SUPER DUPLEX STAINLESS STEEL CLAD STEEL PLATE AND MANUFACTURING METHOD THEREFOR

Abstract

Clad steel plate of super duplex stainless steel and manufacturing method thereof. The clad steel plate of super duplex stainless steel which has a two-layer structure wherein one layer is duplex stainless steel, and the other layer is carbon steel, wherein said duplex stainless steel comprises the following components by weight: C≤0.03%, Mn≤1.20%, Si≤0.80%, Cr: 24.0-26.0%, Ni: 6.0-8.0%, Mo: 3.0-5.0%, N: 0.24-0.32% and the balance being Fe and inevitable impurities; and said carbon steel comprises the following components by weight: C: 0.03˜0.12%, Si: 0.10˜0.45%, Mn: 0.70-1.60%, P<0.020%, S<0.025%, Cu: 0˜0.35%, Cr 0˜0.40%, Ni 0˜0.40%, Nb 0˜0.05%, Mo 0˜0.40%, Ti 0˜0.018%, Al 0.015˜0.045% and the balance being Fe and inevitable impurities. The clad steel plate of the disclosure has good structure strength and corrosion resistance; the clad steel plate is a rolled cladding steel plate and is capable of realizing the metallurgical bonding of cladding and base layer materials, thereby yielding good bonding capability.

Claims

1. A clad steel plate of super duplex stainless steel, which has a two-layer structure wherein one layer is duplex stainless steel, and the other layer is carbon steel, wherein said duplex stainless steel comprises the following components by weight: C≤0.03%, Mn≤1.20%, Si≤0.80%, Cr: 24.0-26.0%, Ni: 6.0-8.0%, Mo: 3.0-5.0%, N: 0.24-0.32%, P≤0.03%, S≤0.02% and the balance being Fe and inevitable impurities; and said carbon steel comprises the following components by weight: C: 0.03˜0.12%, Si: 0.10˜0.45%, Mn: 0.70-1.60%, P: 0˜0.020%; S: 0˜0.025%, Cu: 0-0.35%, Cr: 0˜0.40%, Ni: 0˜0.40%, Nb: 0˜0.05%, Mo: 0˜0.40%, Ti: 0˜0.018%, Al: 0.015˜0.045%, and the balance being Fe and inevitable impurities.

2. The clad steel plate of super duplex stainless steel according to claim 1, wherein an interface between the duplex stainless steel and the carbon steel of the clad steel plate has a shear strength of 290 MPa or more, the clad steel plate has a yield strength of 300˜650 MPa and the clad steel plate has a tensile strength of 400˜900 MPa.

3. The clad steel plate of super duplex stainless steel according to claim 1, wherein the carbon steel of the clad steel plate has a yield strength of 235˜550 MPa; the duplex stainless steel has a yield strength of 550 MPa or more, and a tensile strength of 795 MPa or more.

4. A method of manufacturing clad steel plate of super duplex stainless steel according to claim 1, 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 1100˜1250° C.; 4) rolling the composite billet with an initial rolling temperature of 1070˜1220° C. and a final rolling temperature of 900˜1020° C.; 5) after rolling, cooling the superposed clad steel plate with compressed air or water, wherein the initial cooling temperature is controlled as 880-1000° C., the cooling rate is controlled as 2° C./sec˜40° C./sec, and the final cooling temperature is controlled as 250˜680° 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.

5. The method of manufacturing the clad steel plate of super duplex stainless steel according to claim 4, further comprising tempering thermal treatment with a tempering temperature of 500˜600° C., followed with air cooling treatment.

6. The method of manufacturing the clad steel plate of super duplex stainless steel according to claim 4, wherein in step 4), the pass reduction rate is controlled as 10%˜25%.

7. The clad steel plate of super duplex stainless steel according to claim 2, wherein the carbon steel of the clad steel plate has a yield strength of 235˜550 MPa, the duplex stainless steel has a yield strength of 550 MPa or more, and a tensile strength of 795 MPa or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 is a sectional view of a structure of a composite billet of a clad steel plate of super duplex stainless steel according to the disclosure.

