CORROSION-RESISTANT MARINE COMPOSITE STEEL PLATE AND MANUFACTURING METHOD THEREFOR

Abstract

Disclosed are a corrosion-resistant marine composite steel plate and a manufacturing method therefor. The corrosion-resistant composite steel plate has a two-layer structure, wherein one layer is duplex stainless steel, and the other layer is marine carbon steel; said duplex stainless steel comprises the following components by weight: C≤0.03%, Mn≤2.00%, Si≤1.00%, Cr: 21.0-23.0%, Ni: 4.5-6.5%, Mo: 2.5-3.5%, N: 0.08-0.20%, P≤0.02%, S≤0.025%, and the balance being Fe and inevitable impurities; and said marine carbon steel comprises the following components by weight: 0.03%≤C≤0.13%, Si≤0.50%, Mn: 0.90-1.60%, P≤0.020%, S≤0.025%, Cu≤0.035%, Cr≤0.20%, Ni≤0.40%, Nb: 0.02-0.05%, Ti≤0.02%, Mo≤0.08%, Al≥0.015%, and the balance being Fe and inevitable impurities. A rolled composite steel plate is produced by using a double-barrier vacuum assembly method, so that a reduction in structure weight is achieved while a good structural strength and an excellent corrosion resistance are obtained

Claims

1.-6. (canceled)

7. A corrosion-resistant marine composite steel plate, which has a two-layer structure, wherein one layer is duplex stainless steel, and the other layer is marine carbon steel; said duplex stainless steel comprises the following components by weight: C≤0.03%, Mn≤2.00%, Si≤1.00%, Cr: 21.0-23.0%, Ni: 4.5-6.5%, Mo: 2.5-3.5%, N: 0.08-0.20%, P≤0.02%, S≤0.025%, and the balance being Fe and inevitable impurities; and said marine carbon steel comprises the following components by weight: 0.03%≤C≤0.13%, Si≤0.50%, Mn: 0.90-1.60%, P≤0.020%, S≤0.025%, Cu≤0.035%, Cr≤0.20%, Ni≤0.40%, Nb: 0.02-0.05%, Ti≤0.02%, Mo≤0.08%, Al≥0.015%, and the balance being Fe and inevitable impurities.

8. The corrosion-resistant marine composite steel plate according to claim 7, wherein an interface between the duplex stainless steel and the marine carbon steel of the composite steel plate has a shear strength of 300 MPa or more and a bond strength of 320 MPa or more; and the composite steel plate has a yield strength of 450 MPa or more and a tensile strength of higher than 600 MPa.

9. The corrosion-resistant marine composite steel plate according to claim 7, wherein the marine carbon steel in the composite steel plate is capable of achieving an impact toughness of 120 J or more at the temperature of lower than or equal to 40° C. below zero.

10. The corrosion-resistant marine composite steel plate according to claim 8, wherein the marine carbon steel in the composite steel plate is capable of achieving an impact toughness of 120 J or more at the temperature of lower than or equal to 40° C. below zero.

11. A manufacturing method of the corrosion-resistant marine composite steel plate according to claim 7, comprising the following steps: 1) selecting the thicknesses of duplex stainless steel and carbon steel of a combined billet according to the expected thickness ratio of cladding layer and base layer of the clad steel plate; heating and cogging a continuous casting billet of the carbon steel to required size; cleaning the side of the carbon steel to be composited with the duplex stainless steel so as to expose the metal surface completely; and cleaning up the surface oxide scales and pollutants on the duplex stainless steel; 2) directly superposing the cleaned side of carbon steel with the cleaned side of duplex stainless steel, followed by vacuum welding and sealing at a vacuum degree of 0.001 Pa or less, wherein as a first vacuum control, a first vacuum barrier of two independent vacuum billets up and down are formed by carbon steel and duplex stainless steel; then stacking the vacuum billets such that side of duplex stainless steel opposes to side of duplex stainless surface and in symmetry along thickness direction; applying separating agent between the sides of duplex stainless steel surface for isolation; after stacking, welding and sealing at the peripheries of composite billets followed by vacuumizing to obtain a vacuum degree of 0.01 Pa or less, so that a second vacuum barrier is formed and a composite billet of four-layer structure is formed; 3) heating the composite billet with heating temperature controlled to be 1050˜1190° C.; 4) rolling the composite billet with an initial rolling temperature of 1040˜1170° C. and a final rolling temperature of 850˜1020° C.; 5) after rolling, cooling the superposed clad steel plate with compressed air or water, wherein the initial cooling temperature is controlled as 830˜1000° C., the cooling rate is controlled as 5° C./sec˜40° C./sec, and the final cooling temperature is controlled as 250˜750° C.; and 6) performing plasma cutting on the head and tail and edges of the rolled and superposed clad steel plate, so that the superposed clad steel plate is separated into two sets of finished clad steel plates in up-down symmetry.

