JPS6082651A - Production of alloyed galvanized steel plate - Google Patents

Abstract

PURPOSE:To improve shearing characteristic of steel plate after painting in the production of alloyed galvanized steel plate by reducing carbon content of the steel plate, adjusting the P content to a specified value, and controlling the crystal structure by the combination of the rolling condition and the heat-treating condition. CONSTITUTION:A slab of aluminium killed steel contg. <0.08% C, <0.05% Si, 0.10-0.50% Mn, <0.06% sol.Al and (0.24XC%+0.007)%-0.06% P, and if necessary 0.1-0.6% in total at least one among Nb, V, Ti, is hot-rolled to a plate material at a temp. higher than the Ar3 point. After removing the scale by pickling, the plate is cold rolled with >=40% draft to produce a steel plate of a desired thickness and is wound in the form of coil. The coil is then box-annealed at 650-800 deg.C, hot-dipped, and then alloyed at 450-800 deg.C. When it is precoated, there is no fear of causing delamination of the plated layer at the cut end surface in the stage of shearing and blanking work.

Description

DETAILED DESCRIPTION OF THE INVENTION (Background of the Invention) The present invention relates to a method for manufacturing an alloyed hot-dip galvanized steel sheet (hereinafter abbreviated as "GA steel sheet PA"), which has particularly excellent performance for BRE2-1.

GA steel sheets have extremely excellent corrosion resistance after painting, so they are widely used in home appliances, automobiles, fixtures, etc., which are generally used after painting. On the other hand, in such applications, a so-called precoated coating, in which the coating is applied in advance with a coil coater, is widely used.

Therefore, the usage of GA steel sheets is changing from the conventionally painted after various forming and processing at the customer side to the form where they are subjected to various forming and processing after painting.

Mechanically, there is a change in stress distribution when processing bare plated 4A material and when processing painted plated material, which was not expected when processing bare plated material. There are several problems, but one that has become a particular problem in recent years is that when GA steel sheets are pre-coated, the plating layer peels off at the cut edge during shearing and punching. It is.

Such peeling of the plating layer is caused by the fact that the plating edges of the GA steel sheet are formed from an intermetallic compound with poor workability. In particular, when the elastic modulus of the coating film is high, that is, when a hard coating film is applied, such peeling phenomenon is noticeable. This kind of peeling during processing is caused by pre-coat paint G.
This is a major obstacle to the widespread use of A steel sheets. Further, this type of peeling similarly appears when an impact test is performed, and therefore materials that undergo such peeling of the plating layer often do not meet the specifications of the customer.

(Related Patent Application) The inventors of the present invention have already found that this problem can be improved considerably by adjusting the components in the steel of the base material, and proposed this in Japanese Patent Application No. 57-213432.

The method that the present inventors have proposed in this way was basically to utilize P-added, low-grade (JI4) and to combine this with a plating method. As a result of repeated trial production studies, the means shown in these prior inventions,
In some cases, the strength of the matrix became excessive, resulting in an increase in concentrated load during shearing, and cases were observed in which the shearability deteriorated. For farmers with such a slope, especially C>0.
This was noticeably observed in steel with P addition of 0.08%.

(Object of the Invention) Therefore, the object of the present invention is to provide a steel in which the C content is reduced and the P content is adjusted accordingly, in particular, in which both C and P are reduced, and the shearability after painting is reduced. It is a further object of the present invention to provide an improved process for producing alloyed hot-dip galvanized steel sheets.It is another object of the present invention to reduce the C content, adjust the P content accordingly, and reduce the C content by a combination of rolling and heat treatment conditions. An object of the present invention is to provide a method for manufacturing an alloyed hot-dip galvanized steel sheet with improved shearability by adjusting the crystal structure.

Another object of the present invention is to provide a manufacturing method capable of obtaining a GA steel sheet with sufficient shear properties using a conventional CGL process.

(Summary of the Invention) The present inventors have disclosed the above-mentioned disclosed patents of the present inventors.
As a result of considering the effects of C and P in the steel sheet components on shearability, and also conducting material mechanical studies, we found a further improved component system and processing heat treatment conditions.

The basic principle of the present invention is to reduce as much as possible the shearing load that the steel plate receives during shearing, and to reduce the shearing load that the 114 plates receive as much as possible. The goal is to change the crystal orientation of the steel sheet to a form that improves shear resistance.

According to the findings of the present inventors, in the orientation distribution of αFe in the base steel sheet, αFe (110) is suppressed as much as possible, while αFe (211) and αFe
By forming a texture in which (222) is preferentially grown, shear bendability is improved. The reason is that r 1-F in the alloy layer formed by alloying treatment after hot-dip plating.
It is presumed that the consistency between the cubic crystal of e5Zn21 or F-Fe3Zn1o and the age of the parent phase is mainly improved by forming the above-mentioned texture. Moreover, it has been found that this tendency is particularly remarkable in aluminum-killed steel.