[0048] FIG. 2 is a metallographic structure picture of a clad steel plate of super duplex stainless steel at the joint of a carbon steel layer and a duplex stainless steel layer according to the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] Next, the disclosure will be further described in combination with embodiments and drawings.

[0050] Referring to FIG. 1, the composite billet of the high-corrosion-resistant duplex stainless steel clad steel plate has a four-layer structure, in which the middle two layers 1 and 2 are duplex stainless steel, the upper and lower two layers 3 and 4 are carbon steel; 5 is separating agent, and 6 is closed sealing weld. The separating agent is used to separate two layers of stainless steel and prevent the adhesion between the two layers of stainless steel.

Example 1

[0051] The base carbon steel has a yield strength of 235 MPa or more, and comprises the following chemical components (wt %): C: 0.032, Si: 0.20, Mn: 1.45, P: 0.015, S: 0.002, Al: 0.02, Cu: 0.01, Cr: 0.01, Ni: 0.01, Nb: 0.003, Mo: 0.01 and Ti: 0.003; the duplex stainless steel comprises the following components (wt %): C: 0.014, Si: 0.43, Mn: 0.85, Cr: 25.34, Ni: 7.32, Mo: 4.11, N: 0.30.

[0052] The four-layer symmetrical separation method as shown in FIG. 1 is used to assemble billets: a carbon steel billet, a duplex stainless steel billet, a duplex stainless steel billet and a carbon steel billet are arranged from top to bottom, in which the upper carbon steel billet and the corresponding duplex stainless steel billet are sealed in vacuum, and the lower carbon steel billet and the corresponding duplex stainless steel billet are sealed in vacuum, so as to form two groups of first vacuum systems independent to each other; the second vacuum system is formed by sealing between layer 1 and layer 2 (namely, carbon steel billet and carbon steel billet in this example) shown in FIG. 1 in vacuum to jointly form a double-vacuum system composite billet. The separating agent is filled between the duplex stainless steel surface and the duplex stainless steel surface of two groups of vacuum billets, and then the vacuumized composite billets are rolled by heating and cut into the finished product clad steel plate. As shown in FIG. 2, photographing is performed with a 20× objective lens using the Karl Zeiss optical microscope Axio Imager.M2m. The upper layer is of a super duplex stainless steel microstructure and the lower layer is of a carbon steel microstructure. The middle is the interface between duplex stainless steel and carbon steel, which has been formed a good metallurgical bonding.

[0053] Composite rolling: the heating temperature of 1190° C., the initial rolling temperature of 1170° C., and the final rolling temperature of 950° C.; after rolling, the composite billet is cooled directly by a water cooling method, the initial cooling temperature of 920° C., the cooling rate of 40° C./s, and the final cooling temperature of 600° C., and then the composite billet is naturally cooled to room temperature in air. After rolling, the thickness of the clad steel plate subjected to plasma cutting is (5+30) mm, that is, the thickness of the clad duplex stainless steel is 5 mm and the thickness of the base carbon steel is 30 mm.

[0054] The mechanical properties of the clad steel plate are shown in Table 1. In Table 1, Rp0.2 is the yield strength of the full thickness clad steel plate, Rm is the tensile strength value of the clad steel plate, and A is the elongation of the clad steel plate sample, which reflects the comprehensive mechanical properties of the cladding layer and base layer materials of the clad steel plate. Due to the obvious low temperature sensitivity of carbon steel, a low temperature impact test is usually carried out on base layer carbon steel. As shown in Table 1, the impact property of the clad steel plate is good. Shear strength is a mechanical index to evaluate the bonding level of cladding layer and base layer materials. The shear strength values of three groups of data are all 290 MPa or more.

