Large-sized liquid carbon dioxide ship low-temperature steel plate and preparation method thereof

Abstract

The application discloses a large liquid carbon dioxide ship low-temperature steel plate and a preparation method thereof, and belongs to the field of steel metallurgy. The main chemical components of the steel plate are C, M, Si, Ni, Ni+Cu+Cr, Nb, Al, Ti, Nb+Al+Ti, S, P, and the rest are Fe and inevitable impurity elements. The clean steel smelting process is adopted to prepare a large-thickness continuous casting billet with high purity and high homogenization. The fine quasi-polygonal ferrite+acicular ferrite+carbide-free bainite structure is obtained through low-temperature large reduction (compression ratio greater than or equal to 7) hot mechanical coupling rolling+two-stage controlled rolling and controlled cooling. The large liquid carbon dioxide ship low-temperature steel plate is produced by adopting the TMCP process, has the advantages of large thickness, high strength, -60 DEG C CTOD and the like, meets the construction requirements of the large liquid carbon dioxide ship with low temperature and low pressure, has the advantages of simple manufacturing process, short production period and low alloy cost, and will greatly promote the large-scale development of the liquid carbon dioxide ship.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ship plate steel manufacturing, and relates to a large-scale liquid carbon dioxide marine cryogenic steel plate and a preparation method thereof. BACKGROUND

[0002] According to the data of the Global CCS Institute, the carbon capture and storage market is expected to grow at more than 30% per year, and the global carbon capture amount will reach 7.6 billion tons by 2050. This means that the demand for LCO2 transport ships, which are the main marine tools for carbon capture, utilization and storage (CCUS) technology, will also increase. However, unlike natural gas and ammonia, which can achieve liquid transportation by meeting only one of the low-temperature or high-pressure conditions, LCO2 transport ships store and transport liquid cargo carbon dioxide under low-temperature and high-pressure conditions, and the construction difficulty is relatively large. The current few LCO2 transport ships (including under construction, launched and conceptual design) are only small and medium-sized ships; these small and medium-sized transport ships cannot meet the future demand for LCO2.

[0003] The maximum thickness of the low-temperature steel plate involved in the LR ship classification society standard is 50 mm, and the low-temperature impact requirement is -60℃. For the design of low temperature and low pressure, LT-FH40 low-temperature steel plate is needed, and the thickness of the steel plate reaches 60 mm. According to the requirements of IGC code, the steel plate and the heat-affected zone of welding meet the low-temperature impact requirements of -95℃, and the CTOD performance of the base material and the coarse-grained zone of welding is required to be -60℃. Currently, there is no such product data or technology disclosed at home and abroad.

[0004] Currently, the steel for liquid carbon dioxide storage tanks mostly uses heat-treated steel plates, and a certain amount of Ni is added to improve the low-temperature performance, such as "A manufacturing method of P690QL2 marine storage tank steel" (application number: CN115786820A). The disadvantages are: the Ni, Cr, and Mo contents in the marine storage tank steel are high, the alloy cost is high, and the steel plate needs quenching + tempering heat treatment, which has high manufacturing cost and complex process; at the same time, the CTOD test temperature of the steel plate is -35℃, which cannot meet the requirement of lower temperature. SUMMARY

[0005] The purpose of the present application is to provide a large-scale liquid carbon dioxide marine cryogenic steel plate and a preparation method thereof. In view of the problems in the prior art, based on the low-cost composition design of low C, Nb micro-alloying, and a small amount of Cu + Cr + Ni metal elements, low-temperature large-compression-ratio thermal mechanical coupling rolling and acicular ferrite + carbide-free bainite structure are used to obtain excellent CTOD performance, and the TMCP steel plate ensures that the performance still meets the requirements after PWHT.

[0006] Technical solution: The chemical composition of the large liquid carbon dioxide marine low-temperature steel plate according to the application is as follows: C: 0.04%-0.07%, Mn: 1.50%-1.70%, Si: 0.15%-0.25%, Ni: 0.10%-0.30%, Ni+Cu+Cr≤0.45%, Nb: 0.015%-0.050%, Al: 0.020%-0.080%, Ti: 0.005%-0.025%, Nb+Al+Ti: 0.05%-0.08%, S≤0.0020%, P≤0.010%, and the rest is Fe and inevitable impurity elements.

