JPS5819414A - Sliding member and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a sliding member with high dimensional accuracy and superior wear resistance by treating a specified iron alloy as a base material with stream to form Fe3O4 along the pores and by carrying out gas soft-nitriding. CONSTITUTION:A sintered iron alloy consisting of 0.3-0.2wt% C and the balance essentially Fe and having 6.0-6.8g/cm<3> density is treated with steam to form Fe3O4 films along the pores in at least the sliding surface layer. Gas soft- nitriding is then carried out in an atmosphere of a gaseous mixture consisting of 30-70vol.% heat absorption type gas contg. 0.4-1.5vol% CO2 and the balance ammonia. By this method a nitrided surface layer with improved wear resistance is obtd. Without causing excessively deep nitriding and a dimensional change. The resulting member is suitable for sliding parts used under severe conditions such as the cam of an internal combustion engine and the housing of an oil pump.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sliding member made of an iron-based sintered alloy having excellent wear resistance and a method for manufacturing the same.

For example, materials for sliding parts used under harsh operating conditions, such as internal combustion engine cams, tappets, and oil pump housings, are required to have excellent wear resistance, and traditionally chill cast iron and alloy cast iron have been used. Those that have been heat treated to harden at least the sliding surface layer are used. However, the dimensional accuracy of general cast parts is not good, and cutting work must be performed, but the above-mentioned cast iron rigidity is not good, and there are problems in that the machining cost increases.

Sintered bodies manufactured by powder metallurgy have good dimensional accuracy, high yields, and have good oil retention due to their inherent pores, so sintered alloys are widely used as materials for machine parts. In order to improve wear resistance, iron-based sintered alloys with various alloying elements added have been tried, but under severe usage conditions, the wear resistance of chilled cast iron and It is not as good as that of wear-resistant alloy cast iron. In addition, nitriding is an effective means of improving the wear resistance of steel materials, but nitriding progresses quickly in sintered alloys due to the inherent pores. If R or Ni is added to an iron-based sintered alloy, it will expand during the nitriding process and cause a large dimensional change, so it is not possible to include these alloying elements. Therefore, a nitrided layer having sufficient hardness cannot be obtained, and no significant effect can be expected in improving the wear resistance of iron-based sintered alloys through nitriding treatment.

The present invention solves the above-mentioned problems, and aims to provide a sliding member made of a sintered alloy with good dimensional accuracy and improved wear resistance, and a method for manufacturing the same. The first invention is carbon 0.3~. The base material is an iron-based sintered alloy consisting of 2.0% by weight and the remainder substantially iron9, and at least the sliding surface layer has a structure in which triiron tetroxide and iron nitride coexist around the pores. Regarding sliding parts with excellent wear resistance,
The third invention is a method of steam-treating an iron-based sintered alloy having a density of 9.6.0-A, lrg/am, containing 0.3 to 2.0% by weight of carbon and the remainder being substantially iron. The sliding device according to the first aspect of the present invention is characterized in that triiron tetroxide is formed at least around the pores of the sliding surface layer, and then gas nitrocarburizing treatment is performed in a mixed gas atmosphere consisting of agas. It relates to a method of manufacturing a member.

As a result of research, the inventor conducted steam treatment prior to nitriding the iron-based sintered alloy to reduce the circumference of the pores. IK triiron tetroxide (1
・304) is formed, and then an endothermic gas containing an appropriate amount of carbon dioxide (002) and ammonia (liH) are formed.
3) When the gas nitrocarburizing treatment is performed in a mixed gas atmosphere, the wear resistance is significantly improved without excessively deep nitriding and without causing severe dimensional changes. The reason for this is thought to be as follows: the steam treatment forms a nitride film around the pores, which improves the wear resistance and mechanical properties of the sintered alloy. The mechanical strength, especially the fatigue strength and impact value, are improved, and during the next nitriding treatment, the mixed gas that has entered the pores first reduces the triiron tetroxide, and nitriding progresses from the reduced round iron. - By the above-mentioned reduction and nitriding proceeding simultaneously, the bond between the raw material powder particles is strengthened, and the wear resistance of the highly hard iron nitride produced by nitriding is improved, and the unreduced triiron tetroxide is It is thought that excellent abrasion resistance is exhibited even under severe usage conditions due to the abrasion resistance improving effect and the synergistic effect of both.

