Production method of low-temperature-resistant rare earth microalloyed Q345R steel for pressure vessel

Abstract

The invention discloses a production method of low-temperature-resistant rare earth microalloying Q345R steel for a pressure vessel. The steel for the pressure vessel comprises the following chemical components in percentage by weight: less than or equal to 0.20% of C, less than or equal to 0.55% of Si, 1.20-1.70% of Mn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, less than or equal to 0.030% of Ti, less than or equal to 0.0030% of Ce and the balance of Fe and inevitable impurities. The production method comprises the steps of molten iron pretreatment, converter top and bottom combined blowing, LF refining, RH, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling. The produced product is uniform and fine in structure, stable in performance and good in low-temperature impact toughness at the temperature of-50 DEG C, the full-size (10 * 10 * 55) impact energy value is 92-125 J, and the application effect fed back by customers is good.

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and in particular relates to a production method of low-temperature resistant rare earth micro-alloyed Q345R pressure vessel steel. Background Art

[0002] Pressure vessel steel Q345R is a pressure vessel material widely used in the petroleum, chemical, electric power, food and other industries. Its performance is directly related to the safety and service life of the equipment. Although the traditional Q345R steel has met the basic requirements in terms of strength, toughness, weldability and corrosion resistance, it is still insufficient in extreme working conditions. Therefore, in order to meet production and market needs, a certain amount of rare earth alloys are added in the product production process, which has the functions of purifying molten steel, denaturing inclusions and micro-alloying in the steel. At the same time, the micro-alloying of rare earth can effectively improve the corrosion resistance of the steel strip, improve low-temperature impact toughness, fatigue resistance, and refine the grains, which is convenient for steel cleanliness control and improves the service life of the steel. The present invention combines advanced smelting and rolling technologies to develop a Q345R hot-rolled coil with better performance.

[0003] Chen Minxia et al. (Chen Minxia et al., A method for manufacturing Q345R steel plate, patent accepted, November 10, 2023) studied a method for manufacturing Q345R steel plate. The rolling process route is converter smelting → LF refining → VD vacuum refining → continuous casting → slab heating → controlled rolling → controlled cooling → normalizing heat treatment. The thickness of the steel plate produced is 90-110mm. Alloys such as Nb and V are added to the product composition. The performance of the produced products meets customer requirements. The shortcomings are that the product is designed as medium and thick plate, and the product is heat-treated steel. The addition of rare earths to the product and the production process of thin-gauge steel strips are not introduced.

[0004] Cheng Kangrong et al. (Cheng Kangrong et al., A rolling method for -40℃ impact Q345R, patent accepted, July 13, 2021) introduced a rolling method for -40℃ impact Q345R, which is rolled on a furnace coil mill, and then rolled after controlled cooling. The rolled product is a single plate, and Nb and Ti alloys are added to the product composition system. The disadvantage is that it is rolled on a non-continuous rolling mill. Compared with this patent, the 230mm slab is rolled on 7 continuous rolling mills, and CVC technology is used for rolling. After rolling and cooling, the steel strip is coiled. Its metallographic structure size and grain size are larger and more uneven than those of the steel strip rolled on a 2250mm rolling mill. The alloy cost is relatively high, no rare earth elements are added, and the -50℃ impact is not tested.

[0005] Liu Jianshu et al. (Liu Jianshu et al., A method for producing high-toughness container steel Q345R, patent accepted, May 14, 2024) introduced a method for producing high-toughness container steel Q345R, including continuous casting, ingot heating, rolling and cooling processes. The composition is designed to be C+Mn+Nb, the rolling thickness is 12-30mm, and the product performance and structure are uniform. The disadvantage is that it is a medium and thick plate, and the cost of the product composition system is relatively high compared to this patent. The impact toughness of the -50°C product has not been studied, and no rare earth elements are added to the composition system.

