JPH0615303A - Manufacture of corrosion resistant hot-rolled steel sheet having excellent r average value - Google Patents

Abstract

PURPOSE:To economically manufacture a hot-rolled steel sheet for working having plating layer of zinc-aluminum alloy, good r (average) value and excellent corrosion resistance in good productivity. CONSTITUTION:The manufacturing method of the corrosion resistant hot-rolled steel sheet having excellent r (average) value forming the plating layer in a prescribed range on the steel sheet surface, is obtd. by controlling the temperature history in the process from a casting to the hot-rolling to improve the r (average) value of the steel sheet and injecting the zinc-aluminum alloy powder containing 15-30wt.% aluminum on the steel sheet surface in the temp. range of 200-300 deg.C after executing dry-descaling to the steel sheet surface while recoil- passing the coiled hot-rolled steel sheet.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention has a zinc-aluminum alloy plated layer having a ball impact rating (hereinafter referred to as BI rating) of 2 or less, which indicates plating adhesion, and has an excellent r (average) value. The present invention relates to a method for economically producing a corrosion-resistant hot-rolled steel sheet for working with high productivity.

[0002]

2. Description of the Related Art Conventionally, a method for plating a metal on a hot-rolled steel sheet or the like is, after hot-rolling, once cooled, pickled, and then dipped in a molten bath of plated metal for hot dipping, There is a method in which the pickled steel sheet is immersed in a solution containing a salt of a plating metal and electroplated by direct current electrolysis.

However, both of these methods require a large pickling facility and a plating device, and not only a vast installation place is required, but also a hot plate heating device and its fuel are required in the hot dipping method. Since the electroplating method requires electric power for electrolysis and requires a large amount of equipment cost and energy cost, improvement in overall economic efficiency is strongly desired.

In order to meet the demand for this improvement, the molten metal is applied to the outer surface of the rolled steel sheet which is used in the hot rolling process or the refining process by utilizing the heat energy of the hot rolling process according to Japanese Patent Laid-Open No. 54-146230. There is a proposal to form a uniform plating layer on the surface of the steel sheet by thermal spraying, and economically perform metal plating with a small-scale equipment.

However, this proposal does not remove the scale formed during hot rolling, so that the molten metal is sprayed onto the scale, resulting in poor adhesion of the plating, and pressing after manufacturing. If this is done, the plating layer will peel off and the corrosion resistance will deteriorate.

In addition, in order to overcome these problems, the type of sprayed metal required, the temperature of the steel plate during spraying, the appropriate roughness of the steel plate surface for improving plating adhesion, and the heat for spraying There is no specific description about a desired position in the inter-rolling step or the refining step, and specific implementation conditions for obtaining a plated layer that guarantees adhesion are neither disclosed nor suggested, and are completely unknown.

On the other hand, as to the improvement of the r (average) value of the hot rolled steel sheet, as described in JP-A-59-226149, a method of producing an ultra low carbon steel using Ti by oil lubrication rolling, or As described in JP-A-62-192539, there is a method of manufacturing by adding an alloy such as Nb or Ti.

In the former case, however, the rolling oil used for oil lubrication has a high concentration, and therefore the rolling itself is inevitably carried out under the slip limit conditions, such as rolling temperature, rolling speed, and rollable size. Due to the large restrictions of the above, the deterioration of production efficiency cannot be denied.

Further, there is a drawback that workability and productivity are poor because it requires labor such as removing oil attached to the roll. On the other hand, with regard to the latter, there is a problem that the alloy cost is high and it is not economical because an alloy such as Nb or Ti is used.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, and uses a zinc-aluminum alloy to provide a plating layer having good adhesion to a steel sheet.
An object of the present invention is to provide a method for economically producing a corrosion-resistant hot-rolled steel sheet having an excellent r (average) value with reasonable equipment.

