High-flatness hot-rolled steel plate and production method thereof

Abstract

The present invention discloses a high-flatness hot-rolled steel plate and a production method thereof. The production method includes heating, hot rolling, and temperature-controlled straightening. In the temperature-controlled straightening step, the hot-rolled steel plate undergoes a first-stage straightening process, is then fed into an accelerated cooling device for rapid cooling, and is then allowed to stand before undergoing a second-stage straightening process. After the second-stage straightening process, the plate is fed to a cooling bed for natural cooling, and then undergoes a third-stage straightening process. The present invention eliminates plate shape issues arising from the rolling and cooling processes through staged temperature-controlled straightening, significantly reducing the requirements for plate shape control during the rolling and cooling processes. The resulting steel plate has excellent flatness, with an unevenness of ≤1 mm / m, meeting the requirements for steel structures in industries such as construction, bridges, and shipbuilding. Furthermore, the requirements for plate shape control during the rolling and cooling processes are significantly reduced, making the steel plate universally applicable.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and relates to a production method of a high-straightness steel plate, and a high-straightness hot-rolled steel plate prepared by the production method. Background Art

[0002] In recent years, with the quality upgrade of the domestic equipment manufacturing industry, especially in the construction, bridge and shipbuilding industries, the quality requirements for steel structures have become increasingly higher. One of the indicators is the flatness of the steel plate. Flatness is an important appearance indicator of hot-rolled steel plates, and is usually characterized by unevenness. If the flatness of the steel plate is poor, it will directly affect the accuracy of the steel components, causing great difficulties in the subsequent assembly of the steel components, and will seriously affect the mechanical properties of the steel components.

[0003] However, existing hot-rolled steel plates are very prone to plate shape problems such as waves, warps, and bends during the production process, resulting in poor flatness of the hot-rolled steel plates, which cannot meet the use requirements of steel structures in industries such as construction, bridges, and shipbuilding. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method of high-flatness hot-rolled steel plates, and high-flatness hot-rolled steel plates prepared by the production method, so as to solve the problem that hot-rolled steel plates are prone to produce waves, buckles, warps and other plate shapes during the production process.

[0005] To achieve the above-mentioned object, one embodiment of the present invention provides a method for producing a high-flatness hot-rolled steel plate, comprising the following steps performed in sequence:

[0006] Heating: heating the steel billet;

[0007] Hot rolling: The heated steel billet is fed into the rolling mill and rolled into steel plates;

[0008] Temperature-controlled straightening: The steel plate obtained after hot rolling is straightened in the first stage, then sent to the accelerated cooling device for rapid cooling, and then allowed to stand for the second stage of straightening; after the second stage of straightening, it is sent to the cooling bed for natural cooling, and then the third stage of straightening is carried out after natural cooling.

[0009] Preferably, in the hot rolling process, the final rolling temperature>A r3 , A r3 Indicates the starting temperature of the steel plate's austenite to ferrite transformation;

[0010] In the temperature-controlled straightening process, the straightening temperature of the first stage is >A r3 .

[0011] Preferably, in the temperature-controlled straightening process, the straightening temperature of the second stage is 500°C to A r1 , Ar1 Indicates the temperature at which the transformation from austenite to ferrite in a steel plate ends.

[0012] Preferably, in the temperature-controlled straightening process, the straightening temperature of the third stage straightening is 200-400°C.

[0013] Preferably, in the temperature-controlled straightening process, the standing time is negatively correlated with the thickness of the steel plate.

[0014] Preferably, in the temperature-controlled straightening process, the standing time is 5 to 40 seconds.

[0015] To achieve the above-mentioned object of the invention, one embodiment of the present invention further provides a high-straightness hot-rolled steel plate, which is produced by the above-mentioned production method of the high-straightness hot-rolled steel plate. The chemical composition of the high-straightness hot-rolled steel plate comprises, by mass percentage, C 0.06-0.11%, Si 0.12-0.28%, Mn 1.30-1.70%, Nb 0.01-0.05%, Ti 0.008-0.020%, Ni 0.08-0.40%, Cr 0.08-0.20%, Mo ≤ 0.40%, Cu ≤ 0.40%, and the remainder is Fe and unavoidable impurities; the starting temperature A of the austenite to ferrite transformation of the high-straightness hot-rolled steel plate is 0.175°C. r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

[0016] As a further improvement of one embodiment of the present invention, the yield strength of the high-flatness hot-rolled steel plate is ≥420MPa, the tensile strength is ≥540MPa, the elongation is ≥20%, the yield ratio is ≤0.85, the impact energy KV2 at -40°C is ≥300J, and the impact energy KV2 at -60°C is ≥270J; its structure is a two-phase structure of ferrite + bainite, the proportion of ferrite structure is 40-70%, and the proportion of bainite structure is 30-60%; the unevenness is ≤1mm / m.

