JPS642653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing extremely reliable high quality steel ingots.

In the past, the zone melt method was developed as a method for highly refining semiconductor metal materials such as germanium and silicon, and it has been shown to be an extremely effective means for achieving high purity of metal materials and homogenizing their composition and structure. widely known.

Therefore, attempts have been made to apply this method to steel to obtain high-quality steel ingots, but although it can be carried out on a small-scale laboratory scale, it has not yet been realized on a practical steel scale.

In other words, in the case of practical steel, it is necessary to handle extremely large ingots compared to semiconductor metals, etc., the melting temperature of steel is extremely high, and the melting and solidification of steel involves the generation or absorption of a large amount of gas. Furthermore, it has been difficult to apply the zone melting method used for semiconductor metals to steel as it is, for reasons such as being too expensive and impractical.

By the way, if these difficulties are thoroughly studied, it is clear that all of them can be solved if the optimum refractory for zone melting of steel is found.

The present invention overcomes the above-mentioned difficulties by applying quicklime (CaO)-based refractories as the refractories and using ceramic fiber cloth or bands as reinforcing materials, thereby making zone melting of practical steel ingots possible. It is characterized by the following.

In general, quicklime refractories are obtained from limestone, which is produced in large quantities in Japan, and are of high quality with low impurities and can be obtained in large quantities at extremely low prices.

In addition, quicklime is stable and strong at high temperatures, does not easily volatilize even under high-temperature vacuum conditions, and has a melting point of 2500℃.
It usually has a porosity of close to 50%, has good air permeability, is rich in heat insulation, has the ability to absorb and remove impurities in molten steel, and even when it comes into contact with molten steel, it becomes non-metallic inclusions and It is known to have many excellent properties for steel refining, such as being free from contamination. However, quicklime refractories have a decisive drawback as refractories, as they absorb moisture in the atmosphere and turn into powder, such as slaked lime.As a refractory for ordinary furnaces, they cannot withstand repeated use, and to this day, they cannot withstand repeated use. However, quicklime refractories have only been used in special trials and have not been put into practical use.

In the case of the steel ingot zone melt according to the present invention, there is no need to repeatedly use the refractory, and each steel ingot only needs to be used as a refractory once, so the quicklime refractory has many excellent properties. It was only by making effective use of this that it became possible to produce practical zone melt steel ingots. In other words, quicklime has extremely high refractory properties, so it can withstand the temperature of molten steel and has stable high-temperature strength.It can withstand the weight of molten steel equivalent to that of practical steel when reinforced with ceramic fiber cloth, and has good gas permeability. Since the refining ability for dovetail steel works effectively and it is extremely inexpensive, it has become possible to solve all of the causes of difficulty in zone melting of practical steel.

The present invention will be explained in further detail with reference to embodiments shown in the drawings. The figure shows one embodiment of the present invention, and the present invention is not limited to this example in any way. The figure is a longitudinal sectional view illustrating the process of vertically zone melting a practical steel ingot. Figures 1 and 2 show the process of stamping calcareous refractories on the outer peripheral surface of the steel ingot, Figure 3 shows the heating and firing process, Figure 4 shows the zone melting process, and Figure 5 shows details of the zone melting part. Show the diagram. In the figure, 1 is a steel ingot subjected to zone melting, and from the point of view of thermal efficiency, it is preferable to have a circular cross section, but it is also possible to use a steel ingot with a rectangular cross section obtained by continuous casting or the like as is. A hoist 2 is attached to the top of the steel ingot so that it can be hoisted by a crane or the like.
Further, in order to improve the quality of the zone melt steel ingot, it is preferable to remove black scales from the steel ingot by shot blasting, grinding, etc.

Specific values are described below using as an example the case of zone melt of continuous casting bloom with 315 mm interrupted surface.

First, the stamp starting method will be explained with reference to FIG. A bottom cup 4 made of refractory brick is placed on the surface plate 3. This is used to reinforce the bottom of the stamp, and if it is made of, for example, shamrock, it can be used repeatedly. Next, a stamp metal frame 5 that is split vertically into two is set around the bottom cup. The dimensions of the frame are 75~ on the outer circumference of the steel ingot.
Use something that can make a 100mm thick stamp.

Next, add the calcareous refractory 6 from the inner bottom of the bottom cup.
After stamping up to 150 mm, set the steel ingot 1 on its center. Next, stamp the side of the steel ingot with the same stamp frame 5.
Stamp with calcareous refractory 6 up to the top.

The calcareous refractory 6 is made of, for example, high-purity limestone (CaCOa), quicklime (CaO), or a mixture thereof, which contains particles crushed to 5 mm or less and fine powder, and quicklime-calcium chloride (CaO-CaCl ₂ ).
A binder such as a system flux or an ethanol solution of calcium chloride is used.

By adjusting the amounts and ratios of limestone and calcium chloride used here, it is possible to control the air permeability after firing the stamp.

Next, as shown in FIG. 2, stamping is performed up to the top of the steel ingot while sequentially shifting the stamping split frame 5 to the top of the steel ingot. On the other hand, the stamp is reinforced by wrapping a cloth or band 7 made of glass fiber, asbestos or other ceramic fiber around the finished part of the stamp.

