High-strength hot-rolled strip steel with high weather resistance and manufacturing method therefor

Abstract

The present invention provides a hot-rolled strip steel and manufacturing method therefor. The hot-rolled strip steel comprises the following components in mass percentage: C: 0.04 to 0.15%, Si≤0.50%, Mn: 0.30 to 2.00%, Cr: 1.5 to 4.5%, Cu: 0.10 to 0.60%, P≤0.03%, S≤0.01%, and Al: 0.01 to 0.60%, with the balance being Fe and unavoidable impurities; and further satisfies: 2.5%≤2Mn+Cr≤6.0%, with elemental symbols being substituted with mass percentages of corresponding elements in the hot-rolled strip steel for calculation. The hot-rolled strip steel of the present invention exhibits excellent resistance to atmospheric corrosion and mechanical properties, and can be directly used for supporting bracket structural parts such as guardrails, mast towers and photovoltaics without coating on the surface.

1 . A hot-rolled strip steel, comprising the following components in mass percentage: C: 0.04 to 0.15%, Si≤0.50%, Mn: 0.30 to 2.00%, Cr: 1.5 to 4.5%, Cu: 0.10 to 0.60%, P≤0.03%, S≤0.01%, and Al: 0.01 to 0.60%, with the balance being Fe and unavoidable impurities; and further satisfies: 2.5%≤2Mn+Cr≤6.0%, with elemental symbols being substituted with mass percentages of corresponding elements in the hot-rolled strip steel for calculation. 
     
     
         2 . The hot-rolled strip steel according to  claim 1 , wherein the hot-rolled strip steel further comprises Ni, and the composition of the hot-rolled strip steel satisfies: Ni≤0.40%, and Si+2Ni≥0.10%, with elemental symbols being substituted with mass percentages of corresponding elements in the hot-rolled strip steel for calculation. 
     
     
         3 . The hot-rolled strip steel according to  claim 1 , wherein the hot-rolled strip steel further comprises at least one selected from the following: Ti≤0.15%, Nb≤0.06%, V≤0.15%, Mo≤0.40%, and B≤0.002%. 
     
     
         4 . The hot-rolled strip steel according to  claim 1 , wherein the hot-rolled strip steel further comprises at least one selected from the following: Sb≤0.15%, Re≤0.15%, Ca≤0.015% or Mg≤0.015%. 
     
     
         5 . The hot-rolled strip steel according to  claim 1 , wherein the hot-rolled strip steel has a microstructure being a multiphase structure of polygonal ferrite+bainite containing MA, and the ferrite has a grain size of grade 9 or more, preferably grade 11 or more; wherein in the microstructure, the polygonal ferrite has a content of 40 vol % to 70 vol %, the bainite has a content of 20 vol % to 60 vol %, preferably 30 vol % to 60 vol %, and the fine granular MA in the bainite structure accounts for 30 vol % or more of the bainite; and wherein the microstructure has a pearlite or carbide content of ≤15 vol %. 
     
     
         6 . The hot-rolled strip steel according to  claim 1 , wherein the hot-rolled strip steel has a corrosion rate of 30% or less of that of Q355B steel; and/or, the hot-rolled strip steel has a corrosion depth of ≤0.1 mm during a simulated service cycle of 25 years; and/or, the hot-rolled strip steel has a yield strength of ≥550 MPa, a tensile strength of ≥ 650 MPa, a yield-to-tensile ratio of ≤0.85, an elongation at break of ≥20%, a cold bending performance that meets qualification under the conditions of bending at 180° and D=1t, and an impact energy at −40° C. of 80 J or more. 
     
     
         7 . A manufacturing method for the hot-rolled strip steel according to  claim 1 , comprising the following steps:
 1) Smelting and casting   Smelting molten steel according to the composition according to  claim 1 , and then casting into a slab;   2) Heating   Transferring the slab into a heating furnace or soaking furnace for soaking; heating up the slab such that a slab surface temperature increases from 1050 to 1150° C. in 15 minutes; wherein the heating time of the slab in the soaking section is 20 to 60 minutes; and a tapping temperature of the slab is 1180 to 1230° C.;   3) Rolling   Performing rough rolling after the slab is removed from the heating furnace and sized, wherein high-pressure water descaling with a pressure of 15 MPa or more, preferably 20 MPa or more, is used for the rough rolling stage, and a temperature at a rough rolling outlet is 1040° C. or less; then performing finish rolling to the rough-rolled strip steel, wherein multi-stand continuous rolling is used for the finish rolling, and a final rolling temperature is 820 to 880° C.;   4) Cooling   Adopting laminar flow cooling for cooling, in combination with two-stage cooling, wherein the first stage of cooling is performed to rapidly cool the strip steel to 640 to 690° C. at a cooling rate of ≥150° C./s, preferably 150 to 350° C./s, followed by air cooling for 7 to 14 seconds; and the second stage of cooling is performed to cool the strip steel to 480 to 560° C. at a cooling rate of ≥60° C./s, preferably 60 to 300° C./s, followed by coiling.   
     
     
         8 . The manufacturing method according to  claim 7 , wherein in step 3), the temperature at the rough rolling outlet is 1000 to 1040° C. 
     
     
         9 . The manufacturing method according to  claim 7 , wherein in step 3), in the finish rolling, if the finished hot-rolled strip has a thickness of 3 mm or less, the final rolling temperature is 860 to 880° C.; if the finished hot-rolled strip has a thickness of 3 to 5 mm, the final rolling temperature is 840 to 860° C.; and if the finished hot-rolled strip has a thickness of 5 mm or more, the final rolling temperature is 820 to 840° C. 
     
