JPH0748662A - Production of galvanized steel sheet excellent in plating adhesion and appearance - Google Patents

Abstract

PURPOSE:To produce a high Si-based galvanized steel sheet excellent in plating adhesion and appearance. CONSTITUTION:This galvanized steel sheet is produced by heating a cold rolled sheet contg. 0.01-2.5% Si at 500-800 deg.C sheet temp. in a heating furnace with a weakly oxidizing atmosphere, furthermore heating it to 700-900 deg.C sheet temp. in a ferrous oxide reducing atmosphere, then regulating the infiltrating temp. to 380-520 deg.C while cooling it, and passing it through a galvanizing bath contg. 0.05-20% Al at 410-520 deg.C bath temp. Also, the cold rolled sheet is passed through the galvanizing bath and galvanized while regulating the coating weight, thereafter the galvanized steel sheet is galvanized at 450-600 deg.C sheet temp. so as to regulate the content of Fe in the plating layer to 5-15%.

Description

Detailed Description of the Invention

[0001]

[Industrial application] The present invention relates to a method for producing a hot-dip galvanized steel sheet having excellent plating adhesion and appearance.

[0002]

2. Description of the Related Art The use of high-tensile surface-treated steel sheets has been expanding due to the trend toward weight reduction and strength improvement in the fields of automobiles and building materials. Among them, hot-dip galvanized high-strength steel sheets are disclosed in JP-A-62-23975 and JP-A-60-3331.
Although the steel components responsible for increasing the tensile strength have been studied as in JP-A-8, at the same time, the addition amount of Si, P, etc., which hinders the plating property, in the steel is limited to a relatively small amount.

The production of hot-dip galvanized steel sheets is Japanese Patent Publication No.
As described in many publications such as JP-A-6-11309 and JP-B-57-15665, after the material to be plated is removed by oxidizing and burning surface stains and rolling oil in an oxidizing furnace or a non-oxidizing furnace. It is manufactured by reducing the surface oxide film in a reducing atmosphere and annealing, and immersing it in a zinc plating bath while cooling it to a temperature suitable for plating and adjusting the coating amount. Further, the hot-dip galvanized steel sheet is manufactured by an alloying treatment in which an alloying furnace is used to mutually diffuse the plated layer and the material to be plated.

[0004]

As described above, hot-dip galvanized steel sheet and high-strength galvannealed steel sheet are dealt with by lowering the Si content in the steel in order to secure the plating property, but on the other hand, There is a problem in material design that it is difficult to produce materials including strength. The present invention provides a method for producing a high-Si steel hot-dip galvanized steel sheet which has both plating adhesion and material and is excellent in appearance.

[0005]

As a result of various investigations by the present inventors for the purpose of producing a high-Si steel hot-dip galvanized steel sheet, a material to be plated containing a large amount of Si in the steel was used, and a weak oxidization property was obtained. It has been found that the intended hot-dip galvanized steel sheet can be produced by combining specific operating conditions such as conditions of an atmospheric furnace and an atmospheric furnace capable of reducing Fe-based oxides, conditions for entering the bath, and bath conditions. The summary is that Si is 0.
A cold rolled sheet containing 01 to 2.5% has an air ratio of 0.85 to 1.50.
After heat-treating at a plate temperature of 500 to 800 ° C. in a weak oxidizing atmosphere heating furnace, the plate temperature is set at 70 at a Fe-based oxide reducing atmosphere furnace.
The intrusion plate temperature is set to 3 while heating at 0 to 900 ° C and then cooling.
Adjust to 80-520 ℃, bath temperature is 410-520 ℃
It is a method for producing a hot-dip galvanized steel sheet having excellent plating adhesion and appearance, which is characterized by being produced by passing through a hot-dip galvanizing bath containing 0.05 to 20% of l.

After cold-rolled sheet containing 0.01 to 2.5% of Si is heat-treated at a sheet temperature of 500 to 800 ° C. in a weak oxidizing atmosphere heating furnace having an air ratio of 0.85 to 1.50, The penetration plate temperature is adjusted to 400 to 520 ° C. by heating the plate temperature to 700 to 900 ° C. in a Fe-based oxide reducing atmosphere furnace and then cooling, and the bath temperature is 440 to 520 ° C. and Al is 0.05 to 0. .2
Plating adhesion, which is passed through a hot dip galvanizing bath containing 0%, and is alloyed so that Fe in the plating layer is 5 to 15% at a plate temperature of 450 to 600 ° C while adjusting the coating amount A method for producing a hot-dip galvanized steel sheet having excellent appearance.

