CN101007734A - High temperature-resistant coating material for hot continuous rolling steel billet or continuous rolling blank - Google Patents

Abstract

High-temperature-resistant coating material for hot continuous rolling billet or continuous casting billet, its composition mass percentage is: solute: 40-50%, of which, fire clay 55-70%, water glass 30-45%; solvent: water 50-50% 60%. Described water glass is sodium silicate. The advantages of the present invention are: it is used for the surface coating protection of hot continuous rolling billets or continuous casting billets, and can withstand heat temperatures up to 1300°C; the process is simple and operable; the production cost is low; Rolling finger cracks caused by out-of-phase precipitation; the surface decarburization of billets or continuous casting billets is light, so that the quality of billets or continuous casting billets is good and the pass rate is high.

Description

High temperature resistant coating material for hot rolling billet or continuous casting billet

technical field

The invention relates to a coating material, in particular to a coating material capable of preventing the occurrence of heterogeneous cracks in continuous hot rolling of steel slabs (or continuous casting slabs) and enabling zero decarburization of the product surface on a hot rolling line with flameless cleaning equipment.

Background technique

Hot working deformation is a necessary production process of steel products. Hot working rolling is a commonly used hot working deformation technology, and hot continuous rolling is a common hot working rolling technology. First, the steel billet or continuous casting billet is heated; then, the continuous rolling mill performs hot continuous rolling on the steel billet or continuous casting billet, and produces the steel billet or continuous casting billet into finished products whose dimensions meet the specifications; finally, the finished product is inspected and put into storage.

For hot-rolled steel products in actual production, some special structural steels, high-alloy steels, and high-temperature alloys, due to the narrow optimum thermoplastic deformation temperature (generally, the optimal deformation temperature fluctuation range is 30-50°C), the heating and rolling process The control has brought great difficulties; some high-carbon alloy steels and those with decarburization depth requirements on the surface have a low product qualification rate. This is because: (1) For "special structural steel": in order to meet some specific requirements of steel, a relatively high content of carbon, phosphorus, sulfur, copper and other elements are deliberately added to the steel, and single or multiple elements Added at the same time; these higher content elements exist in single or intermediate equal forms in steel, often with low melting points, and in the conventional rolling temperature range, their deformation ability is very different from the matrix structure of steel, and they are easy to be rolled in the conventional rolling temperature range. Heterogeneous phases (brittle phases and other phases) precipitate in the rolling temperature range. The reason is that the heterogeneous phases are mostly enriched at the grain boundaries, and the low melting point heterogeneous phases on the surface of the slab or continuous casting slab are melted or softened during the rolling heating process. phenomenon, resulting in grain boundary oxidation, forming a surface crack source, and surface cracks expand along the grain boundary during rolling; for surface peeled blanks, the surface grains are coarse, which is more likely to cause local overheating or overburning; in addition, if the blank is not peeled clean, the blank Exposure, the defects that could be rolled and welded can not be welded after heating and oxidation, resulting in rolling waste, resulting in rolling cracks, resulting in failure of normal production. (2) For "high-alloy steel and high-temperature alloy", some iron-based and nickel-based metal materials are difficult to deform, and the deformation temperature range is narrow, and the thermal processing process is difficult. (3) For high-carbon alloy steel and products with decarburization depth requirements on the surface, the controlled rolling method to ensure the decarburized depth of the product cannot meet the technical standards; that is, the high-pressure water descaling plus controlled rolling method , It is also unable to meet the requirements of zero decarburization on the product surface.

So the usual approach is:

1. For the above-mentioned "special structural steel, high-alloy steel, and high-temperature alloy": conduct thermal simulation tests to find the best rolling temperature for this type of steel, and then carry out production. However, for steel rolling workers, the yield rate of this type of steel is still low, and they mainly face three major difficulties: 1. The optimum thermoplastic deformation temperature is narrow, and the fluctuation range of the optimum deformation temperature is generally 30-50°C; 2. The material The segregation of the main components, residual elements and other added trace elements exists objectively. If the segregation exceeds the limit, it will inevitably cause the deviation of the optimal thermoplastic deformation temperature, resulting in: local overheating or overburning; 3. In the finished product When the surface has high requirements, or there are many surface defects of the billet, the usual method is to peel the billet; however, peeling removes defects and also causes coarse grains on the surface of the billet, which is more likely to cause local overheating or overburning. In addition, if the billet is not peeled clean , The billet defects are exposed, and the defects that could be rolled and welded can not be welded after heating and oxidation, resulting in rolling waste. Therefore, when these special structural steels, high-alloy steels, and high-temperature alloys are produced in special steel plants, the output and yield are low. Although the product has high added value, it cannot obtain corresponding economic effects.

2. For high-carbon alloy steel and products with decarburization depth requirements on the surface, for high-carbon alloy steel and products with decarburization depth requirements on the surface, steel billets or continuous casting billets are cleaned by flame and controlled rolling after heating out of the furnace To ensure that the depth of the decarburization layer of the product meets the requirements of the technical standard; however, the flame cleaning metal loss is large (the blank metal loss reaches 2%), and the equipment investment cost is high.

Contents of the invention

The object of the present invention is to provide a high temperature resistant coating material for hot continuous rolling steel slabs or continuous casting slabs, which is used for surface coating protection of hot continuous rolling steel slabs or continuous casting slabs, capable of heat resistance up to 1300°C.

