Composition for preventing oxidation of steel material and method for preventing oxidation of steel material

Abstract

This composition for preventing oxidation of a steel material is characterized by containing silicon carbide and olivine as anti-oxidation components. Thus, the present invention does not contain a highly hazardous substance, has high oxidation resistance at high temperatures, and contributes to the improvement of yield and hot workability.

Description

This application is filed on October 16, 2020, application number 202080100311.9 (PCT / JP2020 / 039143), a divisional application of an invention patent application entitled “Composition for anti-oxidation of steel and method for anti-oxidation of steel”. Technical Field

[0001] The present invention relates to a composition for preventing oxidation of steel, and more particularly to a composition for preventing oxidation of steel when heat-treating steel (slab) for rolling and a method for preventing oxidation of steel. Background Art

[0002] In order to hot-roll poorly workable steels such as alloy steel, rolling must be performed at a high temperature of 1200°C or higher. However, the higher the temperature, the more severe the oxidation of the steel, resulting in a problem of reduced yield. Therefore, an anti-oxidation composition has been developed to prevent this problem.

[0003] For example, there is a composition for preventing oxidation of steel materials, in which 2 to 15 parts by mass of glass powder and 20 to 60 parts by mass of a refractory binder are added to 100 parts by mass of a refractory aggregate containing 30% by mass or more of magnesium oxide (Patent Document 1), an anti-oxidation coating for steel materials having magnesium oxide and ammonium silicate as main components (Patent Document 2), an anti-oxidation coating for steel materials containing alkali-free glass, aluminum powder, silicon carbide, and chromium oxide (Patent Document 3), and an anti-oxidation and decarburization composition containing a flux component, silicon carbide, chromium oxide, and a refractory filler (Patent Document 4).

[0004] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 58-133320, Patent Document 2: Japanese Patent Application Publication No. 2001-49334, Patent Document 3: Japanese Patent Application Publication No. 2016-14177, Patent document 4: Japanese Patent Application Laid-Open No. 5-86415. Summary of the invention

[0005] Problems to be Solved by the Invention The currently developed anti-oxidation compositions for steel materials still have problems to be solved, and there is a problem that it is difficult to say that a sufficient effect can be obtained.

[0006] For example, the anti-oxidation coating of Patent Document 2 has the following problems: the magnesium oxide reacts with water immediately after preparation, and the reaction product makes the coating thicker. Therefore, in addition to the reduced operability, it is difficult to prepare and store the coating in large quantities, and it is impossible to spray because the pipes may be clogged. In addition, there are the following problems: the performance is not very high, and the magnesium oxide is expensive, which is a cost issue.

[0007] In addition, the anti-oxidation coatings or compositions of Patent Documents 1, 3, and 4 all contain glass components, which react with steel at 1200°C or above to form fayalite (Fe2SiO4), thereby corroding the steel. Therefore, even if oxidation is prevented, there is a common problem that the yield of the steel is poor. In addition, Patent Document 3 contains aluminum powder, which is a dangerous substance, and has problems in terms of danger and harmfulness.

[0008] The present inventors conducted intensive research and found that an antioxidant composition containing silicon carbide and olivine does not contain any dangerous or harmful substances, has high antioxidant properties at high temperatures, and contributes to improved yield and hot workability, thereby completing the present invention.

[0009] Means of solving problems The present invention provides a composition for preventing oxidation of steel, characterized by containing silicon carbide and olivine.

[0010] The present invention is also characterized by containing 20 to 70% by mass of silicon carbide and 20 to 70% by mass of olivine.

[0011] In addition, the present invention is characterized in that the median diameter D50 of silicon carbide is 0.2 to 30 μm, and the median diameter D50 of olivine is 5 to 100 μm.

[0012] The present invention is also characterized by further containing either or both of a fine particle filler and a binder.

[0013] The present invention is also a method for preventing oxidation of steel, characterized in that the anti-oxidation composition containing silicon carbide and olivine is applied to the steel, followed by drying and calcining.

