Hot-rolled galvanized steel sheet having excellent galling resistance, formability and sealer-adhesion property and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-2019194792-A1
Application number	US-201716327426-A
Country	US
Kind code	A1
Filing date	Aug 22, 2017
Priority date	Aug 22, 2016
Publication date	Jun 27, 2019
Grant date	—

Abstract

Disclosed are a hot-rolled galvanized steel sheet having excellent galling resistance and formability, and a method for manufacturing the same. The hot-rolled galvanized steel sheet, includes: a base steel; and a hot-rolled galvanizing layer formed on the surface of the base steel, wherein the hot-rolled galvanizing layer provides a hot-rolled galvanized steel sheet having a Mn crystallite having a size of 10 μm or less between the resin dendrites of zinc that form sequins.

First claim

1 . A hot-rolled galvanized steel sheet comprising:
a base steel; and a hot-rolled galvanizing layer disposed on a surface of the base steel, wherein the hot-rolled galvanizing layer contains 0.1 to 0.8 weight percentage (wt %) of aluminum (Al), 0.05 to 1 wt % of manganese (Mn), with a remainder of zinc (Zn) and inevitable impurities, and a surface of the hot-rolled galvanizing layer is provided with a crystallite having a major axis length of 1 to 20 micrometers (μm).

2 . The hot-rolled galvanized steel sheet of claim 1 , wherein the hot-rolled galvanizing layer includes an oxide film, having a thickness of 0.005 to 0.02 μm, on the surface of the hot-rolled galvanizing layer.

3 . The hot-rolled galvanized steel sheet of claim 1 , wherein the crystallite includes 2 to 11 atomic percentage (at %) of Al, 0.6 to 6 at % of Mn, 0 to 2 at % of iron (Fe), and a remainder of Zn.

4 . The hot-rolled galvanized steel sheet of claim 1 , wherein in the crystallite, Mn and Al are present together, and an atomic percentage ratio of Mn and Al (Mn/Al) ranges from 0.2 to 0.6.

5 . The hot-rolled galvanized steel sheet of claim 2 , wherein an Al oxide present in the oxide film has 0.5 to 2 wt % when the Al oxide is converted to Al, and a Mn oxide present in the oxide film 0.05 to 0.2 wt % when the Mn oxide is converted to Mn.

6 . The hot-rolled galvanized steel sheet of claim 1 , wherein a content of Mn in the hot-rolled galvanizing layer, analyzed using a glow discharge mass spectrometer, is that a maximum Mn concentration within a section from a surface portion of a plating layer to a point of t× 1/10 in a thickness direction on the basis of a plating layer thickness t is 110 to 500% higher than a Mn minimum concentration within a section from a point below the point of t× 1/10 to a boundary between the plating layer and the base steel.

7 . The hot-rolled galvanized steel sheet of claim 1 , wherein the hot-rolled galvanizing layer has a spangle having a size of 100 to 400 μm.

8 . The hot-rolled galvanized steel sheet of claim 1 , wherein the aluminum (Al) has 0.15 to 0.5 wt %, the manganese (Mn) has 0.05 to 0.6 wt %, and a total content of Al and Mn is 1 wt % or less.

9 . The hot-rolled galvanized steel sheet of claim 1 , wherein the surface of the hot-rolled galvanizing layer has a friction coefficient of 0.10 to 0.14.

10 . The hot-rolled galvanized steel sheet of claim 1 , wherein the hot-rolled galvanizing layer has hardness of 90 to 130 Vickers hardness (Hv).

11 . The hot-rolled galvanized steel sheet of claim 1 , wherein the hot-rolled galvanizing layer further includes one or more elements selected from titanium (Ti), calcium (Ca), manganese (Mg), nickel (Ni), and antimony (Sb) in such a manner that a total content of the one or more elements is 1% or less (excluding zero).

12 . The hot-rolled galvanized steel sheet of claim 1 , wherein a difference in height between a mountain and a valley of the hot-rolled galvanizing layer is less than or equal to 20% of a thickness of the hot-rolled galvanizing layer.

13 . A method for manufacturing a hot-rolled galvanized steel sheet, the method comprising:
a plating layer forming step of depositing a steel sheet in a hot-rolled galvanizing solution, containing 0.1 to 0.8 weight percentage (wt %) of aluminum (Al), 0.05 to 1 wt % of manganese (Mn), with a remainder of zinc (Zn) and inevitable impurities, and taking out the deposited steel sheet therefrom to form a plating layer that forms a hot-rolled galvanizing layer; a primary cooling step of cooling the steel sheet, on which the hot-rolled galvanizing layer is formed, at a cooling rate of −10 degrees Celsius per second (° C./s) until a temperature of the steel sheet reaches 420° C.; a secondary cooling step of cooling the steel sheet at a cooling rate of −8° C./s until the temperature of the steel sheet reaches 418° C. from 420° C.; and a tertiary cooling step of cooling the steel sheet at a steel sheet temperature of 418° C. or less at a cooling rate of −10° C./s or more to form the hot-rolled galvanizing layer.

14 . The method of claim 13 , wherein the hot-rolled galvanizing solution has a temperature of 440 to 470° C.

15 . The method of claim 13 , further comprising:
a wiping step of blowing nitrogen or air to the steel sheet, taken out from the hot-rolled galvanizing solution, to remove excessive molten zinc adhered to the steel sheet while cooling the steel sheet.

16 . The method of claim 13 , wherein the secondary cooling step is performed by blowing a gas having a temperature ranging from 100° C. to 400° C.

17 . The method of claim 16 , wherein the gas is air or a nitrogen gas.

18 . The method of claim 13 , further comprising:
cleaning a surface of the steel sheet to remove foreign substances before the plating layer forming step; annealing the steel sheet in a nitrogen-hydrogen reducing atmosphere at an A3 transformation temperature or higher; and cooling the annealed steel sheet before being deposited in the hot-rolled galvanizing solution.

19 . The method of claim 13 , further comprising:
temper-rolling a surface of a solidified hot-rolled galvanizing layer after the tertiary cooling step.

20 . The method of claim 13 , wherein the hot-rolled galvanizing solution contains 0.15 to 0.5 wt % of Al, 0.05 to 0.6 wt % of Mn, and a remainder of Zn, and a total content of elements excluding Zn is 1 wt % or less.

Assignees

• Posco

Inventors

• Kim Sang-Heon
• Hwang Hyeon-Seok
• Lee Suk-Kyu
• Jeon Sun-Ho
• Song Yon-Kyun
• Yoo Bong-Hwan

Classifications

• C23C2/40 Primary

  Plates; Strips · CPC title

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C21D9/46 Primary

  for sheet metals · CPC title

• C23C2/18

  Removing excess of molten coatings from elongated material · CPC title

• C22C18/00

  Alloys based on zinc · CPC title