JP2002275573A - Spheroidal carbide alloy white cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the material having high wear resistance is hard to be used for an apparatus to be subjected to large impact because of its high brittleness. SOLUTION: The white cast iron has a composition containing, by weight, 2.0 to 4.0% C, 0.5 to 3.0% Si, 0.06 to 1.5% Mn, 6.0 to 16.0% V, 0.01 to 0.1% Mg and 0 to 5.0% Ni, and the balance substantially Fe with impurities. V carbides which have been imperfectly spheroidal ones are perfectly spheroidized by the molten metal addition treatment of Mg, so that the white cast iron has an impact value of almost >=1.4 times that of the non-treated material having almost the same components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy white cast iron which is a high hardness material having excellent wear resistance and also has toughness.

[0002]

2. Description of the Related Art In a wide variety of industrial equipment and devices, members facing wear action lose their intended functions set for each device due to the progress of their own wear. It is an important factor that affects the operating efficiency of a vehicle.
The abrasion action is roughly classified into various forms, but it is first effective to increase the hardness of the member surface in order to counter abrasion (abrasion) that occurs most commonly with a flowing processing material. The improvement of wear resistance is linked almost in proportion to the hardness. In that sense, white cast iron has conventionally been used for Fe-C alloys,
High hardness composite carbide (double carbide, for example, Fe-Cr-C carbide) in which a considerable amount of Cr is blended.
Alloy white cast iron, which crystallizes in the form of primary crystal or eutectic to satisfy the desired wear resistance, is widely used.

On the other hand, depending on the type of equipment to be applied, simple wear resistance alone cannot fulfill a sufficient function, and there are many cases where it is required to satisfy other requirements.
A particular problem is that the carbide itself, which is a requirement to improve wear resistance, has a negative element that it is hard but brittle, and the form crystallized on the matrix also appears as a plate or mesh. White cast iron, however, is inherently a brittle material and is hard to escape from the drawback of being vulnerable to impact. For this reason, in addition to the high wear resistance, how to have the toughness is a great condition for determining the expansion of the applicable range of the material.

In the prior art of Japanese Patent Publication No. 37-7602, the reason why white cast iron having excellent wear resistance is vulnerable to impact and impact is because the shape of carbide is flaky, plate-like or mesh-like. And C: 1.5-4.8%, Si:
0.2-3.0%, V: 2.0-15.0%, balance Fe
Alloy cast iron, and claims that the addition of V has changed the carbide shape into uniform and fine spherical or pseudospherical precipitates to improve the impact resistance.

On the other hand, in the prior art of Japanese Patent Application Laid-Open No. 11-124651, C: 0.6-6.5, Si: 0.2-3.
0, Mn: 0.2 to 1.0, Cr: 13.0 to 30.
0, Ni: 4.0 to 15.0, V: 4.0 to 15.0
%, With the balance of Fe, and presents a tough high-carbon vanadium-cementite alloy cast iron crystallized mainly with covalently bonded granular or spherical VC-based carbides and Fe-Cr-based carbides in the structure. . This material is fully characterized by having all the properties of corrosion resistance, abrasion resistance, and heat resistance, and in particular, improving the impact resistance due to the crystallization of spherical V carbides. Stainless steel, which has been widely used in various chemical plants and boilers as a material relatively resistant to the oxidizing action of stainless steel, has a low hardness and inferior wear resistance. System alloy cast iron developed (Japanese Unexamined Patent Publication No. 6-240)
However, even with this new material, it cannot be said that this new material may be destroyed in applications with high risk of impact, such as ash sink pipes and propellers for sludge of submersible pumps. Fe- which is flat and brittle in shape
It is stated that the addition of V precipitates the structure of Cr carbide to crystallize granular and spherical V carbide to greatly improve the impact resistance.

