Method for manufacturing high-silicon steel strip by continuous siliconizing

Abstract

A high-silicon steel strip is manufactured. A basic configuration includes partition plates arranged in the longitudinal direction of a furnace to extend from a position in the vicinity of respective gas nozzles to be in parallel to the pass line of the steel strip, and obstacles arranged to face partition-plate rear edges in the longitudinal direction of the furnace to obstruct the flow of the gas along the steel strip so that siliconizing spaces surrounded by the steel strip, the partition plates, and the obstacles are formed; and gaps between the partition-plate rear edges and the obstacles and so forth which form exhaust passages through which gas is discharged from the siliconizing spaces to other spaces inside the furnace so that treatment gas which has been sprayed from the gas nozzles onto a surface of the steel strip to flow through the siliconizing spaces is discharged through the exhaust passages.

Claims

1. A method for manufacturing a high-silicon steel strip in which treatment gas containing Si compounds is sprayed onto a steel strip traveling through a horizontal-type continuous siliconizing furnace to perform a siliconizing treatment on the steel strip, the method comprising: using a continuous siliconizing furnace including gas nozzles (1) arranged above and below a pass line of the steel strip at intervals in a longitudinal direction of the furnace to spray treatment gas onto the steel strip traveling through the furnace, partition plates (2) arranged above and below the pass line of the steel strip in the longitudinal direction of the furnace to extend from a position in the vicinity of the respective gas nozzles (1) to be substantially in parallel to the pass line of the steel strip, and obstacles (3) arranged to face partition-plate rear edges (20) in the longitudinal direction of the furnace to obstruct a flow of the gas along the steel strip, in which spaces surrounded by the traveling steel strip, the partition plates (2), and the obstacles (3) (the spaces excluding a portion in the longitudinal direction where the steel strip is not substantially siliconized) form siliconizing spaces (s) where the steel strip is siliconized by the treatment gas, gaps (e.sub.a) between the partition-plate rear edges (20) and the obstacles (3), and gaps (e.sub.b) between partition-plate side edges (21) and an inner wall of the furnace (the gaps excluding a portion of gaps through which the treatment gas flowing through the siliconizing spaces (s) is not substantially discharged), form exhaust passages (e) through which gas is discharged from the siliconizing spaces (s) to other spaces inside the furnace, and the treatment gas which has been sprayed from the gas nozzles (1) onto a surface of the steel strip to flow through the siliconizing spaces (s) (the treatment gas containing by-products generated by a reaction with the steel strip) is discharged through the exhaust passages (e); and performing the siliconizing treatment under a condition that satisfies relational expressions below:
A=TWL.sub.S10.sup.3/([V.sub.S].sup.1/2S.sub.o),
0.005<A<0.750, where, S.sub.o: total area (mm.sup.2) of the exhaust passages (e) formed above and below the pass line of the steel strip, V.sub.S: total volume (mm.sup.3) of the siliconizing spaces (s) formed above and below the pass line of the steel strip, L.sub.S: length (mm) of the steel strip in the siliconizing spaces (s), W: width (mm) of the steel strip, and T: thickness (mm) of the steel strip.

2. The method for manufacturing a high-silicon steel strip by continuous siliconizing according to claim 1, wherein the siliconizing treatment is performed under a condition that satisfies a relationship of
0.040A0.700.

3. The method for manufacturing a high-silicon steel strip by continuous siliconizing according to claim 1, wherein the obstacles (3) below the pass line of the steel strip are hearth rolls for transporting the steel strip.

4. The method for manufacturing a high-silicon steel strip by continuous siliconizing according to claim 2, wherein the obstacles (3) below the pass line of the steel strip are hearth rolls for transporting the steel strip.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates an embodiment of a method according to aspects of the present invention, where FIG. 1(a) is a diagram illustrating a vertical sectional view of a continuous siliconizing furnace and FIG. 1(b) is a diagram illustrating a horizontal sectional view of the continuous siliconizing furnace.

(2) FIGS. 2(a) and 2(b) are diagrams illustrating regions of siliconizing spaces s and exhaust passages e of FIGS. 1(a) and 2(b) respectively.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(3) One aspect of the present invention is a method for manufacturing a high-silicon steel strip, the method including performing a siliconizing treatment on a steel strip by spraying treatment gas containing Si compounds onto the steel strip traveling through a horizontal-type continuous siliconizing furnace. Here, the term high-silicon steel strip generally denotes a steel strip having a Si content (average concentration) of 3.0 mass % or more.

