JP4514056B2 - Casting method for high Cr cast iron castings - Google Patents

Description

  The present invention relates to a high Cr cast iron casting that can be suitably used as an abrasion resistant member such as an abrasion resistant liner, a rock crusher, and a steel conveying roller, and a method for producing the same.

  High Cr cast iron is used as a wear-resistant material, and as disclosed in JP-A-11-229071 (Patent Document 1) and JP-A-2001-247929 (Patent Document 2), in particular, C is 2 High Cr cast iron with a hypoeutectic composition containing about 5 to 3.5 mass% and about 11 to 22 mass% of Cr is known as an abrasion resistant material having excellent wear resistance.

  High Cr cast iron is generally cast from a high Cr cast iron melt into a mold having a casting space in which a main body portion is formed through a pouring portion (neck portion) from a molten metal portion, and is cooled and solidified. The hot water portion and the main body are separated from each other by breaking the pouring gate, and the main body is hardened and tempered. In order to obtain a predetermined hardness, it is necessary to quench sufficiently, and the cooling rate at the time of quenching is adjusted to be a certain level or more.

Also, high Cr cast iron, especially hypoeutectic composition, has a wide temperature range where solids and liquids coexist, resulting in a decrease in molten metal flow and, as a result, casting defects (shrinkage) are likely to occur. . For this reason, as for the hot water supply part and the pouring gate part, a thing with a sufficient cross-sectional area is installed. Conventionally, when the cross-sectional area Sh of the feeder part and the cross-sectional area Sn of the sprue part are set sufficiently large to Sn / Sh ≧ 0.8, the occurrence of shrinkage is prevented.
Japanese Patent Laid-Open No. 11-229071 JP 2001-247929 A

However, in the case of high-eutectic cast iron with a hypoeutectic composition, if the cross-sectional area of the feeder part and the sprue part is increased, the hardness of the cast part after casting is increased in the portion directly below the sprue part of the main body even if the quenching speed is sufficiently increased. There is a problem that the length is greatly reduced as compared with other portions of the main body. If there is a region with low hardness partially, even when used as a wear-resistant material, uniform wear does not occur, causing a reduction in the life of the member and a failure of the mechanical device. In order to avoid such a problem, it is necessary to perform a process such as removing a portion of the main body portion immediately below the gate portion, which inevitably increases the manufacturing process and the manufacturing cost.
The present invention has been made in view of such a problem, and an object of the present invention is to provide a hypo-eutectic high Cr cast iron casting and a method for producing the same, in which hardness reduction is unlikely to occur in a portion immediately below the gate of the main body.

The method of manufacturing a high Cr cast iron of the present invention, in mass% C: 2.5 to 3.5% Cr: were melted high Cr cast iron containing 11 to 22%, the sprue from the riser portion A mold having Sn / S of 0.10 to 0.75, where S is the average cross-sectional area of the main body, and Sn is the average cross-sectional area of the gate. casting a melt of the high Cr cast iron, it is intended to cool solidify.

According to the manufacturing method of the high Cr cast iron castings of the present invention, since the 0.10 to 0.75 of the Sn / S, C: 2.5~3.5% , Cr: containing 11 to 22% Even in the case of high Cr cast iron with a hypoeutectic composition, the cooling rate of the gate is increased while suppressing the occurrence of shrinkage cavities in the feeder or gate during casting, and the casting body portion and the gate portion The cooling rate difference can be reduced. For this reason, generation | occurrence | production of the secondary carbide | carbonized_material of the part immediately below the gate part in a main-body part, and a reduction | decrease of the amount of solute C can be suppressed, and the hardness fall of the said part in the case of quenching can be prevented. Moreover, since the gate part becomes a small diameter, the cutting | disconnection in a feeder part becomes easy, a main-body part can be easily isolate | separated from a feeder part, and productivity improves.

According to the manufacturing method of the high Cr cast iron castings of the present invention, since the high Cr cast iron even hypoeutectic composition, solidification cooling rate difference of the molten metal between the sprue portion and the body portion is reduced, the main body portion It is possible to suppress a decrease in the amount of solute C due to carbide precipitation at the site immediately below the gate, and thus it is possible to prevent a decrease in the hardness of the site. For this reason, the hardness and quality of the high Cr cast iron casting can be made uniform without removing the portion directly under the gate.

