JP3496577B2 - Hypoeutectic high chromium cast iron material particularly suitable for large products and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high chromium cast iron material, and particularly to a large wear resistant member, for example, a large chromium cast iron having a large wall thickness of 200 mm.

[0002]

2. Description of the Related Art Since ancient times, in equipment such as construction machinery, kiln industry, crushed stone, mining, electric power, dredging, and industrial machinery, the raw materials to be handled, contact with raw materials, and abrasion of members to be abraded are remarkable, and physical properties as a structure In addition to dynamic strength, wear resistance is an important condition, and various wear resistant materials have been developed and used properly according to the application.

The wear-resistant material must be replaced because the wear-resistant material cannot be used for a certain period of time so that the wear-resistant material cannot withstand predetermined work efficiency. Therefore, a material that can withstand a longer period of time and crushes, crushes, and conveys a larger amount of raw materials and that has a high degree of wear resistance for subjecting the material to the intended treatment, such as a structural member, is required to have a predetermined mechanical strength.
High chrome cast iron was widely used among wear resistant materials.

Table 1 shows the well-known ASTM: A532 / A53.
It is an excerpt of the chemical composition of the high chromium cast iron material specified in 2M. Class 1 is so-called Ni-Hard.
Materials, Classes 2 and 3, are high chromium materials, which have a C value in the hypoeutectic range, with Cr as the main component, and Ni and Mo added to precipitate high hardness carbides and disperse them in the matrix. The basic principle is to form a dense and strong wear resistant structure.

[0005]

[Table 1]

However, since the wear resistant material also plays a role as a member that constitutes a machine or device, mechanical strength,
In particular, from the viewpoint of toughness as well, it is necessary to select both the structure and the composition to satisfy both requirements of wear resistance and toughness. By manipulating the content ratio of C and Cr, it is possible to crystallize an appropriate amount of high hardness carbide which is effective for improving wear resistance.
If the carbide content ratio becomes high, the mechanical strength cannot be guaranteed due to the decrease in toughness, and conversely, if the carbide content ratio is decreased, the wear resistance decreases. Therefore, a material having a composition aimed at a hypoeutectic which is slightly lower than the eutectic point defined by the ratio of C and Cr and having an increased matrix hardness by hardening and quenching heat treatment is generally used.

Conventional high chromium cast iron-based materials have C2.5-
A material containing 3.3% by weight of Cr and 15.0 to 30.0% by weight of Cr as main components, to which several% of Ni, Mo and a small amount of carbide-forming elements (W, V, etc.) is added is applied. What has come is the conclusions obtained from the results of local use and research and development, and starting from this basic material, it has evolved into many conventional technologies as described below.

[0008]

Recently, demands for cost reduction due to work efficiency, labor saving, and labor saving have been further increased,
Naturally, there is a trend toward increasing the size of equipment and machinery in pursuit of improved processing capacity. This inevitably means an increase in the size of each individual wear-resistant member itself, and while the function of the member, that is, wear resistance, must be further improved, it faces a major new issue due to the increase in size. . That is, if the wear-resistant member becomes thicker and super-weighted, it becomes difficult to secure the hardening of the base material by quenching due to the mass effect of the member even if the amount of carbide crystallized in the solidification process can be secured, and as a result, the base material is hardened. While the quenching is inadequate, that is, the matrix hardness is low, there is no choice but to limit the application to materials that are expected only to have wear resistance mainly due to the amount of carbide.

In general, in order to secure the hardenability of a metal material by heat treatment, a means for increasing the cooling rate or adding an alloy element having a high quench hardening ability so that it is treated with a low alloy tempered steel is taken. However, in the high chromium cast iron-based material, brittle chromium carbide is crystallized at an area ratio of 30 to 40%, and therefore rapid quenching means using water, oil, etc. cannot be adopted, and therefore air-quenching must be performed. However, if the target member becomes thicker and super heavy, hardenability cannot be secured, the desired base hardness will not be reached at the center part of the wall thickness, and if the cooling rate is increased by forced air cooling quenching with a blower etc., the surface The thermal stress due to the difference in the cooling rate between the inside and the inside often causes quenching cracks. Mo · Mn, which is said to have a high hardening ability, is also a carbide-forming element, so if added in a large amount, massive carbides will be formed to promote embrittlement of the material. Cracking is likely to occur.