In this way, the present invention suppresses the breaking load of the mower 1, and
It is composed of a combination of adjusting the crystal structure of a steel plate, and its gist is as follows: C: 0.08% or less, Si: 0.05% or less, Mn
: 0.10-0.50%, sol, Δ7! :o,
oe% or less (0.24XCf%)+0.007)%≦
P (%) 50.06%, and if necessary, at least one of Nb, ■ and T1 in a total of 0.1 to 0.6%, the balance being Pe and impurities. i;) Alloyed hot-dip galvanizing with excellent shearing properties after painting, which is characterized by performing hot-dip galvanizing after one-hour rolling and cold rolling, and then alloying by continuous or punching. This is a manufacturing method for steel plates.

In addition, when box annealing is performed at 650 to 100°C after cold rolling, P is set to 0.007% as the lower limit, and P(%l
It may be <0.24xC(%)+0.007.

The above-mentioned alloying treatment is preferably performed continuously, and the steel plate temperature at that time is 450 to 570°C.

(Specific embodiments of the invention) The reasons for limitations in the present invention will be explained.

C reduces the intensity level and αPe (11', O)
A lower value is preferable from the viewpoint of suppressing texture formation. on the other hand,
It is possible to adjust the crystal structure by adding P even if it is not a decarburized steel, but considering the balance with strength, it is 0°08%.
It is necessary that the following is true. Generally, when the product of plate thickness x tensile strength exceeds 20kB7mm, shearing properties are significantly reduced. If the C content exceeds 0.08%, the tensile strength becomes excessive and the shearing properties are significantly reduced.
．． 0.3% or less.

6. Si causes solid solution hardening. In the case of a 2GA steel plate, the upper limit was set at 0.05% since this would result in a delay in alloying speed and a decrease in burnodering resistance.

Mn is also necessary to prevent brittleness caused by S, but on the other hand, Mn
An increase in n causes excessive strength and makes it difficult to obtain a desirable m-moon crystal orientation, so the lower limit was set to 0.10% and the upper limit was set to 0.50%.

P plays an important role in the present invention,
In particular, it has the effect of alleviating the adverse effects of C on crystal orientation, at least. .

Addition of 24xC (%l + 0.007% or more is required. The upper limit of pp addition is set at 0.06% from the viewpoint of suppressing strength and adversely affecting alloying rate. In particular, 0.02-0
．． A P content of 0.3% is desirable.

In other words, the P content is (0,24X
c(a + 0.007) %≦P Hl;i;0.
It is necessary to satisfy 0.6%, and within this range,
With aluminum killed steel, both the crystal orientation and strength of the base steel are balanced and excellent shearability can be obtained.

However, when box annealing is performed after cold rolling, the lower limit of the P content may be lowered to 0.007% because the crystal structure can be adjusted by the graining heat treatment.

Al1 is an element necessary for the composition of aluminum quilt steel, and is considered to be involved in the formation of texture due to the precipitation of AρN. However, sol and Aβ content are 0
．． If it exceeds 0.6%, the strength will increase, so set the upper limit to 0.
．． It was set at 06%. The lower limit is generally sufficient to be contained in aluminum killed steel. .

About 0.02% is necessary.

In the prior art, rimmed steel and killed steel were used as GA steel sheets for pre-recording without making any particular distinction in terms of shear resistance, but in the present invention, aluminum killed steel was specifically selected in relation to its crystal structure. It is what you use.

Further, although the type and amount of incidental impurities are not particularly limited, it is preferable that about 0.0030 to 0.0070% of N is contained. Regarding S, the normal content is assumed to be about 0.015% or less.

In another embodiment of the present invention, as described above, pretreatment by box annealing is used in combination prior to the plating treatment. According to the findings of the present inventors, shearability is further improved by using such box annealing in combination than by continuous annealing directly connected to the CGL process. When using box annealing, hot rolling at a temperature of Ar 3 point temperature or higher, cold rolling with a reduction rate of 40% or higher, and annealing temperature of 650 to 800 ° C.
These are conditions that provide a favorable structure and strength for shearability.

Note that this box annealing may be performed by the phyto method (although, of course, more suitable results can be obtained by also performing decarburization.

When such box annealing is performed, the composition range of the target aluminium-killed steel, especially the range of P content, is somewhat relaxed, and the lower limit of P content is set to 0, since the heat treatment improves the structure. It can be set to .007%. Therefore, in this case, the lower limit of the P content does not necessarily have to satisfy the formula: P(m]≧0.24 It will be done.

In another embodiment of the present invention, better results can be obtained if the abrasive temperature in the alloying treatment after hot-dip galvanizing is lower. The upper limit of the monthly feed temperature at that time is 570°C, but preferably 520"C or less. On the other hand, the lower limit is mainly from the point of economic efficiency - (: /150"c, and if it is lower than this, continuous processing It is difficult to do this.If continuous processing is to be carried out, the temperature of the steel plate should be set to 450 to 57.
The temperature is preferably 0°C. On the other hand, in the case of hatch processing,
300-400'c is desirable.

In yet another aspect of the present invention, the harmful effects of C are alleviated by adding C stabilizing elements such as Ti, Nb, and V. Nb, ■ and Ti are at least one of them, a total of 0.1
~0.6% is added.

