JPH0327850A - Method for continuously casting medium carbon steel - Google Patents

Abstract

PURPOSE:To cast a cast slab having little longitudinal crack on the surface by using mold powder containing CaCO3 covered with the specific grain diameter of carbon black at the time of continuously casting medium carbon steel. CONSTITUTION:The medium carbon steel having 0.08-0.16wt.% carbon content and solidifying through reaction is cast with continuous casting. Then, the mold powder containing CaCO3 covered with carbon black having <=100mum the grain diameter is used. By this method, the continuous casting method obtaining the cast slab having no defect can be provided.

Description

[Detailed Description of the Invention] Industrial Field in Icheon> The present invention is directed to the carbon content of 0.08 to 0.0. 16% by weight (hereinafter %
The present invention relates to a continuous casting method for producing a cast slab with no vertical cracks on the surface of the slab in continuous casting of a steel containing 1a, which is referred to as a medium carbon steel. Conventional technology> So-called medium carbon steel with a carbon content TWk of 0.08 to 0.16% tends to have longitudinal δq deviation on the surface of the ER piece during continuous manufacturing. Various studies have been conducted on the mechanism by which such longitudinal cracks occur. The reason why vertical cracks tend to occur in medium carbon steel is that the carbon content of 0.08 to 0.16% is in the peritectic transformation region. This is because the difference between slow and fast growing parts of the solidified shell, that is, the non-uniformity of the solidified shell, is large due to the addition of this transformation stress. It is well known that the degree of non-uniformity in the solidified shell is correlated with the initial amount of heat removed within the mold, and that the degree of non-uniformity in the solidified shell can be alleviated by slow cooling. As these prior art, Japanese Patent Application Laid-Open No. 50-0592
Publication No. 29 describes a method for producing wide continuous cast slabs with few surface defects, which uses oil casting method and powder casting method in combination.
Discloses a method for preventing vertical cracking due to uneven cooling of
JP-A No. 61-092756 discloses a continuous Vt casting method for preventing slab surface cracking and a mold, in which medium-carbon molten steel is poured into a mold with multiple longitudinal grooves of appropriate shape and dimensions on the upper surface of the mold. It's only hard! A method is disclosed in which continuous VT casting is performed without causing surface cracks in the slab by slowly cooling the IF shell. On the other hand, another way of thinking is that the sulfur in the powder diffuses onto the surface of the slab during SR manufacturing, preventing it from becoming concentrated and making the solidified shell brittle.
Publication No. 53 states that the sulfur content is regulated by a formula.
A method has been disclosed that uses casting powder to produce defect-free slabs, thereby saving energy and improving yield. Furthermore, in Japanese Patent Publication No. 59-52014, in continuous Vt casting of medium carbon steel slabs, the negative time TN given by the formula for vibration applied to a water-cooled mold is 0.
．． Within 21 seconds and at 300°C 3.5~8
．． A method for continuous casting of medium-coal slabs is disclosed in which surface cracking of steel slabs is reduced by using a molding powder with a viscosity of 0 bores. Furthermore, Japanese Patent Application Laid-open No. 54-87625 describes carbonate (containing mineral A technique has been disclosed in which a powder containing a limited amount of (1) is added to a mold during continuous casting of steel, thereby improving workability and heat retention without causing sluggishness.