[0017] To achieve the above-mentioned object of the invention, one embodiment of the present invention further provides a high-straightness hot-rolled steel plate, which is produced by the above-mentioned production method of the high-straightness hot-rolled steel plate, wherein the chemical composition of the high-straightness hot-rolled steel plate comprises, by mass percentage, C 0.12-0.16%, Si 0.10-0.40%, Mn 0.90-1.60%, Nb≤0.04%, Ti 0.008-0.020%, Ni≤0.40%, Cr≤0.30%, and the remainder is Fe and unavoidable impurities; the starting temperature A of the austenite to ferrite transformation of the high-straightness hot-rolled steel plate is ... r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

[0018] As a further improvement of one embodiment of the present invention, the yield strength of the high-flatness hot-rolled steel plate is ≥370MPa, the tensile strength is ≥490MPa, the elongation is ≥21%, the yield strength ratio is ≤0.78, the impact energy KV2 at -20°C is ≥300J, and the impact energy KV2 at -40°C is ≥200J; its structure is a two-phase structure of polygonal ferrite + pearlite, the average grain size is 4-12μm, the proportion of polygonal ferrite structure is 60-80%, and the proportion of pearlite structure is 20-40%; the unevenness is ≤1mm / m.

[0019] To achieve the above-mentioned object of the invention, one embodiment of the present invention further provides a high-straightness hot-rolled steel plate, which is produced by the above-mentioned production method of the high-straightness hot-rolled steel plate, wherein the chemical composition of the high-straightness hot-rolled steel plate comprises, by mass percentage, C 0.04-0.08%, Si 0.10-0.40%, Mn 0.90-1.80%, Nb 0.02-0.08%, Ti 0.008-0.020%, Ni≤0.40%, Cr≤0.30%, Mo≤0.30%, Cu≤0.30%, and the remainder is Fe and unavoidable impurities; the starting temperature A of the austenite to ferrite transformation of the high-straightness hot-rolled steel plate is 0.10-0.40 ... r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

[0020] As a further improvement of one embodiment of the present invention, the yield strength of the high-straightness hot-rolled steel plate is ≥480MPa, the tensile strength is ≥570MPa, the elongation is ≥35%, the -20℃ DWTT fracture fiber rate is ≥85%, the -40℃ impact energy KV2 is ≥300J, and the -60℃ impact energy KV2 is ≥200J; its structure is a two-phase structure of acicular ferrite + bainite, the proportion of acicular ferrite structure is 40-80%, and the proportion of bainite structure is 20-50%; the unevenness is ≤1mm / m.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) By controlling the production process of steel plates, especially the straightening process after hot rolling, and performing the first stage straightening on the steel plates immediately after rolling, and taking advantage of the low deformation resistance of the steel plates at high temperatures just after hot rolling, the steel plates can be straightened, which can greatly eliminate the problems of poor straightness such as warping, buckling, edge waves, and middle waves of the steel plates caused by the rolling process; further, after rapid cooling, the steel plates are allowed to stand, and then the second stage straightening is performed. The temperature of the surface layer of the steel plate can be transferred to the core layer by standing, reducing the temperature difference between the surface layer and the core layer of the steel plate, making the temperature field of the steel plate uniform, and avoiding the phenomenon that the phase change of the surface layer of the steel plate ends and the phase change of the core layer ends. The transformation has not yet ended, which leads to the steel plate being warped again under the combined action of phase transformation stress and thermal stress during the second stage of straightening, thereby significantly improving the plate shape; further, after the second stage of straightening, it is sent to the cooling bed for natural cooling, and the third stage of straightening is carried out after a delay to correct the slight warping of the steel plate during the natural cooling process accompanied by stress release; in this way, through staged temperature control and straightening, the plate shape problems generated during the rolling and cooling processes can be eliminated, which greatly reduces the requirements for plate shape control in the rolling and cooling processes. The final steel plate has good straightness, unevenness ≤1mm / m, and is universal.

