600MPa grade steel plate for bifurcation pipe tooth ribs

Abstract

The present invention relates to the technical field of metal materials, and specifically relates to a 600 MPa grade steel plate for bifurcated pipe tooth ribs. Its components, by weight percentage, include: C: 0.072 - 0.090%, Si: 0.12 - 0.19%, Mn: 1.30 - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Cr: 0.25 - 0.30%, Mo: 0.10 - 0.15%, Nb: 0.030 - 0.040%, V: 0.020 - 0.030%, Ti: 0.010 - 0.020%, Als: 0.010 - 0.030%, B: 0.0010 - 0.0020%, Pcm: 0.17 - 0.20%, and the balance is Fe and unavoidable impurities. The steel plate has high strength, good plasticity, and good low-temperature toughness, and the prepared bifurcated pipe is not easily damaged, thus ensuring the reliability of the operation of the hydropower station.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and more specifically, to a 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe. Background Art

[0002] When combined water supply or grouped water supply is adopted in a hydropower station, a single pipe is required to supply water to two or more units, and thus a bifurcation pipe needs to be installed; to ensure the reliability of the operation of the hydropower station, the stability of the bifurcation pipe should be ensured.

[0003] However, the steel plates provided by the related art for manufacturing bifurcation pipes have problems such as low strength, poor plasticity, and poor low-temperature toughness, resulting in the easily damaged bifurcation pipes prepared therefrom and making it difficult to ensure the stable operation of the hydropower station. Summary of the Invention

[0004] The purpose of the present invention is to provide a 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe, which has high strength, good plasticity, and good low-temperature toughness. Using this steel plate to manufacture a bifurcation pipe can ensure that the bifurcation pipe is not easily damaged, thereby ensuring the reliability of the operation of the hydropower station.

[0005] The present invention is implemented as follows:

[0006] The present invention provides a 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe. The components of the 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe, by weight percentage, include:

[0007] C: 0.072 - 0.090%, Si: 0.12 - 0.19%, Mn: 1.30 - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Cr: 0.25 - 0.30%, Mo: 0.10 - 0.15%, Nb: 0.030 - 0.040%, V: 0.020 - 0.030%, Ti: 0.010 - 0.020%, Als: 0.010 - 0.030%, B: 0.0010 - 0.0020%, Pcm: 0.17 - 0.20%, and the balance is Fe and inevitable impurities;

[0008] The thickness of the 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe is 60 - 100 mm.

[0009] In an alternative embodiment, C + Si + Mn = 1.50% - 1.65%.

[0010] In an alternative embodiment, the structure of the 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe is bainite.

[0011] In an alternative embodiment, the manufacturing method of the 600 MPa grade steel plate for the tooth ribs of a bifurcation pipe includes:

[0012] Steelmaking, billet heating, rolling, cooling, and heat treatment;

[0013] The cooling steps include: sequentially cooling the rolled steel plate in a first cooling zone and a second cooling zone; wherein,

[0014] The first cooling zone includes a first sub-cooling zone and a second sub-cooling zone arranged sequentially along the conveying direction of the steel plate;

[0015] Four groups of slot nozzle assemblies are arranged in the first sub-cooling zone. The slot nozzle assembly includes an upper slot nozzle and a lower slot nozzle. The height of the upper slot nozzle is 280 mm - 320 mm, and the cooling water flow rate of the upper slot nozzle is 260 - 280 m 3 / h. The ratio of the cooling water flow rate of the upper slot nozzle to that of the lower slot nozzle is 1:(1.4 - 1.6);

[0016] Eight groups of first high-density nozzle assemblies are arranged in the second sub-cooling zone. The first high-density nozzle assembly includes a first upper high-density nozzle and a first lower high-density nozzle. The height of the first upper high-density nozzle is 280 mm - 320 mm, and the cooling water flow rate of the first upper high-density nozzle is 260 - 280 m 3 / h. The ratio of the cooling water flow rate of the first upper high-density nozzle to that of the first lower high-density nozzle is 1:(1.4 - 1.6);

[0017] Twelve groups of second high-density nozzle assemblies are arranged in the second cooling zone. The second high-density nozzle assembly includes a second upper high-density nozzle and a second lower high-density nozzle. The height of the second upper high-density nozzle is 380 mm - 420 mm, and the cooling water flow rate of the second upper high-density nozzle is 260 - 280 m 3 / h. The ratio of the cooling water flow rate of the second upper high-density nozzle to that of the second lower high-density nozzle is 1:(1.4 - 1.6).

[0018] In an alternative embodiment, the cooling steps further include: when the steel plate moves to the second cooling zone for cooling, controlling the steel plate to swing along a set direction, and the swinging rate is 0.4 ± 0.2 m / s; the set direction forms an angle with the conveying direction of the steel plate;

[0019] The swinging time of the steel plate in the second cooling zone is greater than or equal to 8 min.

[0020] In an alternative embodiment, in the cooling steps, controlling the moving rate of the steel plate in the first cooling zone and the second cooling zone to be 0.3 - 0.5 m / s;

[0021] The water pressure of the spray cooling water of the upper slot nozzle, the lower slot nozzle, the first upper high-density nozzle, the first lower high-density nozzle, the second upper high-density nozzle, and the second lower high-density nozzle is all 0.4 - 0.6 MPa.