[0007] Further, a preparation method of the large liquid carbon dioxide marine low-temperature steel plate LT-FH40, specifically comprising the following steps:

[0008] Step 1: according to the design of each chemical composition, through converter smelting-LF vacuum treatment-RH treatment-continuous casting, it is made into 260-460mm thick continuous casting billet;

[0009] Step 2: the billet is kept at 1050-1150℃, and then rough rolling is carried out, the rough rolling stage is in the austenite recrystallization zone, the single pass reduction is ≥40mm, the rough rolling final rolling temperature is 1000-1050℃, the intermediate billet thickness is ≥3.0h, after the rough rolling is finished, the intermediate billet is watered 3-5 times, the finish rolling stage is in the austenite unrecrystallization zone, and the final rolling temperature is A r3 ±20℃;

[0010] Step 3: the hot-rolled steel plate is cooled: first, the hot-rolled steel plate is cooled by the ultra-fast cooling system of the hot rolling production line at a cooling rate of 20-50℃ / s, and the final cooling temperature is 300-500℃; finally, the steel plate is air-cooled to room temperature, the preparation of the low-temperature steel plate LT-FH40, the thickness of the finished steel plate is 20-60mm, and the rolling compression ratio is ≥7.0.

[0011] Further, the prepared ship plate steel is 10-25% quasi-polygonal ferrite+60-75% acicular ferrite+5-15% low-carbon bainite structure, wherein the average grain size of the ferrite is 5-10μm, and the bainite is mainly carbide-free bainite.

[0012] Further, the prepared ship plate steel has a maximum thickness of 60mm, a yield strength of 410-500MPa, a tensile strength of 520-620MPa, an elongation after fracture of >22%, an impact energy at-95℃ of >200J, a CTOD at-60℃ of the base material and the CGHAZ of >0.5mm, and the CTOD at-60℃ performance of the base material and the welding plate after PWHT is stable.

[0013] Compared with the prior art, the application has the following advantages: 1. The liquid carbon dioxide ship low-temperature steel plate LT-FH40 has fine 10-25% quasi-polygonal ferrite + 60-75% acicular ferrite + 5-15% low-carbon bainite, the yield strength is greater than or equal to 410-450 MPa, the tensile strength is greater than or equal to 510-645 MPa, the elongation after fracture is 19-28%, and the impact energy at -95 DEG C is greater than 200 J, which is much higher than the performance index of the traditional liquefied gas ship C-Mn low-temperature steel plate, and is a major breakthrough in the low-temperature material field; 2. The LT-FH40 low-temperature steel plate has a thickness of 60 mm, the composition meets the composition requirements of the conventional C-Mn low-temperature steel plate, the low-temperature toughness of the base material and the welded joint at -95 DEG C is excellent, the CTOD performance at -60 DEG C is stable, the performance of the base material and the welded joint after PWHT is stable, and the low-temperature and low-pressure design requirements are met, so that the scale of the liquid carbon dioxide ship can be greatly improved, and the requirements of the large liquid carbon dioxide ship steel plate are fully met; 3. The LT-FH40 low-temperature steel plate is produced by using the TMCP process, the alloying amount of Ni+Cu+Cr is less than or equal to 0.45%, the production cost is low, and the large liquid carbon dioxide ship has important significance for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a microstructure diagram of a large liquid carbon dioxide ship low-temperature steel plate in embodiment 1 of the application. DETAILED DESCRIPTION

[0015] The application will be further described below in combination with the drawings and embodiments.

[0016] The large liquid carbon dioxide ship low-temperature steel plate in each embodiment of the application contains the chemical components and mass percentages shown in Table 1, wherein the remaining components are Fe and inevitable impurities.

[0017] Table 1: Large liquid carbon dioxide ship low-temperature steel plate LT-FH40 (mass fraction / wt%)

[0018] Embodiment 1

[0019] The chemical components and mass percentages of the large liquid carbon dioxide ship low-temperature steel plate LT-FH40 are shown in Table 1, and the preparation method specifically includes the following steps:

[0020] Step 1: According to the component design, the liquid carbon dioxide ship low-temperature steel plate LT-FH40 is prepared by converter smelting-LF vacuum treatment-RH treatment-continuous casting into a 460 mm thick continuous casting billet.

