JPS59232275A - Cold rolled steel sheet having excellent phosphate treatability and its production - Google Patents

Abstract

PURPOSE:To improve remarkably phosphate treatability by conducting electricity to a steel sheet having poor phosphate treatability in a soln. contg. a specific compd. with said sheet as a cathode or anode so that a sulfur compd. is adsorbed on the surface of the steel sheet. CONSTITUTION:A cold rolled steel sheet which has poor treatability for formation of a phosphate film by phosphate or a surface treated steel sheet which is galvanized on one surface and which is un-coiled from an un-coiler 1 is subjected to reduction soaking and annealing in a continuous annealing furnace 2 in order to improve the phosphate treatability of the non-plated surface of said sheet. Electricity is conducted at 1-100Coulomb/dm<2> current density to such steel sheet as an anode or cathode in an electrolyte contg. 1 or >=2 kinds among compds. contg. a mercaptan, thiocyane, thiophene deriv., sulfide, disulfide and thiocarbonyl group at 10<-5>-10<-1>mol/l concn. A compd. of 0.01-500mg/m<2> is adsorbed in the form of S on the surface of the steel plate, by which the phosphate treatability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cold-rolled steel sheet, a single-sided surface-treated steel sheet, and a method for manufacturing the same.

The first object of the present invention is to improve the phosphate treatment properties when used by applying phosphate treatment as a base treatment for painting after processing such as press forming, such as for automobile steel sheets. Another object of the present invention is to provide a cold-rolled steel sheet with excellent corrosion resistance after painting.

A second object of the present invention is to provide a single-sided plated copper plate that has excellent phosphate treatment properties and corrosion resistance after painting on the iron side when one side of the steel plate is an iron surface, such as a single-sided plated steel plate. A manufacturing method is provided.

Phosphate treatment properties are affected by the segregated components and concentration on the outermost surface of the steel sheet, the composition and thickness of the oxide film, and the chemical composition of the steel sheet. For example, steel sheets with poor phosphate treatment properties include: (1) Steel sheets whose oxide film formed during the annealing process has been removed by pickling, polishing, grinding, or other methods.

(2) Steel composition: 1% or more chromium, 1% or more Si, T
Steel plate containing one or more types of i0.08% or more.

(3) A steel plate whose one side is iron and the other side is a plating side. ■ When electroplating is used, pickling is performed as a pretreatment for plating, and in many cases, the steel plate is passed through a plating bath, which is a pickling bath. The steel surface of a single-sided electroplated steel sheet has a steel surface that has been affected in the same way as pickling. ■ When using the hot-dip plating method, it is difficult to prevent the plated metal from backing or adhering to the steel surface, and it is also exposed to high temperatures. Since the iron surface comes out of the hot-dip plating bath in a state in which the iron surface is oxidized to some extent, it is unavoidable.

For this reason, there are single-sided hot-dip galvanized steel plates whose iron surfaces are treated by pickling, polishing, or grinding after plating.

The object of the present invention is to dramatically improve the phosphate treatment property of the above-mentioned steel plate, especially the iron surface.

By the way, conventionally, as a means to improve the processability of steel sheets with poor phosphate treatment properties, it has been known to spray a phosphate-based suspension after press forming and degreasing, but immediately before phosphate treatment. .

In order to increase the reactivity of the phosphate treatment solution itself, a method of adding a trace amount of heavy metal salt is also known.

However, for example, the method of spraying a suspension onto a molded product after processing requires a new step to be added to the series of phosphate treatment steps, which imposes a large burden on equipment and costs, and may be difficult to implement depending on the specifications of the existing line. may be impossible. The method of adding heavy metal salts to the treatment liquid itself accelerates the reaction of other parts when treating articles made of parts with various surface textures, such as automobiles, so excessive film deposition may occur depending on the part. There is a worry that it will cause Of course, the cost of the chemical conversion treatment liquid itself also increases.

The present inventors have completely eliminated the drawbacks of these conventional techniques, found a technology that can be easily and reliably applied in the steel sheet manufacturing process, and has a large treatment effect, and has replaced steel sheets with poor phosphate treatment properties with conventional methods. We succeeded in improving the processability by 1, which is comparable to that of box-shaped annealed materials.

