JPS61129257A - Manufacture of continuous casting mold - Google Patents

Abstract

PURPOSE:To form a copper mold for continuous casting of steel as a slowly cooled casting mold by working vertical grooves by chemical etching to a specified thickness or above of the Ni plating layer on the inside wall surface of said mold and subjecting the surface including such vertical grooves to 1 or >=2 kinds of Ni-P plating and Cr plating to a specific thickness or above. CONSTITUTION:The Ni plating layer having >=500mum thickness is provided on the inside wall surface of the copper mold for continuous casting of steel by an electroplating method using a sulfuric acid bath. The plating layer is chemically etched by an FeCl3 soln., by which the suitable grooves, for example, the grooves sized 280mum depth and 50mum wide are formed thereon. The surface thereof is subjected to 1 or >=2 kinds of the Ni-P plating and Cr plating to >=20mum by electroplating. The depth of the grooves is, for example, 280mum to 270mum in this case and the shape of the grooves changes hardly. The suitable groove depth is therefore maintained even after a surface treatment, by which the slow cooling effect of the mold is improved and the surface characteristic of an ingot is improved as well.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a mold for continuous casting of steel, and in particular to a method for manufacturing a mold for continuous casting in which grooves are provided on the inner wall of the mold that comes into contact with molten steel for the purpose of slow cooling. .

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The solidified shell in the mold is then cooled in a cold mold, solidified, and then pulled, but the solidified shell in this mold has unevenness on its surface due to the rapid cooling, resulting in a solidified shell with an uneven thickness.

For this reason, vertical cracks are likely to occur in the mold. If such cracks appear on the mold surface, it is necessary to remove the surface flaws before sending it to the rolling process.The production of solidified cells with such uneven thickness is currently attracting attention for its excellent thermoeconomic efficiency. This is an impediment to the application of direct feed heating (pot charge) or direct feed rolling (direct charge), which are currently being sought after.

As mentioned above, during continuous casting, molten steel is injected into a water-cooled copper mold and a solidified shell is produced. The thickness becomes non-uniform, and therefore thermal stress due to shrinkage acts on the thin part of the solidified shell, resulting in longitudinal cracking. Therefore, in order to prevent such vertical cracking in a continuous casting mold, it is possible to perform slow cooling to equalize the thickness of the so-called initial solidification shell that is generated in the upper part of the mold.

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In a publication published by Verlag GmbH (DUsseldorf), it is described that when continuously casting AQ, in order to improve the surface quality of the mold, the inner surface of the mold is provided with irregularities. Furthermore, P of No. 7 of 1968.

Perminov, et al.
n EnglishJ pages 560-562, 28
A similar statement can be found regarding billet casting of 0 x 280 mm. These reduce the area ratio of the contact area with the molten steel on the inner surface of the mold, resulting in slow cooling as a whole, while increasing the amount of heat removed per unit area of the contact area.
The aim is to eliminate unevenness in the amount of heat removed and achieve uniform cooling.

This idea is also seen in Japanese Patent Publication No. 57-11735, in which the dimensions of the recess are 2.5 mm or less in diameter or width, and the total area ratio of the cough recess is 20% or more, 90%. It is specified as below.

Furthermore, it is specified that the depth of the recesses is desirably 0.3 to 1.0 mm, and that the distance between the recesses is desirably about 1 to 31 mm.

Note that mechanical cutting methods and shot blasting methods are listed as methods for providing such uneven portions.

However, even in the method disclosed in the above-mentioned patent publication, in the case of a continuous casting mold, Ni is plated to a thickness of about 1 mm in order to extend its service life, and then Ni is plated on top of the Ni plating to a thickness of about 1 mm.
- Hard plating such as P alloy or Cr is used. When such thick plating is performed, as mentioned above,
It became clear that the shape of the groove formed into a predetermined shape changed significantly, and that the predetermined groove width or groove depth could not be ensured.

In such a case, the desired effect as a slow cooling mold cannot be obtained.

Furthermore, another method for slow cooling is to spray a refractory on the inner wall of the mold, which is in contact with the molten steel, in order to lower the thermal conductivity of the mold itself, which is made of Cu, which is a material with good thermal conductivity. . However, this method of spraying refractories is not practical because the refractories tend to peel off.

(Problems to be Solved by the Invention) Thus, the purpose of the present invention is to solve the problem of Ni-P alloy and C
It is an object of the present invention to provide a method for manufacturing a continuous casting mold that can maintain a predetermined shape even when hard plating such as r is applied.

