Steel tube having improved corrosion-resistance and method for manufacturing the same
Disclosed is a steel tube with superior corrosion-resistance treated with plating and a manufacturing method of the same. The manufacturing method of the steel tube includes the steps of: preheating a steel tube formed through a milling process; maintaining the temperature of the preheated steel tube above a predetermined temperature, and creating a reduction atmosphere; melting an Al—Zn alloy containing 55 wt % of aluminum and 43.4-44.9 wt. % of zinc, and plating the molten alloy over the surface of the steel tube; cooling the steel tube; and coating the surface of the steel tube with a resin.
1. A method for manufacturing a steel tube with superior corrosion-resistance, the method comprising the steps of:
preheating a steel tube formed through a milling process;
maintaining the temperature of the preheated steel tube above a predetermined temperature, and creating a reduction atmosphere;
plating the molten alloy over the surface of the steel tube by melting an Al—Zn alloy containing 55 wt % of aluminum and 43.4-44.9 wt. % of zinc, and inserting a level block into the molten alloy to raise the level of the alloy, wherein fluctuation of the molten alloy around a plating part is prevented by a separator, and the level is raised, so that the alloy is introduced in the plating part;
cooling the steel tube; and
coating the surface of the steel tube with a resin.
2. The method of claim 1 , wherein the alloy further comprises 0.1-1.6 wt % of silicon.
3. The method of claim 1 , wherein, in the maintaining step, the reduction atmosphere is created by injecting hydrogen-nitrogen mixed gas around the steel tube.
4. The method of claim 1 , wherein the cooling step comprises the sub-steps of:
performing air blasting on the plated steel tube; and quenching the steel tube using cold water.
5. The method of claim 1 , wherein a chromating (III) process is performed as pretreatment of the fifth step.
6. The method of claim 1 , wherein, in the coating step, the surface of the steel tube is coated with a colorless nylon resin.
7. The method of claim 1 , wherein, in the melting step, the plating process is carried out while the steep tube passes vertically upwardly through a plating part storing the molten alloy, and gas is sprayed toward the steel tube so as to control the thickness of the alloy plating.
8. The method of claim 7 , wherein a pressure greater than atmospheric pressure is applied to the bottom of the plating part by means of a pressure control unit, so as to prevent the leakage of the molten alloy in a downward direction between the steel tube and the plating part.