JPS5929097B2 - Wear-resistant cast iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wear-resistant cast iron having a fine two-phase mixed matrix structure.

Research has been conducted and reported on improving the material properties of various cast irons or improving the matrix structure from the viewpoint of plastic workability to produce cast irons having a fine two-layer warm matrix structure of ferrite and pearlite or ferrite and martensite. However, much is still unknown about the mechanical properties of cast iron, which has such a matrix structure.

The purpose of the present invention is to obtain cast iron with excellent wear resistance.
C2, 9-3.8 section, Si 1.5-2.6 section, Mn
The wear-resistant cast iron is composed of 0.8% or less Ni, 2.2% or less Ni, the balance is Fe and unavoidable elements, and is characterized by graphite precipitated in a fine two-phase mixed matrix structure, consisting of two parts of pearlite and ferrite. two phases, or martensite and ferrite
This invention relates to wear-resistant cast iron characterized by flaky or spherical graphite precipitated in a matrix structure in which phases are finely mixed.

The wear-resistant cast iron according to the present invention is produced by making ordinary nickel-containing flaky graphite cast iron or spheroidal graphite cast iron into a pearlite base structure according to standards, heating it, and changing it from a structure in which ferrite, austenite, and graphite coexist to air cooling. By this, a two-phase fine mixed base structure of ferrite grains and pearlite grains is formed, or by water cooling from the above-mentioned coexisting structure, a two-phase fine platform base structure of ferrite grains and martensite grains is formed.

At this time, rapid heating is performed to cause the above-mentioned austenitization to occur finely over the entire surface of the base.

Since austenite nucleation occurs at the phase boundary between cementite and ferrite in pearlite, it is desirable that a large amount of pearlite exist in the structure before heat treatment.

In this way, if air or water cooling is performed from the temperature at which ferrite, austenite, and graphite coexist in the microscopic structure, at room temperature the matrix structure is a mixture of fine ferrite grains and pearlite grains, or fine marten instead of pearlite grains. A matrix structure in which site grains and ferrite grains are mixed is obtained, and according to research by the present inventors, cast iron with such a matrix structure has excellent wear resistance, and especially in the case of the former, the sliding speed against cast iron is It exhibits excellent abrasion resistance in the slow range of chromium plating, and in the case of the latter, it has the property of rarely causing abrasion of the other party under high loads, especially when dealing with a chromium plating layer.

The chemical composition of the cast iron of the present invention is not particularly different from that of conventional nickel-containing cast iron.

C is set a little higher than usual in order to provide wear resistance; if it is too low, chilling will occur easily and shrinkage will increase; if it is too high, it will reduce the tensile strength.
Alternatively, there are problems such as poor castability and coarse structure in thick-walled parts, or increased generation of dross when graphite is spheroidized.

On the other hand, if the amount of Si is small, chill will easily enter, and if the amount is large, embrittlement will occur and toughness will be impaired. There will be Section 6.

In the present invention, it is desirable to form a -tamperite structure before heat treatment, and for this purpose, Mn, which is a pearlite-forming element, is important.Although Mn also has a desulfurization effect, increasing the amount increases shrinkage of cast iron and gas absorption. Since there is a problem that martensite is likely to be formed due to air cooling from a predetermined temperature, the content should be set to 0.s% or less.

Ni is included because it increases the mechanical strength of cast iron, has relatively little effect on graphitization, and has the effect of forming a uniform fine mixed structure of ferrite grains and pearlite grains.
If it exceeds 2.2%, martensite is likely to be formed by air cooling, so the content should be set at 2.2% or less.

The remainder is Fe, P, S and other unavoidable elements such as spheroidizing elements in the case of spheroidal graphite cast iron.

Next, an example will be described.

Example 1 A sliding wear test was conducted using a Kaken-type pin-drum type wear tester, which is convenient for examining the basic relative wear characteristics of piston rings and cylinders.

The sample is cast iron having the chemical composition shown in Table 1.

