AU2020470046A1

AU2020470046A1 - Ew 420 extra thick marine steel sheet and manufacturing method therefor

Info

Publication number: AU2020470046A1
Application number: AU2020470046A
Authority: AU
Inventors: FeiHu BO; LinHeng CEHN; Majun CHE; Jianhua Huang; Hengkun LI; Baowen QIU; Xiaoxue ZHANG; Jinbin Zhao
Original assignee: Nanjing Iron and Steel Co Ltd
Current assignee: Nanjing Iron and Steel Co Ltd
Priority date: 2020-09-24
Filing date: 2020-12-02
Publication date: 2023-05-18
Also published as: WO2022062176A1; CN112501494A

Abstract

An EW 420 extra thick marine steel sheet, which relates to the technical field of steel production. Internal defects such as blank segregation and loosening are reduced and the inclusion elements As, Sn, Sb, Pb, Bi and B are controlled by smelting clean steel; columnar crystals are crushed and austenite grains are refined by means of rough rolling at high temperature, at a low speed and under high pressure; and the objective of controlling tissue morphology and grain size is obtained by means of finish rolling cumulative deformation and cooperative cooling control.

Description

EW 420 EXTRA THICK MARINE STEEL SHEET AND MANUFACTURING METHOD THEREFOR

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of steel production, and specifically relates to an EW 420 extra thick marine steel sheet and a manufacturing method therefor.

BACKGROUND

[0002] China has started the development of offshore oil relatively late, and has owned the offshore oil platform only in the 1980s. In the past decade, the steel sheets for offshore platform manufactured by China itself have been widely used in the offshore oil engineering. At present, China has basically realized the localization of steels lower than the EH36 grade for the offshore platform, accounting for 90% of the steels for the offshore platform. With the implementation of the policies such as "Made in China 2025", "Medium and Long-term Development Plan for Offshore Engineering Equipment Manufacturing Industry", and the National Strategy for South China Sea in China, the support equipment and its key system, and special equipment for deep sea exploration, resource development and utilization, and offshore operation will be vigorously developed in the fields of offshore engineering equipment and high-tech ships. Due to the development and engineering of deep-sea space stations and large floating structures, the demand and requirements for the steels for the offshore platform are increasing, especially for the thick high-strength steels.

[0003] The traditional marine enterprise greatly requires on the performance uniformity and fluctuation value of 420MPa grade marine steel. Generally, the steel sheet is required to be delivered in the quenched and tempered state. However, the quenched and tempered steel sheet generally has poor welding performance, thus high-temperature preheating is required. What's more, less heat input is used for welding. With the high-quality development of the marine equipment, the requirements for the weldability of steel sheets are increasingly higher. With the intellectualization and large-scale of the rolling equipment of iron and steel enterprises, the TMCP state easy-to-weld marine steel is gradually accepted by downstream customers.

[0004] The Chinese patent with the publication number of CN 104674117 discloses a 420MPa grade marine steel sheet and a manufacturing method therefor. The inclusions As, Sn, Sb, Pb, Bi, and B are not effectively controlled, and the smelting process has no practical operability. The actual maximum thickness is only 80 mm. Similarly, The Chinese patent with the publication number of CN 104357742 discloses a 420MPa thick hot-rolled marine steel sheet and a manufacturing method therefor. The inclusions As, Sn, Sb, Pb, Bi, and B are not effectively controlled, the actual thickness is 70 mm., and the electric furnace process is adopted. In the above mentioned two patents, the content of Cr, Cu, C, Si, Mn and other elements is not clearly controlled to improve the welding performance.

SUMMARY

[0005] To solve the above-mentioned technical problems, the present disclosure provides an EW 420 extra thick marine steel sheet, which is composed of the following chemical composition in mass percentage: C: 0.04%-0.07% , Si: 0.15%-0.25%, Mn: 1.30%-1.60%, P <0.013%, S < 0.003%, Nb: 0.010%-0.050%, V: 0.020%-0.040%, Ti: 0.005%-0.020%, Cr: 0.10%-0.20%, Ni: 0.10% 0.70%, Cu: 0.20%-0.30%, Cr + Cu < 0.50%, C + Si/30 + Mn/20 < 0.15%, Al: 0.0250%-0.050%, O 12ppm,N<35 ppm, H< 1.5 ppm, inclusions As< 0.012%, Sn<0.010%, Sb<0.010%, Pb < 0.010%, Bi < 0.010%, and B < 0.003%, and a balance of Fe and inevitable impurities.

