JPH0748632A - Method for removing impurity from scrap iron - Google Patents

Abstract

PURPOSE:To stably remove the impurities (Zn, Sn, Cu, etc.) contained in iron scraps at the time of making steel from the scraps. CONSTITUTION:Iron scraps are melted in an electric furnace or converter to make steel. In this case, the scraps are preheated at 550-1300 deg.C before being melted to previously remove the platings (e.g. Zn and Sn) depositing on the scraps or the impurities contained in the scraps. Consequently, since the nonferrous metals such as Zn and Sn depositing on the scraps are previously removed before melting, a steel having extremely low contents of Zn, Sn, etc., after melting is stably obtained.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel manufacturing method using scrap as a raw material and having a small amount of impurities.

2. Description of the Related Art Due to motorization, domestic sales of automobiles in Japan have reached about 8 million.
Conversely, it can be said that almost the same number of cars are scrapped and scrapped every year. In the past, many cars were simply painted cold-rolled steel sheets, and there was no particular problem even if they were scrapped and melted in an electric furnace to make steel products. However, in recent years, an increasing number of cars use a surface-treated steel plate plated with Zn, Sn or the like in order to improve the corrosion resistance. When these are scrapped and melted in an electric furnace, impurities such as Zn and Sn remain in the steel. Since these impurities segregate at the grain boundaries and cause hot cracking,
In electric furnace steel made from scrap steel such as surface treated steel,
Only low-grade steel products such as concrete bars were made. On the other hand, there is an increasing demand for scraps of surface-treated steel sheets in the future, and there is also a social demand to produce steel products of the same quality as converter steel using electric furnace steel. From molten steel that melts scrap to Zn, Sn, etc. It is a socially important issue to establish a method for removing the impurities. So far, Z
As a method for removing impurities such as n and Sn, vacuum evaporation removal, Ar plasma evaporation, and the like have been tried.
It is hard to say that it is still established industrially.

DISCLOSURE OF THE INVENTION The present invention is based on Zn, Sn
In an electric furnace or converter steelmaking method using a surface-treated steel sheet plated with steel, etc. as a scrap material, it is an object to industrially produce a steel containing a small amount of impurities such as Zn and Sn that cause hot cracking of the steel. And

