Ultrahigh-strength dual-phase steel and manufacturing method therefor

Abstract

Disclosed in the present disclosure is an ultrahigh-strength dual-phase steel. The matrix structure of the ultrahigh-strength dual-phase steel is ferrite and martensite, wherein the ferrite and the martensite are evenly distributed in an island shape. The ultrahigh-strength dual-phase steel contains the following chemical elements in percentage by mass: 0.12-0.2% of C, 0.5-1.0% of Si, 2.5-3.0% of Mn, 0.02-0.05% of Al, 0.02-0.05% of Nb, 0.02-0.05% of Ti, and 0.001-0.003% of B. Further disclosed in the present disclosure is a manufacturing method for the ultrahigh-strength dual-phase steel, comprising the steps of smelting and continuous casting, hot rolling, cold rolling, annealing, tempering, and leveling. The ultrahigh-strength dual-phase steel in the present disclosure has not only good mechanical properties but also excellent delayed cracking resistance and low initial hydrogen content, and can be suitable for manufacturing of vehicle safety structural parts.

1 . An ultra-high-strength dual-phase steel, wherein the ultra-high-strength dual-phase steel has a matrix structure of ferrite + martensite, wherein the ferrite and the martensite are distributed evenly like islands, and wherein the ultra-high-strength dual-phase steel comprises the following chemical elements in mass percentages, in addition to Fe:
 C: 0.12-0.2%, Si: 0.5-1.0%, Mn: 2.5-3.0%, Al: 0.02-0.05%, Nb: 0.02-0.05%, Ti: 0.02-0.05%, B: 0.001%-0.003%.   
     
     
         2 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the chemical elements have the following mass percentages:
 C: 0.12-0.2%, Si: 0.5-1.0%, Mn: 2.5-3.0%, Al: 0.02-0.05%, Nb: 0.02-0.05%, Ti: 0.02-0.05%, B: 0.001%-0.003%, and a balance of Fe and other unavoidable impurities.   
     
     
         3 . The ultra-high-strength dual-phase steel according to  claim 2 , wherein the unavoidable impurities include elements P, S and N, and contents thereof are controlled to be at least one of the following: P ≤0.01%, S≤0.002%, N≤0.004%. 
     
     
         4 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the mass percentages of the chemical elements satisfy at least one of: 
       
         
           
             
               C 
               : 
               0.14 
               − 
               0.18 
               % 
               , 
             
           
         
       
       
         
           
             
               M 
               n 
               : 
               2.5 
               − 
               2.8 
               % 
               . 
             
           
         
       
       . 
     
     
         5 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the martensite has a phase proportion of >90%. 
     
     
         6 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the martensite comprises coherently distributed ε carbides. 
     
     
         7 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the ultra-high-strength dual-phase steel has performances that meet at least one of the following: yield strength ≥900 MPa, tensile strength ≥1300 MPa, elongation after fracture ≥5%, initial hydrogen content ≤10 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength. 
     
     
         8 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the ultra-high-strength dual-phase steel has performances that meet at least one of the following: yield strength ≥930 MPa, tensile strength ≥1320 MPa, elongation after fracture ≥5.5%, initial hydrogen content ≤7 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to 1.2 times of the tensile strength. 
     
     
         9 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the ultra-high-strength dual-phase steel has a yield ratio of 0.70-0.75. 
     
     
         10 . A manufacturing method for the ultra-high-strength dual-phase steel according to  claim 1 , wherein the method comprises steps of: 
 (1) Smelting and continuous casting;   (2) Hot rolling;   (3) Cold rolling;   (4) Annealing: heating to an annealing soaking temperature of 800-850° C. at a heating rate of 3-10° C./s, the annealing time being 40-200 s; and then rapidly cooling at a rate of 30-80° C./s, a starting temperature of the rapid cooling being 670-730° C.;   (5) Tempering: tempering temperature: 260-320° C.; tempering time: 100-400 s;   (6) Temper rolling; and   (7) Electrogalvanizing.   
     
     
         11 . The manufacturing method according to  claim 10 , wherein in step (1), a drawing speed in the continuous casting is controlled at 0.9-1.5 m/min during the continuous casting process. 
     
     
         12 . The manufacturing method according to  claim 10 , wherein in step (2), a cast slab is controlled to be soaked at a temperature of 1220-1260° C.; then rolled with a finishing rolling temperature being controlled at 880-920° C.; then cooled at a rate of 20-70° C./s after the rolling; then coiled at a coiling temperature of 600-650° C.; and then subjected to heat preservation treatment after the coiling. 
     
     
         13 . The manufacturing method according to  claim 10 , wherein in step (3), a cold rolling reduction rate is controlled at 45-65%. 
     
     
         14 . The manufacturing method according to  claim 10 , wherein in step (6), a temper rolling reduction rate is controlled at ≤0.3%; and/or in step (7), double-side electrogalvanizing is performed with a plating layer weight of 10-100 g/m 2  on each side. 
     
     
         15 . The manufacturing method according to  claim 10 , wherein in step (2), a cast slab is controlled to be soaked at a temperature of 1220-1250° C., and a coiling temperature is 605-645° C.; in step (4), the annealing soaking temperature is 805-845° C.; in step (5), the tempering temperature is 260-310° C., and the tempering time is 100-300 s. 
     
     
         16 . The ultra-high-strength dual-phase steel according to  claim 1 , wherein the mass percentages of the chemical elements satisfy at least one of: C: 0.14-0.18%, Mn: 2.5-2.8%. 
     
     
         17 . The ultra-high-strength dual-phase steel according to  claim 2 , wherein the martensite has a phase proportion of >90%, and/or the martensite comprises coherently distributed ε carbides, and/or the ultra-high-strength dual-phase steel has a yield ratio of 0.70-0.75. 
     
     
         18 . The ultra-high-strength dual-phase steel according to  claim 2 , wherein the ultra-high-strength dual-phase steel has performances that meet at least one of the following: yield strength ≥900 MPa, tensile strength ≥1300 MPa, elongation after fracture ≥5%, initial hydrogen content ≤10 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength. 
     
     
         19 . The manufacturing method according to  claim 10 , the chemical elements have the following mass percentages: C: 0.12-0.2%, Si: 0.5-1.0%, Mn: 2.5-3.0%, Al: 0.02-0.05%, Nb: 0.02-0.05%, Ti: 0.02-0.05%, B: 0.001%-0.003%, and a balance of Fe and other unavoidable impurities. 
     
     
         20 . The manufacturing method according to  claim 10 , wherein: the martensite has a phase proportion of >90%; and/or, the martensite comprises coherently distributed ε carbides; and/or, the ultra-high-strength dual-phase steel has a yield ratio of 0.70-0.75; and/or, the ultra-high-strength dual-phase steel has performances that meet at least one of the following: yield strength ≥900 MPa, tensile strength ≥1300 MPa, elongation after fracture ≥5%, initial hydrogen content ≤10 ppm; no delayed cracking when soaked in 1 mol/L hydrochloric acid for 300 hours under a pre-stress of greater than or equal to the tensile strength.