CONTINUOUS CASTING METHOD FOR AUSTENITIC STAINLESS STEEL

Abstract: This invention proposes a continuous casting method for austenitic stainless steel capable of simultaneously establishing productivity and an excellent surface quality of steel sheet. For this purpose, the invention lies in a method of continuously casting austenitic stainless steel by pouring melt of austenitic stainless steel from a tundish through an immersion nozzle into a continuously casting mold of a continuous slab caster, solidifying it in the mold and continually drawing the resulting slab of given size out from the mold, characterized in that a high-speed continuous casting is carried out so as to satisfy a relation of casting speed, superheating degree of molten steel in the tundish, sectional area of discharge port in the immersion nozzle and slab width represented by the following equation: 0.30 ≦ V 0.58 ·W -0.04 ·ΔT·d -0.96 ≦ 0.85 wherein V: casting speed (m/min) W: slab width (mm) ΔT: superheating degree of molten steel in tundish (°C) d: square root of sectional area of nozzle discharge port (mm).

Description: TECHNICAL FIELD This invention relates to a method of continuously casting austenitic stainless steel, and more particularly to a continuous casting method which simultaneously enables surface defects to be prevented and high-speed casting to be carried out. BACKGROUND ART In the production of stainless steel sheets, it is strongly demanded that the sheet surface is more attractive as compared with the surface of other general-purpose steel sheets. Thus a reduction of surface defects needs to be attained even when continuous casting stainless steel. A well known conventional technique for reducing surface defects of austenitic stainless steel sheets involves controlling the cooling rate over a region ranging from the solids temperature of the surface solidification layer portion up to at least 1200°C so as to attain the formation of fine austenite grains as disclosed in JP-A-63-192537. It is also known to control the molten steel components and the superheating degree of the molten steel to attain the formation of fine austenite grains as disclosed in JP-A-3-42150. Recently, the demand for product quality has become increasingly strict. To this end, there has been proposed the individual control of the cooling rate, the superheating degree of the molten steel and the like, but it can not be said that such a mere control is sufficient because surface defects are still created. On the other hand, there have recently been demands to increase the casting speed even when continuous casting in order to improve productivity. However, when the casting speed is increased, there is a tendency for surface defects to be superfluously created. Hitherto therefore, if it is desired to increase the casting speed, it can not be increased sufficiently having regard to the surface quality. Hence the casting speed had to be selected at a low level within a sufficient range and thus an adequate standard and the desired improvement in productivity could not be attained. It is an object of the invention to favorably solve the aforementioned problems in the continuous casting of austenitic stainless steel and to provide a continuous casting method for austenitic stainless steel capable of simultaneously attaining high productivity and excellent surface quality of the steel sheet. According to the present invention there is provided a method of continuously casting austenitic stainless steel by pouring a melt of austenitic stainless steel from a tundish through an immersion nozzle into a continuous casting mold of a continuous slab caster, solidifying it in the mold, and continually drawing the resulting slab of given size out of the mold, characterized in that the continuous casting is carried out at a casting speed of not less than 1.2 m/min and so that the casting speed, the superheating degree of the molten steel in the tundish, the sectional area of the discharge port of the immersion nozzle, and the slab width satisfy the following equation: 0.30 ≤ V 0.58 · W -0.04 · ΔT · d -0.96 ≤ 1.40 wherein V = casting speed (m/min), W = slab width (mm), ΔT = superheating degree of the molten steel in the tundish (°C), and d = the square root of the sectional area of the immersion nozzle discharge port (mm) facing one short side of the mold. provided that said equation has a value of from ≥ 0.30 to ≤ 0.85 in the case where the slab is a thick slab and said equation has a value of from ≥ 0.50 to ≤ 1.40 in the case where the slab is a thin slab produced using a vertical-type twin belt caster or a block caster. Moreover, a casting speed V of not less than 3.0 m/min is particularly advantageous when the continuous slab caster is a vertical-type twin belt caster or a block caster for the continuous production