TABLE-US-00001 TABLE 1 Mechanical properties of clad steel plate has a thickness of (5 + 30) mm Tensile properly Impact energy Shear (full-thickness clad steel plate (base layer strength, (cladding layer + base layer) carbon steel, J* MPa Rp0.2, MPa 367 −40° C. 323 323 Rm, MPa 512 347 378 A, % 29 315 384 *The thickness × width × length 10 mm × 10 mm × 55 mm of the standard specification is used to test samples (the thickness of the base layer carbon steel is 10 mm).

[0055] The cladding layer corrosion resistance of the clad steel plate is based on the ASTM A923C method. The cladding layer material is processed into samples with length and width of 50 mm*25 mm. After the surface was cleaned, the samples were measured and weighed. Then the samples were immersed into 6% FeCl.sub.3 solution at 40° C. for 24 hours for corrosion test. After cleaning and drying, the samples were weighed. The weight-loss corrosion needed to satisfy the corrosion requirement that the corrosion rate was no more than 10 mdd. The intergranular corrosion test was carried out according to ASTM A262E method. The cladding material was processed into two samples with length and width of 80 mm*20 mm. The surface was ground with a sandpaper, sensitized at 675° C. for 1 hour and immersed into boiled sulfuric acid-copper sulfate solution for 15 hours, and then the samples were taken for 1800 bending test. The test results are shown in Table 2.

TABLE-US-00002 TABLE 2 Cladding layer corrosion rest results of clad steel plate has a thickness of (5 + 30) mm Cladding layer corrosion rest result Test method Sample Corrosion rate * Test method Sample Test result ASTM A923C method 1 0.00 mdd ASTM A262E method 1 No cracks 40° C., 24 h 2 0.00 mdd (No cracks on the 2 No cracks surface by 10× observation after bending) * refers to the weight loss of corrosion per unit area per unit time.

Example 2

[0056] The base layer carbon steel adopts carbon steel has a yield strength of 345 MPa, and comprises the following chemical components (wt %): C: 0.12, Si: 0.24, Mn: 0.70, P: 0.015, S: 0.003, Nb: 0.01, Ti: 0.01, Al: 0.025, and Cu, Cr, Ni and Mo are not deliberately added; the duplex stainless steel comprises the following components (wt %): C: 0.018, Si: 0.75, Mn: 0.88, Cr: 24.1, Ni: 6.05, Mo: 3.1, and N: 0.24.

[0057] In this example, the four-layer symmetric separation method which is the same as that in example 1 is used to assemble billets according to the above component system.

[0058] Composite rolling: the heating temperature of 1250° C., the initial rolling temperature of 1220° C., and the final rolling temperature of 1020° C.; after rolling, the composite billet is cooled directly by using compressed air, the initial cooling temperature of 1000° C., the cooling rate of 2° C./s, and the final cooling temperature of 680° C., and then the composite billet is naturally cooled to room temperature in air. After rolling, the thickness of the clad steel plate subjected to plasma cutting is (3+10) mm, that is, the thickness of the cladding layer duplex stainless steel is 3 mm and the thickness of the base layer carbon steel is 10 mm.

[0059] The mechanical properties of the clad steel plate are shown in Table 3. In Table 3, Rp0.2 is the yield strength of the full thickness clad steel plate, Rm is the tensile strength value of the clad steel plate, and A is the elongation of the clad steel plate sample, which reflects the comprehensive mechanical properties of the cladding layer and base layer materials of the clad steel plate. Due to the obvious low temperature sensitivity of carbon steel, a low temperature impact test is usually carried out on base layer carbon steel. Since the base layer carbon steel has the original thickness of 10 mm, and cannot be processed into a sample having a thickness of 10 mm, the base layer carbon steel having a thickness of 7.5 mm is used as an impact sample. Shear strength is a mechanical index to evaluate the bonding level of cladding layer and base layer materials. The shear strength values of three groups of data are all 290 MPa or more.

