A method for improving the edge scale of cold-rolled stock

Abstract

The application discloses a method for improving the edge scale of a cold-rolled raw material, which comprises the following steps: in a heating process, heating a slab and discharging the slab from a furnace, the discharging temperature is 1140-1180 DEG C, the holding time in the furnace is 140-200 min, and the heating atmosphere is weak oxidizing atmosphere; in a rolling process, the discharged slab is subjected to multi-point descaling and rough rolling, the rough rolling adopts a 3+5 rolling mode, the R1 rough rolling rack is rolled for 3 passes, the R2 rough rolling rack is rolled for 5 passes, and the descaling passes are 6-8 passes, so as to obtain an intermediate blank; the intermediate blank is subjected to descaling and finish rolling, the ultra-high pressure water is used for descaling, and a finish-rolled plate is obtained; and in an acid pickling process, the finish-rolled plate is subjected to acid pickling, and the straightening elongation is 1.2-1.7%. Through the low discharging temperature, rolling and increased straightening elongation, the thickness of the edge scale of the strip steel is reduced, the acid pickling effect of the edge of the hot-rolled strip steel is improved, and the surface quality of the product is improved.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and more specifically, to a method for improving the edge sheet of cold-rolled raw materials. Background Technology

[0002] Hot rolling is a rolling process performed above the recrystallization temperature, typically between 1180℃ and 1280℃. Due to the uneven distribution of temperature and oxygen fields during the hot rolling process and after coiling, there are differences in the iron oxide scale between the edges and the center of the strip. The iron oxide scale near the edges is structurally complete and dense, with good bonding to the matrix; while the iron oxide scale near the center is loose, with numerous fine cracks inside, and locally broken and peeled off from the matrix. The iron oxide scale at the edges of the strip is about 40mm thick, but its structure is relatively dense, with a higher Fe3O4 content than in the center. The iron oxide scale in the center of the strip is mainly FeO, and is loose and porous.

[0003] During pickling, the FeO in the middle of the strip is porous, allowing the acid to peel off easily, resulting in high pickling efficiency. However, the iron scale at the edges, primarily composed of Fe3O4 with a dense structure, is chemically dissolved by the acid, leading to low pickling efficiency. Under the same pickling process, the areas that are preferentially pickled remain in continuous contact with the acid, resulting in "over-pickling" and the formation of numerous "erosion cracks" on the strip surface, causing blackening defects. To control over-pickling, the pickling process is usually stopped after the middle is pickled, but the edges are not yet pickled, resulting in edge iron oxide scale defects.

[0004] Therefore, the thickness and transverse differences in the structure of the iron oxide scale on hot-rolled strip are among the main factors contributing to the residual iron oxide scale on both sides of the strip after pickling. Currently, there is an urgent need for a method to improve the iron oxide scale on the edges of the raw materials supplied for cold rolling, so as to reduce the residual iron oxide scale and improve the surface quality of the product after pickling. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a method to improve the edge iron scale of cold-rolled raw materials. By using low furnace exit temperature, low temperature rolling, and increasing the stretching elongation, the thickness of the iron oxide scale on the edge of the strip is reduced, thereby improving the pickling effect of the hot-rolled strip edge and improving the surface quality of the product.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for improving the edge scale of cold-rolled raw materials includes the following steps: In the heating process, the slab is heated and then taken out of the furnace at a temperature of 1140℃~1180℃, with a furnace time of 140min~200min, and the heating atmosphere is a weak oxidizing atmosphere. In the rolling process, the heated steel billet undergoes multi-point descaling and rough rolling. The rough rolling adopts a 3+5 rolling mode, with 3 passes on the R1 roughing mill stand and 5 passes on the R2 roughing mill stand. Descaling takes 6 to 8 passes, yielding an intermediate billet with a thickness of 40mm to 45mm. The intermediate billet then undergoes descaling and finish rolling, using ultra-high pressure water descaling at a flow rate of 275m³ / h. 3 / h~285m 3 / h, to obtain a finely rolled plate; In the pickling process, the precision rolled plate is pickled, and the tensile elongation is 1.2%~1.7%.

[0007] Optionally, in the rough rolling process, the descaling pressure for each pass is 21 MPa to 23 MPa; and the descaling time for each pass is 12 to 20 seconds.

[0008] Optionally, in the rough rolling, the rolling speed per pass is 3.8 m / s to 4.6 m / s, and the total reduction rate is 74% to 87%.

[0009] Optionally, in the finishing rolling process, the descaling pressure of the ultra-high pressure water descaling is 34 MPa to 38 MPa; and the finishing rolling descaling time is 55 s to 70 s.

