JPS60169739A - Corrosion accelerating test method - Google Patents

Abstract

PURPOSE:To predict the life of a material highly accurately, by dividing the corrosion accelerating test of a steel plate into a high temperature low humidity test and a low temperature high humidity test at every specified time period, thereby forming one cycle, spraying a specified amount of salt water, and reproducing the corrosion phenomenon close to a real environment. CONSTITUTION:In the natural environment, temperature is high and humidity is low during the day, the temperature is low and humidity is high during the night. The conditions of the corrosion accelerating test of a steel plate are simulated to above described conditions as close as possible. The steel plate is tested under the following conditions: under the state of high temperature and low humidity, e.g., temperature of 50-70 deg.C and humidity of 50-70% or under the state of low temperature and high humidity, e.g., temperature of 15-25 deg.C and humidity of 80-100%, salt water of, e.g., 25-10mg/100cm<2>, is supplied, and the cycles are changed as shown in the Figure. Since the steel plate is tested in this way, the corrosion of the steel matches the real corrosion, and the test can be conducted in the same corrosion conditions of the natural environment. The accuracy in prediction of the life of a material is enhanced. Since the cycles in two conditions asre used, the test is simple, and the time can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an accelerated corrosion test method for faithfully reproducing the corrosion phenomenon of metal slopes such as bare steel plates and painted steel plates.

<Prior art> As a corrosion acceleration test method for metal materials used in automobile bodies such as bare steel plates, painted steel plates, and steel plates coated with anti-corrosion coating 'iI', a salt spray tester as specified in JI8 is used. (1) Continuously spray salt water onto the test piece in a corrosive environment, and after a certain period of time, evaluate the corrosion form (corrosion status).
There are also methods to evaluate the amount of corrosion.

In addition, JP-A-56-126740 provides a method of evaluating the corrosion form (corrosion status) and corrosion amount after repeating a cycle of salt water spray, forced drying, salt water immersion, and natural drying for a certain period of time. There is.

However, in the former method, the corrosion form obtained by that method is different from the corrosion form obtained by actual vehicle and outdoor exposure tests.
Corrosion phenomena cannot be faithfully reproduced.

In other words, in the actual vehicle and outdoor exposure tests, as shown in Figure 1, on the steel plate 2 with a coating film, corrosion progresses over time without covering the scratches, but the former method In this case, the main focus was on promoting rust, and salt water was continuously supplied under conditions of high temperature and high humidity, so too much Fe 304 was eluted and the second C! This is because, as shown by Q, the rust 3 will cover the wound, and as a result, the progress of corrosion will be inhibited from a certain point onwards.

Furthermore, in the former method, there is no rank correlation in the amount of corrosion. In other words, as shown in Fig. 3, the corrosion width between ordinary steel plate A and antirust steel plate B in actual vehicle and outdoor exposure tests shows that ordinary steel plate A is naturally wider than the corrosion width, but the former method In this case, as shown in FIG. 4, the rust-proof steel plate B will have worse results. This is due to the fact that the salt water is continuously supplied under the conditions of high temperature and high humidity as described above, which promotes the elution of Za from the rust-proof steel sheet. In other words, the former method can be used, for example, when two types of materials are coated on the same steel plate and used to compare and evaluate the corrosion resistance performance between the materials, but it is also used to predict the corrosion χ that will occur in a practical environment. There is a problem in doing so.

In this regard, the latter method (Japanese Unexamined Patent Publication No. 56-126740) solves the problem, but requires four steps in one cycle: salt water spraying, forced drying, salt water immersion, and natural drying.

<Object of the Invention> The object of the present invention is to reproduce the form of corrosion that occurs in a practical environment, and by adopting test conditions that simulate the corrosion conditions of the natural environment as much as possible, the material can be manufactured with high accuracy. The present invention provides an accelerated corrosion test method that enables prediction of the service life of a metal, shortens the testing process, and eliminates the above-mentioned conventional problems.

<Structure of the Invention> The accelerated corrosion test method that characterizes the present invention is one cycle divided into high temperature, low humidity and low temperature, high humidity within a predetermined time, and a predetermined amount of salt water Y is supplied to the low temperature and high humidity. .

<Example> Examples of the method of the present invention will be described below.

First, to explain the background of the method of the present invention, in order to determine the actual corrosive environmental conditions, the weather, wind direction, wind speed, temperature, humidity, dew condensation time, exposure As a result of investigating the board surface temperature, actual vehicle surface temperature, and amount of sea salt particles, the following was ascertained.

(1) Daytime: High temperature and low humidity.

(2) Nighttime: low temperature and high humidity.

(3) Condensation forms on the surface of the actual vehicle at night, and the duration is approximately 1'1.
It is 2 hours.

(4) At night, the actual vehicle surface temperature shows approximately the same value regardless of the difference between light and dark colors, but during the day, the dark color shows a maximum temperature Y that is approximately 20'C higher.