・Specifically, (1) mercaptans, (2) Chiona 7M are applied to a highly clean steel surface from which the oxide film on the surface of the steel plate has been removed.
, (5) Thiophene derivative, (4) Sulfide M, (5
) disulfides, (6) a cold-rolled steel sheet that has adsorbed one or more sulfur compounds selected from thiocarbonyl group-containing compounds in a sulfur content range of 0.01 to 500η/7L2. (Including single-sided plated steel sheets, etc.)
and a method for producing them.

As shown in the examples later, the steel sheet of the present invention has a phosphate treatment property equal to or higher than that of the patch type box annealed material in the normal process, and the coating corrosion resistance when coated is better than that of the patch type box annealed material. 3. The reason why the coating has good corrosion resistance is that the coating inhibits the formation of graphite and other carbonaceous substances and phosphate films such as silicon, aluminum, and compounds that tend to occur on the surface of ordinary patch-type box-type annealed materials. It is thought that this is because surface contaminants that degrade corrosion resistance are removed by the electrolytic treatment, and the treatment effects described below according to the present invention are exhibited, resulting in the formation of a dense phosphate film with extremely few film defects.

Although it has not been completely elucidated why the steel sheet of the present invention has good phosphate treatment properties, it is thought to be due to the following reasons.

The formation of a phosphate film is achieved by the rapid formation of phosphate crystal nuclei in the early stage of phosphate treatment, which results in the formation of dense crystals and the formation of a phosphate film is completed in a short period of time. In order to promote the phosphate treatment reactivity in this manner, a surface conditioner is used in the degreasing solution or after degreasing as a pretreatment for the phosphate treatment. Titanium colloid is mainly used as a surface conditioner. Titanium colloids are adsorbed onto the surface of the steel sheet and act as phosphate crystal nucleus sites (S) to promote phosphate treatment reactivity. If phosphate treatment is carried out without using a surface conditioner, it will take a long time to form a phosphate film and the crystals will become coarse, resulting in a significant deterioration in coating performance.

However, even when a surface conditioning agent is used, steel sheets with poor phosphate treatment properties have a low adsorption amount of titanium colloid, which is a surface conditioning agent, and as the phosphate film takes a long time to form, the crystals become coarse. The coating performance will deteriorate.

The surface of the steel sheet of the present invention contains one of (1) mercaptans, (2) thiocyanates, (ro) thiophene derivatives, (4) sulfides, (5) disulfides, and (6) compounds having a thiocarbonyl group. Two or more types of shredded tobacco are adsorbed. The polar groups in these compounds include sulfur, which has a lone pair of electrons (a pair of electrons that are not used for bonding). It is thought that due to the effect of the lone pair of electrons of sulfur, the adsorption amount of titanium colloid, which is a surface conditioning agent in the above-mentioned phosphate treatment, is increased, and the phosphate treatment properties are significantly improved. Sulfates that do not have lone pairs of electrons do not show any improvement in phosphate treatment. In addition, in the case of sulfites, which have one lone pair of electrons, one of the lone pair of electrons is used to adsorb to the surface of the copper plate, as will be explained later, and the adsorption ability of titanium colloid is lost, resulting in phosphate treatment. It has no effect on improving sex. Therefore, a compound having the effect of improving phosphate treatment properties must have two or more lone pairs of sulfur electrons as a polar group.

Table 1 shows compounds that are effective for phosphate treatment in the present invention.

Table 1 Compound form Class Name -≦H mercaptans -≦CN Thiocyanide ratio -10-R'
Sulfides R-R' Disulfides\ ・.

, CS, a compound having a thiocarbonyl group, such as a mino group.

The amount of sulfur content of the sulfur compound having x electron pairs on the iron surface in the present invention ensures phosphate treatability equivalent to that of ordinary batch-type box-annealed materials, in consideration of phosphate treatability. 0.01~50 Dill
It is selected within the range of p/m2. o, oim9/771
If it is less than ', there is little effect on improving phosphate treatability;
Preferably, the Q is 1rr da/m2 or more. Sword 5
If it exceeds 00 +l19/m2, the appearance will develop color and the quality of the product will deteriorate. Desirably, it is 501n9/m2 or less.