[0014] Effects of the Invention Since the antioxidant composition of the present invention contains silicon carbide and olivine, it can be attached to the periphery of the steel material before hot rolling, thereby suppressing oxidation of the steel material during hot rolling and improving the yield of the steel material during hot rolling.

[0015] Since the antioxidant composition of the present invention contains silicon carbide and olivine, it can be attached to the periphery of the steel material before hot rolling to inhibit the grain boundary oxidation of the steel material during hot rolling. Since the oxidized portion of the grain boundary must be removed from the steel material, the yield of the steel material during hot rolling can be improved by inhibiting the grain boundary oxidation.

[0016] The antioxidant composition of the present invention contains silicon carbide and olivine to suppress grain boundary oxidation, thereby enabling treatment at a high temperature that is impossible without coating, and can also contribute to improving the workability of steel materials with poor hot workability.

[0017] Since the antioxidant composition of the present invention does not contain any highly dangerous substances, it can be made into a highly safe antioxidant composition and also has excellent storage stability.

[0018] The method for preventing steel from being anti-oxidized according to the present invention has high anti-oxidation property at high temperature, and has excellent effects of contributing to improving yield and improving hot workability. DETAILED DESCRIPTION

[0019] The anti-oxidation composition for steel materials of the present invention is a composition containing silicon carbide and olivine. More specifically, it is a composition in which silicon carbide and olivine powders are dispersed in an aqueous medium. Silicon carbide and olivine are components that have an anti-oxidation effect on steel materials.

[0020] The concentration of the silicon carbide and olivine in the composition is 40 to 90% by mass, preferably 60 to 80% by mass, and particularly preferably 65 to 75% by mass, based on the total amount of the two.

[0021] Furthermore, the aqueous medium may contain a fine particle filler, an inorganic binder, a sintering aid, and the like as necessary.

[0022] In the present invention, olivine ((Fe,Mg)2SiO4) is a continuous solid solution of fayalite (Fe2SiO4) and forsterite (Mg2SiO4), and any olivine may be used regardless of the content of the fayalite and forsterite therein.

[0023] In the present invention, if a preferred olivine is listed, for example, olivine containing 1 to 15% of Fe in the form of Fe2O3 and 35 to 55% of Mg in the form of MgO can be listed.

[0024] In the present invention, 20 to 70% by mass, preferably 25 to 60% by mass, and particularly preferably 30 to 50% by mass of silicon carbide is blended.

[0025] 20 to 70% by mass, preferably 25 to 70% by mass, and particularly preferably 35 to 60% by mass of olivine is blended.

[0026] The ratio of silicon carbide to olivine is not particularly limited, but 0.4 to 2.3 parts by weight, more preferably 0.4 to 1.5 parts by weight, and particularly preferably 0.6 to 1.2 parts by weight of olivine is preferably blended per 1 part by weight of silicon carbide.

[0027] In the present invention, silicon carbide can be any silicon carbide having a median diameter D50 of 0.2 to 30 μm, preferably 0.5 to 10 μm, and particularly preferably 0.8 to 5 μm; olivine can be any olivine having a median diameter D50 of 5 to 100 μm, preferably 5 to 80 μm, and particularly preferably 5 to 60 μm.

[0028] In the present invention, although it is not clear at present what effect is produced by using silicon carbide and olivine, it is considered that the anti-oxidation effect is exhibited due to the synergistic effect of silicon carbide and olivine.

[0029] That is, conventional anti-oxidation coatings containing a silica component in the aggregate form fayalite in the form of iron atoms dissolved in the gaps of the silica skeleton at high temperatures, thereby corroding steel materials.

[0030] On the other hand, in the antioxidant composition of the present invention, since olivine forms a structure in which iron or magnesium is filled in the gaps of the silica skeleton, no reaction with steel at 1200° C. as observed between silica and iron is observed. It is also believed that the small amount of fayalite structure with a melting point of about 1200° C. contained in olivine melts slightly and sinters between aggregates, thereby contributing to the formation of a dense film.