As a conventional technique for dealing with an increase in size of a product, Japanese Patent Laid-Open No. 2-115343 discloses C: 2.8-
3.5, Mo: 1.0 to 3.0, Cr: 15 to 25, N
i: 0.5-2.0 (all are wt%) high chromium cast iron containing Ti: 2-5 wt% and N, TiC,
It is said that TiCN was dispersed in the structure to obtain a material (MC type carbide) made of carbide having extremely high hardness.
In JP-A-12553 also, C: 2.5 to 3.5 and Cr:
10-25, Ni: 3.0 or less, Mo: 3.0 or less, T
i: 5.0 to 20.0 (all in weight%), toughness,
He claims that he has developed an alloy cast iron with both excellent wear resistance. Further, in JP-A-6-240403, C: 2.8-
3.6, Cr: 10-20, Ni: 0.5-1.5, M
o: 1.0 to 2.0, W: 0.2 to 0.8, V: 0.5
-1.2, B: 0.2 or less (all in weight%), quenching temperature T (° C.) = Cr (weight%) × 7 + 865 ± 20
By limiting the range, ie low Cr%
Then, by controlling the quenching temperature to a relatively low value, the correlation between the quenching temperature at which the maximum hardness is obtained and Cr% was established.

However, all of these three prior arts are improvements focusing only on further improving the hardness of the precipitated carbides. Therefore, as the size of the product increases, there is a gap between the center of the base and the vicinity of the surface layer. It is impossible to suggest any solution to the difference in cooling rate in the steel, quenching cracks accompanying it, or large variations in hardness, and it is necessary to reduce the difference in wear resistance between the central part of thick wall and the surface layer. It cannot be ignored to solve the problems of the invention. In addition, the previous two cases require the addition of expensive Ti at a considerable compounding ratio, so a large cost increase cannot be ignored.

In order to solve the above problems, the present invention, for example, has a maximum thickness of more than 200 mm and a unit weight of 1
Even for large-sized members that reach nearly 0 tons, both the central part of the wall thickness and the part near the surface layer maintain a high base hardness at almost the same level. Therefore, for large-sized members that are much more wear resistant than the conventional technology. An object of the present invention is to provide a high chromium cast iron material.

[0013]

Maximum wall thickness 2 according to the present invention
High chromium cast iron conforming to及department large-product 00mm is C: 2.80~3.50%, Si: 0.30~1.20
%, Mn: 0.70 to 1.80%, Cr: 15.0 to 3
0.0%, Mo: 2.00 to 4.00%, Ni: 0.7
0 to 2.00%, N: 0.20 to 0.40% (all in weight%), unavoidable impurities, and balance Fe, which is a hypoeutectic high chromium cast iron, and N dissolved as a solid solution in γ-Fe. Has a maximum wall thickness of 2 by increasing the bainite transformation completion time.
Thick central portion even in及department large-scale casting to 300 mm, a base hardness regardless of the surface layer portion micro-Vickers hardness (hereinafter H
(represented by mV) is 800 or more , and the matrix hardness does not change over the entire area of the thick section, thereby solving the above problem.