TABLE-US-00003 TABLE 3 Mechanical properties of clad steel plate has a thickness of (3 + 10) mm Tensile property Impact energy (full thickness clad steel plate (base layer Shear strength, (cladding layer + base layer) carbon steel, J* MPa Rp0.2, MPa 481 0° C. 134 433 Rm, MPa 649 142 451 A, % 24 151 413 *The thickness × width × length 7.5 mm × 10 mm × 55 mm of the standard specification is used to test samples (the thickness of the base layer carbon steel is 7.5 mm).

[0060] The cladding layer corrosion resistance of the clad steel plate is based on the ASTM A923C method. The cladding layer material is processed into samples with length and width of 50 mm*25 mm. After the surface is cleaned, the samples were measured and weighed. Then the samples were immersed into 6% FeCl.sub.3 solution at 40° C. for 24 hours for corrosion test. After cleaning and drying, the samples were weighed. The weight-loss corrosion needed to satisfy the corrosion requirement that the corrosion rate was no more than 10 mdd. The intergranular corrosion test was carried out according to ASTM A262E method. The cladding material was processed into two samples with length and width of 80 mm*20 mm. The surface was ground with sandpaper, sensitized at 675° C. for 1 hour and immersed into boiled sulfuric acid-copper sulfate solution for 15 hours, and then the samples were taken for 1800 bending test. The test results are shown in Table 4.

TABLE-US-00004 TABLE 4 Cladding layer corrosion rest results of clad steel plate has a thickness of (3 + 10) mm Cladding layer corrosion rest result Test method Sample Corrosion rate * Test method Sample Test result ASTM A923C method 1 1.17 mdd ASTM A262E method 1 No cracks 40° C., 24 h 2 1.76 mdd (No cracks on the 2 No cracks surface by 10× observation after bending) * refers to the weight loss of corrosion per unit area per unit time.

Example 3

[0061] The base layer carbon steel adopts carbon steel has a yield strength of 460 MPa, and comprises the following chemical components (wt %): C: 0.09, Si: 0.22, Mn: 0.9, P: 0.013; S: 0.002, Nb: 0.045, Ti: 0.018, Cu: 0.01, Cr: 0.22, and Ni: 0.23; the duplex stainless steel comprises the following components (wt %): C: 0.016, Si: 0.40, Mn: 0.92, Cr: 25.97, Ni: 7.96, Mo: 4.98, and N: 0.32.

[0062] In this example, the four-layer symmetric separation method which is the same as that in example 1 is used to assemble billets according to the above component system.

[0063] Composite rolling: the heating temperature of 1100° C., the initial rolling temperature of 1070° C., and the final rolling temperature of 900° C.; after rolling, the composite billet is cooled directly by water cooling, the initial cooling temperature of 880° C., the cooling rate of 20° C./s, and the final cooling temperature of 550° C., and then the composite billet is naturally cooled to room temperature in air. After rolling, the thickness of the clad steel plate subjected to plasma cutting is (2+8) mm, that is, the thickness of the clad duplex stainless steel is 2 mm and the thickness of the base carbon steel is 8 mm.

[0064] The mechanical properties of the clad steel plate are shown in Table 5. In Table 5, Rp0.2 is the yield strength of the full thickness clad steel plate, Rm is the tensile strength value of the clad steel plate, and A is the elongation of the clad steel plate sample, which reflects the comprehensive mechanical properties of the cladding layer and base layer materials of the clad steel plate. Due to the obvious low temperature sensitivity of carbon steel, a low temperature impact test is usually carried out on base layer carbon steel. Since the base layer carbon steel has the original thickness of 10 mm, and cannot be processed into a sample having a thickness of 10 mm, the base carbon steel having a thickness of 7.5 mm is used as an impact sample. Shear strength is a mechanical index to evaluate the bonding level of cladding layer and base layer materials. The shear strength values of three groups of data are all 290 MPa or more.

TABLE-US-00005 TABLE 5 Mechanical properties of clad steel plate has a thickness of (2 + 8) mm Tensile property Impact energy (full thickness clad steel plate (base layer Shear strength, (cladding layer + base layer) carbon steel, J* MPa Rp0.2, MPa 542 −20° C. 234 503 Rm, MPa 680 231 521 A, % 24 244 490 *The thickness × width × length 7.5 mm × 10 mm × 55 mm of the standard specification is used to test samples (the thickness of the base layer carbon steel is 7.5 mm).