of thin slab. As the immersion nozzle according to the invention, a multi-hole nozzle is particularly favorable. In the case of a multi-hole nozzle, the sectional area of the nozzle discharge port is the total sectional area of the nozzle openings facing a short side of the mold for the continuous casting (e.g. the sectional area of the nozzle opening at one side in the case of a two-hole nozzle, or the total sectional area of the two nozzle openings facing a short side of the mold in case of a four-hole nozzle). As a result of the inventors' studies, it has been found out that the formation of a fine internal solidification structure of austenite grains in the surface layer portion of the cast slab and the reduction of microsegregation of impurity elements accompanied therewith are important for improving the surface properties of the cast slab and hot workability. Furthermore, it has been deduced that, since the solidification structure in the austenite grains is dendritic, in order to form the fine solidification structure it is necessary to control the heat input quantity (Qm) from the molten steel jetted through the discharge port of the immersion nozzle to the initial solidification shell formed just beneath the meniscus portion in the mold of the continuous caster. Moreover, it has been found that the casting speed V, the superheating degree of the molten steel ΔT, the width W of the slab and, the sectional area A of the discharge port of the immersion nozzle in the mold are important parameters for controlling the heat input quantity Qm. As a result, it has been found that cast slabs having a high quality can be obtained even at a high casting speed by controlling these four parameters so as to satisfy a given relationship. According to the studies of Kumada et al (Journal of the Japan Institute of Mechanics, 35 (1969)) and Nakado et al (TETSU-TO-HAGANE, 67(1981), p.1200), the heat input quantity Qm is said to be represented by the following equations: Qm = hm · ΔT hm = 1.42 (k/d 1 ) x (Vn·d 1 ·ρ/η) 0.58 x (C·η/k) 0.43 x (X/d 1 ) -0.62 wherein hm = the heat transfer coefficient, k = the thermal conductivity of the shell, ρ = the density of the molten steel, η = the viscosity of the molten steel, C = the specific heat of the molten steel, d 1 = the nozzle diameter, Vn = the flow rate of the molten steel at the discharge port, and X = the disfance between the discharge port and the collision point. However, most of the parameters in the above equation (1) are unknown in an actual mold of a continuous caster and can not be applied to the actual caster as they are. The inventors have made studies with respect to the application to an actual continuous caster considering the facts that the relationship between the casting speed V and the flow rate Vn of the molten steel at the discharge port is V ∞ Vn (V is proportional to Vn, same as above), the relationship between the width W of the slab and the flow rate Vn of the molten steel at the discharge port is W ∞ Vn, the relationship between the width W of the slab and the distance X between the discharge port and the collision point is W ∞ X, and the thermal conductivity k of the shell, the density p of the molten steel, the viscosity η of the molten steel and the specific heat C of the molten steel are constant and have found out that the above equation (1) can be rewritten as the following equation (2): qm = V 0.58 ·W -0.04 ·ΔT·d -0.96 wherein qm = the index of heat input quantity, V = the casting speed (m/min), W = the slab width (mm), ΔT = the superheating degree of the molten steel in the tundish (°C), and d = the square root (mm) of the sectional area of the nozzle discharge port (one-side of a two-hole nozzle). Thus, the maximum casting speed capable of ensuring the quality of the steel sheet in accordance with the superheating degree of the molten steel, the slab width and the sectional area of the nozzle discharge port can be deduced by previously determining the maximum value of the index of heat input quantity qm which does not cause surface defects whereby high productivity and high quality can simultaneously be established. Moreover, when the index of heat input quantity qm is too small, the fusion of the mold powder is insufficient and hence adhesion of unfused mold powder to the cast slab occurs which results in surface defects in the steel sheet. Therefore, the lower limit of the heat input quantity is defined from such a viewpoint. The experiment conducted for defining the upper limit and lower limit of the heat input quantity will be described below. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a graph showing the relationship between the index of heat input quantity and the surface defect occurring ratio of a cold rolled steel sheet; Fig. 2 is a graph showing the relationship betwen the superheating degree of the molten steel and the secondary dendrite arm spacing; Fig. 3 is a graph showing the relationship between the casting speed and the secondary dendrite arm spacing; Fig. 4 is a graph showing the relationship between the slab width and the secondary dendrite arm spacing; Fig. 5 is a graph showing the relationship between the sectional area of the nozzle discharge port and the secondary dendrite arm spacing; Fig. 6 is a graph showing the relationship between the index of heat input quantity and the secondary dendrite arm spacing; and Fig. 7 is a graph showing the relationship between the index of heat input quantity and the surface defect occurring ratio of a cold rolled steel sheet in the continuous casting operation using a twin belt caster. The casting of 18 wt% Cr - 8 wt% Ni steel (SUS 304) having the chemical composition shown in Table 1 was carried out under various conditions of immersion nozzle (two-hole nozzle), casting speed, superheating degree of the molten steel and slab width as shown in Table 2. Moreover, the thickness of the slab was 200 mm. In order to examine the degree to which the surface layer portion of the slab obtained in this continuous casting had a fine solidification structure, the solidification structure at a depth of 4 mm from the slab surface was inspected to evaluate the formation of fine structure by large and small size of secondary dendrite arm spacing. Thereafter, the cast slab was subjected to hot rolling, cold rolling and pickling to obtain a steel sheet having a thickness of 1.4 mm as a product, which was subjected to visual inspection for the evaluation of the surface quality. The surface defects of the steel sheet were examined by this visual inspection to determine the defect occurring ratio. The defect occurring ratio was defined as a defect occurring index expressed as (length of rejected portion based on the defect)/(full length of steel sheet) x 100. Immersion nozzle in mold Sectional area of one-side discharge port (mm 2 ) 2500 ∼ 5000 Discharging angle (°) 35 downward ∼ 10 upward Casting speed (m/min) 0.6 ∼ 1.6 Superheating degree of molten steel (°C) 10 ∼ 80 Slab width (mm) 700 ∼ 1300 The experimental results for the secondary dendrite arm spacing of the continuously cast slab are shown graphically in Figs. 2-5 as a function of the superheating degree ΔT of the molten steel, the casting speed V, the slab width W and the sectional area A of the nozzle discharge port (sectional area per one hole of a two-hole nozzle). As can be seen from Figs. 2-5, the secondary dendrite arm spacing tends to become large with an increase in the superheating degree ΔT, the casting speed V and the slab width W and with a decrease in the sectional area A of the nozzle discharge port. As can be seen from the relationship between the casting speed V and the secondary dendrite arm spacing (Fig. 3), the scattering is particularly large because the slab width, the superheating degree of the molten steel and the diameter of the discharge port in the immersion nozzle differs. Thus these parameters can not be used as an indication for the fine formation of austenite grain and hence as an indication of surface quality. Now, the index of heat input quantity qm shown by the above equation (2) was calculated for every casting condition and the relationship between the index of heat input quantity qm and the secondary dendrite arm spacing is graphically shown in Fig. 6. From this figure, it is clear that the index of heat input quantity qm has a strong interrelation to the secondary dendrite arm spacing at 2-4 mm beneath the slab surface substantially corresponding to the surface defect depth of a rolled sheet product. Furthermore, the relationship between the index of heat input quantity qm and the occurring ratio of surface defects is shown in Fig. 1. From Fig. 1, it is also clear that the index of heat input quantity qm has a strong interrelation with the surface defect occurring ratio of the product and steel sheets having good quality are obtained when the index of heat input quantity qm is not more than 0.85. That is, when the index of heat input quantity qm is not more than 0.85, the secondary dendrite arm spacing at a position 4 mm below the surface is not more than about 30 µ m as seen from Fig. 6. Further when the index of heat input quantity qm is not more than 0.6, the secondary dendrite arm spacing is not more than 25 µm, whereby the occurrence of surface defect is even more mitigated. On the other hand, when the heat input quantity in the vicinity of the meniscus is too small and hence the index of heat input quantity qm is less than 0.30, adhesion of mold powder is caused, due to infusion of the powder as previously mentioned, to create defects in the steel sheet as shown in Fig. 1. Therefore, it is necessary that