[0006] In summary, the above patents involve research and description of the production and process of pressure vessel steel produced by the Q345R medium and thick plate production line, but fail to clearly explain the detailed production of Q345R rare earth-containing low-temperature resistant pressure vessel steel on the 2250mm coil production line, the product's structure and mechanical properties. Summary of the invention

[0007] The invention aims to provide a production method of low-temperature resistant rare earth microalloyed Q345R pressure vessel steel. The purpose is to strictly control the rare earth addition amount and the adding process by adding a certain amount of Ti and rare earth Ce and controlling the content of gas elements (O, N) on the basis of meeting the standard composition of GB / T 713, so that the inclusions in molten steel are controlled to be low, the molten steel casting is stable, the product yield is high, and a reasonable controlled rolling and controlled cooling process is matched at the same time. The product has uniform and fine structure, stable performance, good low-temperature impact toughness at -50°C, and a full-size (10x10x55) impact energy value of 92-125J. Customers feedback that the application effect is good.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The invention discloses a method for producing low-temperature resistant rare earth microalloyed Q345R pressure vessel steel, wherein the chemical composition of the pressure vessel steel is C: ≤0.20%, Si: ≤0.55%, Mn: 1.20-1.70%, P: ≤0.025%, S: ≤0.025%, Ti: ≤0.030%, Ce ≤0.0030%, and the balance is Fe and unavoidable impurities.

[0010] The production method includes: molten iron pretreatment, converter top and bottom composite blowing, LF refining, RH, continuous casting, slab heating, hot rolling, laminar cooling and coiling;

[0011] The smelting and continuous casting process comprises molten iron pretreatment, converter top and bottom composite blowing, LF refining, RH, and slab continuous casting to form a continuous casting billet;

[0012] In the continuous casting slab heating step, the thickness is 2.00-3.50 mm, the heating temperature is 1240-1270° C., the soaking temperature is 1230-1260° C., and the furnace discharge temperature is 1250±20° C.; the thickness is 3.51-7.00 mm, the heating temperature is 1210-1240° C., the soaking temperature is 1200-1230° C., and the furnace discharge temperature is 1220±20° C.; the thickness is 7.01-16.00 mm, the heating temperature is 1190-1230° C., the soaking temperature is 1180-1220° C., and the furnace discharge temperature is 1200±20° C. The slab furnace time is controlled to be 150-270 min, and the soaking time is 20-40 min.

[0013] In the rough rolling step, the rough rolling adopts the 3+5 mode, and the finishing rolling adopts the 7-stand continuous variable crown rolling mill. The starting rolling temperature of the finishing rolling is automatically controlled by the secondary computer, and the final rolling temperature is 825-885°C;

[0014] Thickness 2.00~6.00mm, intermediate billet thickness 38~45mm, final rolling temperature 870±15℃; Thickness 6.01~10.00mm, intermediate billet thickness 46~50mm, final rolling temperature 850±15℃; Thickness 10.01~16.00mm, intermediate billet thickness 51~65mm, final rolling temperature 840±15℃;

[0015] In the cooling and coiling steps, the thickness is 2.00-6.00 mm, the coiling temperature is 640±15°C, the cooling adopts the laminar cooling method of the "11" mode, which is front dispersion, the cooling method is one-by-one, and the cooling rate is controlled at 30-50°C / s; the thickness is 6.01-10.00 mm, the coiling temperature is 600±15°C, the cooling adopts the laminar cooling method of the "11" mode, which is front dispersion, the cooling method is one-by-one, and the cooling rate is controlled at 20-45°C / s; the thickness is 10.01-16.00 mm, the coiling temperature is 580±15°C, the cooling adopts the laminar cooling method of the "11" mode, which is front dispersion, the cooling method is one-by-one, and the cooling rate is controlled at 20-45°C / s.