[0065] The cladding layer corrosion resistance of the clad steel plate is based on the ASTM A923C method. The cladding layer material is processed into samples with length and width of 50 mm*25 mm. After the surface is cleaned, the samples were measured and weighed. Then the samples were immersed in 6% FeCl.sub.3 solution at 40° C. for 24 hours for corrosion test. After cleaning and drying, the samples were weighed. The weight-loss corrosion needed to satisfy the corrosion requirement that the corrosion rate was no more than 10 mdd. The intergranular corrosion test was carried out according to ASTM A262E method. The cladding material was processed into two samples with length and width of 80 mm*20 mm. The surface was ground with sandpaper, sensitized at 675° C. for 1 hour and immersed into boiled sulfuric acid-copper sulfate solution for 15 hours, and then the samples were taken for 1800 bending test. The test results are shown in Table 6.

TABLE-US-00006 TABLE 6 Cladding layer corrosion rest results of clad steel plate has a thickness of (2 + 8) mm Cladding layer corrosion rest result Test method Sample Corrosion rate * Test method Sample Test result ASTM A923C method 1 0.00 mdd ASTM A262E method 1 No cracks 40° C.,24 h 2 0.35 mdd (No cracks on the 2 No cracks surface by 10× observation after bending) * refers to the weight loss of corrosion per unit area per unit time.

Example 4

[0066] The base layer carbon steel adopts carbon steel has a yield strength of 550 MPa, and comprises the following chemical components (wt %): C: 0.07, Si: 0.32, Mn: 1.55, P: 0.012; S: 0.002, Cu: 0.35, Cr: 0.39, Ni: 0.40, Nb: 0.05, and Ti: 0.018; the duplex stainless steel comprises the following components (wt %): C: 0.016, Si: 0.72, Mn: 0.89, Cr: 25.69, Ni: 7.11, Mo: 3.93 and N: 0.29.

[0067] In this example, the four-layer symmetric separation method which is the same as that in example 1 is used to assemble billets according to the above component system.

[0068] Composite rolling: the heating temperature of 1150° C., the initial rolling temperature of 1110° C., and the final rolling temperature of 990° C.; after rolling, the composite billet is cooled directly by water cooling, the initial cooling temperature of 970° C., the cooling rate is 40° C./s, and the final cooling temperature of 250° C., and then the composite billet is naturally cooled to room temperature in air and tempered for 1 hour at a tempering temperature of 550° C., subsequently is discharged from the furnace to be cooled in the air to room temperature. After rolling, the thickness of the clad steel plate subjected to plasma cutting was (3+12) mm, that is, the thickness of the clad duplex stainless steel is 3 mm and the thickness of the base carbon steel is 12 mm. The mechanical properties of the clad steel plate are shown in Table 7.

[0069] The mechanical properties of the clad steel plate are shown in Table 7. In Table 7, Rp0.2 is the yield strength of the full thickness clad steel plate, Rm is the tensile strength value of the clad steel plate, and A is the elongation of the clad steel plate sample, which reflects the comprehensive mechanical properties of the cladding layer and base layer materials of the clad steel plate. Due to the obvious low temperature sensitivity of carbon steel, a low temperature impact test is usually carried out on base layer carbon steel. As shown in FIG. 7, the clad steel plate has a good impact property. Shear strength is a mechanical index to evaluate the bonding level of cladding layer and base layer materials. The shear strength values of three groups of data are all 290 MPa or more.

TABLE-US-00007 TABLE 7 Mechanical properties of clad steel plate has a thickness of (3 + 12) mm Tensile property Impact energy (full thickness clad steel plate (base layer Shear strength, (cladding layer + base layer) carbon steel, J* MPa Rp0.2, MPa 618 −20° C. 317 568 Rm, MPa 776 287 576 A, % 23 306 495 *The thickness × width × length 10 mm × 10m m × 55m mm of the standard specification is used to test samples (the thickness of the base layer carbon steel is 10 mm),.