(4) FIG. 1 illustrates an embodiment of a method according to aspects of the present invention, where FIG. 1(a) is a diagram illustrating a vertical sectional view of a continuous siliconizing furnace and FIG. 1(b) is a diagram illustrating a horizontal sectional view of the continuous siliconizing furnace. In FIG. 1, reference sign 4 indicates a furnace body (furnace wall), reference sign 5 indicates a heating device, reference sign 6 indicates a steel strip horizontally traveling through the furnace, and reference sign 7 denotes a hearth roll for transporting a steel strip.

(5) Here, although the direction of gas flow is opposite to the transport direction of the steel strip 6 in the longitudinal direction of the furnace in the present embodiment, the direction of gas flow and the moving direction of the steel strip 6 may be the same.

(6) This continuous siliconizing furnace has plural gas nozzles 1, and partition plates 2 and obstacles 3 for forming siliconizing spaces s corresponding to the respective gas nozzles 1.

(7) The gas nozzle 1 described above is used for spraying treatment gas onto a traveling steel strip 6 from above or below the traveling steel strip 6, and plural nozzles (plural pairs, where one pair consists of an upper gas nozzle and a lower gas nozzle) are arranged above and below the pass line of the steel strip at intervals in the longitudinal direction of the furnace.

(8) In accordance with aspects of the present invention, treatment gas is supplied to a steel strip to be subjected to a siliconizing treatment by using a method in which the treatment gas is sprayed onto both surfaces of the steel strip from the gas nozzles 1 in order to increase the reaction efficiency of the treatment gas. By spraying the treatment gas onto the steel strip from the plural gas nozzles 1 arranged at intervals in the longitudinal direction of the furnace, a continuous siliconizing treatment is realized.

(9) The partition plates 2 are arranged above and below the pass line of the steel strip in the longitudinal direction of the furnace to extend from a position in the vicinity of the respective gas nozzles 1 to be substantially in parallel to the pass line of the steel strip. As described below, such partition plates 2 form siliconizing spaces s along with the steel strip 6 and the obstacles 3 so that the treatment gas which is sprayed onto the steel strip 6 is prevented from flowing away from the steel strip 6 (allowed to stay around the steel strip). In addition, the partition plates 2, which are members for preventing atmosphere gas in the furnace from entering the siliconizing spaces s, are arranged at a certain distance from the pass line of the steel strip so that the treatment gas which is sprayed onto the steel strip from the gas nozzles 1 is allowed to directly enter the siliconizing spaces s.

(10) The obstacles 3 described above are arranged to face the partition-plate rear edges 20 in the longitudinal direction of the furnace (the partition-plate edges on the side opposite to the gas nozzles 1 in the longitudinal direction of the partition plates) in order to obstruct the gas flow along the steel strip. Any configuration may be used for the obstacles 3 as long as it is possible to functionally obstruct the gas flow. In the present embodiment, each of the obstacles 3 above the pass line of the steel strip is composed of a plate-like member which is vertically arranged, and each of the obstacles 3 below the pass line of the steel strip is composed of a hearth roll 7 for transporting the steel strip. The plate-like member, of which the upper obstacle 3 is composed, is arranged so that the upper edge of the member is positioned higher than the upper surface of the partition plate 2 and so that the lower edge of the member is close to the pass line of the steel strip and directly above the hearth roll 7 (obstacle 3 below the pass line).

(11) Here, each of the obstacles 3 below the pass line of the steel strip may also be composed of, for example, a plate-like member as in the case of the upper obstacles 3. In this case, the plate-like member, of which the lower obstacle 3 is composed, is arranged so that the lower edge of the member is lower than the lower surface of the partition plate 2 and so that the upper edge of the member is close to the pass line of the steel strip.

(12) Spaces which are surrounded by the traveling steel strip 6, the partition plates 2, and the obstacles 3 form siliconizing spaces s in which the steel strip is siliconized by the treatment gas. Here, such siliconizing spaces s are limited to spaces in which the siliconizing reaction of the steel strip 6 substantially occurs. Therefore, as illustrated in FIG. 1, in the case where the point p at which the treatment gas sprayed from the gas nozzle 1 is brought into contact with the surface of the steel strip is located within the space formed by the partition plates 2 and the steel strip 6, since a siliconizing reaction does not substantially occur in the portion of the space on the side of the gas nozzles from the point p, such a portion of the space is excluded from the siliconizing space s.

