 and 6)
As shown in FIG. 5, it can be seen that ΔHV decreases substantially linearly as the V amount increases.

As shown in FIG. 6, it can be seen that the numerical value of the aperture (%) decreases almost linearly as the V amount increases.
d. Effect of Si (Figs. 7 and 8)
As shown in FIG. 7, ΔHV is substantially constant regardless of the amount of Si.

As shown in FIG. 8, it can be seen that the numerical value of the aperture (%) decreases almost linearly as the Si amount increases.
e. Effect of Mn (FIGS. 9 and 10)
As shown in FIG. 9, ΔHV is substantially constant regardless of the amount of Mn.

As shown in FIG. 10, it can be seen that the numerical value of the aperture (%) decreases almost linearly as the amount of Mn increases.
(3) Evaluation of high temperature softening resistance and cold workability of the piston ring material having the composition of the present invention and the piston ring material having the composition of SKD61 a. High-temperature softening resistance Steel having a composition (% by weight) as shown in Table 3 below was melted in a 10-ton electric melting furnace, and after hot forging, a wire having a diameter of 5.5 mm was obtained by hot rolling. Next, the wire was cold-drawn into a wire having a diameter of 2.00 mm, and then cold-rolled into a rectangular cross section of 1.00 mm × 2.00 mm. The rectangular cross-section rolled material is heated to 1030 ° C., held for 3 minutes and then oil-cooled, then heated to a tempering temperature in the range shown in FIG. 11 and held for 4 minutes to cool by air. And Vickers hardness (HV10) when tempering was performed. FIG. 11 shows the change in Vickers hardness (HV10) when the tempering temperature is taken on the horizontal axis. In FIG. 11, the symbol ◯ indicates the product of the present invention, and the ● indicates SKD61. In addition, Table 4 shows numerical values of actual tempering temperature (° C.) and Vickers hardness (HV10) at each point in FIG.

図１１に示すように、本発明品はＳＫＤ６１と遜色ない程度のビッカース硬さ（ＨＶ１０）を有し、ＳＫＤ６１とほぼ同程度の高温軟化抵抗を備えていることが分かる。

As shown in FIG. 11, the product of the present invention has a Vickers hardness (HV10) comparable to that of SKD61, and has a high temperature softening resistance substantially equal to that of SKD61.

  Moreover, after obtaining the rectangular cross-section rolled material of 1.00 mm x 2.00 mm from the steel having the composition shown in Table 3 by the same process, the rectangular cross-section rolled material was heated to 1030 ° C. and held for 3 minutes for oil cooling. A quenching and tempering treatment was performed in which the temperature was raised to 600 ° C., held for 4 minutes, and air cooled. Next, the rectangular cross-section rolled material was coiled to an outer diameter of 70 mm, and after coiling, it was cut into the shape of the piston ring 1 as shown in FIG. 12, and then the piston ring was heat-treated at 600 ° C. for 1 hour. Thereafter, it was air-cooled to room temperature and further subjected to heat treatment at 550 ° C. for 4 hours. Table 5 shows the hardness (HV0.5) immediately before coiling, after heat treatment at 600 ° C. × 1 hour, and after heat treatment at 550 ° C. × 4 hours.

表５に示すように、本発明品は、熱処理による硬度低下が少なく、ＳＫＤ６１と同程度の高温軟化抵抗を有することが分かる。
ｂ．冷間加工性
表３に示す組成の各鋼１０ｋｇを真空溶解炉で溶解し、インゴットにした後、直径２０mmの丸棒に熱間鍛造し、さらに、球状化焼なましを施して、この試料について前記した冷間加工性の評価（引張試験による絞り（％）の数値の比較）をした。

As shown in Table 5, it can be seen that the product of the present invention has a low hardness reduction due to heat treatment and has a high temperature softening resistance comparable to that of SKD61.
b. Cold workability 10 kg of each steel having the composition shown in Table 3 was melted in a vacuum melting furnace and made into an ingot, then hot forged into a round bar having a diameter of 20 mm, and further subjected to spheroidizing annealing. The cold workability described above was evaluated (comparison of numerical values of drawing (%) by a tensile test).

