JPS60152662A - Steel sheet plated with ternary iron-chromium-zinc alloy and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the titled steel sheet having superior workability and corrosion resistance after coating by forming a layer contg. specified percentages of Fe, Cr and Zn on a steel sheet by plating. CONSTITUTION:A layer consisting of 0.02-2.0wt% Cr and the balance Zn with inevitable impurities is stuck to a steel sheet by plating, and iron in the steel sheet is diffused in the layer by galvannealing to form a layer consisting of 15- 27wt% Fe, 0.02-2.0wt% Cr and the balance Zn with inevitable impurities. Thus, a steel sheet plated with a ternary Fe-Cr-Zn alloy is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a galvanealed steel sheet with excellent workability of the plating layer and corrosion resistance after painting.

Galvanealed steel sheets are produced by applying heat treatment (hereinafter referred to as galvanealing treatment) immediately or briefly after galvanizing to change the plating layer mainly made of metallic zinc to a plating layer mainly made of iron-zinc alloy.
The iron concentration in the plating layer is 8.5 to 13.0% by weight, and the amount of iron on one side is 20 to 100 g/m'. Also,
Because of its relatively excellent plating layer properties such as spot weldability, its use spans many industrial fields such as automobiles, home appliances, and building materials.

In each of the above-mentioned industrial fields, it is customary to mold a galvanealed steel plate into a desired shape, perform treatments such as degreasing and water washing, and pre-painting treatment, and then apply various types of coatings. The purpose of this is to extend product life, improve corrosion resistance, and improve product appearance. However, conventional galvanealed steel sheets suffer from the problem that the plating layer peels off into powder or foil during the forming process (hereinafter referred to as powdering). Corrosion often occurs due to destruction by ultraviolet rays when painted products are exposed to various natural environments for long periods of time, and corrosion due to penetration of corrosive factors (water, air, etc.) into the paint film-plating layer interface. However, it is not always satisfactory for purposes such as extending the product life. For this reason, it is an important issue to improve the processability of the galvanized steel sheet and the snackability after painting.

Furthermore, according to the research conducted by the present inventors, as shown in Table 1, the workability of conventional galvanealed steel sheets is closely related to the iron concentration in the plating layer, and the iron concentration is within the range of about 13% or less. In , the iron concentration deteriorates exponentially as the iron concentration increases.

Table 1 The workability scores shown in Table 1 above were determined by the following method. The test surface was bent 90 degrees with the test surface facing inside, cellophane tape was applied and peeled off, and the amount of zinc powder adhering to the tape was compared and evaluated with a limit sample prepared according to the following criteria.

5... No adhesion of zinc powder 4... Small amount of zinc powder 3... Small amount of zinc powder 2... Large amount of zinc powder 1... Extremely large amount of zinc powder On the other hand, corrosion resistance after painting is determined by the increase in iron concentration The improvement is almost linear. The iron concentration in the plating layer of conventional galvanoiled steel sheets is either an alternative choice depending on which property is important, or an intermediate iron concentration, such as 11%, which is not sufficient for any of the properties. They were forced to choose unfavorable iron concentrations such as

In view of the above-mentioned circumstances, it is an object of the present invention to provide a galvanealed steel sheet that retains the excellent properties of the conventional galvanoiled steel sheet, has excellent plating layer workability, and has excellent post-painting corrosion resistance.

The present invention contains 15 to 27 wt% iron and 0.02 to 27 wt% chromium.
2. The present invention provides an iron-chromium-zinc ternary alloy plated steel sheet containing 50% by weight and the remainder consisting of zinc and unavoidable elements.

The present invention also provides a range of 0.02 to 2. An iron-chromium method characterized in that a plating layer consisting of Owt% chromium, the balance zinc, and unavoidable elements is deposited on a steel sheet, and then galvanized to diffuse the iron in the steel sheet base into the plating layer. - A method for producing a zinc ternary alloy coated steel sheet is provided.

The present invention will be explained in detail below.

The invention shown in FIG. 1 of this defense contains 15 to 27 wt% iron and 0.02 to 2.0 wt% chromium. It is an iron-chromium-zinc ternary alloy plated steel sheet having a plating layer containing 50% by weight and the remainder consisting of zinc and unavoidable elements.

