JP4820490B2 - Method for producing ferrous sintered alloy - Google Patents

Description

【００２３】
上記の目潰し処理の後、焼結体表面の空孔率を観察し、ガス窒化処理を行なった。このとき、比較例として目潰し処理を行なわない焼結体を準備し、これにも同様のガス窒化処理を行なった。該窒化処理は、図１に示す条件で行なった。
【００２４】
表１の条件の中で水溶液を使うバレルおよび研磨加工したサンプルについては、処理後に１２０℃、１時間の条件で乾燥を行ない、サンプル中に浸透した水分を除去した。表１のサンプルにおける残水量は、いずれも０．１質量％以下である。
【００２５】
表１に、上記の目潰し処理後のサンプル表面における空孔の面積比（面積率）と、窒化処理後の抗折力と、窒化処理後のサンプル中央部を切断し窒化状況を観察した結果とを示す。
【００２６】
なお、サンプル表面における空孔率は、サンプル表面を１００倍で写真撮影し、空孔部を黒く塗りつぶし、画像解析により空孔の面積比率を測定した。また、残水量は、次のようにして測定する。すなわち、各サンプルについて乾燥前重量を電子天秤にて１／１００００ｇまで測定し、重量測定済みサンプルについて恒温槽にて所定の温度・時間で乾燥し、サンプルを常温まで自然冷却した後に乾燥後の重量を電子天秤にて再度１／１００００ｇまで測定し、下記算出式（１）にて製品における残水率を算出する。
残水率（％）＝（（乾燥前重量―乾燥後重量）／乾燥後重量）×１００…（１）
また抗折力は、次のようにして測定する。すなわち、試験片として２８×２４×４ｍｍのブレード形状のサンプル（試験片）を用い、国際規格ＩＳＯ３３２５に規定されている抗折力測定装置を基礎とした標点間距離を１０ｍｍにした専用装置を作製し、この試験治具を用い荷重を付加した後に試験片の破壊した荷重を測定し、下記の計算式（２）にて抗折力Ｒ（ＭＰａ）を算出した。
【００２７】
Ｒ＝（３Ｆｌ）／（２ｂｈ²）…（２）
計算式（２）において、Ｆは試験片が破断したときの荷重（Ｎ）、ｌは支点間距離（ｍｍ）、ｂは試験片の厚みに対して直角方向の幅（ｍｍ）、ｈは試験片の荷重方向に対して平行な高さ（厚み）（ｍｍ）である。
【００２８】
表１に示すように、サンプルに表面処理を施さなかったものは、窒化層が内部にまで浸透したため、抗折力が極めて低くなっているのが分かる。表面処理を施したサンプルであっても、表面における空孔率が５％を越えるものは、窒化層が安定していないため、全体的に窒化層の厚みが大きくなっていると同時に部分的に深くまで窒化された部分が多く存在していた。そのため、抗折力が低くなっている。
【００２９】
それに対し、表面における空孔率が５％以下のサンプルは、窒化層の厚みが小さく、サンプル表層のみ窒化されていた。つまり、サンプル内部はほとんど窒化されず、そのため抗折力が高くなっている。したがって、サンプル表面における空孔率は、０％以上５％以下であることが必要である。
【００３０】
（実施の形態２）
次に、本発明の実施の形態２について説明する。本実施の形態２では、実施の形態１で作製したサンプルの中で研磨加工品について乾燥条件を変え、残水量の異なるサンプルを作製し、実施の形態１と同様の条件で窒化処理を行なった。ここで、ショット品は目潰し処理の際に水を使用しないため、水分率が０．００１％より小さい値となっている。
【００３１】
そして、各サンプル表面における窒化層の形成状況を評価した。その結果を表２に示す。
【００３２】
【表２】

【００３３】
表２に示すように、残水量と窒化層の形成状況との間に相関があることがわかる。具体的には、残水量が０．１質量％を越えると、窒化層が形成されなくなるかあるいは不均一に形成されることがわかる。したがって、残水量は０質量％以上０．１質量％以下であることが必要である。
【００３４】
（実施の形態３）
次に、本発明の実施の形態３について説明する。本実施の形態では、Ｆｅ−Ｃｒ合金粉、Ｆｅ−Ｃｒ―Ｍｏ合金粉、Ｆｅ−Ｃｒ―Ｃ合金粉、Ｆｅ−Ｃｒ―Ｍｏ―Ｃ合金粉および黒鉛粉を準備し、これらの１種あるいは２種以上を所定の割合で混合し、下記の表３に示す組成になるように混合粉末を作製した。そして、いずれにも潤滑剤を１質量％添加した。
【００３５】
【表３】

