JPH01177385A - Tinned steel sheet for uncoated can having superior corrosion resistance - Google Patents

Abstract

PURPOSE:To reduce the amt. of sol. Al in the surface layer of a continuously cast Al killed steel sheet to a specified value or below and to improve the corrosion resistance of the steel sheet after tinning by annealing the steel sheet under specified conditions when a tinned steel sheet for an uncoated can is produced. CONSTITUTION:When molten Al killed steel is continuously cast into a steel sheet and the surface of the steel sheet is tinned to produce a tinned steel sheet for an uncoated can, the Al killed steel sheet is annealed, e.g., at 720 deg.C for 5hr in an atmosphere consisting of 95% N2 and 5% H2 to convert part of Al in the surface layer of the steel sheet into AlN and to reduce the amt. of sol. Al in the surface layer of <=30mum thickness to <=0.030%. The steel sheet is then thinned and heated to form an Sn-Fe alloy layer between the resulting Sn layer and the steel sheet. The corrosion resistance of a can made of the tinned steel sheet is not deteriorated because the amt. of sol. Al in the steel sheet is small.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a tin steel plate used as a container material, and particularly to a tin-plated steel plate for unpainted cans.

(Prior art) Tin-plated steel sheets are mostly used as container materials for canned food, and their manufacturing methods, manufacturing conditions, characteristics of the base steel sheets,
Regarding product properties, test methods, etc., please refer to "Tinplate and Tin Free Steel" (September 30, 1970,
(1st edition, 1st printing, published by Agne).

However, container materials must have corrosion resistance corresponding to the contents to be filled, and much research and development is being conducted to improve this corrosion resistance.

In recent years, unpainted cans manufactured using aluminum-killed base steel sheets manufactured by the continuous casting method (CC) without internal coating have been filled with light-colored fruits (pears, peaches, apricots, fruit cocktails, etc.). In some cases, many abnormal cans such as expansion and perforation occur within 6 to 1 month after filling with contents, which has become a problem. In order to solve this problem, the present inventors proposed a method using a base steel plate having a certain degree of integration in a specific direction, as disclosed in Japanese Patent Application No. 61-264313.
In addition, in a tin-plated steel plate whose base steel plate is aluminum killed steel, a method for controlling the product of the amount of tin-iron alloy layer and the crystal plane strength of the base steel plate was previously filed as Japanese Patent Application No. 62-2039'1.

(Problems to be Solved by the Invention) The method of the invention makes it possible to improve the corrosion resistance of tin-plated steel sheets.

However, these methods of the invention of the prior application are sometimes subject to restrictions on the manufacturing conditions of the base steel sheet, and are not necessarily sufficient. The present invention provides an electro-tin-plated steel sheet having a tin-iron alloy layer at the boundary between the tin layer and the base steel sheet,
The object of the present invention is to provide an unpainted tin-plated steel sheet for light-colored cans that has excellent corrosion resistance and is obtained by a method different from that of the prior invention.

(Means for Solving the Problem) The present invention provides a steel plate manufactured by an aluminum killed continuous casting method, in which the solid solution Al contained in the surface layer within at least 30 μm in the plate thickness direction from the surface is o, o3o in weight ratio. A tin-plated steel sheet for unpainted cans is characterized by having a tin-iron alloy layer on the surface of the base steel sheet and a tin layer on top of the tin-iron alloy layer.

The present invention will be explained in detail below. Aluminum-killed steel made by the normal CC method has Al added as a deoxidizing agent and is either dissolved in solid solution in the steel or contains aluminum oxides, nitrides, etc.
It exists in steel in such a state.

