GB2104547A - Anti-wear sintered alloy and method for manufacturing thereof - Google Patents

Abstract

Improved anti-wear sintered alloy contains (a) a hardener consisting of Cr 2.5-25.0 wt%, Mn 0.1-3.0 wt%, P 0.2-0.8 wt%, Cu 1.0-5.0 wt%, Si 0.5-2.0 wt% and Mo less than 3.0 wt%; (b) an additive alloy consisting of one of more elements selected from W 0.1-5.0 wt%, V 0.1-5.0 wt%, Nb 0.1-2.5 wt%, Ti 0.1.-2.5 wt% and Ta 0.1-1.5 wt%, said additive alloy comprising 0.1-10.0 wt% with respect to the total weight of the whole alloys; (c) C 1.5-3.5 wt%, and (d) impurities less than 2 wt%, the balance being Fe. The alloy is manufactured by a method in which a hardener and additive alloys are separately manufactured, these two alloys are blended in appropriate proportions to prepare an alloy powder, a predetermined amount of carbon is added and the mixture is sintered.

Description

SPECIFICATION Anti-wear sintered alloy and method for manufacturing thereof The present invention relates to an anti-wear sintered alloy and a method for manufacturing thereof, and more specifically to an anti-wear sintered alloy the wear-resistance property of which is further improved by adding elements for forming carbide such as W, V, Nb, Ti, Ta to conventional antiwear sintered alloys the compositions of which are disclosed in Japanese patent application No. Sho 53-76107 and British Patent Application 8040546, and its manufacturing method.

Said Japanese patent application No. Sho 53-76107 describes an anti-wear sintered alloy containing Cr 16-26%. P 0.3-0.8%. Cu 1-5%. Mo less than 3%, impurities less than 2%, graphite 1.54.0%, the balance being Fe. On the other hand, British Patent Application No. 8040546 describes an anti-wear sintered alloy containing Cr 2.5-7.5%, P 0.2-0.8%, Cu 1-5%, Mo less than 3%, C 1 .5-3.5%, impurities less than 2%, the balance being Fe. Either of those sintered alloys is superior in wear-resistant property and is of high density and high hardness, so that those applications describe that such sintered alloys are used for slidable parts to be worked under plane pressure, for example, cam shaft, rocker arm pad of valve actuating system of an automobile.

However, in view of the recent and more strongly increasing desire of high performance of an automobile, it has become naturally strict in usage conditions of the above-mentioned rocker arm and cam. Therefore, it has been strongly expected a sintered alloy of composition in which the wearresistant property is further improved than those of the above-mentioned conventional anti-wear sintered alloys.

The primary object of the present invention is to provide a high-durability, high-density, highhardness anti-wear sintered alloy and its manufacturing method.

Another object of the present invention is to provide a mass-producible high-durability, highdensity, high-hardness anti-wear sintered alloy and its manufacturing method.

More specifically, the object of the present invention is to provide a high-durability, high-density high-hardness anti-wesr sintered alloy containing Cr 2.5-25.0%, Mn 0.10-3.0%, P 0.2 0.8%, Cu 1.0-5.0%, Si 0.5-2.0%, Mo less than 3.0%; additive alloy consisting of one or more kinds of W 0.1-5.0%, V 0.1-5.0%, Nb 0.1-2.5%, Ti 0.12.5% and Ta 0.11.5%, said additive alloy being 0.1-10.05 with respect to the total weight of the whole alloys; C 1.53.5% and the impurities less than 2%, the balance being Fe; and its manufacturing method.

Still further object of the present invention is to provide a method for manufacturing a highdurability, high-density, high-hardness anti-wear sintered alloy in which a hardener and additive alloys are separately manufactured, these two alloys are blended at appropriate proportion to prepare an alloy powder, predetermined amount of carbon is added thereto and the mixture is intered.

These and other objects and features of the present invention will become apparent from the following description referred to the attached drawings.

The present invention relates to the improvement of the sintered alloys described in the abovementioned Japanese patent Appln. No. Sho 53-76107 and British Appln. 8040546 (hereinafter, the sintered alloys described in said application will be referred to as "sintered alloy I" and "sintered alloy II", respectively), in which carbide-forming elements are further added to the sintered alloys I and II, whereby providing a sintered alloy having far superior wear-resistant property to the conventional sintered alloys.