(13) In addition, gaps e.sub.a between the partition-plate rear edges 20 and the obstacles 3 and gaps e.sub.b between the partition-plate side edges 21 (both side edges) and the inner wall of the furnace form exhaust passages e through which gas is discharged from the siliconizing spaces s to other spaces inside the furnace. Here, such gaps e.sub.b are limited to the portion through which the treatment gas flowing in the siliconizing spaces s is substantially discharged. Therefore, as illustrated in FIG. 1, in the case where the point p at which the treatment gas sprayed from the gas nozzle 1 is brought into contact with the surface of the steel strip is located within the space formed by the partition plates 2 and the steel strip 6, since the treatment gas is not substantially discharged through the portion of the gaps on the side of the gas nozzles from the point p, such a portion of the gaps is excluded from the gaps e.sub.b.

(14) In FIG. 2, respective regions of the siliconizing spaces s and exhaust passages e (gaps e.sub.a+gaps e.sub.b) are illustrated by a hatched pattern with dashed lines.

(15) The siliconizing spaces s and the exhaust passages e formed by the partition plates 2 and the obstacles 3 as described above are provided for the respective gas nozzles 1.

(16) Here, in the case where a steel strip is subjected to a siliconizing treatment in a continuous siliconizing furnace, it may be taken into a consideration that the whole space in the furnace is used as a siliconizing space without forming siliconizing spaces s separated by partition plates 2 as in the case of aspects of the present invention. However, since it is necessary to place at least heating devices 5, hearth rolls 7 for transporting a steel strip, and gas nozzles 1 in a furnace in order to industrially manufacture a high-silicon steel strip by continuously performing a siliconizing treatment on a steel strip at a high temperature, a large space is necessary in the furnace. Since treatment gas which is sprayed onto the surface of a steel strip from gas nozzles 1 flows away from the steel strip 6 and diffuses in such a large space in the furnace, it is not possible to achieve sufficient reaction efficiency. Therefore, it is necessary to promote a reaction through atmosphere siliconizing by forming siliconizing spaces s through the use of partition plates 2 in order to allow treatment gas to stay around a steel strip.

(17) In addition, in the case where the edges of a steel strip 6 traveling through a furnace are close to the inner wall surface of the furnace, gas does not move smoothly between the siliconizing spaces s above and below the pass line of the steel strip. Therefore, it is necessary to form an exhaust passage e for each of the siliconizing spaces s above and below the pass line of the steel strip.

(18) From the gas nozzles 1, treatment gas is sprayed onto the surface of a steel strip at the entrance of the siliconizing spaces s. In FIG. 1 and FIG. 2, dashed arrows indicate the flow of the gas.

(19) Part of the treatment gas which is sprayed onto the surface of the steel strip from the gas nozzles 1 reacts with the steel strip 6 so that siliconizing occurs. In addition, since the unreacted treatment gas flows in the siliconizing spaces s and stays around the steel strip so that the gas reacts with the steel strip 6, further siliconizing occurs. Finally, the treatment gas containing by-products which has been generated by the reaction with the steel strip 6 is discharged through the exhaust passages e.

(20) As described above, in the case where siliconizing spaces s are formed by partition plates 2, if it is not possible to appropriately discharge by-products generated by a siliconizing reaction from the siliconizing spaces s, iron (iron chloride in the case where the treatment gas contains SiCl.sub.4) in the treatment gas which has been replaced with silicon adheres again to the surface of the steel strip, causing a problem of a deterioration in the surface quality of the steel strip. Therefore, it is not possible to satisfy the following requirements at the same time, that is, requirement (i) that the reaction efficiency of treatment gas be increased, and requirement (ii) that good surface quality of a steel strip be achieved.

(21) Therefore, in accordance with aspects of the present invention, in the continuous siliconizing furnace having the basic configuration described above, the relationship between the volume of the siliconizing spaces s and the area of the exhaust passages e is optimized in accordance with the amount of the steel strip in the siliconizing spaces s, and a siliconizing treatment is performed under the condition that satisfies the relational expressions below.
A=TWL.sub.S10.sup.3/([V.sub.S].sup.1/2S.sub.o), 0.005<A<0.750,

(22) where, S.sub.o: total area (mm.sup.2) of the exhaust passages (e) arranged above and below the pass line of the steel strip,

(23) V.sub.S: total volume (mm.sup.3) of the siliconizing spaces (s) arranged above and below the pass line of the steel strip,

(24) L.sub.S: length (mm) of the steel strip in the siliconizing spaces (s),

(25) W: width (mm) of the steel strip, and

(26) T: thickness (mm) of the steel strip.

