JPH0259029B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a surface plate for unidirectionally solidified steel ingots in the ingot making process of the steel manufacturing process, and more specifically to a bottom pouring surface plate for steel ingots. [Conventional technology] Conventionally, in a vertically long steel ingot, cooling heat was removed from three directions: from the surface plate side and from both sides of the mold, which inevitably caused internal defects such as micro-segregation and hollow defects. It was hot. On the other hand, in a unidirectionally solidified steel ingot, the cooling heat is removed only from one direction from the bottom of the surface plate, and the solidification interface advances upward from the bottom, and the solute concentration that occurs with solidification is By matching the floating direction of the molten steel, conventional problems such as micro-segregation and roughness defects can be improved. This results in
The quality of steel ingots for steel plates has improved. However, in this conventional unidirectionally solidified steel ingot surface plate, cooling heat is removed from three directions in one direction, so the heat removal rate is relatively small, and the solidification of the surface plate and the bottom of the steel ingot is relatively low. Because the surfaces were in direct contact, voids were created early on, and thereafter the heat transfer coefficient decreased dramatically, making it difficult for heat to be removed.
In addition, in the composition of the upper part of the steel ingot, dendrites became coarse, a pseudo pattern due to component segregation (micro-segregation) between dendrite trees appeared on the surface of the steel plate, and inverted V segregation was likely to occur locally in the steel ingot. . For this reason, micro-segregation and inverted V-segregation caused by coarsening of dendrites occur significantly during the ingot-making stage, and in order to reduce this, it is necessary to perform sufficient diffusion annealing of the slab after blooming the steel ingot, which requires a large amount of effort. It has the disadvantage of being expensive. On the other hand, Jikoaki developed a surface plate with a water-cooled structure.
No. 44-14658, and this surface plate consists of a base plate with grooves for passing cooling water, and a top plate made of a copper plate installed on the top surface of the base plate, which are tightened with bolts using compression springs. The one that is attached and fixed is shown. However, this surface plate is for top pouring, and since the injected molten steel directly hits the top plate, there is a high possibility that the top plate will be melted and damaged. Although it is tightened, when the mold is loaded, it will be restrained by the lower end of the mold, and deformation of the top plate, etc. will inevitably occur. Therefore, from the former point of view, there is a serious defect where cooling water flows down directly below the top plate, which could cause an explosion if molten steel reaches that part, and from the latter point of view, there is a serious defect that could cause an explosion, and from the latter point of view, there is a risk of deformation, wear and tear. It is necessary to replace the top plate each time, which has the drawback of placing a heavy burden on workability and economy. [Problems to be Solved by the Invention] The present invention has been proposed to solve the above-mentioned drawbacks, and it is possible to refine the dendrites by cooling the surface plate and strengthening the heat removal from the bottom of the steel ingot. It is an object of the present invention to provide a surface plate for a unidirectionally solidified steel ingot that reduces micro-segregation at the ingot stage and inverted V segregation in localized steel ingots. [Means for Solving the Problems] The present invention is applied to a lower pouring surface plate for steel ingots, and its gist is that pipes for passing cooling water to promote heat removal are arranged on the upper surface of the surface plate part, and A steel bottom plate is placed on the top of the cooling pipe to prevent gaps from forming between the solidified surface of the lower part of the steel ingot and the surface plate surface, thereby enhancing cooling heat removal. Furthermore, the pipe group for cooling water flow includes a first lower base plate having openings through which each nozzle penetrates at each nozzle position of the surface plate, and a second base plate located directly below the lower end of the mold parallel to the first lower base plate. The steel bottom plate is arranged between the bottom plate of the mold and the internal surface which forms the bottom of the mold placed on the bottom plate and removes heat from the bottom of the mold, with a buffer material that absorbs thermal expansion. It was divided into an external surface that abuts the lower end surface. [Operation] By configuring the present invention as described above,
It is possible to achieve even closer adhesion between the deck plate and the steel ingot, making it difficult for air gaps to form between the base plate and the steel ingot, resulting in a high heat transfer coefficient, and cooling heat removal by passing water through the pipe. will be further strengthened. In addition, the bottom plate is divided into an external surface and an internal surface via a buffer material that absorbs thermal expansion, so it is not restricted by the weight of the mold, and the internal surface is free to expand as the molten steel is heated. can. In addition, the cooling water does not pass through the pipes and come into direct contact with the bottom plate, so even if the bottom plate were to melt and the molten steel penetrated through the top plate, the cooling water and molten steel would not come into direct contact. There is no explosion, and explosion accidents are definitely prevented. [Example] Hereinafter, the present invention will be described based on an example with reference to the drawings. First, to explain the known parts of this embodiment,