The anti-wear sintered alloy according to the present invention characterized by containing, in terms of weight, a hardener consisting of Cr 2.5-25.0%, Mn 0,1-3,0%, P 0.2-0.8%, Cu 1.0-5.0%.

Si 0.52.0% and Mo less than 3.0%; additive alloy consisting of one or more kinds of W 0.1-5.0%, V 0.1-5.0%, Nb 0.1-2.5%, Ti 0.12.5% and Ta 0.11.5%, said additive alloy being 0.1-10.0% with respect to the total weight of the whole alloys; C 1.53.5% impurities less than 2%, and the balance being Fe.

In the composing ratio of the hardener, chrome useful for the improvement of wear-resistant property and scuffing-resistant property is 15-25% in the case of the sintered alloy I and is 2.57.5% in the case of the sintered alloy II. To the contrary, the present invention makes it possible to widen the composing range of of Cr to 2.5-25.0% since the additive effects of W, V, Nb, Ti, Ta are remarkable.

This enlargement of the composing range of Cr is also relied upon the application of a later-mentioned method in which two kinds of alloy powders of the present invention are separately prepared, blended and sintered. When Cr is less than 2.5%, it is undesirable, because the wear-resistant property of sintered alloy is inferior. When Cr is more than 25.0%, it is equally undesirable, because the additive effect can not be seen; on the contrary, the slidable property is varied to increase the attack on a piece to be coupled.

Manganese is solid-solved in the matrix to increase the strength of the matrix, and activates the sintering of Fe matrix, inhibits the crystal growth and contributes the fining and spherodization of the carbide, whereby improving the slidable property of the sintered product. However, these effects can hardly be exerted in case that addition of Mn is not exceeding 0.10%. On the other hand, when the addition of Mn exceeds 3.0%, the atomized alloy powder is spherodized and hardened, resulting not only in a heavy drop in the compressibility and moldability of the powder -- which makes it impossible to obtain a desired density or hardness -- but also in an increase of residual austenite in time of sintoring and a drop in the hardness or liability of the sinterability baing lowered through oxidization.

Thus the addition of mn is limited to 0.10-3.0%, preferably 0.10-1.5% in the presentinvention.

Phosphorus contributes to the sintered alloy of the present invention in that it activates the sintering by being solid-solved into the matrix in time of sintering, with effect of not only enabling a sintering at lower temperatures but also giving higher density through the liquid phase by forming a low melting-point steadite phase. Such effects of phosphorus will, however, be unsatisfactory when the addition is less than 2.0%. When the addition exceeds 0.8%, the liquid phase becomes excessive, resulting in abnormal growth of carbide and steadite and embrittlement of the crystalline boundary, which lowers the slidability. Thus the addition of phosphorus is limited to 0.20.8%, preferably 0.350.65%.

Molybdenum just like chrome not only increases the hardness of sintered mass by strengthening the matrix and enhancing the harderability but also improves the slidability by forming a hardened compound carbide with (Fe, Cr, Mo)3C as the main component. Even without addition of Mo, the necessary performance of slidable parts such as the cam may be secured, but Mo addition of less than 3% will be useful, because it has an effect of making the carbide spheroidal and suppressing the aggressiveness of the alloy to the coupled piece. The addition is limited to less than 3%, preferably 0.51.5%, because addition exceeding 3% would cause a network formation of carbide at the crystalline boundary, thereby embrittling the alloy, lowering the slidability and leading to a cost up.

Copper, being solid-solved in the matrix, stabilizes the sintering, increases the strength and hardness of the matrix, fines the carbide and contributes to a spherodization of the latter. When the addition of copper is less than 1.0%, these effects will not emerge; when it exceeds 5.0%, the crystalline boundary will be weakened, resulting not only in a lowered slidability but also in a cost up. Thus the addition is limited to 1 .0-5.0%, preferably 1.53.0%.