[0010] Optionally, in the finishing rolling process, the entry temperature of the finishing rolling is 960℃~1020℃, and the final rolling temperature is controlled at 900℃~930℃.

[0011] Optionally, in the roughing process, the initial rolling temperature is 1140°C~1180°C, and the exit temperature is 980°C~1040°C.

[0012] Optionally, the thickness of the slab is 225mm~235mm.

[0013] Optionally, the pickling speed in the pickling process is 100mpm~220mpm, and the pickling time is 2.5min~5.5min.

[0014] Implementing the embodiments of the present invention will have the following beneficial effects: This invention adjusts a complete set of heating and rolling processes, including furnace exit temperature, furnace time, rough rolling passes, rough descaling, ultra-high pressure descaling, and tension leveling elongation, to reduce the thickness of iron oxide scale on the slab through low-temperature heating. Simultaneously, the low-temperature slab undergoes multiple descaling water injections to suppress the formation of secondary iron oxide scale, further reducing the thickness of iron oxide scale on the surface of the cold-rolled raw material through the impact of ultra-high pressure descaling water. Furthermore, increasing the tension leveling elongation improves the descaling effect, effectively addressing the quality problem of residual iron oxide scale on the edges of the cold-rolled raw material. Attached Figure Description

[0015] Figure 1The image shows a finished pickled product obtained without using the method of improving the edge sheet of cold-rolled raw materials according to the present invention.

[0016] Figure 2 The image shows a finished pickled product obtained by using the method of improving the edge sheet of cold-rolled raw materials according to the present invention.

[0017] Figure 3 The image shows a finished product obtained without employing the method of improving the edge sheet of cold-rolled raw materials according to the present invention.

[0018] Figure 4 This is a photograph of a finished product obtained by using the method of improving the edge sheet of cold-rolled raw materials according to the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0020] Hot-rolled strip steel is produced under high-temperature conditions, resulting in a layer of iron oxide scale on its surface. For further processing and use, pickling is used during deep processing to remove this scale. The pickling process is primarily based on three mechanisms: dissolution, mechanical stripping, and reduction. When the acid solution comes into contact with the iron oxide scale, it reacts and dissolves the scale, a process known as dissolution. When the acid solution penetrates the steel substrate along the gaps in the iron oxide scale, it reacts with the substrate to produce hydrogen gas. The expansion pressure of the hydrogen gas forces the iron oxide scale to detach from the steel surface; approximately 33% of the iron oxide scale is removed in this way, a process known as mechanical stripping. Furthermore, because hydrogen gas has a strong reducing power, high-valence iron oxides are reduced to low-valence oxides, accelerating the dissolution process, a process known as reduction. Due to the uneven thickness and structure of the transverse iron oxide scale on hot-rolled strip steel, pickling at the edges of the strip steel is not completely completed, resulting in edge scale.

[0021] Based on the above analysis, this invention discloses a method for improving the edge sheet of cold-rolled raw materials, comprising the following steps: S1. In the heating process, a low-temperature, rapid, and weakly oxidizing atmosphere is used for control. The slab is heated and then taken out of the furnace at a temperature of 1140℃~1180℃. The furnace time is 140min~200min. The heating atmosphere is a weakly oxidizing atmosphere to reduce the amount of iron oxide scale generated and improve the peelability of iron oxide scale from the steel plate substrate.

[0022] S2. In the rolling process, the heated steel billet is descaled at multiple points and rough rolled. The rough rolling adopts a 3+5 rolling mode, with 3 passes on the R1 rough rolling stand and 5 passes on the R2 rough rolling stand. The descaling passes are 6 to 8 times to increase the descaling time and obtain an intermediate billet with a thickness of 40mm to 45mm.

[0023] S3. Descaling and finishing rolling of the intermediate billet is performed using ultra-high pressure water descaling at a flow rate of 275 m³ / h. 3 / h~285m 3 / h, to obtain a finely rolled plate.

[0024] Specifically, this invention increases the heat exchange rate between the slab and the air, increasing the temperature drop by 20°C to 30°C. Under the premise of ensuring rolling stability, it rolls at the lowest possible temperature, reducing the thickness of the iron oxide scale after rolling.

[0025] S4. In the pickling process, the high-rolled plate is pickled, and the elongation at the tension level is 1.2%~1.7%. This invention controls the elongation by increasing the tension leveling rate. The tension leveler breaks down the surface iron sheet structure through mechanical bending, creating cracks that facilitate the penetration of acid and accelerate pickling efficiency. By increasing the elongation at the tension level to 1.2%~1.7%, the scale-breaking effect is enhanced, causing the edge iron sheet to break deeply and create cracks, thus improving the pickling effect.

