steel plate

Abstract

This invention provides a high-strength hot-dip galvanized steel sheet with excellent surface quality and spot weldability, as well as a method for manufacturing the same. [Solution] A hot-dip galvanized steel sheet according to one aspect of the present invention includes a base steel sheet and a hot-dip galvanized layer formed on the surface of the base steel sheet, wherein the difference between the average Mn / Si value of the surface oxides present in the surface region, which is the region from the interface between the hot-dip galvanized layer and the base steel sheet to a depth of 15 nm, and the average Mn / Si value of the internal oxides present at a depth of 50 to 100 nm from the interface can be 0.5 or more. Here, Mn and Si of each oxide refer to the content (weight %) of Mn and Si components in the oxide measured by EDS, and the average Mn / Si value refers to the average of the Mn / Si values ​​measured for each oxide.

Claims

1. Raw steel sheet and The above includes a hot-dip galvanized layer formed on the surface of the base steel sheet, A hot-dip galvanized steel sheet in which the value obtained by subtracting the average Mn / Si value of the internal oxide located at a depth of 50 to 100 nm from the interface from the average Mn / Si value of the surface oxide located in the surface region up to a depth of 15 nm from the interface is 0.5 or more. Here, Mn and Si for each oxide refer to the content (weight %) of Mn and Si components in the oxide as measured by EDS, and the average Mn / Si value refers to the average of the Mn / Si values ​​measured for each oxide.

2. The hot-dip galvanized steel sheet according to claim 1, wherein the difference in the above-mentioned average values ​​is 0.8 or more.

3. The hot-dip galvanized steel sheet according to claim 1, wherein the average value of the Mn / Si value of the surface oxide is 1.5 or more.

4. The hot-dip galvanized steel sheet according to claim 1, wherein the average value of the Mn / Si value of the surface oxide is 1.7 or more.

5. The hot-dip galvanized steel sheet according to claim 1, wherein the average value of the Mn / Si value of the internal oxide is 1.0 or less.

6. The hot-dip galvanized steel sheet according to claim 1, wherein the average value of the Mn / Si value of the internal oxide is 0.9 or less.

7. The hot-dip galvanized steel sheet according to claim 1, wherein the base steel sheet has a composition comprising C: 0.05 to 1.5%, Si: 2.0% or less, Mn: 1.0 to 20%, S-Al (acid-soluble aluminum): 3% or less, Cr: 2.5% or less, Mo: 1% or less, B: 0.005% or less, Nb: 0.2% or less, Ti: 0.2% or less, V: 0.2% or less, Sb + Sn + Bi: 0.1% or less, and N: 0.01% or less.

8. The stage of providing steel slabs, The steps include reheating the slab to a temperature of 950 to 1300°C, The process involves hot-rolling the reheated slab at a finish-rolling start temperature of 900 to 1,150°C and a finish-rolling end temperature of 850 to 1,050°C to obtain a steel sheet, The steps include winding the steel plate at a temperature range of 590 to 750°C, The process involves pickling the steel plate at a feed speed of 180 to 250 mph, The steps include cold rolling the steel sheet at a reduction ratio of 35-60%, The process involves heating the cold-rolled steel sheet under conditions where the uniform tropical temperature and dew point temperature are 650 to 900°C and -10 to +30°C, respectively, and the atmospheric gas is humid nitrogen containing 5 to 10 volume percent of H2, and then recrystallizing and annealing it by cooling it in a rapid cooling zone at a cooling rate of 5 to 30°C / s. The process involves drawing the steel plate into a molten plating bath at a temperature in the range of 420 to 500°C and molten plating it, A method for manufacturing hot-dip galvanized steel sheets, including the method described above.

9. The method for manufacturing a hot-dip galvanized steel sheet according to claim 8, further comprising the step of alloying the hot-dip galvanized steel sheet at a temperature of 480 to 560°C.

10. The method for producing a hot-dip galvanized steel sheet according to claim 9, wherein the molten plating bath contains 0.10 to 0.15% by weight of Al.

11. The method for producing a hot-dip galvanized steel sheet according to claim 8, wherein the molten plating bath contains 0.2 to 0.25% by weight of Al.

12. The method for producing a hot-dip galvanized steel sheet according to claim 8, wherein the molten plating bath contains 0.7 to 5.7% by weight of Al and 0.7 to 5.7% by weight of Mg.

13. A method for manufacturing a hot-dip galvanized steel sheet according to any one of claims 8 to 12, wherein the sheet feeding speed during the recrystallization annealing is 40 to 130 mpm.

14. A method for manufacturing a hot-dip galvanized steel sheet according to any one of claims 8 to 12, wherein the hydrogen concentration in the rapidly cooled zone during the recrystallization annealing is 25 to 80 volume percent.

15. A method for manufacturing a hot-dip galvanized steel sheet according to any one of claims 8 to 12, wherein the edge portion of the wound steel sheet is heated at 600 to 800°C for 5 to 24 hours.

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