JPS6119759A - Abrasion resistant cast iron - Google Patents

Abstract

PURPOSE:To provide the titled cast iron improved in abrasion resistance, which is constituted of a composition consisting of a specific amount of C, Si, Mn, Ni and Mo, one or more of a carbide forming element selected from Cr, V, W, Nb and Ta and the remainder of Fe and inevitable impurities and has a bainite structure on which one or more of carbide of said carbide forming element is precipitated. CONSTITUTION:The titled cast iron has a composition consisting of, on a wt. basis, 2.4-3.4% C, 2.0-3.0% Si, 0.2-1.0% Mn, 0.5-1.5% Ni, 1.0-2.0% Mo, 0.3-2.0% of one or more of a carbide forming element selected from Cr, V, W, Nb and Ta and the remaider of Fe and inevitable impurities. The structure of said cast iron is based on bainite formed by cast and one or more of Cr7C3, VC, WC and carbide based on Nb and Ta is precipitated thereon. By this constitution, cast iron more enhanced in abrasion resistance and suitable for the intake valve seat used in the dynamic valve mechanism of the internal-combustion engine of an automobile is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to wear-resistant cast iron. INDUSTRIAL APPLICATION This invention can be utilized for an intake valve seat, a valve guide, etc. used in the valve train of the internal combustion engine of an automobile. Here, the intake valve seat is a seat that holds a valve on the side that sucks in mixed gas, and seals the gas by attaching and detaching the valve.

[Prior Art] For example, intake valve seats used in the valve train of an automobile's internal combustion engine have traditionally had wear resistance, lubricity,
It is manufactured from cast iron or sintered alloy in consideration of cost and other factors.

Incidentally, in recent years, in response to demands for improved thermal efficiency, increased output, etc., engines with superchargers, single-cylinder multiple pulp engines, etc. have been developed, and internal combustion engines are becoming more efficient. In view of the fact that the performance of internal combustion engines is increasing, the wear resistance of conventionally used cast iron and sintered alloys is insufficient. Therefore, there is an increasing need to further improve wear resistance.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and it is also an object of the present invention to provide a wear-resistant cast iron with improved wear resistance.

[Means for solving the problem] The wear-resistant cast iron according to the present invention has a carbon content of 2°4 to 3% by weight.
．． 4%, silicon 2.0-3.0%, manganese 0.2-1
．． 0%, nickel 0.5-1.5%, molybdenum 1.0
~2.0%, one or more carbide-forming elements of chromium, vanadium, tungsten, niobium, and tantalum 0.3 to 2.0%, the balance iron, and unavoidable impurities. Its structure is mainly composed of bainite formed in as-cast conditions, and is characterized by having at least one of chromium carbide, vanadium carbide, tungsten carbide, and carbide mainly composed of niobium and tantalum.

The structure of the wear-resistant cast iron according to the present invention is mainly composed of bainite. Bainite is normally produced when properly cooled austenite is subjected to heat treatment such as isothermal transformation, but in the wear-resistant cast iron according to the present invention, bainite is produced as-cast without any heat treatment.

The reason why the structure is bainite is mainly to improve wear resistance, strength, toughness, etc. Graphite usually occurs in bainite. Graphite plays a role in ensuring lubricity. The shape of graphite is generally flaky. The size of the graphite is preferably one that is not coarse, and is generally 30 to 1
A thickness of about 20μ is desirable. The structure contains chromium carbide,
One type of carbide is precipitated out of vanadium carbide, tungsten carbide, and carbide mainly composed of niobium and tantalum. In some cases, two or more of the above carbides may be precipitated. The carbide produced in the present invention is generally a double carbide, and the hardness is usually f-1v1800 ~
It is 2800. The carbide of chromium is generally M7C.
3 type, and carbides mainly composed of vanadium, tungsten, niobium, and tantalum are generally MC type. These carbides are also present on the surface and contribute to wear resistance.

Next, we will discuss the reasons for limiting the composition.

Carbon is necessary to form graphite, to suppress the tendency to chill, and to form the carbides mentioned above. The reason why the carbon content is 2.4 to 3.4% is because if it is less than 2.4%, the tendency to chill increases, which is not preferable in terms of graphite formation.
This is because if it exceeds 4%, graphite becomes coarse and hardness decreases, which is not preferable.

The reason why silicon is set at 2.0 to 3.0% is that if it is less than 2.0%, the tendency to chill increases, which is not preferable in terms of graphite formation.
This is because if it exceeds 3.0%, graphite becomes coarse and hardness decreases, which is not preferable.

The reason for setting f-manganese to 0.2 to 1.0% is that if it is less than 0.2%, the harmfulness of S, which is an unavoidable impurity, cannot be removed, and if it exceeds 1.0%, the tendency to chill increases. This is because it is unfavorable in terms of graphite formation.

Nickel and molybdenum primarily serve to bainitize the as-cast structure. 0.5-1 nickel
．． The reason why the molybdenum content is 5% and the molybdenum content is 1.0 to 2.0% is to convert the structure into bainite in the as-cast state.

When only chromium is included among the carbide-forming elements, the content of chromium is preferably 0.3 to 1.0%. In this case, double carbide of chromium is precipitated in the as-cast bainite.

When only vanadium is included among the carbide-forming elements, the content of vanadium is preferably 0.3 to 1.0%. In this case, double carbide of vanadium is precipitated in the as-cast bainite.

When only tungsten is included among the carbide-forming elements, the content of tungsten is preferably 0.3 to 1.0%. In this case, tungsten carbide precipitates in the as-cast bainite.