[0070] The cladding layer corrosion resistance of the clad steel plate is based on the ASTM A923C method. The cladding layer material was processed into samples with length and width of 50 mm*25 mm. After the surface is cleaned, the samples were measured and weighed. Then the samples were immersed in 6% FeCl.sub.3 solution at 40° C. for 24 hours for corrosion test. After cleaning and drying, the samples were weighed. The weight-loss corrosion needed to satisfy the corrosion requirement that the corrosion rate was no more than 10 mdd. The intergranular corrosion test was carried out according to ASTM A262E method. The cladding layer material was processed into two samples with length and width of 80 mm*20 mm. The surface was ground with sandpaper, sensitized at 675° C. for 1 hour and immersed into boiled sulfuric acid-copper sulfate solution for 15 hours, and then the samples were taken for 1800 bending test. The test results are shown in Table 8.

TABLE-US-00008 TABLE 8 Cladding layer corrosion rest results of clad steel plate has a thickness of (3 + 12) mm Cladding layer corrosion rest result Test method Sample Corrosion rate * Test method Sample Test result ASTM A923C method 1 0.37 mdd ASTM A262E method 1 No cracks 40° C., 24 h 2 0.81 mdd (No cracks on the 2 No cracks surface by 10× observation after bending) * refers to the weight loss of corrosion per unit area per unit time.

Comparative Example

[0071] The materials which are the same as those in example 2 are used to prepare a group of clad steel plates according to the same production process. Property comparison is made.

[0072] The base layer carbon steel adopts carbon steel having a yield strength of 345 MPa, and comprises the following chemical components (wt %): C: 0.12, Si: 0.24, Mn: 0.70, P: 0.015; S: 0.003, Nb: 0.01, Ti: 0.01, Al: 0.025, and Cu, Cr, Ni and Mo are not deliberately added; the duplex stainless steel comprises the following components (wt %): C: 0.018, Si: 0.75, Mn: 0.88, Cr: 24.1, Ni: 6.05, Mo: 3.1, and N: 0.24.

[0073] In this comparative example, according to the above component system, the common four-layer symmetrical separation method is used to assemble the billet, that is, the single vacuum system. A carbon steel billet, a duplex stainless steel billet, a duplex stainless steel billet and a carbon steel billet are arranged from top to bottom in order, and the separating agent is filled between the duplex stainless steel surface and the duplex stainless steel surface. Then the four-layer billets are soldered and sealed into a separate vacuum system at one time. The billet assembling efficiency of this method is higher, but only one vacuum system can be ensured through the welded joint.

[0074] Composite rolling: the heating temperature of 1250° C., the initial rolling temperature of 1220° C., and the final rolling temperature of 1020° C.; after rolling, the composite billet is cooled directly by using compressed air, the initial cooling temperature of 1000° C., the cooling rate of 20° C./s, and the final cooling temperature of 680° C., and then the composite billet is naturally cooled to room temperature in air. After rolling, the thickness of the clad steel plate subjected to plasma cutting is (3+10) mm, that is, the thickness of the cladding layer duplex stainless steel is 3 mm and the thickness of the base layer carbon steel is 10 mm.

[0075] The mechanical properties of the clad steel plate are shown in Table 9. In Table 9, Rp0.2 is the yield strength of the full thickness clad steel plate, Rm is the tensile strength value of the clad steel plate, and A is the elongation of the clad steel plate sample, which reflects the comprehensive mechanical properties of the cladding layer and base layer materials of the clad steel plate. Due to the obvious low temperature sensitivity of carbon steel, a low temperature impact test is usually carried out on base layer carbon steel. Since the base layer carbon steel has the original thickness of 10 mm, and cannot be processed into a sample having a thickness of 10 mm, the base layer carbon steel having a thickness of 7.5 mm is used as an impact sample. Because the rolling process adopted in comparative example is the same as that in example 2, the tensile and impact properties of the clad steel plate provided in this comparative example are basically close to those in example 2. However, since the conventional composite billet is different from that in the billet assembling process of the disclosure, the shear strength value characterizing the bonding capability of the cladding layer and base layer of the clad steel plate is lower, and fluctuation is larger.

