Heavy-gauge q500qenh steel plate and preparation method therefor

Abstract

The present invention relates to the technical field of metallurgy, and discloses a heavy-gauge Q500qENH steel plate and a preparation method therefor. The steel plate comprises the following chemical components in percentage by mass: 0.010-0.080% of C, 0.20-0.50% of Si, 1.00-1.7% of Mn, 0.006-0.020% of P, less than or equal to 0.005% of S, 0.20-1.00% of Ni, 0.20-0.80% of Cr, 0.008-0.030% of Mo, 0.20-0.75% of Cu, 0.01-0.06% of Nb, 0.002-0.020% of Ti, less than or equal to 0.08% of Al, less than or equal to 0.0020% of B, and the balance of Fe and inevitable impurities. In the present invention, by means of a rational composition design, the weather resistance index I of the steel plate reaches 6.5 or higher; moreover, by means of the implementation of a TMCP+T treatment, the DBTT temperature of the prepared steel plate reaches -80°C or lower, and therefore the service safety of the steel plate in a low-temperature environment is greatly improved.

Description

Q500qENH steel plate of large thickness specification and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a Q500qENH steel plate of large thickness specification and a preparation method thereof. BACKGROUND

[0002] The steel used in domestic bridge construction is mostly Q345, Q420 and Q460 grade, and the strength is basically within 500 MPa. On the one hand, with the increase of strength, the plasticity and toughness of the steel plate will inevitably deteriorate; on the other hand, the composition and process design of the steel plate need to consider the matching of strength, toughness and weldability at the same time, and such composition and process window is narrow, which is difficult for the steel plant to stably control. With the increasing requirements of bridge design units and owners for bridge steel, it is inevitable for the bridge steel to develop towards high strength and large thickness, which not only improves the safety of the bridge, but also realizes the light weight, large load and large span of the bridge.

[0003] The bridge is a kind of engineering crossing mountains and rivers, and the post-coating of the bridge will inevitably cause damage to the environment of the bridge site. Green water and green mountains are golden mountains and silver mountains. While constructing infrastructure, the impact on the ecological environment needs to be considered. The weathering steel bridge without coating has been widely used abroad and has good feedback in ecological environment protection. In addition, in the areas with poor geographical environment, it is difficult to maintain the post-coating of the bridge. The application of weathering steel bridge without coating can significantly reduce the economic and ecological cost in the later stage caused by coating and maintenance. At present, the weathering bridge designed and applied in China mostly uses low-strength weathering steel, and the development and application of high-strength weathering steel are basically blank. On the one hand, the application of weathering elements can significantly improve the weather resistance of the steel, but the content of alloy elements in the steel also increases significantly, which may cause the process performance, plasticity and toughness, and weldability of the steel to decline, and reduce the matching of weather resistance, strength and toughness, process performance and weldability. On the other hand, the high-strength bridge steel has the problem of insufficient toughness, and the low-temperature toughness decreases sharply with the increase of strength grade, especially for the large thickness specification of the bridge steel.

[0004] The patent with publication number CN115181911B discloses a super-thick Q500qE bridge steel plate and a production method thereof. The steel plate is prepared by adopting large reduction amount rolling (single pass reduction amount ≥40mm) at one stage high temperature + three-stage cooling, wherein the cooling speed gradually increases in the three-stage cooling, and the control cooling speed is lower than 350℃. The thickness of the prepared steel plate reaches 150mm. However, the rolling method is not suitable for thicker billets, and the three-stage cooling speed control range is narrow and difficult to accurately control. In addition, the patent does not consider the weather resistance.

[0005] The patent with publication number CN 108624744B discloses a Q500qE bridge steel plate and a production method thereof. Different thicknesses of Q500qE grade steel plates are prepared by refining the preparation process of steel plates of different thicknesses, especially the final rolling system and the cooling process. However, the thickness of the finished steel plate is less than 32 mm, which cannot be applied to large thickness specifications, and the weather resistance is not considered.