[0031] Although they are the same magnesium silicate compounds, this phenomenon does not occur in forsterite that does not contain iron atoms, and olivine is specifically suitable for densification of the film. Silicon carbide oxidatively decomposes at high temperatures to produce CO2, which fills the gaps in the coating film and inhibits oxygen in the oxygen atmosphere from reaching the surface of the steel material. It is believed that these effects work synergistically to show the anti-oxidation effect of the present invention.

[0032] In the present invention, the aqueous medium is not particularly limited as long as it is a solvent that can stably hold silicon carbide and olivine in a dispersed state, can adhere to a steel material during coating, and can be easily dried.

[0033] Examples of such an aqueous medium include water, or an aqueous medium obtained by mixing water with a low boiling point solvent such as methanol, ethanol, and isopropanol, or a high boiling point solvent such as ethylene glycol, diethylene glycol, polyethylene glycol, and glycerol.

[0034] The antioxidant composition of the present invention may further contain a fine particle filler. The fine particle filler may be a fine particle filler such as an inorganic oxide pigment. Examples of the inorganic oxide pigment include iron oxide, titanium oxide, and zinc oxide, among which iron oxide is preferred.

[0035] The antioxidant composition may contain 0.1 to 20% by mass, preferably 1 to 15% by mass, and particularly preferably 5 to 15% by mass of a particulate filler. Examples of the particulate filler include those having a median diameter D50 of 0.1 to 3 μm, preferably 0.1 to 2 μm, and particularly preferably 0.1 to 1.5 μm.

[0036] The antioxidant composition of the present invention may further contain a binder. The binder may be any substance that has adhesive strength when dry, and examples thereof include inorganic binders, water-soluble polymers, silane coupling agents, and resin emulsions.

[0037] Examples of the inorganic binder include colloidal silica, alumina sol, zirconia sol, etc., and examples of the water-soluble polymer include carboxymethyl cellulose, xanthan gum, etc. As described above, depending on the temperature, silica reacts with steel to form fayalite, thereby corroding the steel, and therefore undesirable behavior is observed depending on the temperature, but in the present invention, colloidal silica can be used as the inorganic binder.

[0038] In the present invention, the content of the binder is not particularly limited, but is 0.05 to 10% by mass, preferably 0.1 to 5% by mass, for a water-soluble polymer, 0.01 to 10% by mass, preferably 0.1 to 5% by mass, for a silane coupling agent, and 0.1 to 20% by mass, preferably 1 to 10% by mass, for a resin emulsion, relative to the antioxidant composition.

[0039] The antioxidant composition of the present invention may further contain a sintering aid, and examples of the sintering aid include boric acid and its salts, sodium carbonate, etc. These may be contained in the antioxidant composition for steel materials in amounts generally used.

[0040] For example, in the case of boric acid and its salt, 1 to 10% by mass, preferably 2 to 5% by mass, may be contained, and in the case of sodium carbonate, 2 to 20% by mass, preferably 5 to 10% by mass, may be contained.

[0041] The anti-oxidation composition for steel materials of the present invention can be easily prepared by mixing silicon carbide, olivine, and, if necessary, the above-mentioned fine particle filler, binder, and sintering aid in an aqueous medium at room temperature.

[0042] The anti-oxidation composition of the present invention thus obtained can be used for anti-oxidation purposes of steel materials by coating the target steel materials. Examples of steel materials include carbon steel, nickel steel, manganese steel, stainless steel, etc. It is particularly effective for nickel steel and manganese steel. Examples of nickel steel include 9% Ni steel (JIS: G3127), 36% Ni steel (ALLOY36, ASTM: K93600), etc., among which ALLOY36 is preferably used for anti-oxidation purposes. In addition, examples of manganese steel include 13% Mn steel (JIS: G6131), etc.

[0043] The coating method is not particularly limited, and coating can be performed by a method commonly used in the art. Examples of such coating methods include brush coating, roller coating, and spray coating.

[0044] The coating method of the steel material is not particularly limited. For example, the coating method may be applied to the steel material so that the composition of the present invention reaches 100 to 1000 g / m 2 The coating is carried out in a manner of

[0045] Next, after coating, the steel material is dried and calcined. Drying can be carried out at room temperature to heated for about 60 minutes. The calcination before hot rolling is carried out at 800°C to 1300°C for 1 to 4 hours.

