Two-phase flow protection method for hot-rolled plate strip high-speed steel working roll

Abstract

According to the two-phase flow protection method for the hot-rolled plate strip high-speed steel working roller, in the rolling process of the high-speed steel working roller, N gas-liquid two-phase flow nozzles are used for spraying a two-phase mixture composed of water and inert gas to the surfaces of an upper roller and a lower roller on the outlet side of a rolling mill, and the volume fraction of the inert gas in the two-phase mixture is smaller than or equal to 10%. By improving the cooling atmosphere of the high-speed steel working roll in the hot rolling process, on one hand, the cooling effect is improved, and on the other hand, the influence of oxygen, water vapor, roll temperature and other factors on roll surface oxidation glaze is reduced, so that the roll surface oxidation glaze growth is controllable, and meanwhile, crack oxidation corrosion generated on the surface of the working roll is relieved; and therefore, the surface of the high-speed steel working roller can be better protected, and the service life of the high-speed steel working roller is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a two-phase flow protection method for a hot-rolled plate and strip high-speed steel working roll. Background Art

[0002] Existing hot rolling high-speed steel work rolls are widely used in the front section of hot rolling finishing due to their high wear resistance and reliability. Figure 1 As shown in the figure, the temperature of the working roll surface suddenly rises to 400-600℃ at this stage, and then an oxide film is formed on the working roll surface under the influence of oxygen, water vapor and cooling water in the air. The oxide film will quickly transform into a thin layer of oxide glaze under the action of the rolling force, slip and high temperature of the rolling mill. Under different rolling lines and rolling environments, the stable oxide glaze thickness is about 0.1-20μm.

[0003] The development of oxide glaze during hot rolling is a dynamic process, consisting of forming in the initial stage of rolling, dynamic stability in the middle stage, and finally cracking and peeling. In the stable stage of its growth, the oxide glaze is worn away during each bite, and then leaves the bite interval and enters the outlet end for water cooling and immediately generates new oxide glaze, and this cycle is repeated, which effectively protects the surface of the high-speed steel working roll. When the roll surface begins to have tiny cracks due to thermal fatigue after long-term rolling, oxygen and water vapor enter the cracks on the roll surface and oxidize the material near the cracks (such as Figure 2 At the same time, the oxide glaze no longer grows-wears-regrows stably, but begins to form irregularly and rapidly with the increase of roller temperature, and a small part of it peels off, which eventually leads to serious wear of the roller surface and cracks on the working roller surface (such as Figure 3 as shown) and oxide glaze peeling (as shown Figure 4 As shown), this necessitates a roll changing and grinding operation.

[0004] Therefore, how to prolong the stable stage of balanced growth of oxide glaze and ensure the density of oxide glaze is the key to stable production, improving the surface quality of roller surface and strip, and improving rolling efficiency.

[0005] Chinese patent CN107497854A discloses "a method for inhibiting the surface oxidation of the rollers of a hot-rolled strip finishing mill applied in the technical field of strip rolling process methods", and the specific operation steps are: 1) the upper rollers Fa (3), Fb (4), Fc (5) and Fd (6) of the upper working rollers (1) are arranged in sequence from large to small according to the roller diameter size, and the upper rollers Fe (7), Ff (8) and Fg (9) of the upper working rollers (1) are arranged in sequence from small to large according to the roller diameter size, which can inhibit the oxidation phenomenon on the surface of the hot-rolled rollers, reduce the thickness of the oxide film on the surface of the rollers, prevent the oxide glaze on the surface of the rollers from peeling off, improve the quality of the strip steel, and reduce the production cost of the strip steel.

[0006] Chinese patent CN108687134A discloses "a method for reducing thermal stress spalling of oxide film on rollers". The specific operation method is: when rolling the strip, control the F1 biting rolling speed to be no less than 1m / s; control the spray angle and spray pressure of anti-stripping water on the roller inlet side; the spray angle is 45° as the lower limit and the spray water flow is not blocked by the roller as the upper limit; the spray pressure is 8-12bar. By reasonably controlling the spray angle and spray pressure of anti-stripping water on the inlet side of the lower working roller of the finishing rolling, the heat transfer when the strip and the roller are in contact is reduced, thereby reducing the roller temperature and roller thermal stress cracking defects, and improving the surface quality of the product.

[0007] Chinese patent CN110280605B discloses "a method for reducing the peeling rate of oxide film on rolling mill rolls", including heating, rough rolling, finish rolling and cooling, characterized in that the temperature fluctuation range of the whole length of the rolled material is controlled to be ≤10°C, and the target difference of the furnace temperature between the same batch of rolled materials is controlled to be <20°C, and the time difference in the furnace is controlled to be <10min; in the rough rolling, the temperature difference between the RT2 temperature and the final rolling temperature is <150°C; the inlet temperature is <1050°C; after going off the line, the temperature difference between the edge and the middle of the rolling mill roll is controlled to be <20°C, and the temperature of the highest point of the rolling mill roll is ≤60°C.

