JP2002060836A - Method for producing steel material having excellent pickling property and formed member for reforming scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a steel material having excellent pickling properties. SOLUTION: A formed member for reforming scale composed of powder of one or more kinds of carbonates, hydroxides and oxides of alkaline earth- metals and binder is pressed on the surface of the moving steel material, and after applying the worn powder of the above reforming agent, the powder is cooled. The average grain diameter of the above powder is preferably 0.02-10 μm and the binder is preferably one or more kinds of bentnite, kaoliniate, water glass, gypsum and cement. Further, it is preferably that the content of the powder is 60-95.5 mass % and the content of the binder is <=40 mass % in the formed member, and the coating quantity of the formed member for reforming the scale is preferably >=0.02 g/m2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel material having excellent pickling properties, and more particularly, to a scale in which a steel material heated to a high temperature has good peelability and acid solubility. The present invention relates to a method for producing a modified steel material.

[0002]

2. Description of the Related Art In the hot working process of steel materials, that is, steel strips, steel pipes, section steels, bar steels, and wire rods, the surface of the steel material is scaled.
Occurs. When the scale is generated, the yield of the steel material is reduced, and the removal of the scale requires cost and man-hours such as shot blasting and pickling.

[0003] Steel materials plastically processed at high temperatures, for example, carbon steel
An oxide scale is formed on the surface of stainless steel or stainless steel.
In the case of carbon steel, FeO, F
e_TwoO _Three , Fe_ThreeO_Four An oxide scale consisting of three layers is formed.
It is. In the cooling process, FeO becomes αFe and Fe_ThreeO_Four Eutectoid transformation
At normal temperature, the scale is Fe_ThreeO_Four And the main one
You. In a temperature range of 560 ° C. or more, FeO: Fe_ThreeO_Four : F
e_TwoO_Three Is a mixture of approximately 95: 4: 1 mixed
Kale, but when the steel is cooled
In the temperature range, FeO is αFe and Fe_ThreeO_Four Eutectoid transformation
You.

Since FeO has good solubility in acids, descaling by pickling is easy. On the other hand, Fe ₃ O ₄ does not have good solubility in acid, and therefore does not have good descaling properties by pickling, and requires a great deal of cost and man-hour for descaling.
The steel material cooled by the ordinary method in this manner has a scale (Fe ₃ O) having much less acid solubility on the surface than FeO.
₄ and Fe ₂ O ₃ ).

[0005] In order to improve the descaling property, an attempt is made to suppress the eutectoid transformation of FeO in the cooling process and to improve the pickling property by modifying the scale structure at room temperature to a scale mainly composed of FeO. Have been variously studied.

For example, Japanese Patent Application Laid-Open No. 53-37539 discloses that after the completion of hot rolling, at the stage where the steel strip temperature before winding is 550 ° C. or higher, an oxide of an alkaline earth metal, A carbonate or hydroxide is applied, or cooling water mixed with 0.5% or more of these is sprayed to adhere the alkaline earth metal oxide, carbonate or hydroxide to the steel strip surface. A method for producing a hot-rolled steel strip having a good pickling property by winding is disclosed.

Japanese Patent Application Laid-Open No. 53-100130 discloses that a compound such as an alkali metal or an alkaline earth metal is supplied to a surface of a steel sheet in a state of being suspended in a rolling oil in a hot finish rolling process of the steel sheet. Thus, there is disclosed a method for producing a steel sheet having excellent descalability, characterized in that these are adhered to the surface of the steel sheet. In the above method, the suspension is supplied to the interface between the hot-rolling roll and the steel sheet to ensure adhesion to the steel sheet surface.

Further, JP-A-54-116308 discloses that a mixture of one or more of Ca compounds and Mg compounds and one or more of polyphosphoric acid and borax is coated on the slab surface. Then, an antioxidant is applied thereon, and then heated to a predetermined temperature and hot-rolled, thereby
A method for producing a steel material having excellent pickling properties for preventing CaO and MgO from forming a solid solution in eO and preventing transformation of FeO is described.

