A low-temperature impact-resistant steel produced by a CVC tandem mill, its preparation method and application

Abstract

The preparation method of the low-temperature impact-resistant steel provided by the present invention comprises the following steps: heating and flat rolling a continuous casting billet in sequence, and then performing coil rolling by using a CVCplus Steckel mill, including the axial movement of CVC work rolls, to obtain a steel plate with a thickness of 4-6 mm and a width of 2200-3050 mm; the continuous casting billet comprises the following chemical components: carbon, manganese, niobium, titanium, chromium, silicon and iron; the number of passes of the coil rolling is 5-7 times, the reduction rate of the last pass of the coil rolling is 11-13%, the reduction rate of the penultimate pass of the coil rolling is 16-19%, and the reduction rate of the third-to-last pass of the coil rolling is 19-21%; cooling the steel plate to obtain the low-temperature impact-resistant steel; the cooling rate is 5-10 °C / s; the impact toughness of the low-temperature impact-resistant steel at -40 °C is ≥50 J. The use of a CVCplus Steckel mill for coil rolling improves the preparation efficiency of the low-temperature impact-resistant steel and realizes large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure vessels, and particularly relates to a low-temperature impact-resistant steel, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing demand for natural gas, a large number of natural gas storage tanks are required. A natural gas storage tank is a low-temperature pressure vessel. The skin steel of its top structure needs to have a thickness of 4-6 mm, a width of 2200-3050 mm, and needs to meet the requirements of low-temperature impact at -40°C. In order to meet the above technical requirements, temperature-controlled rolling and controlled cooling are required, and the rolling difficulty is extremely high. At the same time, the control difficulty of the steel plate is unprecedentedly strict.

[0003] When using traditional medium-thick or wide-thick plate rolling lines to produce wide and thin steel plates, it is limited by the fast temperature drop rate of the rolled piece during the rolling process. During the rolling process of the steel plate, it becomes thinner and thinner, the rolled piece becomes longer and longer, and the temperature drop of the steel plate will become faster and faster. In order to prepare the skin steel for the top structure of a natural gas storage tank that meets the requirements, the existing process can only implement two heating + two rolling. However, its production efficiency is low and its production stability is poor, making it difficult to carry out large-scale production. Summary of the Invention

[0004] In view of this, the present invention provides a low-temperature impact-resistant steel, a preparation method thereof, and an application thereof. The present invention utilizes a CVCplus Steckel mill to efficiently produce low-temperature impact-resistant steel, and according to the preparation method provided by the present invention, large-scale production of low-temperature impact-resistant container steel can be achieved.

[0005] In order to solve the above technical problems, the present invention provides a preparation method for a low-temperature impact-resistant steel, comprising the following steps:

[0006] The continuous casting billet is heated and flat-rolled in sequence, and then coiled by a CVCplus Steckel mill to obtain a steel plate; the continuous casting billet comprises the following chemical components in mass percentage: 0.05-0.09% C, 1.35-1.65% Mn, 0.10-0.30% Si, 0.02-0.04% Nb, 0.15-0.25% Ti, 0.15%-0.20% Cr, and the balance being iron; the number of passes for the coiling is 5-7 times, the reduction rate of the last pass of the coiling is 11-13%, the reduction rate of the penultimate pass of the coiling is 16-19%, and the reduction rate of the third-to-last pass of the coiling is 19-21%;

[0007] The steel plate is cooled to obtain a low-temperature impact-resistant steel; the cooling rate is 5-10°C / s.

[0008] Preferably, the CVCplus Steckel mill comprises a coiling furnace and a four-high reversing mill; the coiling furnace comprises a front coiling furnace and a rear coiling furnace;

[0009] The tension of the strip steel between the coiling furnace drum and the four-high reversing mill is 18 - 25 t.

[0010] Preferably, the temperature of the coiling furnace is 860 - 930 °C.

[0011] Preferably, the work rolls of the CVCplus furnace mill move axially, and the axial movement amount of the CVC in the last three rolling passes is within 70 mm.

[0012] Preferably, the total reduction ratio of the rolling is 50 - 85%;

[0013] The starting rolling temperature of the rolling is 990 - 1030 °C; the finishing rolling temperature of the rolling is 780 - 862 °C.