When the present inventor casts a high Cr cast iron having a hypoeutectic composition containing 2.5 to 3.5 mass% of C and 11 to 22 mass% of Cr, the hardness after quenching in the portion immediately below the gate portion of the main body portion. As a result of diligently pursuing the cause that could not be obtained sufficiently, the following was found.
That is, since the high Cr cast iron melt having a hypoeutectic composition has poor hot-water flow and is liable to cause shrinkage, as shown in FIG. The cross section of the gate part 2 communicating from the part 1 to the main body part 3 of the mold was also set large. However, if the gate 2 is set to a large size, the cooling rate of the portion immediately below the gate of the main body 3 to which the gate 2 is connected is slower than that of the main body during casting, and secondary carbide precipitates at 1000 ° C. or lower. Then, the solid solution C in the matrix phase is fixed. The hardness of the parent phase martensiticized by quenching depends on the amount of dissolved C at the time of quenching. Therefore, even in the region directly below the gate where C is fixed by the secondary carbide and the amount of dissolved C is reduced. Even if a quenching and cooling rate is given, quenching does not occur sufficiently and the hardness decreases.

Based on this knowledge, the present inventor adds a study on the size (cross section) that governs the cooling rate of the gate 2 and the main body 3, and determines the average cross-sectional area of the main body 3 and the gate 2 as S, When Sn is set, Sn / S is set to 0.10 to 0.75, thereby reducing the cooling rate difference between the gate 2 and the main body 3 while suppressing the generation of shrinkage nests. It was found that a decrease in the hardness of the portion immediately below the gate of No. 3 can be suppressed.
That is, if Sn / S is less than 0.10, the suppression of shrinkage nests is insufficient, while if it exceeds 0.75, the cooling rate difference from the main body 3 becomes large, leading to a decrease in hardness in the portion immediately below the gate. To come. Moreover, by setting Sn / S to 0.75 or less, it becomes possible to easily cut the gate 2, and to easily separate the feeder 2 from the main body 3. Become. Sn / S is preferably 0.1 to 0.5, and more preferably 0.1 to 0.3. In addition, the size (volume) of a hot-water supply part is normally set to about 1/5 to 1/2 with respect to a main-body part.

The C and Cr contents of the hypoeutectic high Cr cast iron used in the present invention are mass% and are limited to C: 2.5 to 3.5% and Cr: 11 to 22% for the following reasons. .
C: 2.5-3.5%
C is necessary in order to obtain sufficient hardness by generating high-hardness primary carbide and ensuring the hardness of the matrix martensite. If it is less than 2.5%, the hardness is insufficient. On the other hand, if it exceeds 3.5%, retained austenite is generated in the parent phase. For this reason, the lower limit of the C amount is 2.5%, and the upper limit is 3.5%.

Cr: 11-22%
Similar to C, Cr is necessary to obtain high hardness by generating high-hardness primary carbide and ensuring the hardenability of the matrix. If it is less than 11%, the amount of primary carbide produced becomes too small, and the solid solution Cr amount in the matrix phase becomes insufficient and the hardenability is lowered, so that sufficient hardness cannot be obtained. On the other hand, if it exceeds 22%, the primary carbide crystallizes in a large amount, but since solid solution C for improving the hardness of the martensite matrix is reduced, sufficient hardness is obtained. Absent. For this reason, the lower limit of the Cr amount is 11%, and the upper limit is 22%.

Ingredients other than the above C and Cr can be appropriately added as known components as high Cr cast iron components. As a preferable component of high Cr cast iron, the following components can be contained, for example.
Si: 0.2 to 1.0%
Si is an element effective for ensuring fluidity of the molten metal during casting and for deoxidation during melting and refining. In order to exhibit such an action effectively, it is preferable to contain 0.2% or more. On the other hand, if the content exceeds 1.0%, the toughness decreases. For this reason, the upper limit is preferably set to 1.0%.

