JPH0712521B2 - Casting method for low silicon hot metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot metal casting method, and more particularly to a low silicon hot metal casting method with a small number of small particles formed by controlling cooling conditions. .

(Prior Art) Generally, pig iron tapped from a blast furnace is mainly used for steelmaking, and a part of it is usually cast pig iron or pig iron for steel making to be a pig iron.

In the above-mentioned pig iron treatment, the mold pig iron is water-cooled in order to improve the efficiency of the pig iron machine. The cooling in this case is usually started by sprinkling cooling when the surface temperature of the mold pig in the mold is around 1000 ° C, and is cooled until the surface temperature of the mold pig is lowered to around 300 ° C. After that, the mold pig is released from the mold, and after the mold is released, water spray cooling is performed to room temperature from the viewpoint of handling.

(Problems to be solved by the invention) However, in the normal pig iron method as described above, when the Si content of the hot metal is 0.2% or less, the hot metal is solidified and then white pig iron is formed (structure of Fe ₃ C and pearlite). However, it becomes fragile and cracks occur in the mold pig during cooling or during handling after cooling, causing breakage.

It is needless to say that the type pig iron produced by such a pig iron method is broken into small pieces, and the commercial value is lowered, and the surface area is increased and the amount of rust is increased. It is also one of the causes of defective casting. Further, in the case of melting with a cupola, mixing of small pieces impairs air permeability in the furnace and causes non-uniform melting, resulting in inconvenience in manufacturing a casting.

Therefore, the present inventors, in view of the above problems, as a result of various trials by changing the sprinkling cooling conditions during the pig iron treatment, by strictly controlling the sprinkling cooling start temperature and the stop temperature than that of the conventional method, It has been found that even in the case of low-silicon hot metal, a method of casting hot metal with less breakage can be obtained.

(Means for Solving the Problems) The present invention provides a pig iron method suitable for low silicon hot metal based on the above findings, and the gist thereof is to cast low silicon hot metal into a mold of a pig iron machine. Then, the mold pig iron in the mold is cooled by sprinkling cooling after the surface temperature of the mold iron has dropped to 800 ° C or lower, and the cooling is stopped at a temperature of 400 ° C or higher, after which the mold pig iron is separated from the mold. This is a method of casting pig iron in which the die is released from the mold and released from the mold.

(Operation) Hereinafter, the operation of the present invention will be described in detail.

The starting temperature of water spray cooling of the mold pig in the mold is 80 at the surface temperature of the mold pig.
The reason for defining as 0 ° C or less is that if water cooling is started from the time when the surface temperature of the mold pig is higher than 800 ° C, the inside of the mold pig may still be in a molten state, and if a large amount of water is sprinkled in such a state. This is because the temperature difference between the inside and the surface becomes large, and the thermal stress causes tensile stress to act on the surface portion that is about to shrink, causing cracks on the surface of the mold pig, which in turn leads to breakage of the mold pig.

Further, the lower limit of the water sprinkling and cooling start temperature of the mold pig is preferably low from the viewpoint of preventing breakage of the mold pig, but on the other hand, it is desirable that it is high from the viewpoint of improving the efficiency of the pig iron. Therefore, the lower limit of the sprinkling cooling start temperature of the mold pig iron is largely determined by the capability of the pig iron machine, and is not specified here.

On the other hand, the reason for setting the sprinkling cooling stop temperature to 400 ° C or higher is to relieve the residual stress due to the heat recovery from the inside of the hot metal after the sprinkling cooling is stopped and reduce the generation of broken pig iron. further,
In order to positively reduce the generation of broken pig iron, the mold pig after mold release is allowed to cool in the atmosphere.

From the viewpoint of handling, it is desirable that the surface temperature of the mold pig is 200 ° C or less when cooling with water spray after releasing from the mold.

Next, the test results conducted by the present inventors will be described.

The inventors of the present invention carried out cast pig iron treatment using low silicon hot metal at various sprinkling cooling start temperatures and cooling stop temperatures, and after cooling, investigated the occurrence of broken pig iron in the mold pig iron.