【００３６】
上記各粉末を８００〜１０００ＭＰａでコンプレッサのベーン（ブレード）形状に成形し、焼結体の密度が６．６〜６．７Ｍｇ／ｍ³となるように真空中１１８０℃〜１２５０℃で１時間の焼結を行なった。その結果、得られた焼結体の密度は、６．６〜６．７Ｍｇ／ｍ³であった。その後、５分のショットブラストを行なって焼結体表面の目潰しを行なった。
【００３７】
このサンプルを真空中１０５０℃で１時間加熱して焼入れし、その後２００℃で１．５時間の焼戻しを行なった。次に、サンプルに研磨加工を行ない、１５０℃で３時間の乾燥を行ない、その後図１の条件で窒化処理を行なった。
【００３８】
上記窒化処理によりサンプル表面に形成された窒化層の厚みは、５０〜１００μｍ程度であった。また、比較のために窒化しないサンプルも作製した。
【００３９】
上記の各サンプルに表３に示す条件で耐摩耗試験を行なった。その結果を表３に示す。表３に示すように、本発明の組成を有するものは、良好な耐摩耗性を示しているのがわかる。
【００４０】
具体的には、サンプルにおけるクロムの含有量が１２質量％未満の場合は硬質粒子となるクロム炭化物の生成量が少なくなり、耐摩耗性が低下する。該含有量が２５質量％を越えると、フェライト相が安定化され易く、焼入れによる硬さ向上が期待されなくなり、耐摩耗性が低下する。したがって、クロムの含有量は、好ましくは１３質量％以上２５質量％以下であり、より好ましくは１６質量％以上２０質量％以下である。
【００４１】
また、サンプルにおける炭素（Ｃ）の含有量が０．５質量％未満の場合，炭化物生成量が少なくなり耐摩耗性が低下し、該含有量が１．５％を越えると、残留オーステナイトの生成量が増加し耐摩耗性が低下する。したがって、炭素の含有量は、好ましくは０．６質量％以上１．５質量％以下であり、より好ましくは０．８質量％以上１．０質量％以下である。
【００４２】
なお、サンプルにモリブデン（Ｍｏ）を添加した場合にも、耐摩耗性は高く維持されており、耐食性を向上させる効果がある。しかし、モリブデンの含有量が０．５質量％未満の場合、モリブデンを添加することによる効果が少なく、モリブデンの含有量が３．０質量％を越えると粉末の硬化が大きく圧縮性が低下するだけでなくコストも上昇する。したがって、サンプルにおけるモリブデンの含有量は、０．５質量％以上３．０質量％以下とした。しかし、モリブデンを添加することによる効果は少なくなるが、モリブデンの含有量を、０．５質量％未満としてもよい。
【００４３】
下記の表４に、原料組成と腐食速度の関係を示す。表４に示すように、モリブデンを所定量添加することにより、耐食性が向上しているのがわかる。
【００４４】
【表４】

