Composition for preventing steel from being oxidized and method for preventing steel from being oxidized

Abstract

The anti-oxidation composition for steel materials of the present invention is characterized by containing silicon carbide and olivine as anti-oxidation components. This composition does not contain any hazardous or harmful substances, exhibits high anti-oxidation properties at high temperatures, and contributes to improved yield and hot workability.

Description

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] Hot rolling of poorly workable steels such as alloy steel requires rolling at temperatures above 1200°C. However, the higher the temperature, the more severe the oxidation of the steel, leading to a reduction in yield. Therefore, anti-oxidation compositions have been developed to prevent this problem.

[0003] For example, there is a composition for preventing oxidation of steel materials comprising 2 to 15 parts by mass of glass powder and 20 to 60 parts by mass of a refractory binder 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 containing 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 a composition for preventing oxidation and decarburization containing a flux component, silicon carbide, chromium oxide, and a refractory filler (Patent Document 4).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 58-133320,

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2001-49334,

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-14177,

[0009] Patent Document 4: Japanese Patent Application Laid-Open No. 5-86415. Summary of the Invention

[0010] Problems to be solved by the invention

[0011] The compositions for preventing oxidation of steel materials that have been developed so far still have problems to be solved, and there is a problem that it is difficult to say that sufficient effects can be obtained.

[0012] For example, the anti-oxidation coating disclosed in Patent Document 2 has problems with low performance and high cost due to the high price of magnesium oxide, as the magnesium oxide reacts with water immediately after preparation, causing the coating to become thicker. This not only reduces workability but also makes it difficult to prepare and store large quantities of the coating. Furthermore, the coating may clog piping, making spraying impossible. Furthermore, the coating also suffers from low performance and the high price of magnesium oxide, which creates cost issues.

[0013] Furthermore, the anti-oxidation coatings or compositions disclosed in Patent Documents 1, 3, and 4 all contain glass components. This glass component reacts with steel at temperatures above 1200°C, forming fayalite (Fe2SiO4), which corrodes the steel. Consequently, even when oxidation is prevented, the yield of the steel is poor. Furthermore, Patent Document 3 contains aluminum powder, a hazardous substance, raising concerns about its hazardous nature.

[0014] The present inventors conducted intensive research and found that an antioxidant composition containing silicon carbide and olivine does not contain any hazardous or harmful substances, has high antioxidant properties at high temperatures, and contributes to improved yield and hot workability, thereby completing the present invention.

[0015] Means of solving problems

[0016] The present invention provides a composition for preventing steel from being anti-oxidized, characterized by containing silicon carbide and olivine.

[0017] The present invention is also characterized by containing 20 to 70% by mass of silicon carbide and 20 to 70% by mass of olivine.

[0018] Furthermore, 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.

[0019] Furthermore, the present invention is characterized by further containing either or both of a fine particle filler and a binder.

[0020] The present invention is also a method for preventing steel from being subjected to oxidation, characterized in that an oxidation preventing composition containing silicon carbide and olivine is applied to the steel, followed by drying and calcining.

[0021] Effects of the Invention

[0022] 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.

[0023] The antioxidant composition of the present invention, containing silicon carbide and olivine, can be applied to the periphery of the steel material before hot rolling to suppress grain boundary oxidation of the steel material during hot rolling. Since grain boundary oxidation must be removed from the steel material, suppressing grain boundary oxidation can also improve the yield of the steel material during hot rolling.

[0024] The antioxidant composition of the present invention contains silicon carbide and olivine to suppress grain boundary oxidation, thereby enabling treatment at high temperatures that would be impossible without coating, and also contributing to improved workability of steel materials with poor hot workability.

[0025] The antioxidant composition of the present invention does not contain any highly hazardous substances and can therefore be made into a highly safe antioxidant composition. Furthermore, it also has excellent storage stability.

[0026] The method for preventing steel from being anti-oxidized according to the present invention has high anti-oxidation properties at high temperatures, and exhibits excellent effects of contributing to improved yield and hot workability. DETAILED DESCRIPTION

[0027] The anti-oxidation composition for steel 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.

[0028] 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 silicon carbide and olivine.

[0029] Furthermore, the aqueous medium may contain a fine particle filler, an inorganic binder, a sintering aid, and the like as necessary.