[0008] Chinese patent CN101003053 discloses "a method for preventing the oxide film on the surface of nickel-chromium rolling rolls from peeling off", which includes the following steps: ① Rough rolling rolls the ferritic stainless steel continuous casting billet at a temperature of 1150±50℃ into a stainless steel intermediate billet at a temperature of 1020-1050℃ and a thickness of no more than 35mm, and installs a heat preservation cover between rough rolling and finishing rolling, and the rough rolling outlet temperature is 1030-1050℃; ② Finish rolling sends the stainless steel strip at a temperature of ≥950℃ into the finishing rolling stand for rolling, and the surface roughness value Ra and the maximum deformation rate of the rollers of the first to third finishing rolling stands are: Ra≤0.9μm, maximum deformation rate≤42%; Ra≤0.6μm, maximum deformation rate≤38%; Ra≤0.6μm, maximum deformation rate≤36%. The cold plate degradation produced by this method is reduced to 1.25%, and the unqualified rate is reduced to 0.2%.

[0009] Chinese patent CN105598172A discloses a "method for preventing the peeling of oxide film on the surface of hot strip steel continuous rolling mill rolls". The method includes the following steps: when the mill is working, at the mill entrance side, coolant is sprayed into the roll gap to keep the roll gap moist; at the mill exit side, coolant is sprayed onto the roll surface in a mist form to keep the roll surface moist. This method can reduce rolling costs, prevent the peeling of oxide film on the roll surface, and avoid rolling defects caused by excessive temperature drop of the steel strip due to a large amount of coolant spraying, thereby ensuring the rolling quality of the steel strip.

[0010] Chinese patent CN111633027A discloses "a rolling method for extending the life of conventional hot-rolled thin-gauge strip steel rolls". Under the premise of controlling the thermal system of the rolled slab, segmented quantitative rolling scheduling, flexible selection of rolling passes by the rough rolling unit and cooling control of the finished product rolling are adopted to extend the damage and shedding time of the oxide film on the surface of the roll to achieve the purpose of extending the life of the roll. The finished product rolling is the finishing mill rolling. Summary of the invention

[0011] The purpose of the present invention is to provide a two-phase flow protection method for hot-rolled high-speed steel working rolls. By improving the cooling atmosphere of the high-speed steel working rolls during the hot rolling process, on the one hand, the cooling effect is improved, and on the other hand, the influence of factors such as oxygen, water vapor and roll temperature on the roll surface oxide glaze is reduced, so that the growth of the roll surface oxide glaze can be controlled, and the oxidation corrosion caused by cracks inside the working roll is reduced, thereby better protecting the roll surface of the high-speed steel working roll and extending the service life of the high-speed steel working roll.

[0012] To achieve the above object, the technical solution of the present invention is:

[0013] A two-phase flow protection method for hot-rolled high-speed steel working rolls. During the rolling process of the high-speed steel working rolls, N gas-liquid two-phase flow nozzles are used at the exit side of the rolling mill to spray a two-phase mixture consisting of water and inert gas onto the surfaces of the upper and lower rolls, wherein the volume fraction of the inert gas in the two-phase mixture is ≤10%.

[0014] Preferably, the inert gas is one or both of nitrogen and argon.

[0015] Preferably, the inert gas contains air in a volume fraction of ≤20%.

[0016] Preferably, the spray angle range of the gas-liquid two-phase flow nozzle is 30 to 135°.

[0017] Preferably, the gas-liquid two-phase flow nozzle comprises a mixing cavity and a containing cavity, and an adjusting nut connecting the two cavities; the containing cavity is provided with a gas inlet and a liquid inlet, and the mixing cavity is provided with a spray outlet.

[0018] The hot-rolled plate and strip high-speed steel working roll is mainly used in the front section (F1-4) of the hot-rolled plate and strip production line. The present invention introduces a two-phase mixture of water and inert gas, and the gas-liquid two-phase mixture is sprayed onto the surface of the working roll through a two-phase flow nozzle. The inert gas and water are mixed in the two-phase flow nozzle, so that the cooling water contains a large amount of inert gas, and then it is sprayed onto the surface of the working roll, which has both cooling effect and inert gas protection effect. N gas-liquid two-phase flow nozzles are used to spray on the upper and lower roll surfaces, where N ≥ 2.