[0009]

However, according to the research results of the present inventors, none of the scale reforming techniques disclosed so far can provide a sufficient effect. A scale modifier consisting of carbonates, hydroxides, oxides and the like of alkaline earth metals is added to the oxide scale generated on the surface of the steel material, or a dispersion / adhesion improver such as a polymer polymer alone. In addition, even when mixed and applied in water or rolling oil, it does not adhere to the surface of the steel material in a high temperature state, and even if it adheres, the effect of improving the pickling property by the scale modification cannot be sufficiently obtained.

That is, according to the method disclosed in Japanese Patent Application Laid-Open No. 53-37539 or Japanese Patent Application Laid-Open No. 53-100130, the scale modifier hardly adheres to the surface of a high-temperature steel material. It was difficult to keep the FeO in the scale generated on the high-temperature steel material uniformly and evenly at room temperature even at room temperature.

If the steel surface cannot be uniformly scale-modified and is partially transformed into Fe ₃ O ₄ with poor pickling properties, the processing speed in the pickling process is limited by that part. In addition, the pickling time could not be reduced, and it was difficult to improve the pickling properties.

During hot rolling of a steel material, a descaling process using high-pressure water or the like is usually performed before and after the hot rolling to prevent flaws due to scale biting or the like. In addition, scaling is performed by hot rolling.
Since the scale cracks and separates, even if the scale is modified in the heating process before hot rolling, the scale is removed by hot rolling. Also, the secondary scale generated after that
Are not modified in this way. For these reasons, the method disclosed in Japanese Patent Application Laid-Open No. 54-116308 failed to improve the pickling property in a processing step in which a steel material was heated and processed a plurality of times.

As described above, in today's demand for strict product surface quality, partial scale residue, which was conventionally allowed, is not allowed, and the conventional manufacturing method results in pickling. Time savings have not been realized.

An object of the present invention is to provide a method for producing a steel material using a molded product for scale modification, which has an oxide scale having good peelability and excellent acid solubility, which is uniformly formed on the surface. It is in.

[0015]

Means for Solving the Problems The inventors of the present invention uniformly and uniformly reform the oxide scale generated on the surface of a high-temperature steel material, suppress the eutectoid transformation in the cooling process, and peel off. Oxidation scale with good acidity and excellent acid solubility, that is, excellent pickling property
The following findings were obtained as a result of various studies on a method of obtaining a steel material having a steel plate.

A. One or more powders of alkaline earth metal carbonates, hydroxides, and oxides are formed using a binder to form a solid (hereinafter, referred to as a "formed product for scale modification"). ), By sliding it on the surface of a high-temperature steel material, the formed object is worn. The resulting wear powder (peeling powder) uniformly and reliably adheres to the steel material surface. By performing the above treatment at a stage where the temperature of the steel material is 580 ° C. or more, the scale on the surface of the steel material after cooling is uniformly reformed, and the pickling efficiency when pickling is significantly improved. In addition, for the sliding of the scale-modified object, it is sufficient to press the molded object against the surface of the steel material during continuous running.

B. By setting the particle size and content of the powder to be contained in the scale-modified product and the type and content of the binder in an appropriate range, the molded product itself can be broken when pressed against a high-temperature steel material. , Deformation, or shape loss can be prevented.

The present invention has been completed on the basis of these findings, and the gist of the invention is described in the following (1) to (5), a method for producing a steel excellent in pickling properties, and in (6). Of the shaped object for scale modification.

(1) One or more powders selected from the group consisting of alkaline earth metal carbonates, alkaline earth metal hydroxides and alkaline earth metal oxides, and a binder. A method for producing a steel product having excellent pickling properties, comprising pressing a shaped object to a surface of a moving steel product at 580 ° C. or higher.

(2) The powder has an average particle size of 0.02 to 1
The method for producing a steel material excellent in pickling properties according to the above (1), which is 0 μm. (3) The binder is one or two of the group consisting of bentonite, kaolinite, water glass, gypsum, and cement.
(1) or (2) above, which is at least species.
3. The method for producing a steel material having excellent pickling properties according to item 1.

