JPH05263207A - High-tensile galvanized steel sheet of high silicon content - Google Patents

Abstract

PURPOSE:To provide a high-tensile galvanized steel sheet of high silicon content especicially improved in the adhesive strength of the galvanization. CONSTITUTION:A layer of Fe2SiO4 and SiO2 having 0.001-1mum thickness is formed on the surface of a steel material (a base material) consisting of, by weight, 0.03-0.20% C, 0.3-2.0% Si, 0.5-2.0% Mn, <=0.03% P, <=0.01% S, 0.0003-0.0060% Ca and 0.01-0.10% Al, and an Fe layer having 0.01-1mum thickness is formed on the layer of Fe2SiO4 and SiO2 and further the Fe layer is galvanized.

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 high Si-containing high-strength galvanized steel sheet having good plating adhesion, and more specifically, a high Si-containing Si content of 0.3% or more. After pre-annealing the steel sheet by rapid oxidation to ensure uniformity of galvanized appearance, adhesion, etc.,
It is a high-Si high-strength hot-dip galvanized steel sheet having excellent adhesion to plating, which is hot-dipped after annealing in a hydrogen-containing atmosphere.

[0002]

2. Description of the Related Art Conventionally, in order to extend the life or improve the design of bare steel materials, which are diversified as structural members for building materials, etc.,
After a certain forming process, some kind of post-treatment such as plating or painting was done by the customer, but due to the cost reduction of the steel material used by omitting the process, there is a strong demand for surface treatment of the supplied steel material. .. In particular, recently, the demand for surface treatment of high-strength steel sheets is increasing. As a surface treatment method whose main purpose is to improve the rust prevention of this high-strength steel sheet,
From the viewpoint of productivity, there is a Zenzimer type hot dip galvanizing method that enables easy thick plating. By using this Sendzimer hot dip galvanizing method, the rolling oil on the surface of the steel sheet is removed in an oxidation furnace containing oxygen to form an appropriate oxide film, and after reduction annealing in an atmosphere containing hydrogen, in a furnace. A method for controlling the plate temperature and plating is already known in JP-A-55-122865. That is, in the non-oxidizing furnace system that does not contain oxygen,
Although the oil on the steel surface can be removed, since the oxidizing atmosphere is weak and easily oxidized Si, Mn, and Al are diffused and oxidized on the surface, these oxides form the steel surface.
These oxides are not reduced in a reducing furnace and cause poor plating wetting and poor plating adhesion. For this purpose, the surface of the steel sheet is oxidized so that the thickness of the oxide film is 400 to 10,000 Å, annealed in an atmosphere containing hydrogen, and hot dip plated.

[0003]

However, according to the prior art, as described above, the non-oxidizing furnace is heated by increasing the air ratio,
It is only the finding that good plating properties can be obtained by reducing and heating after forming the Fe oxide film, and in a continuous line where the line speed, furnace temperature, heat cycle, etc. in the actual operation line are constantly changing, The plating property was not stable even at a high air ratio, and there was a problem in practical use. Therefore, the present invention is a high productivity line, by a method different from the conventional method, without causing non-plating,
It is an object of the present invention to provide a method for obtaining a high Si-containing high-strength hot-dip galvanized steel sheet having stable quality and excellent uniform appearance and good plating adhesion.

[0004]

In order to solve the above-mentioned problems and achieve the object, the gist of the present invention is that the component system and weight concentration of the steel material (base material) is C;
03-0.20%, Si; 0.3-2.0%, Mn;
0.5-2.0%, P; 0.03% or less, S; 0.01
% Or less, Ca; 0.0003 to 0.0060%, Al;
Fe ₂ Si is formed on the surface of a steel material composed of 0.01 to 0.10%.
O ₄ and SiO ₂ layers of 0.001 to 1 μm are applied, and Fe layers 0.01 to 0.01 μm are provided on the Fe ₂ SiO ₄ and SiO ₂ layers.
It is a high-strength galvanized steel sheet having a high Si content, which is characterized by imparting 1 μm and galvanizing the upper part of the Fe layer.

The present invention will be described in detail below. In the present invention, in the case of a high Si-containing steel having a Si concentration of 0.3% or more in the steel, it is generally called a difficult-to-plate material, and Si, M
Since n, Al, P and the like are diffused as oxides on the surface layer of the steel sheet by heating the steel sheet surface, these oxides are concentrated and form the steel surface. Therefore, these oxides
It is not reduced even in a reduction furnace, which impairs the wettability of the plating and deteriorates the adhesion of the plating. Therefore, it is intended to enable hot-dip galvanizing of steel for these difficult-to-plate materials in a highly productive line without plating and with excellent uniform appearance. As annealing conditions for that,
Fe and S that hinder the plating property when immersed in a plating bath
This shows that the i oxide film does not remain.