【００４５】
以上のように、この発明の実施の形態について説明を行なったが、今回開示した実施の形態はすべての点で例示であって、制限的なものではないと考えられるべきである。本発明の範囲は特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれる。
【００４６】
【発明の効果】
以上説明したように、本発明によれば、母材表面における空孔の面積比と母材内部に存在する水分量を適切に規定したので、クロムを含有する鉄系焼結合金の内部が窒化されるのを抑制しながら鉄系焼結合金の表面に均一な窒化層を形成することができる。それにより、鉄系焼結合金の強度、靭性および耐摩耗性を向上することができる。
【００４７】
また、クロムを含有する鉄系焼結合金の基地中に炭化物を分散させることにより母材の強度を上げることができ、この母材表面に本発明の窒化処理を施すことで耐摩耗性をより効果的に向上することができる。なお、母材中に炭化物を均一に分散させることにより、さらに効果的に耐摩耗性を向上することができる。
【００４８】
また、鉄系焼結合金の母材にモリブデンを添加することにより、高温での硬度向上を期待でき、このことも耐摩耗性の向上に寄与し得る。
【図面の簡単な説明】
【図１】 本発明の窒化処理条件を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an iron-based sintered alloy having a uniform nitride layer on the surface and excellent in strength, toughness and wear resistance.
[0002]
[Prior art]
Conventionally, a member called a blade incorporated in a rotary compressor is known as an example of a member formed of an iron-based sintered alloy. The blade is slidably installed in a blade groove provided in a cylinder of the rotary compressor, and is brought into contact with an outer peripheral surface of a roller accommodated in the cylinder. Since the side surface of the blade is in sliding contact with the blade groove and the tip of the blade is in sliding contact with the outer peripheral surface of the roller, the blade must have excellent wear resistance.
[0003]
A technique for improving the wear resistance of the blade is disclosed in, for example, Japanese Patent Publication No. 1-58356.
[0004]
In the above publication, either a steel containing chromium (Cr), a sintered alloy or cast iron is used as a base material of a blade, and this base material is subjected to soft nitriding treatment, and a Fe—Cr—N compound is formed on the surface layer portion thereof. A first layer having a main component is generated, and a second layer in which a compound having the same component as the above compound is scattered below the first layer is generated, and at least in a blade groove formed in the cylinder By removing the first layer on the side surface in sliding contact and exposing the second layer, the blade and the mating member are slidably contacted with each other through the compound interspersed in the second layer. An invention for improving the performance is described.
[0005]
[Problems to be solved by the invention]
However, the sintered alloy has continuous pores from the surface to the inside, and when the above nitriding treatment is simply performed on the sintered alloy, brittle nitrides are formed through the pores to the inside. Therefore, the strength and the like of the sintered alloy that is the base material are reduced.
[0006]
Further, in order to obtain excellent wear resistance by performing nitriding treatment, it is desirable that the base material itself has a higher hardness, but the above publication does not describe characteristics to be provided as a sintered alloy. Therefore, in the invention described in the above publication, it cannot be said that the wear resistance of the blade (sintered alloy) can be effectively improved.
[0007]
The present invention has been made to solve the above problems. An object of the present invention is to improve the strength, toughness and wear resistance of an iron-based sintered alloy containing chromium (Cr) and nitrided on its surface.
[0009]
[Means for Solving the Problems]
The inventors of the present application have made extensive studies on a technique for performing stable nitriding treatment on the surface of the iron-based sintered alloy containing chromium, and the area ratio of pores on the surface of the iron-based sintered alloy and the iron-based sintered alloy. It has been found that the amount of water inside the bond gold affects the nitriding treatment.
[0010]
Therefore, various experiments were conducted, and the area ratio of the pores on the surface of the base material was set to 5% or less, and the amount of moisture existing in the base material was set to 0.1% or less, so that the surface of the iron-based sintered alloy was It has been found that a stable nitriding treatment can be performed.
[0011]
Here, the area ratio of the pores was set to 5% or less because if the area ratio of the pores exceeds 5%, nitriding penetrates into the base material and the base material becomes brittle. This is because the strength decreases. The reason why the moisture present in the base material is defined as 0.1% or less is that when the moisture exceeds 0.1%, nitriding is inhibited and a nitrided layer is hardly formed. The hole area ratio and the water content may be 0%.
[0012]
The base material is preferably composed of chromium in a mass ratio of 12% to 25%, carbon (C) in a mass ratio of 0.5% to 1.5%, iron, and inevitable impurities. The carbide is dispersed inside the base material.
[0013]
Thus, the nitriding treatment is stabilized when the base material contains chromium in a mass ratio of 12% to 25%. In addition, when the chromium content is less than 12%, the carbide dispersion amount decreases, so the wear resistance decreases. When the chromium content exceeds 25%, the effect of improving the wear resistance decreases and the formation of retained austenite. Increases the wear resistance. Therefore, the chromium content in the base material is set to the above range.
[0014]
Carbon (C) is an indispensable element for generating carbide inside the base material. However, if the carbon content is less than 0.5%, the amount of carbide decreases and wear resistance decreases, and if the carbon content exceeds 1.5%, the effect of improving wear resistance decreases, It becomes difficult to increase the density of powder molding. Therefore, the carbon content in the base material is set to the above range.
[0015]
The base material preferably contains molybdenum (Mo) of 3.0% or less by mass ratio.
[0016]
Thus, by containing molybdenum, corrosion resistance improves. When the content of molybdenum is less than 0.5%, the effect of adding molybdenum is reduced, but there is an effect. However, if the molybdenum content exceeds 3.0%, the degree of improvement in corrosion resistance decreases and the cost also increases. Therefore, the content of molybdenum in the base material is set to the above range.
[0017]
The method for producing an iron-based sintered alloy according to the present invention includes a step of crushing the surface of the blade so that the area ratio of pores on the surface is 5% or less, and a nitride layer from the surface to a depth of 20 to 120 μm. And surface nitriding so as to be formed.
[0018]
The crushing process is a barrel or polishing process using an aqueous solution, and the method for producing an iron-based sintered alloy according to the present invention includes a step of drying so that the residual water amount is 0.1 mass% or less after the crushing process. In addition.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIG. 1 and Tables 1 to 3.
[0020]
(Embodiment 1)
A mixed powder obtained by adding 1% by mass of a lubricant to Fe-17% (mass)% Cr-1% by mass C alloy powder was molded into a plate of 25 × 30 × 5 mm at a molding pressure of 882 MPa. The obtained green compact was sintered in a vacuum atmosphere at 1250 ° C. for 1 hour. The density of the sintered body was 6.63 Mg / m ³ .
[0021]
The sintered body was subjected to surface crushing treatment (surface treatment for reducing the area of pores on the surface of the sintered body) under the conditions shown in Table 1 below.
[0022]
[Table 1]

