JP2554792B2 - Method for producing hot-rolled galvanized steel sheet and alloyed hot-dip galvanized steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled galvanized steel sheet and a method for producing an alloyed hot-dip galvanized steel sheet.

[0002]

2. Description of the Related Art Generally, a thick hot-rolled steel sheet (mainly 1.6 mm or more) is used as an original sheet of hot-dip galvanized steel sheet for construction and the like. These steel sheets are usually used after pickling, but the surface after pickling often has local scale residue or local smud formation due to overpickling. Since the unevenness of the surface is rough, there are problems such as non-plating and abnormal development of the alloy layer in the plating layer locally in the conventional hot-dip Zn plating method of the Zenzimer type or the flux treatment. .

[0003]

On the other hand, the pre-Ni plating method proposed by the present inventors and the hot dip Zn plating method utilizing rapid low-temperature heating are applicable not only to cold-rolled steel sheets but also to hot-rolled steel sheets. The pickling conditions are appropriate, the unevenness of the steel sheet is small, and it is an excellent method that can ensure extremely good plating properties in normal hot-rolled pickling materials with no scale residue, etc. Compared with the conventional method when the pickling conditions are poor, the unevenness of the steel sheet surface is particularly large after overpickling, the amount of smud generated is large, or the local scale remains due to insufficient pickling. Then, although the hot-dip galvanizing property is improved, even this method is still inadequate, the distribution of pre-Ni becomes non-uniform, and Ni non-plating is likely to occur locally, resulting in local hot-dip Zn plating. In some cases, in this case Logical, subjected to alloying treatment for prone to alloying defects even after hot-dip Zn plating, and further, it is necessary to improve.

Therefore, the inventors of the present invention have made various studies and found that the surface of the hot-rolled pickled plate in which unevenness is rough or scale remains and smud formation is locally observed has a certain roughness range. Brush scrubber, mechanical polishing such as sandpaper polishing, skin pass, shot blasting,
After adjusting the roughness by a method such as electrolytic polishing, pre-Ni
When plating is performed and hot dipping is performed under a predetermined atmosphere and heating conditions, good plating properties are obtained, and a good alloy plating layer is obtained even when the hot dip Zn plated steel sheet is alloyed. It was found that the plating adhesion was excellent.

As described above, the present invention uses a hot-rolled steel pickled sheet which has particularly large surface irregularities and locally shows scale residue or smud formation. It is intended to provide a method for producing an alloyed hot-dip Zn-plated steel sheet having excellent plating adhesion of a processed part.

[0006]

The inventors of the present invention first adjust the roughness of the surface of a hot rolled pickled steel sheet by various methods such as sandpaper polishing, brush scrubber polishing, skin pass, shot blasting and electrolytic polishing. After that, after pre-Ni plating, after heating under specific heating conditions, hot dip Zn plating is performed to produce hot dip Zn plated steel sheet, and further 470 to 550.
The alloying treatment was also performed within the range of ℃ to produce an alloyed hot-dip plated steel sheet, and its performance and structure were investigated. As a result, the non-plating was eliminated, the plating property became good, and the alloying rate was
It was found to be faster than without polishing. Moreover, the appearance and the plating layer structure are more uniform than in the case of no polishing,
It was found that it also depends on the surface roughness, and the average roughness Ra of about 0.1 to 1.5 μm was favorable. Furthermore, the thickness of the pre-Ni plating and the subsequent heating conditions were changed, and hot dip galvanizing properties and alloying reactivity were observed by appearance, Fe% in the plating layer, changes in the plating layer structure, and the like. Among them, in particular, the steel plate roughness is 0.1 to 1.5 μm, a pre-Ni plating layer is applied to 0.2 to ² g / m ² , and the temperature is heated to 420 to 500 ° C. in a non-oxidizing atmosphere, It was found that, when immersed in a hot-dip Zn plating bath within a period of 15 seconds, the hot-dip Zn plating property and the alloying reactivity were significantly improved. These are the points of the manufacturing method of the present invention.

Furthermore, it is an essential condition that the bath penetration plate temperature after the Ni plating treatment is low, and that the time at which the bath penetration plate temperature is 350 ° C. or higher is short in the process of reaching the bath penetration plate temperature.