In the present invention, the iron concentration in the plating layer is 15 to 27 wt%.
According to the research of the present inventors, the limit is 0.02
~2. Synergistically with the effect of containing Owt% of chromium, the corrosion resistance after painting reaches the target level of the present invention only when the iron concentration is 15wt% or more. Above this, the higher the iron concentration, the better the corrosion resistance. If it exceeds this, the workability of the plating layer will deteriorate compared to the target level of the present invention, and this range is essential for satisfying both the characteristics of corrosion resistance after painting and workability of the plating layer.

The chromium concentration in the plating layer is 0.02 to 2. The reason for limiting the range to Owt% is as follows. In other words, the improvement effect of corrosion resistance after painting due to the inclusion of chromium is 0.01
It is hardly observed below wt%, and the target level of the present invention can only be reached when it is above 0.02wt%. Therefore, the lower limit of the chromium concentration is set to 0.02 wt%. Also,
When the chromium concentration is 0.02 wt% or more, the effect of improving corrosion resistance after painting becomes greater as the amount of chromium increases; When it exceeds Owt%, the processability of the plating layer tends to deteriorate, which deviates from the purpose of the present invention. Therefore, the upper limit of the chromium concentration is set at 2.0%.

Note that the iron concentration in the plating layer is 15 wt% or more, and 0.
The reason why the corrosion resistance after coating is significantly improved by containing 0.2 wt% or more of chromium is that, according to research by the present inventors, the natural electrode potential of the plating layer becomes more noble as the iron and chromium concentrations increase. Therefore, it is inferred that the electrochemical stability of the plating layer, which directly affects the corrosion resistance after painting, is further increased, and as a result, the corrosion resistance after painting is dramatically improved.

In addition, the iron concentration in the plating layer exceeds 27 wt%, or the chromium concentration exceeds 2.5 wt%. According to the research conducted by the present inventors, the reason why the plating layer workability deteriorates when Owt% is exceeded is as follows.
When the iron concentration is in the range of 15 to 271%, the composition of the iron-zinc alloy layer is two-phase r phase, δ phase, or r
28wt%
Since the above results in almost a single r-phase, it is presumed that a change in the iron-zinc alloy phase composition in the plating layer due to a change in iron concentration is a cause of the deterioration of workability. Also, the chromium concentration in the plating layer is 2. Since it has been found that when the amount exceeds Owt%, a hard and brittle substance is produced on the plating surface, it is assumed that the production of this substance is also a cause of deterioration of workability.

The second aspect of the present invention is that the galvanized layer contains 0.02 to 2
．． A method for producing an iron-chromium-zinc ternary alloy plated steel sheet, which comprises containing Owt% chromium and then performing galvanyl treatment. The reason why galvannealing is performed after chromium is included in the plating layer is that, as a result of research by the present inventors, adding chromium in advance reduces the interaction between zinc in the plating layer and iron in the steel sheet base during galvanealing. It has been found that the crystals of the iron-zinc alloy produced by the mutual diffusion reaction, so-called iron-zinc alloying reaction, become finer, and as a result, the workability of the plating layer is significantly improved compared to the case where chromium is not included in advance. Therefore, in the present invention, chromium is preliminarily contained in the plating layer and then galvanized. Note that the improvement effect on the workability of the plating layer occurs when the chromium temperature is approximately 1. It is known that the amount of chromium is the largest when the iron-chromium-zinc 3-element alloy plated steel sheet of the present invention is pre-contained in the plating layer from 0.02 to 2, taking into consideration the corrosion resistance after painting. ．． Owt%.

Regarding the method of incorporating chromium into the galvanized layer prior to galvanyl treatment, the results are obtained by dissolving chromium in a general hot-dip galvanizing bath and immersing the steel sheet in this plating bath for plating. Alternatively, chromium may be contained in the galvanized layer, or chromium and zinc may be plated sequentially by electrolytic plating, resulting in chromium being contained in the galvanized layer.

Hereinafter, the present invention will be specifically explained with reference to Examples.