[0022] In an alternative embodiment, the starting cooling temperature of the steel plate is 860 ± 10 °C.

[0023] In an alternative embodiment, the cooling time of the steel plate in the first cooling zone is 28 - 32 s.

[0024] In an alternative embodiment, the heat treatment steps include: tempering, the tempering temperature is 550 ± 10 °C, the in-furnace time for tempering is 1.5×H1 + 30 min, where H1 is the thickness of the steel plate in mm, and after discharging from the furnace, it is air-cooled.

[0025] In an alternative embodiment, the billet heating steps include: a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 700 - 900 °C, the temperature of the first heating section is 1100 - 1200 °C, the temperature of the second heating section is 1200 - 1250 °C, the temperature of the soaking section is 1200 - 1240 °C, and the in-furnace time for billet heating is (1.0 - 1.2)×H2 min, where H2 is the thickness of the billet in mm;

[0026] The rolling steps include rough rolling and finish rolling; wherein, the starting rolling temperature for rough rolling is 1030 °C to 1080 °C, the roll speed is 1.0 to 2.0 m / s, the reduction per pass is greater than 12%, and the thickness after rough rolling is H1 + (45 - 55) mm, where H1 is the thickness of the steel plate in mm;

[0027] The starting rolling temperature for finish rolling is less than or equal to 940 °C. The finish rolling includes two passes of rolling. The reduction in the last pass is 1.4 - 1.6 mm, the throwing speed is less than 2 m / s, the finishing rolling temperature is 820 - 860 °C, and the relaxation time after rolling is 10 - 15 s.

[0028] The present invention has the following beneficial effects:

[0029] In the composition of the 600 MPa grade steel plate for the bifurcated pipe tooth rib of the present invention, Ni and Cu elements are not contained. It is possible to increase the C content as much as possible while ensuring that the Pcm value (cold cracking sensitivity index, also known as crack sensitivity coefficient) meets less than or equal to 0.20%, so as to achieve the effect of solid solution strengthening; controlling the contents of Cr, Mo, and B can improve the hardenability of the steel plate with a thickness of 60-100 mm, delay the transformation of supercooled austenite to pearlite, and obtain more lath bainite structure; the addition of 0.10-0.15% molybdenum can inhibit the segregation of low-melting-point substances and chromium carbide at the grain boundaries, which is beneficial to reducing temper brittleness; controlling the Nb content at 0.03-0.04% makes the dynamic recrystallization temperature of the steel plate above 940 °C. After completing the relevant rolling process, complete recrystallization of the steel can be achieved, the austenite grains can be refined, and at the same time, it is also beneficial to control the amount of deformed austenite, ensuring the starting cooling temperature of online quenching during the preparation of the steel plate and facilitating deformation-induced nucleation; controlling the content of Ti can not only refine the original austenite grains after slab heating, but also be beneficial to the grain refinement in the coarse-grained zone after the steel plate is welded; adding an appropriate amount of V can promote the precipitation of V(C,N) during the tempering process of the steel plate, ensuring the strength of the steel plate after tempering or welding; P≤0.015%, S≤0.005%. Controlling the amounts of P and S at a low level can avoid segregation caused by high P content, affecting the uniformity of the steel structure, reducing the plasticity and low-temperature toughness of the steel, and can also avoid the adverse effects of S forming sulfide inclusions on the low-temperature toughness, and further avoid causing anisotropy of the performance. Thus, it can be seen that the 600 MPa grade steel plate for the bifurcated pipe tooth rib of the present invention can effectively improve the strength of the steel plate through the regulation of the composition, and ensure the plasticity and low-temperature toughness of the steel plate, ensuring that the bifurcated pipe prepared with the steel plate of the present invention is not easily damaged, thereby ensuring the reliability of the operation of the hydropower station. Brief Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is the metallographic structure diagram of the hot-rolled steel plate in Embodiment 3 of the present invention;

[0032] Figure 2 It is the metallographic structure diagram of the tempered steel plate in Embodiment 3 of the present invention. Detailed Embodiments

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchases.

