JPS5928558A - Molten metal for cast iron excellent in graphitizability - Google Patents

Abstract

PURPOSE:To obtain a molten metal for highly graphitizable cast iron made low in chill crystallization without adding or inoculating any alloy to the molten metal, by using shaft furnace molten iron having unmelted graphite present therein as a molten stock materal. CONSTITUTION:Molten iron tapped from a shaft furnace is mixed in an amount of 40-80% as a stock material for melting. By this method, unmelted graphite carried by the molten iron is present in molten cast iron as it is and, because it acts as a solidification nucleus, extent of super cooling becomes small and chill crystallization is prevented while graphitization is promoted. By this method, because of the sensible heat possessed by the molten iron itself, power consumption and a melting time can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a molten metal for cast iron, which is made of molten metal for cast iron, and has a chlorotizing property with less crystallization of cast iron.

Cast iron; well-known as a molten metal for manufacturing! There is a technology that uses the molten metal left over from the furnace as it is. This is because the casting is made using 100% blast furnace hot metal pouring method, % blast furnace melting method, which results in an extremely high carbon content, resulting in a casting in which only primary graphite crystallizes. becomes. For this reason, although it has excellent heat resistance, it is extremely brittle and has a low tensile strength of less than 101 mA, so it can only be used in limited applications such as ingot cases and surface plates. Ta.

Measures to improve this tensile strength include alloy addition and mechanical stirring of 4'14 K to create a fine graphite shape.
Although uniformization was carried out, the tensile strength could only be improved to about 171η/mal due to the use of a blast furnace melting pot: 10091.

Therefore, with this direct casting method of blast furnace hot metal, it is not possible to produce a porcelain with poor graphitization properties in which less chill crystallizes during cast iron casting as intended by the present invention.

That is, in general, when the molten metal blooms and hardens, vertical placement advances due to the generation of solidified nuclei due to the formation of heterogeneous edges, but supercooling of the molten metal becomes a major driving force for nucleation.

If the cooling rate of the bath water is fast, nucleation is delayed, supercooling becomes thicker, and the solidification temperature becomes lower. For this reason, ledebrite, which is a eutectic of austenite and cementite, crystallizes as the first product. This leadebrite is a very hard material and difficult to work with in its as-cast state. Therefore, in order to perform processing, it is necessary to perform heat treatment to decompose cementite and graphitize it.

Conventionally, method 1, which has been most commonly used to completely prevent chill crystallization, is to add F'e-8i or the like to the molten metal just before pouring to provide solidification nuclei within the molten metal, thereby preventing chill crystallization. There is an inoculation treatment that prevents total emergence. In addition, as another method, a method of adding graphitization promoting elements such as O and Aβ has been used.

However, in these methods, the cost of the molten metal increased due to the confinement and added alloys9, the number of steps required for inoculation was increased, and defects were more likely to occur. On the other hand, the effect of inoculation lasts for about 5 minutes at most, and if more time passes, it fades and becomes ineffective. In order to solve the problem, various attempts were made to find out that there is a large amount of undissolved graphite in blast furnace molten iron, which contains supersaturated carbon, and developed a complex that utilizes this undissolved graphite as solidification nuclei. The present invention has discovered that it can be used as a molten metal for oxidizable cast iron, and provides this as an invention.

That is, the present invention Ll: 40 to 80% of hot metal tapped from a blast furnace is blended as a melting raw material to suppress crystallization of chilled metal.
It is a molten metal for cast iron with excellent graphitization properties.

Therefore, the present invention uses blast furnace molten iron in which unfinished graphite exists in the molten metal as a raw material for melting. Since the solid graphite exists as it is and acts as a solidification nucleus, supercooling is reduced, crystallization of chill is prevented, and graphitization is promoted.

Therefore, the undissolved graphite in the molten metal becomes the solidification nucleus VC.
Although it is introduced on page 15, this differs depending on the above. In addition, “Tetsu-Seitsukukyu” No. 298 (197
9), page 13, it is reported that when mold pig iron is mixed as a raw material for melting, the chill becomes shallower.1 The present invention, as shown in Fig. 1, It has the effect of thinning the V-kochiru metal.

This is because the molten α1
] The undissolved graphite in the mold scatters from the surface of the mold pig iron, reducing the amount of primary crystal graphite that acts as solidification nuclei in the mold pig iron, and because it takes a longer melting time compared to hot metal blend melting, This is because the primary crystal graphite inside dissolves and disappears, the presence of solidification nuclei decreases, and the effect of making the chill shallow becomes smaller.

Here, the reasons for the limitations of the present invention will be described. The present invention uses a molten metal for cast iron containing 40 to 80% of blast furnace hot metal in order to manufacture castings having a strength of F, 025 or more of ordinary cast iron castings with shallow chills, few defects, and omitting processes. be.

The reason why the blend is 40 to 80 Y is that the blast furnace hot metal is 40 to 80 Y.
If the blending ratio is less than 80%, the chill becomes deep because the presence of un-d square graphite as solidification nuclei decreases, and if the blending ratio is more than 80%, the tensile strength becomes 25 kr/- or less, which is a significant decrease. This is to do so.