12. The manufacturing method of the corrosion-resistant marine composite steel plate according to claim 11, the manufacturing method further comprising tempering thermal treatment with a tempering temperature of 500˜600° C., followed with air cooling treatment.

13. The manufacturing method of the corrosion-resistant marine composite steel plate according to claim 11, wherein, in step 4), the pass reduction rate is controlled as 10-25%.

14. The manufacturing method of the corrosion-resistant marine composite steel plate according to claim 11, wherein an interface between the duplex stainless steel and the marine carbon steel of the composite steel plate has a shear strength of 300 MPa or more and a bond strength of 320 MPa or more; and the composite steel plate has a yield strength of 450 MPa or more and a tensile strength of higher than 600 MPa.

15. The manufacturing method of the corrosion-resistant marine composite steel plate according to claim 11, wherein the marine carbon steel in the composite steel plate is capable of achieving an impact toughness of 120 J or more at the temperature of lower than or equal to 40° C. below zero.

16. The manufacturing method of the corrosion-resistant marine composite steel plate according to claim 14, wherein the marine carbon steel in the composite steel plate is capable of achieving an impact toughness of 120 J or more at the temperature of lower than or equal to 40° C. below zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 is a sectional view showing a structure of a composite slab of a corrosion-resistant marine composite steel plate provided in an embodiment of the present invention.

[0054] FIG. 2 is a picture of a metallographic structure of the corrosion-resistant marine composite steel plate provided in the embodiment of the present invention at a position where a carbon steel layer is bonded with a duplex stainless steel layer.

DETAILED DESCRIPTION

[0055] The marine duplex stainless steel composite steel plate and the manufacturing method therefor provided by the present invention will be further explained and described below in conjunction with the brief description of the drawings and the specific embodiments. However, the explanation and description cannot constitute improper limitations on the technical solutions of the present invention.

[0056] Referring to FIG. 1, a composite slab of a corrosion-resistant marine composite steel plate provided by the present invention has a four-layer structure, wherein two middle layers (cladding layer) 1 and 2 are duplex stainless steel; upper and lower layers (base layer) 3 and 4 are marine carbon steel; 5 represents a separating agent; and 6 represents a sealed weld seam.

Embodiment 1

[0057] The carbon steel serving as the base layer adopts EH40 and includes the chemical components (wt %): C: 0.09, Si: 0.25, Mn: 1.30, P: 0.011; S: 0.002, Cr: 0.13, Ni: 0.20, Nb: 0.025, Ti: 0.01. The components (wt %) of the duplex stainless steel are: C: 0.02, Si: 0.25, Mn: 1.25, Cr: 22.53, Ni: 5.45, Mo: 3.08, N: 0.16.

[0058] Assembled composite slab was performed by adopting a four-layer symmetric separation method as shown in FIG. 1, that is, a carbon steel billet, a duplex stainless steel billet, the other duplex stainless steel billet and the other carbon steel billet are sequentially disposed from top to bottom, wherein the carbon steel billet located on an upper layer and the duplex stainless steel billet corresponding to the carbon steel billet located on the upper layer were sealed in vacuum, and the carbon steel billet located on a lower layer and the duplex stainless steel billet corresponding to the carbon steel billet located on the lower layer were sealed in vacuum, so that two groups of first vacuum systems independent from each other were formed; and a second vacuum system was sealed in vacuum between a first layer and a fifth layer (that is, the carbon steel blillets in the present embodiment) as shown in FIG. 1. A double-vacuum-system assembled composite slab is formed jointly by the two systems. A space located between the duplex stainless steel and a surface of the duplex stainless steel of two groups of vacuum slabs was filled with a separating agent, and then, the vacuumized composite slab was rolled by heating and is cut to form a finished composite steel plate.