From the above, it can be seen that (1) the coating material plays a role of isolation and oxidation protection in the heating process of the steel slab or continuous casting slab, and the melting temperature of the low melting point can be increased under the protection of the isolation layer. It can avoid overheating or overburning caused by the precipitation of different phases (brittle phases and other phases) of "special structural steel, high alloy steel, high temperature alloy" billet or continuous casting billet; moreover, if the billet is not clean, the ingot Or when casting slab defects are exposed, the coating can also prevent the defects from being heated and oxidized and cannot be rolled and welded; degree of surface decarburization. (2) During hot continuous rolling, the temperature drop rate of the surface-coated steel slab or continuous casting slab is greatly reduced, which is beneficial to the thermal processing of steel.

To achieve the above object, the technical solution of the present invention is,

The high-temperature-resistant coating material for hot continuous rolling steel slab or continuous casting slab of the present invention, its component mass percentage is:

Solute: 40-50%, of which, fire clay 55-70%, water glass 30-45%;

Solvent: 50-60% water.

Wherein, described water glass is sodium silicate.

The fire clay is used for steelmaking and furnace building, and its main components are Al ₂ O ₃ =50%, SiO ₂ =40%, and other impurities such as MgO and Fe ₂ O ₃ .

The fire clay is resistant to high temperature, and the water glass (sodium silicate) is stirred with the fire clay and diluted with water to form a thin slurry, which increases the viscosity of the paint and makes the paint have better adhesion to the surface of the steel billet.

The preparation method of the above-mentioned coating material is: dilute the fire clay used for steelmaking and furnace building into a thin slurry with water, and it must not fall off prematurely during the rolling process, so as to avoid the contact between the surface of the billet or continuous casting billet during the rough rolling stage. Atmospheric contact, surface defects are not rolled and welded in time, resulting in cracks; and they cannot fall off too late, which will affect the surface quality of the finished product.

When steel slab or continuous casting slab is hot-rolled, apply the high temperature resistant coating material evenly on the surface of steel slab or continuous casting slab (evenly brush on the surface of peeled slab), and wait for rolling after drying. During the rolling heating process, the coating (the surface layer is mainly composed of Al ₂ O ₃ and MgO particles, the inner layer of Al ₂ O ₃ , MgO particles and the original iron oxide or iron atoms on the surface of the billet or continuous casting slab is formed under high temperature. A complex ionic compound of Fe-Al-O or Fe-Mg-O,) forms a dense protective layer (0.1-1 micron) on the surface of the slab or continuous casting slab, which plays the role of isolating the air (during heating and subsequent Preventing the diffusion of oxygen element along the grain boundary to the inside during the rolling process is the key to preventing the cracking of the steel slab or continuous casting slab. It is impossible to realize the whole process of inert gas protection or vacuum state in the existing heating furnace and rolling equipment Yes, a protective layer is applied to the surface of the steel slab or continuous casting slab to ensure that the surface of the steel slab or continuous casting slab does not come into contact with the outside world during the heating and subsequent rolling process, that is, it does not react with oxygen.); in phosphorus removal and rough rolling The surface layer gradually falls off.

Advantages of the present invention:

(1) The process is simple and the operability is strong;

(2) Low production cost;

(3) Avoiding rolling finger cracks caused by heterogeneous precipitation of steel billet or continuous casting billet hot rolling;

(4) The surface decarburization degree of billet or continuous casting billet is light;

(5) The product quality is good and the pass rate is high.

Detailed ways

Embodiment sees table 1,

Table 1 Unit: mass percentage

Example Solute Solvent: water clay water glass Solute amount 1 55 45 40 60 2 70 30 50 50 3 50 50 50 50 4 60 40 40 60 5 65 35 45 55

Example 1: A steel factory produces low-carbon, high-sulfur, phosphorus free-cutting steel, containing S: 0.26-0.35%, P: 0.04-0.07%. A 60-ton electric furnace is used to smelt, a 160-square-meter billet is continuously cast, and a 32-disc coil is produced by continuous rolling.

Abnormalities occurred in the smelting and continuous casting process of this furnace steel during the production period. The continuous casting slab appearance inspection found that: subcutaneous air bubbles and subcutaneous cracks were serious, and there were a large number of subcutaneous air bubbles in the low-magnification inspection. The method of the present invention was implemented, and the continuous casting slab was stripped. The surface is treated with high-temperature-resistant paint, and the rolling heating temperature is 1120-1160°C. The surface material of the billet (or continuous casting billet) is found to fall off after 2-6 passes of rough rolling. The surface of the finished product inspection is clean. No defects were found in the material.

Embodiment 2: Spring steel 60Si2CrVAT for railway speed increase, C: 0.56-0.64%; Si: 1.40-1.80%; Cr: 0.90-1.20%. After the steel billet is heated, it is descaled and rolled by high-pressure water to the finished product. The depth of the surface decarburization layer along the length of the finished product is difficult to uniformly meet the standard requirements.

By coating the surface of the peeled billet with high-temperature-resistant paint and rolling it according to the original process, the depth of the decarburization layer on the surface of the finished product is inspected, and the entire length of the wire reaches zero decarburization on the surface.

Claims (4)

1. High temperature resistant coating materials for hot continuous rolling steel slabs or continuous casting slabs, the mass percentage of its composition is: Solute: 40-50%, of which, fire clay 55-70%, water glass 30-45%, solvent: water 50-60%. 2. The high temperature resistant coating material as claimed in claim 1, characterized in that, said water glass is sodium silicate. 3. The high temperature resistant coating material as claimed in claim 1, characterized in that, said fire clay is fire clay for steelmaking and furnace building, and its main components are Al ₂ O ₃ =50%, SiO ₂ =40% , others are impurities MgO, Fe ₂ O ₃ . 4. The high temperature resistant coating material as claimed in claim 1, which is used for surface protection of hot continuous rolling steel slabs or continuous casting slabs.