[0046] The present invention is further described in detail below by way of examples, but the present invention can be implemented in various other ways without departing from its spirit or main features. Therefore, the above-mentioned embodiments are merely simple examples in all aspects, and the scope of the present invention is as shown in the claims and is not subject to any limitation of the text of the specification. In addition, all modifications or changes belonging to the claims are within the scope of the present invention.

[0047] Examples 1 to 17 The components listed in Table 1 were added to 32 parts by weight of water and 8 parts by weight (in terms of solid content) of colloidal silica, and stirred and mixed at room temperature for 30 minutes to prepare antioxidant compositions of Examples 1 to 17. The antioxidant compositions obtained were heated to 500 g / m 2 The olivine was coated on the steel material listed in Table 1 and dried at room temperature for 1 hour. As olivine, two different particle sizes were used. The median diameter D50 of the olivine recorded as D1 in Table 1 was 52 μm, and the median diameter D50 of the olivine recorded as D2 was 27.1 μm. In addition, the median diameter D50 of silicon carbide was 1.6 μm.

[0048] Next, the steel material coated with the antioxidant composition was calcined at the temperature described in Table 1 for 200 minutes, and then left to cool at room temperature.

[0049] Comparative Examples 1 to 16 Antioxidant compositions of Comparative Examples 1 to 16 were prepared in the same manner as in the Examples using the components listed in Table 1, applied onto steel materials, and then calcined and cooled.

[0050] Evaluation Method The steel materials calcined and cooled in the examples and comparative examples were cut and ground, and the images were obtained using a microscope (VHX-7000, The polished surface was evaluated by measuring internal oxidation and grain boundary oxidation.

[0051] Oxide layer thickness determination criteria ◎: Oxide layer thickness is less than 100μm, ○: The oxide layer thickness is 100 μm or more and less than 150 μm, △: The oxide layer thickness is 150 μm or more and less than 400 μm. ×: The oxide layer thickness is 400 μm or more and less than 1000 μm, XX: The oxide layer thickness is 1000 μm or more.

[0052] Anti-oxidation rate determination standard ◎: Anti-oxidation rate is more than 85%, ○: Anti-oxidation rate is 70% or more and less than 85%, △: Anti-oxidation rate is 50% or more and less than 70%, ×: Anti-oxidation rate is 0% or more and less than 50%, XX: The anti-oxidation rate is lower than 0% (the anti-oxidation rate is a negative value, and oxidation is promoted).

[0053] The oxidation prevention rate (%) was calculated as follows. (1-(thickness of oxide layer when coated / thickness of oxide layer when not coated))×100.

[0054] In the present invention, the pot life (h) is the period from the preparation of the antioxidant composition to the time when the antioxidant composition solidifies and becomes unapplicable to the steel material, and whether the coating can be applied is determined by whether the coating maintains fluidity.

[0055] Applicable time judgment standard ◎: Can be applied even after 1 week at 25°C after preparation. ○: Coating is no longer possible after 3 days or more and less than 1 week at 25°C after preparation. △: Coating is no longer possible after 2 hours or more and less than 3 days at 25°C after preparation. ×: Coating was no longer possible at 25° C. within less than 2 hours after preparation.

[0056] [Table 1] *: As silica, crystalline silica having a median diameter D50 of 7.3 μm was used. [Table 2] In the table, the oxide layer thickness is the total thickness of internal oxidation and grain boundary oxidation.

Claims

1. A coating for steel materials, which is a coating for inhibiting grain boundary oxidation of steel materials during hot rolling, characterized in that: It contains 20 to 70% by mass of silicon carbide, 70 to 20% by mass of olivine, and does not contain magnesium oxide.

2. The coating for steel materials according to claim 1, characterized in that: It also contains either or both of a particulate filler material and a binder.

3. A method for inhibiting grain boundary oxidation of steel, characterized in that: The coating material for steel materials according to claim 1 or 2 is applied to a steel material, dried and calcined.

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