Production method of fine lamellar eutectoid oxide scale steel plate

Abstract

The invention discloses a production method of a fine lamellar eutectoid oxide scale steel plate, which comprises the following steps: (1) carrying out finish rolling on an intermediate billet subjected to rough rolling descaling to obtain a finish rolled plate; (2) cooling the finish-rolled plate to obtain a plate strip; (3) coiling the plate strip to obtain a hot rolled steel coil; (4) cooling the hot rolled steel coil to room temperature; wherein the inlet temperature of finish rolling is less than or equal to 1030 DEG C, and the finish rolling temperature is 850-900 DEG C; the coiling temperature ranges from 540 DEG C to 570 DEG C. According to the method, parameters such as the finish rolling inlet temperature, the finish rolling temperature and the coiling temperature are controlled, a lamellar eutectoid Fe3O4 / alpha-Fe structure accounting for 50% or above of the total oxide scale is generated in the oxide scale on the surface layer of the hot-rolled steel plate, the lamellar spacing of the lamellar eutectoid Fe3O4 / alpha-Fe structure ranges from 80 nm to 200 nm, and the total oxide scale thickness is smaller than 10 microns.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling technology in the field of metallurgy, and relates to a method for producing a fine lamellar eutectoid oxide scale steel plate. Background Art

[0002] As industrial energy conservation and emission reduction and green manufacturing gradually become the only way for the development of the steel industry, a lot of research has been carried out on steel pickling-free production technology both at home and abroad. The representative one is the pickling-free technology with scale control as the core. The scale in pickling-free steel has a strong bonding force with the matrix, can withstand certain deformation without falling off, and the steel plate can be used directly without pickling process.

[0003] The iron oxide scale is composed of Fe203, Fe3O4, eutectoid Fe3O4 / α-Fe and FeO layers. Compared with Fe203 and FeO, Fe3O4 and eutectoid Fe3O4 / α-Fe have higher tensile strength, stronger deformation resistance and are not easy to fall off during processing. At present, the research on pickling-free steel is mainly to control the rolling system and cooling system to increase the content of Fe3O4 and reduce the total thickness of the iron oxide scale. Since the eutectoid Fe3O4 / α-Fe is a lamellar structure composed of alternating growth of α-Fe and Fe3O4, the spacing of this lamellar structure leads to different toughness of the iron oxide scale. The smaller the lamellar spacing, the better the toughness and the less likely it is to fall off when subjected to deformation. At present, there is no research specifically on the method of generating eutectoid Fe3O4 / α-Fe iron oxide scale with fine lamellar spacing. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing fine lamellar eutectoid iron oxide scale steel plate, wherein the generated lamellar eutectoid Fe3O4 / α-Fe structure accounts for more than 50% of the total iron oxide scale, the lamellar spacing is 80nm to 200nm, and the total iron oxide scale thickness is less than 10um.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for producing a fine lamellar eutectoid iron oxide scale steel plate comprises the following steps: (1) Finish rolling the intermediate billet after rough rolling and descaling to obtain a finished rolled plate; (2) cooling the finished rolled sheet to obtain a strip; (3) coiling the strip to obtain a hot-rolled steel coil; (4) Cooling the hot-rolled steel coil to room temperature.

[0006] Furthermore, the inlet temperature of the finish rolling in step (1) of the present invention is ≤1030°C.

[0007] Furthermore, the final rolling temperature of the finishing rolling in step (1) of the present invention is 850°C to 900°C.

[0008] Furthermore, the cooling in step (2) of the present invention adopts front-stage concentrated laminar cooling, and the cooling rate is 30°C / s to 50°C / s.

[0009] Furthermore, the coiling temperature in step (3) of the present invention is 540°C to 570°C.

[0010] Furthermore, in step (4) of the present invention, the hot-rolled steel coils are stacked in a pit and cooled to room temperature.

[0011] Furthermore, the mass percentages of Si, Ni and Cr in the steel plate of the present invention are controlled as follows: Si≤0.5%, Ni≤0.01%, Cr≤0.5%.

[0012] Furthermore, the interlamellar spacing of the lamellar eutectoid Fe3O4 / α-Fe structure in the surface oxide scale of the hot-rolled steel plate produced by the method of the present invention is 80nm to 200nm, the lamellar eutectoid Fe3O4 / α-Fe structure accounts for more than 50% of the total oxide scale, and the total oxide scale thickness is less than 10um.