Next, the reason why the above-mentioned compounds are adsorbed on the steel sheet surface will be described. The polar group of these compounds has a lone pair of electrons on the sulfur atom. On the other hand, steel plates, i.e. iron atoms, have empty d orbitals. 'electron pair (lone pair) that is not used for bonding with sulfur atoms
Adsorbs by sharing electrons between the polar group and iron using the d orbital of the iron atom.

Therefore, the active surface (new surface) without an oxide film or the like on the surface of the steel sheet is easily adsorbed. For example, the adsorption reaction of mercaptans is shown by equation (1).

: is a lone pair of electrons. R is a hydrocarbon. This adsorption is relatively irreversible, and it is not removed by alkaline degreasing or hot water washing, and shows stronger adsorption than physical adsorption.

Next, a manufacturing method using electrolytic treatment will be described.

(1) Mercaptans, (21 thiocyanine 1iJI
, (3) Thiophene derivatives, (4) Sulfides, (5
) disulfides, (6) compounds with thiocarbonyl groups (hereinafter referred to as sulfur compounds) are adsorbed onto the steel plate by immersion in the acid solution, but in this case, as mentioned above, the activity of the steel plate surface Moreover, it is difficult to suppress the target amount of adsorption because adsorption takes time and the adsorption rate changes significantly depending on temperature, concentration, etc. Therefore, we investigated a method that could easily suppress the amount of adsorption in a short time and found that electrolysis with the polarity of the steel plate as an anode or a cathode was effective.

The first reason is that the surface of the steel sheet is activated by electrolytic action to facilitate adsorption of sulfur compounds. That is, in the case of anodic electrolysis, the surface of the steel plate is dissolved, and in the case of cathode electrolysis, the oxide film on the surface of the steel plate is reduced and dissolved, thereby activating the surface of the steel plate and facilitating the adsorption of sulfur compounds.

The second reason is that the adsorption of sulfur compounds is promoted by electrical action.

The behavior differs depending on the form of the sulfur compound, but in the case of anodic electrolysis, as mentioned above, the adsorption reaction of sulfur compounds involves the iron atom receiving and adsorbing the lone electron of the sulfur atom, which is the polar group of the sulfur compound. Adsorption is accelerated by the positive polarity, which has the effect of accepting and taking electrons.

Furthermore, among the sulfur compounds, sodium diethyldithiocarbamate, which is in the form of a neutralized salt, becomes an anion of diethyldithiocarbamic acid in an aqueous solution as shown in formula (2), so that adsorption to the anode is promoted.

(C2Hs)2NcssNa +! (C2H5)2NC
8S-10Na+- (When making a 2j type cathode, mercaptans (R-8IH) and amino groups (
-NH2), e.g. thiourea (, (NH2)
2) 2C8) etc. react with hydrogen ions (H+) in an aqueous solution to become cations as shown in equations (6) and (4), so they promote adsorption to the cathode by electrical action. .

11, S) l + H+ R13H2”
Equation (6) As described above, the electrolytic method activates the surface of the steel sheet to facilitate the adsorption of sulfur compounds, and also promotes the adsorption of sulfur compounds by electrical action. Therefore, sulfur compounds are quickly adsorbed onto the surface of the copper plate by electrolysis, and the amount of adsorption can be controlled by the amount of electricity.

As described above, since electrolysis can be performed at the anode or cathode, many types of steel sheets are subject to the present invention. As will be described in Examples, for example, in the case of a cold-rolled steel sheet having an oxide film formed during the annealing process, the oxide film is removed by cathodic electrolysis, and the i-biased yellow compound is adsorbed.

In addition, in the production of single-sided galvanized steel sheets, after the side that will become the iron surface is coated extremely thinly, when this extremely thin plating is removed to reveal the iron surface, the extremely thin plating is removed by anodic electrolysis and sulfur compounds are removed. It can be adsorbed to the iron surface that appears.

The relationship between the amount of current applied and the amount of adsorption varies depending on the concentration of sulfur compounds in the bath liquid, temperature, and type of sulfur compound, but since it is easy to control the above solution conditions, the amount of current applied and the amount of adsorption of sulfur compounds are determined by assuming that the solution conditions are constant. By investigating the amount in advance, the target amount of adsorption can be easily obtained.