[0014] Preferably, the number of passes of the flat rolling is 6 - 8 times;

[0015] The starting rolling temperature of the flat rolling is ≥ 1020 °C.

[0016] Preferably, the temperature of the heating is 1230 - 1260 °C, and the coefficient of the heating is ≥ 10.0 min / cm;

[0017] The equipment for heating includes a soaking section, the uniformity of the temperature in the soaking section is ≤ 10 °C, and the holding time in the soaking section is greater than or equal to 25 min.

[0018] Preferably, the red - returning temperature after cooling is 620 - 690 °C.

[0019] The present invention also provides a low - temperature impact - resistant steel prepared by the preparation method described in the above technical solution, which includes the following chemical components by mass percentage:

[0020]

[0021] The thickness of the low - temperature impact - resistant steel is 4 - 6 mm, and the width is 2200 - 3050 mm;

[0022] The impact toughness of the low - temperature impact - resistant steel at - 40 °C is ≥ 50 J.

[0023] The present invention also provides an application of the low - temperature impact - resistant steel described in the above technical solution as the skin steel for the top structure of a natural gas storage tank.

[0024] The present invention provides a method for preparing a low-temperature impact-resistant steel, comprising the following steps: heating and flat-rolling a continuous casting billet in sequence, and then performing coil rolling using a CVCplus Steckel mill to obtain a steel plate; the continuous casting billet comprises the following chemical components: carbon, manganese, niobium, titanium, chromium, silicon and iron; the number of passes for the coil rolling is 5 to 7 times, the reduction rate of the last pass of the coil rolling is 11 to 13%, the reduction rate of the penultimate pass of the coil rolling is 16 to 19%, and the reduction rate of the third-to-last pass of the coil rolling is 19 to 21%; cooling the steel plate to obtain a low-temperature impact-resistant steel; the cooling rate is 5 to 10 °C / s. The low-temperature impact-resistant steel provided by the present invention can be used as a low-temperature impact-resistant container steel. The present invention uses a CVCplus Steckel mill for coil rolling, and coiling furnaces are arranged in front of and behind the mill for heat preservation, which improves the preparation efficiency of the low-temperature impact-resistant steel and realizes the large-scale production of low-temperature impact-resistant container steel. The present invention improves the low-temperature impact toughness of the low-temperature impact-resistant container steel by adding niobium, and improves the mechanical strength of the low-temperature impact-resistant container steel by adding titanium and chromium. According to the preparation method provided by the present invention, a low-temperature impact-resistant container steel with a thickness of 4 to 6 mm and a width of 2200 to 3050 mm can be efficiently prepared, and its impact toughness at -40 °C is ≥50 Akv / J. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. is a schematic diagram of a system for preparing a low-temperature impact-resistant steel with a continuous casting billet as the processing object, wherein 1 is a heating furnace, 2 is a descaling machine, 3 is a coiling furnace in front of the mill, 4 is a four-high reversing mill, 5 is a coiling furnace behind the mill, and 6 is a cooling system;

[0026] Figure 2 FIG. is a metallographic structure diagram of the low-temperature impact-resistant container steel prepared in Example 1;

[0027] Figure 3 FIG. is a metallographic structure diagram of the low-temperature impact-resistant container steel prepared in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present invention provides a method for preparing a low-temperature impact-resistant steel, comprising the following steps:

[0029] Heating and flat-rolling a continuous casting billet in sequence, and then performing coil rolling using a CVCplus Steckel mill to obtain a steel plate; the continuous casting billet comprises the following chemical components: carbon, manganese, niobium, titanium, chromium, silicon and iron; the number of passes for the coil rolling is 5 to 7 times, the reduction rate of the last pass of the coil rolling is 11 to 13%, the reduction rate of the penultimate pass of the coil rolling is 16 to 19%, and the reduction rate of the third-to-last pass of the coil rolling is 19 to 21%;

[0030] Cooling the steel plate to obtain a low-temperature impact-resistant steel; the cooling rate is 5 to 10 °C / s.

[0031] In the present invention, the continuous casting billet is heated and flat-rolled in sequence and then coil-rolled by a CVCplus Steckel mill to obtain a steel plate. In the present invention, the continuous casting billet comprises the following chemical components: carbon, manganese, niobium, titanium, chromium, silicon and iron. In the present invention, the preparation method of the continuous casting billet preferably comprises the following steps:

[0032] Mix molten iron, carbon, manganese, niobium, titanium, chromium and silicon for steelmaking to obtain molten steel;

[0033] Cast the molten steel to obtain a continuous casting billet.