Further, the manufacturing method of the high chromium cast iron material according to the present invention is C: 2.80 to 3.50%, Si: 0.30.
1.20%, Mn: 0.70 to 1.80%, Cr: 1
5.0 to 30.0%, Mo: 2.00 to 4.00%, N
i: 0.70 to 2.00%, N: 0.20 to 0.40%
Cause quench cracking in及department large-products (both by weight) and unavoidable impurities, casting the melt hypoeutectic based high chromium cast iron consisting of the remainder Fe, cast care After completion, the maximum thickness 200mm Slow cooling at a non-cooling rate, the phase transformation shifts to the long-term side by the austenite stabilizing action of N, and the hardenability of the matrix is maintained even at the cooling rate, and the central portion of the wall thickness and the surface layer portion are both equal. Ensure high hardness and at least HmV:
The above problem was solved by forming a high hardness base of 800 or more and forming an abrasion resistant structure over the entire area of the wall thickness section together with the ultra-high hardness carbide dispersed and precipitated throughout the base.

The high chromium cast iron material of the present invention has a certain toughness and is controlled to C-Cr in the hypoeutectic range, and is balanced to obtain high hardness forming a root of wear resistance.
The addition of r, Ni and Mo to disperse and precipitate carbides falls within the general principle of the prior art. The greatest technical feature is the strengthening of the base, which is suitable for thick and large-sized products and has a small variation in hardness over the entire thickness section, and as a whole, it is a level that greatly exceeds the base hardness of the conventional technology ( H
The above problem is solved by maintaining the MV of 800 or more).

The effect of evenly and significantly improving the hardness of the matrix is exhibited by ensuring the hardenability of the matrix stably even when the austenite stabilizing element, especially N, has a slow cooling rate. That is, the austenite stable elements such as N, Mn, and Ni have a function of shifting the phase transformation seen in the continuous cooling transformation curve of the matrix structure, that is, the martensite-bainite appearance curve to the long-term side. In particular, in the case of N, it is known that an N atom solid-dissolved in the γ-lattice of Fe as an interstitial type suppresses phase transformation and stabilizes γ-Fe, and the solid-solution N shifts the S curve to the right. At the same time, it has been found that the nucleation of α crystal grains is delayed, the nose of 550 ° C. generated in the Fe—C system is lowered to the low temperature side, and the time for completing the bainite transformation also becomes long. (For example, Eleme
nt of Hardenability ASM [19
50]: 150 etc.) In the present invention, from this viewpoint, the addition of an appropriate amount of a component that shifts the γ to α transformation to the long-term side in various hypoeutectic high-chromium cast iron materials enhances the stability of the quality of thick and large-sized products, particularly The greatest feature is that it was found to be uniform in wear resistance and optimal for leveling up.

Next, the reasons for limiting the chemical composition of the hypoeutectic high chromium cast iron material according to the present invention will be explained. C is Cr,
It is an element that combines with Mo, W, etc. to crystallize hard carbide or secondary precipitates by heat treatment, but if it is less than 2.80% by weight, the amount of the above-mentioned carbide formed (crystallization, precipitation) is insufficient, Reduces wear. On the other hand, if it exceeds 3.50% by weight, carbide is excessively generated, or depending on the Cr content, it becomes a hypereutectic region, and mechanical strength as a structural member cannot be guaranteed due to a decrease in toughness. Therefore, C: 2.80 ~
It was set to 3.50% by weight.

Si is an element necessary for ensuring castability such as deoxidation and fluidity of molten metal, but 0.30% by weight
If the content exceeds 1.20% by weight, the toughness deteriorates and the hardenability is impaired, and solidification cracks due to phase transformation (troostite) occur in the solidification process in thick and super heavy members. It was limited to 30 to 1.20% by weight.

Mn is an element effective for deoxidation and fixing of S which is an unavoidable impurity element, and is effective for securing hardenability by stabilizing austenite, but if it is less than 0.70% by weight, the effect is not observed. If it exceeds 1,80% by weight, the hardenability is impaired due to the stabilization of austenite and the matrix hardness is lowered. As a result, 0.70 to 1.80% by weight
Limited to.

Ni, like Mn, is an element effective in securing hardenability by stabilizing austenite and preventing phase transformation in the solidification process, but if it is less than 0.70% by weight, its effect is not observed and 2.00% by weight. If it exceeds 1.0, the hardenability is impaired and the base hardness is lowered, so the content was made 0.70 to 2.00% by weight.

