Gpa-grade bainite steel having ultra-high yield ratio and manufacturing method for gpa-grade bainite steel

Abstract

GPa-grade bainite steel having an ultra-high yield ratio, containing, in addition to Fe, the following chemical elements in mass percentages: 0.12-0.24% of C; 0.2-0.5% of Si; 1.3-2.0% of Mn; 0.001-0.004% of B; 0.01-0.05% of Al; and at least one of Cr, Nb, Ti, and Mo, wherein Cr≤0.4%, Nb≤0.06%, Ti≤0.1%, and Mo≤0.4%. Also disclosed are a manufacturing method and annealing process for the steel.

1 . A GPa-grade bainite steel having an ultra-high yield ratio, comprising the following chemical elements in mass percentages in addition to Fe and unavoidable impurities:
 C: 0.12-0.24%;   Si: 0.2-0.5%;   Mn: 1.3-2.0%;   B: 0.001-0.004%;   Al: 0.01-0.05%;   at least one of Cr, Nb, Ti and Mo, wherein Cr≤0.4%, Nb≤0.06%, Ti≤0.1%, Mo≤0.4%.   
     
     
         2 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , wherein the mass percentages of the chemical element are:
 C: 0.12-0.24%;   Si: 0.2-0.5%;   Mn: 1.3-2.0%;   B: 0.001-0.004%;   Al: 0.01-0.05%;   at least one of Cr, Nb, Ti and Mo, wherein Cr≤0.4%, Nb≤0.06%, Ti≤0.1%, Mo≤0.4%;   a balance of Fe and other unavoidable impurities.   
     
     
         3 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , wherein the mass percentages of the chemical elements satisfy at least one of:
 C: 0.15-0.20%,   Mn: 1.6-2.0%.   
     
     
         4 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , wherein among the other unavoidable impurities: P≤0.015%; and/or S≤0.004%. 
     
     
         5 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , further comprising at least one of the following chemical elements:
 0<Cu≤0.2%, 0<Ni≤0.2%, 0<V≤0.2%, 0<Ce≤0.2%.   
     
     
         6 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 5 , wherein it satisfies 0.18≤M≤0.27, wherein M=Cr/2.5+Ti+V/5+Nb/1.7+Mo/1.7, wherein Cr, V, Nb, Ti and Mo each represent a value in front of a percent sign in the mass percentage of each chemical element; and/or 0.20≤C b ≤0.27, wherein an equivalent bainite carbon content C b =C−(Mo+Nb)/8−(Ti+V)/4−Cr/12+Ni/10+Mn/20+B×10, wherein each element in the above formula represents a value in front of a percent sign in the mass percentage of the element. 
     
     
         7 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , wherein its microstructure is mainly acicular lower bainite, and a phase proportion of the acicular lower bainite is ≥90%. 
     
     
         8 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 7 , wherein its microstructure further comprises a nano-, submicron- or micron-scale granular carbide precipitate phase that is precipitated dispersively, and a total phase proportion of the granular carbide precipitate phase+acicular lower bainite is ≥99%; preferably, the granular carbide precipitate has a maximum diameter of ≤2 μm. 
     
     
         9 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , wherein it has a tensile strength of ≥980 MPa, a yield strength of ≥900 MPa, a yield ratio of ≥0.9, and a hole expansion rate of ≥55%; preferably a yield strength of ≥950 MPa, and a yield ratio of ≥0.95. 
     
     
         10 . An annealing process for the GPa-grade bainite steel having an ultra-high yield ratio according to  claim 1 , comprising steps of:
 (a) Heating a strip steel to a soaking temperature Ts at a heating rate of ≤50° C./s at a heating stage, wherein Ts is 840-900° C.;   (b) Holding the temperature Ts for 5 minutes or less at a soaking stage;   (c) Cooling to (Ts-80) to (Ts-140) ° C. at a first cooling rate of ≤15° C./s at a slow cooling stage;   (d) Cooling to (Ts-490) to (Ts-440) ° C. at a second cooling rate of ≥(130-Q)° C./s at a fast cooling stage;   (e) Cooling at a third cooling rate for 10-40 s at a controlled cooling stage for self-temperature rise, wherein [(Q-80)/12]≤third cooling rate≤[(Q-80)/8];   (f) Finally, cooling the strip steel in air to room temperature at an air-cooling stage;   wherein Q=C×180+Si×10+Mn×30+Ni×50+Cr×15+Mo×15+B×2000.   
     