[0034] The present invention provides a composition of a 600 MPa grade steel plate for the bifurcated pipe tooth rib, which includes, by weight percentage: C: 0.072 - 0.090% (such as 0.072%, 0.075%, 0.079%, 0.081%, 0.083%, 0.085%, 0.088%, 0.090%, etc.), Si: 0.12 - 0.19% (such as 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, etc.), Mn: 1.30 - 1.40% (such as 1.30%, 1.31%, 1.32%, 1.33%, 1.34%, 1.35%, 1.38%, 1.40%, etc.), P ≤ 0.015% (such as 0.015%, 0.014%, 0.013%, 0.012%, etc.), S ≤ 0.005% (such as 0.005%, 0.004%, 0.003%, 0.002%, etc.), Cr: 0.25 - 0.30% (such as 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, etc.), Mo: 0.10 - 0.15% (such as 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%), Nb: 0.030 - 0.040% (such as 0.030%, 0.032%, 0.033%, 0.035%, 0.038%, 0.040%, etc.), V: 0.020 - 0.030% (such as 0.020%, 0.022%, 0.023%, 0.025%, 0.028%, 0.030%, etc.), Ti: 0.010 - 0.020% (such as 0.010%, 0.011%, 0.012%, 0.014%, 0.016%, 0.018%, 0.020%, etc.), Als: 0.010 - 0.030% (such as 0.010%, 0.013%, 0.015%, 0.017%, 0.020%, 0.022%, 0.023%, 0.025%, 0.028%, 0.030%, etc.), B: 0.0010 - 0.0020% (such as 0.0010%, 0.0012%, 0.0014%, 0.0016%, 0.0018%, 0.0020%, etc.), Pcm: 0.17 - 0.20% (such as 0.18%, 0.19%, 0.20%, etc.), and the balance is Fe and unavoidable impurities; the thickness of the 600 MPa grade steel plate for the bifurcated pipe tooth rib is 60 - 100 mm (such as 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc.).

[0035] In the composition of the 600 MPa grade steel plate for the bifurcated pipe tooth rib of the present invention, Ni and Cu elements are not contained. It is possible to increase the C content as much as possible while ensuring that the Pcm value (cold cracking sensitivity index, also known as crack sensitivity coefficient) satisfies less than or equal to 0.20%, so as to achieve the effect of solid solution strengthening. That is, it can avoid the pitting on the surface of the steel plate caused by the presence of Ni in the composition of the steel plate, and can also avoid the presence of Cu in the composition of the steel plate. Since the melting point of Cu is low, it is easy to cause intergranular melting during the heating of the steel slab, resulting in cracks on the surface of the steel plate. By controlling the contents of Cr, Mo, and B, the hardenability of the steel plate with a thickness of 60 - 100 mm can be improved, so as to delay the transformation of supercooled austenite to pearlite and obtain more lower bainite structure. Even the structure of the steel plate of the present invention can be all bainite. The morphology of lower bainite ferrite is lath-shaped, which is beneficial to obtaining good low-temperature toughness during subsequent tempering. The addition of 0.10 - 0.15% molybdenum can inhibit the segregation of low-melting-point substances and chromium carbide at grain boundaries, which is beneficial to reducing temper brittleness. By controlling the Nb content at 0.03 - 0.04%, the dynamic recrystallization temperature of the steel plate is above 940°C. After completing the relevant rolling process, complete recrystallization of the steel can be achieved, and the austenite grains can be refined (that is, Nb precipitates at high temperature and pins at grain boundaries, which can refine austenite grains). At the same time, it is also beneficial to control the amount of deformed austenite, ensuring the starting cooling temperature of online quenching during the preparation of the steel plate and facilitating deformation-induced nucleation. By controlling the content of Ti, not only can the original austenite grains after slab heating be refined, but also the grains in the coarse-grained heat-affected zone can be refined after the steel plate is welded. That is, Ti precipitates at high temperature and pins at grain boundaries, which can refine austenite grains. By adding an appropriate amount of V, the precipitation of V(C,N) during the tempering process of the steel plate is utilized to ensure the strength of the steel plate after tempering or welding. And vanadium precipitates at low temperature, and the precipitates are dispersed, preventing dislocation slip. P ≤ 0.015%, S ≤ 0.005%. Controlling the amounts of P and S at a relatively low level can avoid segregation caused by high P content, affecting the uniformity of the steel structure, reducing the plasticity and low-temperature toughness of the steel, and can also avoid the formation of sulfide inclusions by S, which has an adverse effect on low-temperature toughness and further avoids causing anisotropy of properties. Thus, it can be seen that through the regulation of the composition, the 600 MPa grade steel plate for the bifurcated pipe tooth rib of the present invention can effectively improve the strength of the steel plate, and ensure the plasticity and low-temperature toughness of the steel plate, ensuring that the bifurcated pipe prepared with the steel plate of the present invention is not easily damaged, thereby ensuring the reliability of the operation of the hydropower station.

[0036] Optionally, without adding Ni and Cu elements, while ensuring the Pcm value, increasing the C content as much as possible, and ensuring that C + Si + Mn = 1.50% - 1.65%, the effect of solid solution strengthening can be achieved. It should be noted that solid solution strengthening is that atoms in the crystal cause lattice distortion. By controlling C + Si + Mn = 1.50% - 1.65%, when the steel plate is stretched, atomic slip is difficult, thus increasing the strength of the steel plate.

[0037] The preparation method of the 600MPa grade steel plate for the bifurcated pipe tooth rib of the present invention includes:

[0038] Steelmaking, billet heating, rolling, cooling and heat treatment;

[0039] The cooling step includes: cooling the rolled steel plate in a first cooling area and a second cooling area in sequence; wherein,

[0040] The first cooling area includes a first sub-cooling area and a second sub-cooling area arranged in sequence along the conveying direction of the steel plate;

[0041] Four groups of slit nozzle assemblies are arranged in the first sub-cooling area. The slit nozzle assembly includes an upper slit nozzle and a lower slit nozzle. The height of the upper slit nozzle is 280mm - 320mm (for example: 280mm, 290mm, 300mm, 310mm, 320mm, etc.). The cooling water flow rate of the upper slit nozzle is 260 - 280m 3 / h (for example: 260m 3 / h, 265m 3 / h, 270m 3 / h, 275m 3 / h, 280m 3 / h, etc.). The ratio of the cooling water flow rate of the upper slit nozzle to that of the lower slit nozzle is 1:(1.4 - 1.6), for example: 1:1.4, 1:1.5, 1:1.6, etc.