[0059] Composite rolling was performed, wherein a heating temperature is 1190° C., an initial rolling temperature is 1170° C., and a final rolling temperature is 850° C.; after rolling, the composite slab was directly cooled in a water cooling way, wherein an initial cooling temperature is 830° C., a cooling speed is 40° C./s, and a final cooling temperature is 420° C.; and then, the composite slab was naturally cooled in air to a room temperature. The composite steel plate which was rolled, separated and cut has a thickness of (4+20) mm, that is, the duplex stainless steel serving as the cladding layer has a thickness of 4 mm, and the carbon steel serving as the base layer has a thickness of 20 mm.

[0060] Mechanical properties of the composite steel plate are shown as table 1. In table 1, Rp0.2 represents the yield strength of a full thickness composite steel plate, Rm represents a tensile strength value of the composite steel plate, and A represents an elongation percentage of the composite steel plate during tensile test and reflects comprehensive mechanical properties of materials of the cladding layer and the base layer of the composite steel plate. The carbon steel has relatively obvious low-temperature sensitivity, and therefore, a low-temperature impact test is generally performed on the carbon steel serving as the base layer. As shown in table 1, the composite steel plate has good impact toughness. The shear strength is a mechanical index for evaluating bonding levels of the materials of the cladding layer and the base layer. Shear strength values of three groups of data are all higher than 300 MPa. Bond strength values of the three groups of data are higher than 320 MPa.

TABLE-US-00001 TABLE 1 Mechanical Properties of Composite Steel Plate with Thickness of (4 + 20) mm Tensile properties (cladding layer and Impact energy base layer of through- (carbon steel Shear Bond thickness composite serving as strength, strength, steel plate) base layer), J* MPa MPa Rp0.2, MPa 508 −40° C. 336 449 458 Rm, MPa 650 351 425 472 A, % 26 324 436 478 *is tested by adopting a specimen with a thickness of 10 mm, a width of 10 mm and a length of 55 mm, which conform to standard specifications (the carbon steel serving as the base layer has a thickness of 10 mm).

[0061] The corrosion resistance of the cladding layer of the composite steel plate was tested according to an ASTM A923C method, the material of the cladding layer was machined to form a specimen with a length of 50 mm and a width of 25 mm, a surface of the specimen was cleaned, then, the specimen was measured in size and weighed and is then soaked in a 6% FeCl.sub.3 solution with a temperature of 25° C. for 24 h to perform a corrosion test, and the specimen was weighed after being taken out, cleaned and blow-dried, wherein the weight-loss corrosion of the specimen needs to meet a corrosion requirement that a corrosion rate is not greater than 10mdd. Moreover, an intergranular corrosion test was performed according to an ASTM A262E method, the material of the cladding layer was machined to form two specimens with each having a length of 80 mm and a thickness of 20 mm, surfaces of the specimens were ground, and then, the specimens were sensitized at 675° C. for 1 h, were soaked into a boiled sulfuric acid-copper sulfate solution for 15 h, were taken out and are then bent for 180° for testing. A test result is shown as table 2.

TABLE-US-00002 TABLE 2 Result of Corrosion Test for Cladding layer of Composite Steel Plate with Thickness of (4 + 20) mm Result of corrosion test for cladding layer Testing Corrosion Test method Specimen rate * Testing method Specimen result ASTM 1 0.00 mdd ASTM A262E 1 No A923 C method cracks method 2 0.00 mdd (requiring no 2 No 25° C., cracks on an cracks 24 h observed surface of 10× after bending) * means corrosion weight loss per unit area per unit time.

Embodiment 2

[0062] The carbon steel serving as the base layer adopts EH36 and includes the chemical components (wt %): C: 0.038, Si: 0.24, Mn: 0.91, P: 0.014; S: 0.002, Nb: 0.025, Ti: 0.01. The components (wt %) of the duplex stainless steel are: C: 0.015, Si: 0.25, Mn: 1.25, Cr: 21.03, Ni: 4.52, Mo: 2.55, N: 0.08.

[0063] In the present embodiment, an assembled slab was performed by adopting a four-layer symmetric separation method same as that in embodiment 1 according to the above-mentioned component system.