Use hot metal having a Si content of 0.05 to 0.20%, cast the hot metal into the mold of the hot metal machine from 1300 ° C, start sprinkling cooling in the temperature range of 1100 to 600 ° C, and set the cooling stop temperature to 300 ° C. , 400, 500 ° C., and the broken pig iron generation rate of the mold pig after cooling was determined by the number ratio. The results are shown in FIG.

Fig. 1 shows the relationship between the sprinkling cooling start temperature and the broken iron occurrence rate. The thick lines, thin lines and chain lines in the figure indicate the broken pig iron occurrence rates at cooling stop temperatures of 300, 400 and 500 ° C, respectively. .

From the point of improving the efficiency of the pig iron machine, the sprinkling cooling start temperature is
Higher is better, but as is clear from FIG. 1, when the sprinkling cooling start temperature exceeds 900 ° C., the rate of broken iron rapidly increases. Therefore, the sprinkling cooling start temperature of 800 ° C or less is inevitable as the temperature that keeps the broken pig iron generation rate low, and also satisfies the efficiency of the pig iron machine, and the sprinkling cooling start temperature of the present invention is 800 ° C or less. This is the reason why it was prescribed.

In addition, the sprinkling cooling stop temperature is preferably as low as possible in consideration of handling of the pig iron after cooling, but the sprinkling cooling stop temperature of 300 ° C has a high rate of broken iron, It is not a preferable temperature for production.

The breakage rates of the cooling stop temperatures of 400 ℃ and 500 ℃ are almost the same at the sprinkling cooling start temperature of 800 ℃ and below, and the breakage rate of the breakage is 300 ℃ even at the cooling stop temperature of 400 ℃. It is less than 1/2 of the rate of occurrence of broken pig iron, and a cooling stop temperature of 400 ° C is sufficient from the viewpoint of the rate of broken pig iron generation. Therefore, in the present invention, the sprinkling cooling stop temperature is set to 400 ° C or higher.

(Example) The configuration of the present invention is as described above, and an example will be described below.

Table 1 shows the chemical components of the hot metal used in the examples. The hot metal A is obtained by dephosphorizing the hot metal tapped from the blast furnace by a conventional method, and the hot metal B is the hot metal tapped from the blast furnace by the conventional method. The Si content of the hot metal is selected to be 0.2% or less at which the hot metal becomes white pig iron, 0.01% for hot metal A and 0.13 for hot metal B.
%.

In both the present invention method and the conventional method, the same hot metal as shown in Table 1 was used, the first half of the cast pig iron treatment was cooled under the cooling conditions of the present invention method, and the latter half was cooled under the conventional method cooling conditions, and the mold pig was completely cooled. After that, the ratio of the broken pig iron was calculated by the number ratio. The results are shown in Table 2.

As shown in Table 2, in the method of the present invention, the rate of occurrence of broken pig iron in both hot metal A and B is a good value of 10% or less.

In the conventional method, the sprinkling cooling start temperature is as high as 1050 ° C or higher, the cooling stop temperature is as low as 350 ° C or lower, and since the sprinkling cooling is performed even after the mold release, the hot metal A and B hot metal breakage rates Is a high value of 70% or more.

As is clear from the results of the above examples, the pig iron method according to the present invention is most suitable for the low silicon molten pig iron casting method.

(Effects of the Invention) As described above, since the method of casting hot metal according to the present invention has the above-described configuration, it is possible to form low-silicon hot metal into a mold having a regular shape. Therefore, the type pig iron according to the method of the present invention has high commercial value, has little breakage during handling and transportation, and since the amount of broken pig iron is small, the amount of rust generated during storage is reduced and the breathability during remelting is also good. It has a good effect on the casting work.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the mold pig surface temperature at the start of sprinkling cooling and the mold pig surface temperature at the time of cooling stop, which affects the rate of broken pig iron production.

Claims (1)

[Claims] 1. A low silicon hot metal is cast into a mold of a cast iron machine to form a mold, and the mold in the mold has a surface temperature of 800.degree.
It is characterized by starting sprinkling cooling after lowering to below, stopping cooling at a temperature of 400 ° C or higher, then releasing the mold pig from the mold, and cooling the mold pig after release to the atmosphere. Method for casting low silicon hot metal.