Silicon, being solid-solved in the matrix, stabilizes the sintering of the Fe matrix, and equally has effects for spherodization of carbide particles. Meanwhile silicon is necessary as an essential deoxidizer of the molten metal when it is atomised to make an alloy powder. The addition of it less than 0.5%, however, will accelerate the oxidization of powder, resulting in a loss of the deoxidized effect, while addition of it exceeding 2% will not only lower the hardenability of the matrix, resulting in a decline of the hardness, but also coarsen the carbide and cause its segregation on the crystalline boundary, resulting in a lower slidability. Thus the addition is limited to 0.52%, preferably 0.71.5%.

Graphite to be used as carbon, being solid-solved in the matrix, increases the hardness and strengthens the matrix; moreover, it improves the wear resistance by forming, together with chrome and molybdenum or other additive alloys, compound carbides and contributing to the formation of steadite phase. The addition of it less than 1.5%, however, will cause insufficiency in the hardness of the matrix and in the volumes of carbide and steadite, while the addition of it exceeding 3.5% will cause a coarsening of the structure and a network growth at the crystalline boundary, thereby substantially deteriorating the slidability and heavily attacking the coupled piece. Thus the addition is limited to 1.53.5%, preferably 1.83.0%.

The components of the additive alloys to be added in the present invention are metallic elements which can be satisfactorily dispersed in the matrix and can form carbides having higher hardness, i.e., W, V, Nb, Ti, Ta. These elements can be added to the hardener, solely or in combination of two or more elemeonts. The composing range of oach alloy component is : W being 0.1-5.0%, V 0.1-5.0%.

Nb 0.1 - 2.5%, Tl 0.1-2.5%, Ta 0.1-1.5%, When the addition of each component is less than the lower limit, additive effect can not be exerted. On the other hand, even when the addition of each component exceeds the upper limit, it is undesirable because not only the additive effect can not be increased, but also aggressiveness to a piece to the coupled is increased and it leads to a cost up. The total additive proportion of the additive alloy to the hardener is 0.110.0% with respect to the total weight of the whole alloys. When the total addition is less than 1.0%, the effect can not be exerted. And when the total addition is more than 20.0%, it is undesirable because the effect in wear-resistant property does not increase and it leads to a cost up.

In the manufacture of the sintered alloy of the above composition, the present invention is also to provide a method for manufacturing sintered mass in which the density of molded powder is raised and wear-resistant property is further excelled, by separately manufacturing hardener powder and additive alloy powder, blending these two kinds of alloy powders in appropriate ratio to prepare an alloy powder, adding a predetermined amount of carbon to the obtained alloy powder and sintering the mixture.

In order to obtain sintered products of alloy composed of various kinds of metallic components, the conventional methods have mixed each alloy element solely or with addition of ferroalloy, then adding a predetermined amount of graphite thereto and mixisng them, molding a desired shape of compression molded product and thereafter, sintering it at high tomperature more than 1000 C. Wateratomizing way has been generally employed for the manufacture of alloy powder.

However, in a case that the above-mentioned conventional method is applied to the alloy according to the composition of the present invention, it is difficult to finely and uniformly disperse the carbide and it leads to the inferior performance of the sintered product when, at the time of addition of the additive alloys of W, V, Nb, Ti, Ta to the hardener components, these alloy elements are added solely or with addition of ferroalloy. On the other hand, in a case that these elements are added as alloy powder components, improved effect in aspect of performance of a sintered product can be obtained.

However, there have remained problems in manufacturing-technical respect since the hardness of alloy powder increased, which renders the drop of powder moldability such as compressibility and so on, and the drop of the life of metallic mold.

According to the present method, in order to suppress the increase of hardness of alloy powder, two kinds of powders of a hardener powder (hereinafter referred to as "alloy powder Ill") and a powder composed of hardener and additive alloy (hereinafter referred to as "alloy powder IV") are separately produced by water-atomizing method; after these two kinds of alloy powders Ill and IV are mixed at appropriate amounts, graphite is added thereto and mixed therewith; and after molding a compression molded product, it is sintered, whereby obtaining compressed powder having high density without nearly dropping powder molding properties such as compressibility and so on. As a result, the obtained sintered product is remarkably superior in wear-resistant property and moreover, the durability thereof is improved since there are scarcely pores in the sintered product.

