JP3130670B2 - Manufacturing method of tough thin cast iron sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a tough thin cast iron sheet, and more particularly to a method for manufacturing a tough and workable thin cast iron sheet.

[0002]

2. Description of the Related Art As tough cast irons, there are ductile cast irons and C / V cast irons obtained by adding a graphite spheroidizing agent such as Mg, Ca, Ce, etc., and spheroidizing the graphite. There is a malleable cast iron obtained by heat-treating the obtained white pig iron. In addition, C /
In V cast iron, graphite does not reach spheroidization but exists as intermediate graphite.

[0003] As a method of manufacturing a tough thin cast iron sheet, a hot iron for cast iron is added with a graphite spheroidizing agent such as Mg, Ca, etc., and then subjected to a graphite spheroidizing treatment. 2. Description of the Related Art A method for producing a thin cast iron plate made of C / V cast iron is known. This method is basically a process using the above-described method for producing ductile cast iron or C / V cast iron, except that it is cast with twin rolls.

[0004]

Among the tough cast irons, when producing ductile cast iron or C / V cast iron, Mg is used.
There is a cost increase due to the addition of a graphite spheroidizing agent such as (ie, graphite spheroidizing treatment), and furthermore, the effect of graphite spheroidizing is lost by fading. When casting for a long time, ordinary graphite spheroidizing treatment cannot cope with the problem, and there is a problem that special graphite spheroidizing treatment, that is, continuous graphite spheroidizing treatment is required.

[0005] In the production of malleable cast iron, there is a problem that heat treatment of white pig iron requires a large amount of heat energy and a long time. That is, as heat treatment of white pig iron, a condition of heating at high temperature for a long time is usually adopted.
Heated for hours.

[0006] The conventional method for producing a tough thin cast iron sheet is as follows.
Except for casting with twin rolls as described above, it is basically a process using the above-described method for producing ductile iron or C / V cast iron. Therefore, in the method for producing a tough thin-plate cast iron sheet, as in the case of the above-mentioned ductile cast iron and C / V cast iron production, there is a cost increase due to the graphite spheroidizing treatment, and further, the continuous graphite spheroidizing treatment is required. There is a point.

In addition, a method for producing a thin cast iron plate made of malleable cast iron by casting white iron into a thin plate and heat-treating it to form a thin plate is also considered as a method for producing a tough thin plate cast iron plate. In this case, as in the case of the malleable cast iron production, there is a problem that heat treatment of white pig iron requires a large amount of heat energy and a long time.

The present invention has been made in view of such circumstances, and has as its object to solve the above-mentioned problems of the prior art and to provide a graphite spheroidizing treatment (the use of a graphite spheroidizing agent). Addition), and a tough thin plate capable of producing a tough thin cast iron plate similarly to the thin cast iron plate obtained by the conventional method of manufacturing a tough thin cast iron plate without performing a heat treatment requiring a large amount of heat energy and a long time. An object of the present invention is to provide a method for manufacturing a cast iron plate.

[0009]

Means for Solving the Problems The present invention is, 10 ² ~10 ^{3 0} K
/ using sec twin roll having a cooling capacity of during the development of the production method of spheroidal graphite cast iron plate, the melt in which the graphite spheroidization treatment by Mg added (hot metal) at a cooling rate of 10 ² ~10 ^{3 0} K / sec When quenched and cast, spheroidal graphite is hardly formed, and is only slightly observed in the cast iron plate after casting.
When heat treatment is performed at 950 ° C. for several minutes, a massive secondary graphite is formed, and as the graphite, a structure having the massive graphite and the spherical graphite (primary graphite) which is very slightly recognized after the casting is obtained. Was done. Thus, since the massive graphite was generated by the heat treatment for an extremely short time, the massive graphite was generated without adding a graphite spheroidizing agent such as Mg, and the tough cast iron sheet was strengthened by the massive graphite. Was confirmed, and the confirmation experiment was performed as follows. That is, 10 ² ~
10 ^{3 0} K / sec composition spheroidal graphite is not produced at all in the cooling rate: were melted hot metal (molten metal) of (Si content less 1.5 wt%), were cast solution water into a thin plate by using the twin-roll Thereafter, the thin cast iron plate was subjected to a heat treatment of heating at 850 to 950 ° C. for several minutes (for example, 5 minutes). As a result, no spheroidal graphite was generated, and the generated graphite was all massive graphite. The heat-treated thin cast iron plate had a structure in which all graphite was composed of massive graphite and the matrix was composed of ferrite.
The thin cast iron sheet had high strength and high ductility, was excellent in toughness, and was similarly tough, like the thin cast iron sheet obtained by the conventional method of manufacturing a tough thin sheet cast iron sheet.

