Method for improving black spot strips on surface of steel plate with self-reddening temperature lower than 650 DEG C

Abstract

The invention discloses a method for improving black spot strips on the surface of a steel plate with the self-reddening temperature lower than 650 DEG C. The method relates to the technical field of metallurgy and comprises the steps that a continuous casting blank is heated to the target temperature; after the heating time reaches a preset value, the continuous casting billets are discharged out of the furnace and enter a descaling box, and furnace oxide scale is removed; the continuous casting billet is conveyed to a roughing mill to be rolled, and descaling is conducted in the first pass, the third pass and the fifth pass; and the continuous casting billet is conveyed to a finishing mill to be rolled, and descaling is conducted in the first pass and the fourth pass. According to the method, descaling is conducted in the first pass, the third pass and the fifth pass of the continuous casting billet rough rolling procedure, descaling is conducted in the first pass and the fourth pass of the finish rolling procedure, the finish rolling descaling technology is optimized, the black spot defect of the surface of the steel plate is effectively overcome, the surface smoothness is improved, and the coating surface quality of a user product is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C. Background Art

[0002] As an important structural material, medium and thick plates are widely used in the fields of shipbuilding, bridges, construction and engineering machinery manufacturing. With the continuous development of these industries, higher requirements are put forward for the surface quality and performance uniformity of steel plates. At present, the color difference problem of "black spots" on the surface of medium and thick TMCP process steel plates seriously affects the performance, reliability and aesthetics of the products, and restricts the further development of related industries. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows: A method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C, comprising: heating the continuous casting slab to a target temperature; After the heating time reaches the preset value, the continuous casting billet is taken out of the furnace and enters the descaling box to remove the furnace-generated iron oxide scale; The continuous casting slab is conveyed to a rough rolling mill for rolling and descaling is performed in the first, third and fifth passes; The continuous casting slab is transported to the finishing mill for rolling and descaling is performed in the first and fourth passes.

[0005] As a preferred solution of the method for improving the black spots and stripes on the surface of the steel plate with a red-returning temperature lower than 650°C of the present invention, wherein: after the continuous casting billet is transported to the rough rolling mill for rolling and descaling is performed in the first pass, the third pass and the fifth pass, it also includes: The continuous casting billet is transported to the intermediate roller table for warming until it meets the second stage rolling temperature requirement.

[0006] As a preferred solution of the method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650° C. described in the present invention, the number of finishing passes is six.

[0007] As a preferred solution of the method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C described in the present invention, the target temperature for heating the continuous casting billet is 1220±30°C.

[0008] As a preferred solution of the method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C according to the present invention, the second-stage rolling temperature of the continuous casting billet is less than or equal to 870°C.

[0009] As a preferred solution of the method for improving the black spots and stripes on the surface of the steel plate with a red-returning temperature lower than 650°C described in the present invention, the final rolling temperature of the continuous casting billet is 820±20°C.

[0010] The beneficial effects of the present invention are: The present invention performs descaling in the first, third and fifth passes of the rough rolling process of the continuous casting slab, and performs descaling in the first and fourth passes of the finishing rolling process, thereby optimizing the finishing rolling descaling process, effectively improving the "black spot" defect on the surface of the steel plate, improving the surface smoothness, and improving the coating surface quality of the user's product. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0012] Figure 1 Location layout diagram of descaling equipment for rolling mill; Figure 2 It is a schematic diagram of the descaling process of the finishing mill; Figure 3 This is the configuration diagram of the rolling mill nozzle; Figure 4 A simulation diagram of descaling in a finishing mill; Figure 5 Microscopic image of iron sheet crushing for curing the overlapping area of ​​descaling notches; Figure 6 The overlapping broken area is further oxidized into a macroscopic image of "black spots"; Figure 7 The cross section of the iron oxide scale in the grayish white, dark black and gray areas (black spots) on the surface of different samples; Figure 8 The grayish white and dark black areas of the iron oxide scale of sample 1; Fig. 9 This is a schematic diagram of the surface results of Scheme 1 in Example 1; Fig.10 This is a schematic diagram of the surface results of Scheme 2 in Example 1; Fig.11 This is a schematic diagram of the surface results of Scheme 3 in Example 1. DETAILED DESCRIPTION

[0013] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation modes and in combination with the accompanying drawings.

[0014] The present application provides a method for improving black spots and stripes on the surface of a steel plate with a red-return temperature lower than 650°C, the method specifically comprising the following steps: Step S101: heating the continuous casting billet to a target temperature.

[0015] Specifically, the target temperature for heating the continuous casting slab is 1220±30°C.

[0016] Step S102: After the heating time reaches a preset value, the continuous casting billet is taken out of the furnace and enters a descaling box to remove the furnace-generated iron oxide scale.

[0017] Step S103: conveying the continuous casting billet to a rough rolling mill for rolling, and descaling the billet in the first, third and fifth passes.

[0018] It should be noted that after the continuous casting billet completes the rough rolling process, it is necessary to transport the continuous casting billet to the intermediate roller table for temperature waiting until the second stage rolling temperature requirement is met.