<Problems to be solved by the invention> The problems of the prior art are described below. First, the technique disclosed in JP-A-50-059229 uses both an oil casting method and a powder casting method. Since the powder casting method is common for continuous molding other than medium carbon steel, it requires new equipment for oil casting, and the number of operating personnel increases, so there is little cost benefit. The technique disclosed in Special Questionnaire No. 61-092756 requires the use of a mold with a special vertical cutout to cast medium-carbon steel, and considering the downtime required for mold replacement, etc., it will never lead to cost reductions. Powders based on ordinary mold powder raw materials that have been melted and homogenized (pre-melt) generally have low sulfur content, and are
This falls within the scope of defect-free chip manufacturing as shown in Publication No. 115653. However, when using powder controlled in this suitable range, although the incidence of vertical cracking in slabs was reduced, it was not completely eliminated. In addition, when attempting to operate within the appropriate range shown in Japanese Patent Publication No. 59-52014, the drawing speed of the slab was reduced to 1.35 m.
/ If it is not less than 1, the solidified shell will break, a so-called breakout, which will cause problems in terms of productivity. Finally, Japanese Patent Application Laid-Open No. 54-87625 is characterized in that the powder does not contain a carbon component because the purpose is to form uniform pores in the molten powder layer directly above the scene.

In contrast, the present invention forms pores in the aerated powder in the gap between the solidified shell and the mold to reduce the thermal conductivity.
For the purpose of slow cooling, the gas generating substance is coated with carbon to prevent the generation of bubbles in the molten layer as much as possible, and in continuous Ui casting of medium carbon steel, defect-free casting without vertical cracks on the surface of the spindle is achieved. This was done to propose a method for continuous Vt casting of pieces. Means for Solving the Problems As a result of repeated research on preventing vertical cracking on the surface of medium-carbon steel Vt cast slabs, the present inventors have found that they can form pores in the mold powder between the solidified shell and the mold. Reduce thermal conductivity,
We have found that the objective can be achieved by slow cooling, and based on this knowledge, we have developed the present invention. The present invention uses CaCO coated with carbon black with particle size loops or less when continuously spinning medium carbon steel that solidifies through a peritectic reaction with carbon content of 0.08 to 0.16%.
This is a continuous casting method for medium carbon steel characterized by using mold powder containing s.