the index of heat input quantity qm defined by equation (2) is not less than 0.30 in view of the desired quality. In the casting method according to the invention, even when the high-speed casting is carried out at a casting speed of not less than 1.2 m/min, preferably not less than 3.0 m/min, the occurrence of surface defects can be prevented by optimizing the diameter of the nozzle discharge port and the superheating degree of the molten steel. In the conventional method, if it is intended to conduct high-speed casting at a casting speed of not less than 1.2 m/min, the index of heat input quantity qm has frequently exceeded 0.85 and hence surface defects have been created. Thus the casting speed could not be enhanced and was about 1.2 m/min at most. The continuously casting machine used in the invention includes not only general-purpose continuous slab casters but also vertical type twin belt casters or block casters for the casting of thin slabs having a thickness of 20-100 mm. As disclosed, for example, in KAWASAKI STEEL GIHO, Vol. 21, No. 3(1989) p.175-181, the vertical-type twin belt caster comprises a pair of endless belts arranged apart from each other in correspondence to the thickness of the thin slab to be cast and a casting space defined by a pair of short mold sides disposed on both side ends of the belt and having an upward-extended, downward-contracted shape (upward extending mold). The molten steel is poured into the upward extending mold through the immersion nozzle and then heat is removed from the molten steel by means of cooling pads arranged on the back side of the endless belt to cast a thin slab. When a slab having a given size is continuously cast by pouring a melt of austenitic stainless steel into the mold of a vertical-type twin belt caster or a block caster through the immersion nozzle and then solidifying it, the high-speed continuous casting can be carried out so that the following equation is satisfied : 0.50 ≦ V 0.58 ·W -0.04 ·ΔT·d -0.96 ≦ 1.40 The continuous casting of austenitic stainless steel has been carried out by variously changing the conditions of the superheating degree ΔT of the molten steel, the casting speed V, the slab width W and the sectional area A of the nozzle discharge port (sectional area per one hole in two-hole nozzle) in the upward extending mold of a vertical-type twin belt caster to obtain the results as shown in Fig. 7, from which it is apparent that when these parameters satisfy the condition of 0.50 ≦ V 0.58 ·W -0.04 ·ΔT·d -0.96 ≦ 1.40, the surface defects are reduced and a cast slab having a good quality is obtained. In such a continuous casting operation using the upward extending mold of the vertical-type twin belt caster, good surface properties are obtained at a higher casting speed as compared with continuous casting using the general-purpose continuous slab caster. This is considered to be due to the fact that in the case where a vertical-type twin belt caster is used, the thickness of the slab is relatively thin and the molten steel is rapidly cooled and hence surface defects hardly occur even at the higher casting speed. Moreover, when the value of V 0.58 · W -0.04 · ΔT · d -0.96 is less than 0.50, there are caused problems such as false wall, surface matting and the like accompanied with a decrease in the molten steel temperature, so that the lower limit of V 0.58 · W -0.04 · ΔT · d -0.96 in the case of a continuous caster for the production of thin slab is 0.50. Thus, it is possible to conduct high-speed casting at a casting speed V of not less than 3.0 m/min in a continuous casting operation using a vertical-type twin belt caster or a block caster. The following Examples illustrate the invention Example 1 Continuous casting was carried out by pouring molten steel comprising C: 0.04 wt%, Si: 0.52 wt%, Mn: 0.90 wt%, P: 0.02 wt%, S: 0.003 wt%, Ni: 9.2 wt%, Cr: 18.3 wt% and N: 0.028 wt% with the remainder being iron and inevitable impurities from a tundish through an immersion nozzle into a mold for the continuous casting, solidifying it in the mold and continually drawing out the resulting slab from the mold. During the continuous casting, the superheating degree AT of the molten steel in the tundish was 48°C, the sectional area of the discharge port in the immersion nozzle (two-hole type nozzle, discharging angle : 5° upward) was 4200 mm 2 per one hole, the slab width W was 1040 mm, the slab thickness was 200 mm, and the casting speed was 1.0 m/min. When the solidification structure of the resulting slab was inspected at a depth of 4 mm from the slab surface, the secondary dendrite arm spacing was 23 µ m. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product showed that the quality was good (qm = 0.66) without surface defects (defect occurring ratio: 0.07). Comparative Example 1 A slab was formed from molten steel having the same chemical composition as in Example 1 by the continuous casting method. In this case, the superheating degree ΔT of the molten steel in the tundish was 28°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 5° upward) was 4200 mm 2 per one hole, the slab width W was 1020 mm, the slab thickness was 200 mm, and the casting speed was 0.6 m/min. The secondary dendrite arm spacing of the resulting slab was 20 µ m when the solidification structure of the slab was inspected at a depth of 4 mm from the slab surface. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product, indicated the presence of defects due to the infusion of mold powder and hence the defect occurring ratio was 0.45 (qm = 0.28). Comparative Example 2 A slab was formed from molten steel having the same chemical composition as in Example 1 by the continuous casting method. In this case, the superheating degree ΔT of the molten steel in the tundish was 46°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 5° upward) was 3000 mm 2 per one hole, the slab width W was 1260 mm, the slab thickness was 200 mm, and the casting speed was 1.5 m/min. The secondary dendrite arm spacing of the resulting slab was 30 µm when the solidification structure of the slab was inspected at a depth of 4 mm from the slab surface. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product, showed that the structure was coarse and a defect occurring ratio of 0.6 (qm = 0.94). Example 2 Continuous casting was carried out by pouring molten steel comprising C: 0.06 wt%, Si: 0.70 wt%, Mn: 1.5 wt%, P: 0.04 wt%, S: 0.008 wt%, Ni: 10.2 wt%, Cr: 19.0 wt% and N: 0.045 wt% with the remainder being iron and inevitable impurities from a tundish through an immersion nozzle into a mold for the continuous casting, solidifying it in the mold and continually drawing out the resulting slab from the mold. During the continuous casting, the superheating degree ΔT of the molten steel in the tundish was 46°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 5° upward) was 4200 mm 2 per one hole, the slab width W was 1260 mm, the slab thickness was 200 mm, and the casting speed was 1.5 m/min. When the solidification structure of the resulting slab was inspected at a depth of 4 mm from the slab surface, the secondary dendrite arm spacing was 26 µm. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product showed that the quality was good (qm = 0.80) without surface defects (defect occurring ratio: 0.08). Example 3 Continuous casting was carried out by pouring molten steel having the same chemical composition as in Example 2 from a tundish through an immersion nozzle into a mold for the continuous casting, solidifying it in the mold and continually drawing out the resulting slab from the mold. During the continuous casting, the superheating degree ΔT of the molten steel in the tundish was 48°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 5° upward) was 4200 mm 2 per one hole, the slab width W was 1260 mm, the slab thickness was 200 mm, and the casting speed was 1.5 m/min. When the solidification structure of the resulting slab was inspected at a depth of 4 mm from the slab surface, the secondary dendrite arm spacing was 27 µm. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product indicated that the quality was good (qm = 0.83) without surface defects (defect occurring ratio: 0.07). Example 4 A Continuous casting was carried out by pouring molten steel comprising C: 0.06 wt%, Si: 0.70 wt%, Mn: 1.5 wt%, P: 0.04 wt%, S: 0.008 wt%, Ni: 10.0 wt%, Cr: 19.0 wt% and N: 0.045 wt% with the remainder being iron and inevitable impurities from a tundish through an immersion nozzle into a mold for the continuous casting, solidifying it in the mold and continually drawing out the resulting slab from the mold. During the continuous casting, the superheating degree ΔT of the molten steel in the tundish was 45°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 45° downward) was 200 mm 2 per one hole, the slab width W was 1040 mm, the slab thickness was 200 mm, and the casting speed was 1.6 m/min. When the solidification structure of the resulting slab was inspected at a depth of 4 mm from the slab surface, the secondary dendrite arm spacing was 26 µm. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product indicated that the quality was good (qm = 1.04) without surface defects (defect occurring ratio: 0.09). Comparative Example 3 A continuous casting was carried out by pouring molten steel having the same chemical composition as in Example 2 from a tundish through an immersion nozzle into a mold for the continuous casting, solidifying it in the mold and continually drawing out the resulting slab from the mold. During the continuous casting, the superheating degree ΔT of the molten steel in the tundish was 51°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 10° downward) was 2500 mm 2 per one hole, the slab width W was 1260 mm, the slab thickness was 200 mm, and the casting speed was 1.6 m/min. When the solidification structure of the resulting slab was inspected at a depth of 4 mm from the slab surface, the secondary dendrite arm spacing was 35 µm. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product indicated that the structure was coarse. The defect occurring ratio was 0.71 (qm = 1.15). Example 5 A continuous casting was carried out by pouring molten steel comprising C: 0.05 wt%, Si: 0.40 wt%, Mn: 1.05 wt%, P: 0.025 wt%, S: 0.005 wt%, Ni: 8.9 wt%, Cr: 18.0 wt% and N: 0.031 wt% with the remainder being iron and inevitable impurities from a tundish through an immersion nozzle into an upward extending mold of a vertical-type twin belt caster, solidifying it in the mold and continually drawing out the resulting thin slab from the mold. During the continuous casting, the superheating degree ΔT of the molten steel in the tundish was 39°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 60° downward) was 4000 mm 2 per one hole, the slab width W was 1700 mm, the slab thickness was 30 mm, and the casting speed was 5.0 m/min. When the solidification structure of the resulting slab was inspected at a depth of 0.5-1.0 mm from the slab surface, the secondary dendrite arm spacing was 23 µm. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product showed the quality to be good (qm = 1.37) without surface defects (defect occurring ratio: 0.09). Comparative Example 4 A thin slab was formed from molten steel having the same chemical composition as in Example 5 by the continuous casting method. In this case, the superheating degree ΔT of the molten steel in the tundish was 40°C, the sectional area of the discharge port of the immersion nozzle (two-hole type nozzle, discharging angle: 60° downward) was 3500 mm 2 per one hole, the slab width W was 1700 mm, the slab thickness was 30 mm, and the casting speed was 6.0 m/min. The secondary dendrite arm spacing of the resulting slab was 35 µm when the solidification structure of the slab was inspected at a depth of 0.5-1.0 mm from the slab surface. Thereafter, the slab was subjected to hot rolling, cold rolling and pickling according to the usual manner to obtain a steel sheet having a thickness of 1.4 mm. Visual inspection of the product indicated a coarse structure and a defect occurring ratio of 1.30 (qm = 1.67). When austenitic stainless steel is continuously cast by the continuous casting method according to the invention, the casting can be carried out at a higher casting speed in accordance with a given superheating degree of the molten steel while ensuring high quality whereby high quality and high productivity can simultaneously be obtained.

Claims: A method of continuously casting austenitic stainless steel by pouring a melt of austenitic stainless steel from a tundish through an immersion nozzle into a continuous casting mold of a continuous slab caster, solidifying it in the mold, and continually drawing the resulting slab of given size out of the mold, characterized in that the continuous casting is carried out at a casting speed of not less than 1.2 m/min and so that the casting speed, the superheating degree of the molten steel in the tundish, the sectional area of the discharge port of the immersion nozzle, and the slab width satisfy the following equation: 0.30 ≤ V 0.58 · W -0.04 · ΔT · d -0.96 ≤ 1.40 wherein V = casting speed (m/min), W = slab width (mm), ΔT = superheating degree of the molten steel in the tundish (°C), and d = the square root of the sectional area of the immersion nozzle discharge port (mm) facing one short side of the mold, provided that said equation has a value of from ≥ 0.30 to < 0.85 in the case where the slab is a thick slab and said equation has a value of from ≥ 0.50 to ≤ 1.40 in the case where the slab is a thin slab produced using a vertical-type twin belt caster or a block caster. A method of continuously casting austenitic stainless steel according to claim 1, wherein said equation has a value of from ≥ 0.50 to ≤ 1.40 and the casting speed V is not less than 3.0 m/min in the case where the slab is a thin slab produced using a vertical type twin belt caster or a black caster.

Inventors: BESSHO NAGAYASU, ITOYAMA SEIJI, MIKI YUJI, NOMURA HIROSHI, YAMADA SUMIO, BESSHO, NAGAYASU, ITOYAMA, SEIJI, MIKI, YUJI, NOMURA, HIROSHI, YAMADA, SUMIO, BESSHO, Nagayasu, Kawasaki Steel Corporation, ITOYAMA, Seiji, Kawasaki Steel Corporation, MIKI, Yuji, Kawasaki Steel Corporation, NOMURA, Hiroshi Kawasaki Steel Corporation, YAMADA, Sumio Kawasaki Steel Corporation
Applicants: KAWASAKI STEEL CO, KAWASAKI STEEL CORPORATION
Application year: 1996
Main classification: B22D11
IPC codes: B22D11