[0011]

According to the present invention, in order to solve the above-mentioned problems, in% by weight, Mn: 0.10 to 0.60.
%, S: 0.001 to 0.012%, and other Fe
And molten steel consisting of unavoidable components are continuously cast, and cooling is performed at 1400 ° C. to 1200 ° C. in the process of 5.0 ° C./min or more to form a slab, and finish rolling of the slab is performed within 60 minutes from the start of casting. After starting and ending at Ar ₃ points or more, the coil is rewound, the hot rolled steel sheet is unwound, and the surface of the steel sheet is dry-descaled, and then the surface of the steel sheet in a temperature range of 200 ° C. to 300 ° C. An excellent r (average) value is characterized in that a zinc-aluminum alloy powder containing 15% to 30% by weight of aluminum is sprayed to form a plating layer in a required range on the surface of the steel sheet. A method for producing a corrosion-resistant hot-rolled steel sheet, which comprises performing dry descaling and then setting a non-oxidizing atmosphere as a carrier atmosphere for the steel sheet until the zinc-aluminum alloy powder is sprayed onto a required range of the steel sheet surface. Look, later with dry de-scaling,
It is a method for producing a corrosion-resistant hot-rolled steel sheet having an excellent r (average) value in which the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed into a required range on the surface of the steel sheet is a reducing atmosphere.

The present invention further provides that, in wt%, Mn: 0.10.
-0.60%, S: 0.001-0.012% is included,
Molten steel composed of other Fe and unavoidable components is continuously cast, cooling is performed at 1400 ° C to 1200 ° C in the process of 5.0 ° C / min or more to form a slab, and finish rolling of the slab is performed for 60 minutes from the start of casting. After starting within ₃ Ar and ending at ₃ points or more, the hot rolled steel sheet is unwound, and the surface of the steel sheet is dry-descaled during rewinding to obtain a surface roughness Ra.
Zinc-aluminum alloy powder having a grain size of 120 mesh or more on the surface of the steel plate in the temperature range of 200 ° C. or more and 300 ° C. or less and containing 15% or more and 30% or less by weight of aluminum. Is a method for producing a corrosion-resistant hot-rolled steel sheet, in which a plating layer is formed in a required range on the surface of the steel sheet by injecting at a pressure of 0.05 MPa or more, and after dry descaling, a zinc-aluminum alloy powder is applied to the steel sheet. Including a non-oxidizing atmosphere in the conveying atmosphere of the steel sheet until it is sprayed onto the required area of the surface, and after dry descaling, until the zinc-aluminum alloy powder is sprayed onto the required area of the steel sheet surface The method for producing a corrosion-resistant hot-rolled steel sheet, wherein the conveying atmosphere of the steel sheet is reduced atmosphere.

The hot-rolled steel sheet for working as used in the present invention means
Steels commonly used for steel sheets in the field of producing and using hot-rolled steel sheets for working, for example, in wt%, C:
0.01-0.10%, Mn: 0.10-0.60%,
Si: 0.001-0.06% and P: 0.001-
0.050%, including S: 0.001-0.012%,
In addition, it refers to steel consisting of Fe and inevitable components.

The inventors of the present invention conducted various experiments and studies in order to achieve the above-mentioned objects, and obtained the following findings. The inventors of the present invention have found that, by weight%, Mn: 0.10 to 0.60%, S: 0.
Steel containing 001 to 0.012% and other Fe and unavoidable components is cast and solidified in a temperature range of 1400 ° C to 1200 ° C at a cooling rate of 5.0 ° C / min or more to obtain a slab. It has been found that a steel plate having a high r (average) value can be obtained by starting the finish rolling of the piece within 60 minutes from the start of the solidification and ending the rolling at the Ar ₃ point or less.

This is because the amount of S precipitated as MnS is secured in a sufficiently solid solution state until the rolling, and fine MnS is precipitated during the rolling, and the fine MnS thus precipitated recrystallizes austenite. Form a well-developed austenite rolling texture, which results in (1
12) Transformation into ferrite with a high degree of surface accumulation r (average)
This is because the value is improved.