Regarding the electrolytic conditions, since the adsorption efficiency of sulfur compounds changes depending on the solution conditions, it is not possible to specify them definitively, but the conditions are generally as follows.

There is no particular regulation on the current density, but it is 1A/dm ~ 200
A/dm is appropriate; if it is less than IA/dm, the adsorption efficiency decreases and it takes a long time to obtain the target adsorption amount.

Moreover, if it exceeds 200 A/dm, the electrolysis voltage will rise significantly and the power consumption will be high, making it uneconomical. 10-100
A range of A/dm is desirable.

The appropriate amount of current is 1 to 100 C/dm, and IC/4m.
If it is less than 2, it will be difficult to obtain the target adhesion amount.

At 100 C/dm or more, the amount of adsorption tends to be excessive. Desirably, a range of 5 to 60 C/dm2 is appropriate. However, in this case, the amount of current applied to the surface of the cold-rolled steel sheet is not the same as the amount of electricity applied to the surface of the cold-rolled steel sheet.If oxidized carbon, molybdenum, etc. are present in a larger amount than usual, an additional amount of electricity is required to remove it. Regarding the concentration, it is 10 to 10-1 mol/! A suitable sulfur compound concentration is 10-5 mol/! If it is less than that, the adsorption efficiency will be low and it will be necessary to increase the amount of current applied in order to obtain the target adsorption amount. If it exceeds 10-1 mol/f, the adsorption reaction in the immersed state will increase, making it difficult to control the adsorption amount by the amount of current applied. Preferably 10-10 mol/! is within the range of

The higher the temperature of the solution, the higher the adsorption efficiency, but from the viewpoint of loss due to evaporation of the solution, consumption of thermal energy, and stability of the sulfur compound, a temperature of less than 70°C is appropriate.

Among the compounds added for reasons such as increasing the conductivity of the solution, the concentration of compounds containing chloride ions, bromide ions, and iodine ions is 10 mol/! The following regulations apply. 10 mol/! of these compounds! If too much is added, the adsorption of sulfur compounds is inhibited and the object of the present invention cannot be achieved.

Next, a specific manufacturing method will be described.

(1) When performing cooling in an oxidizing atmosphere such as direct-fired furnace heating, water-cooling, water-cooling, or air-water cooling, an electrolytic bath is installed on the outlet side of the annealing furnace, and an electrolytic solution containing sulfur compounds is used in the electrolytic bath. After performing cathodic electrolysis with a predetermined amount of current, it is washed with water and dried.

(2) If high-temperature de-furnacing is performed in a box-type annealing furnace,
In front of the refining pressure g machine, an electrolytic cell and a washing tank are installed in series, and electrolytic treatment is performed in the same manner as in (1).

(6) In the case of single-sided hot-dip plated copper sheets, an electrolytic bath and a rinsing bath are installed in conjunction with a pickling tank connected to continuous hot-dipping equipment or iron surface finishing equipment such as grinding equipment, and the electrolytic tank Electrolytic treatment is applied to the surface.

(4) In the case of single-sided electroplated steel sheets, an electrolytic bath and a rinsing bath are provided after the final rinsing bath of the continuous electroplating equipment, and an electrolytic solution containing a sulfur compound is used in the electrolytic bath at a predetermined amount of current. Apply anodic electrolysis to the iron surface.

(5) In the production of single-sided electroplated steel sheets, after applying extremely thin plating to the surface that will be the iron surface and then applying chemical conversion treatment such as hechromate to the plated surface, continuous electroplating equipment,
When manufacturing single-sided electroplated steel sheets by removing extremely thinly plated surfaces in an electrolytic bath installed after the final washing tank of post-treatment equipment such as chemical conversion treatment, sulfur compounds are added to the electrolytic bath and electrolyzed. Anodic electrolysis is performed in the tank to remove the extremely thin plating and reveal an iron surface, and at the same time adsorbs sulfur compounds to the iron surface.