[0026] In one specific embodiment, during rough rolling, the descaling pressure for each pass is 21 MPa to 23 MPa; the descaling time for each pass is 12 s to 20 s.

[0027] In one specific embodiment, during rough rolling, the rolling speed per pass is 3.8 m / s to 4.6 m / s, and the total reduction rate is 74% to 87%.

[0028] In one specific embodiment, during the finishing rolling process, the descaling pressure of the ultra-high pressure water descaling is 34 MPa to 38 MPa; the finishing rolling descaling time is 55 s to 70 s.

[0029] In one specific embodiment, during finishing rolling, the entry temperature is 960℃~1020℃, and the final rolling temperature is controlled at 900℃~930℃.

[0030] In one specific embodiment, during rough rolling, the initial rolling temperature is 1140~1180°C, and the exit temperature is 980°C~1040°C.

[0031] In one specific embodiment, the thickness of the slab is 225mm~235mm.

[0032] In one specific embodiment, the pickling speed in the pickling process is 100mpm~220mpm, and the pickling time is 2.5min~5.5min.

[0033] Specifically, with lower furnace exit temperature and lower temperature rolling, the thickness of the iron oxide scale on the strip surface gradually decreases, which is conducive to pickling. At the same time, by increasing the tension leveling effect, the iron oxide scale on the surface is broken, which is also conducive to the pickling process, and the surface quality of the product is improved.

[0034] The following are specific embodiments. Examples 1-10 The present invention employs a heating process, rolling process, descaling and finishing rolling, and pickling in a low-temperature, rapid, and weakly oxidizing atmosphere to improve the edge scale of the cold-rolled raw material.

[0035] Table 1 Heating process parameters for Examples 1-10

[0036] Table 2 Roughing process parameters for Examples 1-10

[0037] Table 3. Finishing rolling and pickling process parameters for Examples 1-10

[0038] This invention adjusts the heating, rolling, and pickling processes, including furnace exit temperature, furnace time, rough rolling passes, rough descaling, ultra-high pressure descaling, and tension leveling elongation. The slab is heated at a low temperature to reduce the thickness of the iron oxide scale. At the same time, the low-temperature slab undergoes multiple descaling water treatments to inhibit the formation of secondary iron oxide scale. The impact of ultra-high pressure descaling water further reduces the thickness of the iron oxide scale on the surface of the cold-rolled raw material. Meanwhile, by increasing the tension leveling elongation, the descaling effect is improved, effectively addressing the quality problem of residual iron scale on the edges of the cold-rolled raw material.

[0039] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for improving the edge scale of cold-rolled raw materials, characterized in that, Includes the following steps: In the heating process, the slab is heated and then taken out of the furnace at a temperature of 1140℃~1180℃, with a furnace time of 140min~200min, and the heating atmosphere is a weak oxidizing atmosphere. In the rolling process, the heated steel billet undergoes multi-point descaling and rough rolling. The rough rolling adopts a 3+5 rolling mode, with 3 passes on the R1 roughing mill stand and 5 passes on the R2 roughing mill stand. Descaling takes 6 to 8 passes, yielding an intermediate billet with a thickness of 40mm to 45mm. The intermediate billet then undergoes descaling and finish rolling, using ultra-high pressure water descaling at a flow rate of 275m³ / h. 3 / h~285m 3 / h, to obtain a finely rolled plate; In the pickling process, the precision-rolled plate is pickled, and the tensile elongation is 1.2%~1.7%; In the rough rolling process, the descaling pressure for each pass is 21 MPa to 23 MPa; the descaling time for each pass is 12 to 20 seconds. In the roughing process, the rolling speed per pass is 3.8 m / s to 4.6 m / s, and the total reduction rate is 74% to 87%. In the finishing rolling process, the descaling pressure of ultra-high pressure water descaling is 34 MPa to 38 MPa; the descaling time is 55 s to 70 s.

2. The method for improving the edge sheet of cold-rolled raw materials according to claim 1, characterized in that, In the finishing rolling process, the entry temperature is 960℃~1020℃, and the final rolling temperature is controlled at 900℃~930℃.

3. The method for improving the edge sheet of cold-rolled raw materials according to claim 1, characterized in that, In the roughing process, the initial rolling temperature is 1140°C to 1180°C, and the exit temperature is 980°C to 1040°C.

4. The method for improving the edge sheet of cold-rolled raw materials according to claim 1, characterized in that, The thickness of the slab is 225mm~235mm.

5. The method for improving the edge sheet of cold-rolled raw materials according to claim 1, characterized in that, The pickling process has a pickling speed of 100mpm~220mpm and a pickling time of 2.5min~5.5min.

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