JPS59140390A - Manufacture of stainless steel sheet - Google Patents

Abstract

PURPOSE:To obtain a stainless steel sheet having highcorrosion resistance independently of the presence of oxide films on the surfaces of the sheet by plating a cold rolled stainless steel sheet with Ni and by subjecting the plated sheet to annealing-thermal diffusion in an oxidizing atmosphere. CONSTITUTION:A cold rolled stainless steel sheet is plated with Ni or an Ni alloy contg. >=1 kinds among Cr, Mo, Ti, W, P and B, and the plated sheet is subjected to continuous annealing at the recrystallization temp. -1,000 deg.C in an oxidizing atmosphere. Cr in the stainless steel is concentrated in the surface layers of the sheet, and the concn. of Cr in the layers becomes higher than the concn. of Cr in the central layer of the sheet in the thickness direction. Thus, a stainless steel sheet having high corrosion resistance is obtd. The corrosion resistance is maintained whether colored oxide films covering the surfaces of the sheet are removed or not before use. The films are removed by pickling or polishing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a thin stainless steel plate, and particularly to a surface treatment of a thin stainless steel plate.

Conventional manufacturing of thin stainless steel sheets TrsFe, Cr, Ni
Alternatively, steel is made by adding a small amount of additive elements such as IVIo and A4 Ti, and then the steel billet → hot rolling → hot rolled plate annealing and pickling → bright annealing, and oxidation annealing → pickling/temper rolling or polishing to produce a finished product. It is said that

By the way, Cr1Fe, which is the main component of stainless steel, has a stronger affinity for oxygen (compared to Cr1Fe), so it is easily oxidized, and during hot rolling and oxidation annealing, scale is formed with Fe, and oxidation and descaling are repeated several times. Over time, a so-called Cr-free layer is formed in which the Cr content of the surface layer is considerably lower than that of the central component of the plate thickness.

The inventors developed 5US4, which is a typical ferritic stainless steel.
When examining a thin plate of No. 30, the amount of Cr at the center of the plate thickness was 171.
%, whereas the amount of Cr on the outermost surface was only 86%)
2. (Fig. 1) The characteristic of stainless steel sheet is its corrosion resistance and rust resistance, which greatly affects the amount of Cr in the steel. is a big problem. Moreover, what influences the corrosion resistance and rust resistance are the components on the outermost surface ranging from several tens of microns to several micrometers and the density of the Cr2O3 film.

In the process of manufacturing thin stainless steel sheets, scale formation cannot be avoided several times, and to that extent, chromium removal from the surface cannot be avoided. Therefore, it is possible to improve the surface corrosion resistance by plating the final product with CRR, but plating alone does not necessarily lead to improved corrosion resistance because it causes cracks and point defects from a microscopic perspective.

As a result of various experiments, the present inventors have found that before final annealing, that is, after applying N1 plating to a cold-rolled stainless steel sheet, annealing in a corrosive atmosphere (for example, a direct-fired furnace with an air ratio of 10 or more) is possible.
Due to thermal diffusion, Cr in the steel concentrates on the surface, resulting in a Cr concentration higher than near the center of the plate thickness. It has been found that stainless steel sheets with good corrosion resistance can be produced even if the oxidized steel is removed by pickling or polishing.

That is, the structure of the present invention for obtaining the above stainless steel thin plate is as follows.

(1) Ni plating is applied to a stainless steel sheet after cold rolling, and then the temperature is 1000℃ above the recrystallization temperature in an oxidizing atmosphere.
A method for manufacturing a thin stainless steel plate, characterized by carrying out continuous annealing in the following temperature range.

(2) Cr, Mo, Ti, W, P, and Ni are added to the thin stainless steel plate after 't' + rolling, with Ni as the main component.
BO) A method for manufacturing a thin stainless steel plate, which comprises plating an alloy containing two or more types of Taho and continuously annealing the plate in an oxidizing atmosphere at a temperature ranging from a recrystallization temperature to 1000°C.

(3) A method for producing a stainless steel thin plate, which comprises adding the step of pickling or surface polishing the thin plate to remove a surface oxide film to the method of item 1.

(4) In addition to the method of item 2, pickling the thin plate '1. A method for manufacturing a thin stainless steel plate which includes the additional steps of removing a surface oxide film by surface polishing or surface polishing.

The present invention will be explained in detail below.