[0006] The patent with publication number CN 111636034B discloses a production method of an anti-corrosion rare earth high-performance bridge steel Q500qE wide and thick steel plate. The method adds rare earth lanthanum and cerium to improve the corrosion resistance of the steel plate, and adjusts the mechanical properties of the steel plate by high-temperature tempering. However, the weathering index I of the steel plate prepared by this method is only above 5.6, which is lower than the current mainstream weathering steel with a weathering index I≥6.0. In addition, the addition of rare earth elements requires higher technology and equipment for smelting and casting of the steel billet, and there is a risk of exceeding the inclusion of the steel plate.

[0007] The patent with application number CN 202310428603.0 discloses a Nb-V-Ti-B system Q500qENHW weathering bridge steel resistant to large heat input welding. The steel plate is prepared by adding Nb, V, Ti and other micro-alloying elements to refine the grains in the heat-affected zone of the steel plate during welding, thereby ensuring the performance of the heat-affected zone under large heat input conditions. However, the high content of Nb, V and Ti elements increases the preparation cost of the steel plate, limiting its large-scale application.

[0008] SUMMARY

[0009] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a large thickness specification Q500qENH steel plate and a preparation method thereof.

[0010] To solve the above technical problems, the technical solutions of the present application are as follows:

[0011] A large thickness specification Q500qENH steel plate, the chemical composition and mass percentage are as follows: C: 0.010-0.080%, Si: 0.20-0.50%, Mn: 1.00-1.7%0, P: 0.006-0.020%, S:≤0.005%, Ni: 0.20-1.00%, Cr: 0.20-0.80%, Mo: 0.008-0.030%, Cu: 0.20-0.75%, Nb: 0.01-0.06%, Ti: 0.002-0.020%, Al:≤0.08%, B:≤0.0020%, and the balance is Fe and unavoidable impurities.

[0012] As a preferred scheme of the large-thickness-specification Q500qENH steel plate, the carbon equivalent of the steel plate is ≤0.50%.

[0013] As a preferred scheme of the large-thickness-specification Q500qENH steel plate, the cold crack sensitivity coefficient of the steel plate is ≤0.23.

[0014] As a preferred scheme of the large-thickness-specification Q500qENH steel plate, the weathering index of the steel plate is ≥6.5.

[0015] The application further provides a preparation method of the large-thickness-specification Q500qENH steel plate, which comprises the following steps in sequence: molten iron pretreatment, converter smelting, refining, continuous casting, heating, rolling, cooling and tempering.

[0016] As a preferred scheme of the preparation method of the large-thickness-specification Q500qENH steel plate, the continuous casting process comprises: preparing the molten iron into a slab with a section thickness of 460 mm.

[0017] As a preferred scheme of the preparation method of the large-thickness-specification Q500qENH steel plate, the heating temperature of the heating process is 1130-1200℃, the heating speed is 3-8℃ / s, and the soaking time is ≥60 min.

[0018] As a preferred scheme of the preparation method of the large-thickness-specification Q500qENH steel plate, the rolling process comprises recrystallization zone rolling and non-recrystallization zone rolling, the opening rolling temperature of the recrystallization zone rolling is 1050-1170℃, and the thickness of the warm slab is 160-250 mm; the opening rolling temperature of the non-recrystallization zone rolling is ≤770℃, and the final rolling temperature is ≤780℃.

[0019] As a preferred scheme of the preparation method of the large-thickness-specification Q500qENH steel plate, the cooling process comprises: after the rolling of the rolled piece is completed, air cooling is performed to ≤750℃, then water cooling is performed, the cooling speed is 2-10℃ / s, and the temperature range of the red temperature control is ≤480℃.

[0020] As a preferred scheme of the preparation method of the large-thickness-specification Q500qENH steel plate, the tempering temperature of the tempering process is 460-600℃, the tempering soaking time is 180-270 min, and air cooling is performed.

[0021] The application has the following beneficial effects:

[0022] The application makes the weathering index I of the steel plate reach 6.5 or more through reasonable component design, meanwhile, the mechanical properties of the 100mm-thickness steel plate prepared only through the TMCP process meet the requirements of yield strength ≥550MPa, tensile strength ≥680MPa, and impact at-40℃ reaches 200J or more, the preparation process is simple, the strength and toughness are sufficient compared with the index in GB / T 714-2015, the DBTT of the prepared steel plate reaches-80℃ or less through the TMCP+T treatment, and the service safety of the steel plate in a low-temperature environment is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description, and obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative labor.