The composition of the hardener in the alloy powder IV may be the same as that of the alloy powder Ill, but it may reduce the proportion of the hardener so as to suppress the increase of hardness of the alloy powder IV. However, when the proportion of the hardener in the alloy powder IV is too low, the structure of the sintered alloy is rendered to be un-uniform, which is not desirable. Thus, the proportion of the additive alloy in the alloy powder IV is arranged to be 1%-20%.

The composition ratio of the alloy powder IV with respect to the alloy powder Ill is 1050%.

When the ratio is less than 10%, the wear-resistant property becomes inferior since the composition proportion of the additive alloy is too low. On the other hand, when the ratio is more than 50%, it is also undesirable since the sintering is difficult and the aggressiveness to a piece to be coupled increases.

The manufactures of each alloy powder Ill, IV are carried out by water-atomizing method in accordance with the routine process.

The formation of the compression molded product after the mixture of the above two kinds of alloy powders Ill and IV is conducted under the pressure of, for example 4-7 ton/cm2. The density of the molded product is preferably 5.5-6.5 g/cm3.

Sintering is conducted at, for example, 1 100--12000C for 30-120 minutes under the reducing atmosphere or in the vacuum.

The present invention will be more specifically explained referring to examples and comparisons.

EXAMPLE 1 Powder A composed of Fe-2.5Cr-0.1 Mn-0.2P-1 .0Cu-0.5Si-0.1W#).1V-0.1 Nb-0.1Ti-0.1Ta was produced by a water-atomizing method. The powder A was sifted by a sieve of -100 mesh and was added and mixed with graphite 1.7% to be molded at 6 ton/cm2. Then, the obtained molded product was sintered at 11 800C for 60 minutes under the reduced gas atmosphere, thereby obtaining a sintered alloy the alloy composition of which is Fe-2.5Cr-0.1Mn-0.2%-1.0Cu-0.5Si-0.1W-0.1V-0.1Nb-0.1Ti-).1Ts-1.5C.

(In this Example and other Examples and Comparisons, all of numeral values with no specific value shall be expressed by "%" by weight.) EXAMPLE 2 Powder B composed of Fe-2.5Cr-0. 1 Mn-0.2P-1 .OCu-0.5Si-1 .0W-1 .OV-1 .0Nb-1 .0Ti-1 .OTa and powder C composed of Fe-2.5Cr-0. 1 Mn-0.2P-1.0Cu-0.5Si were produced by water-atomizing method.

The powders B and C were sifted by a sieve of -100 mesh, respectively. The powders B and C were composed at the ratio of B : C = 10 : 90. Graphite 1.7% was added thereto and then, they were mixed.

The obtained alloy powder was molded at 6 ton/cm2 and then, the molded product was sintered at 11 800C for 60 minutes under the reduced gas atmosphere, thereby obtaining the same sintered alloy with that of the Example 1.

EXAMPLE 3 Powder D (-100 mesh) composed of Fe-4.9Cr-1 .OMn-O.5P-2.0Cu-1 .0Si-1 .0M1 .0W-2.0V-1 .0Nb was produced under the same process as that of Example 1. Graphite 2.7% was added thereto. The mixture was sintered at 11 200C, thereby obtaining a sintered alloy the alloy composition of which was Fe-4.9Cr-1 .OMn-0.5P-2.OCu-1 .0Si-1 .0M1 .OW-2.OV-1 .ONb-2.5C.

EXAMPLE 4 Powder E composed of Fe-5.OCr-1 .OMn-O.5P-2.0Cu-1 .OSi-1 .0M5.0W-1 0.0V-5.ONb and powder F composed of Fe-5.OCr-1 .OMn-0.5P-2.OCu-1 .OSi-1 .OMo were respectively produced under the similar way with the Example 1. These powders E and F were composed at the ratio of E : F = 20 :80. Graphite 2.7% was added thereto and then, the molded product was sintered at 11 200 C, thereby obtaining a sintered alloy the alloy composition of which is the same as that of the Example 3.

EXAMPLE 5 Powder G composed of Fe-4.9Cr-1 .0Mn-0.5P-2.0Cu-1 .OSi-1 .0Mo5.0W was produced. Graphite 2.7% was added thereto. The mixture was sintered at 11 500C, thereby obtaining a siritered alloy the alloy composition of which is Fe-4.9Cr-1 .OMn-O.5P-2.OCu-1 .OSi-1 .OMo-5.0W-2.5C.