Further, N is an element indispensable for ensuring hardenability by stabilizing austenite, but 0.2
If it is less than 0 % by weight, the effect is not seen, and 0.40% by weight
If it exceeds, supersaturated N is released in the solidification process, which easily causes casting defects due to gas. Therefore 0.20-0.40
Limited to weight percent.

Cr is an important element that combines with C to crystallize hard carbides to ensure wear resistance and to form a solid solution in the matrix to enhance hardenability and mechanical strength. If it is less than 15% by weight, the amount of carbide produced is insufficient, while on the other hand, 30% by weight
If it exceeds, the carbides are excessively generated (crystallized, precipitated) or become a hypereutectic region depending on the C content, and mechanical strength as a structural member cannot be guaranteed due to a decrease in toughness. Therefore, Cr is limited to 15.0 to 30.0% by weight.

Mo is an element that forms a solid solution in the crystallized carbide to increase the hardness and is highly effective in improving the hardenability of the matrix.
At 2.00% by weight, the effect cannot be expected, and at more than 4.00% by weight, excessive carbide is formed to promote embrittlement,
Makes quench cracks more likely to occur. Therefore, Mo is 2.00-4.
It was limited to 00% by weight.

Carbide-forming elements such as W, V, Nb, Ti and B form a solid solution with the crystallized carbide to increase the hardness, and also form a solid solution with a part of the matrix to prevent hard and fine carbide from affecting the embrittlement. The secondary austenite is deposited therein and the secondary austenite is precipitated to destabilize the base austenite to facilitate the martensite-bainite transformation, but at 0.20% by weight or less, the effect is not observed, and the total is 1. A composite addition of more than 00% by weight causes a large amount of secondary carbide to be deposited, depletes C in the matrix, and causes a decrease in matrix hardness due to martensite-bainite transformation. Therefore, the combined addition of the carbide-forming elements is limited to the range of 0.20 to 1.00% by weight in total.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Table 2 shows the chemical components of Examples and Comparative Examples carried out to confirm the action of the present invention. The Comparative Examples are general-purpose materials according to the standard of ASTM Class 2 shown in Table 1. 1 to 3 and improvers 4 to 6 in which known carbide hardening accelerating elements are added to the general-purpose material in an increased amount, and Examples 1 to 3 of the present invention have Cr: 15 to 30% at each level of Ni,
It is composed of a component in which N is added to a known structure reinforced with Mo, particularly for the purpose of shifting the S curve to the long side.

[0026]

[Table 2]

After heating the test pieces composed of the components of these Comparative Examples and Examples to 1000 ° C., they were slowly cooled for a total of 4.75 hours. The basis for this cooling rate is a maximum wall thickness of 200 m
m, air cooling rate of a roller tire body having a unit weight of 8 tons, that is, as cooling quenching in a limit not causing quench cracking, 1000 ° C to 600 ° C: 20 minutes, 600 ° C to 400
C .: 1.1 hr, 400.degree. C. to 150.degree. C .: 3.3 hr, a total of 4.75 hr.

Table 3 shows the final matrix hardness reached in each of the comparative examples and the examples of the components of Table 2 at the slow cooling rate assuming the above-mentioned quenching and quenching, and each test piece with three different types of wear. It is the wear resistance multiple comparing the result obtained by the test with the general-purpose reference material. The general-purpose reference material is a typical example of conventional technology, which is obtained by cutting a general-purpose hypoeutectic 26% high chromium cast iron material to a thickness of 30 mm and subjecting the test result to a standard heat treatment of air-cooled quenching to give a numerical value of 1.0. The numerical value of each test piece is indexed and displayed.

