JPH0588289B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applied to the surface of steel materials, especially steel billet slabs, to prevent oxidation, to prevent the formation of scale in the high-temperature oxidizing atmosphere in a heating furnace, and to easily coat the surface of steel slabs before rolling. The present invention relates to a high-temperature antioxidant coating for steel materials that can be removed and reduces the difference in affinity between oxygen and various metals added to steel materials during hot rolling, as well as the diffusion rate of alloys and oxides. [Prior Art] As is well known, a steel billet slab is heated at a temperature of 1050 to 1200°C in a heating furnace or soaking furnace, and rolled into a product. If the billet slab is made of a steel material on the level of ordinary steel, there will be less scale generation and descaling will be relatively easy. However, if the billet slab is of high-grade steel quality, a large amount of oxidation scale will occur due to the time and temperature in the furnace, and descaling will be difficult, resulting in lower yields, which will reduce productivity, resource savings, and product finishing. This is a problem from this point of view. Conventionally, many high-temperature oxidation-inhibiting paints have been researched and developed in order to prevent oxidation and scaling of steel billet slabs under high temperatures. High-temperature anti-oxidation paints not only prevent oxidation and prevent the formation of scales, but also can be easily removed, and even if scales do occur, the scales can be easily removed together with the paint using high-pressure water before rolling, in other words, descaling is easy. is required. If scale and paint remain during rolling, scratches will occur on the surface of the product. Therefore, the present inventors developed a high-temperature antioxidant paint that satisfies these requirements, and filed applications as Japanese Patent Application Laid-open Nos. 60-251218 and 60-251219. However, when using the paints disclosed in these publications, water vapor condenses on the paint surface near the entrance of the continuous heating furnace due to the temperature difference between the steel material and the heated air, especially in the winter when the outside air temperature is low. It was found that this condensed water eluted a part of the coating film, causing scale formation, and the present inventor provided a coating solution to solve this problem in JP-A-61-64813. However, since the steel material is transferred on metal rolls when it is charged into the heating furnace, when this paint is applied to the steel material, some of the applied paint is physically transferred by the metal rolls. There was a problem in that it peeled off due to impact, etc., and scale formed on the peeled part in the heating furnace. The present inventor has provided a paint that solves this problem as Japanese Patent Publication No. 4-63105 (=Japanese Patent Application No. 63-52565). This paint is composed of the following components: a 20-50% by weight of at least one member from the group of silicon carbide, silicon nitride, stabilized zirconium oxide, mica as a ceramic base material b 25-50 The following three types of alumina are used as ceramic auxiliaries in weight percent: Alumina (1): alpha crystal particles are 1 to 10μ, heated at 1600℃
Flat fine grain alumina with a shrinkage rate of 5% or less when sintered for 3 hours at 1600℃, Alumina (2): Average particle size that has a shrinkage rate of 5% or more and 10% or less when sintered for 3 hours at 1600℃
Flat alumina of 100μ or less with a gelatinization rate of 100% and alumina (3): Na ₂ O content of 0.2 to 0.3% by weight
Ultrafine particle alumina with an average particle size of 0.1-1.5μ c 10-40% by weight of at least one member of the group of neutral aluminum phosphate, colloidal silica, alumina sol as a binder, d 5-10% by weight of Fe, Cu, Ni and at least one member of the group of Cr powder e 5-30% by weight of sodium carbonate as a ceramic sintering accelerator and f 2.5-15% by weight (solids content) polymerizable to form a water-resistant coating and/or copolymer aqueous emulsion or solution g 3-15% by weight of carbon fibers, alumina fibers, which act as aggregates and increase coating bond strength;
At least one mineral fiber from the group consisting of silicon carbide fibers and silicon nitride fibers (However, the total of components a) to g) is 100% by weight) When applying this paint to steel materials, approximately It has been found that coating workability is improved when 10-15% by weight (based on the total paint) of water is incorporated into the composition. [Problems to be Solved by the Invention] Various metals are added to steel materials, particularly high-grade steels, depending on the intended use. In particular, in the case of steel materials with Si added, eutectic phialite (2FeO−SiO ₂ ) of FeO and SiO ₂ is generated at 1170°C, and the phialite melts and penetrates along the γ grain boundaries in the steel material, creating a whisker-like shape. Scale occurs. For this reason, even if scale generation on the surface is reduced or prevented, scratches will occur on the surface of the product unless it is removed to the depth where it has penetrated. Conventional paints and the paint disclosed in Japanese Patent Publication No. 4-63105 mentioned above could not solve this problem. The present inventor has conducted intensive research and has completed a paint that can solve this problem without deteriorating the excellent properties of the paint described in the above-mentioned documents. [Means for Solving the Problems] That is, the present inventor has added 8.5 to 25% by weight (based on solid content) of oxidation as component h) to the paint disclosed in Japanese Patent Application No. 63-52565. The above problem was solved by incorporating at least one oxide from the group consisting of magnesium, chromium oxide and calcium oxide. The object of the present invention is therefore: a 19-43% by weight of at least one member from the group of silicon carbide, silicon nitride, stabilized zirconium oxide, mica as a ceramic base material b 23.5-43% by weight of a ceramic auxiliary agent The following three types of alumina are used as alumina (1): α crystal particles are 1 to 10 μ and heated to 1600℃.