[0023] (2) When the production method of the present invention is used to produce steel plates with different chemical compositions, the steel plates can have different properties and be suitable for different application scenarios. For example, the chemical composition includes, by mass percentage: C 0.06-0.11%, Si 0.12-0.28%, Mn 1.30-1.70%, Nb 0.01-0.05%, Ti 0.008-0.020%, Ni0.08-0.40%, Cr Steel plate with 0.08-0.20%, Mo≤0.40%, Cu≤0.40%, the rest being Fe and unavoidable impurities, yield strength ≥420MPa, tensile strength ≥540MPa, elongation ≥20%, yield strength ratio ≤0.85, -40℃ impact energy KV2 ≥300J, -60℃ impact energy KV2 ≥270J, microstructure of ferrite + bainite, ferrite microstructure ratio of 40-70%, bainite microstructure ratio of 30-60%, can be used as steel plate for bridges; chemical composition by mass percentage includes: C 0.12-0.16%, Si 0.10-0.40%, Mn 0.90-1.60%, Nb≤0.04%, Ti Steel plate containing 0.008-0.020% of Ni, ≤0.40% of Ni, ≤0.30% of Cr, and the remainder being Fe and unavoidable impurities, with a yield strength ≥370MPa, a tensile strength ≥490MPa, an elongation ≥21%, a yield strength ratio ≤0.78, an impact energy KV2 at -20°C ≥300J, an impact energy KV2 at -40°C ≥200J, a two-phase structure of polygonal ferrite + pearlite, an average grain size of 4-12μm, a polygonal ferrite structure ratio of 60-80%, and a pearlite structure ratio of 20-40%, which can be used as a steel plate for ships; the chemical composition, in mass percentage, includes: C 0.04-0.08%, Si 0.10-0.40%, Mn 0.90-1.80%, Nb 0.02-0.08%, Ti Steel plate with 0.008-0.020%, Ni≤0.40%, Cr≤0.30%, Mo≤0.30%, Cu≤0.30%, and the rest being Fe and inevitable impurities, with yield strength ≥480MPa, tensile strength ≥570MPa, elongation ≥35%, -20℃ DWTT fracture fiber rate ≥85%, -40℃ impact energy KV2 ≥300J, -60℃ impact energy KV2 ≥200J, and a two-phase structure of acicular ferrite + bainite, with the proportion of acicular ferrite being 40-80% and the proportion of bainite being 20-50%, and can be used as steel plate for oil pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the metallographic structure diagram of the hot-rolled steel plate with a thickness of 16 mm in Example 1;

[0025] Figure 2is the metallographic structure diagram of the hot-rolled steel plate with a thickness of 40 mm in Example 2;

[0026] Figure 3 This is the metallographic structure diagram of the hot-rolled steel plate with a thickness of 20 mm in Example 3. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0028] One embodiment of the present invention provides a method for producing a high-flatness hot-rolled steel plate and a high-flatness hot-rolled steel plate produced by the production method.

[0029] In terms of process flow, as mentioned above, the production method includes the following steps performed in sequence:

[0030] (1) Heating: heating the steel billet.

[0031] (2) Hot rolling: The heated steel billet is sent to the rolling mill and rolled into steel plates.

[0032] Preferably, the final rolling temperature>A r3 , A r3 It indicates the starting temperature of the transformation from austenite to ferrite, so as to ensure that the subsequent straightening is carried out at a higher temperature, which is beneficial to improve the straightening effect.

[0033] (3) Temperature-controlled straightening: The steel plate obtained after hot rolling is straightened in the first stage, and then sent to the accelerated cooling device for rapid cooling, and then allowed to stand for the second stage of straightening; after the second stage of straightening, it is sent to the cooling bed for natural cooling, and then the third stage of straightening is carried out after natural cooling.

[0034] In this way, by immediately carrying out the first stage straightening on the steel plate after rolling, and taking advantage of the low deformation resistance of the steel plate at the high temperature just after hot rolling, the steel plate is straightened, which can greatly eliminate the problems of poor flatness such as warping, buckling, edge waves, and middle waves of the steel plate caused by the rolling process; further, after rapid cooling, it is allowed to stand, and then the second stage straightening is carried out. By standing, the temperature of the surface of the steel plate can be transferred to the core, reducing the temperature difference between the surface and the core of the steel plate, making the temperature field of the steel plate uniform, and avoiding the situation where the phase change of the surface of the steel plate is completed but the phase change of the core is not completed, which leads to During the second stage of straightening, the steel plate bends again under the combined action of phase change stress and thermal stress, which can significantly improve the plate shape; further, after the second stage of straightening, it is sent to the cooling bed for natural cooling, and the third stage of straightening is carried out with a lag to correct the slight bend that occurs in the natural cooling process of the steel plate accompanied by stress release; in this way, through staged temperature control and straightening, the plate shape problems generated during the rolling and cooling processes can be eliminated, which greatly reduces the requirements for plate shape control in the rolling and cooling processes. The final steel plate has good flatness, unevenness ≤1mm / m, and is universal.