[0006] The technical effects are as follows: Within the chemical composition range of GB712 and standards of the top 10 classification societies, the present disclosure develops the EW 420 extra thick marine steel sheet with a thickness of 81-100 mm. The EW 420 extra thick marine steel sheet is easy to weld, and has stable manufacturing process and excellent mechanical properties. The requirement for the load of mills is not too high, and a wide and heavy plate mill is capable of being used to manufacture the EW 420 extra thick marine steel sheet. Therefore, The EW 420 extra thick marine steel sheet has wide applicability, capable of being manufactured by most steel enterprises manufacturing the wide and heavy plate in China.

[0007] The technical solutions further limited by the present disclosure are as follows:

[0008] The EW 420 extra thick marine steel sheet described above is composed of the following chemical composition in mass percentage: C: 0.04%, Si: 0.15%, Mn: 1. 6 0%, P: 0.013%, S: 0.0025%, Nb: 0.010%, V: 0.040%, Ti: 0.020%, Cr: 0.10%, Ni: 0.10%, Cu: 0.20%, Cr + Cu: 0.30%, C + Si/30 + Mn/20: 0.125%, Al: 0.050%, 0: 0.0012%, N: 0.0035%, H: 0.00015%, the inclusions As: 0.003%, Sn: 0.0003%, Sb: 0.0003%, Pb: 0.005%, Bi: 0.002%, and B: 0.003%, and the balance of Fe and inevitable impurities.

[0009] The EW 420 extra thick marine steel sheet described above is composed of the following chemical composition in mass percentage: C: 0.06%, Si: 0. 2 0%, Mn: 1.50%, P: 0.012%, S: 0.0030%, Nb: 0.025%, V: 0.030%, Ti: 0.005%, Cr: 0.18%, Ni: 0.45%, Cu: 0.25%, Cr + Cu: 0.43%, C + Si/30 + Mn/20: 0.142%, Al: 0.040%, 0: 0.0011%, N: 0.0033%, H: 0.00014%, the inclusions As: 0.002%, Sn: 0.0003%, Sb: 0.0003%, Pb: 0.003%, Bi: 0.001%, and B: 0.002%, and the balance of Fe and unavoidable impurities.

[0010] The EW 420 extra thick marine steel sheet described above is composed of the following chemical composition in mass percentage: C: 0.07%, Si: 0. 2 5%, Mn: 1. 3 0%, P: 0.011%, S:

0.0015%,Nb: 0.050%,V: 0.020%, Ti: 0.015%, Cr: 0.20%,Ni: 0.70%, Cu: 0.30%, Cr+Cu: 0.50%, C + Si/30 +Mn/20:0.143%0 ,Al: 0.025%, 0: 0.0010%,N: 0.0030%, H: 0.00011%, the inclusions As: 0.002%, Sn: 0.0002%, Sb: 0.0002%, Pb: 0.003%, Bi: 0.001%, and B: 0.0015%, and the balance of Fe and unavoidable impurities.

[0011] The EW 420 extra thick marine steel sheet is described above, and a thickness of a steel sheet obtained is 81-100 mm.

[0012] Another object of the present disclosure is providing a method for manufacturing the EW 420 extra thick marine steel sheet. The method comprises:

[0013] steel smelting and continuous casting processes, wherein a content of S is less than or equal to 0.002% after hot metal desulfurization is completed; blowing at a high oxygen lance position is adopted for dephosphorization in a converter smelting process; bottom ingot is clean and free of defects, a slag blocking process is adopted for converter tapping; a white slag smelting process is adopted for refining with a holding time of the white slag greater than or equal to 15 min, and a target alkalinity is 5-7; a vacuum treatment is performed for greater than or equal to 25 min; a seamless calcium wire treatment is performed after the vacuum treatment is completed; a five-port nozzle is adopted for continuous casting, a target temperature of a continuous casting tundish is equal to a liquidus temperature + (5-15) °C, and a casting speed is stable; and

[0014] a rolling process, wherein controlled rolling and controlled cooling processes are adopted, and the controlled rolling process is a two-stage controlled rolling process; a heating temperature of a continuous casting billet obtained before rolling is 1130-1200 °C, a temperature for rough rolling is 960-1060 °C, and an initial temperature for finish rolling is 780-840 °C; a laminar cooling process is adopted after the rolling is completed, a temperature for final cooling is 300-450 °C, and a cooling rate is 7-12 °C/s; and then air cooling is performed.