[0042] Eight groups of first high-density nozzle assemblies are arranged in the second sub-cooling area. The first high-density nozzle assembly includes a first upper high-density nozzle and a first lower high-density nozzle. The height of the first upper high-density nozzle is 280mm - 320mm (for example: 280mm, 290mm, 300mm, 310mm, 320mm, etc.). The cooling water flow rate of the first upper high-density nozzle is 260 - 280m 3 / h (for example: 260m 3 / h, 265m 3 / h, 270m 3 / h, 275m 3 / h, 280m 3 / h, etc.). The ratio of the cooling water flow rate of the first upper high-density nozzle to that of the first lower high-density nozzle is 1:(1.4 - 1.6), for example: 1:1.4, 1:1.5, 1:1.6, etc.

[0043] The second cooling area is provided with twelve groups of second high-density nozzle assemblies. The second high-density nozzle assembly includes a second upper high-density nozzle and a second lower high-density nozzle. The height of the second upper high-density nozzle is 380 mm - 420 mm (for example: 380 mm, 390 mm, 400 mm, 410 mm, 420 mm, etc.). The cooling water flow rate of the second upper high-density nozzle is 260 - 280 m 3 / h (for example: 260 m 3 / h, 265 m 3 / h, 270 m 3 / h, 275 m 3 / h, 280 m 3 / h, etc.). The cooling water flow rate ratio of the second upper high-density nozzle to the second lower high-density nozzle is 1:(1.4 - 1.6), for example: 1:1.4, 1:1.5, 1:1.6, etc.

[0044] It should be noted that when spraying condensed water to cool the lower surface of the steel plate, the height and related technologies of each nozzle are similar, so they will not be elaborated here.

[0045] The cooling step of the present invention has the effect of online quenching, achieving rapid cooling, avoiding reheating and cooling of the steel plate, that is, avoiding offline quenching of the steel plate. This not only reduces production costs, but also utilizes a large number of dislocations inside deformed austenite to refine the grains of the steel plate after cooling, improving the strength and toughness of the steel plate.

[0046] Optionally, high-pressure water pumps are used to spray cooling water in the first sub-cooling area, the second sub-cooling area and the second cooling area. The water pressure for spraying cooling water by the first upper high-density nozzle, the first lower high-density nozzle, the second upper high-density nozzle and the second lower high-density nozzle is 0.4 - 0.6 MPa, for example: 0.4 MPa, 0.5 MPa, 0.6 MPa.

[0047] Optionally, the moving rate of the steel plate in the first cooling area and the second cooling area is 0.3 - 0.5 m / s, for example: 0.3 m / s, 0.4 m / s, 0.5 m / s, etc.

[0048] Optionally, the length of the steel plate is 7 - 9 meters, for example: 7 meters, 8 meters, 9 meters, etc.

[0049] Optionally, when the steel plate moves to the second cooling area for cooling, control the steel plate to swing in a set direction, and the swinging rate is 0.4±0.2 m / s, for example: 0.2 m / s, 0.3 m / s, 0.4 m / s, 0.5 m / s, 0.6 m / s, etc.; the set direction forms an angle with the conveying direction of the steel plate. For example, when the steel plate moves in the front-back direction during cooling, when the steel plate moves to the second cooling area for cooling, control the steel plate to swing in the left-right direction; the swinging time of the steel plate in the second cooling area is greater than or equal to 8 min, for example: 8 min, 8.5 min, 9 min, etc.

[0050] It should be noted that when the steel plate enters the second cooling area for cooling, it can swing while maintaining the conveying state, that is, when the steel plate enters the second cooling area, make the steel plate continue to move in the moving direction from the first cooling area to the second cooling area, and during the moving process, make the steel plate swing; of course, when the steel plate enters the second cooling area for cooling, after the steel plate completely enters the second cooling area, it can be controlled that the steel plate no longer continues to move in the previous moving direction, but stays at the corresponding position for swinging.

[0051] Optionally, the starting cooling temperature of the steel plate is 860±10 °C, for example: 850 °C, 855 °C, 860 °C, 865 °C, 870 °C, etc.

[0052] Optionally, the cooling time of the steel plate in the first cooling area is 28 - 32 s, for example: 28 s, 29 s, 30 s, 31 s, 32 s, etc., and no specific limitation is made here.