[0021] Step 2: The steel billet is kept at 1100℃, and then rough rolling is performed, the rough rolling stage is in the austenite recrystallization zone, the single pass reduction is 42-46mm, the rough rolling final rolling temperature is 1000℃, the intermediate billet thickness is 240mm (4 times the plate thickness), after the rough rolling is completed, the intermediate billet is watered 5 times, the finish rolling stage is in the austenite unrecrystallization zone, and the final rolling temperature is 734℃ (A r3 temperature is 754℃;

[0022] Step 3: The hot-rolled steel plate is cooled: first, the hot-rolled steel plate is cooled at a cooling rate of 50℃ / s by using the ultra-fast cooling system of the hot-rolling production line, and the final cooling temperature is 300℃; finally, the steel plate is air-cooled to room temperature, the finished steel plate thickness is 60mm, and the rolling compression ratio is ≥7.0.

[0023] The ship plate steel prepared in the embodiment is a multi-phase structure of ferrite + pearlite + bainite, wherein the volume fraction of quasi-polygonal ferrite is 15%, the volume fraction of acicular ferrite is 70%, the volume fraction of bainite is 15%, the volume fraction of quasi-polygonal ferrite is 10-25%, and the average grain size of ferrite is 7μm, and the bainite is mainly non-carbide bainite.

[0024] The ship plate steel prepared in the embodiment is subjected to tensile test, impact test and CTOD test, and the specific mechanical properties are shown in Table 2.

[0025] Example 2

[0026] The chemical composition and mass percentage of a large-scale liquid carbon dioxide marine cryogenic steel plate LT-FH40 are shown in Table 1, and the preparation method specifically includes the following steps:

[0027] Step 1: According to the component design, after converter smelting-LF vacuum treatment-RH treatment-continuous casting, it is made into a 260mm thick continuous casting billet;

[0028] Step 2: The steel billet is kept at 1150℃, and then rough rolling is performed, the rough rolling stage is in the austenite recrystallization zone, the single pass reduction is 40-46mm, the rough rolling final rolling temperature is 1000℃, the intermediate billet thickness is 100mm (4 times the plate thickness), after the rough rolling is completed, the intermediate billet is watered 3 times, the finish rolling stage is in the austenite unrecrystallization zone, and the final rolling temperature is 750℃ (A r3 temperature is 757℃;

[0029] Step 3: The hot-rolled steel plate is cooled: first, the hot-rolled steel plate is cooled at a cooling rate of 20℃ / s by using the ultra-fast cooling system of the hot-rolling production line, and the final cooling temperature is 500℃; finally, the steel plate is air-cooled to room temperature, the finished steel plate thickness is 20mm, and the rolling compression ratio is 13.0.

[0030] The ship plate steel prepared in the embodiment is a multi-phase structure of ferrite + pearlite + bainite, wherein the volume fraction of quasi-polygonal ferrite is 20%, the volume fraction of acicular ferrite is 75%, the volume fraction of bainite is 5%, and the average grain size of ferrite is 8 μm.

[0031] The ship plate steel prepared in the embodiment is subjected to tensile test, impact test and CTOD test, and the specific mechanical properties are shown in Table 2.

[0032] Example 3

[0033] The chemical composition and mass percentage of a large-scale liquid carbon dioxide ship low-temperature steel plate LT-FH40 are shown in Table 1, and the preparation method specifically comprises the following steps:

[0034] Step 1: According to the component design, the converter smelting-LF vacuum treatment-RH treatment-continuous casting is carried out to make a 360 mm thick continuous casting billet;

[0035] Step 2: The steel billet is kept at 1050℃, and then rough rolling is carried out, the rough rolling stage is in the austenite recrystallization zone, the single pass reduction is 40-45 mm, the rough rolling final rolling temperature is 1000℃, the intermediate billet thickness is 180 mm (4.5 times the plate thickness), after the rough rolling, the intermediate billet is water-cooled 4 times, the finish rolling stage is in the austenite non-recrystallization zone, and the final rolling temperature is 773℃ (A r3 temperature is 753℃);

[0036] Step 3: The hot-rolled steel plate is cooled: first, the hot-rolled steel plate is cooled by the ultra-fast cooling system of the hot rolling production line at a cooling rate of 40℃ / s, and the final cooling temperature is 350℃; finally, the steel plate is air-cooled to room temperature, and the finished steel plate has a thickness of 40 mm and a rolling compression ratio of 9.0.