[0034] In the present invention, molten iron, carbon, manganese, niobium, titanium, chromium and silicon are mixed for steelmaking to obtain molten steel. There are no special requirements for the preparation method of the molten iron in the present invention, and the conventional method in the art can be adopted. In the steelmaking process of the present invention, it is preferred to perform pretreatment desulfurization of molten iron, deep dephosphorization in the converter, deep desulfurization in LF and ultra-low residual element control; the residual elements include one or more of As, Sb, Sn, Pb, Bi, B and Ca. There are no special requirements for the pretreatment desulfurization of molten iron, deep dephosphorization in the converter, deep desulfurization in LF and ultra-low residual element control in the present invention, and the conventional method in the art can be adopted. In the present invention, the temperature of the molten steel is preferably 1500-1600 °C, more preferably 1548 °C.

[0035] In the present invention, the mass percentage content of phosphorus in the continuous casting billet is preferably ≤0.008%; the mass percentage content of sulfur in the continuous casting billet is preferably ≤0.002%; the mass percentage content of B in the continuous casting billet is preferably ≤0.0005%; the mass percentage content of As in the continuous casting billet is preferably ≤0.03%; the mass percentage content of Sb in the continuous casting billet is preferably ≤0.010%; the mass percentage content of Sn in the continuous casting billet is preferably ≤0.020%; the mass percentage content of Pb in the continuous casting billet is preferably ≤0.010%; the mass percentage content of Bi in the continuous casting billet is preferably ≤0.010%.

[0036] Cast the molten steel to obtain a continuous casting billet. In the present invention, the thickness of the continuous casting billet is preferably 140-160 mm, more preferably 150 mm; the width of the continuous casting billet is preferably 2200-3250 mm, more preferably 3100-3200 mm, and even more preferably 3150 mm. In the present invention, the equipment for casting the billet is preferably a continuous caster. In the present invention, the superheat degree of the molten steel in the continuous casting tundish is preferably 12-16 °C. In the present invention, the dynamic soft reduction technology is preferably adopted during the casting of the billet, and the present invention improves the central segregation and porosity problems of the continuous casting billet by adopting the dynamic soft reduction technology. In the present invention, the central segregation of the continuous casting billet is preferably C0.5 grade or C1.0 grade.

[0037] In the present invention, the heating temperature is preferably 1230 - 1260°C, more preferably 1239 - 1245°C. In the present invention, the heating coefficient is preferably ≥10.0 min / cm, more preferably 10.5 - 11 min / cm. In the present invention, the equipment for heating preferably includes a soaking section, and the temperature uniformity of the soaking section is preferably ≤10°C, more preferably 7 - 9°C; the soaking time of the soaking section is preferably greater than or equal to 25 min, more preferably 32 - 35 min.

[0038] The present invention can improve the rolling plasticity and alloy solid solution through heating, thereby improving the impact toughness of the low-temperature impact-resistant steel.

[0039] In the present invention, before flat rolling, it is preferably further included: descaling the steel plate. The present invention has no special requirements for the descaling, and the conventional methods in this technical field can be adopted.

[0040] In the present invention, the number of passes of flat rolling is preferably 6 - 8 times, more preferably 6 - 7 times. In the present invention, the starting rolling temperature of flat rolling is preferably ≥1020°C, more preferably 1050 - 1100°C. In the present invention, the flat rolling is preferably automatically allocated by a secondary model.

[0041] In the present invention, the CVCplus Steckel mill includes a coiling furnace and a four-high reversing mill; the coiling furnace includes a front coiling furnace and a rear coiling furnace; the tension of the strip steel between the coiling drum of the coiling furnace and the four-high reversing mill is preferably 18 - 25 t, more preferably 22 - 25 t. In the present invention, the bending roll force of the CVCplus Steckel mill is preferably 500 - 1000 t, more preferably 600 - 900 t. The present invention preferably increases or decreases the bending roll force according to the rolling shape of the last 3 passes of coiling and rolling. Specifically, when the rolling shape is an edge wave shape, the bending roll force is increased, and when the rolling shape is a center wave shape, the bending roll force is decreased. In the present invention, the temperature of the coiling furnace is preferably 860 - 950°C, more preferably 920 - 940°C, and even more preferably 930°C.