(4) The above (1) to (3), wherein the content of the powder in the shaped article is 60 to 95.5% by mass and the content of the binder is 40% by mass or less. The method for producing a steel excellent in pickling properties according to any one of the above.

(5) The pickling property as described in any of (1) to (4) above, wherein the amount of the wear powder applied to the surface of the steel material is 0.02 g / m ² or more. Method of manufacturing steel.

(6) One or more powders selected from the group consisting of alkaline earth metal carbonates, alkaline earth metal hydroxides and alkaline earth metal oxides, and a binder. A shaped object for scale reform.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION A scale-modified molded article according to the present invention comprises one of carbonates, hydroxides and oxides of alkaline earth metals.
The seed or two or more kinds of powders (hereinafter simply referred to as “alkaline earth powder”) are made into a solid using a binder.

Examples of the carbonate include CaCO ₃ , MgC
O _{3 and the} like are preferable. As the hydroxide, Ca (O
H) ₂ , Mg (OH) _{2 and the} like are preferred. As the oxide, CaO, MgO and the like are preferable.

These alkaline earth powders preferably have an average particle size of 0.02 μm or more and 10 μm or less. If the average particle size of the alkaline earth powder is less than 0.02 μm, it is processed into a scale-modified product,
It is not preferable because it easily wears when pressed against the steel material surface, and it becomes difficult to control the amount of adhesion. Average particle size is 10μ
If it exceeds m, the toughness of the scale-modified molded article is reduced, and breakage or cracking is liable to occur. More preferably, it is 0.1 μm or more and 8 μm or less.

If the alkaline earth powder is contained in the molded product for scale modification, the scale modification effect is exhibited, but in order to obtain the scale modification effect effective for improving pickling properties, , Mass% (hereinafter,% means mass%) 1
It is preferable to contain 0% or more. More preferably 30
%, More preferably 60% or more.

On the other hand, when the content of the alkaline earth powder is 95.
If it exceeds 5%, the amount of the binder is reduced, the strength of the scale-modified object is reduced, and uniform coating may be difficult. To avoid this, the content of alkaline earth powder should be 9
It is preferable to set it to 5.5% or less.

The binder is preferably an inorganic binder in order to obtain the strength, hardness, abrasion rate, easiness of shaping, heat resistance and the like of the molded article. Particularly, bentonite, kaolinite, water glass, gypsum, cement and the like are suitable. Above all, bentonite which swells water is more preferable from the viewpoint of ease of molding the scale-modified object described below.

Bentonite is a clay mineral composed of very fine crystals and is a montmorillonite ((Cal _1.67 Mg _0.33 )).
Smectite-based hydrated layered silicate mainly composed of SiO ₁₀ (OH) ₁₀ ). Usually, it also contains quartz, α-cristobalite, feldspar, calcite, mica and the like.
Bentonite is inorganic, resistant to heat, and stable up to about 700 ° C., so that it can maintain its caking force even when it comes into contact with high-temperature steel.

Depending on the types of exchangeable cations, bentonite includes sodium bentonite (mainly Na ⁺ , also referred to as swollen soil) and calcium bentonite (Ca ²⁺ or Mg ^2+).
), But any of them may be used. Sodium bentonite remarkably swells and disperses in water to form a stable aqueous colloid, and calcium bentonite has a small swelling power but a high water absorption rate. Considering the workability when mixing the alkaline earth powder and the binder to form a predetermined shape, swelling bentonite which swells in water, such as sodium bentonite, is more preferable.

In addition, among the smectites, beidellite, nontronite, saponite, hectorite, soconite, stevensite, illite and the like can also be used.

