A method for reducing hot rolling stickiness defects of ferritic stainless steel

Abstract

Ferritic stainless steel is a kind of stainless steel material with excellent corrosion resistance and mechanical properties, which is applied in petroleum, chemical industry, electric power and ship field. However, in the process of hot rolling, due to the influence of rolling temperature, rolling speed and rolling pressure and other factors, the defect of sticking roll often occurs, which forms linear roughness on the surface of the strip steel, and the iron scale in the linear roughness is not easy to be cleaned by hot line pickling, causing the iron scale to be left after hot line washing, and the surface iron scale is pressed in after cold rolling. Therefore, how to reduce the sticking roll defect of ferritic stainless steel hot rolling has become a problem to be solved. The application discloses a method for reducing the sticking roll defect of ferritic stainless steel hot rolling. The method effectively reduces the occurrence of the sticking roll defect by adjusting the hot rolling temperature, rolling speed and rolling pressure, and controlling the cooling speed and time. Through the above method, the linear roughness on the surface of the ferritic stainless steel caused by the sticking roll in the hot rolling is obviously reduced, and the linear roughness nonconformity rate is reduced from 3.2% to 0.8%, and the reduction amplitude reaches 75%.

Description

Technical Field

[0001] This invention relates to the fields of metallurgy and stainless steel production, and more particularly to a method for reducing the sticking defect of hot-rolled ferritic stainless steel. Background Technology

[0002] Ferritic stainless steel is a type of stainless steel material with excellent corrosion resistance and mechanical properties, widely used in petroleum, chemical, power, and shipbuilding industries. However, during hot rolling, due to factors such as rolling temperature, rolling speed, and rolling pressure, roll sticking defects often occur, forming linear roughness on the strip surface. In severe cases, the iron oxide scale within the linear roughness is difficult to remove by pickling on the hot wire, resulting in residual iron scale after hot wire washing, which is then pressed into the surface after cold rolling. Therefore, how to reduce roll sticking defects in hot-rolled ferritic stainless steel has become an urgent problem to be solved.

[0003] This invention discloses a method for reducing roll sticking defects in hot-rolled ferritic stainless steel. This method effectively reduces roll sticking defects and improves product quality and yield by adjusting the hot rolling temperature, rolling speed, and rolling pressure, as well as controlling the cooling rate and time. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a method for reducing the sticking defect of hot-rolled ferritic stainless steel rolls.

[0005] The purpose of this invention is achieved as follows: A method for reducing the sticking defects of hot-rolled ferritic stainless steel, comprising the following aspects: (1) Controlling the equiaxed crystal ratio: The equiaxed crystal ratio is controlled between 45-55%. On the one hand, electromagnetic stirring is used during continuous casting, and on the other hand, the hot-rolled finishing temperature is controlled as follows: the finishing temperature is 1050-1080℃, and the final rolling temperature is 900-940℃, so that the finishing process is located in the austenite-ferrite two-phase region; (2) Roll material selection: Ensure that the working rolls of the last two to three stands of the continuous rolling mill are made of M2 high-speed steel rolls; (3) Using emulsion for roll gap lubrication: The emulsion needs to be evenly covered on the roll surface, the emulsion concentration is 5-8%, the water pressure is 3-5 bar, and the total flow rate is 50-100 m³ / h. 3 / h; (4) Strictly control the roll temperature: the roll temperature of the first three stands F1-F3: 300-400℃, the middle two stands F4-F5: 250-300℃, and the last two stands F6-F7: 200-280℃. The inlet and outlet cooling water flow rate is controlled at 5000-8000m³ / h. 3 / h, water pressure: 1-2 bar; (5) Control the rolling speed and deformation rate of each pass: the rolling speed is 1.2~2.0m / s, the deformation rate of the first stand of the finishing mill is 40-50%, the deformation rate of the second and third stands is 30-40%, the deformation rate of the fourth and fifth stands is 20-30%, the deformation rate of the sixth stand is 20-25%, and the deformation rate of the seventh stand is 15-20%.