EXAMPLE 6 Powder H composed of Fe -5.0Cr-1.0Mn-0.5P-2.0Cu-1.0Si-1.0Mo-10.0W and the powder F composed of Fe-5.OCr-1 .OMn-0.5P-2.OCu-1 .0Si-1 OMo were used, and they were composed at the ratio of H : F = 50 : 50. Graphite 2.7% was added thereto. The mixture was sintered at 1 1 50"C, thereby obtaining a sintered alloy the alloy composition of which is the same as that of the Example 1.

EXAMPLE 7 Powder I composed of Fe-22.0Cr-1 .9Mn-0.8P-3.8Cu-2.0Si-2.4Mo-4.8V-2.4Ti-1 .4Ta was produced. Graphite 3.8% was added thereto. The mixture was sintered at 11 500 C, thereby obtaining a sintered alloy the alloy composition of which is Fe-21 .6Cr-1 .9Mn-0.8P-3.8Cu-2.OSi-2.4Mc-4.8V-2.4Ti-1 .4Ta-3.5C.

EXAMPLE 8 Powder J composed of Fe-20.OCr-1 .OMn-0.8P-3.OCu-2.0Si-2.OMo-1 0.OV-5.OTi-3.OTa and powder K composed of Fe--2 5.OCr-3.OMn-0.8P-5.0Cu-2.0Si-3.0Mo were used. These powders J and K were composed at the ratio of J : K = 50 : 50. Graphite 3.8% was added thereto. The mixture was sintered at 11 500 C, thereby obtaining sintered alloy the alloy composition of which is almost same as that of the Example 7.

COMPARISON 1 Graphite 1.7% was added to the powder C of the Example 2. The mixture was sintered at 11 800C, thereby obtaining a sintered alloy the alloy composition of which is Fe-2.5Cr-0.1 Mo-0.2P-1 .OCu-O.5Si-1 SC.

COMPARISON 2 Graphite 2.7% was added to the powder F of the Example 4. The mixture was sintered at 11 200C, thereby obtaining a sintered alloy the alloy composition of which is Fe05.0Cr-1.0Mn-0.5P-2.0Cu-1.0Si-1.0Mo-2.5C.

Engine cams for an internal combustion engine were made of sintered alloys obtained by the above-mentioned Examples and Comparisons. Rocker arms to be coupled were produced by using high Cr cast iron (23% Cr). These test pieces were evaluated their durability on the test machine under the severe conditions of 200 hours to measure depth of wear of the cams and the rocker arm pads to be coupled.

The results are shown in Table 1.

TABLE 1

Property of Wear-reslstant property Density of sintered mass (depth of wear) Remark moded Ratio of Hardness Rocker arm to Hardness of product density HV Cam* be coupled powder Hv (g/cm3) (%) (10 kg) ( m) ( m)** (100 g) Example 1 6.00 93 520 95 13 Powder A260 2 6.30 94 530 50 8 B270 C220 3 5.90 96 580 50 10 D280 4 6.15 97 600 30 8 E300 F250 5 6.00 96 620 55 15 G290 6 6.15 97 650 40 7 H300 F250 7 5.50 95 640 60 16 1330 8 5.95 96 650 35 10 J290 K280 Comparison 1 6.20 92 480 180 25 C220 2 6.20 96 550 100 12 F250 * Wear in cam nose direction ** Maxlmum worn depth of rocker arm pad Following is apparent from the above Table 1.

(1) From the results of the evaluation for sintered products between Comparison 1 and Examples 1, 2, and between Comparison 2 and Examples 3, 4, it is clear that the additive alloys W, V, Nb, Ti, Ta remarkably affect on wear-resistant property. Moreover, it is seen that aggressiveness to the piece to be coupled (rocker arm pad) is little.

