JPS6213201A - Production of galvanized and embossed steel sheet - Google Patents

Abstract

PURPOSE:To improve productivity by executing cold rolling at a specific draft by smoothing rolls prior to embossing thereby increasing strain, decreasing the annealing temp. after embossing and eliminating the need for releveling. CONSTITUTION:An annealed steel strip is subjected to cold rolling at 25-40% draft by the smoothing rolls prior to embossing in the stage of producing an embossed steel sheet by cold rolling the steel strip by embossing rolls to emboss the strip, then annealing and galvanizing the strip. The annealing temp. after the embossing is decreased by such method and even if the annealing temp. is decreased, the base sheet for plating is softened regardless of the ruggedness of patterns to permit the easy shape setting by the leveler and the need for the releveling is eliminated. The productivity is thus improved.

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention involves embossing a plating original plate by cold rolling, and then
A manufacturing method of a hot-dip galvanized finished embossed steel sheet manufactured by hot-dip galvanizing, which is lightweight and easy to correct shape after hot-dip galvanizing by lowering the annealing temperature of the plated original plate after embossing. Regarding.

(Prior art) There are two methods for producing a hot-dip galvanized embossed steel sheet in which irregularities are formed on the surface layer of the sheet: a method in which embossing is applied to the plated original sheet in advance and hot-dip galvanizing is carried out; There is a method in which hot-dip galvanizing is applied to a plated original plate that has not been subjected to galvanizing, and embossing is performed after plating. However, the latter method may cause cracks to occur in the plating layer due to embossing, or the plating layer may become uneven. However, the former method, which does not have the disadvantages of method 2, has been used in the past.

The method used in the United States is to hot-roll rimmed steel, weakly deoxidized steel, or full-killed steel that has been melted using normal steelmaking methods to form a hot-rolled steel strip, and then The strip is descaled by pickling, etc., and then first cold rolled at a high reduction rate to close to the thickness of the product sheet, and then cold rolled using embossing rolls that have been annealed and etched to form irregularities. This is a method in which the plated plates are sequentially applied to form a plated plate, and the plated plate is passed through a continuous annealing hot-dip galvanizing line to undergo continuous annealing and hot-dip galvanizing. The reason why the second cold rolling is performed at a high reduction rate is that if the reduction rate for embossing is increased, the horizontal profile of the embossing roll will be damaged, so the reduction rate cannot be made too high. Annealing is performed before cold rolling with embossing rolls because if the material is cold rolled, it is work hardened and embossing is difficult, so it is necessary to soften the material by annealing it at a temperature higher than the recrystallization temperature. This is because there is.

(Problem to be solved by the invention) However, if it is not possible to increase the rolling reduction during embossing, the rolling reduction for horizontal convex parts is 2 to 3%, and for concave parts it is 15 to 30%, which is normal plating. Since the rolling reduction ratio is lower than 40% or more of the original plate, when annealing is performed after embossing, the concave portions have a certain amount of strain, causing grain gloss and softening, but the convex portions have small strain, so they do not recrystallize. It did not soften. For this reason, the overall grain size was mixed and hard in terms of ML.

By the way, the shape of a hot-dip galvanized embossed steel sheet is damaged by hot-dip galvanizing, so when manufacturing it, the shape is first corrected with a tensicon leveler at the time of steel strip, and then the shape is corrected after cutting. It is corrected using a roller leveler at the time of cutting. However, if the plated original plate is hard as described above before hot-dip galvanizing, it will remain hard after plating because the plating temperature is below the recrystallization temperature. For this reason, even if an attempt was made to correct the shape using a leveler such as the one described above, it could not be corrected, and the object had to be passed through a small-diameter roller leveler and relevelled.

In addition, since the rolling reduction rate during embossing is smaller than the rolling reduction rate (40% or more) for normal plated original plates even in the concave portions, the temperature during continuous annealing is 700°C, which is the temperature at which normal plated original plates are sufficiently softened. Unless the temperature is higher than 750°C, recrystallization will not occur and the product will be in a so-called half-cooked state. For this reason, the fuel cost during continuous annealing was higher than in the case of a normal plate B original plate.