High temperature heating as in the conventional method and 350 ° C.
Under the heating condition in which the above-mentioned time is maintained for a long time, in the case of no pre-Ni plating, an oxide film on the surface of the steel sheet was likely to develop, the hot-dip Zn plating property was poor, and alloying was difficult to proceed. In addition, even if pre-Ni plating is applied after the roughness adjustment, if the pre-Ni layer is heated at a high temperature and the time kept at 350 ° C. or higher is too long, the pre-Ni layer will diffuse into the base metal during heating. , The hot-dip galvanizing property and the adhesion of the processed part after the alloying treatment were not improved. Therefore, pre-N
With i plating, the heating temperature after pre-plating was kept as low as possible, and the activity of the surface of the steel sheet was maintained by shortening as long as possible the time at which Ni was started to diffuse into the base iron. We considered that performing hot dip plating and alloying treatment in this state was a key point in manufacturing, and conducted repeated experiments. As a result, the surface roughness of the hot rolled pickled steel sheet is adjusted to 0.1 to 1.5 μm by mechanical polishing such as brush scrubber, sandpaper polishing, skin pass, shot peening, and electrolytic polishing, and 420 to 5 as it is.
A hot-dip Zn-plated steel sheet having excellent plating properties was obtained only when heated to 00 ° C. and immersed in a hot-dip Zn plating bath within 15 seconds of 350 ° C. or higher in the process.
Further, it has been found that an alloyed hot-dip Zn-plated steel sheet excellent in surface appearance and plating adhesion of a processed part can be obtained only when an alloying treatment is performed under appropriate alloying conditions. The present invention has been completed.

That is, the surface of the hot rolled pickled steel sheet has an average roughness (R
After adjusting the roughness of a) so that the roughness is in the range of 0.1 to 1.5 μm, Ni plating is applied to 0.2 to ² g / m ² , and then the plate temperature is 420 in a non-oxidizing atmosphere. Al-0.05-0.4% within 15 seconds in the process of heating to ~ 500 ° C and the steel plate entering the bath within 15 seconds
A method for producing a hot-dip galvanized steel sheet having excellent plating properties, characterized by being Zn-plated, and an average roughness (Ra) in the range of 0.1 to 1.5 μm on the surface of the hot-rolled pickled steel sheet. After adjusting the roughness, Ni pre-plating is performed at 0.2 to ² g / m ² and the plate temperature is 4 in a non-oxidizing atmosphere.
In the process of heating the steel sheet to 20 to 500 ° C. and invading the bath, the temperature of 350 ° C. or higher is Al within 15 seconds.
Hot-dip galvanizing in a Zn plating bath containing 0.05 to 0.4%, 10 to 4 at 470 to 550 ° C. immediately above wiping.
A method for producing an alloyed hot-dip Zn-plated steel sheet excellent in plating adhesion of a processed part, which comprises performing a 0s alloying heat treatment.

The non-oxidizing atmosphere in the present invention means a non-oxidizing atmosphere (for example, H ₂ 3% + N ₂ , O ₂ number 10 pp.
m) or a reducing atmosphere (eg H ₂ 15% +
N ₂ atmosphere).

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the relationship between the surface roughness of a steel sheet and the hot dip galvanizability and alloyability. This is the case where the pre-Ni plating is 0.5 g / m ² . Hot rolled pickling plate (SS
The roughness is changed by changing the degree of polishing to 411.6 mm), and after surface polishing, the pre-Ni plating layer is plated with 0.5 g / m ² and then O ₂ 60 ppm H ₂ 3% +
Plate temperature up to 450 ° C by energizing heating in N ₂ atmosphere, 350
The temperature kept above ℃ is 2 seconds, and Al 0.
Hot-dip galvanized steel sheet is prepared by hot-dip galvanizing for 3 seconds in a Zn plating bath containing 2% at 450 ° C. The hot-dip Zn plating property is the presence or absence of non-plating, and the plating adhesion by ball impact test (5-grade evaluation 1 is the best). Was evaluated in a three-step manner. In addition, 1 at 500 ℃ directly above the wiping after plating
An alloying hot-dip galvanized steel sheet was produced by performing an alloying heat treatment for 5 seconds, and the degree of alloying was evaluated by 3 ranks in terms of appearance and Fe content in the plating layer. Passed B rank or higher. The evaluation criteria are as follows.

1) Hot-dip Zn plating property score Hot-dip plating property Presence or absence of non-plating Plating adhesion (B.I. score) A None 1 Best B None 2 C Some 3-5 When the surface roughness of the steel sheet is 0.1 to 1.5 μm, both the plating property and the alloying property are good.

Although only the sandpaper polishing method is shown here as a means for imparting roughness to the steel sheet,
The results of skin pass, shot blasting, brush scrubber or electrolytic pickling, and electrolytic polishing were also the same.

