JPH09249954A - Production of hot-dip galvanized steel sheet excellent in workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hot-dip galvanized steel sheet free from deterioration in workability even if a hot rolled steel sheet subjected to sufficient shape modification by a skin pass-rolling is used as the stock. SOLUTION: In a method in which a hot rolled steel sheet is subjected to shape modification and is thereafter applied with continuous galvanizing, when the aging index after the hot rolling is AI (kgf/mm<2> ), the plastic elongation at the time of the shape modification is ε(%) and the line tension of a continuous galvanizing line is T (kgf/mm<2> ), the following relations in the inequality of 0.13ε+0.104AI+0.57>=T>=0.12ε+0.093AI+0.47 is statisfied, where AI is the amt. of the yield point to be increased by heat treatment at 100 deg.C for 60min after the application of 8% tensile prestrain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip galvanized steel sheet which is made of hot-rolled steel sheet and has excellent workability.

[0002]

2. Description of the Related Art Since hot-dip galvanized steel sheets are excellent in corrosion resistance and workability, demand for automobiles, building materials, furniture, containers, home appliances, etc. has been increasing in recent years. Although hot-dip galvanized steel sheets are usually manufactured from cold-rolled steel sheets, the use of hot-rolled steel sheets as a raw material instead of cold-rolled steel sheets allows the cold-rolling process to be omitted, enabling further low-cost manufacturing. Is. In this case, the shape of the hot-rolled steel sheet is generally worse than that of the cold-rolled steel sheet, and the stripability in the continuous plating line is poor.
It is necessary to correct the shape with a skin pass. However, when a hot-rolled steel sheet whose shape is corrected by such a strain load is used as a raw material and subjected to a plating treatment in a continuous hot-dip galvanizing line, there is a problem that the strength is increased and at the same time, the ductility is reduced and the processing is hindered. there were.

As a means for avoiding such deterioration of workability, Japanese Patent Application Laid-Open No. 6-285506 discloses a method of making the skin pass elongation rate for shape correction 0.5% or less. However, in reality, with a skin pass elongation of 0.5% or less, it is often impossible to correct the shape sufficiently, and the stripping speed in the plating line must be reduced, resulting in a decrease in production efficiency or stripping. There were problems such as being impossible. Therefore, there has been a demand for a hot dip galvanizing method that does not deteriorate the workability after plating even if a hot-rolled steel sheet that has been sufficiently shaped by a skin pass or the like is used as a material.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to improve workability even if a hot-rolled steel sheet having a sufficient shape correction with a skin pass or the like is used as a material. Another object of the present invention is to provide a method for producing a hot-dip galvanized steel sheet which does not deteriorate.

[0005]

In order to solve this problem, the inventors of the present invention have various measures to prevent the deterioration of the workability of hot-rolled steel sheet which has undergone sufficient shape correction by skin pass etc. due to hot dip galvanization. investigated.

That is, the steel sheet is hot-rolled and then subjected to a skin pass or the like to have its shape corrected, then reduced in a reducing furnace and then hot-dip galvanized in a plating bath. In the case of galvannealing, the steel sheet is additionally 400-90 in the alloying furnace.
Heat to 0 ° C. However, when a steel sheet whose shape is corrected by performing a skin pass after hot rolling is used, there arises a problem that workability is deteriorated due to increase in strength and decrease in ductility due to these heating steps.

As a result of studying a method capable of preventing such deterioration of workability and obtaining the highest workability, the inventors have found that the workability is deteriorated during annealing in a reducing furnace. We found that it is effective to apply tension to the. However, even if the same tension is applied during heating, the workability may deteriorate, and as a result of further studies including the material of the hot-rolled sheet and the manufacturing conditions before plating, the aging after hot-rolling of the hot-rolled sheet was performed. It was found that the index: AI (kgf / mm ² ) and the plastic elongation at the time of shape correction: ε (%) had an influence. Therefore, a more detailed examination revealed that the AI of hot rolled sheet was
On the other hand, the inventors have found that the best workability can be obtained by optimally controlling the plastic elongation at the time of shape correction and the line tension T (kgf / mm ² ) at the time of annealing, and arrived at the present invention.

That is, the present invention provides a method for producing a continuous hot-dip galvanized steel sheet after straightening the shape of a hot-rolled steel sheet,
The aging index after hot rolling: AI (kgf / mm ² ), the plastic elongation during shape correction: ε (%), and the line tension of the continuous hot-dip galvanizing line: T (kgf / mm ² ) are expressed by the formula (1). A method for producing a hot-dip galvanized steel sheet having excellent workability, characterized by satisfying the relationship.

