HOT-DIP Zn-BASED PLATED STEEL SHEET

Abstract

This hot-dip Zn-based plated steel sheet includes a steel sheet and a plating layer formed on at least part of a surface of the steel sheet, in which the plating layer has a chemical composition that includes, by mass %, Al: 6.00% to 35.00%, Mg: 2.00% to 12.00%, Ca: 0.005% to 2.00%, Si: 0% to 2.00%, Fe: 0% to 2.00%, Sb: 0% to 0.50%, Sr: 0% to 0.50%, Pb: 0% to 0.50%, Sn: 0% to 1.00%, Cu: 0% to 1.00%, Ti: 0% to 1.00%, Ni: 0% to 1.00%, Mn: 0% to 1.00%, Cr: 0% to 1.00%, and a remainder: Zn and impurities, the plating layer has an area ratio of a MgZn.sub.2 phase in a range of 15% to 60% in a cross section in a thickness direction, and the MgZn.sub.2 phase includes a Ca-based intermetallic compound having a circle equivalent diameter of 0.10 m or smaller.

Claims

1. A hot-dip Zn-based plated steel sheet comprising: a steel sheet; and a plating layer formed on at least part of a surface of the steel sheet, wherein the plating layer has a chemical composition that includes, by mass %, Al: 6.00% to 35.00%, Mg: 2.00% to 12.00%, Ca: 0.005% to 2.00%, Si: 0% to 2.00%, Fe: 0% to 2.00%, Sb: 0% to 0.50%, Sr: 0% to 0.50%, Pb: 0% to 0.50%, Sn: 0% to 1.00%, Cu: 0% to 1.00%, Ti: 0% to 1.00%, Ni: 0% to 1.00%, Mn: 0% to 1.00%, Cr: 0% to 1.00%, and a remainder: Zn and impurities, the plating layer has an area ratio of a MgZn.sub.2 phase in a range of 15% to 60% in a cross section in a thickness direction, and the MgZn.sub.2 phase includes a Ca-based intermetallic compound having a circle equivalent diameter of 0.10 m or smaller.

2. The hot-dip Zn-based plated steel sheet according to claim 1, wherein the chemical composition of the plating layer contains one or more selected from the group consisting of, by mass %, Al: 11.00% to 30.00%, Mg: 5.00% to 10.00%, and Ca: 0.10% to 1.00%.

3. The hot-dip Zn-based plated steel sheet according to claim 1, wherein a number density of the Ca-based intermetallic compound that is included in the MgZn.sub.2 phase is 10 pieces/m.sup.2 or more.

4.-6. (canceled)

7. The hot-dip Zn-based plated steel sheet according to claim 2, wherein a number density of the Ca-based intermetallic compound that is included in the MgZn.sub.2 phase is 10 pieces/m.sup.2 or more.

8. The hot-dip Zn-based plated steel sheet according to claim 1, wherein an alloy layer that includes an AlFe-based intermetallic compound and has an average thickness in a range of 0.05 to 3.0 m is provided between the plating layer and the steel sheet.

9. The hot-dip Zn-based plated steel sheet according to claim 2, wherein an alloy layer that includes an AlFe-based intermetallic compound and has an average thickness in a range of 0.05 to 3.0 m is provided between the plating layer and the steel sheet.

10. The hot-dip Zn-based plated steel sheet according to claim 3, wherein an alloy layer that includes an AlFe-based intermetallic compound and has an average thickness in a range of 0.05 to 3.0 m is provided between the plating layer and the steel sheet.

11. The hot-dip Zn-based plated steel sheet according to claim 7, wherein an alloy layer that includes an AlFe-based intermetallic compound and has an average thickness in a range of 0.05 to 3.0 m is provided between the plating layer and the steel sheet.

12. The hot-dip Zn-based plated steel sheet according to claim 1, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the plating layer.

13. The hot-dip Zn-based plated steel sheet according to claim 2, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the plating layer.