[0019] The mechanism of action of the two-phase mixture composed of water and inert gas sprayed onto the surface of the working roll of the present invention is:

[0020] The volume of inert gas in the two-phase mixture exceeds 10%, so that liquid water accounts for the majority of the two-phase mixture, causing the liquid water to flow out in a continuous state. The liquid water impacts the roller surface accompanied by inert gas bubbles. The gas in the gas-liquid two-phase mixture is sprayed onto the roller surface with cooling water in the form of tiny bubbles (the diameter of the bubble is φ0.1mm~φ3mm). Due to the presence of a large number of tiny bubbles, the liquid water has a lower wetting angle on the metal surface than pure water. Therefore, when the liquid water impacts the surface of the working roller, there will be no violent rebound, and almost all the liquid water is wrapped on the surface of the working roller, achieving a better cooling effect when using the same amount of water. At the same time, the inert gas in the two-phase mixture directly acts on the surface of the working roller, isolating the surface of the working roller from the air, greatly improving the effect of protecting the oxide glaze on the surface of the working roller and saving a lot of precious inert gas.

[0021] The introduction of inert gas forms an inert gas layer on the surface of the working roll, reducing the contact between the working roll surface and the oxidizing and corrosive atmosphere such as oxygen and water vapor in the air, so that a uniform oxide glaze layer can be formed on the entire working roll surface, reducing the degree of oxidation on the working roll surface, forming a thinner oxide glaze layer, ensuring that the oxide glaze layer is completely worn out during each bite, stabilizing the balanced growth of the oxide glaze, effectively protecting the surface of the high-speed steel working roll, and slowing down the cracks caused by thermal fatigue on the working roll surface. Even if tiny cracks appear on the working roll surface due to thermal fatigue after long-term rolling, the amount of oxygen and water vapor entering the cracks can be reduced, slowing down the oxidation and corrosion caused by the cracks extending into the working roll, effectively protecting the working roll surface, and improving the surface quality of the hot-rolled strip (for example, reducing the inclusion of iron oxide scale on the strip surface, improving the surface finish, etc.).

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] Chinese patent CN107497854A directly sprays nitrogen into the roll gap at the exit side of the rolling mill. Although inert gas is also used to protect the working rolls, it only introduces inert gas into the ambient atmosphere to expel the oxygen content in the air, making the entire working environment in an oxygen-free state, thereby achieving the purpose of avoiding excessive oxidation of the roll surface. The roller surface is cooled by ordinary spraying of cooling water. However, this method must use a large amount of inert gas, which is very dangerous to use in actual working conditions. It may even cause the entire workshop to be in an oxygen-deficient environment, making it impossible for operators to be present on site, which may cause the risk of suffocation.

[0024] Chinese patent CN112522572A mentions that in the twin-roller thin strip continuous casting process, the rolled strip is cooled by gas atomization cooling, wherein the gas-water ratio of the gas atomization cooling is 15:1 to 10:1. The gas atomization cooling method can effectively reduce the thickness of the oxide scale on the surface of the strip, improve the temperature uniformity of the strip, and improve the surface quality of the strip. In the traditional gas atomization cooling mentioned in the patent, the gas content in the gas-mist two-phase mixture accounts for a large proportion, and the diameter of the liquid droplets is small, which belongs to the dispersed state. The overall gas-mist mixture is a dynamic process, that is, the gas-mist mixture must be sprayed out at a certain speed. However, the proportion of gas in the gas-liquid two-phase flow mixture of the present invention does not exceed 10%, and the liquid water is not atomized, only the inert gas bubbles are mixed in the liquid.

[0025] Beneficial effects of the present invention:

[0026] The present invention stabilizes the balanced growth of oxide glaze by introducing inert gas into liquid cooling water at the outlet side of the rolling mill, so that the oxide glaze thickness is evenly distributed on the entire roller surface, effectively protecting the roller surface of the high-speed steel working roller and slowing down the cracks caused by thermal fatigue on the working roller surface. Furthermore, when tiny cracks appear on the surface of the working roller, the amount of oxygen and water vapor entering the cracks can be reduced, reducing oxidation and corrosion caused by cracks extending into the working roller, effectively protecting the working roller surface and improving the surface quality of the hot-rolled strip.

[0027] The present invention uses a two-phase mixture to spray to cool and protect the working roll surface, reduce the wetting angle between the liquid water and the metal surface, and when the liquid water impacts the working roll surface, there will be no violent rebound, and almost all the liquid water is wrapped on the working roll surface, reducing the amount of cooling water used. At the same time, the inert gas in the two-phase mixture directly acts on the working roll surface, isolating only the working roll surface from the air, rather than placing the periphery of the working roll in an inert gas atmosphere, which can reduce the amount of inert gas used. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of heat conduction between the high-speed steel working roll during use and the strip during the biting process;

[0029] Figure 2 This is a photo of the surface cracks of the high-speed steel work roll causing oxidation of the surrounding material;

[0030] Figure 3 This is a photo of the cracks formed on the surface of the high-speed steel work roll;

[0031] Figure 4 This is a photo of the oxide glaze peeling off the surface of the high-speed steel work roll;

[0032] Figure 5 is a schematic diagram of an embodiment of the present invention;

[0033] Figure 6 Schematic diagram of the structure of a two-phase flow nozzle in an embodiment of the present invention;

[0034] Figure 7 for Figure 6 AA cross-section diagram. DETAILED DESCRIPTION

[0035] The present invention is further described below by way of embodiments and drawings, but this is not intended to limit the present invention. Those skilled in the art may make modifications or improvements based on the basic idea of ​​the invention, but as long as they do not deviate from the basic idea of ​​the invention, they are all within the scope of the present invention.