[0030] In the present invention, olivine ((Fe,Mg)2SiO4) is a continuous solid solution of fayalite (Fe2SiO4) and forsterite (Mg2SiO4), and any olivine can be used regardless of the content of the fayalite and forsterite therein.

[0031] In the present invention, preferred olivine includes, for example, olivine containing 1 to 15% of Fe in the form of Fe 2 O 3 and 35 to 55% of Mg in the form of MgO.

[0032] In the present invention, 20 to 70 mass %, preferably 25 to 60 mass %, particularly preferably 30 to 50 mass % of silicon carbide is blended.

[0033] 20 to 70% by mass, preferably 25 to 70% by mass, particularly preferably 35 to 60% by mass of olivine is blended.

[0034] 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.

[0035] In the present invention, silicon carbide may have a median diameter D50 of 0.2 to 30 μm, preferably 0.5 to 10 μm, and particularly preferably 0.8 to 5 μm; and olivine may have a median diameter D50 of 5 to 100 μm, preferably 5 to 80 μm, and particularly preferably 5 to 60 μm.

[0036] In the present invention, the basis of the effects of using silicon carbide and olivine is not yet clear, but it is believed that the antioxidant effect is exhibited due to the synergistic effect of silicon carbide and olivine.

[0037] Specifically, conventional anti-oxidation coatings containing silica components in their aggregates form fayalite at high temperatures in the form of iron atoms dissolved in the gaps between silica skeletons, thereby corroding steel materials.

[0038] On the other hand, in the antioxidant composition of the present invention, since olivine forms a structure in which iron or magnesium fills the gaps within the silica skeleton, no reaction with steel at 1200°C, as observed between silica and iron, is observed. Furthermore, it is believed that the small amount of fayalite structured sites with a melting point of approximately 1200°C contained in olivine melts slightly and sinters between aggregates, contributing to the formation of a dense film.

[0039] Although similar to magnesium silicate compounds, this phenomenon does not occur with forsterite, which contains no iron atoms, making it particularly suitable for film densification. Silicon carbide oxidatively decomposes at high temperatures, generating CO2, which fills the gaps in the coating and prevents oxygen in the oxygen atmosphere from reaching the steel surface. These effects are believed to synergistically contribute to the antioxidant effect of the present invention.

[0040] 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 the steel material during coating, and can be easily dried.

[0041] Examples of such an aqueous medium include water, and aqueous media obtained by mixing water with a low-boiling-point solvent such as methanol, ethanol, and isopropyl alcohol, or a high-boiling-point solvent such as ethylene glycol, diethylene glycol, polyethylene glycol, and glycerol.

[0042] The antioxidant composition of the present invention may further contain a fine-particle filler. The fine-particle filler may be an inorganic oxide pigment, and examples of the inorganic oxide pigment include iron oxide, titanium oxide, and zinc oxide, among which iron oxide is preferred.

[0043] 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 fine particle filler. Examples of the fine particle 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.

[0044] 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.

[0045] Examples of the inorganic binder include colloidal silica, alumina sol, and zirconia sol, and examples of the water-soluble polymer include carboxymethyl cellulose and xanthan gum. As described above, depending on the temperature, silica reacts with steel to form fayalite, which corrodes the steel. Therefore, undesirable behavior may be observed depending on the temperature. However, in the present invention, colloidal silica can be used as the inorganic binder.

[0046] In the present invention, the content of the binder is not particularly limited. However, the content of the binder 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.

[0047] 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 an amount generally used in the antioxidant composition for steel materials.

[0048] For example, boric acid and its salts may be contained in an amount of 1 to 10% by mass, preferably 2 to 5% by mass, and sodium carbonate may be contained in an amount of 2 to 20% by mass, preferably 5 to 10% by mass.

[0049] The steel material antioxidant composition 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.

[0050] The antioxidant composition of the present invention thus obtained can be applied to a target steel material for oxidation protection. Examples of steel materials include carbon steel, nickel steel, manganese steel, and stainless steel. It is particularly effective against nickel steel and manganese steel. Examples of nickel steel include 9% Ni steel (JIS: G3127) and 36% Ni steel (ALLOY36, ASTM: K93600). Alloy36 is particularly preferred for oxidation protection. Examples of manganese steel include 13% Mn steel (JIS: G6131).

[0051] 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.