[0024] Fig. 1 is a metallographic structure diagram of the steel plate prepared in Example 1;

[0025] Fig. 2 is a metallographic structure diagram of the steel plate prepared in Example 3;

[0026] Fig. 3 is a series of temperature impact energy fitting curve diagrams of the steel plate prepared in Example 3;

[0027] Fig. 4 is a series of temperature impact energy fitting curve diagrams of the steel plate prepared in Example 4. DETAILED DESCRIPTION

[0028] In order to make the content of the application more easily and clearly understood, the following will further describe the application in detail according to the specific embodiments and in combination with the drawings.

[0029] The application provides a Q500qENH steel plate with a large thickness specification, and the chemical components and mass percentages are as follows: C: 0.010-0.080%, Si: 0.20-0.50%, Mn: 1.00-1.7%0, P: 0.006-0.020%, S: ≤0.005%, Ni: 0.20-1.00%, Cr: 0.20-0.80%, Mo: 0.008-0.030%, Cu: 0.20-0.75%, Nb: 0.01-0.06%, Ti: 0.002-0.020%, Al: ≤0.08%, B: ≤0.0020%, and the balance is Fe and inevitable impurities.

[0030] It should be noted that the components of the above steel plate need to meet the following requirements: carbon equivalent CEV ≤0.50, cold crack sensitivity coefficient Pcm ≤0.23, and weathering index I ≥6.5.

[0031] wherein the formula for calculating the carbon equivalent CEV is: CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15. The formula for calculating the cold crack sensitivity coefficient Pcm is: Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B.

[0032] The formula for calculating the weather resistance index I is: I = 26.01Cu + 3.88Ni + 1.20Cr + 1.49Si + 17.28P - 7.29Cu*Ni - 9.10Ni*P - 33.39Cu2).

[0033] The application also provides a preparation method of the large-thickness-specification Q500qENH steel plate, which comprises the following processes in sequence: molten iron pretreatment, converter smelting, refining, continuous casting, heating, rolling, cooling and tempering.

[0034] The continuous casting process is that the molten steel is prepared into a slab with a section thickness of 460 mm.

[0035] The heating temperature of the heating process is 1130-1200℃, the heating speed is 3-8℃ / s, and the soaking time is ≥60 min.

[0036] The rolling process comprises recrystallization zone rolling and non-recrystallization zone rolling. The starting rolling temperature of the recrystallization zone rolling is 1050-1170℃, and the warm slab thickness is 160-250 mm. The starting rolling temperature of the non-recrystallization zone rolling is ≤770℃, and the final rolling temperature is ≤780℃.

[0037] The cooling process comprises the following steps: after the rolling of the rolled piece is completed, air cooling is performed until the temperature is ≤750℃, then water cooling is performed, the cooling speed is 2-10℃ / s, and the control red temperature interval is ≤480℃.

[0038] The tempering temperature of the tempering process is 460-600℃, the tempering soaking time is 180-270 min, and air cooling is performed.

[0039] The application will be further described below through specific examples.

[0040] Example 1: The example provides a large-thickness-specification Q500qENH steel plate, the chemical components are configured according to the mass percentage, and the content of each element is C: 0.03, Si: 0.35, Mn: 1.50, P: 0.01, S: 0.004, Ni: 0.42, Cr: 0.60, Mo: 0.01, Cu: 0.43, Nb: 0.05, Ti: 0.008, Al: 0.02, B: 0.0005, and the balance is Fe and inevitable impurities.

[0041] CEV = 0.42, Pcm = 0.183, and the I index is 6.69.

[0042] The preparation method is as follows: after pretreatment of molten iron, converter smelting, LF+RH refining, 460mm thick slabs are continuously cast on a continuous casting machine. Then the slabs are heated to 1180℃ in a heating furnace, and the soaking segment is kept for 120min. After the slabs are discharged, descaling is performed, and then recrystallization zone rolling is performed at a rolling temperature of 1100℃. The slabs are rolled to a thickness of 170mm, and then air cooling is performed. After the slabs are cooled to 750℃, non-recrystallization zone rolling is performed, and finally 100mm thick plates are rolled at a finish rolling temperature of 715℃. The plates are air cooled to 700℃, and then water cooling is performed at a cooling rate of 5℃ / s. The plates are air cooled to 390℃, and then the red temperature is returned to 390℃. Finally, the plates are air cooled on a cooling bed.