The stamped steel ingot is stored in a heating furnace 8 as shown in Fig. 3 and heated and fired to remove moisture in the stamp material.
The volatile matter in the binder is removed, and the used limestone is completely decomposed to form a uniform quicklime layer on the stamp. At this time, if the pressure in the firing furnace can be reduced, firing will be completed at a low temperature, and the ceramic fiber reinforcement will not be damaged and can be used repeatedly. Third
In the figure, 9 indicates a vacuum exhaust port, and 10 indicates a heating heater. After the firing is completed, the product is stored in a vacuum chamber 11 for zone melting shown in FIG. 4, and vertical zone melting is performed. In the figure, reference numeral 12 denotes a support stand which also serves as a storage part for the induction heating coil 14. The steel ingot is set on the support table and at the same time is held in a suspended state by a hanger 15 across the hanging tool 2. This is important to prevent breakout of molten steel due to bulging due to excessive pressure being applied to the zone melt part due to the weight of the steel ingot.

When the setting is completed, exhaust is exhausted from the vacuum exhaust port 13, input is applied to the induction heating coil, and the circumference of the steel ingot is raised at a constant speed to perform zone melting. The details of the progress of the zone melt are as shown in FIG. 5. heating coil 14
The vicinity of the interior becomes molten 16, flows as shown by the arrow similar to the molten steel in a crucible-type induction furnace, and comes into sufficient contact with the quicklime stamp layer 6, so that impurities such as phosphorus and sulfur and non-metallic inclusions are absorbed and removed. After becoming clean steel, as the coil 14 rises, the zone melt steel 17
As a result, a high-quality steel ingot with a uniform structure is produced, with no defects such as internal porosity or component segregation.

Further, when the zone melting process is carried out under vacuum as in this example, the quicklime refractory has good air permeability, so that the steel is cleaned by degassing hydrogen, oxygen, nitrogen, etc. in the molten steel. Particularly, the method according to the present invention is extremely effective in obtaining a high-purity clean steel ingot of high alloy steel, such as stainless steel or heat-resistant steel, from which impurities are more difficult to remove than ordinary steel.

In one embodiment, aluminum is used as a deoxidizing agent.
18-8 stainless steel ingot with 0.2% alloy added
If the zone melting method according to the present invention is applied under a vacuum of 10 ^-5 torr, the oxygen content can be reduced to several ppm (initial content 250ppm), which is limited to about 30ppm in conventional steel manufacturing methods using AOD and VOD methods. At the same time, sulfur, which is considered to be a limit of about 10 ppm, can be reduced to less than 1 ppm (initial content: 90 ppm). Other impurities and non-metallic inclusions are also absorbed and removed by the molten steel through sufficient contact with the quicklime stamp layer 6, and the zone melt effect is added to achieve high cleaning, resulting in improved pitting corrosion and rusting resistance. can be significantly improved compared to conventional commercially available steels. During the zone melting process, steel undergoes considerable thermal expansion and contraction, and cracks are expected to occur in the sintered parts of the quicklime refractory that come into contact with the steel. Since the sintered layer is rich in powder, the vicinity of the sintered layer is still in the state of powder or quicklime, and is supported by ceramic fiber reinforcing material, which prevents breakout of the molten steel and sufficiently withstands the expansion and contraction of the steel. In the above cases, the calcareous refractory used is 25 to 30 limestone equivalent per 100 steel ingots.
Since the binder is about 1 to 3, the unit consumption of calcareous refractories is not much of a problem, and it can be implemented at almost the same cost as ESR, which is another remelting refining method. After completion of zone melting, water is poured onto the stamp layer 6 to remove calcium hydroxide and the pear stamp layer by powdering them.

The zone melt steel ingot produced by the present invention has extremely high reliability, such as a uniform directionally solidified steel ingot and a uniform ultra-clean defect-free steel ingot, which are impossible with other manufacturing methods. It has the effect of further expansion, and its economic significance is extremely large.

[Brief explanation of drawings]

The figures are longitudinal cross-sectional views illustrating one embodiment of the present invention, and Fig. 1 shows the process of stamping calcareous refractories on the outer peripheral surface of the steel ingot, and Fig. 3 shows the heating and firing process.
FIG. 4 shows the zone melt process, and FIG. 5 shows details during the zone melt process. In the figure, 1 is a steel ingot for zone melting, 2 is a hanging tool for the steel ingot, 3 is a surface plate, 4 is a firebrick bottom cup, 5 is a metal frame for a stamp that is split vertically into two, and 6 is a calcareous fireproof 7 is a reinforcing material for ceramic fiber cloth or band; 8 is a heating and firing furnace; 9 is a vacuum exhaust port; 10
1 is a heater for heating, 11 is a vacuum chamber for zone melting, 12 is a support stand, 13 is a vacuum exhaust port, 1
Reference numeral 4 indicates an induction heating coil, 15 a hanger, 16 a molten steel portion in a zone melt, and 17 a zone melt steel ingot.

Claims (1)

[Claims] 1 Stamp calcareous refractories on the outer circumferential surface of the steel ingot, reinforce the stamp by wrapping a ceramic fiber cloth or band around the outer surface of the stamp, then heat and sinter it, and then create zone melt using an induction heating coil. A zone melt steel ingot manufacturing method characterized by obtaining high quality steel ingots.