HOT PRESS FORMED PRODUCT HAVING EXCELLENT CORROSION RESISTANCE AND METHOD FOR PREPARING SAME
Provided is a hot press formed product, which is prepared by means of hot press forming of a Zn—Al—Mg-based plated steel material comprising base iron and a Zn—Al—Mg-based plated layer, and a method for preparing the same, the hot press formed product comprising an oxide layer formed on the surface thereof, wherein the content ratio of Al to Mg (Al/Mg) in the oxide layer is 0.8 or more.
1 . A hot press formed product prepared by hot-press forming a Zn—Al—Mg-based plated steel material including base iron and a Zn—Al—Mg-based plating layer,
wherein the hot press formed product comprises an oxide layer formed on a surface, and a content ratio of Al to Mg (Al/Mg) in the oxide layer is 0.8 or more.
2 . The hot press formed product of claim 1 , wherein the content ratio of Al to Mg (Al/Mg) in the oxide layer is 0.9 or more.
3 . The hot press formed product of claim 1 , wherein a total coating weight of Zn, Al and Mg in the oxide layer is 700 mg/m 2 or less (exclusive of 0 mg/m 2 ).
4 . The hot press formed product of claim 1 , wherein the oxide layer contains one or two or more selected from the group consisting of Mn, Si and Fe, and a sum of contents of Mn, Si and Fe in the oxide layer is 50% or less relative to a total contents of metals in the oxide layer.
5 . The hot press formed product of claim 1 , wherein a ratio of a total amount of Mg (Mg o ) contained in the oxide layer relative to a total amount of Mg (Mg c ) contained in the plating layer of the hot press formed product is 1 or less.
6 . The hot press formed product of claim 1 , wherein an alloying degree of Fe in the plating layer of the hot press formed product is 20-70%.
7 . The hot press formed product of claim 1 , wherein the Zn—Al—Mg-based plating layer contains: 0.9-3.5% by weight of Mg, and 1.0-15% by weight of Al, with a balance of Zn and other unavoidable impurities.
8 . The hot press formed product of claim 1 , wherein the base iron contains: 0.15-0.35% by weight of C, 0.5% by weight or less (exclusive of 0% by weight) of Si, 0.5-8.0% by weight of Mn, and 0.0020-0.0050% by weight of B, with a balance of Fe and unavoidable impurities.
9 . The hot press formed product of claim 1 , wherein a maximum corrosion depth of a base member after a salt spray test for 1200 hours according to KS R 1127 is 0.5 mm or less.
10 . The hot press formed product of claim 1 , wherein tensile strength is 1300 MPa or more.
11 . A method for preparing a hot press formed product, comprising:
immersing base iron in a Zn—Al—Mg-based plating bath, and performing plating to obtain a Zn—Al—Mg-based plated steel material;
heating the Zn—Al—Mg-based plated steel material to a heating temperature of 600-950° C. at a rate of 10° C./sec or more in a heating furnace; and
forming the Zn—Al—Mg-based plated steel material which has reached the heating temperature with a mold simultaneously with quenching,
wherein a residence time is 120 seconds or less, the residence time representing a time during which the Zn—Al—Mg-based plated steel material which has reached the heating temperature resides in the heating furnace.
12 . The method of claim 11 , wherein the heating temperature is 800° C. or more and 950° C. or less, an average heating rate to the heating temperature is 20° C./sec or more, and the residence time is 60 seconds or less.
13 . The method of claim 11 , wherein the heating is carried out by any one method of radiant heating, high-frequency induction heating and ohmic heating.
14 . The method of claim 11 , wherein the heating is carried out under an inert gas atmosphere.
15 . The method of claim 11 , wherein the content ratio of Al to Mg (Al/Mg) in the Zn—Al—Mg-based plating bath is 0.8 or more.
16 . The method of claim 11 , wherein the base iron is a cold rolled steel plate, and the cold rolled steel plate has a surface roughness of 2.0 μm or less before plating.
17 . The method of claim 11 , wherein the base iron contains: 0.15-0.35% by weight of C, 0.5% by weight or less (exclusive of 0%) of Si, 0.5-8.0% by weight of Mn, and 0.0020-0.0050% by weight of B, with a balance of Fe and unavoidable impurities.
18 . The method of claim 17 , further comprising the following before obtaining the plated steel material:
pre-plating one or more metals selected from the group consisting of Fe, Ni, Cu, Sn and Sb to an average thickness of 5-100 nm on a surface of the base iron; and
annealing the pre-plated base iron.
19 . The method of claim 18 , wherein the annealing is carried out under 1-15% by volume of hydrogen gas and remaining nitrogen gas.