[0037] The ship plate steel prepared in the embodiment is subjected to tensile test, impact test and CTOD test, and the specific mechanical properties are shown in Table 2.

[0038] Table 2 Mechanical properties of plate steel of each embodiment

[0039]

[0040] In addition, Table 3 is the CTOD performance of the plate steel of each embodiment; specifically as follows:

[0041] Table 3 CTOD performance of plate steel of each embodiment

[0042] Example Test item Test temperature / °C CTOD value / mm Example 1 Base metal CTOD -60 1.18 Example 2 Base metal CTOD -60 1.10 Example 3 Base metal CTOD -60 1.30 Example 1 Base metal PWHT CTOD -60 1.22 Example 2 Base metal PWHT CTOD -60 1.25 Example 3 Base metal PWHT CTOD -60 1.31 Example 1 SAW weld joint CGHAZ -60 1.42 Example 2 SAW weld joint CGHAZ -60 1.45 Example 3 SAW weld joint CGHAZ -60 1.58 Example 1 SAW weld joint PWHT CGHAZ -60 1.34 Example 2 SAW weld joint PWHT CGHAZ -60 1.37 Example 3 SAW weld joint PWHT CGHAZ -60 1.18

[0043] Note: PWHT process: charging temperature ≤400℃, heating rate ≤100℃ / h, soaking temperature 580±5℃, holding time 144±5 min.

Claims

1. A large-scale liquid carbon dioxide marine cryogenic steel plate, characterized in that, Its chemical composition by weight percentage is as follows: C: 0.04%~0.07%, Si: 0.15%~0.25%, Mn: 1.50%~1.70%, P≤0.010%, S≤0.0020%, Ni: 0.10%~0.30%, Ni+Cu+Cr≤0.45%, Al: 0.020%~0.080%, Nb: 0.015%~0.050%, Ti: 0.005%~0.025%, Nb+Al+Ti: 0.05%~0.08%, with the remainder being Fe and unavoidable impurity elements; The preparation steps are as follows: (1) Prepare each compound according to the proportion, and make it into a continuous casting billet by going through the process of converter smelting-LF vacuum treatment-RH treatment-continuous casting; (2) The steel billet is kept at a temperature of 1050~1150℃ and then rough rolled; In the rough rolling stage, within the austenite recrystallization zone, the single-pass reduction is ≥40mm, the final rolling temperature is 1000~1050℃, and the intermediate billet thickness is ≥3.5h. After rough rolling, the billet is allowed to cool to the appropriate temperature and then subjected to water quenching 3~5 times. In the finish rolling stage, within the non-recrystallization zone of austenite, the cumulative reduction is ≥35%, and the final rolling temperature is A. r3 ±20℃; (3) Cooling the hot-rolled steel plate; the specific process is as follows: First, the hot-rolled steel plate is cooled by the ultra-fast cooling system of the hot rolling production line at a cooling rate of 20~50℃ / s, and the final cooling temperature is 300~500℃; Finally, the steel plate is air-cooled to room temperature. The preparation of low-temperature steel plate LT-FH40 has a finished steel plate thickness of 20~60mm and a rolling compression ratio ≥7.

0. The prepared ship plate steel has the following structure: 10~25% quasi-polygonal ferrite + 60~75% acicular ferrite + 5~15% low-carbon bainite; wherein, the average grain size of ferrite is 5~10μm, and the bainite is mainly carbide-free bainite.

2. The large-scale liquid carbon dioxide marine cryogenic steel plate according to claim 1, characterized in that, In step (1), the thickness of the continuously cast billet is 260~460mm.

3. The large-scale liquid carbon dioxide marine cryogenic steel plate according to claim 1, characterized in that, The maximum thickness of the prepared ship plate steel reaches 60mm, the yield strength is 410~500MPa, the tensile strength is 520~620MPa, the elongation after fracture is >22%, the impact energy at -95℃ is >200J, and the CTOD at -60℃ of the base material and the welded CGHAZ is >0.5mm.

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