[0042] In the present invention, the number of passes of coiling and rolling is 5 - 7 times, preferably 6 - 7 times; the total reduction ratio of coiling and rolling is preferably 50 - 85%, more preferably 60 - 75%. In the present invention, the reduction ratio of the last pass of coiling and rolling is 11 - 13%, preferably 11.03 - 12.01%; the reduction ratio of the second last pass of coiling and rolling is 16 - 19%, preferably 16.58 - 18.32%; the reduction ratio of the third last pass of coiling and rolling is 19 - 21%, preferably 19.37 - 20.21%. In the present invention, the thickness of the steel plate at the start of coiling and rolling is preferably ≤25 mm. The present invention automatically sets the total reduction ratio of coiling and rolling through a secondary model to obtain a steel plate with the required thickness.

[0043] In the present invention, the work roll of the CVCplus Steckel mill moves axially. During the last three rolling passes, the axial movement of the CVC of the work roll is preferably within 70 mm, more preferably 20 - 50 mm.

[0044] In the present invention, the starting rolling temperature of the rolling is preferably 990 - 1030 °C, more preferably 1000 - 1020 °C; the finishing rolling temperature of the rolling is preferably 780 - 862 °C, more preferably 791 - 858 °C.

[0045] After obtaining the steel plate, the present invention cools the steel plate to obtain a low-temperature impact-resistant steel; the cooling rate is 5 - 10 °C / s, preferably 6 - 8 °C / s. The present invention preferably uses a high-density slit nozzle for cooling. Using a high-density slit nozzle for cooling can improve the cooling efficiency and at the same time improve the tissue uniformity in the low-temperature impact-resistant steel.

[0046] The present invention takes advantage of the rolling process with coiling furnaces both in front of and behind the mill, reasonably distributes the rolling passes and the reduction rate per pass, and ensures the stability of the rolled plate shape.

[0047] The present invention uses the CVC Steckel mill rolling technology. Through the heat preservation effect of the two coiling furnaces in front of and behind the mill, taking into account the three requirements of plate shape, thickness accuracy, and performance, it can stably and highly quality produce low-temperature container steel for liquefied natural gas tank tops with a thickness of 4 - 6 mm and a width of 2500 - 3050 mm, with high production efficiency and stable quality, and the qualified rate is as high as over 99.5%.

[0048] In the present invention, the re-reddening temperature after cooling is preferably 620 - 690 °C, more preferably 653 - 668 °C.

[0049] In the present invention, after cooling, it preferably further includes: sequentially shearing, cold straightening, and flaw detection of the cooled sheet. The present invention has no special requirements for the shearing, cold straightening, and flaw detection, and conventional methods in the art can be used.

[0050] The low-temperature impact-resistant steel prepared by the preparation method according to the present invention has good thickness uniformity. The thickness tolerance of a single steel plate is preferably 0 - 0.2 mm, more preferably 0.08 - 0.1 mm.

[0051] Figure 1 It is a schematic diagram of a system for preparing low-temperature impact-resistant steel with a continuous casting billet as the processing object. Among them, 1 is a heating furnace, 2 is a descaling machine, 3 is a coiling furnace in front of the mill, 4 is a four-high reversing mill, 5 is a coiling furnace behind the mill, and 6 is a cooling system. The present invention uses a four-high reversing mill for flat rolling and coiling rolling.

[0052] The present invention also provides a low-temperature impact-resistant steel prepared by the preparation method described in the above technical solution, including the following chemical components in mass percentage:

[0053]

[0054] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 0.05-0.09% C, preferably 0.071-0.077%.

[0055] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 1.35-1.65% Mn, preferably 1.57-1.59%.

[0056] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 0.10-0.30% Si, preferably 0.22-0.25%.

[0057] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 0.02-0.04% Nb, preferably 0.033-0.036%.

[0058] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 0.15-0.025% Ti, preferably 0.017-0.018%.

[0059] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 0.02-0.055% Al, preferably 0.03-0.04%.

[0060] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises 0.15-0.20% Cr, preferably 0.17-0.18%.

[0061] In the present invention, the low-temperature impact toughness is improved by reducing the mass percentage of C and increasing the mass percentage of Nb in the low-temperature impact-resistant steel, and the mechanical strength of the low-temperature impact-resistant steel is improved by adding Cr and Ti.