[0035] Preferably, the straightening temperature of the first stage straightening is >A r3 To avoid the phase change inside the steel plate when the straightening temperature is too low, which causes the deformation resistance of the steel plate structure to increase, or even increase by more than twice, resulting in a significant increase in the difficulty of straightening; in addition, it can also avoid the temperature of the steel plate being too low during subsequent rapid cooling, which causes the appearance of proeutectoid ferrite, thereby affecting the regulation of the steel plate's organizational properties.

[0036] Preferably, the rest time is negatively correlated with the thickness of the steel plate. That is, the thicker the steel plate, the longer the rest time after rapid cooling should be. This allows the temperature field at the surface and core of the thicker steel plate to become more uniform, avoiding the situation where the phase transformation at the surface is complete while the phase transformation at the core is not.

[0037] More preferably, the standing time is 5 to 40 seconds, which can ensure that the phase transformation of the surface and the core of the steel plate is completed and the temperature of the surface and the core of the steel plate is uniform.

[0038] Preferably, the straightening temperature of the second stage is 500℃~A r1 , A r1 Indicates the temperature at which the transformation of austenite to ferrite in a steel plate ends. By straightening the steel plate after rapid cooling, the warping caused by uneven cooling in the length, width or thickness direction during the rapid cooling process can be improved, thereby improving the straightness of the steel plate. By controlling the straightening temperature of the second stage straightening to 500℃~A r1 , not only can avoid the straightening temperature higher than A r1The above straightening method has poor straightening effect because the phase transformation of the steel plate has not yet been completed. It can also avoid the stress of the steel plate after straightening from not being released due to the straightening temperature being too low, thereby requiring a huge straightening force and high requirements for the straightening equipment.

[0039] Preferably, the straightening temperature of the third stage straightening is 200-400°C. If the straightening temperature is too high, stress release will be incomplete, and there is a risk of the steel plate buckling again after straightening. If the straightening temperature is too low, the internal stress of the steel plate cannot be released after straightening, and there is a risk of springback after straightening. Therefore, the straightening temperature of the third stage straightening is controlled within the range of 200-400°C.

[0040] In this production method, by controlling the production process of the steel plate, especially the straightening process after hot rolling, the steel plate is straightened in stages after rolling, with rapid cooling and natural cooling of the steel plate interspersed in between, and combined with temperature control in each stage and connection between each process, the organizational and structural changes of the steel plate in each stage can be fully utilized, and an excellent straightening effect can be achieved for the steel plate that has already had plate shape problems. The unevenness of the final steel plate can be reduced to below 1 mm / m, which can meet the use requirements of steel structures in industries such as construction, bridges and shipbuilding, and greatly reduces the requirements for plate shape control during rolling and cooling. It has universal applicability.

[0041] One embodiment of the present invention further provides a high-straightness hot-rolled steel plate, which is produced by the above-mentioned production method of the high-straightness hot-rolled steel plate, and the chemical composition thereof comprises, by mass percentage, C 0.06-0.11%, Si 0.12-0.28%, Mn 1.30-1.70%, Nb 0.01-0.05%, Ti 0.008-0.020%, Ni 0.08-0.40%, Cr 0.08-0.20%, Mo ≤ 0.40%, Cu ≤ 0.40%, and the remainder is Fe and unavoidable impurities; the starting temperature A of the austenite to ferrite transformation of the high-straightness hot-rolled steel plate is 0.11%. r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

[0042] Wherein, [C] represents the mass percentage of C, [Mn] represents the mass percentage of Mn, [Cu] represents the mass percentage of Cu, [Cr] represents the mass percentage of Cr, [Mo] represents the mass percentage of Mo, [Ni] represents the mass percentage of Ni, and [Si] represents the mass percentage of Si. The same shall apply to the following and shall not be repeated herein.