[0016] Furthermore, the chemical composition of the pressure vessel steel is, by weight percentage, C: 0.16-0.18%, Si: 0.10-0.20%, Mn: 1.35-1.55%, P: ≤0.015%, S: ≤0.005%, Ti: 0.012-0.020%, O: ≤0.0030%, N: ≤0.0060%, Ce: 0.0025%, and the remainder is Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition of the pressure vessel steel is, by weight percentage, C: 0.17%, Si: 0.15%, Mn: 1.45%, P: 0.011%, S: 0.005%, Ti: 0.017%, O: 0.0015%, Ce: 0.00:20%, and the remainder is Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the pressure vessel steel is, by weight percentage, C: 0.16%, Si: 0.13%, Mn: 1.44%, P: 0.012%, S: 0.003%, Ti: 0.013%, O: 0.0020%, Ce: 0.0020%, and the remainder is Fe and unavoidable impurities.

[0019] Furthermore, the chemical composition of the pressure vessel steel is, by weight percentage, C: 0.138%, Si: 0.12%, Mn: 1.46%, P: 0.010%, S: 0.001%, Ti: 0.015%, O: 0.0018%, Ce: 0.0019%, and the remainder is Fe and unavoidable impurities.

[0020] Furthermore, the molten iron is pre-treated for desulfurization, the converter adopts top and bottom combined blowing smelting technology, ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying, the composition is adjusted to meet the steelmaking requirements, and the converter steelmaking temperature is ≥1620℃; the molten steel after converter smelting is hoisted to the LF refining process for treatment, and ferromanganese, ferrosilicon and ferroaluminum alloy are added according to the composition of the molten steel to adjust to the target composition. In order to reduce inclusions in the steel, micro-calcium treatment is carried out when the LF is out of situ, and the slag fluidity and performance are well controlled. The slag basicity is 7.92, FeO is 1.78, and CaO / Al2O3 is 1.76; the molten steel is transported to the RH for vacuum treatment, during which ferrotitanium alloy is added, the vacuum degree is required to be 1.9mbar, the vacuum time is maintained for 12min, and the circulating pure degassing time is guaranteed to be 9min; vacuum treatment After the treatment, 30kg of rare earth ferrocerium alloy with a Ce content of 30% is added, and the RH ensures that the soft blowing time is 10min; before loading the steel, the argon flow rate is adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed; the overheat of the slab continuous casting is 28℃; the slab is sent to the heating furnace by hot charging; the slab heating temperature is 1260℃, the soaking temperature is 1250℃, the furnace temperature is 1240℃, the heating time is 240min, and the heated slab is subjected to high-pressure water dephosphorization; 2 rough rolling mills and 7 CVC finishing mills are used; the thickness of the intermediate billet is 45.0mm, and the finishing rolling temperature is 870℃; the laminar cooling adopts the front dispersed cooling mode "11", the upper and lower nozzles are separated by one, the cooling rate is 45℃ / s, the coiling temperature is 640℃, and the finished product thickness is 3.0mm.

[0021] Furthermore, the molten iron is pre-treated for desulfurization, the converter adopts top and bottom combined blowing smelting technology, ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying, the composition is adjusted to meet the steelmaking requirements, and the converter steelmaking temperature is ≥1620℃; the molten steel after converter smelting is hoisted to the LF refining process for treatment, and ferromanganese, ferrosilicon and ferroaluminum alloy are added according to the composition of the molten steel to adjust the target composition; in order to reduce inclusions in the steel, micro-calcium treatment is carried out when the LF is out of situ, and the fluidity and performance of the slag are well controlled. The slag basicity is 7.65, FeO is 1.29, and CaO / Al2O3 is 1.99; the molten steel is transported to the RH for vacuum treatment, during which ferrotitanium alloy is added, the vacuum degree is 2.2mbar, the vacuum time is 13min, and the circulating pure degassing time is guaranteed to be 8min; vacuum treatment After the treatment, 30kg of rare earth cerium iron alloy with a Ce content of 30% was added, and the RH soft blowing time was 10min; before steel was added, the argon flow rate was adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed; the overheat of the slab continuous casting was 28°C; the slab was sent to the heating furnace by hot charging; the slab heating temperature was 1235°C, the soaking temperature was 1225°C, the furnace temperature was 1220°C, the heating time was 230min, and the heated slab was subjected to high-pressure water dephosphorization; 2 rough rolling mills and 7 CVC finishing mills were used; the intermediate billet thickness was 44.0mm, and the finishing rolling temperature was 865°C; the laminar cooling adopted the front dispersed cooling mode "11", the upper and lower nozzles were separated by one, the cooling rate was 44°C / s, the coiling temperature was 633°C, and the finished product thickness was 6.0mm.

