JPH04236750A - Production of hot dip zn or zn alloy plated cr-containing steel sheet - Google Patents

Abstract

PURPOSE:To provide the method for producing the hot dip Zn-plated Cr-contg. steel sheet which has an excellent plating propertly, plating adhesion and corro sion resistance by an ordinary hot dip Zn plating stage. CONSTITUTION:The process for producing the hot dip Zn or Zn alloy plated Cr-contg. steel sheet consisting in previously forming an Fe-Ni plating layer of 0.5 to 10wt.% Ni content at 0.01 to 10g/m<2> METSUKE (unit, 200-2000g/m<2>) weight per side on the surface of the steel sheet contg. >=3% Cr at the time of subjecting this steel sheet to the hot dip Zn or Zn alloy plating contg. 0.05 to 80wt.% Al is formed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing hot-dip zinc or zinc-based alloy-plated Cr-containing steel sheets that have excellent hot-dip plating properties, plating adhesion, and corrosion resistance. This method facilitates hot-dip galvanizing of Cr-containing steel sheets such as steel sheets.

0002

2. Description of the Related Art Generally, cold-rolled steel sheets, which are ordinary steel sheets subjected to hot-dip galvanization, are used in a wide range of applications such as automobile bodies, home appliances, and building materials. The main reason is that Zn
It is a well-known fact that the sacrificial anti-corrosion effect of steel improves the corrosion resistance of the steel plate itself. The manufacturing method includes in-line annealing, as typified by the Sendzimir process (U.S. Pat. No. 2,197,622), and also involves removing oxides generated on the surface of the steel sheet immediately before hot-dip galvanizing.
2 - A procedure is adopted in which the surface is reduced in a N2 mixed gas atmosphere and immersed in a hot-dip galvanizing bath as a clean surface.

Therefore, the presence of oxidized scale on the surface of the steel sheet has a large effect on the hot-dip galvanizing properties, and if the surface is not completely clean, no alloy layer will be formed when immersed in the hot-dip zinc bath, resulting in no plating or adhesion of the plating. Sexual defects occur.

[0004] Recently, there has been a demand for plating stainless steel materials with hot-dip zinc for use in architectural exterior materials for roofs and walls, car floor materials, and the like.

However, since these materials have a high amount of Cr in the steel, the oxide film that forms on the surface of the steel sheet is composed of FeO to Cr.
2 O3. As mentioned above, in order to reduce this Cr2O3 by reduction annealing prior to hot-dip galvanizing, it is clear from the thermodynamic relationship that a high H2
Concentration and low D. P. (dew point) is required. Therefore, in order to satisfy these conditions, a gas atmosphere with a dew point of at least -70°C is required, although it depends on the heating temperature of the steel sheet, and it is realistic to actually manufacture galvanized steel sheets under these conditions. It was impossible. Therefore, when hot-dip galvanizing a steel plate containing a large amount of Cr through a normal process, the plating properties and plating adhesion were poor, and a product of satisfactory quality could not be obtained.

[0006] Therefore, a method has been disclosed in which a steel plate containing a large amount of Cr is coated with a dissimilar metal on the surface of the steel plate in advance and hot-dipped.

For example, in JP-A-2-194155 and JP-A-2-194156, molten Zn or molten Zn
Ni and Fe-based plating have been proposed as base pretreatment for alloy plating, but each has problems as shown below.

That is, in Ni pre-plating, after hot-dip plating, the Ni pre-plating layer remains in the plating layer, especially in the vicinity of the steel sheet, and significant galvanic corrosion occurs with the Zn (alloy) coating layer, resulting in a significant decrease in corrosion resistance. . Further, Fe-based (Fe-B) plating has problems in that the thickness of the produced alloy layer is large, and furthermore, the produced alloy layer itself is brittle and has poor workability.

[0009]

[Problems to be Solved by the Invention] In view of the current situation, the object of the present invention is to apply a steel plate containing 3% or more of Cr to a hot-dip Zn (Zn alloy) plating process for ordinary (common steel) steel strip. Another object of the present invention is to provide a method for producing a hot-dip zinc or zinc-based alloy plated Cr-containing steel sheet having excellent plating properties, plating adhesion, and corrosion resistance.