14. The hot-dip Zn-based plated steel sheet according to claim 3, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the plating layer.

15. The hot-dip Zn-based plated steel sheet according to claim 7, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the plating layer.

16. The hot-dip Zn-based plated steel sheet according to claim 8, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the alloy layer.

17. The hot-dip Zn-based plated steel sheet according to claim 9, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the alloy layer.

18. The hot-dip Zn-based plated steel sheet according to claim 10, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the alloy layer.

19. The hot-dip Zn-based plated steel sheet according to claim 11, wherein the steel sheet has an internal oxidation layer in a surface layer area on a side of the alloy layer.

Description

EXAMPLES

[0118] A cold-rolled steel sheet (0.2% C-2.0% Si-2.3% Mn) having a sheet thickness of 0.8 mm was prepared as a steel sheet to be plated.

[0119] After this steel sheet is cut into a size of 100 mm200 mm, then annealing and hot-dip plating were performed using a batch-type hot-dip plating tester.

[0120] In the annealing, annealing was performed at 860 C. for 120 seconds in an atmosphere that includes gas containing 5% H.sub.2 gas and N.sub.2 gas as a remainder and has a dew point of 0 C. in a furnace having oxygen concentration of 20 ppm or lower.

[0121] After the annealing, the steel sheet was air-cooled with N.sub.2 gas, and when the steel sheet temperature reached the bath temperature +20 C., it was immersed in a plating bath having a bath temperature shown in Table 1 for about 3 seconds. The composition of the plating bath and the composition of the formed plating layer were as shown in Table 1.

[0122] The plated base sheet with the plating layer formed thereon was cooled to a temperature of 20 C. or lower under the conditions shown in Table 1, and subjected to post-heat treatment to obtain a plated steel sheet (a hot-dip Zn-based plated steel sheet). The retention time of the post-heat treatment was set to 100 seconds. The time from the completion of the cooling step to the start of the post-heat treatment was set as shown in Table 1.