[0062] In the present invention, by mass percentage, the low-temperature impact-resistant steel comprises the balance of Fe and impurities. In the present invention, the impurities include residual elements, nitrogen, phosphorus and sulfur, and the residual elements include one or more of As, Sb, Sn, Pb, Bi, B and Ca. In the present invention, the mass percentage of phosphorus in the low-temperature impact-resistant steel is preferably ≤0.008%, more preferably 0.007%; the mass percentage of sulfur in the low-temperature impact-resistant steel is preferably ≤0.002%, more preferably 0.001%; the mass percentage of nitrogen in the low-temperature impact-resistant steel is preferably 32-33 ppm; the mass percentage of B in the low-temperature impact-resistant steel is preferably ≤0.0005%, preferably 0.0003-0.0004%; the mass percentage of As in the low-temperature impact-resistant steel is preferably ≤0.03%, preferably 0.003-0.004%; the mass percentage of Sb in the low-temperature impact-resistant steel is preferably ≤0.010%, preferably 0.001%; the mass percentage of Sn in the low-temperature impact-resistant steel is preferably ≤0.020%, preferably 0.001%; the mass percentage of Pb in the low-temperature impact-resistant steel is preferably ≤0.010%, preferably 0.001%; the mass percentage of Bi in the low-temperature impact-resistant steel is preferably ≤0.010%; the mass percentage of Ca in the low-temperature impact-resistant steel is preferably 0.0013-0.0014%.

[0063] In the present invention, the carbon equivalent (CEV) of the low-temperature impact-resistant steel is preferably ≤0.4%, and the cold cracking susceptibility index of the low-temperature impact-resistant steel is preferably ≤0.22%. The low-temperature impact-resistant steel provided by the present invention has excellent welding performance.

[0064] In the present invention, the thickness of the low-temperature impact-resistant steel is 4-6 mm, preferably 5-6 mm; the width of the low-temperature impact-resistant steel is 2200-3050 mm, preferably 2500-3050 mm. In the present invention, the impact toughness of the low-temperature impact-resistant steel at -40°C is ≥50 J, preferably 117-120 J.

[0065] In the present invention, the low-temperature impact-resistant steel has good mechanical strength. The yield strength of the low-temperature impact-resistant steel is preferably 381-390 MPa; the tensile strength of the low-temperature impact-resistant steel is preferably 567-572 MPa; the elongation of the low-temperature impact-resistant steel is preferably 27-27.5%.

[0066] The present invention also provides an application of the low-temperature impact-resistant steel described in the above technical solution as the skin steel of the top structure of a natural gas storage tank.

[0067] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0068] Embodiment 1

[0069] After desulfurizing the hot metal pretreatment, it is mixed with carbon, manganese, niobium, titanium, chromium, and silicon for steelmaking (deep dephosphorization in the converter, deep desulfurization in LF, and ultra-low residual element control), obtaining molten steel at a temperature of 1548 °C; the molten steel is transferred to the continuous casting tundish to control the superheat temperature at 12 - 16 °C, and continuous casting billets are produced (using the dynamic soft reduction technology), obtaining continuous casting billets with a thickness of 150 mm and a width of 3150 mm; the center segregation of the continuous casting billets is at C0.5 level;

[0070] The continuous casting billets are heated at 1239 °C, with a heating coefficient of 10.5 min / cm, and the temperature uniformity in the soaking section of the heating equipment is 8 °C; the soaking time of the continuous casting billets in the soaking section is 32 min; the continuous casting billets after heating are descaled;

[0071] The descaled continuous casting billets are flat-rolled for 6 passes, and the starting rolling temperature is 1020 °C;

[0072] The flat-rolled sheet is coil-rolled for 7 passes by a CVCplus Steckel mill to obtain a steel plate; the tension of the strip between the coiling furnace drum and the four-high reversing mill in the CVCplus Steckel mill is 22 t, the bending roll force of the CVCplus Steckel mill is 800 t, and the temperature of the coiling furnace is 920 °C; the starting rolling temperature of the coil rolling is 1000 °C, and the finishing rolling temperature is 780 - 858 °C; the thickness of the steel plate at the start of coil rolling is 25 mm, the total reduction ratio of the coil rolling is 73%, the reduction ratio of the last pass of the coil rolling is 12.11%, the reduction ratio of the second-to-last pass of the coil rolling is 18.32%, and the reduction ratio of the third-to-last pass of the coil rolling is 20.21%; the CVC axial movement amount in the last three passes of the coil rolling is 45 mm;