     
         10 . The hot-rolled strip steel according to  claim 2 , wherein the hot-rolled strip steel further comprises at least one selected from the following: Ti≤0.15%, Nb≤0.06%, V≤0.15%, Mo≤0.40%, and B≤0.002%. 
     
     
         11 . The hot-rolled strip steel according to  claim 2 , wherein the hot-rolled strip steel further comprises at least one selected from the following: Sb≤0.15%, Re≤0.15%, Ca≤0.015% or Mg≤0.015%. 
     
     
         12 . The hot-rolled strip steel according to  claim 3 , wherein the hot-rolled strip steel further comprises at least one selected from the following: Sb≤0.15%, Re≤0.15%, Ca≤0.015% or Mg≤0.015%. 
     
     
         13 . The hot-rolled strip steel according to  claim 2 , wherein the hot-rolled strip steel has a microstructure being a multiphase structure of polygonal ferrite+bainite containing MA, and the ferrite has a grain size of grade 9 or more, preferably grade 11 or more; wherein in the microstructure, the polygonal ferrite has a content of 40 vol % to 70 vol %, the bainite has a content of 20 vol % to 60 vol %, preferably 30 vol % to 60 vol %, and the fine granular MA in the bainite structure accounts for 30 vol % or more of the bainite; and wherein the microstructure has a pearlite or carbide content of ≤15 vol %. 
     
     
         14 . The hot-rolled strip steel according to  claim 3 , wherein the hot-rolled strip steel has a microstructure being a multiphase structure of polygonal ferrite+bainite containing MA, and the ferrite has a grain size of grade 9 or more, preferably grade 11 or more; wherein in the microstructure, the polygonal ferrite has a content of 40 vol % to 70 vol %, the bainite has a content of 20 vol % to 60 vol %, preferably 30 vol % to 60 vol %, and the fine granular MA in the bainite structure accounts for 30 vol % or more of the bainite; and wherein the microstructure has a pearlite or carbide content of ≤15 vol %. 
     
     
         15 . The hot-rolled strip steel according to  claim 4 , wherein the hot-rolled strip steel has a microstructure being a multiphase structure of polygonal ferrite+bainite containing MA, and the ferrite has a grain size of grade 9 or more, preferably grade 11 or more; wherein in the microstructure, the polygonal ferrite has a content of 40 vol % to 70 vol %, the bainite has a content of 20 vol % to 60 vol %, preferably 30 vol % to 60 vol %, and the fine granular MA in the bainite structure accounts for 30 vol % or more of the bainite; and wherein the microstructure has a pearlite or carbide content of ≤15 vol %. 
     
     
         16 . The hot-rolled strip steel according to  claim 2 , wherein the hot-rolled strip steel has a corrosion rate of 30% or less of that of Q355B steel; and/or, the hot-rolled strip steel has a corrosion depth of ≤0.1 mm during a simulated service cycle of 25 years; and/or, the hot-rolled strip steel has a yield strength of ≥550 MPa, a tensile strength of ≥650 MPa, a yield-to-tensile ratio of ≤0.85, an elongation at break of ≥20%, a cold bending performance that meets qualification under the conditions of bending at 180° and D=1t, and an impact energy at −40° C. of 80 J or more. 
     
     
         17 . The hot-rolled strip steel according to  claim 3 , wherein the hot-rolled strip steel has a corrosion rate of 30% or less of that of Q355B steel; and/or, the hot-rolled strip steel has a corrosion depth of ≤0.1 mm during a simulated service cycle of 25 years; and/or, the hot-rolled strip steel has a yield strength of ≥550 MPa, a tensile strength of ≥650 MPa, a yield-to-tensile ratio of ≤0.85, an elongation at break of ≥20%, a cold bending performance that meets qualification under the conditions of bending at 180° and D=1t, and an impact energy at −40° C. of 80 J or more. 
     
     
         18 . The hot-rolled strip steel according to  claim 4 , wherein the hot-rolled strip steel has a corrosion rate of 30% or less of that of Q355B steel; and/or, the hot-rolled strip steel has a corrosion depth of ≤0.1 mm during a simulated service cycle of 25 years; and/or, the hot-rolled strip steel has a yield strength of ≥550 MPa, a tensile strength of ≥650 MPa, a yield-to-tensile ratio of ≤0.85, an elongation at break of ≥20%, a cold bending performance that meets qualification under the conditions of bending at 180° and D=1t, and an impact energy at −40° C. of 80 J or more. 
     
     
         19 . The hot-rolled strip steel according to  claim 5 , wherein the hot-rolled strip steel has a corrosion rate of 30% or less of that of Q355B steel; and/or, the hot-rolled strip steel has a corrosion depth of ≤0.1 mm during a simulated service cycle of 25 years; and/or, the hot-rolled strip steel has a yield strength of ≥550 MPa, a tensile strength of ≥650 MPa, a yield-to-tensile ratio of ≤0.85, an elongation at break of ≥20%, a cold bending performance that meets qualification under the conditions of bending at 180° and D=1t, and an impact energy at −40° C. of 80 J or more. 
     
     
         20 . The manufacturing method according to  claim 8 , wherein in step 3), in the finish rolling, if the finished hot-rolled strip has a thickness of 3 mm or less, the final rolling temperature is 860 to 880° C.; if the finished hot-rolled strip has a thickness of 3 to 5 mm, the final rolling temperature is 840 to 860° C.; and if the finished hot-rolled strip has a thickness of 5 mm or more, the final rolling temperature is 820 to 840° C.