JPH0341527B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to steel materials such as hot-rolled steel strips, molds, strips, and wire rods, and relates to a scale inhibitor used in hot rolling thereof. As is well known, scale is generated on the surface of the steel material during the hot rolling process of steel material, which reduces the yield of steel material.In addition, secondary scale has the drawback of reducing productivity due to poor pickling properties.This problem has been solved. In order to prevent this, for example, an attempt has been made in which an anti-scaling agent is applied after the finish rolling to the front of the winding machine to suppress the generation of secondary scale. The well-known scale inhibitors include those consisting of one or more compounds of alkali metals, alkaline earth metals, boron, aluminum, manganese, etc., oxides of alkaline earth metals (for example, calcium, magnesium, etc.), and carbonic acid. Those consisting of salts and hydroxides have been proposed. These scale inhibitors are mixed with water and spray coated or roll coated, and sometimes a dispersant is added for the purpose of uniform coating. By the way, although well-known scale inhibitors are somewhat effective, they still have unresolved technical issues such as problems with adhesion to steel materials and low economic efficiency due to cost and post-treatment issues, so they are not widely used. The current situation is that this has not yet been achieved. Therefore, the present inventors developed a scale inhibitor that has good adhesive properties, a high scale prevention effect, and is easy to post-process, and completed the present invention. The gist of the present invention is to use an adhesive consisting of Na ₂ O.3SiO ₂ in an amount of 1 to 30 parts per 100 parts of an alkaline earth metal compound.
The present invention is a hot rolling scale inhibitor for steel materials which is prepared into a slurry by adding water to the hot rolling scale inhibitor. The feature of the present invention is that low melting point substances, namely Na ₂ O・3SiO ₂
(melting point 600℃) is used as an adhesive. The reason for this is that even if a well-known anti-scaling agent is sprayed or laminar flow is applied to the surface of a steel material that is being transported at high speed while maintaining a high temperature, a vapor film is instantaneously formed and water droplets roll onto the surface. The purpose is to solve the technical problem of difficulty in adhesion, that is, when the adhesive according to the present invention is used in an appropriate amount, the concentration of the scale inhibitor is increased, the adhesion force is significantly increased, and the coating efficiency is improved. Next, in the present invention, as the alkaline earth metal compound, one or more of oxides, hydroxides, carbonates, and phosphates of Ca, Mg, etc. are used, and aluminum powder (melting point: about 660°C) , glass powder, such as sodium silicate glass with a softening point of about 500 to 700°C, or both, at a rate of 1 to 10%, or boron oxide (B ₂ O ₃ , melting point of about 450°C or higher) at a rate of 5% or less. May be added. The reason for this is that aluminum powder, glass powder, boron oxide, etc. melt on the surface of the steel material until alkaline earth metal compounds such as calcium carbonate (CaCO ₃ , decomposition temperature 898°C) decompose, and the alkaline earth metal compounds improves adhesion and suppresses oxidation of steel materials,
Or, it acts as an additive to improve modification, and if the amount of aluminum powder or glass powder added is less than 1%, it will not be effective, and if it exceeds 10%, it will reduce the effect of the alkaline earth metal compound. On the other hand, boron oxide has no effect if the amount added is less than 1%, and if it exceeds 5%, the effect decreases and reduces the coating property, so the above-mentioned range of addition amount is desirable. Furthermore, 1 to 30 parts of the adhesive is added to 100 parts of the alkaline earth metal compound, and the reasons for limiting the mixing ratio are as follows. 400°C when the adhesive comes in contact with high temperature steel.
It melts and spreads at ~1100°C to attach powdered alkaline earth metal compounds to steel materials, and inorganic materials with low melting points are ideal as adhesives. If the amount of the adhesive is less than 1 part per 100 parts of the alkaline earth metal compound, it will be insufficient to spread the alkaline earth metal compound, and at least 1 part is required at the bottom. On the other hand, if the amount of the adhesive exceeds 30 parts, the contact between the steel material and the alkaline earth metal compound will be reduced, and the prevention of secondary scale will be insufficient. Here, prevention of secondary scale means reducing the thickness of the scale, but it also includes reducing Fe ₃ O ₄ , which is bad for sulfuric acid pickling properties and peelability, and increasing FeO, which is good for them. Further, a small amount of a dispersant may be added to prevent the scale preventive agent from settling in the aqueous solution before coating. Next, water is added to the mixture of the alkaline earth metal compound and adhesive to form a slurry, and the ratio is 1 to 100 parts of the mixture to 100 parts of water. The reason is as follows. If the mixture is less than 1 part per 100 parts of water, it will not be effective in preventing scale or shortening the pickling time of coated steel materials, but with acidic calcium pyrophosphate, if it is more than 1 part, it will be effective. On the other hand, if the amount exceeds 100 parts, the viscosity of the slurry-like substance becomes high and spray application becomes difficult, and the spray pressure must be increased.
Since splashing increases and coating efficiency decreases, the proportion of the mixture should be 1 to 100 parts per 100 parts of water.
section is appropriate. In the case of the spray method, a nozzle with a diameter of 20 mm or more is preferable because it reduces nozzle clogging, and a nozzle that can coat over long distances is desirable in terms of coating efficiency. Application of the scale inhibitor of the present invention is carried out as follows. (1) Apply by spraying to the steel surface after high-pressure water descaling installed immediately after the heating furnace, or after rough rolling and on the way to the finish rolling exit side. The amount of coating should be about 3 to 20 times higher than the coating after finish rolling. This is to reduce the effects of hot rolling after coating and thermal convection due to the high temperature of the steel material. The discharge pressure is preferably 1 to 10 kg/cm ² (in the case of an air/water spray nozzle, the air pressure is 1 to 6 kg/cm ² ).
If the discharge pressure is too high, the anti-scaling agent will rebound after hitting the steel material, which is not good. (2) Roll coating or spraying is applied to the surface of the steel using rolls on a roll stand during finish rolling. That is, the anti-scaling agent is spread on the back-up roll, or it is spray-coated between the steel material and the work roll or onto the work roll so that it adheres to the surface of the steel material. In the case of spray coating, a discharge pressure of 1 to 6 kg/cm ² (in the case of fluid, the air pressure is 1 to 5 kg/cm ² ) is preferable. The discharge amount (or coating amount) is required to be 1 to 10 times the amount applied after finishing rolling. (3) Apply by spraying to the surface of the steel material immediately after leaving the final stand on the finish rolling exit side. The discharge pressure is preferably 1 to 6 kg/ ^cm2 ; if it is too low, the scale inhibitor will not reach the steel material, and if it is too high, it will be repelled. Several tens of nozzles with a discharge rate of 1 to 10 kg/mm per nozzle are arranged in the width and length directions so that the amount of scale preventive agent deposited on the steel plate becomes an appropriate value. When calcium carbonate is applied as shown in Figure 1, if the calcium oxide amount is 30 mg/m ² (one side), the sulfuric acid pickling time is halved. Furthermore, the coating distance is preferably 50 to 150 cm. If it is too close, the steel material may jump or bend after leaving the finishing mill and hit the nozzle; if it is too far away, the scale preventive agent will not reach the steel material and will be scattered by thermal convection and adhere to the steel material. There are things I don't do. (4) Apply by spraying to the surface of the finished steel material just before and after being rolled up in a winding machine. The coating conditions may be the same as those in (3) above, but after winding, it is sufficient to apply from the side of the rolled steel strip and apply only to both ends of the steel strip. In general, pickling time is longer at both ends of a hot-rolled steel strip than at the center of the width, so it is also effective to install a spray device on the hot-rolling line that can be adjusted to move in the width direction so that only both ends can be coated. It is. Applying the scale inhibitor of the present invention, the above-mentioned (1)
When the treatments from (4) to (4) are performed, no problems occur in rolling or the environment, the amount of secondary scale modification or generation is reduced, and the pickling time is halved. The reason for this is that due to the bending process using rolls in the pickling line,
It is recognized that many cracks occur in the secondary scale and that the hydrochloric acid or sulfuric acid pickling works effectively, resulting in a significant reduction in time. Furthermore, after pickling, the peelability of secondary scale that occurs on the manufactured steel material is also extremely good. Next, the present invention will be explained according to examples. Example 1 A continuously cast 12 ton low carbon steel slab was heated to 1250°C in a heating furnace, extracted, and immediately after high-pressure water descaling, rough rolling, and finishing rolling, a scale inhibitor was applied at a discharge pressure of 2 to 4 kg/cm. ^2. Spray coating was carried out at an air pressure of 2 to 3 kg/cm ² and a coating distance of 45 to 100 cm, and then a 2 mm thick steel strip was wound into a coil after water was poured on a hot run table or after water was not poured. After unwinding, test materials were taken from the center and tail of the coil head and pickled with a 15% sulfuric acid solution at 90°C. The inhibitor of the present invention has extremely high adhesion efficiency and can greatly shorten pickling time. Furthermore, the scale removability is also good upon bending. Table 1 shows the composition of the scale inhibitor, coating conditions, coating and pickling results.