(5) There are very few sea salt particles.

Therefore, the present invention particularly takes into consideration the above items (1) and (2),
The test method was set up under conditions that approximated the actual environment as much as possible.

The conditions are high temperature, low humidity, and a temperature of 50 to 70'C.

Humidity should be 50 to 70 degrees, and temperature should be 15 to 25 degrees at low temperature and high humidity.
C1 humidity is 80-100%, and as illustrated in Figure 5, it is divided into high temperature and low humidity and low temperature and high humidity within a certain period of time.
cycle, supply amount 5 to 2Dm9/da at low temperature and high humidity.
y/10Qcm2 of salt water was supplied.

Therefore, the role of the high temperature and low humidity is to expand the corrosion area under the paint film, and the role of the low temperature and high humidity is to take salt water under the paint film from the wound, and to control the elution of Zf& in the rust-proof steel plate. In addition, the role of the salt water supply is to contribute to the formation of local batteries and promote corrosion.

Regarding the timing of salt water supply when salt water is supplied during low temperature and low humidity, looking at the wind direction and wind speed Y under actual environmental conditions in coastal areas, the wind blows from the sea toward land during the daytime during high temperature and low humidity. The wind speed is also quite strong at 4 to 8 φec, and at night when the temperature is low and high, the wind blows from the land to the sea at the same time, and the wind speed is θ to IBm/see, which is a light breeze. Therefore, most of the sea salt particles are supplied during the daytime during high temperature and low humidity, and in the present invention, it is sufficient to supply salt water during high temperature and low humidity, but if sea salt particles are supplied during high temperature and low humidity, Salt water is supplied during low temperature and high humidity to ensure high temperature and low humidity conditions.2 In addition, the amount of salt water supplied per cycle is Regardless of the length of time, the total amount per day (21i hours) is 5 as mentioned above.
~20 Nil/day/100cm2, for example, if one cycle time is 72 hours,
The amount of salt water supplied during one cycle is approximately 04 to 1.6Q/
100-2-c-A 17.1 cycle, Il time 12
In terms of time, the supply amount is 25 to 1 hour, 9/100 degrees.

The results of the temperature test conducted using the method of the present invention, the test method according to JIS, and the natural environment (outdoor exposure test) are shown in FIGS. 6 to 8.

The symbols in Figures 6 to 8 indicate the following coating systems.

△: Cold rolled steel plate - Dating surface treatment - Anionic electrodeposition coating - Intermediate coating - Top coating: Cold rolled steel plate - Dipping surface treatment - Cationic electrodeposition coating - Intermediate coating - Top coating 0: Rust-preventing steel plate - Dipping surface treatment - Anionic electrodeposition coating - Intermediate coating - Top coating: Rust-preventing steel plate - Dating surface treatment - Cationic electrodeposition coating - Intermediate coating - Top coating Shows superior rust prevention (less corrosion) than painted steel sheets. On the other hand, in the natural environment shown in FIG. 8, the anti-corrosion steel coated plate has a much better anti-corrosion ability than the cold-rolled steel coated plate. The present invention shown in FIG. 6 has a corrosion state that correlates well with the natural environment shown in FIG. 8. Also, regarding the form of corrosion, the corrosion of painted cold-rolled steel sheets according to the tests of the present invention is similar to the corrosion form in the natural environment as shown in Figure 1, where the paint film swells up and rust accumulates underneath. became.

<Effects of the Invention> As described above, according to the present invention, a corrosive environment with conditions similar to those in the natural environment can be obtained, the corrosion form is similar to that of the actual vehicle and outdoor exposure test, and the rank correlation of the amount of corrosion can be established. It is effective in predicting the lifespan of materials with high precision in various rust prevention measures and examining corrosion mechanisms, and has the advantage of shortening the testing process because it is a two-condition cycle of high temperature, low humidity and low temperature, high humidity.

[Brief explanation of drawings]

Figure 1 shows the corrosion form in the actual vehicle and outdoor exposure test, Figure 2 shows the corrosion form in the conventional accelerated test method.
The figure shows the amount of corrosion obtained by actual vehicle and outdoor exposure tests. Figure 4 shows the amount of corrosion obtained by the conventional accelerated test method.
The figure is a cycle diagram showing a simple example of the method of the present invention, Figure 6 is a diagram showing handle cloths of steel plates coated with various coatings by the method of the present invention, and Figure 7 is a diagram showing various coatings of steel plates coated with the conventional accelerated test method (JI8). FIG. 8 is a diagram showing the amount of corrosion of various painted steel plates due to the natural environment.

Claims (1)

[Claims] This is a corrosion acceleration test method for reproducing the corrosion phenomenon of metal materials such as steel plates.It is a "CI cycle" which is divided into high temperature, low humidity and low temperature, high humidity within a predetermined time, and a predetermined amount of salt water is supplied during low temperature and high humidity. A highly distinctive corrosion acceleration test method.