JP2542681B2 - Wear-resistant alloy cast iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention requires not only abrasion resistance but also resistance to surface roughening or seizure resistance, and a rolling roll or the like used hot or cold. The present invention relates to cast iron for tools.

[Conventional technology]

In order to improve the wear resistance of cast iron, it is effective to crystallize or precipitate hard carbide. In particular, carbides such as Mo and V have high hardness, and their effect is great.

On the other hand, since graphite, which is the main structure of cast iron, has good thermal conductivity, it has the effect of suppressing heating and temperature rise due to friction of the tool surface, wear resistance, and the effect of improving skin roughness, and as a solid lubricant. Since it has an action, it is effective in seizure resistance and wear resistance. However, M that forms the above hard carbide
Elements such as o and V are also strong white ironizing elements, and cast iron in which these hard carbides and graphite coexist has not been obtained.

As a wear-resistant alloy cast iron having graphite and carbide, a nihard alloy cast iron has been generally known. This cast iron carbide is mainly composed of M ₃ C and has a small hardness. On the other hand, Japanese Examined Patent Publication No. 61-16415 discloses an alloy cast iron for a rolling roll having Cr carbide, that is, M ₇ C ₃ system or M ₂₃ C ₆ system carbide, but harder MC, M ₄ C ₃ , M
Carbides such as ₆ C and M ₂ C are almost absent, and high wear resistance cannot be expected. Further, as a material in which graphite and hard carbide coexist, there has been a powder sintered alloy from the past, but the manufacturing process is more complicated than the cast alloy, so that the cost becomes high.

[Problems to be solved by the invention]

It was conventional wisdom that it was impossible to make graphite exist in a cast iron material containing a strong elemental white iron. Under such circumstances, an object of the present invention is to provide a novel wear-resistant alloy cast iron in which graphite and hard carbide composed of a strong elemental white iron coexist.

[Means for solving problems]

The present inventor has conducted diligent research to solve the above problems and discovered the following new facts.

(1) There are alloy cast irons having a metallic structure in which graphite and carbides of strong white iron oxide coexist, and the forms of these carbides are MC type, M ₄ C ₃ type, M ₆ C type, M ₂ C type. Hard carbide such as, and occupy 20% or more in area ratio in all carbides.

(2) As a preferable example of chemical composition of the invention alloy cast iron, C2.5-4.0%, Si2.0-5.0%, Mn0.1-1.5%, Ni3-
8% (excluding 3%), Cr7% or less, Mo4-12%, V2-8
%, The balance impurity element and substantially Fe, and can further contain Co2 to 8%.

[Work]

First, according to the present invention, it is possible to obtain an alloy cast iron in which graphite and hard carbide occupying 20% or more of all carbides coexist, and to inexpensively obtain a new tool material having the function and effect exhibited by both graphite and hard carbide. You can That is, the hard carbide has high wear resistance, and the graphite has high thermal conductivity and self-lubricating action. As a result, it is possible to obtain an alloy cast iron that is excellent not only in wear resistance but also in seizure resistance and skin resistance.

Next, the reasons for specifying the chemical composition of the cast iron alloy of the present invention are as follows.

C is an element necessary for crystallizing graphite and forming hard carbide. If the amount is less than 2.5%, it becomes difficult to crystallize graphite and the amount of carbide is small, resulting in insufficient abrasion resistance, seizure resistance, and skin roughening resistance. Also, 4.
Carbide exceeding 0% becomes excessive and the toughness decreases, which is not preferable.

Si is a deoxidizing agent and an effective graphitization promoting element, so 2.0% or more is required. However, if it exceeds 5.0%, the material becomes brittle. In order to crystallize graphite, 0.1% or more of the added Si amount needs to be added by inoculation.

Mn fixes the impurity S as MnS together with the deoxidizing action. If the amount is less than 0.1%, deoxidation is poor. However, if it exceeds 1.5%, retained austenite is likely to be generated, and stable and sufficient hardness cannot be maintained.

Ni is necessary for crystallizing graphite and improving the hardenability of the matrix, and it is necessary to add more than 3%. However, when it exceeds 8%, austenite is excessively stabilized, and transformation to bainite or mantensite is difficult to occur. Therefore, sufficient hardness cannot be obtained, and wear resistance and skin resistance are deteriorated.

Cr is an element that effectively acts to make the base bainite or martensite and maintain the hardness. But,
If it becomes excessive, it inhibits crystallization of graphite and forms Cr-based carbides, that is, M ₇ C ₃ -based and M ₂₃ C _6- based carbides. These carbides have lower hardness than the MC type, M ₄ C ₃ type, M ₆ C type, and M ₂ C type, and reduce wear resistance. Therefore, the upper limit of Cr is 7%.

Mo combines with C to form M ₂ C or M ₆ C-based carbides, and also forms a solid solution in the matrix to strengthen the matrix, thereby increasing wear resistance and high-temperature hardness and temper softening resistance. Contribute to improvement. However, when it becomes excessive, crystallization of graphite is inhibited and M ₆ C-based carbides increase in the balance between C and V,
It is not preferable in terms of toughness and skin resistance. By these
The Mo addition range is 4 to 12%.

V is an essential element for forming MC-based carbide that is effective in improving wear resistance, but when it is excessive, V hinders crystallization of graphite. Therefore, the addition range of V is set to 2 to 8%.