[0029]

[Table 3]

Here, the outline of the three types of abrasion testers is as follows.
2 (pressurization), FIG. 3 (impact), and FIG. 4 (scratching), respectively. 2 is a rubber wheel 1
No. 6 silica sand S is automatically supplied to the circumference tangent line of No. 6, and the test piece TP is pressed against this rubber to measure the amount of wear. In the impact wear tester of FIG. 3, the test piece TP is attached to the four rotating arms 2, and rocks (quartz porphyry) R are made to collide for a predetermined time to measure the wear amount. In the scratch abrasion tester of FIG. 4, the test pieces TP are attached to the four arms 3 and rotated in the metallic silicon M to measure the amount of stirring abrasion per predetermined time. The operating conditions of each abrasion tester are collectively shown in Table 4.

[0031]

[Table 4]

The results of Table 3 are summarized and the vertical axis shows the wear resistance multiple,
FIG. 1 is a graph in which the hardness of the base (HmV) is plotted on the horizontal axis for each wear test, and the correlation between the base hardness and the wear resistance is clearly shown. In particular, the tendency is most remarkable in scratch wear, and the data most directly indicates the fact that the decisive requirement of wear resistance against abrasion wear is governed by the base hardness.

It can be seen from Table 3 that in Comparative Examples 1 to 6, the matrix hardness is remarkably reduced with respect to the reference material having almost the same composition, and the same tendency is recorded in various wear tests, and both of them are recorded. It proves the correlation. On the other hand, in the examples of the present invention, the matrix hardness is far superior to the reference material, and accordingly, the correlation that the wear resistance multiple is obviously superior is established. Both the comparative example and the example are common in that they are hypoeutectic high chromium cast iron materials mainly containing C and Cr and added with Ni and Mo, and there are also test pieces to which carbide strengthening elements such as Nb and W are added. Therefore, there is not much difference in the properties of the precipitated carbides themselves, and there is little doubt that the difference in matrix hardness between the comparative examples and the examples directly connected to the difference in wear resistance. From this, the correctness of the idea that the austenite stable element, which is the gist of the present invention, in particular, the action of shifting the phase transformation to the long-term side by N is the maximum driving force that induces the formation of high hardness of the matrix under the slow cooling condition is correct. Is backed up.

Table 5 shows the chemical composition, hardness after quenching, and abrasion resistance of the materials used in the practical tests conducted on the substance of the roll tire for coal crushing, in comparison with the conventionally used general-purpose materials. It is a thing. The product to which both the example and the general-purpose material are applied is a large cast product having a maximum wall thickness of 200 mm, an average wall thickness of 150 mm, a tire diameter of 2330 mm, and a product weight of 8 tons. While being hardened to the maximum extent possible. As shown in the table, the matrix hardness of the present invention is almost the same even at 20 mm near the surface layer and near the center of the wall thickness, and a high level of HmV: 800 or more is recorded. In the material (conventional technology), even near the surface layer, it does not reach the level of HmV: 700, and it is directly linked to the results of various abrasion resistance tests that reach the center and drop until it approaches HmV: 600.
It is in agreement with the general public that the above-mentioned results of the test piece alone are in line with the above-mentioned results, which is a powerful evidence to support the consideration of the previous test piece.

[0035]

[Table 5]

[0036]

The hypoeutectic high chromium cast iron material according to the present invention is
In particular, it corresponds to the increase in the size of wear-resistant members due to the increase in the size of equipment and facilities, and maintains an almost uniform hardness and unchanged wear resistance as a whole, despite the increase in the wall thickness and total weight, and
It has the ideal duality that the level maintained is far higher than the standard products of the prior art.
This has been understood in the prior art as the key to improving wear resistance is to increase the hardness of the precipitated carbide itself, whereas the carbide itself is the base hardness that is the base even at the same level as the conventional technology. Focusing on the requirement that determines the wear resistance of thick products, an epoch-making means of shifting the curve of the phase transformation rate (S curve) to a long time side in order to ideally realize the requirement. As a result, the effect of being able to enjoy wear resistance far superior to that of the prior art was obtained. It is considered that this invention contributes to the development of the technical field as an invention having a very originality in improving the wear resistance of the high chromium cast iron material.