FIG. 2 is a diagram showing the relationship between the pretreatment heating plate temperature and the plating adhesion of the processed portion. Hot rolled pickling plate (3.2m
m) is roughened with sandpaper to a roughness of Ra 0.5 μm, the Ni plating layer is plated with 0.5 g / m ² and then O ₂ 60
ppm of H ₂ 3% + N sheet temperature 45 electric heating in a ₂ atmosphere
It is heated to 0 ℃ at 350 ℃ or higher for 5 seconds,
Hot-dip galvanizing for 3 seconds in a Zn plating bath containing Al 0.15% at 450 ° C., and immediately after wiping, alloying treatment is performed at 500 ° C. for 20 s to produce an alloyed hot-dip Zn-plated steel sheet, and plating adhesion of the processed part The sex was evaluated. For the workability test, a 25 mm cup drawing test was performed and the degree of blackening was examined by a tape test. The evaluation was made in 5 grades. The evaluation criteria are as follows.

[0016] From this figure, the heating plate temperature before hot dip coating is 420 to 500.
It is clear that an alloyed hot-dip Zn-plated steel sheet having good plating adhesion in the processed part can be obtained in the range of ° C. If the temperature exceeds the specified temperature, the plating adhesion of the processed part will deteriorate, and
If the temperature is lower than 420 ° C., non-plating is likely to occur during hot dipping.

FIG. 3 shows the relationship between the heating temperature and the amount of diffusion of the pre-Ni plating layer into the base iron. Hot rolled pickled steel sheet (Al
After adjusting the surface roughness of the killed SPHC (1.6 mm) to 1.0 μm with a brush scrubber, apply Ni plating at 0.5 g / m
After ^two plating After performing 10 seconds heating to a predetermined temperature by electric heating by O ₂ 60 ppm of H ₂ 3% + N ₂ atmosphere,
The residual rate of the Ni plating layer was obtained by depth direction analysis by Auger analysis. It is clear that the pre-Ni layer begins to diffuse into the base iron at a heating temperature of about 350 ° C, and almost no more remains above 500 ° C.

Next, in the process of reaching the bath penetration temperature after Ni plating, the temperature 35 at which Ni begins to diffuse
FIG. 4 shows the relationship between the time required to reach the bath penetration temperature after reaching 0 ° C. and the plating adhesion of the processed part.

A hot rolled pickled steel sheet (SPHC 1.6 mm) was roughened to 0.5 μm by a brush scrubber, and pre-N
O ₂ 60ppm after i plating layer 0.5g / m ² plating
After heating to a plate temperature of 450 ° C. in an atmosphere of H ₂ 3% + N ₂ , the hot plate is hot-dipped for 3 seconds in a Zn plating bath at 450 ° C. containing 0.15% Al and immediately after wiping.
An alloying hot-dip Zn-plated steel sheet was prepared by performing an alloying treatment at 0 ° C. for 20 seconds, and the plating adhesion of the processed portion was evaluated. The basis weight was 60 g / m ² . 350, which is the scope of the present invention
It is clear that the plating adhesion of the processed part is good when the time from reaching the temperature of 0 ° C to reaching the bath penetration temperature is within 15 seconds.

Sandpaper sanding, skin pass,
The same was true when electrolytic polishing or electrolytic pickling was used.

From these results, in the present invention, the surface is adjusted by polishing or the like so that the surface roughness of the steel sheet is within a certain range, a predetermined amount of pre-Ni plating is applied, and the heating temperature after that is adjusted. Is low, and the time from reaching 350 ° C. to reaching the bath penetration plate temperature is short, and thus hot-dip galvanized steel sheet with excellent plating properties and alloying fusion with excellent plating adhesion of the processed part This is a major point in manufacturing a Zn-plated steel sheet.

The heating method is not particularly limited, but a method for directly electrically heating a steel sheet, an induction heating method,
Various methods such as infrared heating can be applied.

The direct electric heating method is effective in that it is easy to quickly set the heating rate from a thin plate to a thick plate of more than 3 mm, and compact equipment is possible.

The amount of pre-Ni plating applied is 0.2 g / m ²
The reason for the above is that the effect of improving the hot-dip galvanizing property and alloying reaction by Ni has been confirmed. Also, if it is less than 0.2 g / m ² , it is almost the same as that without Ni. The upper limit is set to 2 g / m ² because if it exceeds this value, alloying of the base iron is difficult to proceed and the Ni content in the plating layer becomes too high.