(2) The effects generated by separately producing two kinds of alloy powders at the step of producing alloy and blending them are clarified in comparison of Examples 1 and 2; Examples 3 and 4; Examples 5 arid 6; and Examples 7 and 8. That is, either sintered mass of Examples 2, 4, 6, 8 which conducted the step of blending the alloy powders increased its sintered mass property in comparison with those of Examples 1, 3, 5, 7 which did not conduct such step. Accordingly, the wear ratio of the cams were decreased. Especially, it is seen that since the density of molded products of Comparison 1 and Example 2 are same and the density of the molded products of Comparison 2 and Example 4 are almost same, deterioration of particle compressibility due to the additive components W, V, Nb, Ti, Ta was recovered by the blending operation.This respect is apparent from the comparison of Example 5 and 6, and the comparison of Examples 7 and 8.

(3) The Example 8 is an example which reduced the proportion of the hardener in the alloy powder IV in comparison with the alloy powder Ill, and made the powder hardness to the lower value as Powder J = 290, Powder K = 280. By this arrangement, the drop of density of molded product was largely suppressed, and property of sintered mass was improved and wear-resistant property was raised in accompaniment therewith.

As apparent from the above description, the sintered alloy according to the present invention is remarkably superior to the conventional sintered alloys in wear-resistant property. Moreover, since the aggressiveness to the piece to be coupled is low, it is most suitable for slidable members to be used under high plane pressure, for example, materials of rocker arm pad and cam piece used for valve actuating system of an automobile. Furthermore, when the method of the present invention is used, the drop of powder hardness can be suppressed, so that the density of compression molded product can be raised. Accordingly, the improvement of wear-resistant property can be further expected and the porosity of the sintered mass is reduced, whereby obtaining high strength. Therefore, the slidable products of the sintered mass obtained by the present method have remarkable superiority in durability.

Claims (6)

1. An anti-wear sintered alloy containing (a) a hardener consisting of Cr 2.5-25.0 wt. %, Mn 0.1-3.0 wt.%, P 0.2-0.8 wt. %, Cu 1.0-5.0 Wt. %, Si 0.5-2.0 wt. % and Mo less than 3.0 wt.%; (b) an additive alloy consisting of one or more elements selected from W 0.1-5.0 wt. %, V 0.1-5.0 wt.

%, Nb 0.1-2.5 wt. %, Ti 0.1-2.5 wt. % and Ta 0.1-1.5 wt. %, said additive alloy being 0.1-10.0 wt. % with respect to the total weight of the whole alloys; (c) C 1.5-3.5 wt. %, and (d) impurities less than 2 wt. %, the balance being Fe.

2. An alloy according to claim 1, wherein manganese is 0.10--1.1.5 wt. %, phosphorus 0.35-0.65 wt. %, copper 1.5-3.0 wt. %, silicon 0.7-1.5 wt. %, and molybdenum 0.5-1.5 wt. %.

3. A method for manufacturing an anti-wear sintered alloy which comprises adding, in a proportion of 10-50 wt. %, a first alloy powder composed of a hardener consisting of Cr 2.5-20.0 wt.

%, Mn 0.1-1.0 wt.%, P 0.2-0.8 wt. %, Cu, 1.0--3.0 wt. %, Si 0.5-2.0 wt. % and Mo less than 2.0 wt. %, an additive alloy consisting of one or more elements selected from W 1.0-10.0 wt. %, V 1.0-10.0 wt. %, Nb 1.0-5.0 wt. %, Ti 1.0-5.0 wt. % and Ta 1.0-3.0 wt. %, said additive alloy comprising 1.0-20.0 wt. % with respect to the total weight of the whole alloys; impurities less than 2 wt. %, and the balance being Fe, to a second alloy powder composed of a hardener consisting of Cr 2.5-25.0 wt. %, Mn 0.1-3.0 wt. %, P 0.2-0.8 wt. %, Cu 1.0-5.0 wt. %, Si 0.5-2.0 wt. % and Mo less than 3.0 wt. %, and impurities less than 2 wt. % and the balance being Fe, adding graphite to the mixed alloy powder so as to provide C 1.5-3.5 wt. %, forming a compression molded product and sintering it.

4. A method according to claim 3, wherein a hardener and additive alloys are separately manufactured, these two alloys are blended in appropriate proportions to prepare an alloy powder, a predetermined amount of carbon is added thereto, and the mixture is sintered.

5. A method as claimed in claim 3 and substantially as hereinbefore described with reference to any of Examples 1 to 8.

6. An anti-wear sintered alloy when manufactured by a method as claimed in any of claims 3 to 5.