JPS62109928A - Low oxidation annealing method for corrosion resistant steel sheet containing chromium - Google Patents

Abstract

PURPOSE:To control oxide film formed at annealing to the thickness of the extent without requiring pickling stage, by annealing steel sheet having a specified Cr content at suitable temp. and dew point, in annealing furnace of gaseous atmosphere having a specified compsn. composed of gaseous H2 and N2. CONSTITUTION:Steel sheet contg. 1-19wt% Cr is annealed by annealing furnace of gaseous atmosphere composed of 0-75% gaseous H2 and the balance substantially gaseous N2. Temp. of the annealing is regulated to a prescribed temp. in 650-900 deg.C range determined from Cr content of the steel sheet. Dew point of the gaseous atmosphere is controlled to a prescribed dew point of 0--40 deg.C range determined from annealing temp. of the steel sheet. The annealing carried out for <=60sec soaking time while using continuous annealing furnace for common steel sheet is favorable. By the titled annealing, thickness of oxide film formed on steel sheet is controlled to <=500Angstrom and pickling stage thereafter is made unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of annealing thin steel sheets containing chromium as an alloying component.

[Prior Art] Conventionally, various types of stainless steel sheets have been used as high-grade corrosion-resistant steel sheets. ! l! However, since stainless steel is manufactured using a special method different from 17F steel, it is
It is a valuable steel material. For example, in the bright annealing method for stainless thin steel sheets, hydrogen or an inert gas with a high temperature of 81 degrees Celsius (about 75% hydrogen) is used as the atmosphere gas, and the dew point of the atmosphere gas is set to -50℃ or higher, which increases operating costs. Moreover, the continuous annealing and pickling method uses expensive hydrofluoric acid and alkali salt, which causes the manufacturing cost to be higher than that for annealing ordinary steel. As mentioned above, stainless steel is a high-grade but expensive steel material. For this reason, there is a demand in the market for cheaper and more practical corrosion-resistant thin steel sheets that can be used more widely in automobiles, building materials, and the like. Chromium-containing steel sheets meet this market demand, but the conventional stainless steel scratch annealing method is unsuitable for annealing corrosion-resistant thin steel sheets that contain chromium as an alloying component due to high production costs. On the other hand, when conventional steel annealing methods were used, there was a drawback that it was difficult to descale the oxide film, which was similar to that of an adult cow. Furthermore, Japanese Patent Application Laid-Open No. 58-12645 discloses a method of applying N1 plating to the surface of a steel plate and annealing it in a non-oxidizing manner, but according to this method, the cost increases as the N1 plating is applied.

[Problems to be Solved by the Invention] The present invention is annealing a thin steel sheet containing 1 to 19 percent chromium as an alloy component in a continuous annealing furnace for ordinary steel sheets, which shares equipment with ordinary steel sheets. Regarding annealing technology. More specifically, by performing the annealing under conditions that are gentler than the bright annealing method for stainless steel and that can be controlled in a continuous annealing furnace for ordinary steel sheets, the oxide film produced during annealing can be reduced to a level that does not pose any practical problems. The present invention relates to an annealing method that forms an oxide film with the same properties and does not require a pickling process after annealing.

[Means for Solving the Problems] The present invention contains chromium as an alloy component in an amount of 1 to 19% by weight: 4 In annealing a steel plate, the composition of the atmospheric gas in the furnace is 0 to 75% hydrogen gas. The remaining part is an annealing furnace made essentially of nitrogen, and the annealing temperature is set at a predetermined temperature determined by the chromium content of the thin steel sheet within the range of 650 to 900'C, and the dew point of the atmospheric gas is set at 0 to -40'C. This is a method for annealing a chromium-containing steel sheet in which the thickness of an oxide film in annealing the thin steel sheet is 500 Å or less by controlling the dew point to a predetermined dew point determined by the annealing temperature of the thin steel sheet. This is a continuous annealing furnace that normally anneals thin sheets, and the annealing method described above is such that the soaking time for chromium-containing steel sheets is 60 seconds or less. In the present invention, the predetermined temperature determined by the chromium content refers to #1lfi with a different chromium content in FIG.
F! In the hardness-temperature curve shown for , it refers to the temperature that corresponds to the desired hardness. Specifically, since steel materials with sufficiently low hardness are usually desired, for example, steel materials with a chromium content of 1
．． In the case of 2%, it is annealed at about 700°C as shown in FIG. 2, and for example, in the case of 9°7%, it is annealed at about 800°C.