[0006]

According to the first prior art cited, the affinity with C is very high just by adding an appropriate amount of V without adding a large amount of expensive alloy components. Therefore, the shape of the formed carbide is also spherical or pseudo-spherical, so that the brittleness due to the plate-like, flake-like, and mesh-like shapes is greatly improved, and the hardness of the carbide is extremely high (micro Vickers hardness, It can be evaluated that the abrasion resistance was further enhanced because of about 2700). However, in this case, since the final shape of the carbide is not obtained by artificial control, it is difficult to deny the variation in the rate of completing the shape, and a reliable level of toughness is always provided. Whether or not it is not necessarily guaranteed, there is no doubt that considerable variation will occur due to fluctuations in casting conditions, and the shape of carbides that are naturally and freely crystallized is naturally at the rate of spheroidization I have to say that there is a limit.

On the other hand, the second prior art uses stainless steel as a starting material, proceeds to a high-hardness cementite-based high-carbon alloy cast iron, and further increases wear resistance and toughness by crystallizing spherical or granular carbides by adding V. Although it is a process of providing, it is an essential requirement that a large amount of Cr be added. If at least 13% is not contained, strong Fe-Cr-based carbides do not crystallize, and Ni also contains 4.0%. If it is not contained, martensitization is liable to occur, so that it is an essential requirement. Therefore, the addition of a large amount of alloy components has the disadvantage of significantly increasing the production cost. Furthermore, as in the prior art, since the granulation and spheroidization of V carbides depend not only on artificial control and operation but on the spontaneous reaction between metals, there are many differences in casting conditions. Variations in the action are also unavoidable and do not necessarily guarantee reliable spheroidization and granulation. This is clearly seen in the attached microstructure photograph, in which chrysanthemum petals are unstable, irregular massive carbides, and a large number of Fe-Cr-based carbides mixed in a whisker-like or mesh-like form are crystallized. It can be clearly confirmed from the state where it is.

[0008] Further, regarding the matrix, in both cases of as-cast, annealing and normalizing heat treatment, the structure is austenitic (γ) + cementite (Fe).
-Cr-C) + VC complex is described as almost unchanged, and this is supported by the attached micrograph. After all, the problem is compatibility with the application, and it is suitable for chemical plants and boiler members that emphasize heat resistance and corrosion resistance, but is subject to more severe wear with impact, such as shredders for waste and vehicles. With regard to mill hammers and strikers, the question was that the hardness of the base was lost at a low level, and that even if carbides were made spherical or granular, insufficient results could still be expected. Remains.

In order to solve the above-mentioned problems, the present invention ensures that a carbide, which is a compound of V and C, is crystallized in a spherical form, thereby maintaining a conventional level of abrasion resistance while maintaining a high level of impact resistance. It is an object of the present invention to provide alloy white cast iron having significantly improved ductility and having at least 1.4 times the toughness as compared with the impact resistance of the same component for a wide range of uses such as industrial machinery and civil engineering machinery.

[0010]

The alloy white cast iron according to the present invention has a C: 2.0 to 4.0 and a Si: 0.5 to 100% by weight.
3.0, Mn: 0.06 to 1.5, V: 6.0 to 16.
0, Mg: 0.01 to 0.1, Ni: 0 to 1.0, and the remainder substantially composed of Fe containing impurities. The above problem was solved by the fact that the crystallized carbide provided an impact value that was approximately 1.4 times or more that of an untreated material of almost the same composition.