Regarding the chemical composition of the base material of the sliding member of the present invention, if the carbon content is less than 0.3% by weight, the structure of the sintered alloy becomes mostly soft ferrite, resulting in insufficient mechanical strength. 0% by weight
If the content exceeds 0.3%, the amount of free cementite increases and becomes brittle, so it is best to keep the content within the range of 0.3 to 2.0% by weight.For alloying elements other than carbon, Copper, nickel, chromium, molybdenum, vanadium, titanium and niobium are sintered alloy base materials! Improving mechanical strength,
This is effective in increasing the hardness of the nitrided layer and further improving wear resistance.

The density of the iron-based sintered alloy used for manufacturing the sliding member of the present invention is A
, 0B10-, the mechanical strength of the base material becomes insufficient to the extent that it cannot withstand use under high-load sliding conditions; Since the amount of triiron tetroxide is small and the effect of improving wear resistance is not significant, the range is set to 6.0 to 6. I
It is better to set it as g/am'.

However, the pores in the sintered alloy are interconnected, and the steam treatment produces triiron tetroxide up to the center of the sintered alloy, so the density of the base material of the sliding member of the present invention is higher than this. becomes the density.

Steam treatment is preferably carried out by heating the material to be treated in water vapor to a temperature of 320 to 304 degrees. If the treatment is carried out within this temperature range, a film of iron oxide (P-304) will be formed around the pores. However, if heated to a temperature outside this temperature range, PeO and A-ZOS will be generated, making it impossible to obtain the above-mentioned effects.The processing time is 75%.
Minutes to 3 hours is sufficient.

Nitriding treatment reduces carbon dioxide (00,) to 0. ≠~/, heated in a mixed gas atmosphere of endothermic gas and ammonia (MH3) gas containing 1 volume of phthalate, and generated around the pores -
While reducing triiron tetroxide, it is nitrided from the surface and the inner wall of the pores.However, carbon dioxide in the endothermic gas is reduced to 0. If it is less than 3% by volume, the reduction of triiron tetroxide will proceed too much, making it impossible to obtain a nitrided layer in which triiron tetroxide coexists, and free ferrite will be generated, resulting in a significant decrease in hardness and impairing wear resistance. It becomes like this. Also, carbon dioxide in endothermic gas is 1. If the amount exceeds J volume %, the ability to reduce triiron tetroxide decreases, and the triiron tetroxide film prevents the progress of nitriding. This results in a non-uniform structure in which areas with no ψ coexist locally, resulting in insufficient improvement in wear resistance. Therefore, the amount of carbon dioxide in the endothermic gas ranges from 0 to 1. ! Although it is better to increase the volume, the carbon dioxide content can be controlled by controlling the amount of air mixed during endothermic gas conversion. In addition, the atmosphere gas for the nitriding treatment is similar to the ratio of endothermic gas and ammonia gas in ordinary gas soft nitriding, and the endothermic gas containing the above carbon nitride is used in a volume ratio of 3θ to 70%, with the balance being ammonia gas. It is sufficient to use a mixed gas that is mixed to form a gas.

Next, an experimental example will be explained.

40% by weight of natural graphite powder with an average particle size of 107t', the balance -
Zinc stearin/weight arc was added as a lubricant to the raw material powder blended to make 700 mesh of atomized iron powder, and the mixed powder was compression molded in a mold at a molding pressure of 1/2 o-. The green compact is heated in AX (ammonia decomposition) gas for 0 minutes to a thickness of 7
It was made into a plate-shaped sintered body of mm. The density of the sintered body is lp, 7
g/am”, carbon-containing il is 0.♂j as a result of analysis
It was overweight.