[0043] Through the optimization of the chemical composition design scheme and the strict control of the production process, the high-flatness hot-rolled steel plate finally obtains a yield strength ≥420MPa, a tensile strength ≥540MPa, an elongation ≥20%, a yield strength ratio ≤0.85, an impact energy KV2 at -40°C ≥300J, and an impact energy KV2 at -60°C ≥270J; its structure is a two-phase structure of ferrite + bainite, with the ferrite structure proportion of 40-70% and the bainite structure proportion of 30-60%; the flatness is ≤1mm / m, which is far higher than the flatness requirement of less than 3mm / m for high-flatness steel plates specified in GB / T 709-2019, and can meet the use requirements of steel structures in industries such as bridges. Therefore, it can be used as a high-flatness hot-rolled steel plate for bridges.

[0044] Another embodiment of the present invention further provides a high-straightness hot-rolled steel plate, which is produced by the above-mentioned production method of the high-straightness hot-rolled steel plate, and the chemical composition thereof comprises, by mass percentage, C 0.12-0.16%, Si 0.10-0.40%, Mn 0.90-1.60%, Nb 0-0.04%, Ti 0.008-0.020%, Ni ≤ 0.40%, Cr ≤ 0.30%, and the remainder is Fe and unavoidable impurities; the starting temperature A of the austenite to ferrite transformation of the high-straightness hot-rolled steel plate is r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

[0045] Through the optimization of the chemical composition design scheme and the strict control of the production process, the high-flatness hot-rolled steel plate finally obtains a yield strength of 370MPa or more, a tensile strength of 490MPa or more, an elongation of 21%, a yield strength ratio of 0.78 or less, an impact energy KV2 of 300J at -20°C, and an impact energy KV2 of 200J at -40°C. The structure is a two-phase structure of polygonal ferrite + pearlite, with an average grain size of 4-12μm, a polygonal ferrite structure ratio of 60-80%, and a pearlite structure ratio of 20-40%. The unevenness is 1mm / m or less, which is much higher than the unevenness requirement of less than 3mm / m for high-flatness steel plates specified in GB / T 709-2019. It can meet the use requirements of steel structures in industries such as shipbuilding and can be used as a high-flatness hot-rolled steel plate for ships.

[0046] Another embodiment of the present invention further provides a high-straightness hot-rolled steel plate, which is produced by the above-mentioned production method of the high-straightness hot-rolled steel plate, and the chemical composition thereof comprises, by mass percentage, C 0.04-0.08%, Si 0.10-0.40%, Mn 0.90-1.80%, Nb 0.02-0.08%, Ti 0.008-0.020%, Ni≤0.40%, Cr≤0.30%, Mo≤0.30%, Cu≤0.30%, and the remainder is Fe and unavoidable impurities; the starting temperature A of the austenite to ferrite transformation of the high-straightness hot-rolled steel plate is r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

[0047] Through the optimization of the chemical composition design scheme and the strict control of the production process, the high-straightness hot-rolled steel plate finally has a yield strength of ≥480MPa, a tensile strength of ≥570MPa, an elongation of ≥35%, a -20℃ DWTT fracture fiber rate of ≥85%, an impact energy KV2 of ≥300J at -40℃, and an impact energy KV2 of ≥200J at -60℃; its microstructure is a two-phase microstructure of acicular ferrite + bainite, with the acicular ferrite microstructure proportion of 40-80% and the bainite microstructure proportion of 20-50%; the flatness is ≤1mm / m, which is far higher than the flatness requirement of less than 3mm / m for high-straightness steel plates specified in GB / T 709-2019. It can meet the use requirements of steel structures in industries such as oil pipeline transportation and can be used as high-straightness hot-rolled steel plate for oil pipelines.

[0048] To make the purpose, technical solutions and advantages of an embodiment of the present invention more clear, the embodiment will be further described below in conjunction with Examples 1 to 3 according to an embodiment of the present invention. Obviously, Examples 1 to 3 described are only part of the embodiments of the present invention, not all of them.

[0049] Example 1

[0050] According to the production method of the present invention, a steel billet is prepared into a high-flatness hot-rolled steel plate. The chemical composition of the obtained high-flatness hot-rolled steel plate includes, by mass percentage, C 0.09%, Si 0.21%, Mn 1.5%, Nb 0.025%, Ti 0.015%, Ni 0.13%, Cr 0.15%, Mo 0.04%, and the remainder is Fe and unavoidable impurities. The starting temperature A of the steel plate for the transformation from austenite to ferrite is 0.09%. r3The temperature A at which the austenite of the steel plate transforms to ferrite is 758°C. r1 It is 667℃.

[0051] The production method comprises the following steps performed in sequence:

[0052] (1) Heating: heating the steel billet.

[0053] (2) Hot rolling: The heated steel billet is sent to the rolling mill and rolled into a steel plate with a thickness of 16 mm. The final rolling temperature is 810℃.