[0022] Furthermore, the molten iron is pre-treated for desulfurization, the converter adopts top and bottom combined blowing smelting technology, ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying, the composition is adjusted to meet the steelmaking requirements, the converter steelmaking temperature is ≥1620℃, the molten steel after converter smelting is hoisted to the LF refining process for treatment, ferromanganese, ferrosilicon and ferroaluminum alloy are added according to the composition of the molten steel to adjust to the target composition; in order to reduce inclusions in the steel, micro-calcium treatment is carried out when the LF is out of situ, the fluidity and performance of the slag are controlled, the slag basicity is 9.65, FeO is 1.21, and CaO / Al2O3 is 1.79; the molten steel is transported to the RH for vacuum treatment , titanium iron alloy is added during the process, the vacuum degree is 2.0mbar, the vacuum time is 15min, and the cycle pure degassing time is guaranteed to be 9min; after the vacuum treatment, 30kg of rare earth cerium iron alloy with a Ce content of 30% is added, and the RH soft blowing time is 12min; before steeling, the argon flow rate is adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed; the slab continuous casting overheat is 28℃; the slab is sent to the heating furnace by hot charging; the slab heating temperature is 1210℃, the soaking temperature is 1200℃, the furnace temperature is 1195℃, the heating time is 230min, and the heated slab is dephosphorized by high-pressure water. The width is determined by a fixed width press, 2 rough rolling mills and 7 CVC finishing mills are used; the intermediate billet thickness is 55.0mm, and the finishing rolling temperature is 845℃; the laminar cooling adopts the back-front scattered cooling mode "11", the upper and lower nozzles are separated by one, the cooling rate is 43℃ / s, the coiling temperature is 586℃, and the finished product thickness is 11.75mm.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] The present invention is based on C, Mn, Ti, and is supplemented by a rare earth Ce microalloying alloy design system. By controlling various strengthening elements and changing the morphology and distribution of inclusions, the molten steel is purified and the grains are refined. The produced product has good low-temperature impact toughness, corrosion resistance, and weldability. The inventors have found that the raw material composition and mass ratio provided by the present invention, combined with the controlled rolling and controlled cooling processes, and the rare earth low-temperature resistant pressure vessel steel Q345R is developed using a 2250mm hot rolling production line. It has been successfully applied to pressure vessel materials in low-temperature environments such as petroleum, chemical industry, and electric power, and has the following beneficial effects:

[0025] The present invention provides a low temperature resistant rare earth microalloyed Q345R pressure vessel steel and a production method thereof. Through a reasonable component system design, the hot rolled steel strip contains C: 0.16-0.18%, Mn: 1.35-1.55%, Ce: 0.0010-0.0030%, etc., the microstructure is ferrite + pearlite, the grain size is about 12 levels, and it has good low temperature impact resistance, weldability and corrosion resistance. The mechanical properties and process properties meet the tensile strength ≥510-640MPa, the yield strength ≥345MPa, and the elongation ≥21%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below in conjunction with the accompanying drawings.

[0027] Figure 1 The metallographic structure diagram of the steel strip at 1 / 4 of the longitudinal direction is shown in the embodiment of the present invention;

[0028] Figure 2 It is the casting process of molten steel containing rare earth elements;

[0029] Figure 3 For inclusion photos. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0031] Product production process route:

[0032] KR desulfurization→converter→LF furnace→RH furnace→slab continuous casting

[0033] Heating furnace—rough rolling high-pressure water descaling—fixed width press—E1R1 rough rolling mill—E2R2 rough rolling mill—(insulation cover)—flying shear—finishing rolling high-pressure water descaling—F1~F7 finishing mills—encrypted laminar cooling—coiling—pallet transportation system—sampling and inspection.