TABLE-US-00001 TABLE 1 Manufacturing method Cooling condition Average Average Average cooling rate cooling rate cooling from bath from bath rate from Bath temperature temperature 270 C. Post-Heat treatment temperature to 20 C. to 270 C. to 20 C. Presence or No. Classification ( C.) ( C./s) ( C./s) ( C./s) absence 1 Comparative 480 20.0 20.0 20.0 Presence example 2 Comparative 480 20.0 20.0 20.0 Presence example 3 Invention 420 20.0 20.0 20.0 Presence example 4 Invention 420 20.0 20.0 30.0 Presence example 5 Comparative 460 20.0 20.0 20.0 Presence example 6 Invention 460 20.0 20.0 20.0 Presence example 7 Invention 460 24.7 20.0 30.0 Presence example 8 Invention 470 20.0 20.0 20.0 Presence example 9 Invention 480 20.0 20.0 20.0 Presence example 10 Invention 480 24.4 20.0 30.0 Presence example 11 Invention 480 20.0 20.0 20.0 Presence example 12 Comparative 520 20.0 20.0 20.0 Presence example 13 Invention 500 20.0 20.0 20.0 Presence example 14 Invention 500 24.2 20.0 30.0 Presence example 15 Invention 500 20.0 20.0 20.0 Presence example 16 Invention 550 20.0 20.0 20.0 Presence example 17 Comparative 520 20.0 20.0 20.0 Presence example 18 Comparative 500 5.0 5.0 5.0 Presence example 19 Comparative 580 20.0 20.0 20.0 Presence example 20 Comparative 510 20.0 20.0 20.0 Presence example 21 Invention 540 20.0 20.0 20.0 Presence example 22 Invention 580 15.0 15.0 15.0 Presence example 23 Comparative 540 20.0 20.0 20.0 Presence example 24 Comparative 540 20.0 20.0 20.0 Absence example 25 Invention 550 20.0 20.0 20.0 Presence example 26 Invention 550 23.7 20.0 30.0 Presence example 27 Invention 550 20.0 20.0 20.0 Presence example 28 Invention 560 20.0 20.0 20.0 Presence example 29 Invention 560 23.6 20.0 30.0 Presence example 30 Invention 560 15.0 15.0 15.0 Presence example 31 Invention 560 23.6 20.0 30.0 Presence example 32 Invention 560 20.0 20.0 20.0 Presence example 33 Invention 580 20.0 20.0 20.0 Presence example 34 Comparative 600 20.0 20.0 20.0 Presence example Manufacturing method Post-Heat treatment One side Time to Chemical composition (mass %) of plating layer plating start of Remainder: Zn and impurities layer heat Other adhesion treatment Temperature Total amount No. (h) ( C.) Al Mg Si Ca Fe Kinds value (g/m.sup.2) 1 <0.5 120 4.50 5.00 0.05 0.10 0.20 0.00 40 2 <0.5 120 6.00 0.00 0.05 0.10 0.10 Pb: 0.01 40 0.01 3 <0.5 120 6.00 3.00 0.05 0.03 0.20 0.00 39 4 <0.5 120 6.00 3.00 0.05 0.03 0.20 0.00 39 5 <0.5 120 10.00 3.00 0.05 0.00 0.10 0.00 40 6 <0.5 170 10.00 3.00 0.20 0.10 0.00 0.00 45 7 1.0 170 10.00 3.00 0.20 0.10 0.00 0.00 50 8 <0.5 120 10.00 5.00 0.10 0.10 0.20 0.00 40 9 <0.5 120 15.00 6.00 0.10 0.10 0.10 Mn: 0.001 60 0.001 10 2.0 120 15.00 6.00 0.10 0.10 0.10 0.00 55 11 <0.5 120 15.00 6.00 0.10 0.10 0.20 S : 0.01 50 0.01 12 24 50 20.00 5.00 0.20 0.20 0.20 0.00 50 13 <0.5 120 20.00 7.00 0.20 0.20 0.20 Ni: 0.20 40 0.20 14 3.0 120 20.00 7.00 0.20 0.20 0.20 Ni: 0.20 40 0.20 15 5.0 120 20.00 7.50 0.20 0.20 0.20 0.00 40 16 <0.5 120 20.00 10.00 0.00 0.20 0.10 Sb: 0.05 40 0.05 17 <0.5 50 20.00 5.00 0.20 0.20 0.20 0.00 46 18 <0.5 120 20.00 7.00 0.20 0.20 0.10 0.00 40 19 <0.5 120 20.00 13.00 0.20 0.20 0.10 0.00 45 20 <0.5 120 21.00 8.00 3.50 0.20 0.30 0.00 45 21 <0.5 220 23.00 8.00 0.30 0.40 0.10 Sn: 0.01 45 0.01 22 <0.5 120 23.00 8.00 1.00 0.50 0.20 Ti: 0.01 40 0.01 23 <0.5 120 23.00 8.10 0.20 2.50 0.20 0.00 45 24 <0.5 23.00 8.00 0.20 0.50 0.10 0.00 45 25 <0.5 120 26.00 6.50 0.30 0.40 0.30 Pb: 0.05 30 0.05 26 <0.5 120 26.00 6.50 0.30 0.40 0.30 0.00 30 27 22 120 26.00 5.50 0.30 0.30 0.10 Cu: 0.005 35 0.005 28 <0.5 120 30.00 6.00 0.30 0.40 0.10 0.00 35 29 <0.5 120 30.00 6.00 0.30 0.40 0.10 0.00 35 30 <0.5 120 30.00 5.70 0.40 0.30 0.20 0.00 35 31 <0.5 120 30.00 6.00 0.40 0.30 0.20 0.00 50 32 <0.5 120 30.00 2.00 0.40 0.30 0.20 Cr: 0.015 105 0.015 33 <0.5 120 35.00 8.00 0.45 0.10 0.20 0.00 40 34 <0.5 120 40.00 3.00 0.50 0.56 0.20 0.00 45 The underline indicates a value outside the range of the present invention. indicates data missing or illegible when filed

[0123] With respect to the obtained plated steel sheet, the area ratio of each phase in the plating phase, the number density of the Ca-based intermetallic compound having a circle equivalent diameter of 0.10 m or smaller and the Ca-based intermetallic compound having a circle equivalent diameter of 0.07 m or smaller in the MgZn.sub.2 phase, the thickness of the alloy layer, and the thickness of the internal oxidation layer were measured by the methods described above.