Kaolinite (Al _x (Si ₂ O ₅ ) (OH) ₄ )
Is a clay mineral in which rock is crystallized by physical and chemical weathering. Usually, bentonite and kaolinite are in a powder form, and those having a particle size of about 200 mesh (about 74 μm) are preferable because they have few impurities, but it is not necessary to limit to this. In addition, the effects of the present invention remain unchanged regardless of whether ore produced naturally is dried and pulverized into fine powder or granules, or artificially synthesized.

Cement is an inorganic glue, and is a hydraulic cement represented by Portland cement, an air-hardened cement represented by Kines cement or magnesia cement, and other special cements.
There is no particular limitation as long as it is generally used.

[0035] The content of the binder in the scale-modified object is preferably 0.5% or more in order to secure the moldability and to secure the strength and toughness of the object. The upper limit of the content of the binder is not particularly limited, but if the content of the binder is too high, the obtained molded article becomes too hard and hardly wears, resulting in a scale modification effect. Therefore, the content of the binder is preferably set to 40% or less.

Other auxiliary binders include oils such as linseed oil and vegetable drying oils such as soybean oil, starches such as dextrin, sugars such as oxin sulfide, and organic resins such as synthetic resins. The binder may be contained if it is 10% or less. These binders may be used alone or in combination of two or more.

A method for producing a scale-modified product is a method of mixing and kneading an alkaline earth powder and a binder, and if necessary, an auxiliary binder or water, followed by molding and drying to finish. Alternatively, there is a method in which the kneaded material is subjected to high-pressure molding and finished as needed. However, the method is not limited to the above method, and a known method of forming a solid using a powder and a binder can be used.

The shape and size of the scale-modified object do not need to be particularly limited, and may be appropriately determined according to the shape and size of the target steel material. The molded object for scale reforming obtained as described above is slid on the surface of a steel material by a method such as pressing against a moving steel material, for example, a steel material running continuously, and is worn. The resulting wear powder (peeling powder) uniformly and reliably adheres to the steel material surface.

The surface temperature of the steel at the time of performing the above treatment is 5
80 ° C. or higher is preferred. If the temperature is lower than 580 ° C., the transformation to Fe ₃ O ₄ starts to progress and the alkaline earth metal hardly dissolves in the scale, so that a sufficient scale modifying effect cannot be obtained.

The effect of the present invention can be obtained if the amount of abrasion powder of the scale-modified object supplied to the steel surface is 0.02 g / m ² or more. If it is less than 0.02 g / m ² ,
Depending on the abrasion rate, it may be difficult to obtain the scale modification effect uniformly on the surface and in the thickness direction of the scale.

By the above treatment, FeO on the surface of the steel material
Principal scale - spreading an alkaline earth metal to Le, the scale is dissolved M _x Fe _y O _z: a (M alkaline earth metal). By performing the reforming in this way, it is possible to obtain a scale that remains FeO even at room temperature regardless of the subsequent cooling conditions.

In the composition of the scale, if the volume ratio of wustite (FeO) in which Ca and Mg as alkaline earth metals are dissolved is increased, the adhesion between the scale and the steel base iron is reduced. It is considered that the mechanical releasability is improved.

The method for applying the scale-modified object to the surface of the steel material is not particularly limited, and any method may be used. For example, one example of the case of coating at the time of rolling a steel bar will be described based on the embodiment of the present invention.

FIG. 1 is a layout view of a hot-hole type rolling machine for steel bars according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a heating furnace,
Reference numeral 2 denotes a steel bar material, reference numerals 3 and 4 denote rolls for grooved rolling, reference numeral 5 denotes a rolled steel bar, reference numerals 6 and 7 denote a shaped object for scale reforming, and reference numeral 8 denotes an annealing furnace.

After the bar material 1 is heated to a predetermined temperature in a heating furnace, it is rolled by grooved rolls 3 and 4, and the scale reforming objects 6 and 7 are pressed on the exit side. Due to the sliding of the scale reforming object on the bar steel surface accompanying the feeding of the rolled steel bar to the downstream side, the wear powder of the scale reforming object adheres to the bar steel surface. Thereafter, the steel bar is charged into an annealing furnace and cooled to room temperature.