0010

[Means for Solving the Problems] The present invention provides a solution containing 3% or more C.
When plating a steel plate containing r with hot-dip Zn or hot-dip Zn alloy containing 0.05 to 80% by weight of Al, the surface of the steel plate is coated with a coating weight of 0.1 to 1 per side in advance
F with a Ni content of 0.5 to 10% by weight at 0g/m2
Molten Zn characterized by forming an e-Ni coating layer
Alternatively, the present invention provides a method for manufacturing a hot-dip Zn-based alloy plated Cr-containing steel sheet.

[0011]

[Operation] The present invention will be explained in more detail below.

The present invention was discovered based on the following experimental results.

[0013] 13wt%Cr-0.3wt% as a material
Plate thickness of SUS410 containing Si-0.3wt%Mn 1.
Using a 0 mm cold-rolled steel plate, hot-dip plating was performed using a vertical hot-dip plating apparatus shown in FIG. 1 with a heat pattern shown in FIG. 2. In FIG. 1, 1 is a sample, 2 is an infrared heating furnace, 3 is an infrared heating means, 4 is a hot-dip plating bath, and 5 is an atmospheric gas inlet. The steel plate heating atmosphere at this time was N2-30%H2 with a dew point of -15°C, and the hot-dip coating baths were Zn-0.2%Al (bath temperature 460°C), Zn-5
5% Al (bath temperature 630°C) was used. In addition, the basis weight of Zn (or Zn-based alloy) plating is 100 g/m per side.
2.

[0014] In addition, the material is preliminarily coated with 0.03 per side.
Fe-0.1-18% Ni pre-plating with a basis weight of ~12 g/m2 was electrically applied. FIG. 3 shows the basis weight of Fe-Ni pre-plating and the state of unplated areas (unplated parts) after hot-dip plating. Here, the unplated state was evaluated by the unplated rate shown in the following formula.

[0015] Unplated rate = (area of unplated part/area of measured part) × 100 Base Fe-Ni plating is advantageous for improving hot-dip plating properties, and its effect is due to its basis weight of 0.1 g per side. /m
2 or more, it is remarkable, and it can be seen that no unplating occurs at all.

FIG. 4 shows the influence of the basis weight of the underlying Fe--Ni plating on the plating adhesion of the hot-dip plated steel sheet obtained in the same manner. Here, plating adhesion was evaluated by the following method. Test method: After 2t bending and unbending, the degree of cracking in the plating layer of the processed part was observed and evaluated using a 20x loop; A: Almost no cracking B: Small cracking C: Medium cracking D: Large cracking

[0017] Base Fe-Ni plating is effective for improving plating adhesion after hot-dip plating;
It can be seen that it is noticeable when the i area weight is 0.1 g/m2 or more per side, and when it exceeds 10 g/m2, the plating adhesion deteriorates.

FIG. 5 shows the influence of the Ni content in the base Fe--Ni plating layer on the plating adhesion of the similarly obtained hot-dip galvanized steel sheet. It can be seen that when the content is less than 5 wt%, the thickness of the alloy layer formed during hot-dip plating increases, resulting in a decrease in plating adhesion. Therefore, N in the base plating layer
The i content is required to be 0.5% or more.

FIG. 6 shows the effect of Ni in the underlying Fe-Ni plating layer on the corrosion resistance of the similarly obtained hot-dip plated steel sheet.
Shows the effect of content. Here, the corrosion resistance was evaluated by the following method. Test method: Overhang height 6m on the obtained hot-dip plated steel plate
Erichsen processing of m was performed, and a combined cycle corrosion test was conducted under the conditions shown below. Visual evaluation: A: White rust only, no red rust B: Slight red rust C: Medium red rust D: Large red rust

[0020] If the Ni content in the Fe-Ni base plating layer is less than 0.5%, the adhesion of the plating after hot-dip plating will decrease, leading to a large number of cracks being introduced into the plating layer during processing, resulting in a decrease in corrosion resistance. In addition, if the Ni content exceeds 10%, carvanic corrosion with the Zn plating (Zn-based alloy plating) layer will occur due to the large amount of Ni contained in the alloy layer generated during hot-dip plating. It can be seen that the corrosion resistance similarly decreases.