[0015] The method for manufacturing the EW 420 extra thick marine steel sheet is described above, and a cumulative reduction rate of last three passes in the finish rolling is greater than 30%.

[0016] The beneficial effects of the present disclosure are as follows:

[0017] (1) The present disclosure reduces the content of S through the hot metal pretreatment, realizes the dephosphorization by blowing at the high oxygen lance position in the converter smelting process, and uses the slag blocking process for the converter tapping. The refining time of white slag and the alkalinity are ensured. The inclusions are absorbed as much as possible, and the content of S, 0 and the like is reduced. The seamless calcium wire treatment is adopted to improve the shape of the inclusions. The vacuum treatment is performed for long time under high vacuum to make N < 35 ppm and H < 1.5 ppm. Ultimately, the continuous casting billet with better internal quality is obtained.

[0018] (2) In the present disclosure, the heating temperature of the continuous casting billet before the rolling is 1130-1200 °C to ensure that the austenite grains are refined as much as possible in the case of the complete solid solution of micro-alloyed elements. The high-temperature low-speed high-reduction rolling is adopted for the rough rolling to crush the columnar grains, weld the internal defects of the continuous casting billet, and refine the austenite grains. The cumulative reduction rate of the last three passes in the finish rolling is greater than 30%. The ferrite mechanism is induced through low-temperature large deformation in the crystallization zone, and the fast cooling is performed in the case of high supercooling degree, so that the microstructure and grain size are controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a typical microstructure diagram of a steel sheet obtained in Example 1 under a metallographic microscope;

[0020] FIG. 2 is a typical microstructure diagram of the steel sheet obtained in Example 2 under the metallographic microscope; and

[0021] FIG. 3 is a typical microstructure diagram of the steel sheet obtained in Example 3 under the metallographic microscope.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The examples of the present disclosure provide the EW 420 extra thick marine steel sheet and the manufacturing method therefor. The chemical composition is shown in Table 1.

[0023] Table 1 The chemical composition of the EW 420 extra thick marine steel sheet of Examples 1-3 (wt%)

[0024] Example C Si Mn P S Nb V Ti Cr Al

Example 1 0.04 0.15 1.60 0.013 0.0025 0.010 0.040 0.020 0.10 0.050

Example 2 0.06 0.20 1.50 0.012 0.0030 0.025 0.030 0.005 0.18 0.040

Example 3 0.07 0.25 1.30 0.011 0.0015 0.050 0.020 0.015 0.20 0.025

Cr + C + Si/30 + Fe and unavoidable Example Ni Cu 0 N H Cu Mn/20 impurities

Example 1 0.10 0.20 0.0012 0.0035 0.00015 0.30 0.125 balance

Example 2 0.45 0.25 0.0011 0.0033 0.00014 0.43 0.142 balance

Example 3 0.70 0.30 0.0010 0.0030 0.00011 0.50 0.143 balance

[0025] Example 1

[0026] This example provides the method for manufacturing the EW 420 extra thick marine steel sheet with the thickness of 81 mm. The method is specifically as follows:

[0027] The steel smelting and continuous casting processes are adopted. The content of S is 0.002% after the hot metal desulfurization is completed. The dephosphorization is carried out by blowing at the high oxygen lance position in the converter smelting process. The bottom ingot is clean and free of defects, and the slag blocking process is adopted for the converter tapping. The white slag smelting process is adopted for refining with the white slag holding time of 15 min, and the target alkalinity is 5. The vacuum treatment is performed for 25 min, and the seamless calcium wire treatment is performed after the vacuum treatment is completed. The five-port nozzle is adopted for the continuous casting, the target temperature of the continuous casting tundish is equal to the liquidus temperature + 15 °C, and the casting speed is stable.