The pressing force of the scale-modified object to the surface of the steel material is determined by the relative speed between the scale-modified object and the steel material, the amount of wear powder corresponding to the scale amount (thickness), and the like. It may be determined appropriately in consideration of the situation. The preferred surface pressure is 100 N / mm ² or more.

The same effect can be obtained with carbon steel, stainless steel, and other special steels as the type of steel material according to the present invention. With respect to the composition of the high-temperature scale, a particularly remarkable effect is obtained in the case of carbon steel.

Since the shaped article for scale modification of the present invention is a solid solidified with a binder, its handling is extremely easy. The effect according to the present invention can be obtained not only by hot strip rolling of bars and wires, but also by hot strip rolling, forging, and pipe making.

[0049]

EXAMPLES A molded article for scale modification according to the present invention was produced by the following procedure. Various alkaline earth powders are mixed with a suitable amount of bentonite as a binding agent or a sodium silicate No. 3 equivalent product specified in JIS-K1408 (all commercially available products), and further kneaded by adding water, and : 50m
m, width: 50 mm, and length: 300 mm were molded under high pressure to produce shaped articles for scale modification having various compositions.

Next, it is composed of SCM435 defined in JIS-G4105, having a diameter of 11.2 mm and a length of 5
A steel bar material of 00 mm was prepared. The steel bar material 2 is charged into a heating furnace 1 shown in FIG. 1 and heated to 1100 ° C., and hot-hole rolling is performed by the rolls 3 and 4 for forming a diameter.
At the stage where the temperature reaches various temperatures after the end of the rolling, the tip of the bar passes through the above-described scale reforming moldings 6 and 7 from the upper and lower surfaces and the left and right sides of the bar. At the same time, the shaped objects 6 and 7 are pressed against the surface of the steel bar, and abrasion powder of the shaped product for scale reforming generated by a sliding action between the steel bar and the downstream side is applied to the surface of the steel bar. And cooled.

FIG. 2 is a layout diagram for explaining the positional relationship between the scale-modified object and the steel bar. A total of two pairs of 300 mm long scale reforming objects are provided on the downstream side of the grooved rolls 4 with the length direction parallel to the pass line. A pair of scale modifying objects 6 located on the upper and lower surfaces of the bar 5 and a pair of scales located on the left and right of the bar 5.
Each of the molded objects 7 for reforming is pressed against a bar so as to sandwich the bar with a pressing force of 150 N / mm ² (a pressing device is not shown).

As a comparative example, a steel bar manufactured by changing the temperature of the treatment with the scale-modified object (test number 1)
5) In the case where water having calcium carbonate dispersed therein is sprayed on a steel bar immediately after hot hole rolling by a nozzle (Test No. 16),
Alternatively, when a bar of calcium carbonate suspended in high-viscosity refined mineral oil having a viscosity of 250 cSt / 40 ° C. is sprayed on a steel bar immediately after hot hole rolling with a nozzle (test number 1).
7) was also evaluated. The calcium carbonate content of the suspension water or oil used in Test No. 15 or 16 is
The maximum amount was set within a range where precipitation did not occur, and was set to 1% and 25% by mass%, respectively.

As a conventional example, a hot-rolled roll was rolled under conventional conditions without using a scale modifier to produce a slowly cooled steel bar (Test No. 18). The amount of the scale-modified object powder adhering to the surface of the obtained steel bar was determined from the abrasion loss and the application area of the scale-modified object before and after the treatment.
And the pickling property of the obtained steel bar was investigated by the following method.

Approximately 100 mm of each of the leading and trailing ends of the obtained steel bar was cut and removed as unsteady rolled portions to obtain test materials, which were prepared by using hydrochloric acid: 10%, ferrous chloride: 5%, and inhibitor: The bar was immersed in an acid solution at room temperature containing 0.1%, and the bar steel surface was observed at a magnification of 100 times to measure the time until the scale was completely dissolved and removed. A value obtained by dividing the pickling completion time of each of the steel bars by the pickling completion time required in the conventional example (Test No. 18) was used as an index for evaluating pickling properties. The smaller this value was, the better the pickling properties were determined. Table 1 shows the composition and evaluation results of the scale-modified object.