[0073] The steel plate is cooled by a high-density slit nozzle with a cooling rate of 6 °C / s and a red return temperature of 668 °C; the cooled plate is successively sheared, cold-straightened, and flaw-detected to obtain a low-temperature impact-resistant container steel plate; the thickness of the low-temperature impact-resistant container steel plate is 5.5 mm and the width is 3000 mm; the low-temperature impact-resistant container steel plate includes C 0.071%, Mn 1.57%, P 0.007%, S 0.001%, Si 0.22%, Al 0.03%, Nb 0.033%, Ti 0.018%, Cr 0.17%, N 33 ppm, Pb 0.001%, Sb 0.001%, Sn 0.001%, As 0.003%, Ca 0.0014%, B 0.0003%, with the balance being Fe and impurities; the carbon equivalent of the low-temperature impact-resistant container steel plate is 0.37%, and the cold cracking sensitivity index for welding is 0.17%.

[0074] Example 2

[0075] After desulfurizing the hot metal pretreatment, it is mixed with carbon, manganese, niobium, titanium, chromium, and silicon for steelmaking (deep dephosphorization in the converter, deep desulfurization in LF, and ultra-low residual element control) to obtain molten steel at a temperature of 1548 °C; the molten steel is transferred to the continuous casting tundish to control the superheat temperature at 12 - 16 °C, and continuous casting billets are produced (using the dynamic soft reduction technology) to obtain continuous casting billets with a thickness of 150 mm and a width of 3100 mm; the central segregation of the continuous casting billets is at C1.0 level;

[0076] The continuous casting billets are heated at 1245 °C with a heating coefficient of 10.5 min / cm, and the temperature uniformity in the soaking section of the heating equipment is 8 °C; the soaking time of the continuous casting billets in the soaking section is 35 min; the continuous casting billets after heating are descaled;

[0077] The descaled continuous casting billets are flat-rolled for 6 passes, and the starting rolling temperature is 1020 °C;

[0078] The flat-rolled plate is coil-rolled for 7 passes using a CVCplus Steckel mill to obtain a steel plate; the tension of the strip between the coiling furnace drum and the four-high reversing mill in the CVCplus Steckel mill is 25 t, the bending roll force of the CVCplus Steckel mill is 700 t, and the temperature of the coiling furnace is 940 °C; the starting rolling temperature for coil rolling is 1000 °C, and the final rolling temperature for coil rolling is 791 - 862 °C; the thickness of the steel plate at the start of coil rolling is 25 mm, the total reduction ratio for coil rolling is 72.7%, the reduction ratio for the last pass of coil rolling is 11.03%, the reduction ratio for the second-to-last pass of coil rolling is 16.58%, and the reduction ratio for the third-to-last pass of coil rolling is 19.37%; the CVC axial movement for the last three passes of coil rolling is 30 mm;

[0079] The steel plate is cooled by a high-density slit nozzle with a cooling rate of 6 °C / s and a recrystallization temperature of 653 °C. The cooled sheet is successively sheared, cold-straightened and flaw-detected to obtain a low-temperature impact-resistant container steel plate. The thickness of the low-temperature impact-resistant container steel plate is 6 mm and the width is 3050 mm. The low-temperature impact-resistant container steel plate includes C 0.077%, Mn 1.59%, P 0.007%, S 0.001%, Si 0.25%, Al 0.03%, Nb 0.036%, Ti 0.017%, Cr 0.18%, N 32 ppm, CEV 0.382%, Pcm 0.17%, Pb 0.001%, Sb 0.001%, Sn 0.001%, As 0.004%, Ca 0.0013%, B 0.0004%, with the balance being Fe and impurities. The carbon equivalent of the low-temperature impact-resistant container steel plate is 0.382%, and the cold cracking sensitivity index of welding is 0.17%.

