High hole expansion steel and method for manufacturing therefor

Abstract

The present invention provides a steel and a method for manufacturing therefor. The steel comprises the following components in the percentage by mass: C: 0.01-0.10%; Si: ≤0.2%; Mn: 0.5-2.0%; P: ≤0.02%; S: ≤0.003%; Al: 0.01-0.08%; N: ≤0.004%; V: 0.10-0.50%; O: ≤0.003%; and the balance of Fe and inevitable impurities. The steel of the present invention can be applied in passenger vehicle chassis parts needing high strength and thickness reduction such as a control arm and a subframe.

1 . A steel, comprising the following components in percentage by mass:
 C: 0.01-0.10%; Si≤0.2%; Mn: 0.5-2.0%: P≤0.02%; S≤0.003%; Al: 0.01-0.08%; N≤0.004%; V: 0.10-0.50%: O≤0.003%; and the balance of Fe and inevitable impurities.   
     
     
         2 . The steel as claimed in  claim 1 , characterized in that, the steel further comprises 0.05-0.2%, preferably 0.08-0.15%, more preferably 0.08-0.10% of Ti in percentage by mass. 
     
     
         3 . The steel as claimed in  claim 1 , characterized in that, the steel further comprises one or more components selected from Nb≤0.1%, Cu≤0.5%, Ni≤0.5%, Cr≤0.5%, and B≤0.002% in percentage by mass. 
     
     
         4 . The steel as claimed in  claim 3 , characterized in that, the steel further comprises 0.1-0.5%, preferably 0.20-0.40%, more preferably 0.2-0.3% of Mo in percentage by mass. 
     
     
         5 . The steel as claimed in  claim 1 , characterized in that, the components of the steel satisfy one or more of the following: C: 0.03-0.07%; Si≤0.10%: Mn: 0.8-1.6%: S≤0.0018%; Al: 0.02-0.05%; N≤0.003%; O≤0.002%. 
     
     
         6 . The steel as claimed in  claim 3 , characterized in that, the components of the steel satisfy one or more of the following: Nb≤0.06%, Cu≤0.3%, Ni≤0.3%, Cr≤0.3%, and B≤0.001%. 
     
     
         7 . The steel as claimed in  claim 1 , characterized in that, the steel has a structure of bainite and nano-precipitated VC in bainite. 
     
     
         8 . The steel as claimed in  claim 2 , characterized in that, the steel has a structure of ferrite and bainite, wherein the ferrite contains nano-TiC and the bainite contains nano-VC. 
     
     
         9 . The steel as claimed in  claim 1 , characterized in that, the steel has a yield strength of 500 MPa or more, a tensile strength of 590 MPa or more, preferably 780 MPa or more, and a transverse elongation A50 of 14% or more and 30% or less. 
     
     
         10 . A method for manufacturing the steel of  claim 1 , including the following steps:
 1) Smelting and casting   The composition of  claim 1  is smelted by a converter or an electric furnace, secondary refined by a vacuum furnace, and casted into billets or ingots:   2) Reheating the billets or ingots   Heating temperature≥1100° C., holding time: 1-2 hours;   3) Hot rolling and cooling.   
     
     
         11 . The method as claimed in  claim 10 , characterized in that in step 3), an initial rolling temperature is 1000-1100° C., and rough rolling of 3-5 passes is carried out under high pressure at 950° C. or more to a cumulative deformation of ≥50%, then an intermediate billet is air-cooled or water-cooled to 900-950° C., and finishing rolling of 7 passes is carried out to a cumulative deformation of ≥70%, completing the finishing rolling between 800-900° C. and obtaining a steel strip, thereafter, the steel strip is water-cooled to 400-550° C. at a cooling rate of ≥10° C./s and coiled, then slowly cooling to room temperature at a cooling rate of ≤20° C./s, obtaining a hot-rolled steel strip. 
     
     
         12 . The method as claimed in  claim 10 , characterized in that in step 3), the initial rolling temperature of the hot rolling is 1050-1150° C., and rough rolling of 3-5 passes is carried out under high pressure at 1050° C. or more to a cumulative deformation of ≥50%, then an intermediate billet is heated to 950-1000° C., and finishing rolling of 3-7 passes are carried out to a cumulative deformation of ≥70%, and the finishing rolling temperature is 800-950° C., obtaining a steel strip:
 wherein the cooling is staged cooling, and after finishing rolling, the steel strip is water-cooled to 600-750° C. at a cooling rate of ≥30° C./s, then after air cooling for 1-10 seconds, the steel strip is cooled to 400-550° C. at a cooling rate of ≥10° C./s and coiled, then cooling to room temperature at a cooling rate of ≤20° C./h, obtaining a hot-rolled strip steel. 
 
     
     
         13 . The method as claimed in  claim 11 , characterized in that, the method further includes step 4) Pickling, wherein a pickling operating speed of the hot-rolled strip steel is 30-140 m/min, preferably 30-120 m/min, a pickling temperature is 75-85° C., a straightening rate is ≤3%, rinsing is carried out at 35-50° C., and surface drying and oiling are carried out at 120-140° C. 
     
     
         14 . The steel as claimed in  claim 2 , characterized in that, the steel further comprises one or more components selected from Nb≤0.1%, Cu≤0.5%, Ni≤0.5%, Cr≤0.5%, and B≤0.002% in percentage by mass. 
     
     
         15 . The steel as claimed in  claim 2 , characterized in that, the components of the steel satisfy one or more of the following: C: 0.03-0.07%; Si≤0. 10%: Mn: 0.8-1.6%; S≤0.0018%: Al: 0.02-0.05%; N≤0.003%; O≤0.002%. 
     
     
         16 . The method as claimed in  claim 12 , characterized in that, the method further includes step 4) Pickling, wherein a pickling operating speed of the hot-rolled strip steel is 30-140 m/min, preferably 30-120 m/min, a pickling temperature is 75-85° C., a straightening rate is ≤3%, rinsing is carried out at 35-50° C., and surface drying and oiling are carried out at 120-140° C. 
     
     
         17 . The method as claimed in  claim 12 , characterized in that, the steel further comprises 0.05-0.2%, preferably 0.08-0.15%, more preferably 0.08-0.10% of Ti in percentage by mass. 
     
     
         18 . The method as claimed in  claim 12 , characterized in that, the steel further comprises one or more components selected from Nb≤0.1%, Cu≤0.5%, Ni≤0.5%, Cr≤0.5%, and B≤0.002% in percentage by mass. 
     
     
         19 . The method as claimed in  claim 12 , characterized in that, the steel has a structure of bainite and nano-precipitated VC in bainite. 
     
     
         20 . The method as claimed in  claim 12 , characterized in that, the steel has a structure of ferrite and bainite, wherein the ferrite contains nano-TiC and the bainite contains nano-VC.