FIG. 1 is a schematic view showing a steel plate of the present invention.
FIG. 1A shows a steel material (base material) before galvanizing.
Is. The component system of this base material is shown in Table 1. The requirements for the invention of the present steel material are the burring property and the ductility which have become important for the hot-rolled steel sheet for automobile parts without impairing the economical efficiency and the spot weldability in the alloyed hot-dip galvanized steel sheet with high rust prevention property The present inventor has accomplished the present invention as a result of extensive studies.

[0007]

[Table 1]

The reasons for limiting each constituent element of the present invention will be described in detail below. C is necessary to secure the strength, and the minimum amount is 0.03%. However, if it exceeds 0.20%, the spot weldability deteriorates. Therefore, C is 0.05 to 0.18
%. Si is the most important element in the present invention. In the present invention, it is intended to improve ductility and burring property. What has been overcome in the present invention is that the structure is optimized by the combination with the hot rolling conditions described later, and the ductility and the burring property are improved by the inclusion of this Si. In order to exert this phenomenon, the minimum Si
Is required to be 0.3% or more. The upper limit is set to 2.0% in consideration of plating wettability, plating adhesion, economy, and spot weldability. Mn is an element necessary for securing strength, and is 0.
It is necessary to contain at least 5%. The upper limit was set to 2.0% by comprehensively judging strength stability, economy, spot weldability and the like.

P reduces the spot weldability and makes Ar ₃
Since it is an element that raises the transformation point, its content must be thoroughly reduced, and was made 0.03% or less. It is preferable to lower it to 0.01% or less. And this is
It is also effective when alloying. Further, S must be thoroughly reduced from the viewpoint of spot weldability and burring property, and must be 0.010% or less. Preferably, it should be reduced to 0.002% or less. Further, Ca is added to control the morphology of sulfide inclusions. 0.000
Addition of less than 3% has no morphological control effect and is 0.005%
Addition of not only saturates the effect of morphology control,
On the contrary, since the Ca-based inclusions increase, there is an adverse effect, so the upper limit is set here. Al is necessary as a deoxidizer. If it is less than 0.01%, that effect is not obtained, and if it exceeds 0.10%, alumina-based inclusions increase and deteriorate the ductility of the steel. The structure of the product stage intended by the present invention is composed of bainite whose ductility is improved by containing Si and angular ferrite having grain boundaries which is formed during hot rolling and quenching in some cases. FIG. 1B shows a mixed layer of Fe ₂ SiO ₄ and SiO ₂ having a thickness of 0.001 to 1 μm on the surface layer portion of the steel material (base material) (a). (C) is 0.01 to 1 μm in the surface layer portion of the mixed layer (b) of Fe ₂ SiO ₄ and SiO _2.
Fe layer having a thickness of.

FIG. 2 is a schematic view of the equipment according to the present invention.
A range in which the amount of oxide film formed on the surface of the steel strip does not exceed 1000Å in the heating furnace 3 using a burner that preheats the cold-rolled steel strip 1 in the preheating furnace 2 and then injects a flame perpendicularly to the steel sheet. After heating while controlling with, before entering the soaking furnace 4 and the annealing furnace 5 which are the next reduction zones, the amount of surface-generated oxide film in the heating furnace is actually measured using the oxide film thickness meter 6, Based on this measured value, the reduction capacity was calculated using the heat cycle, line speed, and hydrogen concentration in the reduction zone, and reduction was performed in the annealing furnace 5 so that the optimum range (S region) was reached, and further the inlet side oxidation was performed. The film thickness is learned and calculated by using the actual measurement value by the oxide film thickness meter. That is, the annealing based on the value calculated above should satisfy the calculated inflow side oxide film thickness + a (Å) ≤ reduction capacity (Å) ≤ inflow side calculated oxide film thickness + b × (oxide film thickness) ² (Å) It controls the conditions. Although the coefficient value of Si and the like are stored in the computer for each steel type, it is necessary to perform learning calculation in order to make the calculation model maintenance-free. In this learning calculation, the accuracy is improved by constantly learning the coefficient value and the like using the actual measurement value of the oxide film thickness meter for the entrance side oxide film thickness. This improves the accuracy of feed and forward control by calculation. Subsequently, in the slow cooling zone 7 and the quenching zone 8, the steel strip temperature of 800 to 820 ° C. is set to 450 to 50.
Quench to 0 ° C. After that, the steel strip was hot bridle,
After passing through the snout, it is dipped in the zinc bath 10 in a reducing atmosphere, the amount of adhesion is adjusted by a wiping device, and a hot dip galvanized steel sheet is obtained.