The lower limit of the amount of Al in the bath is set to 0.05%. If the lower limit is less than this, the alloying proceeds excessively during the alloying process, the Γ phase is excessively generated at the base iron interface, and the alloy layer is formed. This is because the plating adhesion of and the red rust resistance of the processed part are not improved.
Further, the upper limit of Al in the bath is 0.4% because Al is less than 0.1%.
This is because if it exceeds 4%, the appearance becomes whitish at the time of plating, a Fe-Al-Zn-based barrier layer other than Ni-Al-Zn is easily formed, and alloying does not proceed during alloying treatment.

The optimum alloying treatment temperature is 470 to 550 ° C. If it is less than 470 ° C, alloying is difficult to proceed, and it is 550
If the temperature exceeds ℃, alloying will proceed too much, the Γ phase will easily develop at the base iron interface, and the plating adhesion will deteriorate. The alloying time is determined by the balance with the alloying temperature.
A range of 40 seconds is suitable. If it is less than 10 seconds, the alloying is difficult to proceed, and if it exceeds 40 seconds, the alloying is too advanced, the Γ phase is likely to develop, and the plating adhesion and the red rust resistance deteriorate.

The coating weight is not particularly limited, but is preferably 10 g / m ² or more from the viewpoint of corrosion resistance and 150 g / m ² or less from the viewpoint of workability. The above results have been described for the case of using only the Zn plating bath.
The same results were obtained in the case of alloyed hot-dip galvanized steel sheet containing b or Pb alone or in a composite amount of 0.2% or less in a trace amount. Regarding the bath temperature, even if it is a Zn bath, Z
Even when a small amount of alloying element is contained in n, ordinary conditions of 430 to 500 ° C. can be used.

Various steel types can be used as the hot rolled pickling plate.

[0029]

The reason why the influence of the surface roughness of the steel sheet during the hot-dip galvanizing and alloying hot-dip Zn plating reaction of the hot-rolled pickled steel sheet is large is not clear yet, but the surface roughness is It is considered that it is a kind of controlling factor of surface reactivity (activation degree).

When the surface roughness is within a certain range, it is considered that the degree of activation of the surface of the base metal is large and the reactivity with pre-Ni plating and molten Zn is improved. It is also considered that the partial smud after pickling or the scale residue is completely removed during the roughness adjustment and the steel sheet is uniformly activated.

Further, in the case where Ni plating is subsequently applied, when the roughness is within a certain range, Ni uniformly covers the surface of the base iron with a thin layer, prevents oxidation of the base iron, and prevents the base iron itself. Since the activity is high and the active points are evenly present on the steel sheet surface, it is easy to react immediately after Ni is eluted during the hot dip Zn plating and the alloying reaction. It is also possible that the degree of activity is improved. It is considered that the active points of the reaction are uniformly distributed by moderate surface roughness and Ni plating, and the effect of grain boundaries and the like are alleviated.

On the other hand, if the surface roughness is too low, Ni will cover the surface of the base iron evenly and thickly when Ni plating is performed, and Ni will be easily eluted during hot dip Zn plating and during alloying treatment. Otherwise, the elution of base iron does not occur easily and the alloying reaction does not proceed easily. In addition, if the polishing is insufficient, it is conceivable that the mud on the surface of the base metal, scale residue, etc. will not be sufficiently removed, and the activity of the base iron will not be sufficient.

Further, if the surface roughness is too large, the elution of the base iron becomes uneven due to the distribution of the projections and recesses of the steel sheet, and Ni does not cover the surface of the base iron uniformly. , The active points of the base metal itself are locally concentrated on the convex portion, and the hot dip Zn plating reaction and the alloying reaction proceed non-uniformly locally. It is thought to be easier.

Further, when the plating layer obtained in the range of the present invention was analyzed, the pretreatment heating plate temperature after Ni pre-plating in the range of the present invention and 350 ° C. to the bath penetration plate temperature were reached. In the case of time, the diffusion of the pre-Ni layer into the ground iron is small, while the heating temperature in the prior art range is high, and when the heating time is long, most of the Ni is contained in the ground iron during heating. It was diffused and changed to a Fe-Ni solid solution layer. It is considered that the difference in the state of Ni at the time of heating caused the difference in the plating layer constitution during the subsequent hot dipping and alloying treatments.

Zn, Fe, Ni and Al are relatively evenly distributed in the plated layer of the alloyed hot dip Zn plated steel sheet produced by the method of the present invention. It had a layered structure. In addition, Γ of the ground iron interface
The phase was also thinly suppressed within 0.8 μm. Although the details are not yet clear, in the case of the present invention, the growth of the Γ phase was suppressed because the pre-Ni layer which remained as it was during heating was a Fe-Al-Zn-Ni barrier. Since it was confirmed that the layer was formed at the base steel interface, it is considered that it becomes a barrier of Γ phase growth at the alloying stage. It is considered that the excellent plating adhesion of the processed part is due to the suppression of the Γ phase.