Samples 81 and 82 in the table are spheroidal graphite cast irons having a matrix structure according to the present invention, which were melted in a high frequency induction electric furnace and
Commercially available Fe-8i-M
g (6.4% Mg) alloy 1.5% was added for legalization treatment, late inoculation was performed with 0.5% commercially available Ca-8i, and cast into a shell mold.

The other samples were made by spheroidizing production molten metal using a conventional method and casting it into a shell shape.

Sample 831 was flake graphite cast iron for liners, and the molten metal for production was cast into a CO2 mold and processed into a drum.

The test materials of each sample thus obtained were subjected to the heat treatment shown in Table 2 to obtain a desired microscopic structure.

After heat treatment, test pieces of 5 mm square x 15 mm were processed from each sample material, and the inner diameter of the mating drum was 110 mm.

They were machined to have an outer diameter of 135 mm and a length of 240 mm. One piece was polished and the other was polished after hard chrome plating.

There is almost no difference in surface roughness between the two, with a maximum of 1.5 microns, and the hardness measured after finishing is as listed in Table 2.

The microscopic structure of each test piece is shown in FIG.

Fig. 1 shows sample S1 air-cooled material with bases of pearlite and ferrite; similarly Fig. 1 shows sample S1 water-cooled material with martensite and ferrite as the base; similarly Fig. 1 shows sample S21.
The base is fine pearlite, and also the first
FIG. 4 corresponds to sample 822, in which the base is tempered troostite, and spheroidal graphite is precipitated in both cases.

The structure of the drum-shaped flaky graphite cast iron S31 is that of a usual gray cast iron, as shown in FIG. 1.

The principle of the Kaken-type abrasion tester used is schematically shown in Figure 2. A test piece 2 is fixed in the middle of a lever 1 whose one end is pivoted, and a weight is suspended from the other end of the lever 1. The test piece 2 is pressed against the circumferential surface of the rotating drum 4 by the weight 3.

The weight of the weight 3 was changed to change the load pressing the test piece 2 onto the rotating drum 4, and the rotational speed of the drum 4 was changed using a continuously variable transmission.

The test conditions were as follows. Load: 5kg/c
r1￥+10kg/crlt rotation speed: 0.5,
1, 2, 3, 4 mAeC friction distance: 30 Km Lubricating oil: Not used. Prior to testing, the drum circumferential contact surface of the test piece was ground to match the outer circumferential curved surface of the drum, and a dial gauge was used to measure the center of the contact surface and other areas. The height from the end was measured and the difference from the height after the test was determined, and the difference in height per friction distance IKm indicates the amount of wear on the test piece.

The amount of wear on the other drum is expressed by measuring the circumferential surface of the drum in the axial direction of the drum using a stylus type roughness meter, drawing the cross section of the wear groove, and expressing the area thereof.

The test was conducted twice under the same conditions, and the average value is shown.

Note that sample S1 was tested against a cast iron (831) drum, and sample S2 was tested against a chrome-plated drum.

Figure 3 shows a contact load of 5 kg/cr against the cast iron drum? i
FIG. 4 shows the wear amount at each rotation speed when the test piece is pressed at 10 kg/criL, and FIG. 4 shows the similar wear amount for a chrome-plated drum as a bar graph.

As can be seen from Figure 3, the change in the wear amount of the test piece when the rotational speed is changed shows roughly the same tendency for each test piece, but when compared at the lowest speed of 0.5 m/sec, the present invention Such a test piece clearly shows less wear than the reference material or the quenched and tempered material under any load.

Also, when comparing the amount of wear on the mating drum, the amount of wear was the lowest when the test piece was made of 81 air-cooled material, and the wear amount was the lowest when the test piece was made of 81 air-cooled material.
/sec, even in the case of air cooling and water cooling, it is recognized that the amount of wear is extremely small when sample S1 with a fine two-phase matrix structure is used as a test piece. For example, when the fine two-phase mixed matrix structure according to the present invention is used as a piston ring material If cast iron is used, it is expected that cylinder wear near top dead center and bottom dead center will be significantly reduced.