[0124] Further, with respect to the obtained plated steel sheets, the end surface corrosion resistance and the workability were evaluated by methods, which will be described later.

[0125] [End Surface Corrosion Resistance]

[0126] A sample of 50100 mm was taken from the plated steel sheet, Zn phosphoric acid treatment (SD5350 system: Nippon Paint Industrial Coatings Co., Ltd. standard) was performed, and then electrodeposition coating (PN110 Powernics Gray: Nippon Paint Industrial Coatings Co. Ltd. standard) was performed so as to obtain a thickness of 20 m, and baking was performed at a baking temperature of 150 C. for 20 minutes. This coated plated steel sheet (the plated steel sheet subjected to electrodeposition coating) was subjected to a combined cycle corrosion test in accordance with JASO (M609-91) to measure the maximum swelling width at three points from the sample end surface, and the average value is calculated to evaluate corrosion resistance after painting.

[0127] In a case where the number of cycles of JASO (M609-91) described above is 150 cycles and the coating film swelling width from the end surface is less than 1.0 mm, it was rated as AAA, in a case where the coating film swelling width is less than 1.5 mm, it was rated as AA, in a case where the coating film swelling width is in a range of 1.5 to 2.5 mm, it was rated as A, and in a case where the coating film swelling width exceeds 2.5 mm, it was rated as B.

[0128] [Workability]

[0129] The workability of the plating layer was evaluated by powdering resistance.

[0130] A plated steel sheet was cut into a size of 40 mm (C)100 mm (L)0.8 mm (t), and this was bent 60 at 5R with the C direction as a bending axis direction by using a V bending tester manufactured by Hoden Seimitsu Kako Kenkyusho Co., Ltd., and then evaluated from the 5-point average value of a peeling width of the plating layer generated by tape peeling.

[0131] Specifically, in a case where no peeling occurs, it was rated as AA, in a case where the average peeling width is in a range of 0.1 to 0.5 mm, it was rated as A, and in a case where the average peeling width exceeds 0.5 mm, it was rated as B.