(6) When annealing is performed in a reducing atmosphere, an electrolytic bath and a washing bath are installed in front of the temper rolling mill after annealing, and an electrolytic bath containing sulfur compounds is used in the electrolytic bath to improve the surface of the steel sheet. The material is subjected to positive electrolytic treatment.

Note that alternating electrolysis is also possible as the electrolysis method), and full-wave rectification, single-wave rectification, and distorted wave rectification can be used for the power source. The electrolyzer can be a conventional vertical or horizontal cell.

Next, examples of the present invention will be described.

Example 1 FIG. 1 is a detailed layout diagram of an example of the present invention in manufacturing a cold rolled copper plate by continuous annealing. Capped copper (C: 0.L
] 6%, Si: 0.01%, Mn: 0.31%) cold-rolled material (thickness: 08 mm) was placed in a 4 m
K passed. That is, the strip uncoiled from the uncoiler 1 is heated in a continuous annealing furnace 2 without oxidation, and then
Photosoak annealing was carried out at 00° C. for 40 seconds, followed by primary air-water cooling to 400” O, followed by overaging treatment for 2 minutes in a non-reducing atmosphere, followed by secondary water cooling. The oxide film generated at this time was 380+I as Fe in the oxide film.
It was lp/de. The material is subjected to the treatment of the present invention in an electrolytic bath 3, then passes through a washing tank 4, a dryer 5, a temper rolling mill 6, and is rolled up in a recoiler 7.

Table 1 shows examples and comparative examples of the present invention.

Embodiment 2 FIG. 2 is an equipment layout diagram of an example of the present invention in manufacturing a single-sided galvanized electroplated steel sheet. Continuously cast aluminum killed steel (
C: 0.05%, Si: 0. C12%, Mn: 0.22
%) of conventional box-shaped annealed cold-rolled steel strip (thickness 0.7 +
+++a) was passed through the equipment shown in FIG. The strip uncoiled from the uncoiler 8 passes through a degreasing tank 9 for pre-plating treatment, a rinsing tank 10, a pickling tank 11, and a rinsing tank 12, after which it is electroplated on one side in a plating tank 13 and washed in a rinsing tank 14.
After being washed with water in the electrolytic bath 15, the film formed in the plating bath is removed and at the same time the treatment of the present invention is applied.
It passes through a dryer 17 and is rolled up into an unroller 18. In this way, in the continuous electroplating apparatus shown in Fig. 2, when one side was plated to a thickness of 60 y/m2 at a line speed of 50 m/min, a blackish brown discoloration occurred on the unplated iron surface at the exit side of the plating tank 16. . Table 2 shows examples and comparative examples of the present invention.

Embodiment 6 FIG. 6 is an equipment layout diagram of an example of the present invention in manufacturing a single-sided lead-plated electroplated steel sheet in which chemical conversion treatment is applied only to the plating surface. Using the same cold-rolled steel plate as in Example 2, a degreasing tank 20 for pre-plating treatment of the strip uncoiled from the uncoiler 19. After passing through the water washing tank 21, pickling tank 22, and water washing N23, the surface to be made into an iron surface is plated with 01 to 55'/7712.
After applying ultra-thin plating, it is washed with water in a washing tank 25, then chemical conversion treatment such as chromate is applied in a chemical conversion treatment tank 26, and after washing with water in a washing tank 27, the extremely thin plating is removed in an electrolytic bath 28, and the iron surface is A washing tank 29 after being exposed and subjected to the treatment of the present invention;
It passes through the dryer 30 and is rolled up onto the uncoiled wire 2-61. The amount of extremely thin coating in this example is 1? /m2 and chromate treatment is 60 chromic acid /m2! , 60m9/rrL2 of chromium was deposited on the galvanized surface by electrolysis in a bath of sulfuric acid 120&'/A at a bath temperature of 40°C and a current flow rate of 20 coulombs/dm. Third
Examples and comparative examples of the present invention are shown in the table.

The pampering liquid used in Examples 2 and 3 was Z n SO4
7) (20200f/#, H2SO425y-/!, N
a2SO4100y-/A, pH1' [l temperature 60°0
It is.

