JPH0463105B2 - - 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 that is removable and prevents damage to the coating due to condensation droplets caused by the temperature difference between the steel and the heated air, especially in the vicinity of continuous heating furnaces. [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 scorching furnace, and rolled into a product. If the billet slab is a steel material on the level of ordinary steel, there will be less scale formation and descaling is 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. Many paints contain silica-based refractories, magnesia-based refractories, low-melting point metals, or inorganic salts, but they also contain Cu, Ni,
Due to differences in operating methods such as steel billet slabs containing Cr, etc. and continuous or batch heating furnaces, there are drawbacks such as insufficient oxidation prevention, scale generation prevention, and removability. Therefore, high-grade steel slabs are now placed in heating furnaces with their surfaces covered with protective covers made of thin iron plates to minimize exposure of the steel surfaces to the oxidizing atmosphere, thereby preventing the occurrence of slab scale. However, this thin iron plate protective cover requires a great deal of labor to attach to the steel material, and is also a factor in deteriorating the fuel consumption rate of the heating furnace because it involves indirect heating. High-temperature anti-oxidation paints are designed to prevent oxidation and to easily remove scale, and even if scale occurs, the scale can be easily removed together with the paint using high-pressure water before rolling; in other words, descaling is easy. something 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 the paints disclosed in these applications are used, water vapor condenses on the coating 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 coagulation furnace eluted part of the paint film, causing scale formation. The applicant has proposed a coating material in Japanese Patent Application Laid-Open No. 61/1989 that solves the above problems without deteriorating the excellent properties of the high temperature antioxidant of the invention described in the above two publications.
- Provided in Publication No. 64813. The coating has the following composition: (a) 20-50% by weight of at least one member from the group of silicon carbide, silicon nitrogen, stabilized zirconium oxide, mica as a ceramic substrate (b) 20 ~50% by weight of the following three types of alumina as ceramic auxiliary agents: Alumina (1): Oblate fine grain alumina with large α crystals and low sintering shrinkage rate, Alumina (2): Stable sintering yield. 100μ
Oblate granular alumina with high pregelatinization rate and alumina (3) with the following average particle size: Low moisture content, medium soda grade, easily sinterable ultra-fine alumina (c) 10-40% by weight neutral as a binder At least one member of the group consisting of aluminum phosphate, colloidal silica, and alumina sol; (d) 5 to 10% by weight of at least one member of the group of Fe, Cu, Ni, and Cr powder; (e) 5 to 30% by weight of ceramic sinter. sodium carbonate as accelerator and (f) 2.5 to 15% by weight (solids content, which is the basis for calculation) of polymerizable and/or copolymers forming water-resistant coatings. Aqueous emulsion or aqueous solution (however, the total of components (a) to (f) is 100% by weight) When applying this paint to the steel painting, approximately 10 to 15% by weight (total amount of the composition) It has been found that the coating workability is improved when water (based on the standard) is mixed into the composition. [Problem to be solved by the invention] 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 may There was a problem in that the material peeled off due to physical impact from metal rolls, etc., and scale was generated on the peeled part in the heating furnace. In order to avoid the formation of this scale, it may be possible to bake and dry the paint before charging it into the heating furnace, but even if this is done, there is a problem that productivity will decrease and economic efficiency will deteriorate. The present invention further applies 3 to 15% by weight of the component (g) to the high-temperature antioxidant paint described in JP-A No. 61-64813.
It is an object of the present invention to provide a high-temperature oxidation-preventing paint that provides better steel products by incorporating at least one mineral fiber from the group consisting of carbon fibers, alumina fibers, silicon carbide fibers, and nitrogen silicon fibers. [Means for solving the problem] In order to achieve the above object, the inventor has solved the above (g)
It has been found that the 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. The mineral fibers used as component (g) are carbon fibers, alumina fibers, silicon carbide fibers and silicon nitride fibers, with particular preference being 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 The mineral fiber used as component (g) can be used in amounts other than 3 to 15% by weight, but if it is less than 3% by weight, it will have little effect as an aggregate;
If it exceeds this amount, the leveling properties of the coating film will deteriorate and the formed coating film will have irregularities. If the amount is within the range of 3 to 15% by weight, such disadvantages will not occur and the physical strength of the coating film can be improved. The ceramic (a) component used as the base material is preferably one with high heat resistance (for example, silicon carbide at 2200℃), and the amount used is the same as components (a), (b), (c), (d), and (e). ), (f) and (g)
(hereinafter abbreviated as all components) must be in the range of 20 to 50% by weight of the total. If component (a) is less than 20% by weight, the coating film will not be formed densely, the amount of permeation of oxidizing atmosphere gas will increase, and the desired antioxidant effect will not be obtained.
When it exceeds 50% by weight, thermal conductivity decreases, heating energy consumption 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℃
sintered for 3 hours), preferably stable at 5% to 10%, with an average particle size at which the gelatinization rate is 100%.