[0034] Embodiment 1:

[0035] A production method of low temperature resistant rare earth microalloyed Q345R pressure vessel steel:

[0036] The molten iron is pre-treated for desulfurization. The converter adopts the top and bottom combined blowing smelting technology. Ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying. The composition is adjusted to meet the steel-making requirements. The converter steel-making temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment. According to the composition of the molten steel, ferromanganese, ferrosilicon, aluminum and other alloys are added to adjust to the target composition. In order to reduce the inclusions in the steel, micro-calcium treatment is carried out when the LF is off-site to control the fluidity and performance of the slag. The slag basicity is 7.92, FeO is 1.78, and CaO / Al2O3 is 1.76. The molten steel is transported to the RH for vacuum treatment. During this period, titanium iron alloy is added. The vacuum degree is required to be 1.9mbar, the vacuum time is maintained for 12min, and the circulating pure degassing time is guaranteed to be 9min. After the vacuum treatment, 30kg of rare earth cerium iron alloy with a Ce content of 30% is added, and the RH guarantees a soft blowing time of 10min. Before steel is added, the argon flow rate is adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed. According to the chemical composition shown in Table 1, the slab continuous casting overheat is 28°C. The slab is sent to the heating furnace by hot charging. The slab heating temperature is 1260°C, the soaking temperature is 1250°C, the furnace temperature is 1240°C, the heating time is 240min, and the heated slab is dephosphorized by high-pressure water. Two rough rolling mills and seven CVC finishing mills are used. The thickness of the intermediate slab is 45.0mm, and the finishing temperature is 870°C. The laminar cooling adopts the front dispersed cooling mode "11" (the upper and lower nozzles are separated by one open), the cooling rate is 45°C / s, the coiling temperature is 640°C, the finished product thickness is 3.0mm, and the mechanical properties test results of the steel strip prepared in the embodiment are shown in Table 2.

[0037] Embodiment 2:

[0038] A production method of low temperature resistant rare earth microalloyed Q345R pressure vessel steel:

[0039] The molten iron is pre-treated for desulfurization. The converter adopts the top and bottom combined blowing smelting technology. Ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying. The composition is adjusted to meet the steel-making requirements. The converter steel-making temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment. According to the composition of the molten steel, ferromanganese, ferrosilicon, aluminum and other alloys are added to adjust to the target composition. In order to reduce the inclusions in the steel, micro-calcium treatment is carried out when the LF is off-site to control the fluidity and performance of the slag. The slag basicity is 7.65, FeO is 1.29, and CaO / Al2O3 is 1.99. The molten steel is transported to the RH for vacuum treatment. During this period, titanium iron alloy is added. The vacuum degree is 2.2mbar, the vacuum time is 13min, and the circulating pure degassing time is guaranteed to be 8min. After the vacuum treatment, 30kg of rare earth cerium iron alloy with a Ce content of 30% is added, and the RH soft blowing time is 10min. Before steel is added, the argon flow rate is adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed. According to the chemical composition shown in Table 1, the slab continuous casting overheat is 28°C. The slab is sent to the heating furnace by hot charging. The slab heating temperature is 1235°C, the soaking temperature is 1225°C, the furnace temperature is 1220°C, the heating time is 230min, and the heated slab is dephosphorized by high-pressure water. 2 rough rolling mills and 7 CVC finishing mills are used. The thickness of the intermediate slab is 44.0mm, and the finishing temperature of the finishing rolling is 865°C. The laminar cooling adopts the front dispersed cooling mode "11" (the upper and lower nozzles are separated by one open), the cooling rate is 44°C / s, the coiling temperature is 633°C, the finished product thickness is 6.0mm, and the mechanical properties test results of the steel strip prepared in the embodiment are shown in Table 2.