The present invention has been completed based on such findings, and the present invention is a method for producing a tough thin cast iron plate having the following configuration. That is, the method for producing a tough thin cast iron sheet according to the present invention comprises the steps of melting hot metal for cast iron having a Si content of 1.5 wt% or less and a carbon saturation of 1 or less, and using the twin rolls to produce 10 ² to 10 10 After casting at a cooling rate of ³⁰ K / sec, 85
This is a method for producing a tough thin cast iron plate, which comprises heating to 0 to 950 ° C. to form massive graphite.

[0011]

The method for producing a tough thin cast iron sheet according to the present invention comprises, as described above, a method for producing hot iron for cast iron having an Si content of 1.5 wt% or less and a carbon saturation of 1 or less by using twin rolls in a range of 10 ² to 10 ^3. After casting at a cooling rate of ⁰ K / sec, it is heated to 850 to 950 ° C. to produce massive graphite, and from the above knowledge, it can be obtained by the conventional method of manufacturing a tough thin cast iron plate. Obviously, a thin cast iron sheet can be produced as strong as a thin cast iron sheet.

Further, there is no need to perform graphite spheroidizing treatment (addition of a graphite spheroidizing agent). Furthermore, the heating after the above casting is 850
It only needs to be heated to about 950 ° C. for several minutes, does not require high-temperature and long-time heating as in the case of the heat treatment of white pig iron in the conventional malleable cast iron production, requires a low heating temperature, and requires an extremely long heating time. short.

Therefore, according to the method of manufacturing a tough thin cast iron sheet according to the present invention, the graphite spheroidizing treatment (addition of a graphite spheroidizing agent) and the heat treatment requiring a large amount of heat energy and a long time are not required. A tough thin cast iron plate can be manufactured in the same manner as the thin cast iron plate obtained by the conventional method of manufacturing a tough thin cast iron plate.

The reasons for limiting the numerical values in the method for producing a tough thin cast iron sheet according to the present invention will be described below. The reason why the Si content of the molten metal is set to 1.5 wt% or less is that if it exceeds 1.5 wt%, flake graphite is formed in the casting process with the twin rolls and does not become spheroidized or agglomerated even after heating at 850 to 950 ° C. This is because the thin cast iron sheet after heating contains flaky graphite together with lump graphite as the graphite, and the flaky graphite reduces toughness and becomes insufficient.

The reason why the carbon saturation is set to 1 or less is that if the carbon saturation is set to more than 1, primary cementite which is difficult to decompose during the twin-roll casting process is generated and remains even after heating, and thus the toughness of the obtained thin cast iron sheet Is decreased and becomes insufficient.
The carbon saturation is the ratio between the carbon content of cast iron and the eutectic carbon content, and is also called the eutectic content. That is, the carbon saturation is S
c, the carbon content of the cast iron is C, the eutectic carbon content is Ce, and the Si content is Si, the carbon saturation Sc is expressed as Sc = C / Ce, where Ce is generally Ce = 4.23-Si / 3.2.