(27) In the case of such a siliconizing treatment, since treatment gas sprayed onto the steel strip 6 stays around the steel strip as a result of its flowing in the siliconizing spaces s, the reaction between the gas and the steel strip is promoted. In addition, atmosphere gas in the furnace does not enter the siliconizing spaces. Therefore, it is possible to achieve high reaction efficiency of the treatment gas. On the other hand, since it is possible to appropriately discharge by-products generated by a siliconizing reaction from the siliconizing spaces s, it is possible to prevent a deterioration in the surface quality of a steel strip due to iron in the treatment gas which has been replaced with silicon again adhering to the surface of the steel strip. Therefore, it is possible to manufacture a high-silicon steel strip having good surface quality with a high reaction efficiency.

(28) In addition, in order to further increase the effects described above, it is preferable to perform a siliconizing treatment under the condition that satisfies the relational expression below, which imposes a severer limitation.
0.040A0.700

(29) It is preferable that A be 0.040 or more, or more preferably 0.070 or more, because this results in a higher reaction efficiency.

EXAMPLES

(30) By performing a siliconizing treatment on steel strips (3.0-mass %-Si containing materials) having a thickness of 0.1 mm by treatment gas containing SiCl.sub.4 in a continuous siliconizing furnace having the equipment configuration illustrated in FIG. 1, high-silicon steel strips (6.5-mass %-Si materials) were manufactured. At that time, the total volume V.sub.S of siliconizing spaces s and the total area S.sub.o of exhaust passages e were changed, and the reaction efficiency of the treatment gas and the surface quality of the high-silicon steel strip manufactured were investigated. The results are given in Table 1.

(31) Here, it is particularly desirable that the reaction efficiency be 0.2 or more. On the other hand, in the case where the reaction efficiency is less than 0.1, there is a significant decrease in efficiency and an increase in cost from the viewpoint of industrial production. Therefore, a case of a reaction efficiency of 0.20 or more was judged as Excellent, a case of a reaction efficiency of 0.15 or more and less than 0.20 was judged as Good, a case of a reaction efficiency of 0.10 or more and less than 0.15 was judged as Fair, and a case of a reaction efficiency of less than 0.10 was judged as Poor. Then, the cases of Excellent, Good, and Fair were judged as satisfactory.

(32) As Table 1 indicates, it was not possible to achieve sufficient reaction efficiency in the case where the value of A was less than the range according to aspects of the present invention. On the other hand, in the case where the value of A was more than the range according to aspects of the present invention, since the amount of gas discharged from the siliconizing spaces s was insufficient due to the area of the exhaust passages e being insufficient, there was a deterioration in the surface quality due to iron powder adhering to the surface of the steel strip.

(33) In addition, among the examples of the present invention, in the case where the value of A was 0.040 to 0.700, it was possible to achieve particularly high reaction efficiency and an excellent surface quality.

(34) TABLE-US-00001 TABLE 1 Steel Strip Size (mm) Total Total Length L.sub.s Volume Area of Steel V.sub.s of S.sub.o of Evaluation Result Strip in Siliconizing Exhaust Surface Reaction Thickness Width Siliconizing Spaces Passages Value Quality of Efficiency No. T W Spaces s s (mm.sup.3) e (mm.sup.2) of A Steel Strip *1 Class 1 0.1 600 1000 121,500,000 53,000 0.103 Good 0.25 Excellent Example 2 0.1 600 1000 121,500,000 7,800 0.698 Good 0.31 Excellent Example 3 0.1 600 1000 121,500,000 7,250 0.751 Poor 0.32 Excellent Comparative (Iron Example Powder Adhesion) 4 0.1 450 1000 121,500,000 53,000 0.077 Good 0.26 Excellent Example 5 0.1 450 1000 121,500,000 100,000 0.041 Good 0.18 Good Example 6 0.1 450 1000 720,000,000 240,000 0.007 Good 0.12 Fair Example 7 0.1 410 1000 45,000,000 1,260,000 0.005 Good 0.05 Poor Comparative Example *1 reaction efficiency = (the amount of SiCl.sub.4 used for reaction)/(the amount of SiCl.sub.4 supplied to the furnace)

REFERENCE SIGNS LIST

(35) 1 gas nozzle 2 partition plate 3 obstacle 4 furnace body 5 heating device 6 steel strip 7 hearth roll 20 partition-plate rear edge 21 partition-plate side edge s siliconizing space e.sub.a, e.sub.b gap e exhaust passage