[0028] The rolling process is adopted. The rolling process includes the controlled rolling and controlled cooling processes, and the controlled rolling process is the two-stage controlled rolling process. The heating temperature of the continuous casting billet before the rolling is 1200 °C, and the temperature for the rough rolling is 1060 °C. The high-temperature low-speed high-reduction rolling is performed, and the reduction of the first pass is 40 mm. The initial temperature for the finish rolling is 840 °C, and the cumulative reduction rate of the last three passes is 30%. The laminar cooling process is adopted after the rolling is completed, the temperature for the final cooling is 450 °C, and the cooling rate is 12 °C/s. Then, the air cooling is performed, to obtain the EW 420 extra thick marine steel sheet with the thickness of 81 mm.

[0029] Example 2

[0030] This example provides the method for manufacturing the EW 420 extra thick marine steel sheet with the thickness of 90 mm. The method is specifically as follows:

[0031] The steel smelting and continuous casting processes are adopted. The content of S is 0.0018% after the hot metal desulfurization is completed. The dephosphorization is carried out by blowing at the high oxygen lance position in the converter smelting process. The bottom ingot is clean and free of defects, and the slag blocking process is adopted for the converter tapping. The white slag smelting process is adopted for refining with the white slag holding time of 18 min, and the target alkalinity is 6. The vacuum treatment is performed for 30 min, and the seamless calcium wire treatment is performed after the vacuum treatment is completed. The five-port nozzle is adopted for the continuous casting, the target temperature of the continuous casting tundish is equal to the liquidus temperature + 10 °C, and the casting speed is stable.

[0032] The rolling process is adopted. The rolling process includes controlled rolling and controlled cooling processes, and the controlled rolling process is the two-stage controlled rolling process. The heating temperature of the continuous casting billet before the rolling is 1150 °C, and the temperature for the rough rolling is 980 °C. The high-temperature low-speed high-reduction rolling is performed, and the reduction of the first pass is 42 mm. The initial temperature for the finish rolling is 800 °C, and the cumulative reduction rate of the last three passes is 30%. The laminar cooling process is adopted after the rolling is completed, the temperature for the final cooling is 350 °C, and the cooling rate is 8 °C/s. Then, the air cooling is performed, to obtain the EW 420 extra thick marine steel sheet with the thickness of 90 mm.

[0033] Example 3

[0034] This example provides the method for manufacturing the EW 420 extra thick marine steel sheet with the thickness of 100 mm. The method is specifically as follows:

[0035] The steel smelting and continuous casting processes are adopted. The content of S is 0.0015% after the hot metal desulfurization is completed. The dephosphorization is carried out by blowing at the high oxygen lance position in the converter smelting process. The bottom ingot is clean and free of defects, and the slag blocking process is adopted for the converter tapping. The white slag smelting process is adopted for refining with the white slag holding time of 20 min, and the target alkalinity is 7. The vacuum treatment is performed for 34 min, and the seamless calcium wire treatment is performed after the vacuum treatment is completed. The five-port nozzle is adopted for the continuous casting, the target temperature of the continuous casting tundish is equal to the liquidus temperature + 5 °C, and the casting speed is stable.

[0036] The rolling process is adopted. The rolling process includes controlled rolling and controlled cooling processes, and the controlled rolling process is the two-stage controlled rolling process. The heating temperature of the continuous casting billet before the rolling is 1130 °C, and the temperature for the rough rolling is 960 °C. The high-temperature low-speed high-reduction rolling is performed, and the reduction of the first pass is 45 mm. The initial temperature for the finish rolling is 780 °C, and the cumulative reduction rate of the last three passes is 30%. The laminar cooling process is adopted after the rolling is completed, the temperature for the final cooling is 300 °C, and the cooling rate is 7 °C/s. Then, the air cooling is performed, to obtain the EW 420 extra thick marine steel sheet with the thickness of 100 mm.

[0037] It can be seen from FIGs. 1-3 that the EW 420 extra thick marine steel sheet has the fine and uniform bainite as the main structure and excellent comprehensive mechanical properties through reasonable composition design and precise controlled rolling process.