The gist of the present invention is as follows. When iron scraps (scraps) are melted in an electric furnace or converter to produce steel, the scraps are preheated at 550 ° C or higher and 1300 ° C or lower before being subjected to melting, so that the plated products adhered to the scraps (For example, Zn, Sn, etc.) or mixed impurities are removed in advance. The present invention will be described in detail below. The present inventor, after melting iron scraps including the surface-treated steel plate in an electric furnace,
Paying attention to the fact that it is not easy to separate Zn and Sn in molten steel, and that the melting points of Zn, Sn, etc. of the plated steel sheet are much lower than that of iron, in a non-oxidizing atmosphere before charging in an electric furnace. , Above the melting point of these plated products, eg 550 ° C
By heating to the above temperature to dissolve and elute the plated product, molten steel with impurities equivalent to converter steel was obtained in electric furnace steel. The heating temperature in advance may be a temperature equal to or higher than the melting point of the non-ferrous metal plated on the iron scrap, but if it exceeds 1300 ° C., the oxidation rapidly increases even in a non-oxidizing atmosphere. The heating temperature was 1300 ° C. or lower. Fig. 1 shows the relationship between the heating temperature when iron scrap including surface-treated steel sheet is preheated in Ar atmosphere and the total residual amount of Zn and Sn in molten steel. Was observed, and it was 0.02% or less at 800 ° C. Moreover, these methods were also effective for iron scraps containing non-ferrous metals such as Cu. In the case of containing Cu, the Cu concentration could be reduced to 0.2% or less by preheating the iron scraps before charging the electric furnace at 1085 ° C. or higher, which is the melting point of copper. When the Zn, Sn, and Cu described above are dissolved and eluted by preheating, the impurities can be more effectively removed by treating under reduced pressure. As the atmospheric condition, a non-oxidizing atmosphere is desirable, but for a plated deposit such as Zn or Sn, the plated product is separated from the iron scrap by heating at 550 ° C. or more even in an oxidizing atmosphere. In addition, it is possible to remove these non-ferrous metals to some extent. Further, by preheating iron scraps to 550 ° C. or more before melting in an electric furnace, the contaminants such as plastics and rubber are also melted or eluted, so that it is also effective for the treatment of iron scraps containing non-metals. These preheating may be provided separately from the electric melting furnace, or may be combined with the electric melting furnace. It is also effective when a large amount of scrap is used in the converter. Example 1. Iron scraps including the surface-treated steel plate were shredded into small pieces, placed in a preheating furnace, sealed with Ar gas, and then heated at 800 ° C. by induction heating to melt to elute the nonferrous metal plated on the iron scraps. . Next, the iron scraps were transferred to an electric furnace, and a carbonaceous material was charged therein, and oxygen was melted for 80 minutes while being blown with 40 Nm ³ / ton of oxygen. Next, the molten steel is put into the refining furnace from the electric furnace, and Ar for stirring the molten steel is put in from the bottom of the pan.
While charging Nm ³ / ton, the alloy was charged into the molten steel from a hopper installed on a pan to reduce the molten steel and at the same time control the temperature of the molten steel. Next, the slab having a thickness of 125 mm was obtained by injecting the refined molten steel into a tundish and casting it while drawing it at 3 m / min. A part of the obtained slab was cut out and the concentration of impurities was investigated. The results are shown in Table 1. Example 2 Iron scraps containing a surface-treated steel sheet copper wire were shredded into small pieces, put into a preheating furnace capable of vacuum heating, the inside of the furnace was first replaced with Ar, and then depressurized to 1 kPa, by induction heating. Heated at 1100 ° C. The non-ferrous metal component in the iron scrap was melted and then vaporized as metal vapor. The vaporized vapor was cooled in the middle of the duct and recovered as metal. Next, the iron scrap was transferred to an electric furnace, charged with carbonaceous material, and melted by an arc for 80 minutes while blowing oxygen at 40 Nm ³ / ton. Next, the molten steel is put into the refining furnace from the electric furnace, and Ar for stirring the molten steel is introduced from the bottom of the pan at 50 Nm ³ / ton, while the alloy is put into the molten steel from the hopper installed on the pan to reduce the molten steel and at the same time. The temperature was adjusted. The slab having a thickness of 125 mm was obtained by pouring the refined molten steel into a tundish and drawing it out at 3 m / min. A part of the obtained slab was cut out and the concentration of impurities was investigated.
The results are shown in Table 2. Example 3. Iron scraps including surface-treated steel plates are shredded into small pieces, then put into a preheating furnace and 700 with a gas burner.
Preheating was performed at 0 ° C., and the non-ferrous metal plated on the iron scrap was separated from the iron scrap. Next, the iron scraps were transferred to an electric furnace, and a carbonaceous material was put therein, and oxygen was blown at 40 / ton, and was melted by an arc for 80 minutes. Next, the molten steel is put into the refining furnace from the electric furnace, while Ar for stirring the molten steel at 50 m ³ / ton is introduced from the bottom of the pot, the alloy is introduced into the molten steel from the hopper installed on the pot to simultaneously reduce the molten steel. Temperature. Next, the slab with a thickness of 125 mm was obtained by injecting the refined molten steel into a tundish, drawing it out at 3 m / min, and casting. A part of the obtained slab was extracted and the concentration of impurities was investigated. The results are shown in Table 3.

According to the present invention, as can be seen from the examples, steel containing a very small amount of Zn, Sn and Cu can be obtained from scraps such as scrapped vehicles.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the preheating temperature of iron scrap and the concentrations of zinc and tin in molten steel after electromelting.

[Procedure amendment]

[Submission date] April 6, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Method of removing impurities from iron scrap

Claims (1)

[Claims] When melting iron scrap (scrap) in an electric furnace or a converter to make steel, 55
Plated material (eg Zn, Sn) attached to scrap by preheating at 0 ° C or higher and 1300 ° C or lower
Etc.) or mixed impurities are removed in advance.