On the other hand, the present inventors have investigated the plating adhesion of corrosion-resistant hot-rolled steel sheets used in the market, and as a result,
It has been found that the corrosion-resistant hot-rolled steel sheet, which has been satisfied in each application, has a BI adhesion rating of 2 or less. The BI rating of 1 indicates the best plating adhesion, and the larger the value, the lower the plating adhesion.

In order to elucidate the controlling factor of this plating adhesion, the present inventors have made a detailed investigation of the boundary between the base steel surface and the plating layer of the above-mentioned steel sheet, and as a result, the metal powder injected onto the steel sheet has a superplastic flow. As a result, it was found that the unevenness on the surface of the ground iron bites and adheres.

Based on the above findings, the present inventors utilize the high temperature of hot-rolled steel sheet and remove the scale on the surface of the hot-rolled steel sheet during rewinding and passing the hot-rolled steel sheet rolled after rolling. The experiment of producing a plated steel sheet by spraying pure zinc and zinc-aluminum alloy powder on the exposed bare steel surface was repeated, and the findings of FIG. 1 were obtained.

According to this FIG. 1, the present inventors have found that the steel plate temperature is in the range of 200 ° C. to 300 ° C.
When zinc-aluminum alloy powder containing 30% or more of aluminum is sprayed onto the surface of the steel sheet, BI
It has been found that a plated steel sheet having a high adhesion of 2 or less is obtained.

Further, it has been found that, in removing the scale, it is desirable to increase the roughness of the surface of the base metal at the same time as removing the scale. This is because the scale removes the plating layer directly on the base metal to improve the plating adhesion, and the metal powder sprayed on the surface of the base metal, which has a rough surface, bites into the irregularities on the surface of the base iron for an anchoring effect. Occurs,
This is because the adhesion of the plating layer brings stability for a longer period of time.

As a descaling method suitable for this, it has been found that there are dry descaling methods such as shot blasting, grit blasting, brushing roll, and arc discharge.

In order for the metal powder sprayed on the unevenness of the surface of the base metal thus descaled to bite and melt to form a plating layer with good adhesion on the steel sheet, it is necessary to collide the powder with a strong spraying pressure. I found out that there is.

Therefore, after heating to 250 ° C., the surface of the hot-rolled steel sheet subjected to the various dry descaling described above is
The surface roughness, powder particle size, and spraying pressure were variously changed, and an alloy powder of zinc and aluminum having an aluminum content of 25% by weight was sprayed, and the adhesion of each plating layer was evaluated by BI rating. The result is shown in FIG.

From this FIG. 2, the inventors found that the surface roughness was R
It was found that when the a value is 3 μm or more and the grain size of the alloy powder is 120 mesh or more and the spraying pressure of the alloy powder is 0.05 MPa or more, the plating adhesion having a BI rating of 1 can be obtained.

As the metal forming the plated layer for corrosion resistance, there are zinc, aluminum, lead, an alloy of zinc and aluminum, an alloy of zinc and iron having an iron content of about 5% by weight or less, and the like. The melting point of these metals is about 70 above 327 ° C.
It is in the temperature range of 0 ° C or lower, and is 3 or higher than the melting points of these.
In the hot rolling process, the high temperature range of 0 ° C to 200 ° C is from the end of finish rolling to the winding, and the position of good productivity and economical efficiency is determined based on the melting point of the metal used for injection during that period. It turned out to be good.

As for the pretreatment of plating, from the viewpoint of productivity and economical efficiency, if there is a scale between the plating layer and the base metal, the scale is easily peeled off and the plating adhesion is deteriorated. It is preferable to simultaneously remove the scale to prevent the above and simultaneously optimize the roughness of the surface of the steel sheet to increase the contact area between the base steel and the plating layer to promote the alloying reaction. It was found that high-pressure water descaling or dry descaling without using a liquid is good for this purpose, and concretely, dry blasting, such as shot blasting, grit blasting, brushing roll, and vacuum arc discharge method, is good. However, in the case of high-pressure water descaling, if water remains on the steel plate after descaling, the generation of new scale is promoted and the alloying reaction during powder injection is hindered. It is necessary to drain enough water with gas.

