JPH0967640A - Production of spheroidal graphite cast iron product, and spheroidal graphite cast iron product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cast iron product excellent in the balance among tensile strength, elongation, and stability of elongation by means of existing equipment by increasing Mn content while controlling a time for Mn addition in a melting stage for producing a spheroidal graphite cast iron product. SOLUTION: In the melting stage for producing a spheroidal graphite cast iron product, Mn or Mn alloy is added to a molten metal in the course between the completion of spheroidizing treatment and casting. By this method, the spheroidal graphite cast iron product, in which tensile strength and elongation are maintained or improved and the dispersion of elongation is decreased, is obtained. The amount of Mn in a raw material and also the amount of Mn to be added can properly be set, and it is preferable to regulate the amount of Mn, after addition, to 0.50-0.70wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a spheroidal graphite cast iron product used for automobile parts, machine parts, lids for underground structures and general strength members, and a spheroidal graphite cast iron product obtained by the method.

[0002]

2. Description of the Related Art In recent years, spheroidal graphite cast iron products have been widely commercialized as automobile parts and lid bodies and receiving frames of underground structures because of their advantages of strength comparable to steel and complicated shape of casting. In the case of producing this spheroidal graphite cast iron product, steel scrap, pig iron, raw materials such as return material are melted using a melting furnace such as cupola and electric furnace at an appropriate ratio, and after spheroidizing treatment, It is formed by pouring the molten metal into a mold. On the other hand, in the lid main body and the receiving frame of the underground structure, since the vehicle is installed on the road surface through which the vehicle complicatedly passes, stability of expansion that stays within a certain range is required from the viewpoint of impact resistance and deformation prevention. Has been. On the other hand, the content of Mn in the chemical composition of the spheroidal graphite cast iron product is 0.5%.
It is said that if the above is exceeded, both tensile strength and elongation decrease (for example, page 593, lines 2 and 3 of "Revised 4th Edition Casting Handbook" issued by Maruzen Co., Ltd. on January 20, 1986). Therefore, C is usually 3.0 to 4.0 by weight%.
%, Si; 2.0 to 3.5%, Mn; 0.4% or less,
P: 0.1% or less, S: 0.02% or less, Mg: trace amount and the balance is substantially Fe.

[0003]

However, according to the experiment conducted by the applicant of the present invention, the Mn content is 0.5%.
It is confirmed that the tensile strength and the elongation decrease, but the variation of the elongation is reduced and the stability of the elongation is improved, and it is suitable for use in the lid body and the receiving frame of the underground structure. It was speculated that there is. The present invention is based on the above findings, keeping in mind that the content of Mn is increased, and by controlling the addition timing of Mn, the tensile strength and elongation can be maintained or improved with existing equipment, and the elongation can be improved. It is an object of the present invention to provide a method for producing a spheroidal graphite cast iron product capable of ensuring the stability of

[0004]

Means for Solving the Problems The present invention has been proposed in view of the above, and in a melting process for producing a spheroidal graphite cast iron product, the spheroidal graphite cast iron product is not melted during the spheroidizing process but after the pouring process, The present invention relates to a method for producing a spheroidal graphite cast iron product characterized by adding Mn or an Mn alloy, and a spheroidal graphite cast iron product obtained by the method. Specifically, the final component amount of Mn is 0.50 to 0.70%. It is preferable to add them so that

In the present invention, the construction and method not mentioned above can be implemented in any manner in accordance with the production of a known spheroidal graphite cast iron product. For example, raw materials (melt composition) such as steel scrap, pig iron, return material, etc.
And use a melting furnace such as a cupola (acidic cupola, basic cupola) or electric furnace (arc type electric furnace, induction furnace) to perform desulfurization treatment using a desulfurizing agent as needed. May be. Also, for the spheroidizing treatment, pure Mg, Ni-Mg alloy, Cu-Mg alloy,
Using a spheroidizing agent such as Fe-Si-Mg alloy, Ca-Si salts, rare earth metals, etc., known pouring method, tundish method (adding ladle with lid), porous plug method, plunger method, in-mold method , Strume method, Converter method,
Pressure addition method, T-knock method, vortex method, or method of injecting Mg wire (diameter 3.2 mm) into ladle molten metal at a speed of 152-3048 mm / s, special treatment with siphon ladle The spheroidizing of graphite may be carried out by a treatment method such as a pan method, a mold is held down by a weight, and a reaction portion on the mold is treated on the mold.