[Brief description of drawings]

FIG. 1 is a relational diagram of matrix hardness (HmV) and wear resistance multiple, which summarizes the test results of Examples of the present invention and Comparative Examples.

FIG. 2 is a schematic view of a pressure wear tester used for confirming the effect of the present invention.

FIG. 3 is a schematic view of the impact wear tester.

FIG. 4 is a schematic view of a scratch abrasion tester.

[Explanation of symbols]

1 rubber wheel Two arms Three arms S No. 6 silica sand R quartz porphyry M metal silicon TP test piece

Front page continuation (72) Inventor Yoshiaki Shingu 1-12-19 Kitahori, Nishi-ku, Osaka City Kurimoto Iron Works Co., Ltd. (56) Reference JP 59-129720 (JP, A) JP 2-115343 (JP, A) JP-A-6-240403 (JP, A) JP-A-8-291358 (JP, A) Special Table 8-510298 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) C22C 37/08 C22C 33/08

Claims (4)

(57) [Claims] 1. C: 2.80 to 3.50%, Si: 0.
30 to 1.20%, Mn: 0.70 to 1.80%, C
r: 15.0-30.0%, Mo: 2.00-4.00
%, Ni: 0.70 to 2.00%, N: 0.20 to 0.
40% (all by weight) and inevitable impurities, balance F
In hypoeutectic system high chromium cast iron consisting of e, the thickness center portion also in及department large-castings maximum wall thickness to 200mm by N was dissolved into gamma-Fe to increase the bainite transformation completion time, in the base hardness irrespective of the surface layer portion micro-Vickers hardness (HmV) is more than 800, over the entire thickness sectional large-products department及its maximum thickness 200mm you characterized in that the base hardness unchanged Hypoeutectic high-chromium cast iron material suitable for. 2. In addition to the basic components of hypoeutectic high chromium cast iron as set forth in claim 1, W, V, Nb, Ti and B are further added.
1 or 2 or more components selected from the above carbide forming elements are added in a range of 0.20 to 1.00% by weight in total, and precipitation,
Hypoeutectic based high chromium cast iron material which is adapted to large-scale product department及to the maximum wall thickness of 200mm you said that there was high because the carbide hardness that crystallized out. 3. C: 2.80 to 3.50%, Si: 0.
30 to 1.20%, Mn: 0.70 to 1.80%, C
r: 15.0-30.0%, Mo: 2.00-4.00
%, Ni: 0.70 to 2.00%, N: 0.20 to 0.
40% (all by weight) and inevitable impurities, balance F
casting a hypoeutectic system high chromium cast iron melt consisting e, after cast complete care, also cooled at a slower rate limit to prevent quenching cracks in及department large-products to the maximum wall thickness 200 mm, the N The austenite stabilizing effect shifts the phase transformation to the long-term side to maintain the hardenability of the matrix even at the cooling rate, ensuring that both the central portion and the surface layer portion of the wall thickness have high hardness and at least a micro Vickers hardness. Characterized by forming a high hardness matrix having a hardness (HmV) of 800 or more, and forming an abrasion resistant structure over the entire area of the thick section in combination with the ultra-high hardness carbide dispersed and precipitated and crystallized throughout the matrix. The maximum wall thickness you 200
及department manufacturing method of hypoeutectic based high chromium cast iron conforming to large-scale products mm. 4. In addition to the basic components of hypoeutectic high chromium cast iron according to claim 3, W, V, Nb, Ti and B are further added.
1 or 2 or more components selected from the above carbide forming elements are added in a range of 0.20 to 1.00% by weight in total, and precipitation,
Hypoeutectic system manufacturing method of the high chromium cast iron adapted及department in large-scale products maximum thickness 200mm you characterized that there was high because the carbide hardness crystallized out.