JPH0333795B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing turn sheets used for the outer frames of automobile gasoline tanks and radiators, and is aimed at dramatically increasing the corrosion resistance of the turn sheets. Conventional technology Conventional turn sheets are cold-rolled thin sheets of common steel that are turn-plated (approximately 5 to 15% Sn added to Pb).
It is mainly used as the outer frame of automobile gasoline tanks and radiators, but automobiles used in coastal regions and automobiles used in cold regions are severely corroded due to the harmful effects of antifreeze agents used on roads, and their durability is limited. The number of years has led to inferior results. Problems to be Solved by the Invention Under these circumstances, there has been a demand for a turn sheet that is corrosion resistant like stainless steel and has good solderability. However, although stainless steel has good corrosion resistance, it has poor solderability, so turn plating is difficult to form as is, and turn sheets cannot be manufactured. Means for Solving the Problems The present invention provides a method for manufacturing a turn sheet with poor corrosion resistance, which simultaneously improves corrosion resistance and solderability by applying turn plating to the surface of a Cr-containing iron base material such as stainless steel. Solved the problem of adhesion of turn plating to stainless steel plate surface.
This was solved by applying Ni-based plating and heating it to over 500℃ in a reducing atmosphere. That is, the present invention applies to cold-rolled thin sheets of Cr-containing iron base materials.
This is a method for producing a turn sheet with excellent corrosion resistance, which is characterized by applying Ni or Ni alloy plating, then heating to 500°C or higher in a reducing atmosphere, and then applying a turn sheet. By the way, the present applicant previously published Japanese Patent Application Laid-Open No. 59-140389.
The ``Method for Manufacturing Stainless Steel Thin Sheets'' discloses the production of stainless steel thin sheets with good corrosion resistance by applying Ni plating to cold-rolled stainless steel sheets and then continuously annealing them. When the thin stainless steel plate manufactured in this way is annealed for a long time, Cr will thermally diffuse from the base stainless steel and a passive film of Cr will be formed on the surface, but by setting an appropriate atmosphere, temperature, and time, ,
The outermost surface is Ni or Ni alloy, and it is possible to obtain a state in which Cr has not yet diffused to the surface.
If the plate is passed through a tank in which the turns are melted in such a state, a turn plating with good adhesion can be formed. In this way, the plating thickness and annealing conditions that provide good plating adhesion for Ni or Ni alloys and prevent Cr from diffusing to the outermost surface are suitable for Cr-containing iron base materials such as various stainless steel sheets and Cr-containing heat-resistant steels. Varies depending on quantity. Steel types with a high Cr content naturally have a fast Cr diffusion rate to the outermost surface, and on the other hand, from the material standpoint,
The annealing temperature and time are also limited to some extent by the steel type. Note that similar restrictions exist in the case of off-line heat treatment for plating adhesion. The heating atmosphere in the present invention is a reducing atmosphere containing 1% or more of _H2 , and the heating treatment is a continuous treatment, so the soaking time is about 10 to 60 seconds. As a result of various studies by the present inventors on the above-mentioned constraint conditions, as shown in Figure 1 (soaking for 30 seconds), Cr-containing
It was found that the adhesion of turn plating is good if the thickness of Ni or Ni alloy plating is thicker than the diagonal line determined by the Cr content of the iron base material. In other words, the diagonal lines marked ◎ in the figure indicate steel types with a Cr content of 17% or more, typically SUS304 or
This is SUS430. SUS304 is an austenitic stainless steel, so the annealing temperature must be 1000℃ or higher, and in that case, the thermal diffusion rate of Cr becomes faster, so the plating thickness is 5μm.
More than that will be needed. In this case, increasing the thickness of the plating increases the economic cost, so
It is also possible to perform a reheat treatment only to improve plating adhesion by Ni plating, and then turn plating (this manufacturing method is referred to as offline manufacturing). Even in this offline case, heat treatment at 500℃ or higher is required to improve plating adhesion.
At this time, the plating thickness may be 0.01 μm as shown in the figure. For SUS430, annealing time is 800℃~900℃×
Since the soaking time is 10 to 20 seconds, the thickness of the Ni plating needs to be about 1 μm. The diagonal lines marked with ○ indicate SUS410 with a Cr content of approximately 13%.
This shows the case of low-priced stainless steel such as SUS409, and the annealing temperature of this steel type is around 700 to 800℃.
The Ni plating thickness may be about 0.05 to 0.1 μm. Furthermore, in the case of steel sheets with low Cr content (Cr = 1%), the annealing temperature is 700~
Since the temperature is 800°C, it is possible to reduce the amount of Ni plating. In this way, depending on the corrosion resistance required for the turn sheet, the base material containing Cr iron can be selected from SUS304 to SUS430.