In the basic configuration, Ni: 1.
0. To 5.0, and Mo: 0.01 to 0.8% is further added to further improve the wear resistance of the microstructure as a base phase of lower bainite or martensite to further improve the purpose. May be achieved. Ni,
Whether Mo is added or not and the amount of Mo added depend on whether the matrix is a pearlite phase, a lower bainite or martensite phase, or how to balance abrasion resistance and impact resistance required depending on the use conditions of the product.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the components of the alloy white cast iron of the present invention will be described below. C: 2.0- from the Fe-C phase diagram as far as cast iron is concerned
Although it is a 6.67% C Fe-C alloy, a critical difference appears in its structure due to the relationship with Si, and Maurer (M
According to the structure diagram of Aurer, the area of white cast iron is point A (C: 4.3%, Si: 0%, eutectic point) and point B (C:
1.0%, Si: 2.0%) and a horizontal axis,
The range is a right-angled triangle surrounded by the vertical axis. In the present invention, C:
Although this range is covered by 2.0 to 4.0%, a range of 2.5 to 3.5% is recommended for practical use. Si: Si is in the range of 0 to 2.0% according to the above structure diagram, but Si is an indispensable component from the viewpoint of deoxidation during melting and molten metal flow during casting, and is at least 0.5% If not included, sound casting is difficult. Further, the range of white cast iron expands due to the effect of the addition of other components, but if it exceeds 3.0%, the toughness is degraded, and the range falls within the range where graphite crystallization is allowed. %, But preferably 1.0 to 2.5% is recommended.

V: At least 6.0% is required to combine with the contained C to crystallize a carbide having a high hardness. However, if it exceeds 16.0%, the balance with C to be bonded sooner is lost, and it is not possible to crystallize only the added carbide, so that not only the effect is not accompanied but also the impact resistance is lowered. Therefore, it was limited to 6.0 to 16.0%. However, practically, it is 8.0 from the result of the embodiment described later.
The range of 13.0% is preferred. Mg is an indispensable element for reliably changing the shape of the V carbide crystallized in the natural solidification process into a spherical or granular shape that can be formed into an unstable chrysanthemum valve shape as it is.
According to the bubble theory, which is one of the spherical graphitization theories proposed for spheroidal graphite cast iron, Mg added to the cast iron melt becomes bubbles, and graphite grows centripetally from the outer periphery of the bubbles. I have. Even when the base component is white cast iron as in the cast iron of the present invention, it is unclear whether such Mg bubbles are elements that spheroidize carbides, and the deoxidizing effect of Mg itself is inherently unknown. It is also conceivable to reduce spherical vanadium carbide to a spherical form. In any case Mg
It is speculated that the addition contributes to promoting spheroidization. M
In order to ensure a sufficient spheroidization reaction in anticipation of instantaneous explosive combustion and oxidation consumption, the same addition technique as in the case of spheroidal graphitization was used. The amount and method of addition must be such that residual components of 0.01% to 0.1% can be confirmed.

Ni: The presence or absence of addition changes the structure of the base,
Hardness and wear resistance are greatly affected by the structure. In particular, in the case of a product that emphasizes abrasion resistance, it has been confirmed that if added in an amount of 0.04% or more, it is possible to form martensite by heat treatment. In order to convert the as-cast martensite into a matrix, it is necessary to add 1% or more, preferably 1 to 3%.
% Can be recommended. The presence or absence and amount of addition are determined depending on the thickness of the product (cast product) and whether the emphasis is on wear resistance or toughness. Should be kept at 5.0%, and eventually the amount added is limited to 0 to 5.0%. In addition, Mn is effective for deoxidation adjustment and desulfurization during dissolution, and at the very least is indispensable, but on the other hand, it also has a remarkable function to promote white ironing and a function that promotes segregation cannot be ignored. Therefore, it is limited to 0.06 to 1.5%. There is no particular problem for P and S as long as they are in the same category as that of ordinary cast iron. However, S is a factor that inhibits spheroidization as in the case of graphite. It is necessary.

[0015]

EXAMPLE In order to confirm the function and effect of the present invention, a comparative example in which white iron to which desired V was added was cast without processing, and a spheroidizing treatment in which Mg was added to a molten metal having almost the same components. Specimens of each example were prepared, and the impact value, the hardness, the wear coefficient obtained as a result of the impact wear test, and the spheroidization ratio of carbide measured by image processing of each microstructure photograph By contrast, the difference between the two due to the presence or absence of the addition of Mg can be known purely.