This sintered body is heated in water vapor at 370'Ot/C for 2 hours to perform steam treatment, and then carbon dioxide o, PX (prepan metamorphosed) gas containing a volume arc and ammonia gas are mixed in equal amounts by volume. 120 to 370'O in a mixed gas atmosphere
Gas nitrocarburizing treatment was performed by heating for a minute, and the following tests were conducted. Using comparative materials, the carbon dioxide content in the RX gas was 0.2.
The same test was conducted on a product manufactured in the same manner as the above-mentioned sliding member of the present invention (hereinafter referred to as the present invention material) except for the volume%.

Tissue observation The results of microscopic structure observation from the surface to the inside are shown in the second
It is as shown in Figure 1 of Zusha. FIG. 1 is a micrograph at a magnification of 100 times showing the structure of a cross section perpendicular to the surface of the surface layer of the material of the present invention. ／龜〜Q、
A micrograph with a magnification of ≠ OO times in a depth range of 3 trillion rams,
FIG. 3 is a micrograph at a magnification of 0.00 to 0.0 times showing the structure of a plane parallel to the surface at a position where 0.2 mm from the surface has been removed by polishing. In the figure, CI) FA coating surface (2 companies pores, ■ indicates triiron tetroxide, (I) indicates ε (162-3N) phase, (!!'5tj pearlite).

From Figure 1, the material of the present invention has a depth of about 0.3 mm from the surface.
From FIG. 2, it can be seen that a large amount of phase (b) is generated at least 0.0 mm from the surface. It can be seen that Gisai iron trioxide (■) and ε phase (B) coexist and ψ at a depth of /'@~0.3Lm. Very fine black spots of Fi can be seen scattered in the ε phase (b), and these black spots are thought to be traces of oxygen released to the outside when triiron tetroxide is reduced. From FIG. 3, it can be seen that at a depth of O42 am from the surface, pores @, triiron tetroxide (2), ε phase) and pearlite (2) coexist.

Figure ≠ is a micrograph at a magnification of 100 times showing the structure of a cross section perpendicular to the surface of the surface layer of the comparative material, and Figure 5 is a micrograph showing the structure of the surface layer of the comparative material at a magnification of 100 times from the surface shown in Figure μ. This is a micrograph with a magnification of 0.00 times in the depth range of OA -0.211 mm.In the figure, (/Ha is the surface, (/ is the pores, (/→ is the ε phase, and (#) is the pearlite. In the comparative material, the ε phase (/4Q) is generated in the surface layer, but unlike the present invention material, triiron tetroxide is not present in the surface layer, and Figure 5 shows free 7-elite. (/J) is slightly criticized.

The respective components of these phases were confirmed by the X1m diffraction test described below.

X@ Diffraction Test The component phases were examined by XI# diffraction from the surface toward the inside, and the results shown in Table 1 were obtained.

In the table, εFi1.2 to 3Msα is ferrite. a
(7-Elite) Since ferrite in butterfly pearlite and free ferrite are detected in total, the table also shows the presence or absence of free 7-Elite as observed in the microscopic structure observation. The mark ◎ indicates that a large amount was detected, the mark ○ indicates that a small amount was detected, and the mark X indicates that it was not detected.

From the table, it can be seen that in the range from the surface to a depth of 0.1 mm for both the inventive material and the comparative material, triiron tetroxide is reduced and exhausted during nitriding and is no longer observed, and is almost composed of the ε phase. It can be seen that a large amount is generated in a depth range of 0.2vnrn from the surface.

