Method for reducing pulverization and peeling of oxide scale on surface of hot-rolled high-strength wheel steel

Abstract

The invention discloses a method for reducing pulverization and peeling of oxide scale on the surface of hot-rolled high-strength wheel steel, and belongs to the technical field of steel rolling. The method comprises the steps of casting blank heating, descaling after a heating furnace, rough rolling, high-pressure water descaling before finish rolling, finish rolling, cooling and coiling. In the finish rolling procedure, the finish rolling inlet temperature is smaller than or equal to 1010 DEG C, cooling water ISC between racks of F1 to F4 is opened, the water amount is 30% to 60%, the finish rolling temperature is 830 DEG C to 850 DEG C, and the finish rolling threading speed Vt is determined according to the thickness h of a finished wheel steel product: when h is smaller than or equal to 5 mm, Vt is larger than or equal to 5.5 m / s; and when h is greater than or equal to 10mm, Vt is greater than or equal to 3.1 m / s. According to the method, the eutectoid reaction of the scale on the surface of the strip steel is controlled through the hot rolling process, so that the structure of the scale is controlled, the final microstructure of the scale is a compact structure, and the problem that the scale is pulverized and peeled off is effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling, and in particular relates to a method for reducing the powdering and peeling of iron oxide scale on the surface of hot-rolled high-strength wheel steel. Background Art

[0002] Wheels are important safety components for automobiles. Steel wheels are made from steel plates through a series of strict manufacturing processes such as rolling or spinning, welding, and painting. They have the advantages of high precision, light weight, long fatigue life, and reliable safety. At the same time, as an automotive exterior component, wheels have very strict surface quality requirements. There must not be defects such as pits and dents on the surface. Surface defects can not only affect the appearance of the product, but surface damage also has a great impact on the service performance of the material. Usually, high-strength wheel steel controls the thickness of the surface oxide scale by lowering the heating temperature, increasing the descaling pressure, and reducing the silicon content; however, during use, it was found that the oxide scale was powdered and peeled off. During the unwinding stage of the steel coil, the shed iron oxide powder gathers and adheres to the unwinding roller. The shed iron oxide will also gather during the processing and transportation of the sheet. Due to the high hardness of the iron oxide, the gathered iron oxide will form pits or pits on the surface of the steel plate under pressure. During the processing, the powdered and shed iron oxide increases the friction between the mold and the plate, affecting the rolling quality of the rim material and the spinning quality of the spoke material, causing surface pits and other defects, seriously affecting the quality of the finished wheel. At the same time, it will also cause mold damage and affect the service life of the mold. Severe surface defects cause the product to be scrapped. Minor defects caused by the powdering and shedding of iron oxide must be repaired later, which not only increases costs but also reduces production efficiency. Therefore, the powdering and peeling of iron oxide on the surface of hot-rolled high-strength wheel steel has become a difficult problem that needs to be solved urgently in the field of hot-rolled wheel steel technology. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for reducing the powdering and peeling of iron oxide scale on the surface of hot-rolled high-strength wheel steel. The technical solution adopted by the present invention is: A method for reducing the powdering and flaking of iron oxide scale on the surface of hot-rolled high-strength wheel steel, comprising the steps of heating the ingot, descaling after the heating furnace, rough rolling, descaling with high-pressure water before finishing rolling, finishing rolling, cooling, and coiling; In the finishing process, the finishing inlet temperature is ≤1010°C, the inter-stand cooling water ISC of F1-F4 is turned on, the water volume is 30-60%, the final rolling temperature is 830-850°C, and the finishing rolling threading speed V t Determined according to the finished wheel steel thickness h: When h≤5.0mm, V t ≥5.5m / s; when h≥10mm, V t ≥3.1m / s.

[0004] Furthermore, in the casting heating process, the total furnace residence time of the casting is 180 to 240 minutes; the residence time of the casting in the third heating section and the soaking section is 60 to 75 minutes; and the steel tapping temperature is 1220 to 1260°C.

[0005] Furthermore, in the descaling process after the heating furnace, double header descaling is used, and the descaling pressure is greater than 23MPa.

[0006] Furthermore, in the rough rolling process, the two rough rolling mills R1 and R2 adopt a 1+5-pass rolling mode, that is, the steel plate is rolled by the first rough rolling mill R1 and the second rough rolling mill R2 in sequence, the first rough rolling mill R1 rolls the steel plate in one pass, and the second rough rolling mill R2 rolls the steel plate in five passes; the rough rolling outlet temperature is controlled at 1040-1080°C, the rough rolling inlet descaling pressure is greater than 23MPa, and the intermediate billet thickness is 35-45mm.

[0007] Furthermore, in the high-pressure water descaling process before finishing rolling, double header descaling is used, and the descaling pressure is greater than 23 MPa.