[0013] The inventive principle of the technical solution of the present invention is: Controlling a lower finishing temperature can inhibit the growth of iron oxide scale and control the total iron oxide scale thickness at a lower level; low coiling temperature can inhibit the precipitation of Fe3O4 in the iron oxide scale in the FeO layer; stacking and cooling in a pit after coiling can keep the steel coils warm and slow down the cooling rate, and the pit is oxygen-poor, providing better conditions for eutectoid; Si, Ni, and Cr elements in steel can cause the presence of olivine, making the iron oxide scale easy to break and easy to generate Fe2O3, but not easy to generate eutectoid structure, so their content needs to be controlled.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The present invention controls the lamellar spacing of the lamellar eutectoid Fe3O4 / α-Fe structure within the range of 80nm to 200nm by controlling the rolling and cooling of the finishing rolling and coiling processes, and controlling parameters such as the finishing rolling inlet temperature, the finishing rolling outlet temperature and the coiling temperature. The lamellar eutectoid Fe3O4 / α-Fe structure accounts for more than 50% of the total amount of iron oxide scale, the FeO content is low, and the total iron oxide scale thickness is less than 10um. The iron oxide scale within the range of the lamellar spacing and the proportion has good toughness and is not easy to fall off when subjected to processing deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the measurement diagram of the interlamellar spacing of lamellar eutectoid Fe3O4 / α-Fe in Example 1; Figure 2 This is a measurement diagram of the total thickness of the oxide scale in Example 1; Figure 3 This is the structure diagram of the iron oxide scale in Example 2; Figure 4 This is the structure diagram of the iron oxide scale of Example 3; Figure 5 This is the structure diagram of the iron oxide scale of comparative example 1. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0017] The weight percentages of the components in the steel billet of this embodiment are: C: 0.439%, Si: 0.2341%, Mn: 0.6773%, S: 0.0011%, P: 0.0133%, Ni: 0.0095%, Cr: 0.0176%, Alt: 0.0356%, and the rest are iron and residues; the production method thereof comprises: (1) The descaled intermediate billet after rough rolling is subjected to finish rolling, with the finish rolling inlet temperature being 1015°C and the final rolling temperature being 871°C to obtain a finished rolled sheet; (2) cooling the finished rolled sheet by front-stage concentrated laminar cooling at a cooling rate of 34.7° C. / s to obtain a sheet strip; (3) coiling the strip at a coiling temperature of 559° C. to obtain a hot-rolled steel coil; (4) Stacking the hot-rolled steel coils in a pit and cooling them to room temperature.

[0018] The measurement diagram of the total thickness of the iron oxide scale on the surface of the steel plate in this embodiment is as follows Figure 1 As shown, the average total thickness is 9.049 μm; the iron oxide scale contains Fe3O4 and lamellar eutectoid Fe3O4 / α-Fe structure. The lamellar spacing measurement diagram of the lamellar eutectoid Fe3O4 / α-Fe structure is shown in Figure 2 As shown, the average value is 173nm, and the lamellar eutectoid Fe3O4 / α-Fe structure accounts for 75% of the total iron scale. This type of iron scale is not easy to fall off during processing and deformation. Example 2

[0019] The weight percentages of the components in the steel billet of this embodiment are: C: 0.415%, Si: 0.3154%, Mn: 0.7059%, S: 0.0010%, P: 0.0159%, Ni: 0.0071%, Cr: 0.0205%, Alt: 0.0213%, and the rest are iron and residues; the production method thereof comprises: (1) The descaled intermediate billet after rough rolling is subjected to finish rolling, with the finish rolling inlet temperature being 1030°C and the final rolling temperature being 900°C to obtain a finished rolled sheet; (2) cooling the finished rolled sheet by front-stage concentrated laminar cooling at a cooling rate of 40.2° C. / s to obtain a sheet strip; (3) coiling the strip at a coiling temperature of 540° C. to obtain a hot-rolled steel coil; (4) Stacking the hot-rolled steel coils in a pit and cooling them to room temperature.

