500 mpa grade low yield ratio weather-resistant bridge steel and manufacturing method therefor

Abstract

Disclosed is 500-MPa low-yield-ratio weather-resistant bridge steel and a manufacturing method therefor; the weather-resistant bridge steel includes the following components in percentage by mass: C: 0.04%-0.09%, Si: 0.15%-0.30%, Mn: 1.40%-1.50%, P: 0.009%-0.015%, S: ≤0.002%, Nb: 0.020%-0.050%, Ti: 0.010%-0.020%, V: 0.010%-0.030%, Cu: 0.30%-0.40%, Ni: 0.30%-0.45%, Cr: 0.45%-0.60%, Mo: 0.08%-0.15%, Alt: 0.02%-0.04%, and the balance Fe and inevitable impurities; through scientific component designing and a matched manufacturing method combining controlled rolling and cooling and tempering, the weather-resistant bridge steel has a low yield ratio, high low-temperature toughness and high elongation.

What is claimed is: 
     
         1 . 500 MPa low-yield-ratio weather-resistant bridge steel, comprising the following components in percentage by mass: C: 0.04%-0.09%, Si: 0.15%-0.30%, Mn: 1.40%-1.50%, P: 0.009%-0.015%, S: ≤0.002%, Nb: 0.020%-0.050%, Ti: 0.010%-0.020%, V: 0.010%-0.030%, Cu: 0.30%-0.40%, Ni: 0.30%-0.45%, Cr: 0.45%-0.60%, Mo: 0.08%-0.15%, Alt: 0.02%-0.04%, and the balance Fe and inevitable impurities. 
     
     
         2 . The 500-MPa low-yield-ratio weather-resistant bridge steel according to  claim 1 , wherein a metallographic structure is tempered bainite. 
     
     
         3 . The 500-MPa low-yield-ratio weather-resistant bridge steel according to  claim 1 , wherein a 8 mm-80 mm thick steel plate has a yield ratio ≤0.83. 
     
     
         4 . The 500-MPa low-yield-ratio weather-resistant bridge steel according to  claim 3 , wherein an atmospheric corrosion resistance index I ≥6.5. 
     
     
         5 . The 500-MPa low-yield-ratio weather-resistant bridge steel according to  claim 1 , wherein in the components in percentage by mass, C is 0.06%-0.09% and Mn is 1.40%-1.46%. 
     
     
         6 . A manufacturing method for the 500-MPa low-yield-ratio weather-resistant bridge steel according to  claim 1 , comprising processes of smelting, continuous casting, soaking, rolling, relaxation, cooling and off-line tempering,
 wherein a continuous casting billet is heated in the soaking process until a center temperature reaches 1130° C.-1230° C.;   the rolling process is to conduct recrystallization zone rolling and non-recrystallization zone rolling on a descaled continuous casting billet, and an accumulated deformation amount of the recrystallization zone rolling is 50% or more of a thickness of the continuous casting billet;   an intermediate billet holds a temperature at 800° C.-990° C., a temperature-holding thickness is 2 times-4 times of a final-product thickness, the non-recrystallization zone rolling is conducted after a temperature is reached, and a finishing temperature is controlled to be 790° C.-830° C.;   in the relaxation process, relaxation is conducted until an initial cooling temperature is 730° C.-760° C.;   the cooling process is to conduct laminar cooling from the initial cooling temperature, control a self-tempering temperature to be 420° C.-600° C., and then conduct air-cooling to a room temperature; and   in the off-line tempering process, a tempering temperature is 450° C.-550° C., heat preservation is conducted at the temperature for 20 min-40 min, heat preservation time being proportionate to the final-product thickness, and then natural cooling is conducted to the room temperature.   
     
     
         7 . The manufacturing method according to  claim 6 , wherein a 150 mm-320 mm thick continuous casting billet is used in manufacturing of a 8 mm-80 mm thick final product. 
     
     
         8 . The manufacturing method according to  claim 7 , wherein in the continuous casting process, stacking cooling is conducted on the continuous casting billet for 24 h or more, stacking cooling time increases with increasing of a thickness of the continuous casting billet, and for a 320 mm continuous casting billet, the stacking cooling time is 48 h or more. 
     
     
         9 . The manufacturing method according to  claim 8 , wherein a uniform temperature of the continuous casting billet in the soaking process is less than 20° C. 
     
     
         10 . The manufacturing method according to  claim 9 , wherein in the soaking process, heating time ≥ the thickness of the continuous casting billet * 1 min/mm.