[0053] It should be noted that when cooling the steel plate, starting from when the steel plate enters the cooling device, that is, starting from when the steel plate enters the first cooling area, turn on the slit nozzle assembly and the first high-density nozzle assembly. Approximately 15 seconds later, when the steel plate moves out of the cooling area corresponding to the slit nozzle assembly and enters the cooling area corresponding to the first high-density nozzle assembly, the slit nozzle assembly can be turned off, and only the first high-density nozzle assembly is kept on. Further, when the slit nozzle assembly and the first high-density nozzle assembly of the steel plate are turned on for approximately 10 seconds, the second high-density nozzle assembly in the second cooling area can be turned on, and the cooling water flow rate of the second high-density nozzle assembly is gradually increased until the cooling water flow rate of the second high-density nozzle assembly increases to 260 - 280 m 3 / h.

[0054] In the present invention, the heat treatment steps include: tempering, the tempering temperature is 550±10 °C (for example: 540 °C, 545 °C, 550 °C, 555 °C, 560 °C, etc.), the in-furnace time for tempering is 1.5×H1 + 30 min, H1 is the thickness of the steel plate in mm, and it is air-cooled after being taken out of the furnace.

[0055] In the present invention, the steps of billet heating include a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 700 - 900 °C (for example: 700 °C, 730 °C, 750 °C, 770 °C, 800 °C, 820 °C, 850 °C, 880 °C, 900 °C, etc.), the temperature of the first heating section is 1100 - 1200 °C (for example: 1100 °C, 1130 °C, 1150 °C, 1170 °C, 1200 °C, etc.), the temperature of the second heating section is 1200 - 1250 °C (for example: 1200 °C, 1230 °C, 1250 °C, etc.), the temperature of the soaking section is 1200 - 1240 °C (for example: 1200 °C, 1210 °C, 1220 °C, 1230 °C, 1240 °C, etc.). The residence time of the billet in the furnace is (1.0 - 1.2) × H2 min (for example: 1.0 × H2 min, 1.1 × H2 min, 1.2 × H2 min, etc.), where H2 is the thickness of the billet in mm.

[0056] The rolling steps include rough rolling and finish rolling; among them, the starting rolling temperature of rough rolling is 1030 °C - 1080 °C (for example: 1030 °C, 1040 °C, 1050 °C, 1070 °C, 1080 °C, etc.), the roll speed is 1.0 - 2.0 m / s (for example: 1.0 m / s, 1.2 m / s, 1.5 m / s, 1.7 m / s, 2.0 m / s, etc.), the reduction per pass is greater than 12% (for example: 12%, 12.5%, 13%, etc.), the thickness after rough rolling is H1 + (45 - 55) mm (for example: H1 + 45 mm, H1 + 50 mm, H1 + 55 mm, etc.), where H1 is the thickness of the steel plate in mm; Adopting high-temperature, low-speed and large reduction rolling can reduce the deformation resistance and rolling torque, make the deformation more favorable to penetrate into the core of the steel plate, and at the same time achieve complete recrystallization and fully refine the austenite grains.

[0057] The starting rolling temperature of finish rolling is less than or equal to 940 °C (for example: 940 °C, 930 °C, 920 °C, 910 °C, etc.). The finish rolling includes two passes of rolling. The reduction of the last pass is 1.4 - 1.6 mm (for example: 1.4 mm, 1.5 mm, 1.6 mm, etc.), the throwing speed is less than 2 m / s (for example: 1.0 m / s, 1.2 m / s, 1.5 m / s, 1.7 m / s, 2.0 m / s, etc.), the finishing rolling temperature is 820 - 860 °C (for example: 820 °C, 830 °C, 840 °C, 850 °C, 860 °C, etc.), reducing the warping at the head and tail. The relaxation time after rolling is 10 - 15 s (for example: 10 s, 11 s, 12 s, 13 s, 14 s, 15 s, etc.), which is beneficial to the temperature uniformity of the steel plate before entering the water.

[0058] It should be noted that by controlling the Nb content to be 0.03 - 0.04% and the dynamic recrystallization temperature to be above 940°C, after the first-stage rolling (rough rolling) is completed, complete recrystallization of the steel is achieved, the austenite grains are refined, and at the same time, it is beneficial to control the temperature and the amount of deformed austenite in the second-stage rolling (finish rolling), ensuring the starting cooling temperature of online quenching and facilitating deformation-induced nucleation.

[0059] It should also be noted that the steelmaking steps include: converter smelting, LF refining, RH vacuum refining, continuous casting, billet cleaning and other process steps, all of which are similar to the related technologies and will not be elaborated here.

[0060] The present invention will be further described in detail below in conjunction with embodiments.

[0061] Embodiment 1

[0062] The components of the steel plate for the bifurcation pipe tooth rib of 600 MPa grade, by weight percentage, include: C: 0.072, Si: 0.15%, Mn: 1.36%, P: 0.012%, S: 0.005%, Cr: 0.25%, Mo: 0.12%, Nb: 0.032%, V: 0.025%, Ti: 0.012%, Als: 0.025%, B: 0.0015%, Pcm: 0.176%, and the balance is Fe and inevitable impurities; among them, C + Si + Mn = 1.582%.

[0063] Process steps:

[0064] 1) Billet heating process: The preheating section temperature of the 250 mm thick billet is 750°C, the first heating section is 1150°C, the second heating section is 1230°C, the soaking temperature is 1220°C, the time in the furnace is 270 minutes, and rolling is carried out after reaching the temperature.