A schematic illustration of the above is shown in FIG. That is, FIG. 3 shows the balance between oxidation and reduction as a change in time. The iron oxide film thickness increases in the oxidation zone, and thereafter the oxide film is reduced in the reduction zone, and FeO reduction is completed after t ₁ . The figure shows a state in which Si enrichment is subsequently started and Si enrichment progresses within t-t ₁ hours, and reduction is performed up to an allowable range of the reducing ability. Further, FIG. 4 schematically shows a locus of the balance between oxidation and reduction. During the oxidation / reduction process, an oxide film still remains when entering the zinc bath, so that the alloying property shows a poor state. Next, the oxidation / reduction process shows the limit of remaining iron oxide film. Further, the oxidation / reduction process is related to the present invention,
Belong to the proper operating range. Or, it shows the limit point of surface enrichment of Si, and it is in a state where Si atoms have not reached the surface layer of the pure iron layer (iron layer after the oxide film has been reduced). At this time, the SiOx film is on the surface,
Since the reaction between the steel plate and the bath is hindered, the plating adhesion results in a poor result. Therefore ,, is a conventional oxidation / reduction process, and the present invention corresponds to and, but is a limit point of the present invention.

The thickness of the mixed layer of Fe ₂ SiO ₄ and SiO ₂ is 0.001 μm before annealing and cannot be less than this. Further, if it exceeds 1 μm, peeling from this portion occurs, so it is necessary to suppress it to less than this. The thickness of the Fe layer is 0.01 μm from the viewpoint of ensuring plating adhesion.
The above is necessary. Also, if it exceeds 1 μm, it is brittle Fe-Z
Since an n-alloy is formed and the workability is deteriorated, it is necessary to suppress it below this value. (D) shown in FIG. 1 is a zinc-plated layer having a thickness of 3 to 50 μm on the surface layer portion of the Fe layer (c). Table 2 shows the components of the zinc plating of the second invention. This galvanized steel sheet has excellent corrosion resistance and is mainly used for building materials and home appliances.

When Pb exceeds 0.02%, the interface portion causes peeling with time, so it is necessary to suppress it to this level or less.
Sb is the core of the spangle pattern, and the optimum spangle pattern condition is 0.10% or more and 0.3.
It is 0% or less. If this is removed, it will not be generated. Table 3 shows the components of the zinc plating of the third invention. This galvanized steel sheet is also mainly used for building materials and home appliances. Al
Is less than 0.05%, the Fe-Z is brittle at the plating interface.
An n-layer is formed and the plating adhesion is impaired. If it exceeds 0.35%, the appearance will be impaired, so it is necessary to suppress it to below this value. Pb is the core of the spangle pattern, and the condition for producing the optimum spangle pattern is 0.10% or more and 0.30% or less. If this is removed, it will not be generated.

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

According to the present invention, the Si concentration in the steel is 0.3.
In the case of steel with a high Si content of more than 100%, Fe has traditionally been used in the surface layer.
_The problem that a galvanized steel sheet with good adhesion was not formed due to the formation of a mixed layer of ₂ SiO ₄ and SiO ₂
By forming the layer, the plating adhesion can be improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing a steel plate of the present invention,

FIG. 2 is a schematic view of equipment according to the present invention,

FIG. 3 is a diagram schematically showing the oxidation-reduction balance as a change with time;

FIG. 4 is a diagram schematically showing a locus of oxidation / reduction balance.

[Explanation of symbols]

 1 Steel strip 2 Preheating furnace 3 Heating furnace 4 Soaking furnace 5 Annealing furnace 6,9 Oxide film thickness meter 7 Slow cooling zone 8 Quenching zone 10 Zinc bath

Claims (3)

[Claims] 1. The component system and weight concentration of the steel material (base material) are C: 0.03 to 0.20%, Si: 0.3 to 2.0%,
Mn; 0.5 to 2.0%, P; 0.03% or less, S;
0.01% or less, Ca; 0.0003 to 0.0060
%, Al; 0.01 to 0.10% of the steel material is applied to the surface layer of Fe ₂ SiO ₄ and SiO ₂ layers of 0.001 to 1 μm, and the Fe layer 0 is formed on the Fe ₂ SiO ₄ and SiO ₂ layers. A high Si content high-strength galvanized steel sheet, characterized in that the Fe layer is zinc-plated on top of 0.01 to 1 μm. 2. The component system and weight concentration of zinc plating are A
1; 0.05 to 0.35%, Pb; 0.020% or less,
Sb: 0.10 to 0.30%, the balance being Zn, the high Si content high tensile galvanized steel sheet according to claim 1. 3. The component system and weight concentration of galvanizing are A
1; 0.05 to 0.35%, Pb; 0.10 to 0.30
%, And the balance being Zn. The high Si content high tensile galvanized steel sheet according to claim 1, characterized in that.