[0020] The structure of the iron oxide scale on the surface of the steel plate in this embodiment is shown in the figure Figure 3 As shown, the average total thickness is 5.828μm; the oxide scale contains Fe3O4 and lamellar eutectoid Fe3O4 / α-Fe structure, the average interlamellar spacing of the lamellar eutectoid Fe3O4 / α-Fe structure is 185nm, and the lamellar eutectoid Fe3O4 / α-Fe structure accounts for 71.3% of the total iron scale. This type of oxide scale is not easy to fall off during processing and deformation. Example 3

[0021] The weight percentages of the components in the steel billet of this embodiment are: C: 0.442%, Si: 0.2683%, Mn: 0.6413%, S: 0.0012%, P: 0.0159%, Ni: 0.0056%, Cr: 0.0089%, Alt: 0.0415%, and the rest are iron and residues; the production method thereof comprises: (1) The descaled intermediate billet after rough rolling is subjected to finish rolling, with the finish rolling inlet temperature being 1000°C and the final rolling temperature being 850°C to obtain a finished rolled sheet; (2) cooling the finished rolled sheet by front-stage concentrated laminar cooling at a cooling rate of 31.3° C. / s to obtain a sheet strip; (3) coiling the strip at a coiling temperature of 570° C. to obtain a hot-rolled steel coil; (4) Stacking the hot-rolled steel coils in a pit and cooling them to room temperature.

[0022] The structure of the iron oxide scale on the surface of the steel plate in this embodiment is shown in the figure Figure 4 As shown, the average total thickness is 9.773μm; the oxide scale contains Fe3O4 and lamellar eutectoid Fe3O4 / α-Fe structure, the average interlamellar spacing of the lamellar eutectoid Fe3O4 / α-Fe structure is 192nm, and the lamellar eutectoid Fe3O4 / α-Fe structure accounts for 58.6% of the total iron scale. This type of oxide scale is not easy to fall off during processing and deformation.

[0023] Comparative Example 1

[0024] The weight percentages of the components in the steel billet of this comparative example are: C: 0.439%, Si: 0.2341%, Mn: 0.6773%, S: 0.0011%, P: 0.0133%, Ni: 0.0095%, Cr: 0.0176%, Alt: 0.0356%, and the rest are iron and residues; the production method thereof comprises: (1) The descaled intermediate billet after rough rolling is subjected to finish rolling, with the finish rolling inlet temperature being 1040°C and the final rolling temperature being 910°C to obtain a finished rolled sheet; (2) cooling the finished rolled sheet by front-stage concentrated laminar cooling at a cooling rate of 35.7° C. / s to obtain a sheet strip; (3) coiling the strip at a coiling temperature of 590° C. to obtain a hot-rolled steel coil; (4) directly stacking the hot-rolled steel coils and cooling them to room temperature.

[0025] The structure of the iron oxide scale on the surface of the steel plate in this comparative example is shown in Figure 5 As shown, the average total thickness is 11.695μm; the iron oxide scale contains FeO, Fe3O4 and lamellar eutectoid Fe3O4 / α-Fe structure, the average interlamellar spacing of the lamellar eutectoid Fe3O4 / α-Fe structure is 265nm, and the lamellar eutectoid Fe3O4 / α-Fe structure accounts for 16.8% of the total iron scale. Due to the small content of Fe3O4 and lamellar eutectoid Fe3O4 / α-Fe in the iron oxide scale, and the large amount of FeO, the iron oxide scale is easy to break and fall off after processing and deformation.

Claims

1. A method for producing a fine lamellar eutectoid iron oxide scale steel plate, characterized in that: The following steps are involved: (1) Finish rolling the intermediate billet after rough rolling and descaling to obtain a finished rolled plate; (2) cooling the finished rolled sheet to obtain a strip; (3) coiling the strip to obtain a hot-rolled steel coil; (4) Cooling the hot-rolled steel coil to room temperature.

2. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: The inlet temperature of the finishing rolling in step (1) is ≤1030°C.

3. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: The final rolling temperature of the finishing rolling in step (1) is 850°C to 900°C.

4. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: The cooling in step (2) adopts front-stage concentrated laminar cooling, and the cooling rate is 30°C / s to 50°C / s.

5. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: The coiling temperature in step (3) is 540°C to 570°C.

6. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: In step (4), the hot-rolled steel coils are stacked in a pit and cooled to room temperature.

7. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: The mass percentages of Si, Ni and Cr in the steel plate are controlled as follows: Si≤0.5%, Ni≤0.01%, Cr≤0.5%.

8. The method for producing a fine lamellar eutectoid iron oxide scale steel sheet according to claim 1, characterized in that: The interlamellar spacing of the lamellar eutectoid Fe3O4 / α-Fe structure in the surface oxide scale of the steel plate produced by the method is 80nm-200nm, the lamellar eutectoid Fe3O4 / α-Fe structure accounts for more than 50% of the total oxide scale, and the total oxide scale thickness is less than 10um.

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