[0065] 2) Rolling process: Two-stage rolling is adopted. The rough rolling starting temperature is 1058°C, the roll speed is 2.0 m / s, the pass reduction rate is 12%, and the thickness after rough rolling (i.e., the thickness of the steel plate to be) is 110 mm; the finish rolling starting temperature is 880°C, double-pass rolling is adopted, the reduction of the last pass is 1.5 mm, the throwing speed is 1.2 m / s, the finishing temperature is 860°C, and the thickness of the rolled steel plate is 60 mm.

[0066] 3) Cooling process: Relax for 10 seconds after rolling, use 3 high-pressure water pumps, the water pressure is 0.5 MPa, the roll speed is 0.4 m / s, the length of the steel plate is 8 meters, and the starting cooling temperature is 855°C. The cooling parameters are shown in the following two tables:

[0067]

[0068]

[0069] When the steel plate is in the cold zone of the second cooling area, control the steel plate to swing at a speed of 0.4 m / s for 8 minutes, and then the steel plate passes through the roller table and is taken offline for non-destructive ultrasonic flaw detection.

[0070] 4) Heat treatment process: The tempering temperature is 550 °C, the time in the furnace is 120 minutes, and it is air-cooled after being taken out of the furnace.

[0071] Example 2

[0072] The components of the steel plate for the bifurcated pipe tooth rib with a grade of 600 MPa include, by weight percentage: C: 0.090, Si: 0.19%, Mn: 1.35%, P: 0.015%, S: 0.005%, Cr: 0.26%, Mo: 0.15%, Nb: 0.030%, V: 0.022%, Ti: 0.010%, Als: 0.029%, B: 0.0014%, Pcm: 0.196%, and the balance is Fe and unavoidable impurities; among them, C + Si + Mn = 1.63%.

[0073] Process steps:

[0074] 1) Blank heating process: The preheating section temperature of the 295-mm-thick blank is 850 °C, the first heating section is 1200 °C, the second heating section is 1250 °C, the soaking temperature is 1240 °C, the time in the furnace is 330 minutes, and rolling is carried out after reaching the temperature.

[0075] 2) Rolling process: Two-stage rolling is adopted. The rough rolling starting temperature is 1030 °C, the roll speed is 1.8 m / s, the pass reduction rate is 13%, and the thickness after rough rolling (i.e., the thickness of the steel plate to be) is 130 mm; the finish rolling starting temperature is 940 °C, double-pass rolling is adopted, the reduction of the last pass is 1.5 mm, the throwing speed is 1.1 m / s, the finish rolling temperature is 855 °C, and the thickness of the rolled steel plate is 80 mm.

[0076] 3) Cooling process: Relax for 12 seconds after rolling. Use 3 high-pressure water pumps, the water pressure is 0.5 MPa, the roll speed is 0.4 m / s, the length of the steel plate is 8 meters, and the starting cooling temperature is 860 °C. Please refer to the following two tables for the cooling parameters:

[0077]

[0078]

[0079] When the steel plate is in the cold zone of the second cooling area, control the steel plate to swing at a speed of 0.2 m / s for 12 minutes, and then the steel plate passes through the roller table and is taken offline for non-destructive ultrasonic flaw detection.

[0080] 4) Heat treatment process: The tempering temperature is 540 °C, the time in the furnace is 150 minutes, and it is air-cooled after being taken out of the furnace.

[0081] Example 3

[0082] The components of the steel plate with 600 MPa grade for the bifurcation pipe tooth ribs, by weight percentage, include: C: 0.08, Si: 0.14%, Mn: 1.39%, P: 0.011%, S: 0.003%, Cr: 0.29%, Mo: 0.11%, Nb: 0.035%, V: 0.026%, Ti: 0.014%, Als: 0.029%, B: 0.0017%, Pcm: 0.187%, and the balance is Fe and inevitable impurities; among them, C + Si + Mn = 1.61%.

[0083] Process steps:

[0084] 1) Blank heating process: The preheating section temperature of the 295 mm thick blank is 800 °C, the first heating section is 1180 °C, the second heating section is 1240 °C, the soaking temperature is 1230 °C, the time in the furnace is 350 minutes, and rolling is carried out after reaching the temperature.

[0085] 2) Rolling process: Two-stage rolling is adopted. The rough rolling starting temperature is 1055 °C, the roll speed is 1.9 m / s, the reduction rate per pass is 14%, and the thickness after rough rolling (i.e., the thickness of the steel plate to be rolled) is 160 mm; the finishing rolling starting temperature is 900 °C, double-pass rolling is adopted, the reduction of the last pass is 1.5 mm, the throwing speed of the steel is 1.8 m / s, the finishing rolling temperature is 860 °C, and the thickness of the rolled steel plate is 100 mm.

[0086] 3) Cooling process: Relax for 15 seconds after rolling, use 3 high-pressure water pumps, the water pressure is 0.5 MPa, the roll speed is 0.4 m / s, the length of the steel plate is 8 meters, and the starting cooling temperature is 858 °C. Please refer to the following two tables for the cooling parameters:

[0087]

[0088]

[0089]

[0090] When the steel plate is in the cold zone of the second cooling area, control the steel plate to swing at a speed of 0.6 m / s for 15 minutes, and then the steel plate passes through the roller table and is taken offline for non-destructive ultrasonic flaw detection.