J: As mentioned above, when a thin stainless steel plate is plated with Ni and annealed in an oxidizing atmosphere, Cr in the steel becomes concentrated on the surface. Not only does Ni in the stainless steel diffuse into the plated steel by thermal diffusion during annealing, and Cr in the stainless steel diffuses into the Ni layer on the surface to make the concentration uniform, but also due to the oxidizing atmosphere, This seems to be because Cr, which has a stronger affinity for oxygen, is concentrated on the surface more than in the center layer of the plate.

Moreover, once a Cr2O3 oxide film is formed, unlike an Fe oxide film, it is dense and difficult to grow. ), the scale film thickness is 0.1~Q, 2 I
t Ill, and even if the scale is removed, a sufficient Cr-enriched layer remains.

Figure 2 i1″3: Shows the state of thermal diffusion due to annealing of Ni-plated stainless steel, with (A) before I/;J annealing and (B) depth from the outermost surface of the plate thickness after annealing. TC according to
Fe, Ni.

The amount of each component of Cr and O is shown. Before annealing, the layer is 100% Ni up to 0.5 to 0.6 μm from the outermost surface, but after annealing, N1 diffuses into the inside as shown in (B).
It can be seen that Cr is concentrated on the surface.

Recently, stainless steel sheets have been increasingly used as exterior materials such as roofs and exterior walls. In this case, it is often used as a paint rather than as a white shiny metal. By the way, even if high-quality paint is used for the paint, since it is an organic material, it cannot prevent aging and must be repainted every 5 to 10 years. Even if you use highly corrosion-resistant stainless steel, it is a waste to repaint it.

Therefore, maintenance-free inorganic coatings can maintain the color tone permanently. So-called colored stainless steel has these properties, but due to the long processing time in conventional wet chemical conversion treatments, it was impossible to continuously chemically treat strip-shaped stainless steel sheets, and we created equipment to do so. It was not manufactured because it was too expensive.

The thin stainless steel plate of the present invention is plated, and the annealing temperature is
By adjusting the annealing time, colors can be selected from golden to brown, reddish-purple 1W, bluish-purple, and black, making it possible to produce colored stainless steel at a much lower cost than conventional wet chemical conversion treatments.

Conventional colored stainless steel is treated with wet chemical conversion and then sealed, but like plating, it is not possible to completely prevent point defects. Since the method of the present invention performs Ni plating and annealing-Cr diffusion, point defects are completely prevented and corrosion resistance is excellent.

Furthermore, only Ni plating (, Cr, Mo, Ni, etc.)
'l'i.

One or more elements such as W, P, 13, etc., 1% to 50
Not only does the alloy plating containing within the range of % have better corrosion resistance, but it also has a richer color tone, which is a completely new attempt in the production of colored stainless steel.

Even if a stainless steel sheet is manufactured by applying N1 or Hohe 1 alloy plating and then performing oxidation annealing, pickling, and temper rolling using the existing AP (annealing-pickling) line, it will still be the same as the conventional stainless steel sheet. We were able to create products with better corrosion resistance.All of these were made by applying highly corrosion resistant metal plating to the stainless steel surface and by thermal diffusion.
This forms a highly corrosion-resistant alloy film of several micrometers.

Next, the relationship between the Cr content in the steel in the present invention will be described.

How much Cr is required in a thin stainless steel plate plated with Ni alloy? Change the Cr content in the steel from 0 to 9% and make a test material. N1 and Ni-Cr alloy plating. 5μm, heat annealed in a direct fire furnace with an air ratio of 12 (about 5%) to 850℃ to 900℃, and remove the oxide scale with 5%HCt + 2%l-1NO1 mixed acid (50℃)
After descaling and temper rolling, a corrosion resistance test was conducted. Table 1 shows the pickling time and the results of the corrosion resistance test.

Table 1 Cr content in steel and pickling and corrosion properties of plated and annealed materials□
□□□□□□□-1 N4:1) Steel components other than Cr trJ, C: 0.
03. Si: 0.25. M+]: 0.30. S:
0.001. P:0. O15, remaining Fe f.

4-2) Corrosion resistance evaluation method A: No rust B: Slight black rust C
: Significant black rust D: Black rust has spread over the entire surface.

■T: Black rust flows and the rust color is dark F: Rust spreads over the entire surface with pitting corrosion Even in this example, the pickling resistance of l4i-Cr alloy plating was always good at 51 points, and the corrosion resistance after descaling was 43% by Cr content.
If the Cr content is below 7%, it will be deteriorated, and if it is 7% or more, it will be 5.
It showed corrosion resistance higher than US430.