[0006] (1) The current of the electromagnetic stirring is 1650-1800A, the stirring frequency is 4.5-6.0HZ, and the electromagnetic stirring reversal time is 50-60 seconds.

[0007] The beneficial effects of the present invention are: by using the above method, the linear roughness on the surface of ferritic stainless steel caused by sticking to the hot rolling roller is significantly reduced, and the linear roughness non-compliance rate is reduced from 3.2% to 0.8%, a reduction of 75%. Attached Figure Description

[0008] The present invention will now be further described with reference to the accompanying drawings.

[0009] Figure 1 This is the equilibrium phase diagram of ferrite and austenite of the present invention.

[0010] Figure 2 These are diagrams showing the sticking of rolls made of different materials during hot rolling. Detailed Implementation

[0011] This invention proposes a method to reduce the sticking defect of hot-rolled ferritic stainless steel. The method mainly includes the following steps: 1. Controlling the equiaxed grain ratio: To ensure that ferritic stainless steel does not stick to the rolls during hot rolling, the equiaxed grain ratio is generally controlled between 45-55%. On the one hand, electronic stirring must be used during continuous casting, with an electromagnetic stirring current of 1650-1800A, a stirring frequency of 4.5-6.0HZ, and an electromagnetic stirring reversal time of 50-60 seconds. On the other hand, to obtain more restored equiaxed grain structures, a reasonable hot-rolling finishing temperature also needs to be controlled.

[0012] Based on the equilibrium phase diagram, the hot-rolled finishing mill process is formulated as follows: finishing mill inlet temperature 1050-1080℃, finishing mill temperature 900-940℃. This ensures that the finishing mill process is located in the austenite-ferrite two-phase region, resulting in high elongation and facilitating smooth rolling.

[0013] 2. Roll Material Selection: Tests show that the material of the hot rolling work rolls has a significant impact on hot rolling roll sticking. From... Figure 2 It can be seen that the sticking of M2 high-speed steel rolls is least pronounced after rolling time exceeds 10 minutes. Therefore, to ensure the surface quality of the strip, at least the last two to three stands of the continuous rolling mill should use M2 high-speed steel rolls.

[0014] 3. Use emulsion for roll gap lubrication. The emulsion evenly covers the roll surface, reducing friction and heat during rolling and decreasing the adhesion between the material and the roll, effectively preventing roll sticking. The emulsion concentration is generally controlled at 5-8%, water pressure at 3-5 bar, and total flow rate at 50-100 m³ / h. 3 / h.

[0015] 4. Strictly control roll temperature. Excessive roll temperature will cause the oxide film on the roll surface to melt, accelerating roll wear, affecting strip shape control during rolling, and even leading to problems such as steel sticking and strip breakage. Conversely, excessively low roll temperature will increase the coefficient of friction during rolling, increasing rolling torque and easily causing mill chatter, affecting the stability of the rolling process. To ensure a good strip surface, the roll temperature should be: 300-400℃ for the first three stands (F1-F3), 250-300℃ for the middle two stands (F4-F5), and 200-280℃ for the last two stands (F6-F7). The inlet and outlet cooling water flow rate should be controlled at 5000-8000 m³ / h. 3 / h, water pressure: 1-2 bar.

[0016] 5. Control rolling speed and deformation rate of each pass: Control the rolling speed within the range of 1.2 m / s to 2.0 m / s to ensure uniform temperature distribution of the steel during the rolling process and reduce roll sticking caused by localized overheating. The deformation rate is 40-50% for the first stand of the finishing mill, 30-40% for the second and third stands, 20-30% for the fourth and fifth stands, 20-25% for the sixth stand, and 15-20% for the seventh stand. This deformation rate design ensures uniform deformation of the steel during the rolling process and reduces roll sticking caused by stress concentration. Example 1

[0017] Steel grade: SUS430, continuous casting billet thickness: 200mm, hot rolling thickness: 3.0mm.