In addition, in the present invention, controlling the dew point to a predetermined dew point determined by the annealing temperature means that the dew point of the furnace atmosphere gas is controlled at each annealing temperature t shown in FIG.
It refers to operating at a temperature within the range of 1° from the 1° 11 Ei line for N degrees. Specifically, for example, if n1A melon is annealed at 700"C, the dew point is set to 0°C or higher.
For example, the annealing temperature is 800° (for example, the dew point is -117°C to 1°C).

[Effect mechanism 1. 4 types of cold-rolled 0 (carbon chloride) containing thin steel sheets are annealed under different annealing conditions, and the 4'J+ car exhaust muffler is made with the oxide film still attached. Table 1 shows the results of annealing furnace atmosphere gas composition: 1.5% N2, the rest being essentially N2.As is clear from Table 1, when the thickness of the oxide film is 500 Å or more, During muffler processing, the oxide film peels off, the die wear is large, and weldability is also extremely poor.

On the other hand, when the thickness of the oxide film was 500 Å or less, the oxide film hardly peeled off, and both formability and weldability were good. Table 2 shows the results of annealing five types of cold-rolled low-carbon chromium-containing thin steel sheets with different chromium contents under varying annealing conditions, then chromium plating, and then painting, and testing the paint adhesion. Stainless steel has poor paint adhesion, and the method used to improve this problem is to apply chrome plating and then paint.This method was used to evaluate the paint adhesion. As is clear from Table 2, the thickness of oxide 1 is 500
When the thickness was 500 Å or more, the paint adhesion was poor, but when it was 500 Å or less, the paint adhesion was good.

Based on the results shown in Tables 1 and 2 regarding muffler molding and paint adhesion, the inventors determined that the thickness of the surface oxide film is the quality of the chromium-containing thin steel sheet that is the object of the present invention. If it is less than 500 Å.

It was confirmed that there were no problems during normal use.

We will explain how to set the number of people to 0 or more. FIG. 1 is a diagram showing the relationship between annealing conditions and oxide film thickness, and is a diagram that summarizes the above-mentioned Tables 1 and 2 and the results of related annealing tests (not shown). Table 2 shows experimental examples in which the ratio of hydrogen gas in the atmospheric gas consisting of nitrogen gas and hydrogen gas was changed. It was found that the annealing temperature and the dew point of the atmospheric gas shown in FIG. 1 have a strong relationship with the thickness of the oxide film.

Furthermore, the shorter the annealing time, the better for low oxidation.
Continuous annealing methods are suitable for the present invention. In Figure 1, the annealing time is 30 seconds, but if it is within 60 seconds, the relationship between the annealing temperature and the oxidized plate thickness falls within the range shown in Figure 1, so the annealing time is 60 seconds.
It may be as short as possible, 0 seconds or less. The line E in Figure 1 is the limit line at which the thickness of the oxide film is 500 mm, and annealing should be performed so that the dew point of the atmosphere gas in the furnace reaches the temperature shown in the area below the line E. is important. For example, when annealing at 700'C, the dew point of the atmospheric gas is 0°C or less, and when annealing at 800'C, the dew point of the atmospheric gas is -17°C or less, and if the soaking time is 30 seconds, the thickness of the oxide film will increase. This shows that a chromium-containing thin steel sheet having a thickness of 500 Å or less can be obtained.