The present invention will be described in detail below. The slab is hot-rolled, pickled, cold-rolled, etc., and the cold-rolled sheet produced is galvanized as a material to be plated, or is further alloyed and wound. Such a galvanized steel sheet is manufactured. As a steel component, Si is an element that is very effective in strengthening the strength, and 0.01% in order to secure the target material.
% Or more must be added. However, if the content of Al exceeds 2.5% in the steel, the Si-based oxide film formed on the surface of the material to be plated in the heating zone becomes strong and the reactivity with the plating bath decreases even if the operating conditions of the hot dip plating process are variously examined. As a result, non-plating is likely to occur. Further, the alloying rate decreases as the Si content increases, and if it exceeds 2.5%, the productivity is extremely reduced. Therefore, the Si content in the steel is set to 2.5% or less.

A cold rolled sheet having such a steel component is used as a material to be plated. In a hot dip coating line having a weak oxidizing atmosphere furnace-Fe-based oxide reducing atmosphere furnace, an air ratio of 0.85 to 1.5 and a plate temperature of 500 to 500 in the weak oxidizing atmosphere furnace.
The material to be plated is heated at 800 ° C. In a weak oxidizing atmosphere furnace, dirt on the surface of the material to be plated, rolling oil, etc. are burned and removed, and the air ratio (the ratio of the air amount to the theoretical air amount required to completely burn the fuel) and the plate temperature conditions are adjusted. By the thickness of the oxide film generated on the surface of the plated material,
The quality of the oxide film formed can be controlled. In this case, when the air ratio is less than 0.85, easily oxidizable elements such as Si in the steel are more likely to be preferentially oxidized than Fe, and the oxides of easily oxidizable elements such as Si do not cover the surface mainly. It becomes reducible.

As the air ratio increases, Fe, which occupies most of the steel together with easily oxidizable elements such as Si, is easily oxidized, and the oxidation of Fe suppresses the enrichment of the surface of the steel such as Si and mainly forms an Fe-based oxide film. To do. However, when the air ratio exceeds 1.5, the Fe-based oxide is thickly formed, and the Fe-based oxide cannot be sufficiently reduced during the reduction step, and the plating property is deteriorated. Therefore, the air ratio is 0.85 to 1.5. Further, when the plate temperature is less than 500 ° C., the amount of oxide film formed is small, but when the Fe-based oxide is reduced in the Fe-based oxide reducing atmosphere furnace, the content of Si or the like contained in the plated material is easily reduced. The surface concentration of the oxidizing element is promoted, which hinders the plating property.
If the temperature exceeds 800 ° C., the amount of oxide film formed on the surface of the material to be plated becomes extremely thick, and the Fe-based oxide cannot be reduced sufficiently during the reduction step, which hinders the plating property. Therefore, the plate temperature was set to 500 to 800 ° C.

After the heat treatment in this way, Fe is again added.
Plate temperature 700-900 ° C in an atmosphere furnace that can reduce oxides
Heat to. In this heating furnace, it is necessary to reduce the Fe-based oxide generated in the weakly oxidizing atmosphere furnace to secure reactivity with the plating bath and to secure the material. In addition, the inside of the furnace is F
Low dew point, low O ₂ concentration, H
An inert gas atmosphere containing ₂ is required. If the temperature is less than 700 ° C., the material to be plated cannot be sufficiently recrystallized and the material cannot be secured, and the reduction rate of the Fe-based oxide is slow, and the Fe-based oxide remains and the plating property is deteriorated. If the temperature exceeds 900 ° C., recrystallization occurs, but the crystal grain size becomes too large, which may cause skin roughness. Further, the Fe-based oxide generated in the weakly oxidizing atmosphere furnace is reduced, and the easily oxidizable element such as Si contained in the material to be plated is concentrated to form a hard-to-reduce film. Therefore, the heating plate temperature of 700 to 900 ° C. and the atmosphere capable of reducing Fe oxide were set as the conditions in which the oxidation-reduction balance of the Fe-based oxide film necessary to secure the material and the plating property was well balanced.

Then, it is cooled and immersed in a hot dip galvanizing bath. In the case of hot-dip galvanized steel sheet, penetration plate temperature: 380-5
20 ° C, bath temperature; 410-520 ° C, Al in bath: 0.05
-20%. These factors affect the reactivity between the material to be plated and the bath and the appearance such as gloss. Penetration plate temperature is 380 ℃
If it is less than Fe, the reactivity between the material to be plated and the bath is significantly reduced and Fe
Since the growth of the -Al-Zn-based alloy layer is suppressed and the material to be plated is continuously threaded, the bath temperature decreases and the appearance after plating is adversely affected. If the temperature exceeds 520 ° C, the reactivity between the bath and the material to be plated will increase and the alloy layer will become thicker, which will tend to lower the plating adhesion during processing, and if continuously threaded, the bath temperature will gradually rise, and the operation will increase. Cause problems. Therefore, the penetration plate temperature was set to 380 to 520 ° C.