[0064] Composite rolling was performed, wherein a heating temperature is 1050° C., an initial rolling temperature is 1040° C., and a final rolling temperature is 850° C.; after rolling, the composite slab was directly cooled in a water cooling way, wherein an initial cooling temperature is 830° C., a cooling speed is 20° C./s, and a final cooling temperature is 480° C.; and then, the composite slab was naturally cooled in air to a room temperature. The composite steel plate which was rolled, separated and cut has a thickness of (3+10) mm, that is, the duplex stainless steel serving as the cladding layer has a thickness of 3 mm, and the carbon steel serving as the base layer has a thickness of 10 mm.

[0065] Mechanical properties of the composite steel plate are shown as table 3. In table 3, Rp0.2 represents a yield strength of a full thickness composite steel plate, Rm represents a tensile strength value of the composite steel plate, and A represents an elongation percentage of the composite steel plate during tensile test and reflects comprehensive mechanical properties of materials of the cladding layer and the base layer of the composite steel plate. The carbon steel has a relatively obvious low-temperature sensitivity, and therefore, a low-temperature impact test is generally performed on the carbon steel serving as the base layer. As shown in table 3, the composite steel plate has a good impact toughness. The shear strength is a mechanical index for evaluating bonding levels of the materials of the cladding layer and the base layer. Shear strength values of three groups of data are all higher than 300 MPa. Bond strength values of the three groups of data are higher than 320 MPa.

TABLE-US-00003 TABLE 3 Mechanical Properties of Composite Steel Plate with Thickness of (3 + 10) mm Tensile properties (cladding layer and base layer of Impact energy through-thickness (carbon steel Shear Bond composite serving as strength, strength, steel plate) base layer), J* MPa MPa Rp0.2, MPa 473 −40° C. 243 465 433 Rm, MPa 623 258 437 459 A, % 25 231 421 447 * is tested by adopting a specimen with a thickness of 10 mm, a width of 10 mm and a length of 55 mm, which conform to standard specifications (the carbon steel serving as the base layer has a thickness of 10 mm).

[0066] The corrosion resistance of the cladding layer of the composite steel plate was tested according to an ASTM A923C method, the material of the cladding layer was machined to form a specimen with a length of 50 mm and a width of 25 mm, a surface of the specimen was cleaned, then, the specimen was measured in size and weighed and was then soaked in a 6% FeCl.sub.3 solution with a temperature of 25° C. for 24 h to perform a corrosion test, and the specimen was weighed after being taken out, cleaned and blow-dried, wherein the weight-loss corrosion of the specimen needs to meet a corrosion requirement that a corrosion rate is not greater than 10mdd. Moreover, an intergranular corrosion test was performed according to an ASTM A262E method, the material of the cladding layer was machined to form two specimens with each having a length of 80 mm and a thickness of 20 mm, surfaces of the specimens were ground, and then, the specimens were sensitized at 675° C. for 1 h, were soaked into a boiled sulfuric acid-copper sulfate solution for 15 h, were taken out and are then bent for 180° for testing. A test result is shown as table 4.

TABLE-US-00004 TABLE 4 Result of Corrosion Test for Cladding layer of Composite Steel Plate with Thickness of (3 + 10) mm Result of corrosion test for cladding layer Testing Corrosion Test method Specimen rate * Testing method Specimen result ASTM 1 0.00 mdd ASTM A262E 1 No A923 C method cracks method 2 0.00 mdd (requiring no 2 No 25° C., cracks on an cracks 24 h observed surface of 10× after bending) * means corrosion weight loss per unit area per unit time.

Embodiment 3

[0067] The carbon steel serving as the base layer adopts EH36 and includes the chemical components (wt %): C: 0.13, Si: 0.26, Mn: 1.59, P: 0.015; S: 0.002, Nb: 0.02, Ti: 0.01. The components (wt %) of the duplex stainless steel are: C: 0.03, Si: 0.25, Mn: 1.75, Cr: 22.95, Ni: 6.47, Mo: 3.50, N: 0.20.

[0068] In the present embodiment, slab assembly was performed by adopting a four-layer symmetric separation method same as that in embodiment 1 according to the above-mentioned component system.