Flat fine grain alumina with a shrinkage rate of 5% or less when sintered for 3 hours at 1600℃, Alumina (2): Average particle size that has a shrinkage rate of 5% or more and 10% or less when sintered for 3 hours at 1600℃
Flat alumina of 100μ or less with a gelatinization rate of 100% and alumina (3): Na ₂ O content of 0.2 to 0.3% by weight
Ultrafine particle alumina with an average particle size of 0.1 to 1.5μ c 9.5 to 33.5% by weight of at least one member of the group of neutral aluminum phosphate, colloidal silica, alumina sol as a binder, d 5 to 9% by weight of Fe, Cu, Ni and at least one of the group of Cr powders e 5-25% by weight of notalium carbonate as a ceramic sintering accelerator and f 2.5-13% by weight (solids content) polymerizable to form a water-resistant coating. and/or copolymer aqueous emulsion or solution g 3-13% by weight of carbon fibers, alumina fibers, which act as aggregates and increase coating bond strength;
At least one mineral fiber from the group consisting of silicon carbide fibers and silicon nitride fibers h 8.5 to 25% by weight of at least one from the group consisting of magnesium oxide, chromium oxide and calcium oxide
Composed of oxides of seeds, provided that the total of components a) to h) is 100
It is a high-temperature antioxidant paint for steel materials that is % by weight.
In addition, the proportions of components a) to g) are as specified in patent application No. 63-52565.
The difference from the proportions described in the specification is due to the selection of the most appropriate range from the influence of the addition of component h) and compatibility with the purpose of the present invention. The present inventors believe that component h) reacts with magnesium oxide, chromium oxide, and calcium oxide in the eutectic of phialite in the high-temperature antioxidant paint of the present invention to raise the melting point to 1250°C, and at a heating temperature of 1200°C. It has been found that melt penetration can be prevented. h) The magnesium, chromium, and calcium oxides used as components must be in the range of 8.5 to 25% by weight based on the solid content of the paint. If it is less than 8.5% by weight, the effect of raising the melting point of phialite is small, and if it is more than 25% by weight, no additional effect can be obtained, and furthermore, it adheres firmly to the steel surface and descaling properties are reduced. 8.5-25% by weight
No such inconvenience will occur if the amount is within the range of . Ceramic component a) as the base material should preferably have high heat resistance (for example, silicon carbide at 2200°C), and the amounts used are components a), b), c), d), e), and f).