[0054] (3) Temperature-controlled straightening: The steel plate obtained after hot rolling is immediately sent to the straightening machine for the first stage of straightening. The straightening temperature of the first stage of straightening is 776℃; then the steel plate is sent to the water cooling zone of the accelerated cooling device for rapid cooling to 586℃. After leaving the water cooling zone, it is allowed to stand for 5s and then the second stage of straightening is carried out. The straightening temperature of the second stage of straightening is 562℃; after the second stage of straightening, it is sent to the cooling bed for natural cooling. After natural cooling, the third stage of straightening is carried out. The straightening temperature of the third stage of straightening is 282℃.

[0055] The metallographic structure of the steel plate after temperature control straightening is tested. Figure 1 It can be seen that the high-flatness hot-rolled steel plate of Example 1 has a two-phase structure of ferrite + bainite, with the ferrite structure ratio being 60% and the bainite structure ratio being 40%. This structure can ensure that the steel plate has excellent strength and toughness and a low yield strength ratio.

[0056] The mechanical properties of the steel plate after temperature control straightening were tested, and the yield strength of the high-flatness hot-rolled steel plate of Example 1 was measured to be 443 MPa, the tensile strength was 563 MPa, the elongation was 26%, the yield strength ratio was 0.79, the impact energy KV2 at -40°C was 362 J, the impact energy KV2 at -60°C was 304 J, and the flatness was 0.6 mm / m, which can meet the use requirements of steel structures in industries such as bridges. Therefore, it can be used as a high-flatness hot-rolled steel plate for bridges.

[0057] Example 2

[0058] According to the production method of the present invention, a steel billet is prepared into a high-flatness hot-rolled steel plate. The chemical composition of the obtained high-flatness hot-rolled steel plate includes, by mass percentage, C 0.14%, Si 0.24%, Mn 1.3%, Nb 0.02%, Ti 0.015%, Ni 0.03%, Cr 0.05%, and the remainder is Fe and unavoidable impurities. The starting temperature A of the steel plate for the transformation from austenite to ferrite is 0.14%. r3 The temperature A at which the austenite of the steel plate transforms to ferrite is 761°C. r1 It is 676℃.

[0059] The production method comprises the following steps performed in sequence:

[0060] (1) Heating: heating the steel billet.

[0061] (2) Hot rolling: The heated steel billet is sent to the rolling mill and rolled into a steel plate with a thickness of 40 mm. The final rolling temperature is 820℃.

[0062] (3) Temperature-controlled straightening: The steel plate obtained after hot rolling is immediately sent to the straightening machine for the first stage of straightening. The straightening temperature of the first stage of straightening is 816℃; then the steel plate is sent to the water cooling zone of the accelerated cooling device for rapid cooling to 612℃. After leaving the water cooling zone, it is allowed to stand for 30s to allow the steel plate to return to temperature, and then the second stage of straightening is carried out. The straightening temperature of the second stage of straightening is 632℃; after the second stage of straightening, it is sent to the cooling bed for natural cooling. After natural cooling, the third stage of straightening is carried out. The straightening temperature of the third stage of straightening is 380℃.

[0063] The metallographic structure of the steel plate after temperature control straightening is tested. Figure 2 It can be seen that the high-flatness hot-rolled steel plate of Example 2 has a two-phase structure of polygonal ferrite + pearlite, with an average grain size of 10 μm, a polygonal ferrite structure ratio of 78%, and a pearlite structure ratio of 22%. This structure enables the steel plate to have a low yield ratio and good low-temperature toughness without the addition of the precious alloying element Ni.

[0064] Mechanical properties testing was performed on the steel plate after temperature control straightening, and the results showed that the high-flatness hot-rolled steel plate of Example 2 had a yield strength of 404 MPa, a tensile strength of 548 MPa, an elongation of 29%, a yield strength ratio of 0.73, an impact energy KV2 of 306 J at -20°C, an impact energy KV of 248 J at -40°C, and a roughness of 0.8 mm / m. These steel plates can meet the requirements for use in steel structures in industries such as shipbuilding, and can be used as high-flatness hot-rolled steel plates for ships.

[0065] Example 3

[0066] According to the production method of the present invention, a steel billet is prepared into a high-flatness hot-rolled steel plate. The chemical composition of the obtained high-flatness hot-rolled steel plate includes, by mass percentage, C 0.05%, Si 0.21%, Mn 1.72%, Nb 0.045%, Ti 0.015%, Ni 0.13%, Cr 0.15%, Mo 0.14%, and the remainder is Fe and unavoidable impurities. The starting temperature A of the steel plate for the transformation from austenite to ferrite is 0.05%. r3 The temperature A at which the austenite of the steel plate transforms to ferrite is 746°C. r1 It is 658℃.