The reason why the content of chromium, vanadium, and tungsten is set as above is that it is difficult to form double carbides when the content is less than 0.3%, and when it exceeds 1.0%, the tendency to chill increases, which is not preferable.

In producing the wear-resistant cast iron according to the present invention, the melting temperature is 1350-1650°C, and the pouring temperature is 1250-1650°C.
At 1550°C, the cross-sectional thickness of the casting can be 5-15 mm.

[Effects of the Invention] As shown in the test examples described below, the wear-resistant cast iron according to the present invention has a small increase in contact width and a small wear scar area, and has improved wear resistance compared to conventional products.

Therefore, it is suitable as a wear-resistant material for use in valve seats, valve guides, etc.

[Test Example 1] First, intake valve seats used in the valve train of an internal combustion engine of an automobile were manufactured from wear-resistant cast iron according to the present invention and a comparative material. Table 1 shows the compositions of the wear-resistant cast iron according to the present invention and comparative materials from which valve seats were made.

In Table 1, AlB and C indicate comparative materials (materials conventionally used for valve seats), D, E,
F and G each indicate the materials of the present invention.

Specifically, a valve seat was manufactured using wear-resistant cast iron according to the present invention as follows. The melting temperature was 1500° C., the pouring temperature was 1400° C., and a cylindrical rough material with an outer diameter of φ33, an inner diameter of φ13, and a length of 1501 RR1 was cast. A valve of a predetermined shape was fabricated from this crude material by machining.

In this test, the above-mentioned intake valve seat was specifically assembled into an engine, and a durability test of 6,800 rllll for 1,150 hours was conducted. The wear resistance of the valve seat was measured by the amount of increase in the contact width of the valve seat. Here, the term "increase in contact width" means the amount of increase in the width of the surface struck by the valve. The test results are shown in Table 1.

For the materials of the present invention, the increase in contact width for each of E, F, and G was as small as 0.18 to 0.25 mm. In particular, the test piece with precipitated chromium carbide was the smallest, showing improved wear resistance. On the other hand, the increase in contact width of the comparative material was as large as 0.33, 0.45, and 0.64 mm. From the above, it can be seen that the wear-resistant cast iron according to the present invention has improved wear resistance compared to conventional products.

For reference, a photograph of the microscopic structure of the material of the present invention is shown in FIG. The large black sushi-shaped substance is carbon, and the amoeba-shaped white substance in the lower center and lower left side is chromium carbide.
The thin white crystals are bainite.

[Test Example 2] First, samples were prepared using wear-resistant cast iron according to the present invention and a comparative material. The shape of the test piece is a plate, and its size is 25
x 60 x 5 am. The compositions of the wear-resistant cast iron according to the present invention and comparative materials are shown in Table 2.

Specifically, samples were prepared using the wear-resistant cast iron according to the present invention as follows.

The melting temperature was 1500℃, the pouring temperature was 1400℃, and 1
A plate-shaped rough material measuring 50×150×101III1 was cast. A sample having the above shape was fabricated from this rough material by machining.

Figure 2 shows an outline of the human friction and wear test. In this test, as shown in FIG.
was slid for a predetermined distance while being pushed with a predetermined load and sliding speed. The wear resistance was evaluated based on the size of the wear scar area formed in the sliding movement of the test piece 1. The test conditions at this time were: final load 6.3 kg, sliding speed Q, 3 m.
/5eC1 sliding distance is 100m, and rotating body 2 is JI
It was made from heat-resistant steel equivalent to s-suHi.

The test results are shown in Figure 3. As shown in FIG. 2, test pieces Cr(e) to Cr(g), test pieces V(e
) ~ test piece V (g), test piece Nb (e) ~ test piece Nb (
g>, the wear scar area was 15 mm2 or less in all cases. On the other hand, the wear scar area of the comparative material was as large as 19 mm2 or more.

This also shows that the wear-resistant cast iron according to the present invention has excellent wear resistance.

FIG. 2 is a side view schematically showing a friction and wear test. FIG. 3 is a graph showing the results of the friction and wear test.

Claims (7)

[Claims] (1) Carbon 2.4-3.4%, silicon 2.0-2.0% by weight
3.0%, manganese 0.2-1.0%, nickel 0.5
~1.5%, molybdenum 1.0-2.0%, one or more carbide-forming elements of chromium, vanadium, tungsten, niobium and tantalum 0.3-2.0%, balance iron, unavoidable Cast iron with a composition consisting of impurities, whose structure is mainly composed of bainite formed in as-cast conditions, and has at least one of chromium carbide, vanadium carbide, tungsten carbide, and carbide mainly composed of niobium and tantalum. Wear-resistant cast iron. (2) The wear-resistant cast iron according to claim 1, wherein the chromium content is 0.3 to 1.0% by weight. (3) The wear-resistant cast iron according to claim 1, wherein vanadium is contained in an amount of 0.3 to 1.0% by weight. (4) The wear-resistant cast iron according to claim 1, wherein the content of tungsten is 0.3 to 1.0% by weight. (5) The total amount of niobium and tantalum is 0.8 to 2 by weight
．． 0% wear-resistant cast iron according to claim 1. (6) A rotating body made of heat-resistant steel equivalent to JIS-SUH1 is pressed with a load of 6.3 kg, and the sliding speed is 0.3 m.
/sec when sliding 100m, the wear scar area is 1
The wear-resistant cast iron according to claim 1, which has a thickness of 5 mm^2 or less. (7) The wear-resistant cast iron according to claim 1, which is used for an intake valve seat used in a valve train of an internal combustion engine of an automobile.