and g) (hereinafter referred to as all components) totaling 19~
Must be in the range of 43% by weight. a) Ingredients are 19
If it is less than 43% by weight, the coating film will not be formed densely and the amount of oxidizing gas permeated will increase, making it impossible to obtain the desired antioxidant effect, and if it exceeds 43% by weight, the thermal conductivity will decrease and heating energy will be consumed. increases and energy loss increases. Alumina as a ceramic auxiliary agent [component b)]
are flat particles with a high gelatinization rate [alumina (1) and alumina (2)] and ultrafine particles with easy sinterability [alumina
(3)]. Alumina (1) has α-crystal particles of 1 to 10 μm in size, has a small sintering shrinkage rate of 5% or less (sintered at 1600° C. for 3 hours), and is a flat fine particle with excellent hiding power. Alumina (2) has a sintering shrinkage rate of 10% or less (1600℃
(3 hours), preferably 5% to 10%, stable, gelatinization rate of 100%, average particle size of 100μ or less, 20μ or more, preferably 30 to 60μ, flat particles with hiding power. be. Alumina (3) has a Na ₂ O content of 0.2-0.3% by weight
Medium soda grade and average particle size 0.1~
Alumina is easily sintered because it has ultrafine particles of 1.5μ. This alumina has low water content,
Advantageously, it is, for example, 0.2% by weight or less. Alumina as a ceramic auxiliary agent [component b)]
When the coating film thickness is 100 μm or less, if it is less than 23.5% by weight, a dense coating film with sufficient hiding power cannot be obtained, and if it is more than 43% by weight, the removability of the coating film becomes poor. Alumina (1), (2) and (3) are mutually (1.5~
It has been found that advantageous results are obtained when a weight ratio of 3):(0.5 to 2):(1 to 3) is used. At least one type [component c)] of the group consisting of neutral aluminum phosphate, colloidal silica, and alumina sol used as a binder stabilizes the bonding of the ceramic base material, which is component a), and also improves the adhesion to the steel material. It is used to enhance the properties of the ingredients, and the amount used should be in the range of 9.5 to 33.5% by weight of the total ingredients. This binder is
If it is less than 9.5% by weight, the mixed mixture will be hard and will not have adhesion to the steel surface, and if it is less than 33.5% by weight, the effect as a binder will not increase. Metal powder [component d)] consisting of at least one of the group of Fe, Cu, Ni, and Cr powders is placed in an oxidizing atmosphere in a heating furnace (generally O ₂ in exhaust gas: 1 to 2%).
A reducing atmosphere is maintained in order to avoid or minimize contact with the steel surface. If the metal powder content is less than 5% by weight, the surface of the steel material will become an oxidizing atmosphere, and if it exceeds 9% by weight, the metal powder will react with or weld to the steel material at high temperatures, changing the properties of the steel material surface, so-called product surface, and causing adverse effects. . Ceramic sintering accelerator [component e)] is 300~
It accelerates the sintering of the ceramic base material and binder at 800℃, and plays the role of hardening the paint mixture, increasing the adhesion strength to the steel surface, and making the paint film denser. 5% by weight is the lower limit to maintain a suitable sintering rate. If it is less than 5% by weight, the sintering condition will be poor (weak), the strength between the coatings in the mixed mixture will decrease, and the surface of the steel material will deteriorate due to an eroded area of the oxidizing atmosphere.
If it exceeds % by weight, the coating film will not be formed densely. f) The amount of ingredients used is 2.5 as solid content.
~13% by weight (based on the total amount of paint), especially 2.5
~10% by weight is preferred. If it is less than 2.5% by weight, it will not be effective, and if it exceeds 13% by weight,
Combustion of this component in a continuous furnace generates gases that can cause blistering and reduced peeling of the coating. g) The mineral fiber used as a component acts as an aggregate in the high-temperature antioxidant paint of the present invention, increases the bonding strength of the paint film, prevents the penetration of high-temperature oxidizing gases, and increases the strength against physical impact. do the work. These include carbon fiber, alumina fiber, silicon carbide fiber and silicon nitride fiber,
Particular preference is given to carbon fibers and alumina fibers. Advantageously, these mineral fibers have a length of less than 10 mm. If the length is longer than 10 mm, the fibers will protrude onto the surface of the paint film, impairing the leveling properties of the paint and causing unevenness in the formed paint film. Particularly preferred mineral fibers have a diameter of 10-20 μm and a length of 300-1000 μm.
It is advantageous that g) The mineral fiber used as a component is 3 to 13
It can be used in amounts other than 3% by weight, but if it is less than 3% by weight, it will have little effect as an aggregate, and if it exceeds 13% by weight, the leveling properties of the coating will deteriorate and the formed coating will become uneven. If the amount is within the range of 3 to 13% by weight, such disadvantages will not occur and the physical strength of the coating film can be improved. In the case of the paint of the present invention, in addition to the water contained in component f), an appropriate amount of water may be mixed as necessary in order to improve coating workability. The water content in the paint, including the amount contained in component f), is approximately 10%.