Embodiment 4 FIG. 4 is an equipment layout diagram of the present invention train in manufacturing cold-rolled steel sheets by continuous annealing. T1 addition steel (C: 0.01%,
A cold regular material (plate thickness (+, 8 mm)) of Si: 0.5%, Mn: 1.0%, Ti: 202% was passed through the equipment shown in Fig. 4. It was rolled up from the uncoiler 32. The IJ tube is heated in a reducing atmosphere in a continuous annealing furnace 33.
After soaking and annealing at 00°C for 60 seconds and cooling in the furnace, the electrolytic bath 34
The process according to the present invention is carried out in a washing tank 65, then dried (36), passed through a temper rolling mill 37, and then rolled up in a recoiler 32.Table 4 shows examples and comparative examples of the present invention.FIG. An example of an electrolytic cell is shown below.

The evaluation method for samples in Examples and Comparative Examples is as follows. In the Examples and Comparative Examples, phosphate treatment was carried out in Japan.
It was treated with Bt 6118, a spray type phosphate treatment solution manufactured by ξ-Car Rising Co., Ltd.

The treatment method is FC4328A degreaser, concentration 10y-/
! , treatment temperature 60°C, treatment time 120 seconds, after spray degreasing and water washing, using Bt3118, total acidity 15-17 points, free acidity 0.4-0.7 points, accelerator concentration 1.5-2.0 points , Zn+” 10DD~800
A solution adjusted to ppm was used. The film formation completion time is the time until the phosphate film is uniformly formed on the sample surface and no exposed substrate is visible, and the judgment is made by observing the treated surface with a scanning electron microscope (X500). Ta. The short time required to complete film formation indicates that the phosphate treatment reactivity is improved. In the determination after 120 seconds of treatment, the amount of film was measured as usual, and the crystal size was determined using a scanning electron microscope (x500). Film amount is 15~2.0i
? /m2 is an appropriate amount, and the smaller the crystal size, the better, and usually 15 to 25 μm is appropriate.

The SST (salt spray test) results show that the board that has been phosphate treated at 120" above was air-baked at 120°C x 10'. 2D~21μ electrodeposition coating, 180°0×
After baking 60', make a cross cut to reach the substrate with a sharp knife, and use 5% salt solution to JISZ-237.
1, the cross-cut portion was peeled off with cellophane tape after being sprayed with salt water for 1000 hours. Corrosion resistance after painting is good if the peeling width is small.

Next, a comparison between the method of the present invention and a comparative example in each example will be explained.

Table 1 shows the case where the oxide film generated during continuous annealing in Example 1 was removed. In Example 1-1 of Table 1, the 1-layer film was subjected to the treatment of the present invention in a sulfuric acid bath at a cathode i%. The time required to complete the formation of the acid salt film is short, indicating that the phosphate treatment reactivity is significantly improved. In addition, a dense phosphate film with a small crystal size was formed, and the corrosion resistance after painting was equivalent to or better than that of the ordinary box-shaped annealed material of Comparative Example B.

Example 1-2 and Comparative Example 2 are cases in which the silicon oxide film was removed by cathodic electrolysis in a phosphate solution, and similarly to the above, the performance of the Example was significantly improved compared to the Comparative Example, and the present invention was improved. Due to this effect, the 'rFJi of Comparative Example B exhibits performance equivalent to or better than that of conventional annealing.

Table 2 shows the case of improving the quality of the steel surface of the single-sided electrogalvanized steel sheet of Example 20. In Comparative Example 4 in Table 2, the iron surface that came into contact with the sulfuric acid acidic plating bath in the plating bath had a blackish brown appearance, poor phosphate treatment properties, and poor corrosion resistance after painting. In Comparative Examples 5 and 6, the appearance was improved by anodic electrolysis, but the other performances were poor. Example 2-1 and Example 2-2 are examples of the present invention in which a sulfur compound was added to a sulfuric acid bath and a boric acid solution, respectively, and the appearance, phosphate treatment properties, and post-painting corrosion resistance were the same as those of Comparative Example 8. Shows performance equivalent to or better than cold-rolled steel sheets.