Since Mn added to the molten metal in the present invention is expensive, a Mn alloy such as an Fe-Mn alloy having a price about ⅕ may be used as a substitute. Of 0.50 to 0.70% makes it possible to maintain or improve the tensile strength and elongation and to secure the stability of elongation. The amount of Mn in the raw material and the amount of Mn to be added later can be appropriately set. In particular, when added so that the final component amount of Mn is 0.50 to 0.70%, tensile strength, elongation, A spheroidal graphite cast iron product having an excellent balance of elongation stability and the like can be obtained.

According to the present invention having the above-mentioned constitution, not only the elongation can be stabilized, but also the tensile strength and the elongation are maintained or improved contrary to the description in the above-mentioned document ("Revised 4th Edition Casting Handbook"). be able to.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to explain the present invention,
An example of a lid body that is a spheroidal graphite cast iron product that closes the upper opening of an underground structure will be described.

The lid main body is made of steel scrap, pig iron,
A return material and the like are mixed in an appropriate ratio, C: 3.6%, Si;
2.8%, Mn; 0.35%, P; 0.01%, S;
0.006%, Mg; 0.03%, the balance being substantially Fe
According to JIS G 5502
“F”, which is the standard name for the five types of spheroidal graphite cast iron products specified in
It is a material equivalent to "CD700". This manufacturing (dissolution) process
As shown in FIG. 1, first, the above raw materials were melted in an electric furnace to adjust the components, then spheroidized, transferred to a pouring ladle, and cast into a mold.

According to the above-mentioned melting process, the Mn amount of the raw material was increased or decreased to manufacture lid bodies for underground structures of Comparative Examples 1 to 3 below.

[Comparative Example 1] A lid main body was manufactured from raw materials as described above (Mn content was 0.35%).

[Comparative Example 2] A lid body was manufactured from raw materials having a Mn content of 0.45%.

[Comparative Example 3] A lid body was manufactured from raw materials having an Mn content of 0.55%.

Next, after the spheroidizing treatment in the melting step and during casting, Fe-Mn (Fe20% -Mn8
0%) was added to produce lid bodies for underground structures of Examples 1 to 5 below.

[Example 1] Fe-M was used in a pouring ladle using the raw materials as described above (Mn content was 0.35%).
n (Fe20% -Mn80%) was 0.
A lid body having a final Mn content of 0.50% was manufactured by adding 1875% (= 0.15% of Mn).

[Example 2] Fe-M was used in a pouring ladle using the raw materials as described above (Mn content was 0.35%).
n (Fe20% -Mn80%) was 0.
A lid body having a final Mn content of 0.60% was manufactured by adding 3125% (= Mn of 0.25%).

[Embodiment 3] Fe-M was used in a pouring ladle using the raw materials as described above (Mn content was 0.35%).
n (Fe20% -Mn80%) was 0.
A lid body having a final Mn amount of 0.70% was manufactured by adding 4375% (= 0.35% of Mn).

[Embodiment 4] Fe-Mn (Fe20% -Mn) was poured into a pouring ladle by using raw materials with Mn content of 0.45%.
80%) was added to the total weight of 0.1875% (= Mn 0.15%) to produce a lid body having a final Mn content of 0.60%.

[Embodiment 5] Fe-Mn (Fe20% -Mn) was prepared in a pouring ladle by using raw materials with Mn content of 0.55%.
80%) was added to 0.0625% (= 0.05% Mn) based on the total weight to manufacture a lid body having a final Mn amount of 0.60%.

The tensile strength and elongation of the lid bodies of Comparative Examples 1 to 3 and Examples 1 to 5 thus obtained were measured according to JIS Z.
2241 (Metallic material tensile test method), and the results are shown in Table 1. The final Mn amount and M in the raw materials
n amount (indicated as original hot water Mn amount in Table 1), post-added Mn
The amounts are shown together. The stability of elongation and the range of variation in elongation were measured according to JIS Z 9041 (method of processing measured values) and are also shown in Table 1.

[0021]

[Table 1]

Comparing Comparative Example 1 with Comparative Examples 2 and 3 from Table 1, it was confirmed that the elongation and the tensile strength were certainly decreased when the Mn amount was increased in the melting furnace. Regarding the degree, it was confirmed that Comparative Examples 2 and 3 in which the Mn content was increased were higher than Comparative Example 1, and there was less variation in elongation. In addition, the lower limit value of the variation range of elongation is also in Comparative Example 2,
3 was larger than Comparative Example 1.