[0019] Step S104: conveying the continuous casting billet to a finishing mill for rolling, and descaling the billet in the first and fourth passes.

[0020] Specifically, the location layout of the descaling equipment for the finishing mill is as follows: Figure 1 As shown, the principle is that multiple nozzles are arranged in parallel with a certain deflection angle to remove the iron oxide scale on the surface of the incoming steel plate, see Figure 2 and Figure 3 During the descaling process, the descaling ability is weak in the overlapping area of ​​the notches. Figure 4 The first descaling in the first finishing rolling will result in the Fe2SiO4 formed in the critical layer between the oxide layer and the matrix not being completely removed, thus causing some FeO to adhere. The presence of Fe2SiO4 will reduce the heat transfer of the matrix, thus affecting the further deformation of FeO (the deformation capacity of FeO decreases as the surface temperature decreases, and the overlapping area belongs to the supercooling area. If the second and third finishing rolling passes are descaled, the FeO in the overlapping area will have poor plastic deformation and will break during the final rolling deformation process. Figure 5 , under the action of the roller cooling water, a low-temperature oxygen-poor structure is further formed). Therefore, the second descaling is set at the fourth rolling pass, waiting for the temperature of the overlap zone to rise, and the last pass is prohibited from being descaled (because the steel plate is at a lower temperature in the last pass, adding descaling will cause the overlap zone to be further overcooled, and a surface air film will be formed, and the oxidation ability will be weakened. Then it will quickly enter the cooling unit. When the cooling temperature is low, the overlap zone cannot be further oxidized, thus forming an oxygen-poor "black spot" strip, see Figure 6-8 ).

[0021] The following is further described by means of specific examples.

[0022] Example 1: The steel plate thickness is 44 mm, the steel plate model is GB / T713.2-Q345R-ZQSD, and the steel plate composition is: C: 0.15%, Si: 0.26%, Mn: 1.52%. The blank size is: 260×2260×2100 mm; the target size is: 44×2335×11810 mm.

[0023] Heating process: Slab heating temperature 1220±30℃, soaking zone temperature 1220±20℃, heating coefficient ≥7.3min / cm, soaking coefficient ≥1.4min / cm Rolling and descaling methods:

[0024] Other processes: After the steel plate is rolled, it undergoes hot straightening, cooling bed, stack cooling, shearing, and finished product storage. The steel plate is inspected before the finished product is stored.

[0025] The surface results of Scheme 1 are shown in the figure, the surface results of Scheme 2 are shown in the figure, and the surface results of Scheme 3 are shown in the figure.

[0026] The following three schemes were tested and verified: 1) In scheme 1, the 1st, 2nd and 1st, 3rd pass finishing rolling descaling, the surface "black spots" are densely distributed and present an irregular distribution; 2) In scheme 2, an empty passage is added for descaling, and the surface shows the characteristics of "black spots" stripes; 3) Scheme 3 adds a fifth descaling pass based on Scheme 1, and the irregular and dense "black spots" on the surface are improved.

[0027] Based on Scheme 2, the descaling of the empty pass was cancelled, and the typical "black spot" strip was improved accordingly. Therefore, Scheme 3 is better than Schemes 1 and 2. At the same time, by comparing the four descaling processes in Scheme 3, it was found that the descaling surface of the 1st and 4th passes of finishing rolling was the best.

[0028] Therefore, the technical solution of the present application performs descaling in the first, third and fifth passes of the rough rolling process of the continuous casting billet, and performs descaling in the first and fourth passes of the finishing rolling process, thereby optimizing the finishing rolling descaling process, effectively improving the "black spot" defects on the surface of the steel plate, improving the surface smoothness, and improving the surface quality of the user's product coating.

[0029] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A method for improving black spots on the surface of a steel plate with a red-returning temperature lower than 650°C, characterized in that: include: heating the continuous casting slab to a target temperature; After the heating time reaches the preset value, the continuous casting billet is taken out of the furnace and enters the descaling box to remove the furnace-generated iron oxide scale; The continuous casting slab is conveyed to a rough rolling mill for rolling and descaling is performed in the first, third and fifth passes; The continuous casting slab is transported to the finishing mill for rolling and descaling is performed in the first and fourth passes.

2. The method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C according to claim 1, characterized in that: After the continuous casting slab is transported to the rough rolling mill for rolling and descaling is performed in the first pass, the third pass and the fifth pass, the method further comprises: The continuous casting billet is transported to the intermediate roller table for warming until it meets the second stage rolling temperature requirement.

3. The method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C according to claim 1, characterized in that: The finishing passes are six times.

4. The method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C according to claim 1, characterized in that: The target temperature for heating the continuous casting slab is 1220±30℃.

5. The method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C according to claim 1, characterized in that: The second stage rolling temperature of the continuous casting billet is less than or equal to 870°C.

6. The method for improving black spots and stripes on the surface of a steel plate with a red-returning temperature lower than 650°C according to claim 1, characterized in that: The final rolling temperature of the continuous casting billet is 820±20℃.

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