Also, according to Figure 4, which shows the results when using a chrome-plated drum, it seems that at a load of 5 kg/cyrY, the amount of wear of sample S2 (air-cooled material) is slightly greater than that of other samples, but at a load of 10 kg /crtt, when sample S2 (air-cooled material) or sample S2 (water-cooled material) was used as the test material, the amount of drum wear was smaller compared to other samples, especially sample S2 (
It is worth noting that with water-cooled materials, the drum wear is so minimal that it is hardly noticeable.

Therefore, when a hard material such as a chromium plating layer is used as a mating material, if it is desired to reduce the wear of the mating material, it can be seen that a water-cooled material having a fine mixed matrix structure of martensite and ferrite is suitable.

Example 2 Sample S1 is the one used in Example 1, and comparative material S2
No. 3 and S24 were made by casting molten metal for production, which had been subjected to the usual spheroidization treatment, into a 002 type.

The chemical composition is shown in Table 3.

After casting, each sample was subjected to the heat treatment shown in Table 4, and then processed into a cylindrical test piece with an outer diameter of 40 mm, an inner diameter of 16 mm, and a length of 10 mm. The diameter was 5 to 6 microns.

The average value of hardness of each test piece is as appended to Table 4.

An Amsura type abrasion tester was used as the abrasion tester, and the outer peripheral surfaces of the two test pieces were brought into contact with each other vertically, and the upper test piece was 166 mm.
．． 5r, p, m, and the lower test piece was rotated at 185 r, p, m, and a rolling and sliding wear test was conducted in which rolling and simultaneous sliding of 12.6 mm per rotation were caused.

The test conditions were as follows. Contact load: 30,
50, 70ky Lubricating oil: Not used. The amount of wear on the test piece is determined by removing it from the test machine every 30,000 to 100,000 revolutions of the lower shaft depending on the contact load and wear condition. After degreasing and cleaning, weigh it on a chemical balance. was measured, and the weight loss was defined as the amount of wear.

FIGS. 5 to 7 show changes in the amount of wear depending on the rotational speed.

Figure 5 is for a load of 30kg, Figure 6 is for a load of 50kg.
Fig. 7 shows the case where the load is 70 kg, but according to these figures, the test piece S1 according to the present invention is the comparative material S23.
．． Compared to S24, it cannot be said that the amount of wear is necessarily lower when the number of revolutions is low, but when the number of revolutions increases, comparison material S2
3. While S24 wears rapidly, the present invention material S
1, the increase in wear amount is small, and this tendency is observed for load 3 in Figure 5.
It is clearly observed when the weight is 0 kg.

In other words, the inventive material S1 shows faster wear than the comparison material at the beginning of the test (while the rotation speed is low), but then there is a stable period in which no increase in the amount of wear is observed, and after that the wear progresses rapidly. It can be seen that there are few

Example 3 A scientific research rotary wear test similar to that in Example 1 was conducted on flaky graphite cast iron having a fine two-phase mixed structure as a matrix.

The chemical compositions of the samples are as shown in Table 5, and samples S5 and S7 have the matrix structure of the present invention.
Similar tests were conducted using test material S32 (water-cooled) and flake graphite cast iron, which was sampled from a customary molten cast iron.

The counterpart was a cast iron drum made of S31 used in Example 1.

Samples 85 and 87 were melted in a high-frequency induction electric furnace as usual and cast into shell molds to a diameter of 20 mm, and each sample was heat treated as shown in Table 6.

Among these samples, 950 for Sl, S5, 87
After heating and air cooling at °CX for 16.5 hours, each was subjected to the heat treatment shown in Table 6, and sample 831 was subjected to strain relief annealing.
A test piece measuring 5 mm x 15 mm was cut out and used for the test.

In addition, sample 832 is a piston ring material (
Test pieces of similar dimensions were cut from the as-cast specimens.

The hardness of each test piece is as listed in Table 6.

FIG. 8 shows a typical microscopic structure of each sample after heat treatment.

Figures 8 1 and 2 show the air-cooled and water-cooled structures of sample S5, and Figures 8 3 and 4 show the air-cooled and water-cooled structures of sample S7, respectively. The water-cooled material has a mixed structure of fine ferrite and martensite.