[0067] The production method comprises the following steps performed in sequence:

[0068] (1) Heating: heating the steel billet.

[0069] (2) Hot rolling: The heated steel billet is sent to the rolling mill and rolled into a steel plate with a thickness of 20 mm. The final rolling temperature is 790 °C.

[0070] (3) Temperature-controlled straightening: The steel plate obtained after hot rolling is immediately sent to the straightening machine for the first stage of straightening. The straightening temperature of the first stage of straightening is 765℃; then the steel plate is sent to the water cooling zone of the accelerated cooling device for rapid cooling to 546℃. After leaving the water cooling zone, it is allowed to stand for 8s and then the second stage of straightening is carried out. The straightening temperature of the second stage of straightening is 522℃; after the second stage of straightening, it is sent to the cooling bed for natural cooling. After natural cooling, the third stage of straightening is carried out. The straightening temperature of the third stage of straightening is 256℃.

[0071] The metallographic structure of the steel plate after temperature control straightening is tested. Figure 3 It can be seen that the high-flatness hot-rolled steel plate of Example 3 is a two-phase structure of acicular ferrite + bainite, with the proportion of acicular ferrite structure being 50% and the proportion of bainite structure being 50%. This structure can ensure that the steel plate has high strength and good low-temperature toughness at the same time, and can especially meet the -20°C DWTT performance requirements.

[0072] The mechanical properties of the steel plate after temperature control straightening were tested, and the yield strength of the high-flatness hot-rolled steel plate of Example 3 was measured to be 506 MPa, the tensile strength was 636 MPa, the elongation was 42%, the -20°C DWTT fracture fiber rate was ≥85%, the -40°C impact energy KV2 = 389 J, the -60°C impact energy KV2 = 324 J, and the flatness was 0.6 mm / m. It can meet the use requirements of steel structures in industries such as oil pipeline transportation and can be used as a high-flatness hot-rolled steel plate for oil pipelines.

[0073] In general, the present invention has the following beneficial effects compared with the prior art: by performing the first stage straightening on the steel plate immediately after rolling, the steel plate is straightened by taking advantage of the low deformation resistance of the steel plate at the high temperature just after hot rolling, which can greatly eliminate the problems of poor straightness of the steel plate such as warping, buckling, edge waves, and middle waves caused by the rolling process; further, after rapid cooling, the steel plate is allowed to stand, and then the second stage straightening is performed. The temperature of the surface layer of the steel plate can be transferred to the core by standing, reducing the temperature difference between the surface layer and the core layer of the steel plate, making the temperature field of the steel plate uniform, and avoiding the situation where the phase change of the surface layer of the steel plate is completed but the phase change of the core layer is not completed, which leads to the phase change stress of the steel plate during the second stage straightening. Under the combined action of heat and thermal stress, the steel plate will bend again, which can significantly improve the plate shape; after the second stage straightening, it is sent to the cooling bed for natural cooling, and the third stage straightening is carried out after a delay to correct the slight curvature of the steel plate caused by stress release during the natural cooling process; in this way, through staged temperature control and straightening, the plate shape problems generated during the rolling and cooling processes can be eliminated, and the requirements for plate shape control in the rolling and cooling processes are greatly reduced. The final steel plate has good flatness and unevenness ≤1mm / m, which can meet the use requirements of steel structures in industries such as construction, bridges and shipbuilding, and greatly reduces the requirements for plate shape control during rolling and cooling, and has universal applicability.

[0074] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0075] The detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for producing a high-flatness hot-rolled steel plate, characterized in that: The process includes the following steps in sequence: Heating: heating the billet; Hot rolling: The heated billet is sent to the rolling mill and rolled into steel plate, and the final rolling temperature is >A r3 , A r3 Indicates the starting temperature of the steel plate's austenite to ferrite transformation; Temperature controlled straightening: The first stage straightening is carried out on the steel plate obtained after hot rolling. The straightening temperature of the first stage straightening is >A r3 Then it is sent to the accelerated cooling device for rapid cooling, and then it is left to stand for the second stage of straightening. The straightening temperature of the second stage is 500℃~A r1 , A r1 Indicates the end temperature of the transformation from austenite to ferrite of the steel plate; after the second stage straightening, it is sent to the cooling bed for natural cooling, and then the third stage straightening is carried out after natural cooling. The straightening temperature of the third stage straightening is 200-400℃.