[0069] Composite rolling was performed, wherein a heating temperature is 1160° C., an initial rolling temperature is 1130° C., and a final rolling temperature is 1000° C.; after rolling, the composite slab was cooled in a compressed air cooling way, wherein an initial cooling temperature is 980° C., a cooling speed is 5° C./s, and a final cooling temperature is 750° C.; and then, the composite slab was naturally cooled in air to a room temperature. The composite steel plate which was rolled, separated and cut has a thickness of (2+8) mm, that is, the duplex stainless steel serving as the cladding layer has a thickness of 2 mm, and the carbon steel serving as the base layer has a thickness of 8 mm.

[0070] Mechanical properties of the composite steel plate are shown as table 5. In table 5, Rp0.2 represents the yield strength of a through-thickness composite steel plate, Rm represents a tensile strength value of the composite steel plate, and A represents an elongation percentage of the composite steel plate during tensile test and reflects comprehensive mechanical properties of materials of the cladding layer and the base layer of the composite steel plate. The carbon steel has relatively obvious low-temperature sensitivity, and therefore, a low-temperature impact test is generally performed on the carbon steel serving as the base layer. As shown in table 5, the composite steel plate has good impact toughness. The shear strength is a mechanical index for evaluating bonding levels of the materials of the cladding layer and the base layer. Shear strength values of three groups of data are all higher than 300 MPa. Bond strength values of the three groups of data are higher than 320 MPa.

TABLE-US-00005 TABLE 5 Mechanical Properties of Composite Steel Plate with Thickness of (2 + 8) mm Tensile properties (cladding layer and base layer of Impact energy through-thickness (carbon steel Shear Bond composite serving as strength, strength, steel plate) base layer), J* MPa MPa Rp0.2, MPa 468 −40° C. 129 417 425 Rm, MPa 634 134 429 441 A, % 25 138 443 453 * is tested by adopting a specimen with a thickness of 7.5 mm, a width of 10 mm and a length of 55 mm (the carbon steel serving as the base layer has a thickness of 7.5 mm).

[0071] The corrosion resistance of the cladding layer of the composite steel plate was tested according to an ASTM A923C method, the material of the cladding layer was machined to form a specimen with a length of 50 mm and a width of 25 mm, a surface of the specimen was cleaned, then, the specimen was measured in size and weighed and is then soaked in a 6% FeCl.sub.3 solution with a temperature of 25° C. for 24 h to perform a corrosion test, and the specimen was weighed after being taken out, cleaned and blow-dried, wherein the weight-loss corrosion of the specimen needs to meet a corrosion requirement that a corrosion rate is not greater than 10mdd. Moreover, an intergranular corrosion test was performed according to an ASTM A262E method, the material of the cladding layer was machined to form two specimens with each having a length of 80 mm and a thickness of 20 mm, surfaces of the specimens were ground, and then, the specimens were sensitized at 675° C. for 1 h, were soaked into a boiled sulfuric acid-copper sulfate solution for 15 h, were taken out and were then bent for 180° for testing. A test result is shown as table 6.

TABLE-US-00006 TABLE 6 Result of Corrosion Test for Cladding layer of Composite Steel Plate with Thickness of (2 + 8) mm Result of corrosion test for cladding layer Testing Corrosion Test method Specimen rate * Testing method Specimen result ASTM 1 0.00 mdd ASTM A262E 1 No A923 C method cracks method 2 0.00 mdd (requiring no 2 No 25° C., cracks on an cracks 24 h observed surface of 10× after bending) * means corrosion weight loss per unit area per unit time.

Embodiment 4

[0072] The carbon steel serving as the base layer adopts EH40 and includes the chemical components (wt %): C: 0.07, Si: 0.25, Mn: 1.50, P: 0.013; S: 0.002, Cr: 0.10, Ni: 0.10, Nb: 0.03, Ti: 0.01. The components (wt %) of the duplex stainless steel are: C: 0.02, Si: 0.25, Mn: 1.20, Cr: 22.72, Ni: 5.41, Mo: 3.13, N: 0.16.

[0073] In the present embodiment, slab assembly was performed by adopting a four-layer symmetric separation method same as that in embodiment 1 according to the above-mentioned component system.

[0074] Composite rolling was performed, wherein a heating temperature is 1180° C., an initial rolling temperature is 1150° C., and a final rolling temperature is 1020° C.; after rolling, the composite slab was directly cooled in a water cooling way, wherein an initial cooling temperature is 1000° C., a cooling speed is 40° C./s, and a final cooling temperature is 250° C.; and then, the composite slab was naturally cooled in air to a room temperature. Next, the composite slab was tempered at the temperature of 550° C. for 1 h, was then taken out of a furnace and was air-cooled to a room temperature. The composite steel plate which was rolled, separated and cut has a thickness of (3+12) mm, that is, the duplex stainless steel serving as the cladding layer has a thickness of 3 mm, and the carbon steel serving as the base layer has a thickness of 12 mm.