In a general Sendzimer type hot-dip galvanizing line, a low-grade aluminum guild steel plate (thickness: 0.7 mm) is coated in a hot-dip galvanizing bath (with a chromium concentration adjusted to various levels in the range of 0 to 2.5%). After forming plating layers with different chromium concentrations by immersing the aluminum in a bath with an aluminum concentration Q of 1θwt% and a bath temperature of 500°C, it was introduced into a galvaneal furnace, and heated at a heating temperature of 500 to 700°C and a residence time in the furnace. Galvanil treatment is performed under heating conditions of 4 to 50 seconds to achieve a chromium concentration of 0 to 2.
Various iron-chromium-zinc ternary alloy plated steel sheets were manufactured, each having an iron concentration of 10 to 35 wt%, the balance being zinc, aluminum, and other unavoidable elements. In addition, in the galvanil treatment, when the target iron concentration is high, the heating temperature is set high, or the residence time in the furnace is set long.

Regarding the iron-chromium-zinc ternary alloy plated steel sheet manufactured as described above, the post-painting corrosion resistance and plating workability were examined using the following methods. The results are shown in FIGS. 1 to 3.

(1) Evaluation method for erodibility after painting After performing general degreasing, washing with water, and drying in sequence, apply a cationic hard electrodeposition coating (Nileclone 9000 Black manufactured by Kansai Paint Co., Ltd., with a film thickness of 20 mm after baking. -) is used as a test piece, and after making a cross cut that reaches the base steel plate,
A salt spray test according to JIS Z 2371 was conducted for 480 hours, and the maximum erosion width on one side from the center of the cut was measured.
The smaller the erosion width, the better the corrosion resistance after painting.

(2) Method for evaluating processability of plating layer Bend it 90 degrees with the test surface inside, peel off cellophane tape, and measure the amount of zinc powder adhered to the tape using the limit sample prepared according to the following criteria. A comparative evaluation was made.

5... No adhesion of zinc powder 4... Small amount of zinc powder 3... Small amount of zinc powder 2... Large amount of zinc powder 1... Extremely large amount of zinc powder From Figure 1, the corrosion resistance after painting is according to the present invention. The iron concentration reaches the lower limit or higher when the iron concentration is 20 wt% or more. Further, it can be seen that the workability of the plating layer reaches the lower limit of the target level of the present invention or more when the iron concentration is in the range of 15 to 27 wt%.

However, as is clear from Figure 2, there is no 0 in the plating layer.
．． By containing 0.2 wt% of chromium, the corrosion resistance after painting reaches the lower limit of the target level of the present invention at an iron concentration of 15% + 1% or more. concentration. That is, by including 10 μm of iron, the iron concentration range in which the corrosion resistance after coating is good is expanded. Furthermore, it is clearly seen by comparing FIG. 1 and FIG. 2 that the workability of the plating layer is also improved by adding chromium. Furthermore, the workability of the plating layer can be improved by including chromium, which has an iron concentration of 28w.
It can be seen that the target level of the present invention cannot be achieved at t% or more.

Furthermore, from Figure 3, the corrosion resistance after painting is 0.0% for chromium.
The target level of the present invention is reached only by containing 2 wt% or more, and in the range of chromium concentration of 0.02 to 2.0%, the workability of the plating layer improves almost linearly as the chromium concentration increases. , it can be seen that the improvement effect is almost saturated when the chromium concentration exceeds about 2.Owt%.Also, the workability of the plating layer reaches the target level of the present invention when the chromium concentration is in the range of 0.02 to 2.Owt%. However, about 2.
It can be seen that when the chromium concentration exceeds Owt%, the workability of the plating layer deteriorates rapidly as the chromium concentration increases.

[Brief explanation of the drawing]

2 Figure 1 shows the case where the plating layer does not contain any chromium.
Figure 2 shows the relationship between the iron concentration in the plating layer, the corrosion resistance after painting, and the workability of the plating layer.
FIG. 3 is a diagram showing the relationship between the iron concentration in the plating layer and the corrosion resistance after painting and the workability of the plating layer. FIG. 3 is a diagram showing the relationship between the chromium concentration in the plating layer and the corrosion resistance after painting and the workability of the plating layer.

Claims (2)

[Claims] (1) 15 to 27 tons of iron and 0.02 to 2.0 tons of chromium.
An iron-chromium-zinc ternary alloy plated steel sheet having a plating layer containing 0 wt% and the remainder consisting of zinc and unavoidable elements. (2) 0.02-2. A plating layer consisting of Owt% chromium, the balance zinc and unavoidable elements is deposited on the steel plate,
A method for manufacturing an iron-chromium-zinc ternary alloy plated steel sheet, which comprises subsequently performing galvanyl treatment to diffuse iron in the steel sheet base into the plating layer.