Figure 2 is a diagram showing the annealing temperature and hardness after annealing when a chromium-containing steel sheet is annealed with a soaking time of 30 seconds, and shows that the annealing temperature is determined by the chromium content of the thin steel sheet. FIG. Figure 2 shows the hardness after annealing of a low-carbon chromium-containing thin steel sheet with chromium as a substantial alloying component and a soaking time of 30 seconds. By annealing thin steel sheets containing chromium at a temperature of 30 seconds, it is easy to obtain the same relationship as shown in Figure 2 through experiments each time. It does not limit the composition of the alloy.

Next, as an example of applying the present invention, chromium is 9.7
A cold-rolled thin steel sheet containing 1% by weight of carbon dioxide was annealed to achieve a target hardness of Hv150 after annealing and an oxide film thickness of 500 Å.
The following annealing method will be explained.

From Figure 2, the appropriate annealing temperature is 800°C, and the annealing time and atmosphere gas composition are as explained in page 11, soaking time is 30 seconds, hydrogen gas is 0 to 75%, and the rest is nitrogen. It is better to use gas. From FIG. 1, it is preferable to control the dew point of the atmospheric gas to -17° C. or lower.

[Example code] Next, the present invention will be explained in detail.

1. A cold-rolled thin steel plate with a thickness of 0.4 mm containing 4.8% by weight of chromium was annealed at a temperature of 750°C, a soaking time of 30 seconds, an annealing furnace atmosphere gas composition of H21.5%, N298.5%, and dew point. Annealed at -10'C. The oxide film of the obtained steel plate was 300
The formability, weldability, and paintability after Cr plating were all good. 850' C1 soaking time 20 seconds, annealing furnace atmosphere gas composition 8220%, N280%, dew point -
The oxide film of the steel sheet obtained by annealing at 30°C was 250, and the formability, weldability, and paintability after Cr plating were all good.

[Effect of the invention] According to the present invention, when handling chromium-containing thin steel, the soaking time is 60
Within seconds, the composition of the surrounding gas is hydrogen gas 0 to 75.
%, and the remainder is substantially nitrogen gas, and the W point of the ambient gas is annealed in the range of 0 to -40°C. After annealing, an excellent chromium-containing thin steel sheet can be produced without descaling treatment such as pickling. Production became = I ability.

These annealing conditions can be controlled in a continuous annealing furnace for ordinary steel sheets.
Therefore, according to the present invention, chloride,
It has now become possible to anneal containing thin steel sheets in a continuous annealing furnace for ordinary steel sheets. In addition, the present invention significantly eases the annealing conditions that are caused by the high operating cost of the bright annealing method for stainless steel, and when applied to a bright annealing furnace for stainless steel, the operating cost can be significantly reduced. decreases to 1.

Since the chromium-containing thin steel sheet manufactured by the present invention has a thin oxide film, it can be easily descaled by pickling. Therefore, even when using pickled steel plates, the cost of descaling can be significantly reduced.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between annealing conditions and oxide film thickness, and Figure 2 is a diagram showing the relationship between annealing temperature and hardness after annealing, where a is 1.2.
% chromium steel, b is 4.8% chromium steel, C is 9.
7% chromium steel, d is 12-17% chromium steel.

Claims (2)

[Claims] (1) When annealing a thin steel sheet containing 1 to 19% by weight of chromium, the composition of the atmosphere gas in the furnace is 0 to 75% hydrogen gas.
The rest of the annealing furnace is made essentially of nitrogen, and the annealing temperature is set to 6.
At a predetermined temperature determined by the chromium content of the thin steel sheet within the range of 50 to 900°C, the dew point of the atmospheric gas is set to 0 to -40°C.
A low oxidation annealing method for a chromium-containing corrosion-resistant thin steel sheet, in which the thickness of an oxide film during annealing of the thin steel sheet is 500 Å or less by controlling the dew point to a predetermined dew point determined by the annealing temperature of the thin steel sheet within the range of °C. (2) The low oxidation annealing method for a chromium-containing corrosion-resistant thin steel sheet according to claim 1, wherein the annealing furnace is a continuous annealing furnace for ordinary steel thin sheets, and the soaking time is 60 seconds or less.