Regarding the surface roughness of the steel sheet formed at the time of descaling, the rougher the surface roughness, the larger the surface area and the more easily the alloying reaction occurs. In order to investigate the influence of the surface roughness of the steel sheet on the plating adhesion, Zn powder or Al powder having a grain size of 150 mesh or more is used at 30 ° C to 200 ° C higher than the melting point of the metal.
An experiment was conducted in which the steel was heated to a high temperature and the roughness was adjusted.

FIG. 2 shows an example of the result, which shows the experimental result when Zn powder is injected onto a steel plate whose melting point is 100 ° C. higher than the melting point. It was found that a score of 1 (score according to a ball impact test) was obtained, and a score of 2 was obtained even at 0.3 to 0.4 μm, and sufficient plating adhesion with no practical problems was obtained.

In the BI score, 1 indicates that the plating adhesion is the best, and the larger the value, the worse the plating adhesion is. As a corrosion-resistant hot rolled steel sheet for processing applications,
Most preferred is a BI score of 1.

To prevent the generation of new scale after descaling, it is necessary to spray the powder after descaling. It is more desirable to maintain a space between the descaling and the powder injection in an inert gas atmosphere such as argon or nitrogen, a mixed atmosphere of an inert gas and hydrogen, or a non-oxidizing or reducing atmosphere such as a hydrogen atmosphere.

In this case, it goes without saying that descaling or powder injection may be carried out in a non-oxidizing or reducing atmosphere.

Regarding the particle size of the metal powder to be sprayed, if the powder is too large, the heat conduction will be poor and it will be difficult to melt. In order to investigate the influence of the particle size of the metal powder on the plating adhesion, Zn powder or Al powder is heated to a temperature 30 ° C. to 200 ° C. higher than the melting point of the metal, and the surface roughness is 0.5 μm or more in Ra value. An experiment was conducted to inject the steel sheet that had been adjusted.

FIG. 1 shows an example of the result, which shows the experimental result when the Zn powder is sprayed on a steel plate whose melting point is 100 ° C. higher than the melting point. It was proved that when it was properly melted, a BI score of 1 was obtained and the plating adhesion was good, and that a BI score of 2 was obtained even when the mesh size was 50 or more and less than 150 mesh, and the adhesion was not a problem in practical use. The present invention has achieved the object by utilizing the above respective findings.

[0034]

EXAMPLES The present inventors carried out the present invention by installing a dry descaling device, a metal powder injection device for plating, and an atmosphere gas injection device between a hot-rolled steel sheet rewinding machine and a skin pass rolling machine. .

The chemical composition of the steel under test at that time is shown in Table 1 in% by weight.
Table 2 shows the hot rolling conditions, descaling conditions, spraying distance of plating metal, and atmospheric conditions. Aluminum content and particle size of plating metal, spraying pressure, spraying angle, spraying time, spraying thickness and the time Table 3 shows the steel plate temperature and the like, skin pass rolling conditions, and plating adhesion.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

As is clear from Tables 2 and 3, steel plate Nos. Satisfying all the requirements of claim 4 are listed. 1 to 7 showed good plating adhesion showing a BI rating of 1, and steel sheets having an r (average) value of 1 or more were obtained. Further, a steel plate No. that satisfies all the requirements of claim 1 8 to 12 have a BI score of 2 and an r (average) value of 1
As described above, a hot-rolled steel sheet with high corrosion resistance and excellent r (average) value was obtained.

On the other hand, steel sheet No. in which S is out of the lower limit of the present invention. 13. Steel plate No. 13 whose cooling rate during solidification is out of the lower limit of the present invention. 14, Steel plate No. 1 whose time from solidification to the start of finish rolling deviated from the upper limit. 15, finish rolling finish temperature is A
steel sheet No. which got off to a r ₃ points In each of the 16 comparative examples, r (average)
The value was as low as 0.90 or less. In addition, the steel sheet No. with the alloy powder component removed Steel plate No.
In each of Comparative Examples 19 and 20, the plating adhesion was poor at 3 to 4 and the required corrosion resistance was not obtained.