As shown in FIGS. 1 and 2, when producing a unidirectionally solidified steel ingot, a heat-retaining sleeve 2 is attached to the entire inner wall of a mold 1. From an injection pipe (not shown) to a runner 6 and nozzles 7, 7...
Molten steel is poured down through ... to form ingots. Next, to explain the characteristic parts of this embodiment, a plurality of square pipes 12a through which cooling water is passed are arranged on the upper surface of the upper surface plate part 4, and a square pipe group 12 is arranged.
(Fig. 3), and a steel bottom plate 11 is further laid thereon. Figures 4a and 4b show the structure of the cooling water piping, which consists of two supply headers 14, two discharge headers 15, and rectangular pipes 12a, 12a... connecting them. It is composed of a group of pipes 12 for passing cooling water. In addition, as shown in FIG. 2, square pipe groups 12, 12
The lower bottom plates (first lower plate 13a, second lower plate 13, 13) are arranged on a steel surface plate having the same height as the rectangular pipe groups 12, 12. be done. This lower bottom plate is a first lower bottom plate 13a provided at the nozzle 7 position of the surface plate portion 4.
and a second lower bottom plate 13, 13 provided at a position directly below the lower end of the mold 1 parallel to the first lower bottom plate 13a.
The first lower bottom plate 13a is provided with holes 13b, 13b, . . . through which the nozzles 7, 7, . . . penetrate. Further, second lower bottom plates 13, 13 provided directly below the lower end of the mold 1 are arranged to carry the weight of the mold 1 via the bottom plate 11. Further, the square pipe group 12, the lower bottom plate 1
The bottom plate 11 disposed on the upper surface of the steel ingot 10 is arranged on the inner surface 11 corresponding to the lower end opening of the mold 1 in order to absorb thermal expansion accompanying the temperature rise during casting of the steel ingot 10.
It is divided into two parts: a and an external surface 11b facing the lower end of the mold 1, and a buffer material 16 for absorbing thermal expansion is filled between them. FIG. 3 shows a schematic perspective view of parts between the mold and the upper surface plate according to the present invention.
is arranged, followed by square pipe group 1 at both ends.
2, 12 and the square pipe group are sandwiched between the second lower bottom plates 13, 13,
The inner surface 11a of the bottom plate and the outer surface 11b of the bottom plate, which are divided into two, are laid on the upper surfaces of the first lower bottom plate 13a, the square pipe group 12, and the second lower bottom plate 13, and are designed for use in unidirectionally solidified steel ingots. A board is constructed. Note that 8 shown in FIGS. 1 and 2 represents mortar that seals the nozzle 7, and the outer periphery of the nozzle 7 is filled with dry sand 9 to achieve sealing. Furthermore, the inner surface 11a of the bottom plate and the outer surface 11b of the bottom plate
As shown in FIGS. 1 and 2, the buffer material 16 absorbs thermal expansion between the molds 1 and 1, and corresponds to the lower end opening of the mold as shown in FIGS. Therefore, the inner surface 11a of the bottom plate can freely expand due to the heating of the injected molten steel. In this embodiment, the number of nozzles 7, 7... is three per mold, but it is not limited to three, and may be changed depending on the size of the mold 1. Of course. Moreover, the square pipe 12a,
12a..., but a circular pipe may be used and the space between it and the bottom plate 11 may be filled with a material having high thermal conductivity. In addition, a small gap is provided between the square pipes 12a, 12a for thermal expansion as shown in FIG. The structure is such that the direction of cooling water flow is alternately reversed. In addition, if the upper surface area of the upper and lower surface plates 4 and 5 is narrow, the cooling water supply side header 14 and the discharge side header 15 are each
The cooling water may flow in only one direction. Note that this embodiment uses two surface plates, the upper surface plate section 4 and the lower surface plate section 5, but the lower surface plate section 5
In the other embodiment, the only difference is that the nozzle 7 is not provided and the positions of the dry sand 9 and the sealing mortar 8 are lowered. When considering this embodiment, the inventors considered in advance both air and water as the types of fluid for heat removal, and the thickness of the bottom plate 11 and the dimensions of the square pipes 12a, 12a, etc. according to each. It was investigated. First, as a result of experimental studies, it was confirmed that the thickness of the bottom plate 11 is 10 mm or more to prevent damage to the square pipes 12a, 12a, . . . directly below due to melting of the bottom plate 11. Next, we considered a method of using water as a surface plate cooling fluid from before pouring molten steel until the end of solidification, and a method of using air until after pouring molten steel and then switching to water. 12a...
The appropriate dimensions of ... were evaluated by heat transfer calculations. In Fig. 5a, the heat transfer calculation results between A1, B1, C1 and A2, B2, C2 in Fig. 5b are shown in Table 1 and under the following conditions. , 12a... Even if it is injected into the pipe, the temperature of the pipe itself is low because the cooling capacity is small.
It has become clear that when the temperature rises to 400 to 900°C, pressure resistance is generated due to rapid evaporation at the start of water flow, making water flow difficult. To prevent this, a large flow rate of water is required, which is impractical. On the other hand, even before injection of molten steel, the square pipes 12a, 1
2a... If water passes through the square pipes 12a, 1
2a... only raises the temperature to a maximum of 70℃ and does not interfere with subsequent water flow.