On the other hand, it will be understood that the matrix structure of the comparison material S32 in FIG. 8 and 5 is a pearlite structure containing steadite, and the matrix structure of the material of the present invention is completely different from that of the comparison material.

The test machine and test conditions used are the same as in Example 1.

An example of the test results is shown in FIG. 9 when the contact load is 5 kg/crit.

The 85 and S7 air-cooled specimens made of flaky graphite cast iron according to the present invention have slightly more wear than the 81 air-cooled specimens, which are also made of spheroidal graphite cast iron, but at low speeds they are roughly the same, and the water-cooled ones are equivalent. In either case, the amount of wear is significantly smaller than that of 832, which is a common gray cast iron.

Furthermore, wear of the mating material is not observed in the S5.87 air-cooled material at low speeds, and is minimal even when the speed increases, and is less than in the case of gray cast iron S32.

However, in the case of water-cooled materials, the wear of the mating material is greater than in the case of air-cooled materials or gray cast iron, probably due to the increased hardness.

As explained above, flaky graphite cast iron or spheroidal graphite cast iron having a base of fine two-phase mixed structure according to the present invention has superior wear resistance compared to gray cast iron or standard or quenched and tempered spheroidal graphite cast iron. However, the amount of wear is small, especially in low-speed friction, and the mating material is less likely to wear out.

Therefore, when used as a piston ring in a reciprocating device where wear near top dead center and bottom dead center is a problem, such as a piston, it can be used as a wear-resistant material because it can reduce wear on itself and reduce wear on the mating cylinder. It has a great effect.

[Brief explanation of drawings]

1 and 2 are photographs showing the microscopic structure of the spheroidal graphite cast iron according to the present invention, and FIGS. 14 and 3 are photographs showing the microscopic structure of the usual spheroidal graphite cast iron used as a contrast material, and FIG. 1 5
Figure 2 is a photograph showing the microscopic structure of flaky graphite cast iron used as the drum material for an abrasion tester, Figure 2 is an explanatory diagram schematically showing the principle of the Kaken-type sliding wear test, and Figure 3 is a photograph showing the microscopic structure of flaky graphite cast iron used as the drum material for the wear tester. A graph showing the results of a sliding wear test on a cast iron drum, Figure 4 is a graph showing the results of a similar test on a chrome plated drum, and Figure 5 is the result of the same rolling and sliding wear test with a load of 30 kg. Graphs showing the same, Figure 6 is the same load 50kg, Figure 7 is the same load 7
A similar graph in the case of 0kp, FIG. 8 is a photograph showing the microstructure of the flaky graphite cast iron according to the present invention and a conventional gray cast iron used as a contrast material, and FIG. 9 is a photograph showing the microstructure of the flaky graphite cast iron according to the present invention. 3 is a graph similar to FIG. 3 showing the results of a sliding wear test on a cast iron drum. S1 air cooling, S1 water cooling, spheroidal graphite cast iron according to the present invention, 821, S22, 823, S24...
・Spheroidal graphite cast iron contrast material, S5 air-cooled, S5 water-cooled, S7 air-cooled, S7 water-cooled...Flake graphite cast iron according to the present invention, S
32...Flake graphite cast iron contrast material, S31...
・Drum material: gray cast iron.

Claims (1)

[Claims] IC2, 9 to 3.8%, sil, 5 to 2.6%,
A wear-resistant cast iron consisting of Mn of 098 or less, Ni of 2.2 or less, the remainder Fe and unavoidable elements, and characterized by having graphite precipitated in a fine two-phase mixed matrix structure. 2. The wear-resistant cast iron according to claim 1, which has a matrix structure in which two phases of pearlite and ferrite are finely mixed. 3. The wear-resistant cast iron according to claim 1, which has a matrix structure in which two phases of martensite and ferrite are finely mixed. 4 Claim 1, in which graphite is precipitated in flakes,
The wear-resistant cast iron according to item 2 or 3. 5 Claim 1, in which graphite is precipitated in a spherical shape,
The wear-resistant cast iron according to item 2 or 3.