They are flat particles with a hiding power of 100μ or less and 20μ or more, preferably 30 to 60μ. 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 0.5μ. 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 25% by weight, a dense coating film with sufficient hiding power cannot be obtained, and if it is more than 50% 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 of the group consisting of neutral aluminum phosphate, colloidal silica, and alumina sol [component (c)] used as a binder stabilizes the bonding of the ceramic base material, which is the component (a), and also stabilizes the bonding of the ceramic base material. It is used to increase the adhesion with
must be within the range. This binder has 10
If the amount is less than 40% by weight, the mixed paste will be hard and cannot adhere to the steel surface, and if it is less than 40% 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 is less than 5% by weight, the surface of the steel material will become an oxidizing atmosphere, and if it exceeds 10% 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 to 800
It accelerates the sintering of the ceramic base and binder at ℃, 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 proper sintering rates. 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 the weight percentage, the coating film will not be formed densely and will deviate from the initial purpose. The amount of component (f) used is 2.5 to 2.5% as solid content.
15% by weight (based on the total amount of paint), especially from 2.5
Preferably it is 13% by weight. If it is less than 2.5% by weight, no effect will be obtained, and if it exceeds 15% by weight, gas will be generated by combustion of this component in a continuous heating furnace, which may cause blistering and reduced peeling of the coating film. In the case of the paint of the present invention, an appropriate amount may be added in addition to the water contained in component (f) in order to improve coating workability. The water content in the paint, including the amount contained in component (f), is preferably about 10 to 15% by weight (based on the entire paint). [Example] The present invention will be explained in more detail below with reference to Examples. Example 1 Silicon carbide 18% by weight Silicon nitrogen 5% by weight Mica 5% by weight Alumina (1) ^* 7% by weight Alumina (2) ^** 16% by weight Alumina (3) ^*** 6% by weight Neutral aluminum phosphate 3 Weight% Colloidal silica 3% by weight Alumina sol 8% by weight Copper powder 3% by weight Nickel powder 4% by weight Sodium carbonate 9% by weight Vinyl acetate/ethylene/vinyl chloride copolymer emulsion 7% by weight *Alumina (1): Average particle size 5μ, Flat high alpha alumina with a sintering shrinkage rate of 5% or less (1600℃, sintering for 3 hours), **Alumina (2): average particle size 45μ, sintering shrinkage rate 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
(content 0.25% by weight), diameter 15-20μ, average length 500μ, length distribution
A mixture is prepared containing 6% by weight of alumina fibers with a spinel structure (α-Al ₂ O ₃ ) of 300-1000 μ and a suitable amount of water. This paint was applied at a thickness of 50 μ and 100 μ to unheated thick plate steel, ultra-tensile steel and ordinary steel, respectively, and after air drying for 24 hours, 10 ml of paint was applied to the surface for 5 seconds as a water resistance test. / m ² was sprayed with tap water for 4 hours to check the damage.
There was no leakage of the paint film. Separately, after applying a coating film to the same thickness on the above steel materials, the coating was transferred on a metal roll as is done in practice, and the peeling status of the coating film was observed (roll transfer peeling rate ). In addition, the impact strength after air drying for 24 hours was measured by a Dupont drop test (300 mm height, 200 g steel ball). The steel materials were heated and rolled under the furnace time and furnace temperature shown in Table 2 below. Table 2 shows the measurement results regarding scale generation in a high-temperature oxidizing atmosphere in a heating furnace, peelability during transfer with metal rolls, removability with high-pressure water, and impact resistance test. Examples 2-7 These Examples were conducted similarly to Example 1. However, the amounts of each component used at that time are shown in Table 1. The carbon fibers used in Examples 2, 5, 6 and 7 had a diameter of 10-20μ and an average length.
500μ, length distribution 400-600μ. In the water resistance test of these paints, no paint film was washed away. Other test results are listed in Table 2. Comparative Example 1 The same procedure as Example 1 was carried out using the paints corresponding to Examples 1 and 2 in JP-A-61-64813 as Comparative Examples A and B. The composition of each component is shown in Table 1. In the case of these paints, no paint film was washed away. Other test results are shown in Table 2. Abbreviations in Table 1 have the following meanings. *Ac/E-CP emulsion = vinyl acetate/ethylene copolymer emulsion (solid content 50% by weight) **Ac/E/PV-CP emulsion = vinyl acetate/ethylene/vinyl chloride emulsion (solid content 50% by weight) ***Alumina (1), (2) and (3) are the same as described in Example 1.

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Claims (1)

[Scope of Claims] 1 (a) 20 to 50% by weight of at least one member of the group consisting of silicon carbide, silicon nitride, stabilized zirconium oxide, and mica as a ceramic substrate; (b) 25 to 50% by weight of The following three types of alumina are used as ceramic auxiliaries: 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
(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 at least one member from the group of Fe, Cu, Ni and Cr powders; (e) 5-30% by weight of sodium carbonate as ceramic sintering accelerator; (f) 2.5-15% by weight of solids content; (based on the calculation) an aqueous emulsion or solution of a polymerizable and/or copolymer forming a water-resistant coating; and (g) 3 to 15% by weight, acting as an aggregate and bonding the coating. Carbon fiber, alumina fiber to increase strength,
An antioxidant paint for steel comprising at least one type of mineral fiber from the group consisting of silicon carbide fiber and silicon nitride fiber, provided that the total of components (a) to (g) is 100% by weight.