A further object of the present invention is to provide a method for manufacturing a continuous casting mold having a vertical groove shape that has a slow cooling effect, that is, a vertical groove having a width of 750 μm or less and a depth of 60 μm or more. It is.

(Means for solving the problem) The present inventors continued their efforts to develop an excellent method that overcomes the drawbacks of the prior art as described above. Even if plating is applied, the original shape will not be preserved, but thick Ni plating is performed first, and this Ni
The present invention was completed by discovering that when a groove is formed on the plating by chemical corrosion, the thin shape is preserved even if a normal Ni-P alloy or Cr hard plating is applied afterwards.

Specifically, Ni plating is applied to a Cu plate to a thickness of 500 μm or more, narrow vertical grooves are formed in this old plating layer by chemical etching, and then harder Ni-P and/or Cr plating is applied.

Therefore, the gist of the present invention is to: (i) apply Ni plating to a thickness of 500 μm or more on a copper plate that is in contact with molten steel and forms the inner wall of a steel continuous casting mold;
ii) Machining vertical grooves in the obtained Ni plated layer by chemical corrosion, and (iii) further applying one or both of Ni-P plating and Cr plating to a thickness of 20 μm or more in the thus obtained vertical grooves. This is a method for manufacturing a continuous casting mold for the purpose of slow cooling, which is characterized by increasing the thickness of the mold.

Here, the Ni plating, Ni--P plating, Cr plating, and plating may be appropriately selected from conventional ones, and are not particularly limited. In either case, electroplating may be carried out using a sulfuric acid bath or a bath combined with fluoride. Although so-called electroless plating can also be used, electroplating is preferable because it provides thick plating.

Also, the chemical corrosion of the nickel plating layer is preferably 75 mm wide.
It is preferable to use the photoetching method in order to form vertical grooves with a depth of 0 μm or less and a depth of 60 μm or more. For example, a FeC/+3 solution can be used as the etchant. If necessary, electrolytic corrosion may be used in combination.

(Operation) Next, the present invention will be further explained with reference to the accompanying drawings.
In the figure, vertical grooves (not shown) are machined on the inner surface 2 of the copper mold. The upper part of the molten steel injected into the mold 1 from the immersion nozzle 3 is covered with mold powder 4, and the molten steel is slowly cooled. FIG. 2 shows a partial cross-sectional view of the inner surface of the mold. The vertical grooves 5 are preferably provided regularly in the longitudinal direction of the inner surface of the mold 2, and their cross-sectional shape is such that, as described above, they prevent the inflow of mold powder while allowing the inflow of air. In the figure, convex portion 6
constitutes the contact area with the molten steel, and heat is removed through this area.

In the present invention, the range to which 114 is applied is preferably the inner surface area of the mold within 300+ nm from the upper end of the mold, and the width W of the vertical groove is 250 to 750 μm, and the depth D of the groove is 60 to 300 μm. The openings are adjusted so that the area ratio occupied by these vertical grooves is 20 to 90%, preferably 40 to 90%. Note that this area ratio is for the area where the vertical grooves are provided, and is not for the entire area of the inner surface of the mold.

FIG. 3(A) is an explanatory diagram schematically showing a method of forming a surface plating layer by a conventional method, and FIG. 3(B) is a diagram showing a method of forming a surface plating layer according to the present invention.

In the case shown in FIG. 3(A), the copper plate 20 is
Notching and processing pm 21 with depth β1 and width d, then Ni thick plating (thickness 500 μm or more) and N
i+P, Cr plating was applied sequentially, and the final depth was 12,
A groove having a width d2 is formed.

On the other hand, in the case shown in FIG. 3(B), after the copper plate 26 is thickly plated with Ni (thickness of 500 μm or more), the Ni plated layer 27 is coated with a depth of 21 and a width of d.
1, followed by i&Ni+P and Cr plating, and finally a groove with a depth of 2 and a width of d2 is formed.

FIG. 4 shows changes in groove depth in case A and case B, which respectively correspond to FIGS. 3(A) and 3(B) above.

In case B (indicated by white circles in the figure), the original groove depth is almost maintained, whereas in case A (
(indicated by white triangles in the figure), it can be seen that it is less than half.