[0008] Furthermore, the cooling process adopts a front-stage cooling process, the middle point temperature is controlled at 500-680°C, and the cooling rates of the two terminal stages are controlled at 20-40°C / s.

[0009] Furthermore, in the coiling process, the coiling temperature is 460-600° C., a fan is used during the coiling process, and the steel coils are stacked in a ventilated place after coiling.

[0010] Furthermore, the Fe 3 O 4 Area ratio ≥65%.

[0011] Furthermore, the components of the wheel steel and their mass percentages are: C: 0.07-0.10%, Si: 0.06-0.15%, Mn: 1.0-1.85%, P < 0.015%, S ≤ 0.005%, Nb: 0.030-0.060%, Ti: 0.015-0.030%, Cr ≤ 0.5%, A1: 0.015-0.050%, and the remainder is Fe and unavoidable impurities.

[0012] Furthermore, the finished hot-rolled high-strength wheel steel product has a thickness h in two thickness ranges of 3.5 mm to 5.0 mm and 10 to 13 mm.

[0013] The beneficial effects of the above technical solution are as follows: the present invention controls the eutectoid reaction of the iron oxide scale on the surface of the strip through the hot rolling process, thereby controlling the structure of the iron oxide scale, so that the final iron oxide scale microstructure is a dense structure, and the Fe content of the third iron oxide scale on the surface of the hot-rolled high-strength wheel steel product is3 O 4 The ratio is ≥65%, which effectively solves the problem of iron oxide scale powdering and peeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a cross-sectional structure diagram of the iron oxide scale on the surface of hot-rolled high-strength wheel steel produced by conventional process; Figure 2 This is a cross-sectional structural diagram of a typical iron oxide scale on the surface of the hot-rolled high-strength wheel steel obtained in the present invention. DETAILED DESCRIPTION

[0015] The hot-rolled steel billets in each embodiment were cast into billets with a thickness of 230 mm. The chemical composition and mass percentage of the cast billets are shown in Table 1.

[0016] The heating process of each embodiment adopts a regenerative heating furnace, and descaling is performed after the furnace. The rough rolling equipment consists of two rough rolling mills, and descaling is performed at the rough rolling entrance. The finishing rolling equipment consists of 7 finishing mills. According to the rolling direction, the 7 finishing mills are numbered F1, F2, F3, F4, F5, F6, and F7 in sequence. Descaling is performed at the finishing rolling entrance. The post-rolling cooling process adopts a laminar cooling process with ultra-fast cooling, and the coiling process adopts a down coiler.

[0017] Embodiment 1: The ingot with chemical composition and mass percentage as described in Table 1 is placed in a heating furnace for heating for 240 minutes. The ingot stays in the third heating section and the soaking section for 75 minutes. The steel is discharged after heating to 1260°C. After heating, the slab is descaled by 29MPa double-pipe high-pressure water after the furnace, and then rough rolled. The descaling pressure at the entrance of rough rolling is 25MPa. R1 / R2 uses 1+5 passes. After R2 rolling, the intermediate billet thickness is 35mm, and the rough rolling outlet temperature RDT is 1080°C; the finishing rolling inlet temperature is 1010°C, the finishing rolling threading speed is 7.2m / s, the ISC of F1~F4 is turned on, the water volume is 30%, the finishing rolling outlet thickness is 3.5mm, and the final rolling temperature is 850°C; the cooling mode is the front-end cooling process, the midpoint temperature is 680°C, and the cooling rate of the two end sections is 40°C / s. The coiling temperature is 600°C, and the fan is put into the coiling process with an air volume of 40000m 3 / h, wind pressure is 270Pa, and steel coils are stacked in a ventilated place.

[0018] After testing, the Fe content of the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product obtained in this embodiment is 3 O 4 The proportion is 68%.

[0019] Embodiment 2: The ingot with chemical composition and mass percentage as described in Table 1 is placed in a heating furnace for heating for 180 minutes. The ingot stays in the third heating section and the soaking section for 60 minutes. The steel is discharged after heating to 1220°C. After heating, the slab is descaled by 25MPa double-pipe high-pressure water after the furnace, and then rough rolled. The descaling pressure at the entrance of rough rolling is 24MPa. R1 / R2 uses 1+5 passes. After R2 rolling, the intermediate billet thickness is 45mm, and the rough rolling outlet temperature RDT is 1040°C; the finishing rolling inlet temperature is 970°C, the finishing rolling threading speed is 3.1m / s, the ISC of F1~F4 is turned on, the water volume is 60%, the finishing rolling outlet thickness is 13mm, and the final rolling temperature is 830°C; the cooling mode is the front-end cooling process, the midpoint temperature is 500°C, and the cooling rate of the two end sections is 20°C / s. The coiling temperature is 460°C, and a fan is put into the coiling process with an air volume of 40000m 3 / h, wind pressure is 270Pa, and steel coils are stacked in a ventilated place.