[0132] The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Plating layer MgZn.sub.2 phase Ca-based Ca-based intermetallic intermetallic compound phase compound phase Mg.sub.2Si phase of 0.10 m or less of 0.10 m or less Ternary Circle- Number density Number density (AlZn) equivalent (piece/(m (piece/(m phase structure diameter No. Classification Area % m)) m)) area % area % (m) 1 Comparative 25 0 0 10 65 example 2 Comparative 0 0 0 12 88 example 3 Invention 26 6 0 16 58 example 4 Invention 25 6 6 16 59 example 5 Comparative 13 0 0 0 87 example 6 Invention 33 3 0 30 37 example 7 Invention 33 3 3 31 36 example 8 Invention 39 8 0 31 30 example 9 Invention 43 12 0 41 16 example 10 Invention 44 12 9 40 16 example 11 Invention 44 15 0 43 13 example 12 Comparative 40 0 0 44 16 example 13 Invention 40 13 0 42 18 example 14 Invention 41 13 10 42 17 example 15 Invention 49 14 0 41 10 example 16 Invention 55 13 0 34 5 example 17 Comparative 38 0 0 44 18 example 18 Comparative 45 0 0 43 7 example 19 Comparative 70 11 0 25 5 example 20 Comparative 35 0 0 43 12 12.0 example 21 Invention 48 2 0 45 7 example 22 Invention 49 12 0 43 4 1.9 example 23 Comparative 83 0 0 0 6 example 24 Comparative 48 0 0 15 37 example 25 Invention 44 13 0 49 7 example 26 Invention 43 13 10 49 8 example 27 Invention 46 10 0 50 4 example 28 Invention 44 11 0 53 3 example 29 Invention 42 11 8 53 5 example 30 Invention 39 8 0 55 6 example 31 Invention 40 7 5 55 5 example 32 Invention 32 7 0 65 3 example 33 Invention 20 7 0 70 10 example 34 Comparative 25 0 0 75 0 example Plating layer Other intermetallic compound Internal Evaluation Circle- oxidation End equivalent Alloy layer layer surface Mg.sub.2Si phase diameter Thickness Thickness corrosion No. Area % (m) Area % (m) (m) resistance Workability 1 0.0 0.0 0.2 1.1 B A 2 0.0 0.0 0.2 1.2 B A 3 0.0 0.0 0.1 0.2 1.5 A A 4 0.0 0.0 0.1 0.2 1.5 AA A 5 0.0 0.4 0.1 0.2 2.0 B A 6 0.0 0.0 0.3 1.5 A AA 7 0.0 0.0 0.3 1.5 AA AA 8 0.0 0.0 0.3 2.0 A AA 9 0.0 0.2 0.2 0.2 1.0 AAA AA 10 0.0 0.0 0.2 1.0 AAA AA 11 0.0 2.1 0.2 0.3 1.9 AAA AA 12 0.0 0.0 0.2 0.2 1.8 B AA 13 0.0 0.4 0.1 0.3 2.0 AAA AA 14 0.0 0.0 0.2 1.8 AAA AA 15 0.0 0.2 0.2 0.3 1.4 AAA AA 16 0.0 3.0 6.2 1.6 2.0 AAA AA 17 0.0 0.0 0.3 0.2 2.0 B AA 18 0.0 0.5 5.0 0.3 1.5 B AA 19 0.0 0.0 0.2 2.1 A B 20 10.0 0.0 0.3 2.2 B B 21 0.0 0.0 0.2 2.0 AA AA 22 4.0 0.1 0.2 0.4 2.0 AAA AA 23 0.0 2.5 11.0 0.3 2.0 A B 24 0.0 0.0 0.2 0.3 2.0 B A 25 0.0 0.3 0.2 0.4 1.9 AAA AA 26 0.0 0.0 0.4 1.8 AAA AA 27 0.0 0.4 0.2 0.4 1.2 AAA AA 28 0.0 0.0 0.6 1.1 AAA AA 29 0.0 0.0 0.6 1.1 AAA AA 30 0.0 0.4 0.2 0.6 1.3 AA AA 31 0.0 0.0 0.7 1.4 AAA AA 32 0.0 0.6 0.2 0.8 1.4 AA AA 33 0.0 0.0 1.0 1.5 AA AA 34 0.0 0.0 2.1 2.2 B A The underline indicates a value outside the range of the present invention. indicates data missing or illegible when filed

[0133] As can be seen from the results in Tables 1 and 2, in Nos. 3, 4, 6 to 11, 13 to 16, 21, 22, and 25 to 33, which are the present invention examples, the chemical composition and the area ratio of the MgZn.sub.2 phase in the cross section in the thickness direction were within the range of the present invention, and the MgZn.sub.2 phase contained a Ca-based intermetallic compound. Therefore, the end surface corrosion resistance and the workability were exceptional.

[0134] On the other hand, in Nos. 1, 2, 5, 12, 17 to 20, 23, 24, and 34, which are comparative examples, one or more of the chemical composition, the area ratio of the MgZn.sub.2 phase in the cross section in the thickness direction, and the number density of the Ca-based intermetallic compound in the MgZn.sub.2 phase were out of the range of the present invention. As a result, either the end surface corrosion resistance or the workability was inferior.