That is, in order to apply hot-dip Zn (Zn-based alloy) plating, which is the main focus of the present invention, to a Cr-containing steel plate such as stainless steel, which has no unplated areas and has excellent plating adhesion and corrosion resistance, the steel plate is A Fe-Ni coating layer with a Ni content of 0.5 to 10% by weight is applied in advance to 0.1 to 10 g per side of the
It is important to form m2.

[0022] The effect is insufficient if it is less than 0.1 g/m2, and if it exceeds 10 g/m2, the thickness of the alloy layer formed during hot-dip plating becomes large and cracks are likely to occur during processing. Limited to the basis weight.

Furthermore, if the Ni content in the Fe-Ni plating layer is less than 0.5% by weight, the plating adhesion after hot-dip plating will decrease, and if it exceeds 10% by weight, the corrosion resistance after hot-dip plating will deteriorate.
In particular, the content is limited to the above range since the corrosion resistance in processed parts decreases.

It is generally known that the addition of Cr to steel contributes to improving corrosion resistance, but even if hot-dip Zn (Zn-based alloy) plating is applied as in the present invention, the same tendency remains. If the Cr content is less than 3% by weight, the corrosion resistance is insufficient, so the Cr content in the steel is set to 3% by weight or more.

Cr-containing steels, including stainless steel sheets, generally contain C, Si, Mn, Ni, Al, Mo, and Cu.
, Ti, Nb, V, W, Co, Zr, N, etc.
If Fe--Ni is applied as the base plating, it will not directly affect the hot-dip plating properties and the plating adhesion after hot-dip plating, which are the subject matter of the present application, so there is no limitation. Furthermore, S, O, P, and B, which may be mixed in as unavoidable impurities, are not particularly limited as there is no problem if they are at the level of normal impurities.

[0026] The amount of Al added to the hot-dip Zn plating bath is
As is generally known, in the case of pure Zn, it is easy to form a brittle intermetallic compound with the Fe substrate, so 0.05
This can be prevented by containing % or more of Al.
The lower limit was set to 0.05%. Furthermore, if the Al amount exceeds 80%, the sacrificial anticorrosion ability of Zn itself (plating layer) in the material after hot-dip plating will decrease, and even if Fe-Ni plating is applied to the base, which is the gist of this application, Also, since the effect of improving plating adhesion was small, the upper limit was set at 80%.

[0027] Electroplating is the most common method for coating Fe--Ni on Cr-containing steel sheets, and it can be carried out using any bath such as a sulfate bath or a chloride bath as a plating solution. Further, the Ni content in the base Fe--Ni plating layer can be controlled by changing the Ni ions in the plating solution or the cathode electrolytic current density.

[0028]

EXAMPLES The effects of the present invention will be explained below based on examples, but the invention is not limited thereto.

(Example 1) A cold-rolled plate with a thickness of 0.8 mm shown in Table 1 was used as a test material, and the base plating was Fe-Ni, which is the gist of the present invention, and Fe, Ni, and Fe were used as a comparative example. -B was applied by electroplating. The electroplating conditions are as shown below.

(1) Fe-Ni plated steel sheet was previously subjected to alkaline electrolytic degreasing and hydrochloric acid pickling treatment, and then FeSO4.7H2O180g/l+70g/
In a bath (p
Fe--Ni plating was performed by cathodic electrolytic treatment at 10-80 A/dm2 at H1.2-1.5). The Fe-Ni basis weight was controlled by changing the amount of electricity applied. Further, the Ni content in the plating layer was controlled by changing the amount of NiSO4.6H2O added and the current density.

(2) After preliminarily performing alkaline electrolytic degreasing and hydrochloric acid pickling treatment on the Fe-plated steel sheet, FeSO4 .7H2 O 200g/l+
50 to 80 A/dm in a 60°C plating solution (pH 1.2 to 1.5) containing 100 g/l of Na2 SO4
Fe plating was performed by performing cathodic electrolytic treatment in step 2. The Fe basis weight was controlled by changing the amount of electricity applied.