You can freely choose from SUS410 to SUS410, and in some cases it is also possible to use a base material with lower Cr than conventional stainless steel (12% or more Cr). Therefore, in the present invention, the Cr-containing iron base material used as the base material for producing a turn sheet with good corrosion resistance has a Cr content of 1.
% or more thin steel plate. Further, in the turn plating pretreatment conditions according to the present invention, the amount of Ni plating is specified by the Cr content as described above, and the heating temperature after Ni plating is also specified thereby. As described above, the heating step includes both a case where the cold-rolled sheet is annealed and a case where the sheet is heated off-line after the annealing process. In offline production, it is only necessary to improve the adhesion of the Ni plating, so a heating temperature of 500°C or higher is sufficient. Therefore, in the present invention, the heating temperature in a reducing atmosphere is specified to be 500°C or higher. Next, the solderability and corrosion resistance of turn sheets produced using the method of the present invention will be explained based on Examples. Example 1 A SUS430 cold-rolled plate was plated with Ni to a thickness of 0.1 to 1 μm, heated at 800°C for 20 seconds by continuous annealing, and turned plated (Pb: 98%, Sn:
8%) to produce a turn sheet with good corrosion resistance. Table 1 shows the solder wettability and corrosion resistance tests. As is clear from Table 1, do not use Ni plating.
SUS430 cannot be turn-plated, and of course cannot be soldered. With Ni plating having a plating thickness of 0.1 μm, dot-like unplated areas appeared in the turn plating after annealing, and the areas where no turns were attached were not even soldered. When the Ni plating was 0.5 μm or more, the turn plating was beautiful and no inferior to normal turn sheets, and the corrosion resistance showed a tendency to be significantly better than ordinary steel turn sheets. Example 2 Cr content in SUS410 and 409D and other steels is 10
% or less, cold-rolled sheets were plated with Ni, and turned sheets were made by changing the plating thickness and annealing temperature. I took the test. SUS410 with a Cr content of 13% requires Ni plating of 0.1 μm or more at an annealing temperature of 800°C, and SUS409D requires an annealing temperature of 850°C because it contains Ti, so Ni plating of 0.5 μm or more is required. . Steel with a Cr content of 7% or less has a small Cr content and the annealing temperature can be lowered, so turn plating can be performed with Ni plating of 0.05 μm or more, and the Cr content can be reduced.
For 1.0% steel, a plating thickness of 0.01 μm is sufficient. However, even with a Cr content of 1.0%, steel without Ni plating will not be sufficiently turn-plated because a very thin Cr passive film is formed during the annealing process. Example 3 Where corrosion resistance is most strictly required
It is also possible to manufacture a turned sheet of SUS304 (18% Cr, 8% Ni) by using the method of the present invention. SUS304 has a high annealing temperature, so if the Ni plating is thin, Cr in the SUS will diffuse to the surface.
The turn is not sufficiently sharp. Approximately 5 μm is required at an annealing temperature of 1000°C. In the case of SUS304, rather than using Ni plating as a pre-annealing treatment, it is more economical to apply Ni plating to 304 after annealing off-line, annealing it again for thermal diffusion, and then turn plating. In this case, as is clear from Table 3, when the re-annealing temperature is 400° C. or lower, mutual diffusion at the interface between the plating layer and the base material is insufficient and plating adhesion tends to deteriorate. Example 4 Various tests were also conducted on Ni alloy plating, which is thought to have good corrosion resistance and good solderability. The results are shown in Table 4 (the base plate is SUS410).
Cold rolled plate, annealing temperature 800℃ x 20sec). As is clear from Table 4, Ni-P shows the same or better corrosion resistance than Ni plating alone.
Ni-B, Ni-P-B alloy plating, and alloy plating with Cu or Fe has good plating properties, but corrosion resistance is slightly inferior. Ti, Mo, W, etc. are also considered as other components of the Ni alloy, but there are problems in that the plating bath is expensive and bath management is difficult.

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[Table] Effects of the Invention The present invention can be applied to non-solderable stainless steel.
Alternatively, by pre-plating with Ni alloy, improving plating adhesion through thermal diffusion during annealing, and turn-plating during the cooling process of continuous annealing, we can create a turn sheet that has significantly better corrosion resistance than conventional ordinary steel turn sheets. Can be manufactured economically.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the Cr content of a Cr-containing iron base material, heating temperature (soaking for 30 seconds), and Ni or Ni alloy plating thickness.

Claims (1)

[Scope of Claims] 1. A cold-rolled thin sheet of a Cr-containing iron base material is coated with the range shown in FIG. The Ni or Ni alloy is pre-plated by controlling the thickness so that the thickness is controlled, and then soaked in a reducing atmosphere at a temperature of 500℃ or higher for 10 to 60 seconds, followed by turn plating. A method for producing a turn sheet with excellent corrosion resistance. 2. The method according to claim 1, wherein the plating metal in the preliminary plating is a Ni alloy containing Ni as a main component and containing one or both of P or B.