Weather-resistant bridge steel and manufacturing method thereof

Abstract

This disclosure relates to a weather-resistant bridge steel and its manufacturing method. A steel billet with a specific composition is subjected to hot rolling and cooling steps under specific conditions, resulting in a steel material containing a specific proportion of granular ferrite, acicular granular ferrite, and toughened ferrite structures, possessing specific mechanical properties and grain size. The bridge steel of this invention exhibits weather resistance, preventing further corrosion, while retaining certain mechanical properties.

Claims

1. A weathering-resistant bridge steel, comprising, by weight 100%,: 0.05% to 0.1% carbon; not more than 0.3% silicon; 0.5% to less than 1% manganese; not more than 0.01% phosphorus; not more than 0.005% sulfur; 0.1% to 1% chromium; not more than 0.5% molybdenum; 0.01% to 0.1% niobium and vanadium; 0.1% to 1% nickel; 0.3% to 1% copper; 0.01% to 0.05% aluminum; and not more than 0.05% calcium. Nitrogen not exceeding 0.01% by weight; and the remainder of iron and unavoidable impurities, wherein the weathering bridge steel comprises 45% to 55% by volume granular iron structure, 30% to 40% by volume acicular granular iron structure and 10% to 20% by volume ductile iron structure.

2. The weathering bridge steel as described in claim 1, wherein the weathering bridge steel contains at least 0.1% by weight of molybdenum.

3. The weather-resistant bridge steel as described in claim 1, wherein the grain size of the ferrous microstructure is 5 μm to 15 μm.

4. The weathering bridge steel as claimed in claim 1, wherein the weathering bridge steel has a yield strength greater than 400 MPa, a tensile strength of 490 MPa to 640 MPa, and an L-direction elongation greater than 30%.

5. The weathering bridge steel as described in claim 1, wherein the weathering bridge steel absorbs a low-temperature impact energy greater than 240 J at LT at 0°C.

6. The weathering steel for bridges as described in claim 1, wherein the weathering steel for bridges does not contain ferroalloy structure or ferroalloy structure.

7. A method for manufacturing weather-resistant bridge steel, comprising: providing a steel billet, wherein, based on 100% by weight of the total weight of the steel billet, the steel billet comprises: 0.05% to 0.1% by weight carbon; not more than 0.3% by weight silicon; 0.5% to less than 1% by weight manganese; not more than 0.01% by weight phosphorus; not more than 0.005% by weight sulfur; 0.1% to 1% by weight chromium; not more than 0.5% by weight molybdenum; 0.01% to 0.1% by weight niobium and vanadium; 0.1% to 1% by weight nickel; 0.3% to 1% by weight copper; 0.01% to 0.05% by weight aluminum; not more than 0.05% by weight calcium; not more than 0.01% by weight nitrogen; and the balance being iron and unavoidable impurities; and subjecting the steel billet to a heating step; Following the heating step, the steel billet undergoes a hot rolling step to obtain a hot-rolled steel sheet, wherein the final rolling temperature of the hot rolling step is 760°C to 830°C; and the hot-rolled steel sheet undergoes a cooling step to obtain the weather-resistant bridge steel, wherein the cooling step comprises: a water cooling step of the hot-rolled steel sheet, cooling it to 450°C to 550°C at a cooling rate of 8°C / second to 13°C / second; and after the water cooling step, an air cooling step of the hot-rolled steel sheet, wherein the weather-resistant bridge steel comprises 45% to 55% by volume of ferrous granular structure, 30% to 40% by volume of acicular ferrous granular structure, and 10% to 20% by volume of ductile ferrous structure.

8. A method for manufacturing weather-resistant bridge steel as described in claim 7, wherein one of the heating steps is performed at a heating temperature of 1100°C to 1200°C.

9. A method for manufacturing weather-resistant bridge steel as described in claim 7, wherein the rolling temperature of the hot rolling step is 780°C to 1000°C.

10. A method for manufacturing weather-resistant bridge steel as described in claim 7, wherein the weather-resistant bridge steel absorbs a low-temperature impact energy greater than 240 J at LT at 0°C.

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