[0043] Example 2: The present example provides a large thickness specification Q500qENH steel plate, the chemical composition is configured according to mass percent, and the content of each element is C: 0.07, Si: 0.25, Mn: 1.3, P: 0.007, S: 0.003, Ni: 0.56, Cr: 0.40, Mo: 0.02, Cu: 0.35, Nb: 0.03, Ti: 0.013, Al: 0.04, B: 0.0005, and the balance is Fe and inevitable impurities.

[0044] CEV = 0.42, Pcm = 0.183, and the I index is 6.69.

[0045] The preparation method is as follows: after pretreatment of molten iron, converter smelting, LF+RH refining, 460mm thick slabs are continuously cast on a continuous casting machine. Then the slabs are heated to 1180℃ in a heating furnace, and the soaking segment is kept for 120min. After the slabs are discharged, descaling is performed, and then recrystallization zone rolling is performed at a rolling temperature of 1100℃. The slabs are rolled to a thickness of 170mm, and then air cooling is performed. After the slabs are cooled to 750℃, non-recrystallization zone rolling is performed, and finally 100mm thick plates are rolled at a finish rolling temperature of 715℃. The plates are air cooled to 700℃, and then water cooling is performed at a cooling rate of 5℃ / s. The plates are air cooled to 390℃, and then the red temperature is returned to 390℃. Finally, the plates are air cooled on a cooling bed.

[0046] Example 3: The present example provides a large thickness specification Q500qENH steel plate, the chemical composition is configured according to mass percent, and the content of each element is C: 0.04, Si: 0.35, Mn: 1.50, P: 0.01, S: 0.004, Ni: 0.42, Cr: 0.60, Mo: 0.01, Cu: 0.43, Nb: 0.05, Ti: 0.008, Al: 0.02, B: 0.0005, and the balance is Fe and inevitable impurities.

[0047] Among them, CEV = 0.47, Pcm = 0.188, and I index = 6.70.

[0048] The preparation method is as follows: After hot metal pretreatment, converter smelting, and LF+RH refining, a 460mm thick slab is continuously cast in a continuous casting machine. It is then heated to 1150℃ in a heating furnace and held at that temperature for 100 minutes in the soaking zone. Afterward, the slab is removed from the furnace, descaled, and rolled in the recrystallization zone at an initial rolling temperature of 1060℃ to a thickness of 220mm. It is then allowed to cool in air. After reaching 720℃, the slab is rolled in the non-recrystallization zone to a final thickness of 100mm at a final rolling temperature of 760℃. The plate is then cooled in air to 725℃, followed by water cooling at a rate of 8℃ / s and a reddening temperature of 430℃, then air-cooled on a cooling bed. After air cooling, it is tempered at 510℃ for 240 minutes and finally air-cooled to room temperature.

[0049] Example 4: This example provides a thick Q500qENH steel plate with a chemical composition configured by mass percentage. The content of each element is as follows: C: 0.06, Si: 0.25, Mn: 1.3, P: 0.007, S: 0.003, Ni: 0.56, Cr: 0.40, Mo: 0.02, Cu: 0.35, Nb: 0.03, Ti: 0.013, Al: 0.04, B: 0.0005, with the balance being Fe and unavoidable impurities.

[0050] Among them, CEV = 0.42, Pcm = 0.183, and I index = 6.69.

[0051] The preparation method is as follows: After hot metal pretreatment, converter smelting, and LF+RH refining, a 460mm thick slab is continuously cast in a continuous casting machine. It is then heated to 1180℃ in a heating furnace and held at that temperature for 120 minutes in the soaking zone. Afterward, the slab is removed from the furnace, descaled, and rolled in the recrystallization zone at an initial rolling temperature of 1100℃ to a thickness of 170mm. It is then allowed to cool in air. After reaching 750℃, the slab is rolled in the non-recrystallization zone to a final thickness of 100mm at a final rolling temperature of 715℃. The plate is then cooled in air to 700℃, followed by water cooling at a rate of 5℃ / s and a reddening temperature of 390℃, then air-cooled on a cooling bed. After air cooling, it is tempered at 580℃ for 200 minutes and finally air-cooled to room temperature.