Normally, the amount of iCrCr is about 7% or more compared to stainless steel, but as mentioned earlier, it is 17%Cr0) 5U843
Even at zero, the amount of Cr on the outermost surface is 8 to 9.

In this example, if Ni or N1 alloy plating is applied even if the Cr content in the steel is about 7%, and annealing is performed in an oxidizing atmosphere, the Cr in the steel will concentrate on the surface of the J-J and Ni - Cr -
A highly corrosion-resistant Fe alloy film can be formed.

When the amount of Cr in the steel is 4% or less, Cr cannot be sufficiently concentrated on the surface, making it impossible to form an alloy film with high corrosion resistance. Therefore, the stainless steel sheet in the present invention refers to a thin steel sheet with a Cr content of 7 or more.

Ni and N1 alloy plating can be applied using either electrolytic plating or electroless chemical plating, but when installing in-line in front of an existing AP line, electrolytic plating is recommended due to line speed. It is efficient because the plating thickness can be ensured in a short time.

Next, examples manufactured using the method of the present invention will be described.

<Example 1> 5US409 (11% Cr) with a plate thickness of 0.8 mm
) N1 and N1 alloy re 0.5~]0μm on cold rolled plate
Colored stainless steel was produced by plating and heating at 85°C to 900°C in an open-fired furnace with an air ratio of 2 (approximately 5%), and a corrosion resistance test was conducted. The color tone after annealing and the results of the corrosion resistance test are shown in Table 2. The corrosion resistance evaluation method is the same as in Table 1.

According to the table below, Ni was applied to 5US4Q9 stainless steel thin plate.
HoN again! It showed corrosion resistance higher than USUS 430, which is alloy plated and oxidized annealed color stainless steel. Of these, N
Auger analysis from the surface of a Metsky oxidation annealed test piece revealed that the notched N1 entered the steel as shown in Figure 2.
Ni-Cr is concentrated on the surface of Cri in stainless steel.
-Fe alloy is formed, and the oxide film of this alloy is thought to exhibit good corrosion resistance.

<Example 2> A 2D material obtained by pickling, descaling and temper rolling the colored stainless steel produced in Example 1 and a steel plate polished to ≠600 were subjected to a corrosion resistance test. The results are shown in Table 3.

The oxide film thickness after oxidative annealing was 0.1 to 0.2 μm, and the alloy film of Ni and Cr remained sufficiently even after descaling by pickling or polishing, and showed corrosion resistance of 5US430 or higher. In particular, N'1-Cr alloy plating is very easy to pickle and polish, and the pickling time could be reduced from 115 to IAo compared to unplated stainless steel sheets.

In the case of plating and oxidation annealing before annealing, it is useful to be able to select the type of plating depending on the strength and process of using colored stainless steel or pickling and polishing.

[Brief explanation of drawings]

Figure 1 is a graph showing the change in Cr content from the surface to the center of thickness of a 5US430 cold-rolled plate, and Figure 2 is a graph showing the state of thermal diffusion due to annealing of Nl Metsugi stainless steel thin plate. Before annealing, CB) fi shows after annealing -0 Patent applicant Representative patent attorney Tomoyuki Yafuki (and 1 other person) Figure 1

Claims (4)

[Claims] (1) N1 plating is applied to a stainless steel sheet after cold rolling, and then it is heated to 1000℃ above the recrystallization temperature in an oxidizing atmosphere.
A method for manufacturing a thin stainless steel plate, characterized by carrying out continuous annealing in the following temperature range. (2) After cold rolling, a stainless steel sheet is coated with Ni as the main component and Cr, Mo, Ti, W, P, and H.
A method for producing a thin stainless steel sheet, which comprises plating an alloy containing two or more types of stainless steel sheets, and continuously annealing the plate in an oxidizing atmosphere at a temperature ranging from a recrystallization temperature to 1.000°C. (3) Ni plating is applied to the cold-rolled stainless steel thin plate, and then heated to 1000°C above the recrystallization temperature in an oxidizing atmosphere.
1. A method for manufacturing a stainless steel sheet, characterized by carrying out continuous annealing in the following temperature range, and further removing a surface oxide film by pickling or surface polishing the thin sheet. (4) After cold rolling, a stainless steel sheet is plated with an alloy containing one or more of Cr, Mo, Ti, W, P, and B as a Nl-generating component, and recrystallized in an oxidizing atmosphere. 1. A method for producing a stainless steel thin plate, which comprises continuously annealing the thin plate at a temperature in the range of 1000° C. or higher, and then pickling or surface polishing the thin plate to remove a surface oxide film.