[0038] After the smelting and rolling treatment is completed, the transverse tensile properties and transverse cold bending properties of the EW 420 extra thick marine steel sheet obtained in Examples 1-3 at the 1/4 and 1/2 thicknesses are shown in Table 2, and the transverse impact properties and Z-direction properties are shown in Table 3.

[0039] Table 2 The transverse tensile properties and transverse cold bending properties of the EW 420 extra thick marine steel sheet obtained in Examples 1-3 at the 1/4 and 1/2 thicknesses

[0040] Wide cold Yield strength Tensile strength Elongation Example Location bending MPa MPa

% (b=5a)

At the 1/4 thickness 458 571 29 d=3a Example 1 At the 1/2 thickness 453 569 28.5 qualified

At the 1/4 thickness 457 567 26.5 d= 3a Example 2 At the 1/2 thickness 445 547 25 qualified

At the 1/4 thickness 449 551 24 d=3a Example 3 At the 1/2 thickness 439 545 23 qualified

[0041] Table3 The transverse impact properties and Z-direction properties of the EW 420 extra thick marine steel sheet obtained in Examples 1-3 at the 1/4 and 1/2 thicknesses

[0042] - 40 °C AKV. J Z-direction section Example Location shrinkage rate (%) 1 2 3 Average 1 2 3 Average

Example At the 1/4 thickness 391 373 375 380 1 At the 1/2 thickness 325 355 301 327

Example At the 1/4 thickness 337 306 352 332 66 74 68 69 2 At the 1/2 thickness 301 286 307 298 Example At the 1/4 thickness 339 326 326 330 69 67 67 68 3 At the 1/2 thickness 209 337 259 268

[0043] The impact properties of the welded joint of the EW 420 extra thick marine steel sheet obtained in Example 3 under the condition of the heat input of 50 kJ/cm are shown in Table 4.

[0044] Table4 The impact properties of the welded joint of the EW 420 extra thick marine steel sheet obtained in Example 3 under the condition of the heat input of 50kJ/cm

[0045] Thickness Temperature Impactlocation 1 2 3 (mm) (°C) At the WM 167 159 176 location of 2 FL 176 132 188 100 -40 mm below FL+1 255 189 266 surface FL+2 342 321 291

FL+3 218 238 241 FL+5 211 191 246 FL+7 206 212 203 FL+20 210 264 252 WM 113 193 136 FL 136 142 109 FL+1 312 321 246 At the 1/2 FL+2 218 284 272 thickness FL+3 175 160 189 FL+5 174 106 156 FL+7 144 125 157 FL+20 122 174 158

[0046] It can be seen from Tables 2 and 3 that the mechanical properties of the EW 420 extra thick marine steel sheet obtained in Examples 1-3 meet the performance requirements of E420 grade ultra-high-strength marine steel sheet in the standards of major classification societies. The yield strength is > 439 MPa, the tensile strength is > 545 MPa, the elongation is > 23%, and the Z direction section shrinkage rate is > 66%. It can be seen from Table 4 that the impact properties of the welded joint under the condition of the heat input of 50 kJ/cm is excellent, which meets the requirements of the EW 420 extra thick marine steel sheet. The present disclosure has stable manufacturing process, and the EW 420 extra thick marine steel sheet has excellent mechanical properties.

[0047] In addition to the above-mentioned examples, the present disclosure may also have other examples. All technical solutions formed by equivalent replacements or transformations shall fall within the protection scope of the present disclosure.