TABLE-US-00009 TABLE 9 Mechanical properties of clad steel plate has a thickness of (3 + 10) mm Tensile property Impact energy (full thickness clad steel plate (base layer Shear strength, (cladding layer + base layer) carbon steel, J* MPa Rp0.2, MPa 466 0° C. 145 352 Rm, MPa 632 148 273 A, % 25 137 309 *The thickness × width × length 7.5 mm × 10 mm × 55 mm of the standard specification is used to test samples (the thickness of the base layer carbon steel is 7.5 mm).

[0076] The cladding layer corrosion resistance of the clad steel plate is based on the ASTM A923C method. The cladding layer material is processed into samples with length and width of 50 mm*25 mm. After the surface is cleaned, the samples were measured and weighed. Then the samples were immersed in 6% FeCl.sub.3 solution at 40° C. for 24 hours for corrosion test. After cleaning and drying, the samples were weighed. The weight-loss corrosion needed to satisfy the corrosion requirement that the corrosion rate was no more than 10 mdd. The intergranular corrosion test was carried out according to ASTM A262E method. The cladding layer material was processed into two samples with length and width of 80 mm*20 mm. The surface was ground with sandpaper, sensitized at 675° C. for 1 hour and immersed into boiled sulfuric acid-copper sulfate solution for 15 hours, and then the samples were taken for 180° bending test. The test results are shown in Table 10.

[0077] The corrosion test in this comparative example is compared with that in example 2, it can be seen from comparison results that due to adoption of the same rolling process, the cladding corrosion resistance material is almost not affected. The main difference between the two is from the bonding control capability of the cladding layer and base layer materials.

TABLE-US-00010 TABLE 10 Cladding layer corrosion rest results of clad steel plate has a thickness of (3 + 10) mm Cladding layer corrosion rest result Corrosion Test method Sample rate * Test method Sample Test result ASTM A923C method 1 1.55 mdd ASTM A262E method 1 No cracks 40° C., 24 h 2 1.93 mdd (No cracks on the surface 2 No cracks by 10× observation after bending) * refers to the weight loss of corrosion per unit area per unit time.

TABLE-US-00011 TABLE 11 Comparison of assembled billet rolling situations adopting conventional composite billet assembling process and composite billet assembling process in the disclosure Quantity of successfully Quantity of test rolled assembled Success rate Process manner assembled billets billets of rolling Conventional process 10 6  60% Composite billet 9 9 100% assembling process in the disclosure

[0078] As shown in Table 11, comparison of assembled billet rolling situations adopting conventional billet assembling process and composite billet assembling process in the disclosure shows that the double-vacuum barrier rolling method is adopted for expensive corrosion-resistant alloy clad steel plate, such as duplex stainless steel. The quantity of test assembled billets is 9 groups, the quantity of successful rolling is 9 groups, and the rolling success rate reaches 100%. From the rolling success rate of the assembled billets, the rolling success rate of the composite assembled billet rolling process provided by the disclosure is significantly improved compared with that of the conventional composite assembled billet rolling process. Among them, the conventional composite billet assembling process is a once whole sealed welding single system vacuum billet assembling manner, which has high requirements for vacuum control process, and easily causes rolling failure and low yield. The billet assembling solution of the disclosure is a four-layer symmetrical separation method, that is, a double-vacuum system, and the rolling reliability can be considerably improved. According to comparison of assembled billet rolling situations in examples of the disclosure and comparative example in Table 11, the bonding property of the clad steel plate provided by the billet assembling solution of the disclosure is higher and more stable.