If the bath temperature is less than 410 ° C., the viscosity of the bath increases and the controllability of the adhesion amount and the appearance after plating deteriorate. Also, the reactivity with the material to be plated is greatly reduced, and non-plating is likely to occur. If the temperature exceeds 520 ° C., the reactivity between the bath and the material to be plated increases and the alloy layer grows easily, and the plating adhesion during processing decreases. Further, the evaporation of the bath is promoted and adheres to the inner wall of the snout, etc., and the adhered substance that adheres to the strip adheres to the strip to deteriorate the appearance after plating. Further, the plate temperature on the outlet side of the pot becomes high, and the cooling rate until reaching the top roll must be increased, so that defective appearance such as uneven gloss is likely to occur. Therefore, the bath temperature was set to 410 to 520 ° C.

When the Al concentration in the bath is less than 0.05%, the growth of the alloy layer in the plating bath becomes remarkable, which makes it difficult to control the coating amount and it is not preferable from the viewpoint of the plating adhesion during processing. It also reduces the gloss after galvanizing.
When Al is added in excess of 20%, the melting point of the bath rises sharply, the alloy layer grows rapidly with it, the operating conditions are greatly changed, and the plating adhesion is lowered. It was set to 05 to 20%. Thus, a hot dip galvanized steel sheet is manufactured.

In the case of producing an alloyed hot-dip galvanized steel sheet, the sheet temperature of the steel sheet after reheating is 400 to 520.
C, bath temperature: 440-520 C, Al in the bath: 0.05-
0.20%. These factors influence the reactivity between the material to be plated and the bath. If the penetration plate temperature is less than 400 ° C., the reactivity between the material to be plated and the bath is significantly reduced, the growth of the Fe—Al—Zn alloy layer is suppressed, and the material to be plated is continuously passed through the bath temperature. Deteriorates and adversely affects the appearance after plating. If it exceeds 520 ° C., the reactivity between the bath and the material to be plated increases, the Fe—Al—Zn alloy layer decreases, the Fe—Zn alloy layer increases, and the powdering resistance decreases.

Therefore, the penetration plate temperature was set to 400 to 520 ° C. If the bath temperature is less than 440 ° C, the viscosity of the bath increases and the controllability of the adhesion amount and the appearance after plating deteriorate. Also, the reactivity with the material to be plated is reduced. If the temperature exceeds 520 ° C, the reactivity between the bath and the material to be plated increases, the Fe-Al-Zn alloy layer decreases, the Fe-Zn alloy layer increases, and the powdering resistance decreases. Therefore, the bath temperature was set to 440 to 520 ° C. If the Al concentration in the bath is less than 0.05%, the growth of the alloy layer in the plating bath will be remarkable, which makes it difficult to control the coating amount and is also not preferable in terms of powdering resistance. In addition, Fe that suppresses alloying when the Al concentration in the plating bath increases
The amount of the -Al-Zn alloy layer increases, and during alloying in an alloying furnace, higher temperature is required for a long time, which hinders productivity. Therefore, the Al concentration in the bath is 0.05 to 0.20.
%.

Further, the strip coming out of the hot dip galvanizing bath enters the alloying furnace while controlling the amount of deposition. In the alloying furnace, Fe in the plating layer is 5 to 15% at a plate temperature of 450 to 600 ° C.
Heat to become. If it is less than 450 ° C, it takes time to diffuse and contain Fe of the material to be plated in the plating layer,
It is insufficient to further improve the adhesion between the plated material and the plated layer by diffusing Fe. If the temperature exceeds 600 ° C, the reaction between the material to be plated and the plating layer is promoted and the adhesion between them is sufficiently improved, but a thick alloy layer detrimental to the powdering resistance is formed.
It was set to 00 ° C. When Fe in the plating layer is less than 5%, alloying is not sufficient and uneven appearance and poor plating adhesion are likely to occur. If it exceeds 15%, it becomes an overalloy, and conversely, poor adhesion such as powdering is likely to occur. Therefore, in the production of the alloyed hot-dip galvanized steel sheet, Fe in the plating layer was set to 5 to 15% at a plate temperature of 450 to 600 ° C. as an alloying treatment condition for ensuring plating adhesion and appearance.