[0040] Embodiment 3:

[0041] A production method of low temperature resistant rare earth microalloyed Q345R pressure vessel steel:

[0042] The molten iron is pre-treated for desulfurization. The converter adopts the top and bottom combined blowing smelting technology. Ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying. The composition is adjusted to meet the steel-making requirements. The converter steel-making temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment. According to the composition of the molten steel, ferromanganese, ferrosilicon, aluminum and other alloys are added to adjust to the target composition. In order to reduce the inclusions in the steel, micro-calcium treatment is carried out when the LF is out of place to control the fluidity and performance of the slag. The slag basicity is 9.65, FeO is 1.21, and CaO / Al2O3 is 1.79. The molten steel is transported to the RH for vacuum treatment. During this period, titanium iron alloy is added. The vacuum degree is 2.0mbar, the vacuum time is 15min, and the circulating pure degassing time is guaranteed to be 9min. After the vacuum treatment, 30kg of rare earth cerium iron alloy with a Ce content of 30% is added, and the RH soft blowing time is 12min. Before steel is added, the argon flow rate is adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed. According to the chemical composition shown in Table 1, the slab continuous casting overheat is 28°C. The slab is sent to the heating furnace by hot charging. The slab heating temperature is 1210°C, the soaking temperature is 1200°C, the furnace temperature is 1195°C, the heating time is 230min, and the heated slab is subjected to high-pressure water dephosphorization. The width is determined by a fixed-width press, and 2 rough rolling mills and 7 CVC finishing mills are used. The thickness of the intermediate slab is 55.0mm, and the finishing temperature of the finishing rolling is 845°C. The laminar cooling adopts the back-to-front scattered cooling mode "11" (the upper and lower nozzles are separated by one open), the cooling rate is 43°C / s, the coiling temperature is 586°C, the finished product thickness is 11.75mm, and the mechanical properties test results of the steel strip prepared in the embodiment are shown in Table 2.

[0043] Figure 1 and Figure 3 The typical microstructure and impurity diagram of the steel strip prepared in this embodiment, from which it can be seen that the microstructure is ferrite and a small amount of pearlite, the grain size is about 12, and the inclusions are all ≤1.0. The chemical composition of the steel strip prepared in this embodiment is shown in Table 1, and the mechanical properties test results are shown in Table 2.

[0044] Table 1 Chemical composition of Examples 1 to 3 of the present invention (wt%)

[0045]

[0046]

[0047] Table 2 Mechanical properties and impact test results of the steel strips prepared in Examples 1 to 3 of the present invention

[0048]

[0049] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel, characterized in that: The chemical composition of the pressure vessel steel is C: ≤0.20%, Si: ≤0.55%, Mn: 1.20-1.70%, P: ≤0.025%, S: ≤0.025%, Ti: ≤0.030%, Ce ≤0.0030%, and the balance is Fe and unavoidable impurities. The production method includes: molten iron pretreatment, converter top and bottom composite blowing, LF refining, RH, continuous casting, slab heating, hot rolling, laminar cooling and coiling; The smelting and continuous casting process comprises molten iron pretreatment, converter top and bottom composite blowing, LF refining, RH, and slab continuous casting to form a continuous casting billet; In the continuous casting slab heating step, the thickness is 2.00-3.50 mm, the heating temperature is 1240-1270° C., the soaking temperature is 1230-1260° C., and the furnace discharge temperature is 1250±20° C.; the thickness is 3.51-7.00 mm, the heating temperature is 1210-1240° C., the soaking temperature is 1200-1230° C., and the furnace discharge temperature is 1220±20° C.; the thickness is 7.01-16.00 mm, the heating temperature is 1190-1230° C., the soaking temperature is 1180-1220° C., and the furnace discharge temperature is 1200±20° C. The slab furnace time is controlled to be 150-270 min, and the soaking time is 20-40 min. In the rough rolling step, the rough rolling adopts the 3+5 mode, and the finishing rolling adopts the 7-stand continuous variable crown rolling mill. The starting rolling temperature of the finishing rolling is automatically controlled by the secondary computer, and the final rolling temperature is 825-885°C; Thickness 2.00~6.00mm, intermediate billet thickness 38~45mm, final rolling temperature 870±15℃; Thickness 6.01~10.00mm, intermediate billet thickness 46~50mm, final rolling temperature 850±15℃; Thickness 10.01~16.00mm, intermediate billet thickness 51~65mm, final rolling temperature 840±15℃; In the cooling and coiling steps, the thickness is 2.00-6.00 mm, the coiling temperature is 640±15°C, the cooling adopts the laminar cooling method of the "11" mode, which is front dispersion, the cooling method is one-by-one, and the cooling rate is controlled at 30-50°C / s; the thickness is 6.01-10.00 mm, the coiling temperature is 600±15°C, the cooling adopts the laminar cooling method of the "11" mode, which is front dispersion, the cooling method is one-by-one, and the cooling rate is controlled at 20-45°C / s; the thickness is 10.01-16.00 mm, the coiling temperature is 580±15°C, the cooling adopts the laminar cooling method of the "11" mode, which is front dispersion, the cooling method is one-by-one, and the cooling rate is controlled at 20-45°C / s.

2. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 1, characterized in that: The chemical composition of the pressure vessel steel is calculated by weight percentage as follows: C: 0.16-0.18%, Si: 0.10-0.20%, Mn: 1.35-1.55%, P: ≤0.015%, S: ≤0.005%, Ti: 0.012-0.020%, O: ≤0.0030%, N: ≤0.0060%, Ce: 0.0025%, and the balance is Fe and unavoidable impurities.

3. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 2, characterized in that: The chemical composition of the pressure vessel steel is calculated by weight percentage as follows: C: 0.17%, Si: 0.15%, Mn: 1.45%, P: 0.011%, S: 0.005%, Ti: 0.017%, O: 0.0015%, Ce: 0.00:20%, and the balance is Fe and unavoidable impurities.

4. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 2, characterized in that: The chemical composition of the pressure vessel steel is, by weight percentage, C: 0.16%, Si: 0.13%, Mn: 1.44%, P: 0.012%, S: 0.003%, Ti: 0.013%, O: 0.0020%, Ce: 0.0020%, and the remainder is Fe and unavoidable impurities.

5. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 1, characterized in that: The chemical composition of the pressure vessel steel is calculated by weight percentage as follows: C: 0.138%, Si: 0.12%, Mn: 1.46%, P: 0.010%, S: 0.001%, Ti: 0.015%, O: 0.0018%, Ce: 0.0019%, and the remainder is Fe and unavoidable impurities.

6. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 3, characterized in that: The molten iron is pre-treated for desulfurization. The converter adopts the top and bottom combined blowing smelting technology. Ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying. The composition is adjusted to meet the steel-making requirements. The converter steel-making temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment. Ferromanganese, ferrosilicon and ferroaluminum alloy are added according to the composition of the molten steel to adjust to the target composition. In order to reduce the inclusions in the steel, micro-calcium treatment is carried out when the LF is out of place to control the fluidity and performance of the slag. The slag basicity is 7.92, FeO is 1.78, and CaO / Al2O3 is 1.

76. The molten steel is transported to the RH for vacuum treatment. During this period, ferrotitanium alloy is added. The vacuum degree is required to be 1.9mbar, the vacuum time is maintained for 12min, and the circulating pure degassing time is guaranteed to be 9min. The vacuum treatment result After the beam is formed, 30 kg of rare earth ferrocerium alloy with a Ce content of 30% is added, and the RH is guaranteed to ensure a soft blowing time of 10 minutes; before loading the steel, the argon flow rate is adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed; the overheat degree of the slab continuous casting is 28°C; the slab is sent to the heating furnace by hot charging; the slab heating temperature is 1260°C, the soaking temperature is 1250°C, the furnace discharge temperature is 1240°C, and the heating time is 240 minutes. The heated slab is subjected to high-pressure water dephosphorization; 2 rough rolling mills and 7 CVC finishing mills are used; the intermediate slab thickness is 45.0 mm, and the finishing rolling temperature is 870°C; the laminar cooling adopts the front dispersed cooling mode "11", the upper and lower nozzles are separated by one, the cooling rate is 45°C / s, the coiling temperature is 640°C, and the finished product thickness is 3.0 mm.

7. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 4, characterized in that: The molten iron is pre-treated for desulfurization. The converter adopts the top and bottom combined blowing smelting technology. Ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying. The composition is adjusted to meet the steel-making requirements. The converter steel-making temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment. Ferromanganese, ferrosilicon and ferroaluminum alloy are added according to the composition of the molten steel to adjust the target composition. In order to reduce the inclusions in the steel, micro-calcium treatment is carried out when the LF is out of place to control the fluidity and performance of the slag. The slag basicity is 7.65, FeO is 1.29, and CaO / Al2O3 is 1.

99. The molten steel is transported to the RH for vacuum treatment. During this period, ferrotitanium alloy is added. The vacuum degree is 2.2mbar and the vacuum time is 13min. The circulating pure degassing time is guaranteed to be 8min. The vacuum treatment is completed Then 30kg of rare earth ferrocerium alloy with a Ce content of 30% was added, and the RH soft blowing time was 10min; before steel was added, the argon flow rate was adjusted to make the molten steel in a soft blowing state to prevent the molten steel from being exposed; the overheat degree of the slab continuous casting was 28℃; the slab was sent to the heating furnace by hot charging; the slab heating temperature was 1235℃, the soaking temperature was 1225℃, the furnace discharge temperature was 1220℃, the heating time was 230min, and the heated slab was subjected to high-pressure water dephosphorization; 2 rough rolling mills and 7 CVC finishing mills were used; the intermediate billet thickness was 44.0mm, and the finishing rolling temperature was 865℃; the laminar cooling adopted the front dispersed cooling mode "11", the upper and lower nozzles were separated by one, the cooling rate was 44℃ / s, the coiling temperature was 633℃, and the finished product thickness was 6.0mm.

8. The method for producing low temperature resistant rare earth microalloyed Q345R pressure vessel steel according to claim 5, characterized in that: The molten iron is pre-treated for desulfurization. The converter adopts the top and bottom combined blowing smelting technology. Ferromanganese and ferrosilicon alloy are added to the converter for deoxidation and alloying. The composition is adjusted to meet the steel-making requirements. The converter steel-making temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment. Ferromanganese, ferrosilicon and ferroaluminum alloy are added according to the composition of the molten steel to adjust the target composition. In order to reduce the inclusions in the steel, micro-calcium treatment is carried out when the LF is out of place to control the fluidity and performance of the slag. The slag basicity is 9.65, FeO is 1.21, and CaO / Al2O3 is 1.

79. The molten steel is transported to the RH for vacuum treatment. During Add titanium iron alloy, vacuum degree is 2.0mbar, vacuum time is 15min, and the cycle pure degassing time is guaranteed to be 9min; after the vacuum treatment, add 30kg of rare earth cerium iron alloy with 30% Ce content, and the RH soft blowing time is 12min; before steel is added, adjust the argon flow rate to make the molten steel in a soft blowing state to prevent the molten steel from being exposed; the overheat degree of slab continuous casting is 28℃; the slab is sent to the heating furnace by hot charging; the slab heating temperature is 1210℃, the uniform heating temperature is 1200℃, the furnace temperature is 1195℃, the heating time is 230min, and the heated slab is dephosphorized by high-pressure water. The width is determined by the fixed width press, 2 rough rolling mills and 7 CVC finishing mills are used; the thickness of the intermediate slab is 55.0mm, and the finishing rolling temperature is 845℃; the laminar cooling adopts the back-front scattered cooling mode "11", the upper and lower nozzles are separated by one, the cooling rate is 43℃ / s, the coiling temperature is 586℃, and the finished product thickness is 11.75mm.

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