JPS6030752B2 - Method for producing cold-rolled steel sheet with excellent intermediate rust prevention properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cold rolled steel sheet that has intermediate rust prevention ability from the time the cold rolled steel sheet is supplied from a steel sheet manufacturer until it is painted by a user. be.

Conventionally, rolled steel sheets are coated with anti-corrosion oil at the steel sheet manufacturer before being shipped. When used as steel sheets for automobiles, automobile manufacturers plank and press the cold-rolled steel sheets, install them into the car body, and then paint them. In this process, the period from pressing to assembly into the car body is usually about 1 to 2 weeks, but in some cases it can take 1 to 2 months, and in the knockdown method overseas, from pressing to painting process. This period can last for several months. In order to prevent rust when these parts are stored for a long period of time, automobile manufacturers apply anti-rust oil to the pressed parts, and if rust occurs, remove the rust using a grinder or the like. The present invention relates to a method for producing cold-rolled steel sheets with excellent bare rust resistance, which eliminates the need for intermediate rust prevention measures by automobile manufacturers as described above. Further, the present invention will be described in detail.

The present invention uses Ni before the Rentsugi hammering process, which is the manufacturing process of cold-rolled steel sheets.
A corrosion-resistant film with good adhesion and workability is formed on the surface of a cold-rolled steel sheet by plating a thin film and subsequently annealing it for a short time using a continuous hammer.

If the surface of the rolled steel sheet is still coated with Ni, the adhesion to the base material is poor, and the coating may peel off during press working, making it impossible to obtain corrosion resistance. If phosphorous annealing is performed after plating, Ni will form an alloy layer in which Ni is diffused into the base iron, resulting in a corrosion-resistant coating with good adhesion. On the other hand, corrosion resistance is determined by the surface concentration of the plated metal, so in the case of a long-term oxidation, such as a box-scorched anchor, there will be a large amount of diffusion into the base iron, making it impossible to ensure the surface concentration as a corrosion-resistant film. To obtain the necessary corrosion resistance, the surface adhesion of plated metal should be at least 0.59.
/dm2 is required. Further, in order to improve adhesion, it is necessary to diffuse the metal, and if the average diffusion distance is 500 A or more, good adhesion can be obtained. Therefore, as a plated metal film, the surface concentration (adhesion amount) after annealing is 0.
．． Optimum is a coating having an average diffusion distance of 5/9/dm2 or more and an average diffusion distance of 500 A or more inside the base iron.

In normal box-coating, due to the long anchoring time, there is a large amount of diffusion from the surface into the interior of the base steel, and a large plating thickness is required to obtain the required surface concentration.

For example, in the case of aluminum killed steel box phosphor dulling, 9/d of 0.5
In order to ensure a surface concentration of dm2, the initial plating thickness must be 100 dm2 or more. In this way, when a large amount of plating is applied, not only is there a problem in terms of cost, but the diffusion layer becomes thicker and the material changes accordingly.
Press formability is also a problem. On the other hand, in the present invention, since Rentsugi ware is used for which the sintering time is short, even if the initial plating amount is small, diffusion into the interior is slight and the surface concentration hardly changes. Even with such short-time burning, there is diffusion within the base iron of the plated metal, and the average diffusion distance is approximately 500 to 1.
000△, and the adhesion of the plating film during press working is sufficient. If the upper limit coating amount is 50 dm2 or more, the plating film will peel off during press working. Therefore, 5
09/dm2 or less is preferable. Next, we will talk about plating methods for plating metals. As a plating method, any method such as electroplating, displacement plating, or vapor deposition plating may be used. From the viewpoint of workability, electroplating is preferable.
If organic substances such as rolling oil are attached to the steel plate to be plated, it is necessary to remove them using an alkali or the like. In the method of the present invention, if the plate temperature is maintained at 500°C or higher for less than 1 minute, the thickness of the Ni alloy layer formed will be small, resulting in insufficient processing adhesion of the Ni plating film and causing peeling during press forming. Become.

Moreover, if the time exceeds 15 minutes, the thickness of the Ni alloy layer will increase, and the material quality of the cold-rolled steel sheet of the main pot will not be obtained, which will cause problems in press forming.
Therefore, it is necessary to set the range to 1 minute or more and 15 minutes or less. It has been confirmed that the present invention improves not only intermediate rust prevention but also corrosion resistance after painting.

That is, cold-rolled steel sheets are assembled after being press-worked, and after degreasing, phosphate treatment is performed if necessary, and painting such as dew coating is applied. The steel sheet according to the present invention has better corrosion resistance than ordinary rolled steel sheet when painted according to these steps. Example 1 An unannealed cold-rolled steel strip coil was subjected to Ni electroplating on the existing electroplating line shown in FIG. 1, and then passed through the continuous Akatsuki line shown in FIG. 2.