[0020] After testing, the Fe content of the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product obtained in this embodiment is 3 O 4 The proportion is 67%.

[0021] Embodiment 3: The ingot with chemical composition and mass percentage as described in Table 1 is placed in a heating furnace for heating for 210 minutes. The ingot stays in the third heating section and the soaking section for 70 minutes. The steel is discharged after heating to 1240°C. After heating, the slab is descaled by 24MPa double-pipe high-pressure water after the furnace, and then rough rolled. The descaling pressure at the entrance of rough rolling is 26MPa. R1 / R2 uses 1+5 passes. After R2 rolling, the intermediate billet thickness is 39mm, and the rough rolling outlet temperature RDT is 1060°C; the finishing rolling inlet temperature is 1000°C, the finishing rolling threading speed is 5.5m / s, the ISC of F1~F4 is turned on, the water volume is 45%, the finishing rolling outlet thickness is 5mm, and the final rolling temperature is 850°C; the cooling mode is the front-end cooling process, the midpoint temperature is 590°C, and the cooling rate of the two end sections is 30°C / s. The coiling temperature is 570°C, and the fan is put into the coiling process with an air volume of 40000m 3 / h, wind pressure is 270Pa, and steel coils are stacked in a ventilated place.

[0022] After testing, the Fe content of the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product obtained in this embodiment is 3 O 4 The proportion is 72%.

[0023] Embodiment 4: The ingot with chemical composition and mass percentage as described in Table 1 is placed in a heating furnace for heating for 230 minutes. The ingot stays in the third heating section and the soaking section for 60 minutes. The steel is discharged after heating to 1220°C. After heating, the slab is descaled by 26MPa double-pipe high-pressure water and then rough rolled. The descaling pressure at the entrance of rough rolling is 23.5MPa. R1 / R2 uses 1+5 passes. After R2 rolling, the intermediate billet thickness is 45mm, and the rough rolling outlet temperature RDT is 1060°C; the finishing rolling inlet temperature is 980°C, the finishing rolling threading speed is 3.8m / s, the ISC of F1~F4 is turned on, the water volume is 60%, the finishing rolling outlet thickness is 10mm, and the final rolling temperature is 830°C; the cooling mode is the front-stage cooling process, the midpoint temperature is 550°C, and the cooling rate of the two final stages is 25°C / s. The coiling temperature is 460°C, and a fan is put into the coiling process with an air volume of 40000m 3 / h, wind pressure is 270Pa, and steel coils are stacked in a ventilated place.

[0024] After testing, the Fe content of the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product obtained in this embodiment is 3 O 4 The ratio is 70%.

[0025] Embodiment 5: The ingot with chemical composition and mass percentage as described in Table 1 is placed in a heating furnace for heating for 210 minutes. The ingot stays in the third heating section and the soaking section for 68 minutes. The steel is discharged after heating to 1240°C. After heating, the slab is descaled by 23.5MPa double-pipe high-pressure water after furnace descaling and then rough rolled. The descaling pressure at the entrance of rough rolling is 26MPa. R1 / R2 uses 1+5 passes. After R2 rolling, the intermediate billet thickness is 45mm, and the rough rolling outlet temperature RDT is 1050°C; the finishing rolling inlet temperature is 980°C, the finishing rolling threading speed is 3.5m / s, the ISC of F1~F4 is turned on, the water volume is 50%, the finishing rolling outlet thickness is 12mm, and the final rolling temperature is 830°C; the cooling mode is the front-end cooling process, the midpoint temperature is 500°C, and the cooling rate of the two end sections is 20°C / s. The coiling temperature is 460°C, and the fan is put into the coiling process with an air volume of 40000m 3 / h, wind pressure is 270Pa, and steel coils are stacked in a ventilated place.

[0026] After testing, the Fe content of the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product obtained in this embodiment is 3 O 4 The proportion is 66%. Example

[0027] The ingot with chemical composition and mass percentage as shown in Table 1 is placed in a heating furnace for heating. 240 minutes, the ingot stays in the third heating section and the soaking section for 75 minutes, and the heating temperature reaches 1250℃ for steelmaking. After heating, the slab is descaled by 25.5MPa double-pipe high-pressure water after furnace descaling and then rough rolled. The descaling pressure at the entrance of rough rolling is 25MPa, and R1 / R2 uses 1+5 passes. After R2 rolling, the thickness of the intermediate billet is 38 mm, and the rough rolling outlet temperature RDT is 1075℃; the finishing rolling inlet temperature is 1000℃, the finishing rolling threading speed is 6.2m / s, the ISC of F1~F4 is turned on, the water volume is 45%, the finishing rolling outlet thickness is 4.0mm, and the final rolling temperature is 845℃; the cooling mode is the front-stage cooling process, the midpoint temperature is 650℃, and the cooling rate of the two stages at the end is 35℃ / s. The coiling temperature is 580℃, and the fan is put into the coiling process with an air volume of 40000m 3 / h, wind pressure is 270Pa, and steel coils are stacked in a ventilated place.