Thus, according to the present invention, it is possible to obtain a GA steel sheet having a shear-resistant shear plating layer that does not peel off even when shearing is performed after coating. In particular, when a hard coating film is provided, the shear stress at the interface between one plating layer increases and peeling of the plating layer becomes noticeable, but according to the present invention, even in such a case, the shearing property is high. C A l
The il board is (M).

The present invention will be further explained below based on Examples.

Hot rolling was started by heating slabs of aluminum killed steel having the chemical composition shown in Table 1 to 1180°C, finishing rolling at 860°C, and finishing the slabs to a thickness of 3m11. Then, the winding temperature was set to 630°C and the winding was completed.

Furthermore, after pickling, 62% cold rolling was added, and then /8 dip galvanizing alloying treatment was performed using the conventional sensimire line. The alloying treatment was carried out continuously at a steel sheet temperature of 550°C. The plate thickness after cold rolling is 0.50 m11, and the amount of Zn deposited in the plating is 42 to 52 g/rr+, Fe
The content was 10.2-12.8%. All steel plates were subjected to temper rolling at a reduction rate of 0.4% after completion of the alloying treatment to give them a beautiful surface suitable for painting steel plates.

Test pieces were collected from the steel sheets obtained in this way, and various property tests were conducted. Panels for painting of 100 x 200 + U size were prepared, and after degreasing and chemical conversion treatment were performed using commercially available krisher and zinc phosphate treatment agents. A 10 μm thick epoxy baking paint was applied as a base coat and an acrylic baking paint was applied as a top coat to give a total thickness of 2,511 m. The pencil hardness of the paint film after painting was 3H.

This sample was sheared using an electric shear at a room temperature of 15° C. and a clearance of 0.06 mm, perpendicular to the rolling direction, with the painted surface facing downward. After shearing, attach Sellotape to the cut edge of the sample on the die side, remove the part that can be peeled off, and average peel 1ii11rl] (parallel to the rolling direction).
was measured.

The results of the shear test after painting of the GA steel plate used as the test material are summarized in a graph in the attached drawing. The C50.03% cumulative month was recognized to have significantly superior performance among the examples of the present invention.

In addition, in the figure, the symbol "@" indicates that the peeling I+] is less than 0.10 mm, "○" indicates that the peeling is less than 0.10 to 0.15 mm, and "
△” is 0°15~0.25mm (less than), “×” is 0
．． 2 cases of 25 mm or more are shown respectively.

Example 1 was repeated using a steel type having the chemical composition shown in Table 2, but in this example, hot-dip galvanizing and alloying treatment using Senshimia Line were carried out at 740°C for 2 hours.
Box annealing was performed for 0 hours. However, box annealing was not performed for the rimmed steel of steel type M24.

Table 2: Steel type No. which is the box annealed steel obtained in this example,
0.12.0 during peeling for 21, 22, and 23, respectively.
．． 1080, 1O+nm, respectively, equivalent (, P level C
It exhibited superior shearing properties compared to C and A steel sheets that were subjected to continuous annealing directly connected to the GL process.

In addition, the steel type No. 24 rimmed steel base is 0.4
01111], and the shear test results were extremely inferior to those of equivalent C, P level Δe-guild steel.

[Brief explanation of drawings]

The accompanying drawing is a graph summarizing the test results of the shear test in Example 1 of the present invention. Applicant: Sumitomo Kin 1ji Jigyo Kaisha” (Company agent: Patent attorney Akira Hirose -

Claims (4)

[Claims] (1) By weight, c: o, oa% or less, Si: 0.05% or less, Mn
: 0.10-0.50%, sol, A (1:
0.06% or less, fO, 24Xc (%) + 0.007
1%≦P(%)50.06%, further Nb if necessary,
A total of at least one of V and Ti is o, i to 0.
Aluminum guild steel having a composition satisfying 6%, balance Fe and impurities of I1 is hot rolled,
A method for producing an alloyed hot-dip galvanized steel sheet with excellent shearability after painting, which comprises cold rolling, then hot-dip galvanizing, and then alloying. (2) The temperature of the steel plate when performing the alloying treatment is 450℃.
The manufacturing method according to claim 1, wherein continuous processing is carried out at a temperature of ~570°C. (3) Weight ■%, c: o, o 8% or less, Si: 0.05% or less, Mn
: 0.10-0.50%, sol, A7! :
0.06% or less P: o, oo7 to 0.06%, and if necessary, at least 1 of Nb, , V and T1
Aluminum killed steel having a composition that satisfies a total of 0.1 to 0.6% seeds, the balance Fe and incidental impurities is hot rolled at a temperature higher than the Δr3 transformation point temperature, pickled, and then heated for 40 minutes. Cold rolling is performed at a reduction rate of 650 to 800% or more.
A method for manufacturing an alloyed hot-dip galvanized steel sheet with excellent shearing properties after coating, characterized by box annealing at ℃, followed by hot-dip galvanizing, and then alloying treatment. (4) The temperature of the steel plate when performing the alloying treatment is 450℃.
The manufacturing method according to claim 3, wherein continuous processing is performed at a temperature of ~570°C.