[0023]
After the above crushing treatment, the porosity of the sintered body surface was observed and gas nitriding treatment was performed. At this time, a sintered body that was not subjected to the crushing process was prepared as a comparative example, and a similar gas nitriding process was performed on the sintered body. The nitriding treatment was performed under the conditions shown in FIG.
[0024]
The barrel using an aqueous solution under the conditions shown in Table 1 and the polished sample were dried at 120 ° C. for 1 hour after the treatment to remove moisture permeated into the sample. The amount of residual water in the samples in Table 1 is 0.1% by mass or less.
[0025]
Table 1 shows the area ratio (area ratio) of vacancies on the sample surface after the above-mentioned crushing treatment, the bending strength after nitriding treatment, and the results of observing the nitriding situation by cutting the center portion of the sample after nitriding treatment. Indicates.
[0026]
The porosity of the sample surface was measured by taking a photograph of the sample surface at a magnification of 100 times, painting the pores black, and measuring the area ratio of the pores by image analysis. Moreover, the amount of residual water is measured as follows. That is, the weight before drying of each sample is measured with an electronic balance to 1/10000 g, the weight-measured sample is dried in a constant temperature bath at a predetermined temperature and time, the sample is naturally cooled to room temperature, and then the weight after drying. Is again measured with an electronic balance to 1/10000 g, and the residual water rate in the product is calculated by the following calculation formula (1).
Residual water ratio (%) = ((weight before drying−weight after drying) / weight after drying) × 100 (1)
The bending strength is measured as follows. In other words, a 28 x 24 x 4 mm blade-shaped sample (test piece) was used as a test piece, and a dedicated device with a distance between gauge points of 10 mm based on a bending strength measuring device stipulated in international standard ISO 3325 was used. After producing and applying a load using this test jig, the load at which the test piece was broken was measured, and the bending force R (MPa) was calculated by the following formula (2).
[0027]
R = (3Fl) / (2bh ² ) (2)
In the calculation formula (2), F is the load (N) when the specimen is broken, l is the distance between supporting points (mm), b is the width (mm) in the direction perpendicular to the thickness of the specimen, and h is the test. The height (thickness) (mm) is parallel to the load direction of the piece.
[0028]
As shown in Table 1, it can be seen that in the case where the sample was not subjected to the surface treatment, the bending strength was extremely low because the nitride layer penetrated into the inside. Even in the case of a surface-treated sample, if the porosity on the surface exceeds 5%, since the nitride layer is not stable, the thickness of the nitride layer is increased as a whole and partially Many portions were deeply nitrided. Therefore, the bending strength is low.
[0029]
On the other hand, in the sample having a porosity of 5% or less on the surface, the thickness of the nitride layer was small, and only the sample surface layer was nitrided. That is, the inside of the sample is hardly nitrided, so that the bending strength is high. Therefore, the porosity on the sample surface needs to be 0% or more and 5% or less.
[0030]
(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the second embodiment, among the samples produced in the first embodiment, the dry conditions were changed for the polished product, samples having different residual water amounts were produced, and nitriding was performed under the same conditions as in the first embodiment. . Here, since the shot product does not use water in the crushing process, the moisture content is less than 0.001%.
[0031]
And the formation condition of the nitride layer in each sample surface was evaluated. The results are shown in Table 2.
[0032]
[Table 2]

[0033]
As shown in Table 2, it can be seen that there is a correlation between the amount of residual water and the formation state of the nitride layer. Specifically, it can be seen that when the amount of residual water exceeds 0.1% by mass, the nitrided layer is not formed or formed unevenly. Therefore, the amount of residual water needs to be 0 mass% or more and 0.1 mass% or less.
[0034]
(Embodiment 3)
Next, a third embodiment of the present invention will be described. In the present embodiment, Fe—Cr alloy powder, Fe—Cr—Mo alloy powder, Fe—Cr—C alloy powder, Fe—Cr—Mo—C alloy powder and graphite powder are prepared, and one or two of these are prepared. More than the seeds were mixed at a predetermined ratio, and a mixed powder was prepared so as to have the composition shown in Table 3 below. And 1 mass% of lubricant was added to all.
[0035]
[Table 3]