[0028] After testing, the Fe content of the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product obtained in this embodiment is 3 O 4 The ratio is 73 %.

[0029] Table 1 Chemical composition and mass percentage of the ingots in each embodiment (%)

[0030] In Table 1, the balance is Fe and unavoidable impurities.

[0031] Depend on Figure 1 It can be seen that the structure of the strip iron scale cross section produced by the original process is mainly composed of Fe 3 O 4 , FeO and a small amount of eutectoid phase, of which FeO accounts for about 45-52% and is distributed in large blocks. 3 O 4 The ratio is about 48-55%.

[0032] Depend on Figure 2 It can be seen that the typical structure of the cross section of the strip iron scale produced by the present invention is mainly composed of Fe 3 O 4 Composition, of which Fe 3 O 4 The proportion is about 68%.

[0033] Depend on Figure 1 , Figure 2 By comparison, the iron scale of the strip steel produced by the present invention is mainly composed of Fe 3 O 4 The composition of the iron oxide scale is dense, and there is no large-sized block FeO, which reduces the probability of powdering and peeling of the surface iron oxide scale in the subsequent processing.

Claims

1. A method for reducing the powdering and peeling of iron oxide scale on the surface of hot-rolled high-strength wheel steel, characterized in that: It includes the processes of heating the ingot, descaling after the heating furnace, rough rolling, descaling with high pressure water before finishing rolling, finishing rolling, cooling and coiling; In the finishing process, the finishing inlet temperature is ≤1010°C, the inter-stand cooling water ISC of F1-F4 is turned on, the water volume is 30-60%, the final rolling temperature is 830-850°C, and the finishing rolling threading speed V t Determined according to the finished wheel steel thickness h: When h≤5.0mm, V t ≥5.5m / s; when h≥10mm, V t ≥3.1m / s.

2. The method for reducing the powdering and flaking of iron oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 1, characterized in that: In the above-mentioned casting heating process, the total furnace residence time of the casting is 180 to 240 minutes; the furnace residence time of the casting in the third heating section and the soaking section is 60 to 75 minutes; and the steel tapping temperature is 1220 to 1260°C.

3. The method for reducing the powdering and flaking of iron oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 2, characterized in that: The descaling process after the heating furnace uses double headers for descaling, and the descaling pressure is greater than 23MPa.

4. The method for reducing the powdering and flaking of oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 3, characterized in that: In the rough rolling process, the two rough rolling mills R1 and R2 adopt a 1+5-pass rolling mode, the rough rolling outlet temperature is controlled at 1040-1080° C., the rough rolling inlet descaling pressure is greater than 23 MPa, and the intermediate billet thickness is 35-45 mm.

5. The method for reducing the powdering and flaking of iron oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 4, characterized in that: The high-pressure water descaling process before finishing rolling uses double headers for descaling, and the descaling pressure is greater than 23 MPa.

6. The method for reducing powdering and flaking of oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 5, characterized in that: The cooling process adopts a front-stage cooling process, the middle point temperature is controlled at 500-680°C, and the cooling rates of the two terminal stages are controlled at 20-40°C / s.

7. The method for reducing the powdering and flaking of iron oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 6, characterized in that: In the coiling process, the coiling temperature is 460-600° C., a fan is used during the coiling process, and the steel coils are stacked in a ventilated place after coiling.

8. The method for reducing the powdering and flaking of oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 7, characterized in that: The area ratio of Fe3O4 in the tertiary oxidation scale on the surface of the hot-rolled high-strength wheel steel product is ≥65%.

9. The method for reducing powdering and flaking of oxide scale on the surface of hot-rolled high-strength wheel steel according to any one of claims 1 to 8, characterized in that: The components of the wheel steel and their mass percentages are: C: 0.07-0.10%, Si: 0.06-0.15%, Mn: 1.0-1.85%, P < 0.015%, S ≤ 0.005%, Nb: 0.030-0.060%, Ti: 0.015-0.030%, Cr ≤ 0.5%, A1: 0.015-0.050%, and the balance is Fe and unavoidable impurities.

10. The method for reducing the powdering and flaking of oxide scale on the surface of hot-rolled high-strength wheel steel according to claim 9, characterized in that: The finished hot-rolled high-strength wheel steel has a thickness h of two ranges: 3.5 mm to 5.0 mm and 10 to 13 mm.

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