In addition, in the inventive material, the ε phase and triiron tetroxide coexist in the depth range of 2 to 0.1 mm from the surface, and no free ferrite is observed, whereas in the comparative material, Triiron tetroxide is 0.0% from the surface. Finally, it was detected at the location of JWRWA, and it is the ferrite that coexists with triiron tetroxide. The above-mentioned difference between the material of the present invention and the comparative material is also recognized by the above-mentioned microscopic observation of the structure.

Hardness test with a load of 200g from the surface to the inside! When the Vickers hardness was measured and the change in hardness was determined, the results shown in FIG. 6 were obtained.

From the same figure, the hardness of the inventive material shows a slight decrease up to a depth of 0.3 mm from the surface, while the comparative material exhibits a sharp decrease in hardness at a depth of 0.2 mya from the surface. , it can be seen that the material of the present invention has excellent wear resistance.

Wear test The present invention material, the comparative material, and cast iron 1 as another comparative material.
A test piece with a thickness of Jmm was taken from a conventional sliding member manufactured by forcibly chilling 030 using a cold metal, and a wear test on the surface layer was performed using an Okoshi type rapid wear tester. The materials of the present invention were tested both as-is as nitrided and after the surface layer was ground by 002 mm to form a layer in which triiron tetroxide and ε phase coexisted on the surface.

The test conditions are as follows. Final load +4. Jkp,
Friction speed: /, /4'm/sea, friction distance' Aoo
rn.

Lubricating oil: AO”o motor oil 4130/drop/s
ea supply, mating rotor material, chrome molybdenum steel 80M≠3j with hardness of +HHOJO.

The test results are shown in FIG. The comparison sintered alloy material nitrided in a mixed gas containing an endothermic gas containing 0.2% by volume of carbon dioxide had the highest amount of wear, and the inventive material as nitrided showed significantly more wear than this. It can be seen that the wear resistance is significantly improved, and the wear resistance is superior to that of conventional chilled cast iron. Furthermore, the surface layer is O0λIll! ! The wear resistance of the material of the present invention which has undergone one grinding process is further improved compared to the material of the present invention which has been subjected to nitriding treatment. From the above results, it can be understood that creating a structure in which triiron tetroxide and iron nitride coexist greatly contributes to improved wear resistance.

As explained above, the sliding part of the present invention has excellent wear resistance even under severe usage conditions, and also has good dimensional accuracy and good oil retention due to the presence of pores, which are unique to sintered alloys. The manufacturing method is simply to subject the sintered alloy to steam treatment and nitriding treatment with a specified atmospheric gas,
It does not require special equipment and has great industrial utility value.

[Brief explanation of the drawing]

1 to 3 are microscopic photographs showing the structure of the surface layer of the sliding member of the present invention, and FIGS. 1 and 5 are microscopic photographs showing the structure of the surface layer of the comparative material. ■ and (/must means stomata, (J) means triiron tetroxide) and (
/4Q is the ε(y·2-3N) phase. Figure 11h is a graph showing the change in hardness from the surface of the nitrided layer toward the inside, and Figure 7 is a graph showing the results of an abrasion test using an Okoshi rapid abrasion tester. Figure x4th υ Figure 6 jllT figure

Claims (1)

[Claims] / The base material is an iron-based sintered alloy consisting of 0.3 to 2.0% by weight of carbon and the remainder substantially iron, and at least the sliding surface layer has pore shoulders m! A sliding member with excellent wear resistance that has a combination ring in which four-three-layered iron and iron nitride coexist. 2. Steam treatment is applied to an iron-based sintered alloy containing 0.3 to 20 parts by weight of carbon and having a density of 6.0 to 6,000 g/oml to remove at least the pores of the sliding surface layer. iron tetroxide is formed around the iron tetroxide, and gas nitrocarburizing treatment is performed in a zero atmosphere of a mixed gas consisting of nimoair gas. Method for producing a sliding member with excellent wear resistance, using a base sintered alloy as a base material and having at least a sliding surface layer having a structure in which triiron tetroxide and iron nitride coexist around pores 0