[0036]
Each of the above powders is molded into a vane shape of a compressor at 800 to 1000 MPa, and the sintered compact has a density of 6.6 to 6.7 Mg / m ³ for 1 hour at 1180 ° C. to 1250 ° C. in a vacuum. Sintering was performed. As a result, the density of the obtained sintered body was 6.6 to 6.7 Mg / m ³ . Thereafter, the surface of the sintered body was crushed by performing shot blasting for 5 minutes.
[0037]
The sample was quenched in a vacuum at 1050 ° C. for 1 hour and then tempered at 200 ° C. for 1.5 hours. Next, the sample was polished, dried at 150 ° C. for 3 hours, and then subjected to nitriding under the conditions shown in FIG.
[0038]
The thickness of the nitride layer formed on the sample surface by the nitriding treatment was about 50 to 100 μm. For comparison, a sample that was not nitrided was also produced.
[0039]
Each of the above samples was subjected to an abrasion resistance test under the conditions shown in Table 3. The results are shown in Table 3. As shown in Table 3, it can be seen that those having the composition of the present invention exhibit good wear resistance.
[0040]
Specifically, when the chromium content in the sample is less than 12% by mass, the amount of chromium carbide that forms hard particles decreases, and the wear resistance decreases. When the content exceeds 25% by mass, the ferrite phase is easily stabilized, and the improvement in hardness by quenching is not expected, and the wear resistance is lowered. Accordingly, the chromium content is preferably 13% by mass or more and 25% by mass or less, and more preferably 16% by mass or more and 20% by mass or less.
[0041]
In addition, when the carbon (C) content in the sample is less than 0.5% by mass, the amount of carbide produced is reduced and the wear resistance is reduced, and when the content exceeds 1.5%, residual austenite is produced. The amount increases and wear resistance decreases. Therefore, the carbon content is preferably 0.6% by mass or more and 1.5% by mass or less, and more preferably 0.8% by mass or more and 1.0% by mass or less.
[0042]
In addition, even when molybdenum (Mo) is added to the sample, the wear resistance is maintained high, and there is an effect of improving the corrosion resistance. However, when the molybdenum content is less than 0.5% by mass, the effect of adding molybdenum is small, and when the molybdenum content exceeds 3.0% by mass, the powder is hardened and the compressibility is reduced. Not only will the cost increase. Therefore, the content of molybdenum in the sample is set to 0.5% by mass or more and 3.0% by mass or less. However, the effect of adding molybdenum is reduced, but the molybdenum content may be less than 0.5% by mass.
[0043]
Table 4 below shows the relationship between the raw material composition and the corrosion rate. As shown in Table 4, it can be seen that the corrosion resistance is improved by adding a predetermined amount of molybdenum.
[0044]
[Table 4]

[0045]
As described above, the embodiment of the present invention has been described. However, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and includes meanings equivalent to the terms of the claims and all modifications within the scope.
[0046]
【The invention's effect】
As described above, according to the present invention, the area ratio of pores on the surface of the base material and the amount of moisture present in the base material are appropriately defined, so that the inside of the iron-based sintered alloy containing chromium is nitrided. Thus, a uniform nitride layer can be formed on the surface of the iron-based sintered alloy while suppressing this. Thereby, the strength, toughness, and wear resistance of the iron-based sintered alloy can be improved.
[0047]
Moreover, the strength of the base material can be increased by dispersing carbide in the base of the iron-based sintered alloy containing chromium, and the wear resistance can be further improved by applying the nitriding treatment of the present invention to the surface of the base material. It can be effectively improved. Note that the wear resistance can be further effectively improved by uniformly dispersing carbide in the base material.
[0048]
Further, by adding molybdenum to the base material of the iron-based sintered alloy, an improvement in hardness at high temperatures can be expected, which can also contribute to an improvement in wear resistance.
[Brief description of the drawings]
FIG. 1 is a diagram showing nitriding conditions of the present invention.

Claims (1)

Inside, carbide is dispersed, chromium in a mass ratio of 12% to 25%, carbon in a mass ratio of 0.5% to 1.5%, molybdenum in a mass ratio of 3.0% or less, Crushing the surface by barrel or polishing using an aqueous solution so that the area ratio of vacancies in the surface of the base material containing the balance composed of iron and inevitable impurities is 5% or less;
And a step of surface nitriding treatment as the nitride layer to a depth of 20~120μm from the surface is formed,
A method for producing an iron-based sintered alloy, which is dried so that a residual water amount is 0.1% by mass or less after the crushing treatment .

Images