[0075] Mechanical properties of the composite steel plate are shown as table 7. In table 7, Rp0.2 represents the yield strength of a through-thickness composite steel plate, Rm represents a tensile strength value of the composite steel plate, and A represents an elongation percentage of the composite steel plate during tensile test and reflects comprehensive mechanical properties of materials of the cladding layer and the base layer of the composite steel plate. The carbon steel has relatively obvious low-temperature sensitivity, and therefore, a low-temperature impact test is generally performed on the carbon steel serving as the base layer. As shown in table 7, the composite steel plate has good impact toughness. The shear strength is a mechanical index for evaluating bonding levels of the materials of the cladding layer and the base layer. Shear strength values of three groups of data are all higher than 300 MPa. Bond strength values of the three groups of data are higher than 320 MPa.

TABLE-US-00007 TABLE 7 Mechanical Properties of Composite Steel Plate with Thickness of (3 + 12) mm Tensile properties (cladding layer and base layer of Impact energy through-thickness (carbon steel Shear Bond composite serving as strength, strength, steel plate) base layer), J* MPa MPa Rp0.2, MPa 524 −40° C. 263 468 495 Rm, MPa 660 245 476 482 A, % 26 259 432 485 * is tested by adopting a specimen with a thickness of 10 mm, a width of 10 mm and a length of 55 mm, which conform to standard specifications (the carbon steel serving as the base layer has a thickness of 10 mm).

[0076] The corrosion resistance of the cladding layer of the composite steel plate was tested according to an ASTM A923C method, the material of the cladding layer was machined to form a specimen with a length of 50 mm and a width of 25 mm, a surface of the specimen was cleaned, then, the specimen was measured in size and weighed and was then soaked in a 6% FeCl.sub.3 solution with a temperature of 25° C. for 24 h to perform a corrosion test, and the specimen was weighed after being taken out, cleaned and blow-dried, wherein the weight-loss corrosion of the specimen needs to meet a corrosion requirement that a corrosion rate is not greater than 10mdd. Moreover, an intergranular corrosion test was performed according to an ASTM A262E method, the material of the cladding layer was machined to form two specimens with each having a length of 80 mm and a thickness of 20 mm, surfaces of the specimens were ground, and then, the specimens were sensitized at 675° C. for 1 h, were soaked into a boiled sulfuric acid-copper sulfate solution for 15 h, were taken out and were then bent for 180° for testing. A test result is shown as table 8.

TABLE-US-00008 TABLE 8 Result of Corrosion Test for Cladding layer of Composite Steel Plate with Thickness of (3 + 12) mm Result of corrosion test for cladding layer Testing Corrosion Test method Specimen rate * Testing method Specimen result ASTM 1 0.00 mdd ASTM A262E 1 No A923 C method cracks method 2 0.00 mdd (requiring no 2 No 25° C., cracks on an cracks 24 h observed surface of 10× after bending) * means corrosion weight loss per unit area per unit time.

Comparative Example

[0077] A contrast test was performed by adopting the same carbon steel and stainless steel materials as those in embodiment 2.

[0078] The carbon steel serving as the base layer adopts EH36 and includes the chemical components (wt %): C: 0.038, Si: 0.24, Mn: 0.91, P: 0.014; S: 0.002, Nb: 0.025, Ti: 0.01. The components (wt %) of the duplex stainless steel are: C: 0.015, Si: 0.25, Mn: 1.25, Cr: 21.03, Ni: 4.52, Mo: 2.55, N: 0.08.

[0079] In the present comparative example, an assembled slab was performed by adopting a common four-layer symmetric separation method according to the above-mentioned component system, that is, a single-vacuum system. A carbon steel billet, a duplex stainless steel billet, the other duplex stainless steel billet and the other carbon steel billet were sequentially disposed from top to bottom, and a separating agent was brushed between the duplex stainless steel and a surface of the duplex stainless steel; and then, the four layers of slabs were seal-welded at one time to form an independent vacuum system. The method is higher in slab assembly efficiency and is capable of guaranteeing one vacuum system by virtue of a weld seam.