[0017]

EXAMPLES Examples of the present invention will be described below. Table 1 shows the studied steel composition values. A slab containing this component was hot rolled, pickled and cold rolled to prepare a material to be plated. Example 1 The operating conditions shown in Table 2 were set in a continuous hot-dip galvanizing line of a non-oxidizing furnace (NOF) -reducing furnace (RTF) system using a material to be plated (Table 1) of a cold-rolled plate having the title steel component. Then, hot dip galvanizing was performed, and the amount of adhesion was controlled to 55 g / m ² , and then an alloying treatment was performed to manufacture an alloyed hot-dip plated steel sheet. The alloyed hot-dip galvanized steel sheet produced under the conditions of the range of the present invention did not cause non-plating, had good appearance and plating adhesion, and had no special problems in operation (Table 2). On the other hand, the galvannealed steel sheet produced under the comparative conditions had microscopic unplating or unalloying, impaired the appearance, and had poor plating adhesion (Table 2).

[0018]

[Table 1]

[0019]

[Table 2]

* Appearance ◎ No unplating with the naked eye △ Micro unplated or unalloyed parts remain. × Small non-plating * Plating adhesion Square tube press (Blank diameter 150 × 150 mm, depth 25
mm), the amount of plating peeling was measured, and the value obtained by dividing the amount by the amount of adhesion was defined as the peeling area. ^{1: 2 ~ 7cm 2 2:} 7 ~12cm 2 3: 12~17cm 2 4: 17~22cm 2 5: 22~

Example 2 An operation shown in Table 3 in a continuous hot-dip galvanizing line of a non-oxidizing furnace (NOF) -reducing furnace (RTF) system using a material to be plated (Table 1) of a cold-rolled sheet having the above-mentioned steel composition. The conditions were set, hot dip galvanizing was performed, and the amount of adhesion was controlled to 100 g / m ² to produce a hot dip plated steel sheet. The hot-dip galvanized steel sheet produced under the conditions of the range of the present invention did not cause non-plating, had good appearance and plating adhesion, and had no special problems in operation (Table 3). On the other hand, the hot-dip galvanized steel sheet produced under the comparative conditions had microscopic non-plating and uneven appearance, impaired the appearance, and had poor plating adhesion (Table 3).

[0022]

[Table 3]

* Appearance ◎ No non-plating with the naked eye △ Micro-non-plating or appearance of non-uniform portions × Small non-plating * Plating adhesion V-shaped bending (angle 60 °) was performed to evaluate the degree of plating removal in the processed part did. ◎ No peeling at all △ Fine peeling × Small peeling

[0024]

As described above, the hot-dip galvanized steel sheet manufactured according to the present invention is excellent in appearance and plating adhesion without occurrence of non-plating and can be manufactured without any special problems in operation. It is effective.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C22C 38/02 (72) Inventor Toshita Miyakoshi 1-1 No. 1 Hibatacho, Tobata-ku, Kitakyushu, Fukuoka Japan Steel Co., Ltd. Yawata Works (72) Inventor Hisashi Yagami 1-1 Hibahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture New Nippon Steel Co., Ltd. Yawata Works

Claims (2)

[Claims] 1. A cold-rolled sheet containing Si in an amount of 0.01 to 2.5% is heat-treated at a sheet temperature of 500 to 800 ° C. in a weak oxidizing atmosphere heating furnace having an air ratio of 0.85 to 1.50, and then, While heating to a plate temperature of 700 to 900 ° C. in an Fe-based oxide reducing atmosphere furnace and then cooling, the intrusion plate temperature is adjusted to 380 to 520 ° C.
A method for producing a hot-dip galvanized steel sheet having excellent plating adhesion and appearance, which is characterized by comprising passing through a hot-dip galvanizing bath containing Al at 0.05 to 20% at a bath temperature of 410 to 520 ° C. 2. A cold-rolled sheet containing Si in an amount of 0.01 to 2.5% is heat-treated at a sheet temperature of 500 to 800 ° C. in a weak oxidizing atmosphere heating furnace having an air ratio of 0.85 to 1.50, and then, The penetration plate temperature is adjusted to 400 to 520 ° C. by heating the plate temperature to 700 to 900 ° C. in a Fe-based oxide reducing atmosphere furnace and then cooling, and the bath temperature is 440 to 520 ° C. and Al is 0.05 to 0. After passing through a hot dip galvanizing bath containing 20%, and performing plating while adjusting the amount of coating adhesion, the plate temperature is 450 to 6
A method for producing a hot-dip galvanized steel sheet having excellent plating adhesion and appearance, which is characterized by performing an alloying treatment such that Fe in a plating layer is 5 to 15% at 00 ° C.