0.13ε + 0.104 AI + 0.57 ≧ T ≧ 0.12ε + 0.093 AI + 0.47 (1) However, AI is 100 ° C. × 6 after 8% tensile prestrain is applied.
This is the amount of increase in the yield point due to the 0 minute heat treatment.

Here, the plastic elongation (ε
(%)) Is the elongation rate (%) after temper rolling (pressure adjustment) in the skin pass, and the elongation rate (%) after the leveler loading of the roller leveler and the tension leveler in the leveler.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Next, in the method of the present invention, 0.13ε
+0.104 AI + 0.57 ≧ T ≧ 0.12ε + 0.093 AI + 0.47 Aging index after hot rolling: AI (kgf /
mm ² ), plastic elongation during shape correction: ε (%) and line tension of continuous hot-dip galvanizing line: T (kgf / mm
^The reason for defining ² ) is explained below.

FIG. 1 shows a laboratory melting material (C: 0.04% by weight).
(Hereinafter abbreviated as%), Si: 0.01%, Mn: 0.
3%, P: 0.01%, S: 0.009%, SolA
1: 0.05%, N: 0.0040%)
= 0.5 kgf / mm ² hot rolled sheet was skin-passed up to various skin pass pressure control rates (corresponding to the amount of plastic elongation) and no tension and tension: 0.8 kgf / mm ² equivalent to hot dip galvanizing Heat treatment (680 ° C x 60 seconds → 500 ° C x
The mechanical properties (elongation) after 10 seconds) are shown. With no tension, the elongation decreases as the skin pass pressure regulation rate increases, and even with a skin pass pressure regulation rate of 0.2 to 0.5%, 3 to 6%.
The decrease in the elongation of On the other hand, when tension is applied, it is understood that the elongation hardly decreases up to the skin pass pressure regulation rate of 1.5%. However, when the skin pass pressure regulation rate was 2.0% or more, the elongation was lowered.

FIG. 2 shows a laboratory melting material (C: 0.04%,
Si: 0.01%, Mn: 0.3%, P: 0.01%,
S: 0.009%, SolAl: 0.05%, N: 0.
0040%), after hot-rolled sheets with various AI levels adjusted to skin pass with a skin pass pressure regulation ratio of 1.0%, heat treatment equivalent to hot dip galvanizing with tension of 0.7 kgf / mm ^2. (680 ° C x 60 seconds → 500 ° C x 10
The mechanical properties (elongation) after performing the second) are shown. Even if the skin pass pressure regulation rate and the tension during heat treatment are the same, A
It can be seen that the elongation decreases as I increases.

FIG. 3 shows a laboratory melting material (C: 0.04%,
Si: 0.01%, Mn: 0.3%, P: 0.01%,
S: 0.009%, SolAl: 0.05%, N: 0.
0040%), a hot-rolled sheet of AI = 0.5 kgf / mm ² was skin-passed at a skin pass pressure regulation ratio of 1.0%, and then heat treated at various tensions (680 ° C. × 680 ° C.). The mechanical properties (elongation) after 60 seconds → 500 ° C. × 10 seconds) are shown. In FIG. 3, the region where the effect of tension on the ductility is maximized is A, the region where the effect is reduced and saturated is B, and the region where the effect is small and the tension dependency is large and difficult to control is C. It can be seen that the elongation decreases when the tension is low, even when the AI and the skin pass pressure regulation rate are the same. On the other hand, even if the tension is increased too much, the elongation decreases, so that the tension must be controlled within the optimum range in order to obtain the best ductility.

Therefore, the present inventors have found that the aging index after hot rolling in actual operation: AI and the plastic elongation during shape correction and the line tension required to prevent workability deterioration (decrease in ductility) after continuous hot dip galvanizing. I investigated the relationship. The results are shown in FIGS. 4, 5 and 6. In the evaluation of ductility in each figure, the regions were designated as A, B and C as in FIG. As shown in each figure, the aging index after hot rolling (AI (kgf / mm ² )), skin pass pressure regulation rate (ε (%)) and line tension (T (kgf
/ Mm ² )) satisfies the relationship of the formula (1), it is possible to prevent the deterioration of the material due to the decrease of ductility, and if the relationship of the formula (1) is not satisfied, the deterioration of the material cannot be prevented.

0.13ε + 0.104 AI + 0.57 ≧ T ≧ 0.12ε + 0.093 AI + 0.47 (1) However, AI: 100 ° C. × 6 after applying a tensile prestrain of 8%
Amount of increase in yield point by applying 0 min heat treatment.

