JPS63235485A - Method for manufacturing hot-dip galvanized steel sheets - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and heat resistance of a plated steel sheet, by previously applying iron plating to the under-mentioned steel sheet so as to improve the adhesive strength of hot dip metal coating at the time of applying hot dip metal coating to a rustless steel sheet containing Cr by a specific amount or more. CONSTITUTION:A rustless steel sheet containing >=5wt.% Cr is subjected to iron plating. This iron plating can be carried out by the known method, but, in order to secure the adhesive strength of preplating, it is desirable to carry out pretreatment, such as striking, if necessary. Subsequently, hot dip metal coating is applied to the above steel sheet. By this method, even in the case where heat treatment is performed under the usual annealing conditions, the homogeneity and adhesive strength of plating can be remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides molten metal with excellent corrosion resistance and plating adhesion;
The present invention relates to a method for manufacturing a hot-dip alloy plated steel plate, and relates to a method for manufacturing a hot-dip plated steel plate using a rust-proof base steel plate containing Cr.

(Prior art) In a method of hot-dipping common steel, prior to hot-dipping, any one of Ni, Co, Mo, Cu, Cr, or a specific alloy thereof is plated to improve the adhesion of the plating. The method is JP-A-57-76176.
, Japanese Patent Publication No. 57-140864. Japanese Patent Publication No. 56-33463
．． This is disclosed in Japanese Patent Application Laid-open No. 57-114650. In addition, a method of plating iron prior to hot-dip plating using ordinary steel to improve adhesion was disclosed in JP-A-57-70.
No. 268.

Furthermore, as shown in Japanese Patent Publication No. 52-335'79, Cr is a material that requires high heat resistance and high corrosion resistance.
A steel sheet is known that is made by coating steel containing 5 to 15% of aluminum with aluminum.

(Problems to be Solved by the Invention) Although the galvanized steel sheets manufactured using the above-mentioned common steel have a fairly good corrosion resistance, they may be used in cases where a high degree of corrosion resistance is required, or in cases where the plating film has defects. Since the base steel plate itself has poor rust resistance, it cannot be said that the corrosion resistance is sufficient.

In order to solve the problem of the corrosion resistance of galvanized steel plates based on ordinary steel, a galvanized steel plate based on a steel plate containing Cr as described above has been proposed. It turned out that there was a problem.

The purpose of the present invention is to solve the problems of conventional matted steel sheets using steel sheets containing Cr, and to provide a method for producing hot-dip galvanized steel sheets that have excellent corrosion resistance and, at the same time, excellent heat resistance. It is in.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention uses a rust-free steel sheet containing 5 or more Cr by weight, and plated with iron as a pre-plating prior to dense melt plating. , followed by hot-dip plating.

Chromium-based rust-free steel does not necessarily have sufficient corrosion resistance and heat resistance on its own, but its properties (corrosion resistance) can be improved by further plating with metals or alloys.

heat resistance) is dramatically improved.

In the manufacturing method of continuous hot-dip galvanized steel sheets, heat treatment is usually performed in a reducing gas prior to plating, and the purpose of this is to clean the surface of the galvanized steel sheet by reducing oxides and to perform annealing to soften the cold-rolled structure. The steel plate enters a heat treatment furnace and is heated, but the entrance to the furnace is in an oxidizing atmosphere, and the surface of the steel plate is first oxidized, and then the oxide is reduced with a reducing gas.

Next, the steel plate is placed in a plating bath. .

However, Cr-containing steel sheets are significantly more easily oxidized than ordinary steel, and once oxidized, they are difficult to be reduced even by the heat treatment in the reducing gas described above, so it is extremely difficult to hot-dip plate them as they are, and there is no need for any pre-treatment. We found that this is necessary.

Therefore, we continued our research, and when performing hot-dip plating using a steel plate containing Cr, by first plating with iron and then pouring the molten metal, we were able to improve the uniformity of the plating even when heat-treated under normal annealing conditions. It has been found that adhesion can be greatly improved. Furthermore, when aluminum is used as the molten metal, a plated steel sheet with excellent heat resistance can be obtained.

The reason for using a steel plate with a Cr content of 5 cm or more in weight in the present invention is that by containing 5% or more of Cr, the base steel plate itself has corrosion resistance, so even if a defect occurs in the plating film, the plated steel plate remains intact. This is because it is possible to suppress a large decrease in corrosion resistance.

The chromium-based rust-free steel sheet used in the present invention may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a cold-rolled annealed sheet.

Iron plating on these steel plates may be performed by a known method. However, in order to ensure the adhesion of pre-plating, it is desirable to perform pre-treatment such as strike plating as necessary. The amount of plating metal deposited depends on the steel, composition, and conditions of the continuous hot-dip metal plating line (gas composition, plate temperature,
It is difficult to determine in general terms (depending on the plating bath composition, plating bath temperature), but it is necessary to be 0.1 f/- or more. Although the upper limit is not limited, the higher the amount, the more disadvantageous it is in terms of cost, and inevitably there is an optimal amount.

Examples will be described below.

Example 1 Steel composition is Cr: 16%, C: 0.05%, Mn
: 0.35%, Ag: 0.06%, Si: 0.02%,
2~4f/rr of iron under the conditions shown below on a cold rolled steel plate with a thickness of 1.0+m containing other unavoidable impurity elements. Then, in a continuous hot-dip plating line, it was annealed at 700"C for 12 minutes in a reducing gas, followed by hot-dip plating with pure aluminum (bath temperature 680"C). The amount of aluminum plating is 60~709/rr? Closed.

The results of evaluating the plating adhesion of the steel plate after plating are shown in Table 1 in comparison with the case where no iron is plated (iron adhesion amount: 09/y&).

O Iron plating conditions Plating bath composition FeSO4-7H20: 1409/
1(NH,)2804: 30 li/Current density loA/ai PH2,0 Plating bath temperature 50℃ Table 1 Evaluation of plating adhesion was performed by bending the test piece as shown in Figure 1, and removing the plating. The area was measured and the scores are shown in Table 2 below. In FIG. 1, 1 is a plating original plate (rust-proof plate), and 2 is a plating layer.

Table 2 Plating rating Example 2 Using the same rust-free steel plate as in Example 1, applying iron to the steel plate under the same plating conditions at 1 to 59/rr? Plating, followed by annealing at 700°C for 2 minutes in a reducing gas in a continuous hot-dip plating line, followed by 10% 5i-Al! hot-dip plating (
(bath temperature: 650°C). Plating amount is 100-1
2of/rr? And so. The plating adhesion was comparatively evaluated in the same manner as in Example 1, and the results are shown in Table 3.

(Effects of the Invention) When carrying out hot-dip plating using a steel plate containing Or by Fuakamei, plating adhesion is greatly improved by performing iron plating in advance.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a plating adhesion test method after hot-dip plating. 1... Plating original plate 2... Plating layer

Claims (1)

[Claims] A method for producing a hot-dip galvanized steel sheet, the method comprising plating a rust-free steel sheet containing 5% by weight or more of Cr with molten metal, the surface of which is plated with iron in advance, and then molten metal is plated thereon.