In addition, although the aluminum concentration in steel is controlled to 0.02% to 0.07%, the actual relationship between the corrosion resistance of unpainted light-colored fruit cans and the steel Φ aluminum concentration is not clear. . However, the present inventors conducted a state distribution of aluminum in steel in the thickness direction and investigated in detail the relationship between the corrosion resistance of unpainted light-colored fruit cans and the aluminum concentration in steel, and as a result, as shown in Figure 1. It has been found that the corrosion resistance of unpainted light-colored fruit cans is influenced by the amount of dissolved M in the surface layer of the base steel plate. Here, solid solution M refers to At, which is obtained by dissolving the sample in 10 sulfuric acid (aluminum nitride also dissolves a little, but the amount was negligible as a result of the experiment), filtering it, and then analyzing it by ICP (high-frequency induced plasma spectrometry). It's about quantity. From FIG. 1, it has been found that when the amount of solid solution Al is reduced, the number of cans that have been bead-processed (a process in which the side walls of the can are made uneven in order to increase the strength of the can) with corrosion resistance defects is significantly reduced.

Here, the number of cans with poor corrosion resistance refers to the number of cans in which the amount of iron eluted in the solution is 3 ppm or more. As a method for reducing the solid solution M, the solid solution M in the steel sheet itself may be controlled to an appropriate amount by reducing the amount of At added as a deoxidizing agent. To this end, it is necessary to perform treatments such as low-temperature tapping and vacuum degassing in order to reduce inclusions such as dissolved oxygen and oxides in the molten steel. In this case, the amount of solid solution M can be suppressed to a certain value or less not only in the surface layer of the steel plate but also in the entire thickness direction.

In addition, as a method to reduce the solid solution M only in the surface layer of the steel sheet, increase the annealing temperature, lengthen the annealing time, or add ammonia or the like to the atmospheric gas to nitride M in the surface layer, thereby reducing Total At ( Even if the amount of solid solution M+ nitride of At oxide particles M, etc. is the same, the solid solution M can be reduced only in the surface layer. Figure 2 shows an analysis of the state of M in the depth direction during annealing under commonly used annealing conditions: annealing temperature 620°C, annealing time 5 hours, annealing atmosphere, hydrogen 5%, nitrogen 95%, dew point -30°C. Show the results. Further, FIG. 3 shows the results of analyzing the state of At in the depth direction as annealing flexibility at an annealing temperature of 720°C, annealing time of 5 hours, annealing atmosphere of 5% hydrogen, 95% nitrogen, and a dew point of -30°C.

It is clear from FIG. 3 that the solid solution At in the surface layer of the υ steel sheet is reduced by nitriding during annealing.

In this way, the electrolytic tin-plated steel sheet using the base steel sheet in which the solid solution M in at least the surface layer portion is controlled to an appropriate value has significantly improved corrosion resistance. That is, in the aluminum killed continuous casting material, the solid solution Al in the layer within at least 30 μm in the plate thickness direction from the surface is 0.030 mm or less in weight ratio, preferably 0.
．． Corrosion resistance is significantly improved by using a base steel plate having a corrosion resistance of 0.022% or less, most preferably 0.02% or less.

In addition, in the present invention, at least 30μ in the thickness direction from the steel plate surface
The reason why the amount of solid solute M in the layer within m is controlled is that, as mentioned above, in the present invention, the At content of the steel sheet itself is suppressed and the content of solid solute M is controlled not only in the surface layer of the steel sheet but also in the entire thickness direction. may be suppressed to 0.03% or less, but the amount of solid solute M in the layer within 30 μm from the steel plate surface in the plate thickness direction is 0.030%.
This is because sufficient corrosion resistance can be obtained simply by controlling as follows.