When passing through the electroplating line, spray degreasing was first performed in degreasing tank 2.

The degreasing conditions are shown in Table 1. Table 1 Subsequently, washing was performed in washing tank 3, and Ni electroplating was performed in plating tank 4.

The Ni electroplating conditions are shown in Table 2. Subsequently, wash with water 5,
Drying 6 was performed, and the product was wound into a coil without applying rust preventive oil. Table 2 shows the conditions for continuous anchorage line threading.

After the coil was taken out, it was charged into the scorching anchor furnace 9 without degreasing or washing with water. The corpse hammer conditions are shown in Table 3. Table 3 Table 4 shows the annealing gas composition.

Table 4 Table 5 shows the gentle rolling conditions in which skin pass rolling was performed in the skin pass rolling mill 15 after annealing under the above conditions.

Table 5 After temper rolling, it was wound into a coil without applying rust preventive oil.

The rust prevention properties of the cold rolled steel sheet thus obtained were investigated. The test pieces used in the rust prevention test were degreased under the conditions shown in Table 6, dried with 100% water leakage after degreasing, and then subjected to the rust prevention test. The test results are shown in Table 8.

Symbol A in Table 8 is a normal cold-rolled steel sheet and is outside the scope of the present invention. B
, C, D, and E are of the present invention. It was confirmed that the cold-rolled steel sheet according to the present invention did not develop rust even after 60 days of indoor baking and had excellent intermediate rust prevention properties. Example 2 A sheet was passed through a Rentsugi annealing line in which electroplating equipment was installed in front of the annealing furnace shown in FIG. 3, nickel electroplating was performed, and Rentsugi annealing was performed.

The steel strip coil after cold rolling was taken out and first degreased in a degreasing bath. Subsequently, Ni electroplating was performed, water washing and drying were performed, and phosphor dulling was performed, followed by temper rolling and winding into a coil shape.

The threading conditions of degreasing, water washing, nickel electroplating, and sea bream rolling conditions were the same as in Example 1. The rust prevention test results of the cold rolled steel sheet according to the present invention manufactured in this manner are shown in Table 8 with symbols F and G.
, day, 1.

Both exhibit excellent rust prevention properties. Example 3 In the method of Example 1, nickel displacement plating was performed instead of nickel electroplating.

Table 6 shows the nickel displacement plating conditions.

Table 6 Rust prevention properties of the cold rolled steel sheet according to the present invention obtained in this manner,
The test results are shown in Table 8 with symbols J, K, L, and M.

All exhibit excellent steel resistance.

Example 4 In the method of Example 2, nickel displacement plating was performed instead of nickel electroplating.

The nickel displacement plating conditions were the same as in Example 3. The bell proofing test results of the cold-rolled steel sheets according to the present invention thus obtained are shown in Table 8 with symbols N, 0, P, and Q. All of them show excellent rust prevention performance.

Example 5 Nickel electroplating was performed in the same manner as in Example 1, followed by continuous light rolling under the sintering conditions shown in Table 7, followed by temper rolling and winding into a coil.

Table 7 Note that the primary cooling method was air-water cooling.

The atmospheric gas composition and flow rate are the same as in Example 1. The rust prevention test results of the cold-rolled steel sheets according to the present invention thus obtained are shown in Table 8 with symbols R, S, T, and U. All exhibit excellent rust prevention properties. Example 6 Nickel electroplating was performed in the method of Example 2,
Subsequently, continuous dawn anchoring was carried out under the same conditions as shown in Example 5.

The steel resistance test results of the cold-rolled steel sheets according to the present invention thus obtained are shown in Table 8 with symbols V, W, X, and Y. All exhibit excellent rust prevention properties.

Table 8

[Brief explanation of the drawing]

Figure 1 shows the layout of the existing electroplating line, Figure 2 shows the layout of the continuous Akatsuki hammer line, and Figure 3 shows the layout of the Rentsugi hammer line equipped with a plating tank. 1...Coil payout machine, 2...Degreasing tank, 3...Water wash, 4...
・Plating tank, 5...Washing tank, 6...Dryer, 7...Lubrication machine, 8...Coil winding machine, 9...Continuous dulling furnace, 1
0... Heating furnace, 11... Soaking furnace, 12... Primary cooling furnace, 1
3... Overaging furnace, 14... Secondary cooling furnace, 15...
Temper rolling mill. O diagram Oz diagram Power 3 diagram

Claims (1)

[Claims] 1 Ni plating is performed before continuous annealing in the manufacturing process of cold rolled steel sheets, and the plate temperature is maintained at 500°C or higher for 1 minute or more.15
A method for producing a cold-rolled steel sheet with excellent intermediate rust prevention properties, characterized by carrying out continuous annealing within a range of minutes.