<Saku Kawa> In the present invention, wI.
IW powder containing CaCO1 was used. CaCO. When the mold powder is melted, the generated gas flows in through bubbles, and the pore area ratio in the powder film after solidification increases even without solidification of the powder film, and the amount of heat removed from the mold becomes small (first Figure (a
)reference). In other words, pores are formed in the mold powder film 7 in the gap between the solidified shell 6 and the mold 9 to reduce thermal conductivity, cool the molten steel slowly, and cast a defect-free slab with no vertical cracks on the slab surface. (See Figure 1(b)). The operation of the present invention will be explained in more detail. The pores in the conventional powder film 111 after being introduced and solidified are generated as the powder film crystallizes. Crystallization of the powder film increases the frictional force between the slab and the mold, which impedes casting stability, increases the possibility of breakout, and increases the occurrence of gluing, which is unfavorable in terms of quality. ．． Now, we will explain how to increase the pore area ratio without crystallizing the powder film. In continuous Sjuzo of steel, c, stop, eight ZtOst CaO, Mano
It is common to use continuous casting powder containing rF as the main component. The purpose of using the powder is to prevent solidification and oxidation of the molten steel surface by coating and insulating the surface of the molten steel in the mold, to prevent inclusions on the surface of the slab by absorbing non-metallic inclusions that emerge from the molten steel, and to protect the mold and Sli. By uniformly inflowing lubrication between the slabs, breakouts are prevented and cracks are prevented from occurring on the slab surface. In particular, breakouts and scratches on the slab surface are prevented by setting the viscosity of the powder after melting within an appropriate range according to the drawing speed. In the present R91, a component that generates gas when melted, such as CaCO3, is mixed into these main components, and the pore area ratio in the powder film is increased without crystallizing the powder film due to bubbles of the generated gas. The aim is to increase the amount of heat removed from the mold by increasing it. Gas is generated even with Ca(Ollt), etc., but since generation for 1 hour is unfavorable in terms of surface quality, carbon dioxide or an organic resin that generates gas is preferable.
Figure 2 shows a schematic diagram of the shape of mold powder on molten steel during continuous VT casting.* Can of C a CO 2 and CO. The decomposition reaction occurs in the molten layer, where the temperature increases as it descends from the semi-molten layer 4 to the molten layer 3 in FIG. In normal cases, bubbles rise into the atmosphere? Although it may seem like a waste of time, the CO2 gas bubbles that decompose near the copper casting mold 9 flow into the space between the mold and slab together with the molten powder before rising and escaping into the atmosphere. A more advantageous way to do this is to coat it with carbon black.
Since the particle size of this carbon black needs to be evenly attached to the base material particles, it is necessary to adhere to the base material particles evenly.
Im or less is preferable. On the other hand, the degree of crystallization of the powder film can be controlled by adjusting the crystallization temperature of the base material, which is the main component of the mold powder, so the pore area ratio can be controlled independently of the crystallization of the powder film. In addition, when a large amount of carbonate powder is used, the CO gas generated generates dust, which worsens the working environment, but this is a particular problem because most of the current methods use automatic dosing machines to introduce powder into molds. This is not the case. <Examples> Examples according to the present invention will be described below. The composition of the medium carbon steel used in the Examples and Conventional Examples is shown in Table 1, and the mold powder used in the Examples and Conventional Examples is shown in Table 2.
The CaCOs used in the examples were coated with carbon black having a particle size of 100 #1 or less. Continuous casting was performed using the above medium carbon steel and mold powder under the following operating conditions. OvI type vibration condition stroke: 7.8m N. S rate: lO%0 (negative strip rate) *0) According to formula F: Mold vibration frequency (Cρ-) vll: Drawing speed (m/m) 0 drawing speed 1.45 ~ 1.48 m / mw + O slab dimensions Width 600m, thickness 100am? Temperature of molten steel heating in the mold ΔT = 14-19°C (representative point) Test casting was performed under the above conditions, and the powder film near the meniscus was detected and observed using a W4 microscope. The relationship between the amount of heat removed from the mold and the pore area ratio at that time is shown in section A in Figure 1(a). As expected, due to the generation of CO gas, the pore area ratio increased to about 15 compared to the conventional powder (marked with ●).
% (recently 13.5%), and the amount of heat extracted from the mold is also decreasing. In addition, the relationship between the vertical crack occurrence index on the slab surface and the pore area ratio is shown in Figure 1 (part A in BL).
Compared to the conventional powder (marked with ●), both the vertical cracking index and the pore area ratio are significantly reduced. The degree of occurrence of longitudinal cracks was quantified and used as a longitudinal crack occurrence index, and the results are shown in Table 3. It was found that the method of the present invention has a remarkable effect on suppressing longitudinal cracks. In addition, the viscosity of conventional powder is 1 at 1300℃.
．． It was 5 poise. There was also concern that the surface quality of the slab would be damaged due to the generation of gas, but the pinholes and plowholes on the surface were the same as with conventional powder! there were. Effects of the Invention> As described above, according to the method of the present invention, in continuous casting of medium carbon steel, it is possible to produce slabs with significantly fewer vertical cracks on the slab surface than in the past.

[Brief explanation of drawings]

Figure 1 (a) is a characteristic diagram showing the relationship between the pore area ratio in the powder film and the amount of heat removed from the mold, and Figure 1 (b) is the relationship between the pore area ratio in the powder film and the vertical crack occurrence index. Figure 2 is a schematic diagram showing the state of the powder in the mold. l... Molten steel, 3... Molten layer, 5... Powder layer? Grain layer, 7... Powder film, 9... Cast copper plate. 2... Hot water surface, 4... Semi-molten layer, 6... Solidified shell, 8... Slap bear,

Claims (1)

[Claims] When continuously casting medium carbon steel that solidifies through a peritectic reaction with a carbon content of 0.08 to 0.16% by weight, a grain size of 100
A continuous casting method for medium carbon steel, characterized in that a mold powder containing CaCO_3 coated with carbon black of micrometer or less is used.