Regarding the width of the groove, as shown in the graph in Figure 5, in case A (indicated by a white circle in the figure), the groove width is It expands to more than twice its original size. On the other hand, in case B (indicated by white triangles in the figure) according to the method of the present invention, it is clearly seen that the original groove width is preserved.

As described above, in order to obtain a predetermined vertical groove shape for slow cooling, Ni# and plating must be coated with 500. It can be seen that it is effective to form grooves on the Ni by corrosion after applying more than +zm. The reason why the Ni plating thickness is set to 500 .mu.m or more is that even if the depth of the groove is about 500 .mu.m, the base of the copper plate will not be exposed.

In addition, when plating with Ni+P and/or Cr plating after forming grooves on Ni plating, the plating thickness is 2 to prevent seizure of the surface layer.
A thickness of 0 μm or more is sufficient. There are no particular restrictions on this point.

Next, the present invention will be further explained by examples.

Stopper short side 250mm, long side 1600mm, depth 700mm
Vertical grooves were provided on the inner surface of the water-cooled copper mold over the entire area within 300 mm from the upper end of the mold using the following two methods.

Process 1 (comparative example): Good for chemical corrosion (corrosion liquid: FeCl3 solution) on copper plate,
Ni plating (thickness 11I1m) was applied to this by electroplating using a sulfuric acid bath, and Nr was also electroplated.
+P and Cr plating was applied to a total thickness of 35 μm.

Process ■ (example of the present invention): Copper plate is plated with Ni (
Then, a groove with a depth of 280 μm and a width of 500 μm was formed by chemical etching using Fe (1!3 solution). On top of this, Ni+P and Cr plating was also electroplated to a total thickness of 35 μm. It was applied.

FIG. 6 shows the results of measuring surface irregularities using a surface roughness meter for both methods. For process I, the depth is 3
00 μm to 150 μm, but in process ① according to the present invention, it decreased from 280 μm to 27011 μm.
The shape of the vortex is almost unchanged from the time to m.

Continuous casting was actually carried out using three types of molds: the two molds used in the above example and a conventional mold without any grooves. 12.5m R curved 2-straw) L'
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Table 2 shows the mold surface vertical cracking index when each mold was used.

In the case of ordinary molds without grooves and the molds processed by process (1), vertical cracks were present throughout the mold, but in the molds manufactured by the method of the present invention, vertical cracks were completely absent.

Table 1 Table 2

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of a mold according to the invention; FIG.
A partial cross-sectional view of the inner wall of the mold; Figures 3 (A) and CB) are explanatory diagrams schematically showing mold groove forming by the conventional method and the method of the present invention; Figure 4 is the diagram after corrosion in the conventional method and the method of the present invention. A graph showing the relationship between the groove depth and the final groove depth; FIG. 5 is a graph similar to FIG. 4 regarding the groove width; and FIG. It is an explanatory view showing a shape typically. 1: Mold 2: #mold inner surface 3: Immersion nozzle 4: Mold powder applicant
Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Akira Hirose - (1 other person) See/Zuo 4 Cabinet Recommendations 11;, Are M 2 yen (μ class) procedures? C Hosho (Method) April 3, 1985 Manabu Shiga, Commissioner of the Patent Office1, Indication of the case 1982 Patent Application No. 2502242, Name of the invention Method for manufacturing continuous casting molds3, Proceeding the procedure Relationship with the case Patent applicant Address 5-15 Kitahama, Higashi-ku, Osaka Name (211) Sumitomo Metal Industries Co., Ltd. 4, Agent 6 Uramasa Subject Subject of the detailed description of the invention in the specification (Contents of dark amendments) 1) r Hand- on the last line of page 2 to line 2 of page 3 of the specification
Published by Buch (Dusseldorf)
``Handbuchdes Stranggies''
sens), Or, Erhard Herman
Author: ^luminium-Verlag GmbH (
Published by Junosseldorf, West Germany.'' (2) rsteel in Engl on page 3, line 6
ishJ should be corrected to ``Steelin English j''.

Claims (1)

[Claims] To a copper plate that is in contact with molten steel and that constitutes the inner wall of a mold for continuous casting of steel; (i) to apply Ni plating to a thickness of 500 μm or more; (ii) to the obtained Ni plating layer; It is characterized by comprising processing the vertical grooves by chemical corrosion, and (iii) further applying one or both of Ni-P plating and Cr plating to a thickness of 20 μm or more on the thus obtained vertical grooves. A method for manufacturing continuous casting molds for slow cooling.