Table 6 shows how to prevent appearance defects on the iron surface in the plating bath and when chemical conversion treatment such as chromate treatment is applied to the plating surface after plating, when producing the single-sided electrogalvanized steel sheet of Example B. In order to prevent the quality of the iron surface from deteriorating due to contact with these chemical conversion treatment solutions, an extremely thin plating is applied to the iron surface in advance, and the extremely thin plating is removed after the chemical conversion treatment to reveal the iron surface. It is about. In Comparative Example 8, a sulfuric acid bath was used, and in Comparative Example 9, a phosphate bath was used to remove the very thin plating by anodic electrolysis to make an iron surface appear. Compared to the cold rolled steel sheet of Comparative Example 7 in Table 2, Comparative Example 8 has poor phosphate treatment properties and post-painting corrosion resistance, and Comparative Example 9 takes a long time to complete the formation of the phosphate film. In the case of the examples of the present invention in which a sulfur compound was added to the sulfuric acid bath and the phosphate bath of Example B-1 and Example 6-2, respectively, the phosphate treatment properties and post-painting corrosion resistance were the same as those of Comparative Example 7. Shows performance equivalent to or better than steel plate. In addition, the amount of current required to remove extremely thin plating of 1 no/m2 zinc is 50 coulombs/dm.
Example No.1, No.2 and Comparative Example No.8,
The amount of residual lead on the iron surface of No. 9 is 0.002. P/m2 or less.

Table 4 shows the case of Ti-added steel in continuous annealing of Example 4. Comparative Example 11 is T that is continuously annealed in a reducing atmosphere.
This is an i-added steel sheet, and its phosphate treatment properties and post-painting corrosion resistance are poor compared to Comparative Examples 4 and 8, which were subjected to normal box-shaped annealing. Example 4 is the one in which the present invention was applied after the completion of continuous annealing, and Comparative Example 10
J, lyphosphate treatability and post-painting corrosion resistance are significantly improved, and furthermore, the steel sheet exhibits performance equivalent to or better than that of the cold rolled steel sheet of Comparative Example 4.8.

As described above, the method of the present invention has better phosphate treatment properties than the comparative examples, and not only is it superior as a finished product, but also improves workability, for example, descaling and phosphate treatment properties. It is also excellent in terms of things like making it work.

[Brief explanation of the drawing]

1 to 4 are layout diagrams of an apparatus according to an embodiment of the present invention, and FIG. 5 is an enlarged view of an electrolytic cell of the apparatus according to an embodiment of the present invention. 1... Uncoiler - 12... Continuous annealing furnace, 6 Electrolytic tank, 4 Washing tank, 5... Dryer, 6... Temper rolling mill,
7 Recoiler, 8 Uncoiler 19 Degreasing tank, 10 Washing tank, 11 Pickling tank, 12 Washing tank, 1
6. Plating tank, 14. Washing tank, 15. Electrolytic tank, 16
・Washing tank, 17-dryer, 78・Recoiler, 19...
・Uncoiler-120...Degreasing tank, 21...Washing tank,
22. Pickling tank, 26.. Washing tank, 24. Plating tank, 25
...Washing tank, 26・Chemical treatment tank, 27・Washing tank, 28
・Electrolytic cell, 29...Washing tank, 60 ・Dryer, filter 1・
・Recoiler, 32... Uncoiler - 16 filter... Continuous annealing furnace, 34 ゛ Electrolytic cell, 35 Washing tank, 36... Dryer, 37. Temper rolling mill, 68. Recoiler, 39...
Electrode, 40, presser roll, 41... Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) Mercaptans (2) on the surface of cold-rolled steel sheets
) Thiocyanates (6) Thiophene derivatives (4) Sulfides (5) Disulfides (6) Contains one or more compounds having a thiocarbonyl group, and has a sulfur content of 0.01 to 500rn? A cold-rolled steel sheet with excellent phosphate treatment properties, characterized by adsorbing a compound of /m'. (2) The above (1) mercaptans, (2) thiocyanates, (6) thiophene derivatives, (4) sulfides, (
51 disulfides, (6) compounds having a thiocarbonyl group, and 10-5 to 1o-
Production of a cold-rolled steel sheet with excellent phosphating properties, characterized by electrolyzing the steel sheet in a solution containing 1 mol/j with the polarity of the steel sheet as an anode or an anode at a current flow rate of 1 to 100 corons/dm2. Method.