[0080] In order to make a comparison, a rolling process provided in the comparative example is kept consistent with that in embodiment 2. Composite rolling was performed, wherein a heating temperature is 1050° C., an initial rolling temperature is 1040° C., and a final rolling temperature is 850° C.; after rolling, the composite slab was directly cooled in a water cooling way, wherein an initial cooling temperature is 830° C., a cooling speed is 20° C./s, and a final cooling temperature is 480° C.; and then, the composite slab was naturally cooled in air to a room temperature. The composite steel plate which was rolled, separated and cut has a thickness of (3+10) mm, that is, the duplex stainless steel serving as the cladding layer has a thickness of 3 mm, and the carbon steel serving as the base layer has a thickness of 10 mm.

[0081] Mechanical properties of the composite steel plate are shown as table 9. In table 9, Rp0.2 represents the yield strength of a full thickness composite steel plate, Rm represents a tensile strength value of the composite steel plate, and A represents an elongation percentage of the composite steel plate during tensile test and reflects comprehensive mechanical properties of materials of the cladding layer and the base layer of the composite steel plate. The carbon steel has relatively obvious low-temperature sensitivity, and therefore, a low-temperature impact test is generally performed on the carbon steel serving as the base layer. As shown in table 9, the composite steel plate in the comparative example has good impact toughness close to that in embodiment 2. Seen by comparison, the shear strength and bond strength for representing comprehensive properties of the composite steel plate are lower than those in embodiment 2, and the shear strength changes greatly. Due to the adoption of the production process as that in embodiment 2, the stainless steel in the comparative example also has a good corrosion resistance, as shown in table 10.

TABLE-US-00009 TABLE 9 Mechanical Properties of Composite Steel Plate with Thickness of (3 + 10) mm Tensile properties (cladding layer and base layer of Impact energy through-thickness (carbon steel Shear Bond composite serving as strength, strength, steel plate) base layer), J* MPa MPa Rp0.2, MPa 486 −40° C. 253 394 382 Rm, MPa 631 226 403 379 A, % 24 235 256 354 * is tested by adopting a specimen with a thickness of 10 mm, a width of 10 mm and a length of 55 mm, which conform to standard specifications (the carbon steel serving as the base layer has a thickness of 10 mm).

TABLE-US-00010 TABLE 10 Result of Corrosion Test for Cladding layer of Composite Steel Plate with Thickness of (3 + 10) mm Result of corrosion test for cladding layer Testing Corrosion Test method Specimen rate * Testing method Specimen result ASTM 1 0.00 mdd ASTM A262E 1 No A923 C method cracks method 2 0.00 mdd (requiring no 2 No 25° C., cracks on an cracks 24 h observed surface of 10× after bending) * means corrosion weight loss per unit area per unit time.

TABLE-US-00011 TABLE 11 Comparison of Rolling Situations of Assembled Slabs Realized by Adopting Conventional Assembly Process and Assembly Process Provided by Present Invention Number of Number of slabs in successfully Rolling Process test group rolled slabs success rate Conventional process 5 3  60% Assembled process 40 40 100% provided by present invention

[0082] As shown in table 11 in which rolling situations of assembled slabs realized by adopting a conventional assembly process and an assembly process provided in the present solution, a relatively expensive corrosion-resistant alloy composite steel plate such as duplex stainless steel is rolled by adopting a two-vacuum-barrier rolling method, there are 9 groups of slabs in a test group, the 9 groups of slabs are successfully rolled, and therefore, the success rate of rolling reaches 100%. It can be seen from the rolling success rate of the assembled slabs that the rolling success rate achieved by adopting the assembly process provided by the present invention is remarkably increased as comparison with that achieved by using a conventional assembly process. The conventional assembly process is a vacuum slab assembly method for wholly seal-welding a single system at one time, and the assembly process is high in vacuum control process requirement, likely to result in rolling failure and slightly low in yield. The assembly solution of the present invention is realized by using a four-layer symmetric separation method, that is, a double-vacuum system is adopted, so that the rolling reliability can be greatly improved. In combination with the comparison of the rolling situations of assembled slabs in the embodiments of the present invention and the comparative example in table 11, the bond property of the composite steel plate provided by the assembly solution of the present invention is higher and more stable