The cooling rate during casting with twin rolls is 10 ²
As 10 ^{3 0} are we K / sec, the to less than 10 ^{2 0} K / sec becomes insufficient cooling capacity in the casting process in the twin roll can not produce the plate, also could plates produced also toughness of the thin plate cast iron plate becomes insufficient to decrease in order to generate the flake graphite, whereas 10 ^{3 0} K / sec to greater than the cooling rate is too fast it is difficult to produce plates of ultra-thin, further, the first This is because crystalline cementite is generated and the toughness of the cast iron plate is reduced and becomes insufficient. Note that ⁰ K is a unit indicating an absolute temperature.

When heating after casting with twin rolls, the heating temperature is set at 850 to 950 ° C. The reason is that if the temperature is lower than 850 ° C., it is difficult to form massive graphite and the quantity is insufficient. This is because graphitization has no positive effect and wastes energy. In addition, upon heating after the above casting,
The heating time may be several tens of seconds, and if it is several minutes, it is even more sufficient, and it is not particularly necessary to further heat. As a method of heating after casting, it is not always necessary to adopt a method of cooling a thin cast iron sheet after casting and then heating it to 850 to 950 ° C., as described above. For this reason, after casting, the thin cast iron plate is continuously 850-95.
A method of merely passing through an annealing furnace maintained at 0 ° C may be used,
Alternatively, after the thin cast iron sheet is wound after casting and before cooling (that is, while having the self-heating), 850 to 950 is generated by the self-heating.
A method of maintaining the temperature at ° C may be used.

[0018]

EXAMPLES Si content: 1.0 wt%, the carbon saturation: 0.8 cast iron for hot metal was melted in, by casting using a twin roll having a cooling capacity of the solution pig iron 10 ² ~10 ^{3 0} K / sec A thin cast iron plate was continuously obtained, and the thin cast iron plate was continuously passed through an annealing furnace maintained at 850 to 950 ° C., and then naturally cooled. still,
The thin cast iron sheet before the introduction of the post-casting annealing furnace is not completely cooled and is in a relatively high temperature state, though slightly cooled.

The thin cast iron sheet thus manufactured was subjected to a structure observation and a test for mechanical properties.
As a result, this thin cast iron plate had a structure in which all the graphite was made of massive graphite and the matrix was made of ferrite. Further, as shown in FIG. 1, similar to a thin cast iron sheet obtained by a conventional method of manufacturing a tough thin cast iron sheet, it may have high strength and high ductility and excellent toughness, and may be a similarly tough tough thin cast iron sheet. confirmed.

[0020]

According to the method for producing a tough thin cast iron sheet according to the present invention, the graphite spheroidizing treatment (addition of a graphite spheroidizing agent) and the heat treatment requiring a large amount of heat energy and a long time can be performed. A tough thin cast iron sheet can be manufactured similarly to a thin cast iron sheet obtained by a conventional method of manufacturing a tough thin cast iron sheet. Therefore, such an excellent tough thin-plate cast iron plate can be manufactured under conditions of high economic efficiency, high productivity and low thermal energy.

[Brief description of the drawings]

FIG. 1 is a view showing the tensile strength and elongation of a tough thin plate cast iron plate according to an example and a tough thin plate cast iron plate obtained by a conventional method (a method using a graphite spheroidizing treatment).

Continuation of the front page (56) References JP-A-4-197552 (JP, A) JP-A-2-25836 (JP, A) JP-A-63-50418 (JP, A) JP-A-60-50114 (JP, A) , A) JP-A-58-6935 (JP, A) JP-B-39-1338 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/06 330 C21D 5/00 , 9/46 C22C 33 / 08,37 / 04

Claims (1)

(57) [Claims] 1. A hot metal for cast iron having an Si content of 1.5 wt% or less and a carbon saturation of 1 or less is cast at a cooling rate of 10 ² to 10 ³⁰ K / sec using twin rolls, and then 850 to 950. A method for producing a tough thin-plate cast iron sheet, characterized by producing massive graphite by heating to a temperature of ℃.