[0018] 1. Electromagnetic stirring is used in continuous casting. The electromagnetic stirring current is 1700A, the stirring frequency is 5.0HZ, the electromagnetic stirring reversal time is 50 seconds, the hot rolling finishing mill inlet temperature is 1075℃, the finishing mill temperature is 930℃, and the equiaxed crystal ratio is over 48%.

[0019] 2.7 The work rolls of the last three stands of the finishing mill, F5, F6 and F7, are made of M2 high-speed steel rolls.

[0020] 3. All finishing mill units use emulsion for roll gap lubrication. The emulsion concentration is 6.5%, the water pressure is 5 bar, and the total flow rate is 90 m³ / s. 3 / h.

[0021] 4. The temperature, cooling water flow rate, and cooling water pressure of the work rolls of each stand in the finishing mill are controlled as shown in the table below.

[0022]

[0023] Results: The above methods significantly reduced the linear roughness on the surface of ferritic stainless steel caused by sticking to the hot rolling rollers, and the linear roughness non-compliance rate decreased from 3.2% to 0.6%. Example 2

[0024] Steel grade: SUS430, continuous casting billet thickness: 200mm, hot rolling thickness: 5.0mm.

[0025] 1. Electromagnetic stirring is used in continuous casting. The electromagnetic stirring current is 1650A, the stirring frequency is 6.0HZ, the electromagnetic stirring reversal time is 55 seconds, the hot rolling finishing mill inlet temperature is 1070℃, the finishing mill temperature is 935℃, and the equiaxed crystal ratio is over 50%.

[0026] 2.7 The work rolls of the last three stands of the finishing mill, F5, F6 and F7, are made of M2 high-speed steel rolls.

[0027] 3. All finishing mill units use emulsion for roll gap lubrication. The emulsion concentration is 6.0%, the water pressure is 4.0 bar, and the total flow rate is 82 m³ / s. 3 / h.

[0028] 4. The temperature, cooling water flow rate, and cooling water pressure of the work rolls of each stand in the finishing mill are controlled as shown in the table below.

[0029]

[0030] Results: The above methods significantly reduced the linear roughness on the surface of ferritic stainless steel caused by sticking to the hot rolling rollers, and the linear roughness non-compliance rate decreased from 3.2% to 0.2%.

[0031] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for reducing the sticking defect of hot-rolled ferritic stainless steel, characterized in that: Including the following aspects: (1) Control the proportion of equiaxed crystals: The proportion of equiaxed crystals is controlled between 45-55%. On the one hand, electromagnetic stirring is used in the continuous casting process, and on the other hand, the hot rolling finishing temperature is controlled as follows: the finishing rolling inlet temperature is 1050-1080℃, and the finishing rolling temperature is 900-940℃, so that the finishing rolling process is located in the austenite-ferrite two-phase region. (2) Selection of roll material: Ensure that the work rolls of the last two to three stands of the continuous rolling mill are made of M2 high-speed steel rolls; (3) Use emulsion for roll gap lubrication: The emulsion should be evenly covered on the roll surface, with an emulsion concentration of 5-8%, a water pressure of 3-5 bar, and a total flow rate of 50-100 m³ / h. 3 / h; (4) Strictly control the roll temperature: the roll temperature for the first three stands F1-F3 is 300-400℃, for the middle two stands F4-F5 it is 250-300℃, and for the last two stands F6-F7 it is 200-280℃. The inlet and outlet cooling water flow rate is controlled at 5000-8000 m³ / h. 3 / h, water pressure: 1-2 bar; (5) Control the rolling speed and deformation rate of each pass: The rolling speed is 1.2 to 2.0 m / s, the deformation rate of the first stand of the finishing mill is 40-50%, the deformation rate of the second and third stands is 30-40%, the deformation rate of the fourth and fifth stands is 20-30%, the deformation rate of the sixth stand is 20-25%, and the deformation rate of the seventh stand is 15-20%; (1) The current of the electromagnetic stirring is 1650-1800A, the stirring frequency is 4.5-6.0HZ, and the electromagnetic stirring reversal time is 50-60 seconds.

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