[0043]

According to the present invention, the T
It has a good r (average) value without the use of alloys such as i and Nb and without oil lubrication rolling, and the adhesion of the zinc-aluminum alloy plating layer with a small-scale facility. Since it can be imparted well with good productivity and economically, the industrial effect brought to the art is extremely large.

[Brief description of drawings]

FIG. 1 shows the relationship between the surface roughness Ra value of the steel sheet before spraying the plating metal powder and the plating adhesion shown by the BI score.
It is the chart shown by the powder particle size of a level.

FIG. 2 is a chart showing the relationship between the particle size of the plated metal powder and the plating adhesion shown by BI score, with two levels of surface roughness Ra values.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 12, 1993

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Method for producing hot-rolled steel sheet with excellent corrosion resistance and r average value

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Wakita 1 Nishinosu, Oita City, Oita Prefecture Shin-Nippon Steel Co., Ltd. Oita Works (72) Inventor Kaoru Kawasaki 20-1 Shintomi, Futtsu-shi New Nippon Steel Co., Ltd. Company Technology Development Division

Claims (6)

[Claims] 1. A molten steel containing Mn: 0.10 to 0.60%, S: 0.001 to 0.012% by weight, other Fe and inevitable components, is continuously cast during the process. Cooling from 1400 ° C to 1200 ° C is performed at 5.0 ° C / min or more to form a slab, and finish rolling of the slab is started within 60 minutes from the start of casting, and Ar ₃
After finishing at a point or more, the surface of the steel sheet is dry-descaled during rewinding and rolling of the hot-rolled steel sheet that has been wound up, and then weight% is applied to the surface of the steel sheet in a temperature range of 200 ° C to 300 ° C. Is used to form a plating layer in a required range on the surface of the steel sheet by injecting a zinc-aluminum alloy powder containing 15% or more and 30% or less of aluminum.
A method for producing a corrosion-resistant hot-rolled steel sheet having excellent (average) value. 2. The non-oxidizing atmosphere of the steel sheet after the dry descaling until the zinc-aluminum alloy powder is sprayed onto the surface of the steel sheet in a required range. The method for producing a corrosion-resistant hot-rolled steel sheet having excellent r (average) value described in 1. 3. The method according to claim 1, wherein after the dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed onto a required area of the steel sheet surface is a reducing atmosphere. A method for producing a corrosion-resistant hot-rolled steel sheet excellent in the described r (average) value. 4. A molten steel containing Mn: 0.10 to 0.60%, S: 0.001 to 0.012% by weight, and Fe and other unavoidable components is continuously cast during the process. Cooling from 1400 ° C to 1200 ° C is performed at 5.0 ° C / min or more to form a slab, and finish rolling of the slab is started within 60 minutes from the start of casting, and Ar ₃
After finishing at the point or more, the hot rolled rolled steel sheet is wound back, and the surface of the steel sheet is dry-descaled in the rewinding to make the surface roughness Ra value of 3 μm or more, and then 200 ° C. or more 3.
Zinc-aluminum alloy powder having a grain size of 120 mesh or more and containing 15% or more and 30% or less by weight of aluminum is sprayed at a pressure of 0.05 MPa or more on the surface of the steel plate in a temperature range of 00 ° C or less. Forming a plating layer in a required range on the surface of the steel sheet (average)
Of excellent corrosion resistance hot rolled steel sheet. 5. The non-oxidizing atmosphere of the steel sheet after the dry descaling until the zinc-aluminum alloy powder is sprayed to a required range on the surface of the steel sheet. The method for producing a corrosion-resistant hot-rolled steel sheet having excellent r (average) value described in 1. 6. The method according to claim 4, wherein after the dry descaling, the conveying atmosphere of the steel sheet until the zinc-aluminum alloy powder is sprayed on the surface of the steel sheet in a required range is reduced. A method for producing a corrosion-resistant hot-rolled steel sheet excellent in the described r (average) value.