Complex-phase steel having high hole expansibility and manufacturing method therefor

Abstract

Disclosed in the present invention is complex-phase steel having high hole expansibility. The complex-phase steel has a microstructure of ferrite and bainite. The complex-phase steel having high hole expansibility comprises the following chemical elements in percentage by mass: C: 0.06-0.09%, Si: 0.05-0.5%, Al: 0.02-0.1%, Mn: 1.5-1.8%, Cr: 0.3-0.6%, Nb≤0.03%, Ti: 0.05-0.12%, and the balance of Fe and inevitable impurities. In addition, also disclosed in the present invention is a manufacturing method for the foregoing complex-phase steel having high hole expansibility. The method comprises the following steps: (1) smelting and casting; (2) heating; (3) hot-rolling; (4) phosphorous removal; (5) laminar cooling: a relaxation time period is controlled to be 0-8 s, and a laminar cooling rate is 40-70° C./s; (6) coiling; (7) leveling; and (8) pickling. The complex-phase steel having high hole expansibility can simultaneously satisfy the requirements for hole expansibility and good plasticity.

1 . A complex-phase steel having high hole expansibility, wherein the microstructure of the complex-phase steel having high hole expansibility is ferrite+bainite, and mass percentages of chemical elements of the complex-phase steel having high hole expansibility are:
 C: 0.06-0.9%, Si: 0.05-0.5%, Al: 0.02-0.1%, Mn: 1.5-1.8%, Cr: 0.3-0.6%, Nb≤0.03%, Ti: 0.05-0.12%, and a balance of Fe and inevitable impurities.   
     
     
         2 . The complex-phase steel having high hole expansibility according to  claim 1 , wherein the Nb content is 0.015-0.03%. 
     
     
         3 . The complex-phase steel having high hole expansibility according to  claim 1 , wherein in the inevitable impurities, P≤0.03%, S≤0.02%, and N≤0.005%. 
     
     
         4 . The complex-phase steel having high hole expansibility according to  claim 1 , wherein the mass percentage contents of chemical elements satisfy one of the following formulas:
   0.2%≤Cr−0.5(Si+Al)≤0.42%;
     0.08%≤3.3Nb+Ti≤0.20%.
   
     
     
         5 . The complex-phase steel having high hole expansibility according to  claim 1 , wherein the microstructure has microalloy precipitates, which include (Ti, Nb)C and NbN. 
     
     
         6 . The complex-phase steel having high hole expansibility according to  claim 1 , wherein a tensile strength and the mass percentage contents of chemical elements satisfy:
 tensile strength Rm=343+789×C+170×Si+132×Mn+195×Cr+843×(Nb+Ti)−207×Al, wherein the dimension of the tensile strength Rm is Mpa.   
     
     
         7 . The complex-phase steel having high hole expansibility according to  claim 6 , wherein the complex-phase steel having high hole expansibility has a transverse tensile strength of ≥780Mpa, a yield strength of ≥700Mpa, an elongation rate A 50  of ≥5%, and a punching hole expansion rate of ≥50%. 
     
     
         8 . The complex-phase steel having high hole expansibility according to  claim 1 , wherein the complex-phase steel having high hole expansibility has a transverse tensile strength of ≥800Mpa, a yield strength of ≥730Mpa, an elongation rate A 50  of ≥15%, and a punching hole expansion rate of ≥70%. 
     
     
         9 . A method for manufacturing the complex-phase steel having high hole expansibility of  claim 1 , comprising the following steps:
 (1) Smelting and casting;   (2) Heating;   (3) Hot rolling: a total reduction rate is controlled to be ≥80%, a rough rolling is controlled to be rolled in a recrystallization area, and a rough rolling outlet temperature is 1020-1100° C.; a quasi constant speed rolling process is adopted in a finish rolling process, a finish rolling speed is controlled at 6-12 m/s, and a steel rolling acceleration is controlled to be ≤0.005 m/s 2 ; a finish rolling temperature is controlled at 840-900° C.;   (4) Phosphorus removal;   (5) Laminar cooling: a relaxation time is controlled at 0-8 s and a cooling rate of laminar cooling is controlled at 40-70° C./s;   (6) Coiling;   (7) Flattening;   (8) Pickling.   
     
     
         10 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein in step (2), a heating temperature is 1200-1260° C. 
     
     
         11 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein in step (4), a phosphorus removal pressure is controlled to be 15-35Mpa. 
     
     
         12 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein in step (6), a coiling temperature is 480-560° C. 
     
     
         13 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein in step (7), a flattening rolling force is controlled to be 100-800 tons, and a flattening elongation rate meets 1.5%. 
     
     
         14 . The complex-phase steel having high hole expansibility according to  claim 4 , wherein a tensile strength and the mass percentage contents of chemical elements satisfy: tensile strength Rm=343+789×C+170×Si+132×Mn+195×Cr+843×(Nb+Ti)−207×Al, wherein the dimension of the tensile strength Rm is MPa. 
     
     
         15 . The complex-phase steel having high hole expansibility according to  claim 5 , wherein a tensile strength and the mass percentage contents of chemical elements satisfy: tensile strength Rm=343+789×C+170×Si+132×Mn+195×Cr+843×(Nb+Ti)−207×Al, wherein the dimension of the tensile strength Rm is MPa. 
     
     
         16 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein the Nb content is 0.015-0.03%. 
     
     
         17 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein the mass percentage contents of chemical elements satisfy one of the following formulas: 0.2%≤Cr−0.5(Si+Al)≤0.42%, and 0.08%≤3.3Nb+Ti≤0.20%. 
     
     
         18 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , a tensile strength and the mass percentage contents of chemical elements satisfy: tensile strength Rm=343+789×C+170×Si+132×Mn+195×Cr+843×(Nb+Ti)−207×Al, wherein the dimension of the tensile strength Rm is MPa. 
     
     
         19 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein the complex-phase steel having high hole expansibility has a transverse tensile strength of ≥780 MPa, a yield strength of ≥700 MPa, an elongation rate A 50  of ≥15%, and a punching hole expansion rate of ≥50%. 
     
     
         20 . The method for manufacturing the complex-phase steel having high hole expansibility according to  claim 9 , wherein the complex-phase steel having high hole expansibility has a transverse tensile strength of ≥800 MPa, a yield strength of ≥730 MPa, an elongation rate A 50  of ≥15%, and a punching hole expansion rate of ≥70%.