The drawing (%) of the product of the present invention is 73 to 77, the numerical value of the drawing (%) of SKD61 is 70, the numerical value of the drawing (%) of the product of the present invention is higher, and the product of the present invention is cold worked. It turns out that it is excellent in property.
(4) Relationship between quenching temperature and hardness (HV0.5) of the product of the present invention and heating time and hardness (HV0.5) during quenching of the product of the present invention The piston ring of the present invention having the composition shown in Table 3 The material was melted, and after hot forging, a wire with a diameter of 5.5 mm was obtained by hot rolling. Next, the wire was cold-drawn into a wire having a diameter of 2.00 mm, and then cold-rolled into a rectangular cross section of 1.00 mm × 2.00 mm. The rectangular cross-section rolled material is subjected to quenching and tempering processes in which it is heated to 950 to 1070 ° C., held for 3 minutes, air cooled or oil cooled, then heated to 600 ° C. and held for 4 minutes to air cool. The result of having measured hardness (HV0.5) about what was done is shown in FIG. In FIG. 13, line (a) is the hardness immediately after oil-cooled quenching, line (b) is the hardness immediately after air-cooled quenching, line (c) is the hardness immediately after oil-cooled tempering, and line (d) is Indicates the hardness immediately after air cooling and tempering.

  As apparent from FIG. 13, if quenched from 980 to 1070 ° C., 500 HV0.5 or more can be obtained as the hardness after tempering, whether air cooling or oil cooling.

  Also, the above-mentioned rectangular cross-section rolled material is heated to 1030 ° C., held for 2.64 to 5.31 minutes and then oil cooled, then heated to 600 ° C. and held for 4 minutes for air cooling, quenching and baking FIG. 14 shows the result of measuring the hardness (HV0.5) of the sample subjected to the return treatment. In FIG. 14, line (e) indicates the hardness immediately after oil-cooling and quenching, and line (f) indicates the hardness immediately after oil-cooling and tempering. It can be seen that the hardness after tempering hardly changes in the range of the heating time shown in FIG.

It is a figure which shows the relationship between Cr content (%) and high temperature softening resistance (change of Vickers hardness). It is a figure which shows the relationship between Cr content (%) and aperture_diaphragm | restriction (%). It is a figure which shows the relationship between Mo content (%) and high temperature softening resistance (change of Vickers hardness). It is a figure which shows the relationship between Mo content (%) and aperture_diaphragm | restriction (%). It is a figure which shows the relationship between V content (%) and high temperature softening resistance (change of Vickers hardness). It is a figure which shows the relationship between V content (%) and aperture_diaphragm | restriction (%). It is a figure which shows the relationship between Si content (%) and high temperature softening resistance (change of Vickers hardness). It is a figure which shows the relationship between Si content (%) and aperture_diaphragm | restriction (%). It is a figure which shows the relationship between Mn content (%) and high temperature softening resistance (change of Vickers hardness). It is a figure which shows the relationship between Mn content (%) and aperture (%). It is a figure which shows the relationship between tempering temperature and Vickers hardness. It is a perspective view of a piston ring. It is a figure which shows the relationship between quenching temperature and hardness. It is a figure which shows the relationship between the heating time at the time of quenching, and hardness. It is the schematic which shows the state which inserts the piston ring which consists of Si-Cr steel which gave Cr plating into a piston ring groove | channel. It is the schematic which shows the state which inserts the piston ring which consists of martensite-stainless steel which performed the nitriding process into a piston ring groove | channel. It is the schematic which shows the state which inserts the piston ring which consists of martensite-stainless steel which performed the ion plating process after the nitriding process in a piston ring groove | channel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piston ring 2 ... Chrome plating 3 ... Nitriding process 4 ... Ceramic coating 5 ... Base material 6 ... Base material 7 ... Piston ring groove

Claims (2)

  C is 0.4 to 0.5% by weight, Si is 0.7% by weight or less, Mn is 0.8% by weight or less, Cr is 3.0 to 4.0% by weight, and Mo is 0.8 to 1.% by weight. A piston ring material having a composition of 3% by weight, V of 0.2 to 0.7% by weight, and the balance of Fe and inevitable impurities.   A piston ring using the piston ring material according to claim 1.

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