(3) Ni-plated steel sheet was previously subjected to alkaline electrolytic degreasing and hydrochloric acid pickling treatment, and then treated with NiSO4 .6H2 O 300g/l+
10 to 20 A/dm in a 60°C plating solution (pH 1.0 to 1.2) containing 100 g/l of Na2 SO4
Ni plating was performed by performing cathodic electrolytic treatment in step 2. The Ni basis weight was controlled by changing the amount of electricity applied.

(4) After preliminarily performing alkaline electrolytic degreasing and hydrochloric acid pickling treatment on the Fe-B plated steel sheet, FeSO4.7H2O 200g/l+
By performing cathodic electrolytic treatment at 50 A/dm2 in a 60°C plating solution (pH 1.0 to 1.2) containing 100 g/l Na2 SO4 + 0.5 g/l tartaric acid,
Fe-B plating was performed. The basis weight was controlled by changing the amount of electricity applied.

Using the steel plate obtained by the above method, a hot-dip plating experiment was conducted using the vertical hot-dip plating apparatus shown in FIG. At this time, the steel plate heating atmosphere prior to immersion in the hot-dip plating bath was N2 - 50% H2. P. -20
℃. The heat pattern at that time is shown in FIG. 7, and the Al concentrations in the hot-dip plating bath are 0.100 wt% (bath temperature 470°C), 4.6 wt% (bath temperature 450°C), 48
wt% (bath temperature 640°C), 55wt% (bath temperature 650°C)
, 72 wt% (bath temperature 660°C) and 84 wt% (bath temperature 680°C). In addition, molten Zn
(Zn-based alloy) Plating weight is 70g/m per side
It was set as 2.

[0035] Regarding the hot-dip Zn (Zn-based alloy) plated steel sheet thus obtained, the hot-dip plating property (uncoated rate)
, plating adhesion and corrosion resistance were investigated using the methods shown below.

(a) Hot-dip plating property The area ratio of the unplated part (unplated part) of the obtained hot-dip Zn (Zn-based alloy) coated steel sheet, that is, the unplated ratio = (area of unplated part/measurement) area of part) x 1
Evaluation was made based on the unplated rate defined as 00.

(b) The plating adhesion test piece was subjected to bending and unbending for 2t (t: plate thickness), and the extent of cracking in the plating layer at the processed part was observed using a 20x loop, as shown below. evaluated. A: Almost no cracks B: Small cracks C: Moderate cracks D: Large cracks

(c) Corrosion resistance The obtained hot-dip Zn (Zn-based alloy) plated steel sheet was subjected to Erichsen processing with an overhang height of 6 mm, and the following cycle corrosion test (360 cycles) was conducted to determine the rust after the test. The situation was determined visually. Evaluation: A: White rust only, no red rust B: Slight red rust C: Medium red rust D: Large red rust

Table 2 shows the evaluation results. ■ Regarding Invention Examples 1 to 15 and Comparative Examples 1 to 18, Fe-N was applied in advance within the scope of the present invention as a pretreatment for the steel plate.
By applying i-plating, no unplating occurs during hot-dip Zn (Zn-based alloy) plating, and hot-dip Zn (Zn-based alloy) plating with extremely excellent plating adhesion and corrosion resistance.
It can be seen that a containing steel plate can be obtained.

[0040] However, if the Fe-Ni basis weight is 0.1
When it is less than g/m2, it is not possible to completely prevent non-plating during hot-dip plating, the adhesion of the plating is not good, and the corrosion resistance of the obtained steel sheet is also found to be insufficient.

On the other hand, if the Fe-Ni basis weight exceeds 10 g/m2 per side, the effect of preventing non-plating during hot-dip plating is sufficient, but the thickness of the alloy layer formed during hot-dip plating tends to increase. , plating adhesion decreases. Therefore, it can be seen that the corrosion resistance of the processed portion is also reduced. On the other hand, if the Ni concentration in the base Fe-Ni plating layer is less than 0.5% or if only Fe is used as the base plating, unplated areas will occur during hot-dip plating, and the adhesion of the plating will not be sufficient. The obtained molten Zn (Zn
The corrosion resistance of plated steel sheets is also insufficient. therefore,
When used for exterior materials such as building materials, the appearance of red rust becomes noticeable, indicating that it cannot be applied.