     
         11 . A manufacturing method for a GPa-grade bainite steel having an ultra-high yield ratio, comprising steps of:
 (1) Smelting and casting;   (2) Hot rolling;   (3) Post-rolling cooling and coiling;   (4) Pickling and cold rolling.   (5) The annealing process according to  claim 10 .   
     
     
         12 . The manufacturing method according to  claim 11 , wherein in the step (2), a heating temperature is controlled at 1150-1260° C.; an initial rolling temperature of finishing rolling is controlled at 1100-1220° C.; and a final rolling temperature of finishing rolling is controlled at 900-950° C. 
     
     
         13 . The manufacturing method according to  claim 11 , wherein in step (3), a cooling rate is controlled at 30-150° C./s, and a coiling temperature is controlled at 450-580° C. 
     
     
         14 . The manufacturing method according to  claim 11 , wherein in step (4), a cold rolling reduction rate is controlled at ≥50%. 
     
     
         15 . The manufacturing method according to  claim 11 , wherein the GPa-grade bainite steel having an ultra-high yield ratio comprising the following chemical elements in mass percentages in addition to Fe and unavoidable impurities:
 C: 0.12-0.24%;   Si: 0.2-0.5%;   Mn: 1.3-2.0%;   B: 0.001-0.004%;   Al: 0.01-0.05%;   at least one of Cr, Nb, Ti and Mo, wherein Cr≤0.4%, Nb≤0.06%, Ti≤0.1%, Mo≤0.4%.   
     
     
         16 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 2 , wherein the mass percentages of the chemical elements satisfy at least one of C: 0.15-0.20%, and Mn: 1.6-2.0%; and/or among the other unavoidable impurities: P≤0.015%; and/or S≤0.004%; and/or the GPa-grade bainite steel having an ultra-high yield ratio further comprises at least one of the following chemical elements: 0<Cu≤0.2%, 0<Ni≤0.2%, 0<V≤0.2%, 0<Ce≤0.2%. 
     
     
         17 . The GPa-grade bainite steel having an ultra-high yield ratio according to  claim 16 , wherein it satisfies 0.18≤M≤0.27, wherein M=Cr/2.5+Ti+V/5+Nb/1.7+Mo/1.7, wherein Cr, V, Nb, Ti and Mo each represent a value in front of a percent sign in the mass percentage of each chemical element; and/or 0.20≤C b ≤0.27, wherein an equivalent bainite carbon content C b =C−(Mo+Nb)/8−(Ti+V)/4−Cr/12+Ni/10+Mn/20+B×10, wherein each element in the above formula represents a value in front of a percent sign in the mass percentage of the element. 
     
     
         18 . The annealing process for the GPa-grade bainite steel having an ultra high yield ratio according to  claim 10 , wherein the mass percentages of the chemical element of the GPa-grade bainite steel having an ultra-high yield ratio are:
 C: 0.12-0.24%;   Si: 0.2-0.5%;   Mn: 1.3-2.0%;   B: 0.001-0.004%;   Al: 0.01-0.05%;   at least one of Cr, Nb, Ti and Mo, wherein Cr≤0.4%, Nb≤0.06%, Ti≤0.1%, Mo≤0.4%; a balance of Fe and other unavoidable impurities.   
     
     
         19 . The annealing process for the GPa-grade bainite steel having an ultra high yield ratio according to  claim 18 , wherein the mass percentages of the chemical elements satisfy at least one of C: 0.15-0.20%, and Mn: 1.6-2.0%; and/or among the other unavoidable impurities: P≤0.015%; and/or S≤0.004%; and/or the GPa-grade bainite steel having an ultra-high yield ratio further comprises at least one of the following chemical elements: 0<Cu≤0.2%, 0<Ni≤0.2%, 0<V≤0.2%, 0<Ce≤0.2%. 
     
     
         20 . The manufacturing method according to  claim 15 , wherein the mass percentages of the chemical element of the GPa-grade bainite steel having an ultra high yield ratio are:
 C: 0.12-0.24%;   Si: 0.2-0.5%;   Mn: 1.3-2.0%;   B: 0.001-0.004%;   Al: 0.01-0.05%;   at least one of Cr, Nb, Ti and Mo, wherein Cr≤0.4%, Nb≤0.06%, Ti≤0.1%, Mo≤0.4%; a balance of Fe and other unavoidable impurities.