(Means for Solving the Problems) The present invention provides a manufacturing method that solves the above-mentioned problems in the conventional method for manufacturing hot-dip galvanized embossed steel sheets. be.

When manufacturing hot-dip galvanized embossed steel sheets, the present invention
Since it was not possible to increase the reduction rate during embossing of the plating original plate, and the distortion was insufficient, in the conventional manufacturing method, a secondary cold rolling using a smooth roll was performed before embossing to reduce the distortion. It was made so that it would become so. That is, the present invention uses a smooth roll to perform secondary cold rolling at a reduction rate of 25 to 40% before embossing to increase strain and omit re-levelling, and the annealing temperature is lower than that of normal plating. 700 which is the annealing temperature of the original plate
This made it possible to lower the temperature to as low as ℃.

The reason why the lower limit of the rolling reduction rate was set at 25% is that if it is less than 25%, there will be insufficient strain and the horizontal protrusions of the steel strip will not soften sufficiently even after annealing, and the annealing temperature will be lowered to 700°C. The reason why the upper limit was set at 40% is that if it exceeds 40%, the work hardening becomes large.
This is because embossing becomes difficult.

The present invention will be explained below with reference to Examples.

(Example) A steel having the composition shown in Table 1 is melted by a conventional method and hot rolled to produce a sheet with a thickness of 2.5 who and a sheet width of 123.
Four coils of 0 mm hot rolled steel strip were manufactured. Next, two coils of each of these hot-rolled steel strips are cold-rolled, embossed, hot-dip galvanized, and shaped according to the method of the present invention and the conventional method, resulting in a hot-dip galvanized embossed steel sheet! ! ! I left it behind. The manufacturing conditions were the same for both the method of the present invention and the conventional method, except for cold rolling. In addition, hot-dip galvanizing is performed on a continuous annealing hot-dip plating line, and annealing after embossing is performed at the same time as hot-dip galvanizing, and shape correction after plating is also performed using only those installed on the plating line (tensilan leveler and roller leveler). I did it.

Table 1 shows the manufacturing conditions, Table 2 shows the hardness, flatness, and weave of the obtained hot-dip galvanized steel sheets, and Figures 1 and 2 show the results of Examples NOI and NO4, respectively. The original plate structure is shown.

Table 2 shows that the hardness of the hot-dip galvanized embossed steel sheet made by the method of the present invention is HV115 or less in both the uneven parts, the flatness can be sufficiently straightened with a leveler installed in the plating line, and the braided fiber is also It is well-sized.

On the other hand, the NO3 plated plate produced by the conventional method has a small distortion in the plated original plate and a low annealing temperature, so it does not recrystallize.
The original plate is hard, so the shape cannot be corrected at level 2-.
Re-leveling is required.

In addition, since the convex parts of the NO4 plate made by the conventional method do not recrystallize, the original plate is hard and has poor flatness.
0% must be sent to the re-leveler process.

(Effects) As described above, according to the present invention, the annealing temperature after embossing can be lowered, and even if it is lowered, the original plate is softened regardless of the unevenness of the pattern, and the shape can be easily corrected with a leveler. can be done.

Therefore, the fuel cost for annealing after embossing can be reduced compared to the conventional method, and the conventional re-leveling process is no longer necessary, improving productivity.

[Brief explanation of the drawing]

Figure 1 is a photograph showing the original plate structure of a hot-dip galvanized embossed steel sheet manufactured by Example 801 (the method of the present invention), and Figure 2 is a photograph showing the hot-dip galvanized embossed steel sheet manufactured by Example N04 (conventional method). This is a photograph showing the original plate structure.

Claims (1)

[Claims] In a method for manufacturing an embossed steel sheet in which an annealed steel strip is cold-rolled with an embossing roll to embossing it, and then annealed and hot-dip galvanized, the method includes cold rolling with a smooth roll at a reduction rate of 25 to 40% before embossing. A method for producing a hot-dip galvanized embossed steel sheet.