【table】

[Table] Example 2 In the same manner as in Example 1 above, acidic calcium pyrophosphate 20 was added as a scale inhibitor just before winding.
%, sodium silicate 2%, water 78% aqueous solution,
After collecting the test material, the secondary scale properties were investigated. As shown in Table 2, when the scale preventive material of the present invention was used, the scale thickness was reduced to about 1/3 compared to the conventional material (uncoated), and the hydrochloric acid cleaning time was reduced to about 1/2. Furthermore, the coating efficiency of the inhibitor of the present invention was 5 to 10 times higher than that of a single aqueous solution of calcium acid pyrophosphate.

【table】 [Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amount of CaO deposited and the washing time with sulfuric acid.

Claims (1)

[Claims] 1. 1 to 30 parts of an adhesive consisting of Na ₂ O.3SiO ₂ is blended to 100 parts of an alkaline earth metal compound,
A hot rolling scale inhibitor for steel materials made into a slurry by adding water. 2 1 to 10% to the adhesive consisting of Na ₂ O and 3SiO ₂
Mix 1 to 30 parts of an adhesive made of either Al powder or glass powder, or 1 to 5% B ₂ O ₃ to 100 parts of an alkaline earth metal compound, and add water. A hot rolling scale inhibitor for steel materials in slurry form.