The preparation of the test pieces was all the same under the same conditions. That is, the material whose components have been adjusted is inserted into a graphite crucible, melted in a high-frequency furnace, heated, and then cast in a mold made of chromite sand as it is in the comparative example. In the embodiment, M
g After casting, immediately cast into chromite sand mold,
In each case, a test block having a cross section of 10 × 10 mm was prepared, and a Charpy impact test specimen specified by JIS was cut out.
The sample after the test was measured for Rockwell C hardness (HRC) and converted to Shore hardness (HS) for display. Table 1 collectively shows the chemical components of Examples and Comparative Examples, the presence / absence of Mg treatment, and the types of bases. And the base is perlite group 1 (Claim 1)
And the base is divided into two groups of lower bainite or martensite group 2 (Claim 2), and examples and comparative examples are included in each group. The comparative examples included in each group include components and bases according to the examples of the same group. Table 2 shows the test results of the impact value, hardness, and wear coefficient of these examples and comparative examples.

[0017]

[Table 1]

[0018]

[Table 2]

A dry wear tester was used to measure the impact wear coefficient. As shown in FIG. 4, the test device is attached to four arms 2 protruding from the rotary shaft 1, and the rotary shaft 1 is rotated by the electric motor 3 for a predetermined time to convert the test sample into quartz porphyry R. The weight loss of each test piece TP generated during the collision was measured, and compared with the weight loss of the standard material (SS400), and used as an index of the superiority of the abrasion resistance.

[0020] The spheroidization rate of the carbide is J
It is determined according to the provisions of IS G5502 (spheroidal graphite cast iron product). According to the regulations, the microscope magnification is 800
Double over 5 fields of view to determine the average value. FIG. 5 (A)
The number of carbides in the visual field that has reached the standard spheroidization shown in (B) is counted, and the ratio to the total number of carbides in the entire visual field is indicated by%, which is referred to as the spheroidization rate, and is calculated by computer image processing. In some cases, this is followed. FIG. 2 shows an example of the image processing.

FIG. 1 (A) is a microscopic photograph of Example 2 and FIG. 1 (B) is a microscopic photograph of Comparative Example 1 in which image processing is performed. The structure is revealed by nital corrosion and the magnification is 800 times. . FIGS. 2 (A) and 2 (B) show the textures of the test pieces of Example 2 and Comparative Example 1 by image processing and binarized carbide shapes. Image analysis of shape factor K for each carbide particle Determined by Area M of each carbide particle, circumference S
Is calculated, and a shape factor K = 4πM / S2 is calculated from the particle size.
(A) Counted as acceptable particles that reached spheroidization as shown in (B). In order to avoid errors, fine particles having a circle-equivalent area of 2 μm or less in diameter were excluded from the particles for which the shape factor was determined. Table 3 shows an example of calculating the shape factor for each carbide particle and calculating the spheroidization ratio for one field of view of each sample of Example 2 and Comparative Example 1, depending on the presence or absence of spheroidization treatment by adding Mg. The difference in spheroidization is clearly shown.

[0022]

[Table 3]

FIGS. 3A and 3B show another embodiment of N
Group 2: i: 2.74%, Mo: 0.45%
7 is a photograph of a microstructure of Example 4 according to (Claim 2) and Comparative Example 3 which is substantially the same component and is untreated, in which a base is revealed by nital corrosion. The V-carbide observed in white in the photograph has a spheroidized or rod-shaped form in Comparative Example 3, whereas the V-carbide of Example 4 has clearly achieved spheroidization. In addition, as for the base structure, a mixed structure of martensite and lower bainite structure having high hardness and excellent abrasion resistance is obtained as-cast with respect to the pearlite of Example 2 in FIG. ing. For this reason, in Example 4, martensite having characteristics excellent in wear resistance by heat treatment after casting,
It is considered easy to form a bainite structure.
A summary of the results of measuring the spheroidization rate of the carbide described above for all the test specimens listed in Table 1 (the average value of the spheroidization rates in five visual fields for each test specimen was taken as the final spheroidization rate). Is Table 4.