[0036] See also Figure 5 The two-phase flow protection method for the hot-rolled high-speed steel working roll of the present invention is as follows: during the rolling process of the high-speed steel working roll, at the exit side of the rolling mill, N gas-liquid two-phase flow nozzles C are used to spray a two-phase mixture composed of water and inert gas onto the surface of the high-speed steel working roll upper roll A and the high-speed steel working roll lower roll B, wherein the volume fraction of the inert gas in the two-phase mixture is ≤10%.

[0037] Preferably, the inert gas is one or both of nitrogen and argon.

[0038] Preferably, the inert gas contains air in a volume fraction of ≤20%.

[0039] Preferably, the spray angle α of the gas-liquid two-phase flow nozzle ranges from 30 to 135°.

[0040] like Figure 6 , Figure 7 As shown, the gas-liquid two-phase flow nozzle C includes a mixing chamber 1 and a containing chamber 2 and an adjusting nut 3 connecting the two chambers; the containing chamber 2 is provided with a gas inlet 4 and a liquid inlet 5, the liquid inlet 5 is connected to the water collecting tank through a pipeline, and the mixing chamber 1 is provided with a spray outlet 6.

[0041] The embodiment adopts the method of the present invention to treat the high-speed steel working roll, and the comparative example adopts the conventional method of cooling the working roll by only spraying cooling water. The specific implementation of the process parameter control is shown in Table 1.

[0042] Under the premise that other conditions are the same, within a roll changing cycle, the working roll after leaving the machine is not ground, and the surface hardness of the working roll is directly measured using a Leeb hardness tester (LD). The standard deviation method is used to calculate the average hardness, hardness deviation and standard deviation of the working roll surface. The uniformity of the oxide glaze thickness on the working roll surface is reflected by the hardness uniformity. The more uniform the hardness of the working roll, the more uniform the oxide glaze thickness generated on the surface. The specific test results are shown in Table 1.

[0043] As can be seen from Table 1, when the working roll is cooled by the conventional method of using only single-phase cooling water, the standard deviation of the hardness of the working roll surface in the unground state is measured to be above 2.7%. However, when the method of the present invention is used, the standard deviation of the hardness of the working roll surface in the unground state is measured to be below 1.3%. This proves that the oxide glaze thickness obtained by the method of the present invention is more uniform and stabilizes the balanced growth of the oxide glaze.

[0044] The service life of the embodiments of the present invention and the comparative examples was measured under the same conditions of use. The results showed that the service life of the working rolls in embodiment 1 of the present invention was increased by 5% compared with that in comparative example 1, the service life of the working rolls in embodiment 2 of the present invention was increased by 10% compared with that in comparative example 2, and the service life of the working rolls in embodiment 3 of the present invention was increased by 12% compared with that in comparative example 3.

[0045] The above results prove that the method of the present invention prolongs the period of balanced growth of oxide glaze, reduces oxidation and corrosion of the working roll, and effectively protects the surface of the working roll.

[0046]

Claims

1. A two-phase flow protection method for hot-rolled high-speed steel working rolls, characterized in that: During the rolling process of the high-speed steel working rolls, N gas-liquid two-phase flow nozzles are used to spray a two-phase mixture of water and inert gas onto the upper and lower roll surfaces at the mill outlet, wherein the volume fraction of the inert gas in the two-phase mixture is ≤10%.

2. The two-phase flow protection method for hot-rolled high-speed steel working rolls according to claim 1 is characterized in that: The inert gas is one or both of nitrogen and argon.

3. The two-phase flow protection method for hot-rolled strip high-speed steel working roll according to claim 1 or 2, characterized in that: The inert gas contains air with a volume fraction of ≤20%.

4. The two-phase flow protection method for hot-rolled high-speed steel working rolls according to claim 1 is characterized in that: The spray angle range of the gas-liquid two-phase flow nozzle is 30 to 135 degrees.

5. The two-phase flow protection method for hot-rolled high-speed steel working rolls according to claim 1 or 4, characterized in that: The gas-liquid two-phase flow nozzle comprises a mixing cavity and a containing cavity, and an adjusting nut connecting the two cavities; the containing cavity is provided with a gas inlet and a liquid inlet, and the mixing cavity is provided with a spray outlet.

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