Mn: 0.6 to 2.0%
Mn improves the hardenability of high Cr cast iron and is particularly effective in suppressing bainite. If the content is less than 0.6%, such an effect is insufficient. On the other hand, if the content exceeds 2.0%, the retained austenite becomes excessive and the hardness is lowered. For this reason, the lower limit of the amount of Mn is 0.6%, and the upper limit is 2.0%.

Mo: 1.0-3.0%
Mo improves the hardenability of high Cr cast iron and is particularly effective in suppressing pearlite. If it is less than 1.0%, such an effect is insufficient, while if it exceeds 3.0%, the product is saturated. For this reason, the lower limit of the Mo amount is 1.0%, and the upper limit is 3.0%.

N: 0.01 to 0.15%
N improves the hardenability of the high Cr cast iron, and has an effect of suppressing the transformation of austenite to bainite having a low hardness by dissolving in the base. If it is less than 0.01%, such an action is insufficient, while if it exceeds 0.15%, the retained austenite in the base becomes excessive, and the hardness is lowered instead. For this reason, the lower limit of the N amount is 0.01%, and the upper limit is 0.15%.

  Hereinafter, although the high Cr cast iron casting of the present invention and the manufacturing method thereof will be described more specifically with reference to examples, the present invention is not construed as being limited by the examples.

High Cr cast iron having the following composition was melted, and the molten metal was cast at 1480 ° C. into a casting test mold (sand mold) shown in FIG. The dimensions of the mold are: body part: D (depth) 200 × W (horizontal width) 400 × H (height) 400 mm, gate part: D50-150 × W100-350 × H100 mm, feeder part: φ300 × H400 mm. After the molten metal cooled and solidified, the casting was taken out from the mold, the casting was cut at the pouring part, the main body part separated from the feeder part was heated to 950 ° C., and then quenched and tempered.
・ High Cr cast iron composition (mass%, balance Fe and impurities)
C: 2.95%, Si: 0.5%, Mn: 0.7%,
Cr: 14.5%, Mo: 1.8%, N: 0.05%

  After quenching and tempering, the occurrence of casting defects (shrinkage cavities) was observed in the main body of the casting, and the hardness of the main body immediately below the gate and the central portion of the main body was measured. The casting defect was determined to be defective when a shrinkage nest of 1 mm or more was observed at the central portion of the main body. In addition, the hardness was measured by measuring the Vickers hardness Hv at a load of 10 kg at a central part of the main body part and a central part of the upper surface of the main body after removal of the pouring gate and a part 20 mm deep from the upper surface (a part directly below the pouring gate part). When the difference in hardness between the two parts was less than 50, it was determined to be acceptable. The survey results are shown in Table 1.

From Table 1, sample Nos. 1 to 9 in which Sn / S is within the range of the present invention do not generate a large shrinkage nest of 1 mm or more, and the hardness difference between the central part of the mold body and the part directly below the gate is Hv30. The hardness of the casting body was uniform.
On the other hand, Sample Nos. 11, 13, and 15 of the comparative example had Sn / S less than 0.10, and although there was no problem in hardness difference, a large shrinkage nest of 1 mm or more was observed. On the other hand, Sample Nos. 12 and 14 have Sn / S of over 0.75 and the size of the gate is large, so a shrinkage nest of 1 mm or more was not observed, but the hardness difference appeared as Hv 52 and 54, Non-uniform hardness was observed.

It is a perspective view which shows the external appearance of the high Cr cast iron casting, or the external shape of the casting space of the casting_mold | template.

Explanation of symbols

1 Pusher part 2 Pouring part 3 Body part

Claims (1)

High Cr cast iron containing C: 2.5-3.5% and Cr: 11-22% at mass%, and has a casting space in which the main body is formed from the feeder via the neck. A method for producing a high Cr cast iron casting, wherein the molten high Cr cast iron is cast into a mold and cooled and solidified.
A method for producing a high Cr cast iron casting, wherein Sn / S is 0.10 to 0.75, where S is the average cross-sectional area of the main body and Sn is the average cross-sectional area of the gate.

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