(Example 1) Steel having the steel components shown in Table 1 was melted in a converter. A
The component system is steel made by the conventional method, and the B component system is related to the present invention, which is the steel obtained by vacuum degassing the A component system. is o,
Aluminum was added so as to achieve oz%, and continuous casting was performed. Furthermore, through the normal manufacturing process of a base steel plate for electroplating, the plate thickness is 0.2. A base steel plate was obtained. Strain relief annealing was carried out at an annealing temperature of 620°C, annealing time of 5 hours, annealing atmosphere of 5 ml of hydrogen, 95% nitrogen, and a dew point of -30°C.
The second cold rolling was performed. The steel plate after cold rolling is further processed.
After normal degreasing and pickling, #75 tin plating was performed in a sulfuric acid acid bath, and after reflow treatment under normal heating conditions, it was immediately cooled with water. Furthermore, cathodic electrolysis treatment was performed in a sodium dichromate solution. Based on the tin-plated steel sheet manufactured in this way,
Cans are made using the Sudronik welding method (each unpainted, with bead processing), and the contents are pears).
After filling, 45 cans each of both A component system and B component system were stored at room temperature for 9 months. After 9 months, the canned solution was analyzed and the number of cans with iron elution in the solution of 3'PPm or more was counted.The relationship between the number of cans with corrosion resistance defects and the amount of solid dissolved M in the surface layer within 50 μm from the steel plate surface. are shown in Table 2.

In addition, in the B component system shown in Table 2, the content of solid solution M was 0.025% throughout the entire thickness direction.

The test methods in Table 2 are shown below.

l) Solid solution A1 = Dissolve the sample in 10% sulfuric acid, filter through IC
Value of M analyzed by P (high-frequency induced plasma analysis method) (wt%) 2) AIN: Using a constant potential electrolyzer, a certain amount of the sample is electrolyzed in a non-aqueous electrolyte, and then extracted. AM was analyzed using the extraction CP analysis method in which the residual was filtered and decomposed with aqua regia (weight qb) 3) Total AL:
The value of At analyzed by ICP analysis after dissolving the sample in aqua regia (wt%) 4) Number of cans with corrosion resistance defects: The amount of iron eluted in the canned solution was 3.
Table 2 shows that the number of cans with the component (B) according to the present invention having a corrosion resistance defect is smaller than that with the component (A) according to the conventional method.

(Example 2) The steel component A component system of Example 1 was continuously cast, and a base steel plate with a thickness of 0.2 m was obtained through the usual manufacturing process of a base steel plate for electroplating. Furthermore, after changing the strain relief annealing conditions, a second cold rolling was performed, and after normal degreasing and pickling, #5 tin plating was performed in a sulfuric acid acid bath, and reflow treatment was performed under normal heating conditions. After that, it was immediately cooled with water. Furthermore, cathodic electrolysis treatment was performed in a sodium dichromate solution. Based on the tin-plated steel sheets manufactured in this way, cans are made by the Sudronik welding method (unpainted cans, with bead processing), filled with pear (Pear), and then stored for a long period of time. I did it. A component system is based on the conventional method, C component system,
The D component system is related to the present invention. Table 3 shows the annealing conditions, both at room temperature and A.

Experimental results after storing 45 cans for 9 months for each of the C and D component systems are shown. The analytical value of M is the value for a thickness within 30 μm from the surface of the steel plate.

The test method in Table 3 is the same as in Example 1.

Table 3 shows that the AIN in the surface layer of the steel sheet increases and the solid solution Al decreases during annealing compared to the (A) component system according to the conventional method and the (C) and (D) component system according to the present invention. It can be seen that this reduces the number of cans with poor corrosion resistance.

(Effects of the Invention) As explained above, the tin plate manufactured from the aluminum killed continuous casting material of the present invention and whose base material is a base steel plate in which the hardness mA1 of at least the surface layer is controlled to an appropriate value has excellent corrosion resistance and is free from corrosion. Suitable for paint cans.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the corrosion resistance of unpainted light-colored fruit cans and the amount of dissolved M in the surface layer of the base steel plate, and Figure 2 is the graph in the thickness direction of the base steel plate when annealed under normal conditions. FIG. 3 is a graph showing the results of analyzing the state of M in the thickness direction of the base steel plate when high-temperature annealing is performed. Figure 1 Rotating Al (WtX) fijl sea bream (μm)

Claims (1)

[Claims] (1) A steel plate manufactured by the aluminum killed continuous casting method, in which solid solution Al contained in the surface layer within at least 30 μm in the thickness direction from the surface is 0.030% or less by weight. Electro-tin-plated steel sheet with excellent corrosion resistance, consisting of a tin-iron alloy layer and a tin layer above it.