[0052] The mechanical properties of the steel plates obtained in the above embodiments are shown in Table 1. The metallographic structure of the steel plate obtained in Example 1 is shown in Figure 1. The metallographic structure of the steel plate obtained in Example 3 is shown in Figure 2. The series of temperature impact energy fitting curves for the steel plate obtained in Example 3 are shown in Figure 3. The series of temperature impact energy fitting curves for the steel plate obtained in Example 4 are shown in Figure 4.

[0053] Table 1

[0054] As can be seen from the data in Table 1, both the above-mentioned embodiments 1 and 2 meet the mechanical property requirements of GB / T 714-2015 for Q500qE grade steel, and the DBTT of embodiments 3 and 4 reaches below-80℃ after tempering on the basis of embodiments 1 and 2.

[0055] Therefore, the technical scheme of the present application makes the weathering index I of the steel plate reach 6.5 or more through reasonable component design, at the same time, the 100mm thick steel plate prepared only through TMCP process meets the yield strength ≥550MPa, tensile strength ≥680MPa, and the impact at-40℃ reaches 200J or more, the preparation process is simple, the strength and toughness are sufficient compared with the index in GB / T 714-2015, through TMCP+T treatment, the DBTT temperature of the prepared steel plate reaches below-80℃, greatly improving the service safety of the steel plate in low temperature environment.

[0056] In addition to the above embodiments, the present application can also have other implementation manners; any technical scheme formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present application.

Claims

1. A thick Q500qENH steel plate, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.010~0.080%, Si: 0.20~0.50%, Mn: 1.00~1.7%, P: 0.006~0.020%, S: ≤0.005%, Ni: 0.20~1.00%, Cr: 0.20~0.80%, Mo: 0.008~0.030%, Cu: 0.20~0.75%, Nb: 0.01~0.06%, Ti: 0.002~0.020%, Al: ≤0.08%, B: ≤0.0020%, with the balance being Fe and unavoidable impurities.

2. The thick Q500qENH steel plate according to claim 1, characterized in that: The carbon equivalent of the steel plate is ≤0.50%.

3. The thick Q500qENH steel plate according to claim 1, characterized in that: The cold cracking sensitivity coefficient of the steel plate is ≤0.

23.

4. The thick Q500qENH steel plate according to claim 1, characterized in that: The weather resistance index of the steel plate is ≥6.

5.

5. A method for preparing a thick Q500qENH steel plate according to any one of claims 1-4, characterized in that: The process includes, in sequence, molten iron pretreatment → converter smelting → refining → continuous casting → heating → rolling → cooling → tempering.

6. The method for preparing Q500qENH steel plates with large thickness specifications according to claim 5, characterized in that: The continuous casting process includes: preparing molten steel into slabs with a cross-sectional thickness of 460 mm.

7. The method for preparing Q500qENH steel plates with large thickness specifications according to claim 5, characterized in that: The heating process has a heating temperature of 1130–1200℃, a heating rate of 3–8℃ / s, and a heat soaking and heat preservation time of ≥60min.

8. The method for preparing Q500qENH steel plates with large thickness specifications according to claim 5, characterized in that: The rolling process includes recrystallization zone rolling and non-recrystallization zone rolling. The initial rolling temperature for recrystallization zone rolling is 1050–1170℃, and the thickness of the billet to be heated is 160–250 mm. The initial rolling temperature for non-recrystallization zone rolling is ≤770℃, and the final rolling temperature is ≤780℃.

9. The method for preparing Q500qENH steel plates with large thickness specifications according to claim 5, characterized in that: The cooling process includes: after the rolled workpiece is air-cooled to ≤750℃, it is then water-cooled at a cooling rate of 2~10℃, and the temperature range for the re-reddening temperature is controlled to be ≤480℃.

10. The method for preparing Q500qENH steel plate with large thickness as described in claim 5, characterized in that: The tempering process involves a tempering temperature of 460–600°C, a tempering holding time of 180–270 min, and air cooling.

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