~15% by weight (based on the total paint) is preferred. [Example] The present invention will be explained in more detail below with reference to Examples. Example 1 Silicon carbide 15% by weight Silicon nitride 4% by weight Mica 4% by weight Alumina (1) ^* 6% by weight Alumina (2) ^** 14% by weight Alumina (3) ^*** 5% by weight Neutral aluminum phosphate 3% by weight % Colloidal silica 3% by weight Alumina sol 7% by weight Copper powder 3% by weight Nickel powder 4% by weight Sodium carbonate 8% by weight Vinyl acetate/ethylene/vinyl chloride copolymer emulsion 6% by weight Alumina fiber 5% by weight Alumina (1): Flat high alpha alumina with an average particle size of 5μ and a sintering shrinkage rate of 5% or less (sintered at 1600℃ for 3 hours) Alumina (2): Average particle size of 45μ and a sintering shrinkage rate of 5%
Flat alumina with a gelatinization rate of 100% as follows (sintered at 1600℃ for 3 hours) Alumina (3): average particle size 0.4μ, particle size distribution 0.1
~1.5μ medium soda grade alumina ( _Na2O
Included 0.25 % by weight) 〓 〓 〓 μ）））））））））））））
300-1000μ spinel structure (α-A ₂ O ₃ )
A mixture is prepared containing 13% by weight of magnesium oxide as well as a suitable amount of water in addition to the alumina fibers. This paint is applied to steel materials containing 0.4% Si for hot rolling.
Coat with a coating thickness of 100μ, and apply the steel material to the second coating described below.
It was heated and rolled under the furnace time and furnace temperature shown in the table. The measurement results (depth of formation of firerite and number of formed pieces) of scale generation due to firerite formation in a high-temperature oxidizing atmosphere in a heating furnace are summarized in the second section.
Shown in the table. Examples 2-5 These Examples were conducted similarly to Example 1. However, the amounts of each component used at that time are shown in Table 1. Test results for these paints are listed in Table 2. Comparative Example 1 Comparative Examples A and B were prepared in the same manner as in Example 1, using paints corresponding to Examples 1 and 2 of Japanese Patent Application No. 63-52565. The composition of each component is shown in Table 1. The test results for these paints are also shown in Table 2.

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Claims (1)

[Scope of Claims] 1 a 19-43% by weight of at least one member of the group consisting of silicon carbide, silicon nitride, stabilized zirconium oxide, and mica as a ceramic base material b 23.5-43% by weight as a ceramic auxiliary agent The following three types of alumina, Alumina (1): α crystal particles are 1 to 10μ, 1600
Flat fine grain alumina with a shrinkage rate of 5% or less when sintered for 3 hours at 1600℃, Alumina (2): Average shrinkage rate of 5% or more and 10% or less when sintered for 3 hours at 1600℃ particle size
Flat alumina of 100μ or less with a gelatinization rate of 100% and alumina (3): Na ₂ O content of 0.2 to 0.3% by weight
ultrafine particle alumina with an average particle size of 0.1 to 1.5 μ; c 9.5 to 33.5% by weight of at least one member of the group of neutral aluminum phosphate, colloidal silica, alumina sol as a binder; d 5 to 9% by weight of Fe, Cu, at least one of the group of Ni and Cr powders e 5-25% by weight of sodium carbonate as ceramic sintering accelerator and f 2.5-13% by weight (solids content) polymerized to form a water-resistant coating 3 to 13% by weight of carbon fibers, alumina fibers, which act as aggregates and increase the bond strength of the coating, g.
At least one mineral fiber from the group consisting of silicon carbide fibers and silicon nitride fibers h 8.5 to 25% by weight of at least one from the group consisting of magnesium oxide, chromium oxide and calcium oxide
Composed of oxides of seeds, provided that the total of components a) to h) is 100
High temperature anti-oxidation paint for steel material which is % by weight.