Claims

WHAT IS CLAIMED IS: 1. An EW 420 extra thick marine steel sheet, wherein the EW 420 extra thick marine steel sheet is composed of the following chemical composition in mass percentage: C: 0.04%-0.0 7 %, Si: 0.15%-0.25%, Mn: 1.30%-1.60%, P < 0.013%, S< 0.003%, Nb: 0.010%-0.050%, V: 0.020% 0.040%, Ti: 0.005%-0.020%, Cr: 0.10%-0.20%, Ni: 0.10%-0.70%, Cu: 0.20%-0.30%, Cr + Cu < 0.50%, C + Si/30 + Mn/20 < 0.15%, Al: 0.0250%-0.050%, 0 < 12 ppm, N < 35 ppm, H < 1.5 ppm, inclusions As < 0.012%, Sn < 0.010%, Sb < 0.010%, Pb < 0.010%, Bi < 0.010%, and B < 0.003%, and a balance of Fe and inevitable impurities.
2. The EW 420 extra thick marine steel sheet according to claim 1, wherein the EW 420 extra thick marine steel sheet is composed of the following chemical composition in mass percentage: C: 0.04%, Si: 0.15%, Mn: 1.60%, P: 0.013%, S: 0.0025%, Nb: 0.010%, V: 0.040%, Ti: 0.020%, Cr: 0.10%, Ni: 0.10%, Cu: 0.20%, Cr + Cu: 0.30%, C + Si/30 + Mn/20:0.125%, Al: 0.050%, 0: 0.0012%, N: 0.0035%, H: 0.00015%, the inclusions As: 0.003%, Sn: 0.0003%, Sb: 0.0003%, Pb: 0.005%, Bi : 0.002%, and B: 0.003%, and the balance of Fe and inevitable impurities.
3. The EW 420 extra thick marine steel sheet according to claim 1, wherein the EW 420 extra thick marine steel sheet is composed of the following chemical composition in mass percentage: C: 0.06%, Si: 0.20%, Mn: 1.50%, P: 0.012%, S: 0.0030%, Nb: 0.025%, V: 0.030%, Ti: 0.005%, Cr: 0.18%, Ni: 0.45%, Cu: 0.25%, Cr + Cu: 0.43%, C + Si/30 + Mn/20: 0.142%, Al: 0.040%, 0: 0.0011%, N: 0.0033%, H: 0.00014%, the inclusionsAs: 0.002%, Sn: 0.0003%, Sb: 0.0003%, Pb: 0.003%, Bi: 0.001%, and B: 0.002%, and the balance of Fe and unavoidable impurities.
4. The EW 420 extra thick marine steel sheet according to claim 1, wherein the EW 420 extra thick marine steel sheet is composed of the following chemical composition in mass percentage: C: 0.07%, Si: 0.25%, Mn: 1.30%, P: 0.011%, S: 0.0015%, Nb: 0.050%, V: 0.020%, Ti: 0.015%, Cr: 0.20%, Ni: 0.70%, Cu: 0.30%, Cr + Cu: 0.50%, C + Si/30 + Mn/20: 0.143%, Al: 0.025%, 0: 0.0010%, N: 0.0030%, H: 0.00011%, the inclusions As: 0.002%, Sn: 0.0002%, Sb: 0.0002%, Pb: 0.003%, Bi: 0.001%, and B: 0.0015%, and the balance of Fe and unavoidable impurities.
5. The EW 420 extra thick marine steel sheet according to claim 1, wherein a thickness of a steel sheet obtained is 81-100 mm.
6. A method for manufacturing an EW 420 extra thick marine steel sheet, wherein the method comprises: steel smelting and continuous casting processes, wherein a content of S is less than or equal to 0.002% after hot metal desulfurization is completed; blowing at a high oxygen lance position is adopted for dephosphorization in a converter smelting process; bottom ingot is clean and free of defects, a slag blocking process is adopted for converter tapping; a white slag smelting process is adopted for refining with a holding time of the white slag greater than or equal to 15 min, and a target alkalinity is 5-7; a vacuum treatment is performed for greater than or equal to 25 min; a seamless calcium wire treatment is performed after the vacuum treatment is completed; a five-port nozzle is adopted for continuous casting, a target temperature of a continuous casting tundish is equal to a liquidus temperature + (5-15) °C, and a casting speed is stable; and a rolling process, wherein controlled rolling and controlled cooling processes are adopted, and the controlled rolling process is a two-stage controlled rolling process; a heating temperature of a continuous casting billet obtained before rolling is 1130-1200 °C, a temperature for rough rolling is 960-1060 °C, and an initial temperature for finish rolling is 780-840 °C; a laminar cooling process is adopted after the rolling is completed, a temperature for final cooling is 300-450 °C, and a cooling rate is 7-12 °C/s; and then air cooling is performed.
7. The method for manufacturing the EW 420 extra thick marine steel sheet according to claim 6, wherein a cumulative reduction rate of last three passes in the finish rolling is greater than %.