〔Effect of the invention〕

As explained above, according to the present invention, the bottom plate and the steel ingot are in close contact with each other, making it difficult to form voids, and the heat transfer coefficient is high.
In addition, cooling heat removal is strengthened by passing water through the pipe. Therefore, it is possible to further reduce the inverted V segregation of the unidirectionally solidified steel ingot and improve the yield, and also to prevent the harmful effect of promoting micro-segregation at the ingot-forming stage, which has the effect of eliminating the need for diffusion annealing treatment of the blooming slab. play.

[Brief explanation of drawings]

Figure 1 is a sectional view taken along line BB in Figure 2 of an embodiment of the present invention, Figure 2 is a sectional view taken along line AA in Figure 1, and Figure 3 is a schematic diagram of the parts between the mold and the upper surface plate. A perspective view, FIG. 4 is a structural diagram of the cooling piping, FIG. 4a is a plan view,
FIG. 4b is a perspective view, FIG. 5a is an explanatory diagram of the heat transfer state according to the embodiment of FIG. 1, FIG. 5b is a partially enlarged sectional view of the embodiment of FIG. 1, and FIG. 6 is a conventional device. a and the first
Fig. 7 is an explanatory diagram of the solidification rate of the conventional device and the embodiment of Fig. 1. Fig. 8 is a diagram of the dendrite secondary arm of the conventional device and the embodiment of Fig. 1. FIG. 3 is an explanatory diagram of intervals. DESCRIPTION OF SYMBOLS 1... Mold, 2... Heat insulating sleeve, 3... Heat insulating material, 4... Upper surface plate part, 5... Lower surface plate part, 6... Runway, 7... Nozzle, 8... Mortar, 9... ... Dry sand, 10... Steel ingot, 11... Bottom plate, 11a... Inner surface of bottom plate, 11b... External surface of bottom plate, 12... Square pipe group, 12a... Square pipe, 13... Second
lower bottom plate, 13a... first lower bottom plate, 14...
...Supply side header, 15...Discharge side header, 16...
...Buffer material.

Claims (1)

[Claims] 1. A lower pouring plate for steel ingots, which includes a plurality of pipes for flowing cooling water laid on the upper surface of the platen, and a plurality of pipes laid on the pipe group in contact with the lower surface of the mold. The group of pipes for passing the cooling water includes a first lower floor plate having an opening through which each nozzle penetrates at each nozzle position of the surface plate, and the first lower base plate. The steel bottom plate forms the bottom of the mold placed on the bottom plate with a buffer material that absorbs thermal expansion interposed between the second lower bottom plates located parallel to the bottom end of the mold. A surface plate for a unidirectionally solidified steel ingot, characterized by being divided into an internal surface that removes heat from molten steel from the bottom, and an external surface that contacts the lower end surface of the mold.