[0042] When the Ni concentration in the base Fe-Ni plating layer is 1
If it exceeds 0%, non-plating that occurs during hot-dip plating will be completely prevented, and the plating adhesion after hot-dip Zn (Zn-based alloy) plating will be good, but the Ni concentration in the alloy layer that will be formed will be large. This causes local galvano corrosion with the Zn (Zn-based alloy) plating layer, causing Zn (Zn-based alloy)
The corrosion resistance decreases because the rate of disappearance increases.

It can be seen that when plain Ni is applied as the base plating, unplating that occurs during hot-dip plating can be completely prevented, but the plating adhesion is extremely poor and the corrosion resistance is insufficient. The cause of this is the Fe mentioned above.
- This is considered to be the same as when the Ni content in the Ni plating layer exceeds 10%.

On the other hand, when Fe-B plating is applied to the base, the non-plating that occurs during hot-dip plating can be completely prevented, but the adhesion of the plating is inferior to that of the Fe-Ni base within the scope of the present invention. , it can be seen that the corrosion resistance is insufficient. This means that when Fe-B plating is applied to the base,
This is thought to be because the thickness of the alloy layer produced during hot-dip Zn (Zn-based alloy) plating is larger than that in the case of Fe-Ni. Therefore, the corrosion resistance of the processed part is affected by molten Zn (
It is thought that cracks are more likely to be introduced into the plating layer (Zn-based alloy), resulting in a decrease.

■ Invention Examples 1 to 11 and Comparative Examples 2 and 9
Regarding ~15, when materials with various Cr contents are subjected to Fe-Ni plating and hot-dip Zn alloy plating, unplating during hot-dip plating can be completely prevented, and the hot-dip Zn alloy has excellent plating adhesion and corrosion resistance. It can be seen that a Zn alloy plated Cr-containing steel sheet can be obtained.

■ Invention examples 14 and 15 and comparative example 19
If the Al concentration in the hot-dip Zn plating bath exceeds 80 wt%, the plating adhesion after hot-dip plating will decrease even if the base Fe-Ni plating, which is the gist of the present invention, is applied, and as a result, the processing area will deteriorate. It can be seen that the corrosion resistance decreases.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

Effects of the Invention As mentioned above, by using the method of the present invention, molten Zn can be applied to Cr-containing steel sheets, which was previously considered difficult.
(Zn-based alloy) plating can be done in a normal process, making it easy to manufacture hot-dip Zn (Zn-based alloy) plated Cr-containing steel sheets with excellent plating adhesion and corrosion resistance, which has a great effect on industrial development. .

[Brief explanation of the drawing]

FIG. 1 is a diagram of a vertical melt gluing apparatus used in the present invention.

FIG. 2 is a diagram showing a heat pattern of hot-dip plating.

FIG. 3 is a diagram showing the relationship between the basis weight of Fe-Ni plating and the unplated rate.

FIG. 4 is a diagram showing the relationship between base Fe-Ni plating weight and plating adhesion.

FIG. 5 is a diagram showing the relationship between Ni content in the Fe-Ni plating layer and adhesion.

FIG. 6 is a diagram showing the relationship between Ni content in a Fe-Ni plating layer and corrosion resistance.

FIG. 7 is a diagram showing a heat pattern of hot-dip plating performed in an example.

[Explanation of symbols]

1 Sample 2 Infrared heating furnace 3 Infrared heating means 4 Hot-dip plating bath 5 Atmosphere gas inlet

Claims (1)

[Claims] [Claim 1] A steel plate containing 3% or more of Cr.
When performing hot-dip Zn or hot-dip Zn-based alloy plating containing 0.05 to 80% by weight of Ni, the surface of the steel sheet is preliminarily coated with a coating weight of 0.1 to 10 g/m2 per side and a Ni content of 0.5. A method for producing a Cr-containing steel plate plated with molten Zn or a molten Zn-based alloy, the method comprising forming a Fe-Ni coating layer of ~10% by weight.