Comparing Examples 1 and 2 with Comparative Example 1 from Table 1, Examples 1 and 2 are common in that raw materials (Mn content is 0.35%) having the same blending ratio as Comparative Example 1 are used. It was confirmed that Mn was added to the pouring ladle and the elongation was improved. Further, when Examples 1 and 2 are compared with Comparative Examples 2 and 3, which have almost the same final Mn amounts, the elongations of Comparative Examples 2 and 3 were reduced as compared with Comparative Example 1 as described above. Examples 1 and 2 of similar final Mn content
In contrast to Comparative Example 1, the elongation was improved rather than decreased, and the effect of the present invention was clearly recognized. In particular, in Example 2, not only the stability of elongation is higher than that of Comparative Examples 2 and 3, but also the tensile strength is higher, and the lower limit of the variation in elongation is also increased, so that a lid body having stable quality can be obtained. You can

Comparing Example 3 with Comparative Example 1 from Table 1, Example 3 shows that raw materials (Mn having the same mixing ratio as in Comparative Example 1 are mixed).
Although the amount is 0.35%), the tensile strength could be improved even though Mn was increased in the pouring ladle to double the amount of Mn.

Comparing Example 4 with Comparative Example 2 from Table 1, Example 4 shows that raw materials (Mn having the same mixing ratio as in Comparative Example 2) are mixed.
Although the amount is 0.45%), the tensile strength could be improved by increasing Mn in the pouring ladle.

Comparing Example 5 with Comparative Example 3 from Table 1, Example 5 shows that raw materials (Mn having the same mixing ratio as in Comparative Example 3 are mixed).
The amount is 0.55%), but the tensile strength can be slightly improved by increasing Mn in the pouring ladle, and the elongation stability can be the highest. did it.

From a comprehensive perspective, when the amount of Mn is increased by appropriately mixing the raw materials, both elongation and tensile strength decrease, but in each of the examples of the present invention, Mn from spheroidizing treatment to casting is decreased. In this case, since the final component amount of Mn was adjusted to 0.50 to 0.70 wt% by adding an appropriate amount in the pouring ladle in this case, the decrease in tensile strength and elongation was suppressed, or the tensile strength and elongation were suppressed. One or both of them could be improved. Furthermore, each of the examples of the present invention was able to reliably improve the stability of elongation. Further, in each of the examples of the present invention, the range of variation in elongation could be reduced or maintained, and the lower limit thereof could be increased.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and may be carried out in any manner as long as the configuration described in the claims is not changed. it can.

[0029]

As described above, according to the present invention, in the melting step, Mn is added to the molten metal between the spheroidizing treatment and the casting, not when the raw materials are melted. It is added so as to be 50 to 0.70%, and not only maintains or improves tensile strength and elongation as compared with those prepared by appropriately mixing raw materials, but also
It is possible to secure the stability of elongation. Furthermore, by adding an appropriate proportion of Mn in the pouring ladle,
Compared with a standard mixture of raw materials, tensile strength, elongation, stability of elongation can be improved, and quality improved spheroidal graphite cast iron products can be manufactured with existing equipment Therefore, it can be used for manufacturing a spheroidal graphite cast iron product such as a lid body or a receiving frame for an underground structure in which impact resistance and stability of elongation within a certain range are important.

[Brief description of drawings]

FIG. 1 is a flow chart showing a melting process of the present invention.

Claims (3)

[Claims] 1. In a melting step for producing a spheroidal graphite cast iron product, Mn is contained in the molten metal after spheroidizing treatment and before casting.
Alternatively, a method for manufacturing a spheroidal graphite cast iron product is characterized in that a Mn alloy is added. 2. The Mn weight% after addition is 0.50 to 0.7.
The spheroidal graphite cast iron product manufacturing method according to claim 1, wherein the content is 0%. 3. In a melting step for producing a spheroidal graphite cast iron product, Mn is contained in the molten metal after spheroidizing treatment and before casting.
Alternatively, Mn alloy is added, and the Mn weight% after addition is 0.5
A spheroidal graphite cast iron product characterized by being 0 to 0.70%.