2. The method for producing a high-flatness hot-rolled steel plate according to claim 1, wherein: In the temperature-controlled straightening process, the standing time is negatively correlated with the thickness of the steel plate.

3. The method for producing a high-flatness hot-rolled steel plate according to claim 2, wherein: In the temperature-controlled straightening process, the standing time is 5 to 40 seconds.

4. A high-flatness hot-rolled steel plate, characterized in that: The high-flatness hot-rolled steel plate is prepared by the production method of any one of claims 1 to 3, wherein the chemical composition of the high-flatness hot-rolled steel plate comprises, by mass percentage, C 0.06-0.11%, Si 0.12-0.28%, Mn 1.30-1.70%, Nb 0.01-0.05%, Ti 0.008-0.020%, Ni 0.08-0.40%, Cr 0.08-0.20%, Mo≤0.40%, Cu≤0.40%, and the rest are Fe and unavoidable impurities; the starting temperature A of the high-flatness hot-rolled steel sheet for the transformation from austenite to ferrite r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature of the austenite to ferrite transformation of the high flatness hot rolled steel sheet A r1 = 723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

5. The high-flatness hot-rolled steel plate according to claim 4, characterized in that: Its yield strength ≥420MPa, tensile strength ≥540MPa, elongation ≥20%, yield strength ratio ≤0.85, -40℃ impact energy KV2 ≥300J, -60℃ impact energy KV2 ≥270J; Its structure is a two-phase structure of ferrite + bainite, the ferrite structure ratio is 40-70%, and the bainite structure ratio is 30-60%; the unevenness is ≤1mm / m.

6. A high-flatness hot-rolled steel plate, characterized in that: The high-straightness hot-rolled steel sheet is produced by the production method of any one of claims 1 to 3, wherein the chemical composition of the high-straightness hot-rolled steel sheet comprises, by mass percentage, C 0.12-0.16%, Si 0.10-0.40%, Mn 0.90-1.60%, Nb ≤ 0.04%, Ti 0.008-0.020%, Ni ≤ 0.40%, Cr ≤ 0.30%, and the remainder is Fe and unavoidable impurities; the starting temperature of the austenite to ferrite transformation of the high-straightness hot-rolled steel sheet is A r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+23.1[Si]+15.9[Cr].

7. The high-flatness hot-rolled steel plate according to claim 6, characterized in that: Its yield strength ≥370MPa, tensile strength ≥490MPa, elongation ≥21%, yield strength ratio ≤0.78, -20℃ impact energy KV2 ≥300J, -40℃ impact energy KV2 ≥200J; Its structure is a two-phase structure of polygonal ferrite + pearlite, with an average grain size of 4 to 12 μm, a polygonal ferrite structure ratio of 60 to 80%, and a pearlite structure ratio of 20 to 40%; the unevenness is ≤1 mm / m.

8. A high-flatness hot-rolled steel plate, characterized in that: The high-flatness hot-rolled steel plate is prepared by the production method of any one of claims 1 to 3, wherein the chemical composition of the high-flatness hot-rolled steel plate comprises, by mass percentage, C 0.04-0.08%, Si 0.10-0.40%, Mn 0.90-1.80%, Nb 0.02~0.08%, Ti 0.008~0.020%, Ni≤0.40%, Cr≤0.30%, Mo≤0.30%, Cu≤0.30%, and the rest are Fe and unavoidable impurities; the starting temperature A of the high flatness hot rolled steel plate for the transformation from austenite to ferrite r3 =910-308[C]-78.6[Mn]-20[Cu]-15.4[Cr]-79.2[Mo]; the end temperature A of the transformation of austenite to ferrite of the high-flatness hot-rolled steel sheet r1 =723-40.7[Mn]-16.5[Ni]+ 23.1[Si]+15.9[Cr].

9. The high-flatness hot-rolled steel plate according to claim 8, characterized in that: Its yield strength ≥480MPa, tensile strength ≥570MPa, elongation ≥35%, -20℃ DWTT fracture fiber rate ≥85%, -40℃ impact energy KV2 ≥300J, -60℃ impact energy KV2 ≥200J; Its structure is a two-phase structure of acicular ferrite + bainite, the proportion of acicular ferrite structure is 40-80%, and the proportion of bainite structure is 20-50%; the unevenness is ≤1mm / m.

Images