[0052] There is no particular limitation on the coating method for steel. For example, the coating method may be such that the composition of the present invention reaches 100 to 1000 g / m 2 coating is carried out in a manner of

[0053] After coating, the steel is dried and calcined. Drying can be done at room temperature or heated for about 60 minutes. Calcining before hot rolling is done at 800°C to 1300°C for 1 to 4 hours.

[0054] The present invention is further described below with reference to examples. However, the present invention may be embodied in various other forms without departing from its spirit or essential features. Therefore, the above-described embodiments are merely illustrative in all respects, and the scope of the present invention is defined by the claims and is not limited in any way by the specification. Furthermore, all variations and modifications within the scope of the claims are intended to be within the scope of the present invention.

[0055] Examples 1 to 17

[0056] 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 at room temperature for 30 minutes to prepare antioxidant compositions of Examples 1 to 17. The obtained antioxidant compositions were heated to a concentration of 500 g / m 2 The steel materials listed in Table 1 were coated with the coating and dried at room temperature for 1 hour. Two types of olivine with different particle sizes were used. The median diameter D50 of the olivine designated D1 in Table 1 was 52 μm, while the median diameter D50 of the olivine designated D2 was 27.1 μm. Furthermore, the median diameter D50 of silicon carbide was 1.6 μm.

[0057] Next, the steel material coated with the antioxidant composition was calcined at the temperature listed in Table 1 for 200 minutes and then allowed to cool at room temperature.

[0058] Comparative Examples 1 to 16

[0059] 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. These compositions were then applied to steel materials, sintered, and cooled.

[0060] Evaluation Method

[0061] The steel materials sintered and cooled in Examples and Comparative Examples were cut and ground, and the ground surfaces were evaluated by measuring internal oxidation and grain boundary oxidation using a microscope (VHX-7000, manufactured by KEYENCE Corporation).

[0062] Oxide layer thickness determination criteria

[0063] ◎: Oxide layer thickness less than 100μm,

[0064] ○: Oxide layer thickness is 100 μm or more and less than 150 μm,

[0065] △: Oxide layer thickness is 150 μm or more and less than 400 μm,

[0066] ×: The oxide layer thickness is 400 μm or more and less than 1000 μm,

[0067] XX: The oxide layer thickness is 1000 μm or more.

[0068] Anti-oxidation rate determination standard

[0069] ◎: Anti-oxidation rate is more than 85%,

[0070] ○: Anti-oxidation rate is 70% or more and less than 85%,

[0071] △: Anti-oxidation rate is 50% or more and less than 70%,

[0072] ×: Anti-oxidation rate is 0% or more and less than 50%,

[0073] XX: The anti-oxidation rate is less than 0% (the anti-oxidation rate is a negative value, which promotes oxidation).

[0074] The anti-oxidation rate (%) was calculated as follows.

[0075] (1-(thickness of oxide layer when coated / thickness of oxide layer when not coated))×100.

[0076] In the present invention, the pot life (h) is the period from preparation of the antioxidant composition to curing of the antioxidant composition and its application to the steel material is impossible. Whether the coating can be applied is determined by whether the coating maintains fluidity.

[0077] Applicable time determination criteria

[0078] ◎: Can be applied even after 1 week at 25°C after preparation.

[0079] ○: Coating is no longer possible after 3 days or more and less than 1 week at 25°C after preparation.

[0080] △: Coating is no longer possible after 2 hours or more and less than 3 days at 25°C after preparation.

[0081] ×: Coating was no longer possible at 25° C. within less than 2 hours after preparation.

[0082] [Table 1]

[0083]

[0084] *: As silica, crystalline silica having a median diameter D50 of 7.3 μm was used.

[0085] [Table 2]

[0086]

[0087] In the table, the oxide layer thickness is the total thickness of internal oxidation and grain boundary oxidation.

Claims

1. A coating for anti-oxidation of steel, characterized in that: An aqueous medium contains 20-70 mass % of silicon carbide having a median diameter D50 of 0.2-30 μm and 20-70 mass % of olivine having a median diameter D50 of 5-100 μm, and further contains one or both of a fine-particle filler and a binder, and does not contain magnesium oxide.

2. A method for preventing steel from being oxidized, characterized in that: The anti-oxidation coating according to claim 1 is applied to a steel material, dried, and then calcined.

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