[0036]

EXAMPLES Table 1 shows examples of the production method of the present invention and the obtained samples. * Indicates a comparative material manufactured by a manufacturing method other than the present invention. A hot-rolled pickled steel sheet (1.6 mm) having the composition shown in Table 2 was used as the base. Surface adjustment is carried out by sandpaper polishing, skin pass, shot blasting, brush scrubber polishing, electrolytic pickling and electrolytic polishing to change the surface roughness, and pre-Ni plating by electroplating in a sulfuric acid acidic bath to change the adhesion amount. After that, pretreatment heating is performed in an atmosphere of O ₂ 60 ppm, H ₂ 3% + N ₂ by changing the time from reaching the bath penetration plate temperature of 350 ° C. to reaching the bath penetration plate temperature, and then bath temperature of 450. ℃, 3se
Hot-dip plating was carried out in c. Further, after wiping, alloying heat treatment was performed at 450 to 550 ° C. for 5 to 40 seconds to prepare samples having various plating layer compositions. The coating weight was 60 g / m ² . The hot-dip galvanizing properties, the appearance of alloyed hot-dip zinc plating, and the plating adhesion of the processed part were evaluated according to the above-mentioned test method and evaluation criteria.

No. 1 to 39, the steel sheet obtained by the manufacturing method within the scope of the present invention has hot dip galvanizability, alloying degree,
Excellent adhesion to the processed part.

In comparison, the surface roughness of the base metal after polishing, the amount of the pre-Ni plating layer deposited , the time from reaching the plate temperature of 350 ° C. to reaching the bath penetration plate temperature, Al in the bath, alloying When the processing conditions deviate from the scope of the present invention (No. 40 to 5)
7), the plating property, the degree of alloying, and the plating adhesion of the processed part are poor.

Further, in No. Nos. 58 to 60 are cases where a trace amount of another alloy element was contained in the plating bath, and also in this case, excellent performance was exhibited.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

INDUSTRIAL APPLICABILITY As described above, according to the manufacturing method of the present invention, hot dip galvanized steel sheet using hot rolled pickling sheet and alloying hot dip galvanized steel sheet have unprecedented plating properties, alloying properties, and workability. Since the performance such as the plating adhesion of the parts can be obtained, its industrial significance is extremely large.

[Brief description of drawings]

1A and 1B are views showing the relationship between the surface roughness of a steel sheet and the hot dip galvanizability and alloyability.

FIG. 2 is a diagram showing a relationship between a pretreatment heating plate temperature and plating adhesion of a processed portion.

FIG. 3 is a diagram showing a relationship between a heating plate temperature and a pre-Ni plating residual rate.

FIG. 4 is a diagram showing the relationship between the time from the plate temperature reaching 350 ° C. to the bath penetration plate temperature and the plating adhesion of the processed part.

Claims (2)

(57) [Claims] 1. The surface of a hot-rolled pickled steel sheet has an average roughness (Ra).
After adjusting the roughness so that the roughness is in the range of 0.1 to 1.5 μm, the Ni pre-plated layer is plated at 0.2 to ² g / m ² and the plate temperature is 420 to 500 ° C. in a non-oxidizing atmosphere. In the process of heating the steel sheet to the temperature of 350 ° C. or higher in the process until the steel sheet penetrates the bath, Al 0.05 to 0.4
% Hot-dip Zn-plated steel sheet having excellent plating properties, which is characterized by immersing in a Zn-plating bath containing 50% to perform hot-dip galvanizing. 2. The average roughness (Ra) of the surface of the hot rolled pickled steel sheet.
After adjusting the roughness so that the roughness is in the range of 0.1 to 1.5 μm, the Ni pre-plated layer is plated at 0.2 to ² g / m ² and the plate temperature is 420 to 500 ° C. in a non-oxidizing atmosphere. In the process of heating the steel sheet to the temperature of 350 ° C. or higher in the process until the steel sheet penetrates the bath, Al 0.05 to 0.4
% Hot-rolled alloying fusion with excellent plating adhesion in the processed part, characterized by dipping in Zn plating containing 10% and hot dipping, and immediately after wiping, alloying heat treatment is performed at 470 to 550 ° C. for 10 to 40 seconds. A method for manufacturing a Zn-plated steel sheet.