[0091] 4) Heat treatment process: The tempering temperature is 550 °C, the time in the furnace is 180 minutes, and it is air-cooled after leaving the furnace.

[0092] Comparative Example 1

[0093] Comparative Example 1 is similar to Example 1, the differences are: C: 0.072%, Si: 0.12%, Mn: 1.30%, C + Si + Mn = 1.49%, Pcm: 0.167, and other parameters refer to Example 1.

[0094] Comparative Example 2

[0095] Comparative Example 2 is similar to Example 1, except that: C: 0.09%, Si: 0.19%, Mn: 1.40%, C + Si + Mn = 1.68%, Pcm: 0.193, and other parameters refer to Example 1.

[0096] Comparative Example 3

[0097] Comparative Example 3 is similar to Example 1, except that: C: 0.17%, Si: 0.25%, Mn: 1.10%, C + Si + Mn = 1.52%, Pcm: 0.26, and other parameters refer to Example 1.

[0098] Comparative Example 4

[0099] Comparative Example 4 is similar to Example 1, except that the composition contains 0.15% Ni and 0.18% Cu, and other parameters refer to Example 1.

[0100] The yield strength, tensile strength and other properties of the steel plate in Comparative Example 4 are not much different from those in Example 1. However, there are many pockmarks on the surface of the steel plate in Comparative Example 4, and obvious cracks exist on the surface of the steel plate.

[0101] Comparative Example 5

[0102] Comparative Example 5 is similar to Example 1, except that Mo is not contained in the composition, and other parameters refer to Example 1.

[0103] Comparative Example 6

[0104] Comparative Example 6 is similar to Example 1, except that the content of Mo in the composition is 0.05%, and other parameters refer to Example 1. Upper bainite exists in the structure of Comparative Example 6.

[0105] Comparative Example 7

[0106] Comparative Example 7 is similar to Example 1, except that in the first cooling zone, the heights of the upper slit nozzle and the first upper high-density nozzle are both 400 mm, and other parameters refer to Example 1.

[0107] Comparative Example 8

[0108] Comparative Example 8 is similar to Example 1, except that in the second cooling zone, the swing of the steel plate is not controlled, and other parameters refer to Example 1.

[0109] Comparative Example 9

[0110] Comparative Example 9 is similar to Example 1, except that: in the first cooling zone, the heights of the upper slot nozzles and the first upper high-density nozzles are both 400 mm, and in the second cooling zone, the swinging of the steel plate is not controlled, and other parameters refer to Example 1.

[0111] Comparative Example 10

[0112] Comparative Example 10 is similar to Example 1, except that: C: 0.072%, Si: 0.12%, Mn: 1.30%, C + Si + Mn = 1.49%, Pcm: 0.167, in the first cooling zone, the heights of the upper slot nozzles and the first upper high-density nozzles are both 400 mm, and in the second cooling zone, the swinging of the steel plate is not controlled, and other parameters refer to Example 1.

[0113] Comparative Example 11

[0114] Comparative Example 11 is similar to Example 1, except that: C: 0.17%, Si: 0.25%, Mn: 1.10%, C + Si + Mn = 1.52%, Pcm: 0.26, in the first cooling zone, the heights of the upper slot nozzles and the first upper high-density nozzles are both 400 mm, and in the second cooling zone, the swinging of the steel plate is not controlled, and other parameters refer to Example 1.

[0115] Compare the properties of the steel plates in each example and comparative example, as shown in the following table:

[0116]

[0117]

[0118] The steel plate properties of the embodiments of the present invention meet: tensile strength Rm: 635 - 657 MPa, yield strength Rel: 505 - 525 MPa, elongation A ≥ 22%, average -20°C transverse V-notch impact ≥ 150 J, Pcm is 0.18% - 0.20%. The comprehensive properties such as tensile strength, yield strength, elongation and transverse V-notch impact absorption performance of the embodiments of the present invention are superior to those of the comparative examples. The steel plates of the embodiments of the present invention are used to prepare penstock bifurcations, which can ensure their quality and are not easily damaged.

[0119] According to Figure 1 and Figure 2 it can be known that the steel plate structure is bainite, and the carbide distribution is uniform, which is beneficial to the strength and toughness of the steel plate.

[0120] In summary, the 600 MPa grade steel plate for penstock bifurcations of the present invention has high strength, good plasticity and good low-temperature toughness. Using it to prepare penstock bifurcations can ensure that the penstock bifurcations are not easily damaged, thus ensuring the reliability of the operation of the hydropower station.