The elongation rate (%) after pressure adjustment in the skin pass and the elongation rate (%) after leveler loading are almost equivalent from the actual operation results, and both satisfy the equation (1). If the line tension is less than 0.3 (kgf / mm ² ), fluttering will occur in the threaded plate.
f / mm ² ) or more is preferable. The manufacturing conditions of the hot-rolled sheet are not particularly specified, the steel piece after continuous casting is
The above effects can be obtained by either reheating after cooling to room temperature, reheating without cooling to room temperature, or hot rolling by directly sending the film as it is. Further, usually hot-rolling-shape correction is often performed descaling in the pickling line and then subjected to hot dip plating, but even if this pickling descaling step is omitted, there is no effect on the effect of the present invention. There is no.

[0018]

Next, an embodiment of the present invention will be described. [Example 1] In the composition shown in Table 1, a hot-rolled sheet having a plate thickness of 2.3 mm in which AI was changed according to the winding temperature was subjected to skin passes up to various skin pass pressure control rates, and then to a pickling line. The scale was removed by changing the line tension in the reducing furnace to various levels, and the continuous hot dip galvanizing line was passed. The reducing furnace temperature of the plating line was changed in the range of 630 to 890 ° C, and the zinc plating bath temperature was 500 ° C. Table 2 shows the steel of the A component in Table 1, Table 3 shows the B steel of Table 1, and Table 4 shows the Table 1
C steel, Table 5 shows D steel of Table 1, and Table 6 shows E steel of Table 1 respectively showing mechanical properties (elongation) after passing through the hot dip galvanizing line.

From the results shown in Table 2, Table 3, Table 4, Table 5 and Table 6, even if the AI (winding temperature) and the temperature in the reducing furnace are the same, the line tension is adapted to the present invention. It can be seen that it is possible to obtain an elongation that is at least 5% higher than when the line tension deviates from the range of the present invention.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Table 6]

[0026]

As is apparent from the above examples, according to the present invention, it is possible to reduce workability at low cost by preventing deterioration of material such as ductility after plating which occurs when a hot-rolled steel sheet is used as an original plate. It is possible to provide a method for producing a continuous hot-dip galvanized steel sheet excellent in heat resistance. Therefore, according to the production method of the present invention, the production efficiency is improved and the cost reduction effect is great, and an extremely useful effect in industry is brought about.

[Brief description of drawings]

FIG. 1 shows various hot-rolled sheets after various skin passes,
The figure which shows the relationship between skin pass pressure regulation and elongation at the time of heat-processing corresponding to hot dip galvanizing.

FIG. 2 is a diagram showing a relationship between AI and elongation when a hot-rolled sheet having various AI levels adjusted to skin is subjected to a skin pass and then a heat treatment equivalent to hot dip galvanizing.

FIG. 3 is a diagram showing a relationship between tension and elongation when a hot-rolled sheet is skin-passed and then heat-treated corresponding to hot dip galvanizing with various tensions.

FIG. 4 Aging index after hot rolling in actual operation: AI = 0.
Shows a 5 kgf / mm ² and straightening time of workability deterioration after the plastic elongation and continuous galvanizing relationship line tension required to prevent (decrease in ductility).

FIG. 5: Aging index after hot rolling in actual operation: AI = 2.
FIG. 7 is a graph showing a relationship between 7 kgf / mm ² and plastic elongation during shape correction and line tension required to prevent workability deterioration (decrease in ductility) after continuous hot dip galvanizing.

FIG. 6 Aging index after hot rolling in actual operation: AI = 5.
The figure which shows 0 kgf / mm < ² > and the plastic elongation at the time of shape correction, and the line tension required in order to prevent workability deterioration (ductility fall) after continuous hot dip galvanizing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshimasa Funakawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A method of continuously hot-dip galvanizing a hot-rolled steel sheet after its shape is corrected, wherein the aging index after hot rolling is AI.
(Kgf / mm ² ) and plastic elongation during shape correction: ε
(%) And line tension of continuous galvanizing line: T
A method for producing a hot-dip galvanized steel sheet with excellent workability, characterized in that (kgf / mm ² ) satisfies the relationship of the equation (1). 0.13ε + 0.104 AI + 0.57 ≧ T ≧ 0.12ε + 0.093 AI + 0.47 (1) However, AI is 100 ° C × 6 after applying 8% tensile prestrain.
This is the amount of increase in the yield point due to the 0 minute heat treatment.