[0080] Cutting is carried out at 1 / 4 of the thickness of the low-temperature impact-resistant container steel prepared in Examples 1 and 2, and the metallographic structure of the cutting surface is observed to obtain a metallographic structure diagram, as Figures 2 - 3 . Among them Figure 2 is the metallographic structure diagram of the low-temperature impact-resistant container steel prepared in Example 1, Figure 3 is the metallographic structure diagram of the low-temperature impact-resistant container steel prepared in Example 2. From Figure 2 and Figure 3 , it can be seen that the low-temperature impact-resistant container steel plate provided by the present invention has a uniform and fine structure, the grain size of the structure is 10.0 grades, the structure type is: ferrite + pearlite, contains a small amount of bainite, and the banded structure grade is 0.5 grade.

[0081] Comparative Example 1

[0082] The steel plate is prepared according to the method of Example 1, except that the reduction rate in the last pass of coiling is 8.1%, the reduction rate in the second last pass of coiling is 14.3%, the reduction rate in the third last pass of coiling is 17.1%, and at the same time, the CVC function is not put into use, and the working roll of the CVCplus reversing mill does not move axially.

[0083] Comparative Example 2

[0084] The steel plate is prepared according to the method of Example 1, except that the axial movement amount of CVC in the last three passes of coiling is 90 mm and the cooling rate is 3 °C / s.

[0085] The mechanical properties of the low-temperature impact-resistant container steel prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are detected according to GBT 713-2014 and GBT 3531-2014, and the results are listed in Table 1.

[0086] Table 1 Mechanical properties of the steel plates prepared in Examples 1, 2 and Comparative Examples 1, 2

[0087]

[0088] As can be seen from Table 1, the low-temperature impact-resistant steel provided by the present invention has good mechanical properties and thickness uniformity, and can be used as the steel for low-temperature impact-resistant containers.

[0089] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of a low-temperature impact-resistant steel, comprising the following steps: The continuous casting billet is heated and flat-rolled in sequence and then coiled by a CVCplus Steckel mill to obtain a steel plate; the continuous casting billet comprises the following chemical components in mass percentage: 0.05-0.09% C, 1.57-1.59% Mn, 0.10-0.30% Si, 0.02-0.04% Nb, 0.017-0.018% Ti, 0.15%-0.20% Cr and the balance of iron; the number of passes of the coiling is 5-7 times, the reduction rate of the last pass of the coiling is 11-13%, the reduction rate of the second last pass of the coiling is 16-19%, and the reduction rate of the third last pass of the coiling is 19-21%; the working roll of the CVCplus Steckel mill moves axially, and the axial movement amount of the CVC during the last three passes of coiling is within 70 mm; The steel plate is cooled to obtain the low-temperature impact-resistant steel; the cooling rate is 5-10 °C / s; the thickness of the low-temperature impact-resistant steel is 4-6 mm, and the width is 2200-3050 mm.

2. The preparation method according to claim 1, wherein The CVCplus Steckel mill comprises a coiling furnace and a four-high reversing mill; the coiling furnace comprises a front coiling furnace and a rear coiling furnace; The tension of the strip steel between the coiling drum of the coiling furnace and the four-high reversing mill is 18-25 t.

3. The preparation method according to claim 2, characterized in that, The temperature of the coiling furnace is 860-930 °C.

4. The preparation method according to claim 1, wherein The total reduction rate of the coiling is 50-85%; The starting rolling temperature of the coiling is 990-1030 °C; the finishing rolling temperature of the coiling is 780-862 °C.

5. The preparation method according to claim 1, characterized in that The number of passes of the flat rolling is 6-8 times; The starting rolling temperature of the flat rolling is ≥1020 °C.

6. According to the preparation method described in claim 1, characterized in that, The heating temperature is 1230-1260 °C, and the heating coefficient is ≥10.0 min / cm; The heating equipment comprises a soaking section, the temperature uniformity of the soaking section is ≤10 °C, and the soaking time of the soaking section is greater than or equal to 25 min.

7. According to the preparation method described in claim 1, characterized in that, The recalescence temperature after cooling is 620-690 °C.

8. The low-temperature impact-resistant steel prepared by the preparation method according to any one of claims 1-7, comprising the following chemical components in mass percentage: The thickness of the low-temperature impact-resistant steel is 4-6 mm, and the width is 2200-3050 mm; The impact toughness of the low-temperature impact-resistant steel at -40 °C ≥50 J.

9. Application of the low-temperature impact-resistant steel according to claim 8 as the skin steel of the top structure of a natural gas storage tank.

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