The alloy cast iron of the present invention may contain Co in addition to the above elements. Co is a preferable element from the viewpoint of imparting heat resistance by temper softening resistance and secondary hardening, but if it is excessive, it reduces toughness. Therefore, the range of addition of Co is 2-8%.

Except for the above-mentioned elements, impurities are practically used and Fe is used.
The main impurities are P and S, but P is preferably 0.1% or less for preventing embrittlement, and S is similarly 0.08% or less.

In the cast iron alloy of the present invention, in addition to specifying the above-mentioned chemical components, it is necessary to inoculate with a Si-containing inoculant before pouring the molten metal into the mold in the molten state. The amount of inoculated Si needs to be 0.1% or more by weight due to crystallization of graphite, but if it exceeds 0.5%, the inoculum becomes difficult to uniformly dissolve in the molten metal, and the cast alloyed iron tends to have uneven structure. .

〔Example〕

Example 1 The alloyed cast irons of the present invention having the components indicated by the sample symbols A and B in Table 1 were melted at 1600 ° C. using a high frequency induction melting furnace,
When tapping, inoculate 0.3% of Fe amount with Fe-Si alloy, 1550 ℃
A test piece was produced by casting in a sand mold with a diameter of 100 mm and a depth of 100 mm. The metallographic structure was examined microscopically at a position of 15 mm from the outer peripheral surface of this test piece. Graphite and hard carbide were observed in all the test pieces. Of these, an example of the metallographic structure of test piece B is shown in FIG.
In the figure, (1) is the structure in the non-corroded state, and (2) is the structure after the corrosion. In Fig. 1 (1), flaky and massive graphite is clearly seen. The graphite area ratio in this case was 2%. Graphite is also seen in FIG.
Furthermore, the lumps of crystals are M ₄ C _{3 of} V, the grains of crystals are MC of V, and the crystals of spine are Mo.
It was an M ₆ C-based carbide. The area of these hard carbides accounted for 85% of the total carbide area in this case.

Example 2 The specimen manufactured in Example 1 was quenched from 1050 ° C. and 55
After heat treatment of tempering at 0 ℃, After adjusting to the hardness shown, a small sleeve roll test piece having an outer diameter of 60 mm and a length of 40 mm was processed. The test piece was mounted on a rolling wear tester shown in FIG. 3 to test the wear resistance. In the figure, 5 and 5'are rolls as test pieces. As a conventional material for comparison, an alloy cast iron roll test piece similar to the Cr carbide type alloy cast iron for rolling rolls described in Japanese Patent Publication No. 61-16415 was manufactured. This roll test piece is shown as a test piece symbol C in Table 1.

 The conditions of the rolling wear test are as follows.

Rolling material: SUS304 Rolling rate: 25% Rolling speed: 150m / min Rolling material temperature: 900 ℃ Rolling distance: 300m Roll cooling method: Water cooling After the test, the part of the surface of the roll specimen that came into contact with the rolling material is worn and concave become. In addition, when rough skin or seizure occurs, small unevenness occurs on the worn surface. The wear / skin roughness profile of each sample was measured with a surface roughness meter (SURFCOM). An example is shown in FIG. In the figure (1), the sample symbol B
(Invention) Upper roll, (2) shows the situation of the sample roll C (conventional) upper roll. Table 1 also shows the average depth of the worn portion of each upper roll.

From these test results, it is understood that the alloy cast irons A and B of the present invention have markedly higher wear resistance and smaller unevenness on the wear surface than the conventional alloy C cast iron for rolling rolls of Cr carbide.

From the above examples, it is expected that the alloy cast iron of the present invention will be put to practical use as a cast iron for tools and will exhibit extremely excellent performance. When used as a rolling roll, it should be used as a sleeve or ring type roll, or basically as a composite roll by the continuous overlay casting method disclosed in Japanese Examined Patent Publication No. 444903/1989. And so on.

〔The invention's effect〕

According to the present invention, a cast iron for tools having an unprecedented metallographic structure in which graphite and hard carbide coexist, which is excellent in seizure resistance and roughening resistance, is manufactured by a simple manufacturing process of casting. It became possible to do. And
It can be applied to wear-resistant members for various applications and can achieve extremely excellent performance improvement.

[Brief description of drawings]

FIG. 1 shows a photograph of the metal structure of the cast iron alloy of the present invention,
When (1) does not corrode, (2) shows the state after corrosion. FIG. 2 shows the profile of the surface of the test piece when a rolling wear test was carried out, (1) showing the example of the present invention, and (2) showing the state of the conventional alloy cast iron. FIG. 3 is a schematic explanatory view of the spread wear tester. 1: Heating furnace, 2: Rolled material 4: Rolling machine, 5: Upper roll (test piece) 5 ': Lower roll (test piece), 8: Winding machine

Claims (2)

(57) [Claims] 1. The chemical composition of C2.5-4.0% by weight, Si2.0-
5.0%, Mn0.1-1.5%, Ni3-8% (excluding 3%), Cr7
% Or less (excluding 0%), Mo4 to 12%, V2 to 8%, balance impurity elements and substantially Fe, having graphite and carbide, MC type, M4C3 type, M6C type and M2C type carbide A wear-resistant alloy cast iron characterized by a total area ratio of 20% or more of all carbides. 2. A wear-resistant alloy cast iron according to claim 1, further comprising Co2 to 8% by weight.