[0055]

[Table 1] As can be seen from Table 1, in Test Nos. 1 to 14, the pickling property evaluation index was 0.75 or less, and the pickling time was significantly reduced as compared with the conventional example (uncoated). Further, when the solubility of the scale in acid was observed, the solubility of the scale of these steel bars was good, and the scale on the surface of the steel material was uniformly dissolved, and there was no scale residue, and the surface was good. Among them,
In Test No. 3 in which the average particle diameter of the alkaline earth metal powder was small and a large amount of abrasion powder adhered, a further excellent effect was confirmed. Moreover, although the pickling property was improved as the content of the alkaline earth metal powder in the molded product for scale modification was higher, the content was 60% as shown in the results of Test Nos. 10 to 12. Even below, it was significantly improved over the conventional method. The amount of the scale-modified object applied to the bar is
Although it depends on the content of the binder, it was also confirmed that the effect was excellent when the content was 0.02 mg / m ² or more. When the surface temperature of the steel material against which the scale-forming object is pressed is less than 800 ° C, there is an effect of improving pickling properties, but the effect is slightly inferior to that when treated at 800 ° C or higher. Met.

In Test No. 15 in which the surface temperature of the steel material against which the molded product for scale modification was pressed was less than 580 ° C., the effect of improving the pickling property was not recognized so much. Test No. 16, in which the alkaline earth metal powder was dispersed in water without using a binder,
And in test number 17 suspended in high viscosity mineral oil,
The part that could not be scale-modified (Fe ₃ O ₄ There was a portion where the transformation had progressed), and the solubility of that portion in acid was poor, resulting in a scale residue. Therefore, the pickling properties were not so much improved as compared with the conventional example (no coating).

[0057]

As described above, according to the method for producing a steel excellent in pickling properties according to the present invention, the scale generated in the steel heated to a high temperature has good peelability and good acid solubility. The scale can be uniformly and uniformly modified, and as a result, the time for pickling can be significantly reduced. Further, the shaped article for scale modification of the present invention is easy to handle and has excellent uniformity of coating on the surface of steel material, and thus is extremely useful for realizing scale modification of steel material.

[Brief description of the drawings]

FIG. 1 is a layout diagram of a hot-hole type rolling machine for steel bars according to an embodiment of the present invention.

FIG. 2 is a layout diagram for explaining a positional relationship between a scale-modified object and a steel bar.

[Explanation of symbols]

1: heating furnace, 2: steel bar material, 3 and 4: rolls for grooved rolling, 5: steel bars, 6 and 7: shaped articles for scale modification,
8: annealing furnace.

Claims (6)

[Claims] 1. A binder comprising one or more powders selected from the group consisting of alkaline earth metal carbonates, alkaline earth metal hydroxides and alkaline earth metal oxides, and a binder. A method for producing a steel material having excellent pickling properties, comprising pressing a shaped object against a surface of a moving steel material at 580 ° C or higher. 2. The powder has an average particle size of 0.02 to 10
The method for producing a steel material having excellent pickling properties according to claim 1, wherein the thickness is μm. 3. The acid according to claim 1, wherein the binder is at least one member selected from the group consisting of bentonite, kaolinite, water glass, gypsum, and cement. A method for producing steel with excellent washability. 4. The powder content in the shaped object is 60
The method for producing a steel material having excellent pickling properties according to any one of claims 1 to 3, wherein the content of the binder is 40 mass% or less. 5. The amount of abrasion powder applied to the surface of the steel material is 0.
The amount is at least 02 g / m < ² >.
The method for producing a steel material excellent in pickling properties according to any one of the above. 6. A binder comprising one or more powders selected from the group consisting of alkaline earth metal carbonates, alkaline earth metal hydroxides and alkaline earth metal oxides, and a binder. Shaped object for scale modification.