[0121] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A 600MPa grade steel plate for the bifurcated pipe tooth rib, characterized in that, the components of the 600MPa grade steel plate for the bifurcated pipe tooth rib do not contain Ni and Cu, and by weight percentage include: C: 0.072 - 0.090%, Si: 0.12 - 0.19%, Mn: 1.30 - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Cr: 0.25 - 0.30%, Mo: 0.10 - 0.15%, Nb: 0.030 - 0.040%, V: 0.020 - 0.030%, Ti: 0.010 - 0.020%, Als: 0.010 - 0.030%, B: 0.0010 - 0.0020%, Pcm: 0.17 - 0.20%, and the balance is Fe and unavoidable impurities; C + Si + Mn = 1.50% - 1.65%; the thickness of the 600MPa grade steel plate for the bifurcated pipe tooth rib is 60 - 100mm; wherein, the preparation method of the 600MPa grade steel plate for the bifurcated pipe tooth rib includes: steelmaking, billet heating, rolling, cooling and heat treatment; the cooling step includes: cooling the rolled steel plate in a first cooling area and a second cooling area in sequence; the first cooling area includes a first sub-cooling area and a second sub-cooling area arranged in sequence along the conveying direction of the steel plate; The first sub-cooling zone is provided with four groups of slot nozzle assemblies. The slot nozzle assembly includes an upper slot nozzle and a lower slot nozzle. The height of the upper slot nozzle is 280 mm - 320 mm. The cooling water flow rate of the upper slot nozzle is 260 - 280 m 3 / h. The ratio of the cooling water flow rate of the upper slot nozzle to that of the lower slot nozzle is 1:(1.4 - 1.6); The second sub-cooling zone is provided with eight groups of first high-density nozzle assemblies. The first high-density nozzle assembly includes a first upper high-density nozzle and a first lower high-density nozzle. The height of the first upper high-density nozzle is 280 mm - 320 mm, and the cooling water flow rate of the first upper high-density nozzle is 260 - 280 m 3 / h. The cooling water flow rate ratio of the first upper high-density nozzle to the first lower high-density nozzle is 1:(1.4 - 1.6); The second cooling area is provided with twelve groups of second high-density nozzle assemblies. The second high-density nozzle assembly includes a second upper high-density nozzle and a second lower high-density nozzle. The height of the second upper high-density nozzle is 380 mm - 420 mm, and the cooling water flow rate of the second upper high-density nozzle is 260 - 280 m 3 / h. The cooling water flow rate ratio of the second upper high-density nozzle to the second lower high-density nozzle is 1:(1.4 - 1.6).

2. The 600MPa grade steel plate for the bifurcated pipe tooth rib according to claim 1, characterized in that, the structure of the 600MPa grade steel plate for the bifurcated pipe tooth rib is bainite.

3. The 600MPa grade steel plate for the bifurcated pipe tooth rib according to claim 1, characterized in that, the cooling step further includes: when the steel plate moves to the second cooling area for cooling, controlling the steel plate to swing along a set direction, and the swinging rate is 0.4 ± 0.2m / s; the set direction forms an angle with the conveying direction of the steel plate; the swinging time of the steel plate in the second cooling area is greater than or equal to 8min.

4. The 600MPa grade steel plate for the bifurcated pipe tooth rib according to claim 1, characterized in that, in the cooling step, controlling the moving rate of the steel plate in the first cooling area and the second cooling area to be 0.3 - 0.5m / s; the water pressure of the spray cooling water of the upper slit nozzle, the lower slit nozzle, the first upper high-density nozzle, the first lower high-density nozzle, the second upper high-density nozzle and the second lower high-density nozzle is all 0.4 - 0.6MPa.

5. The 600MPa grade steel plate for the bifurcated pipe tooth rib according to claim 1, characterized in that, the starting cooling temperature of the steel plate is 860 ± 10°C.

6. The 600MPa grade steel plate for the bifurcated pipe tooth rib according to claim 1, characterized in that, the cooling time of the steel plate in the first cooling area is 28 - 32s.

7. The 600MPa grade steel plate for the bifurcated pipe tooth rib according to any one of claims 1 - 5, characterized in that, The steps of the heat treatment include: tempering, the temperature of the tempering is 550 ± 10 °C, the in-furnace time of the tempering is 1.5×H1 + 30 min, where H1 is the thickness of the steel plate in mm, and after taking out of the furnace, it is air-cooled.

8. The 600 MPa grade steel plate for the bifurcated pipe tooth rib according to any one of claims 1-5, characterized in that the steps of heating the blank include: a preheating section, a first heating section, a second heating section and a soaking section, the temperature of the preheating section is 700 - 900 °C, the temperature of the first heating section is 1100 - 1200 °C, the temperature of the second heating section is 1200 - 1250 °C, the temperature of the soaking section is 1200 - 1240 °C, and the in-furnace time of heating the blank is (1.0 - 1.2)×H2 min, where H2 is the thickness of the blank in mm; the steps of the rolling include rough rolling and finish rolling; wherein, the starting rolling temperature of the rough rolling is 1030 °C to 1080 °C, the roll speed is 1.0 to 2.0 m / s, the reduction rate per pass is greater than 12%, and the thickness after rough rolling is H1 + (45 - 55) mm, where H1 is the thickness of the steel plate in mm; the starting rolling temperature of the finish rolling is less than or equal to 940 °C, the finish rolling includes two passes of rolling, the reduction of the last pass is 1.4 - 1.6 mm, the throwing speed is less than 2 m / s, the final rolling temperature is 820 - 860 °C, and the relaxation time after rolling is 10 - 15 s.

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