In this way, when blast furnace hot metal is used as the molten raw material>:'-4, without going through the steps such as adding an alloy and performing all inoculation treatments, the present invention as shown in FIG. It is possible to prevent the crystallization of chill, and compared to the case of mixed type pig iron, the chill is shallower and has a greater effect.

In addition, due to the sensible heat of the hot metal itself, compared to conventional melting methods, the amount of electricity used is lower and the melting time is shorter, leading to energy savings and improved production efficiency.

The present invention, which is new and useful for fjζ, is characterized in that, in addition to the above-mentioned blending of 40 to 80% blast furnace hot metal, in order to sustain the action of this unmelted graphite as solidification, the melting temperature gold i , s o o ℃ V, below, and DJ t should be held within 30 minutes.

This is because if the holding time is longer than 30 minutes in a high-temperature layer group at 1,550°C, undissolved graphite becomes molten and extinguished, so the effectiveness of undissolved graphite as a solidification nucleus decreases. It's for a reason.

Next, the effects of the present invention will be explained based on examples.

Table IK shows the melting conditions of the present invention and the conventional method.
4,67%0,0.52%S1,O,39%M
Blast furnace hot metal with the following components: n, 0.08% P, and 0.014% S was used.

Table 1 Total melt weight 'k1.8t, blast furnace hot metal 'e900kF
The molten metal was poured into a low frequency induction furnace charged with 9 ook of steel scrap in advance, and heated to 1.500°C through a composition adjustment process.
It was dissolved by raising the temperature to .

Is the conventional method used as a comparison material also the total melt weight? ! -1,81 as type Qt 900 kg, copper scrap 360 kf, return feather 't
No. 540 was charged into a low frequency induction furnace under the same melting conditions as the method of the present invention.

The obtained molten metals were tapped at 1,500°C, and 1.
A plate chill test piece (1 c#) was placed at 380°C.

At this time, in order to check the effect of inoculation,
A plate chill test piece was also collected for the case where 03% Fe-8i was inoculated.

As shown in Figure 2, which shows the plate chill depth with and without inoculation for the present sushi light and the conventional method, the method of the present invention improved the depth of plate chill compared to the conventional method (approximately 172 mm). .

It can be seen that there were many solidification nuclei as can be seen in the center of the sump sample that was rapidly cooled immediately after the start of eutectic crystallization in Figures 3 (a) and (b).

Furthermore, as Example 2, the present inventors focused on the relationship between melting temperature and holding time, and found that the melting temperature, holding time, and plate temperature when all the blast furnace hot metal was received in the same process as in Example 1, and the same proportions were mixed. The relationship between the chill depth is shown in Figure 4.The melting temperature of molten metal mixed with 50% blast furnace hot metal '1z according to the method of the present invention is 3 cases: kl + 450°C, 1 + 500°C, and 1v550°C, and the holding time is 15 minutes and 2/30. Case,
A total of 6 cases were tested.

In addition, the melting temperature of 50% type iron in the conventional method is 1.450℃.
, 2 cases at 1,500°C with no holding time.

As a result, as shown in Figure 4, the melting temperature is high even in the method of the present invention, and the plate chill depth increases as the holding time increases, which is the same level as the general melting temperature J, 450°C by the conventional method. The melting temperature according to the method of the present invention is 1,
The upper limit is 500°C and a holding time of 30 minutes.

In addition to the above examples, the method of the present invention has the same level of chill depth as the conventional method with all inoculation treatments, even without inoculation treatment, and in order to make the chill shallower as in the conventional method, inoculation is not performed. There was no need to carry out this process, and the Y/seed process could be omitted.

Furthermore, as shown in Table 2, the melting power and melting time of the method of the present invention is approximately 1/3 the melting power and approximately 172 times longer than that of the conventional method using molded pig mixture, which has the advantages of energy saving and productivity improvement. It is a big thing.

In addition, when continuous dissolution is performed, as shown in Table 3,
This invention has a greater improvement effect.

Table 2 Table 3

[Brief explanation of drawings]

Figure 8141 is a graph showing the relationship between the blast furnace hot metal blending ratio, the mold pig iron blending ratio, chill depth, and tensile strength. Figure 2 is a microscopic image (x5) showing the metallographic structure of a eutectic cell with the chill depth of the blast furnace hot metal mix and the mold pig iron mix (using mold pig iron). The aj3/1 diagram is a graph showing the relationship between melting temperature and holding time and plate chill depth. 1: Change in chill depth of molten @[: blend 2: Change in chill depth of type Wre blend 3: Change in tensile strength of hot metal blend 4: Plate chill depth under conditions without inventive inoculation 5 : Plate chill depth 6 with inoculation of the present invention: Plate chill depth 7 without conventional inoculation: Plate chill depth 8 with conventional inoculation: Invention U,' Board chill depth 9 for r time 15 minutes
: // Board chill depth 10 in 30 minutes:
Plate chill depth of conventional method pig mix

Claims (1)

[Claims] (], 1 Takashi, 1 door) from; taste, and melted 2↑λ,
7 - Graphitization method 3-1 type, which is characterized by containing 40 to 80% as a raw material for melting and completely suppressing chill crystallization. Molten metal for iron.