[0024]

[Table 4]

If the components, impact value, hardness, impact wear coefficient and spheroidity of the examples and comparative examples are comprehensively determined, there is no significant difference between the untreated comparative example and the Mg-treated example in the base structure itself. First of all, a remarkable difference in impact value appears despite not being seen. Impact value is Ni or Mo
In the case of Group 1 containing no or only low, the bases were not different from the pearlite, but the average impact value of 9.2 J / cm 2 of the example was 6.0 J / cm 2 of the comparative example.
cm3, 1.53 times of cm2, Ni: 3%, Mo: 0.
In Group 2 of about 5%, the base was not different from lower bainite or martensite, but Examples 4 and 5 in Comparative Example 3 were 1.66 to less in impact value.
It is 1.64 times, and in each of the embodiments, the impact value is surely greatly improved, and at least approximately 1.4 times or more.

As described above, the hardness of the base itself is not significantly different from that of the embodiment and the comparative example, and as a result, the impact wear coefficient falls within the substantially same level range according to the difference in hardness. As described above, there is a remarkable large difference in the impact value, and it is difficult to recognize a clear difference between the hardness and the abrasion resistance. And it was concluded that the result was based solely on the presence or absence of the spheroidization treatment by the addition of Mg, which is the only difference in the components.

[0027]

As described above, the alloy white cast iron according to the present invention has the effect of greatly improving the impact resistance while maintaining the wear resistance at substantially the same level. And because of that N
There is no need to mix a large amount of expensive alloying elements such as i and Cr, and the method can be reliably performed only by molten metal treatment. Therefore, it is far more economically advantageous than the conventional technology. As a result,
In particular, it is an ideal material that simultaneously satisfies the toughness and wear resistance suitable for all wear members including crushers, crushers, other hammers and strikers where impact wear crucially controls the function of the device The contribution to the industry is extremely large.

[Brief description of the drawings]

FIG. 1 is a photograph (magnification: 800) of a microscopic structure revealed by corrosion in Example 2 (A), which is an embodiment of the present invention, and in Comparative Example 1 (B) having substantially the same components.

FIG. 2 shows images (A) and (B) obtained by binarizing a carbide as a spheroidization rate measurement object of the same example and comparative example by image processing.
Are indicated by.

FIG. 3 (Example 4 (A)) in another embodiment of the present invention.
And a photograph (magnification: 800) of a microstructure revealed by corrosion in Comparative Example 3 (B).

FIG. 4 is a partial cross-sectional front view showing an outline of a wear tester used for a wear test.

FIGS. 5A and 5B show two forms of a standard recognized as a sphere on a tissue in accordance with JIS regulations.

[Explanation of symbols]

 Reference Signs List 1 rotation axis 2 arm 3 motor TP test piece R quartz porphyry

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Tachibana 2-7-1, Ayumino, Izumi-shi, Osaka Inside the Osaka Prefectural Institute of Advanced Industrial Science and Technology (72) Mamoru Takemura 2--7, Ayumino, Izumi-shi, Osaka No. 1 Inside the Osaka Prefectural Institute of Industrial Science and Technology (72) Inventor Mitsuaki Matsumuro 2-7-1 Ayumino, Izumi-shi, Osaka Pref.

Claims (2)

[Claims] 1. C: 2.0 to 4.0 in terms of% by weight, S
i: 0.5 to 3.0, Mn: 0.06 to 1.5, V:
6.0-16.0, Mg: 0.01-0.1, Ni: 0
1.0, the remaining substantially composed of Fe containing impurities, and in the microscopic structure, a V-carbide crystallized by the treatment of adding a molten metal of Mg to the mother phase of pearlite almost uncrystallized material of substantially the same component. Spherical carbide alloy white cast iron characterized by having an impact value almost 1.4 times or more. 2. The method according to claim 1, wherein Ni: 1.0-5.
0, Mo: Spherical carbide alloy white cast iron characterized in that the microstructure containing 0.01 to 0.8% substantially enhances wear resistance as a matrix of lower bainite or martensite.