980 mpa-grade bainite high hole expansion steel and manufacturing method therefor

Abstract

Disclosed are a 980 MPa-grade bainite high hole expansion steel and a manufacturing method therefor. The steel contains the following chemical components in percentages by weight: 0.05-0.10% of C, 0.5-2.0% of Si, 1.0-2.0% of Mn, P≤0.02%, S≤0.003%, 0.02-0.08% of Al, N≤0.004%, Mo≥0.1%, 0.01-0.05% of Ti, Cr≤0.5%, B≤0.002%, O≤0.0030%, and the balance of Fe and other inevitable impurities. The high hole expansion steel of the present invention has a yield strength of ≥800 MPa and a tensile strength of ≥980 MPa, has a good elongation rate (the transverse A 50 being ≥11%) and hole expansion performance (the hole expansion ratio being ≥40%), and can be applied to a position on a chassis part of a passenger car, such as a control arm and a vice frame, where high strength and thinning are required.

1 . A 980 MPa grade bainite high hole expansion steel having a chemical composition based on weight percentage of: C 0.05-0.10%, Si 0.5-2.0%, Mn 1.0%-2.0%, P≤0.02%, S≤0.003%, Al 0.02-0.08%, N≤0.004%, Mo≥0.1%, Ti 0.01-0.05%, Cr≤0.5%, B≤0.002%, O≤0.0030%, and a balance of Fe and other unavoidable impurities, wherein the high hole expansion steel has a microstructure of bainite+residual austenite. 
     
     
         2 . The 980 MPa grade bainite high hole expansion steel according to  claim 1  further comprising one or more elements of Nb≤0.06%, V≤0.05%, Cu≤0.5%, Ni≤0.5% and C≤a0.005%. 
     
     
         3 . The 980 MPa grade bainite high hole expansion steel according to  claim 1  having a chemical composition based on weight percentage of: C 0.05-0.10%, Si 0.5-2.0%, Mn 1.0%-2.0%, P≤0.02%, S≤0.003%, Al 0.02-0.08%, N≤0.004%, Mo≥0.1%, Ti 0.01-0.05%, Cr≤0.5%, B≤0.002%, O≤0.0030%, Nb≤0.06%, V≤0.05%, Cu≤0.5%, Ni≤0.5%, Ca≤0.005%, and a balance of Fe and other unavoidable impurities, wherein the 980 MPa grade bainite high hole expansion steel comprises at least one of Nb, V, Cu, Ni and Ca. 
     
     
         4 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of C is 0.06-0.08%. 
     
     
         5 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of Si is 0.8-1.6%. 
     
     
         6 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of Mn is 1.4-1.8%. 
     
     
         7 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of S is controlled at 0.0015% or less, and/or the content of N is controlled at 0.003% or less. 
     
     
         8 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of Al is 0.02-0.05%. 
     
     
         9 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of Ti is 0.01-0.03%. 
     
     
         10 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of Mo is ≥0.15%. 
     
     
         11 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the content of Cr is 0.2-0.4%, and/or the content of B is 0.0005-0.0015%, and/or the content of Mo is 0.1-0.55%. 
     
     
         12 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the high hole expansion steel has a yield strength of ≥800 MPa, a tensile strength of ≥980 MPa, a traverse elongation A 50 ≥10%, and a hole expansion ratio of ≥40%. 
     
     
         13 . The 980 MPa grade bainite high hole expansion steel according to  claim 1 , wherein the high hole expansion steel has yield strength of ≥850 MPa, a tensile strength of ≥1000 MPa, a traverse elongation A 50 ≥11%, and a hole expansion ratio of ≥50%. 
     
     
         14 . A manufacture method of the 980 MPa grade bainite high hole expansion steel according to  claim 1 , which comprises the following steps:
 1) Smelting and casting:   Smelting the above composition according to  claim 1  by a converter or an electric furnace, secondary refining by a vacuum furnace, and then casting it into a blank or ingot;   2 ) Re-heating the blank or ingot at the heating temperature of 1100-1200° C., holding for 1-2 hours;   3) Hot rolling:   the blank or ingot is hot rolled at an initial rolling temperature of 950˜1100° C. and has a cumulative deformation of ≥50%, after 3-5 passes of heavy reduction rolling at ≥950° C.; the intermediate blanket is then held till 920-950° C., then subjected to final 3-7 passes of rolling with cumulative deformation of ≥70% the final rolling temperature is 800-920° C.;   4) Cooling:   first, air-cooling for 0-10 s is carried out, and then the strip steel is water cooled to 400-550° C. at a cooling speed of ≥0° C./s, for coiling, and naturally cooled to room temperature after coiling;   5) Pickling   the running speed of pickling of the strip steel is adjusted in the range of 30˜100m/min, the pickling temperature is controlled at 75˜85° C., and the tensile levelling rate is controlled at ≥2%, and the strip steel is rinsed, and the strip steel surface is dried and oiled at the temperature of 120-140° C.   
     
     
         15 . The manufacture method of the 980 MPa grade bainite high hole expansion steel according to  claim 14 , wherein after step 5) of pickling, the strip steel is rinsed at a temperature of 35-50° C., and the strip steel surface is dried and oiled at 120-140° C. 
     
     
         16 . The 980 MPa grade bainite high hole expansion steel according to  claim 2 , wherein the content of Nb, V is ≤0.03%, respectively; the content of Cu, Ni is ≤0.3%, respectively; and/or the content of Ca is ≤0.002%. 
     
     
         17 . The manufacture method of the 980 MPa grade bainite high hole expansion steel according to  claim 14 , wherein the 980 MPa grade bainite high hole expansion steel has a chemical composition based on weight percentage of: C 0.05-0.10%, Si 0.5-2.0%, Mn 1.0%-2.0%, P≤0.02%, S≤0.003%, Al 0.02-0.08%, N≤0.004%, Mo≥0.1%, Ti 0.01-0.05%, Cr≤0.5%, B≤0.002%, CO≤0.0030%, Nb≤0.06%, V≤0.05%, Cu≤0.5%, Ni≤0.5%, Ca≤0.005%, and a balance of Fe and other unavoidable impurities, wherein the 980 MPa grade bainite high hole expansion steel comprises at least one of Nb, V, Cu, Ni and Ca. 
     
     
         18 . The manufacture method of the 980 MPa grade bainite high hole expansion steel according to  claim 14 , wherein in the composition of the 980 MPa grade bainite high hole expansion steel:
 the content of C is 0.06-0.08%;   the content of Si is 0.8-1.6%;   the content of Mn is 1.4-1.8%;   the content of S is controlled at 0.0015% or less, and/or the content of N is controlled at 0.003% or less;   the content of Al is 0.02-0.05%;   the content of Ti is 0.01-0.03%;   the content of Mo is ≥0.15%; and/or   the content of Cr is 0.2-0.4%, and/or the content of B is 0.0005-0.0015%, and/or the content of Mo is 0.1-0.55%.   
     
     
         19 . The manufacture method of the 980 MPa grade bainite high hole expansion steel according to  claim 14 , wherein the high hole expansion steel has a yield strength of ≥800 MPa, a tensile strength of ≥980 MPa, a traverse elongation A 50 ≥10%, and a hole expansion ratio of ≥40%. 
     
     
         20 . The manufacture method of the 980 MPa grade bainite high hole expansion steel according to  claim 14 , wherein:
 in step 3), the blank or ingot is hot rolled at an initial rolling temperature of 950-1100° C. and has a cumulative deformation of ≥60%; the intermediate blanket is subjected to final 3-7 passes of rolling with cumulative deformation of ≥85%;   in step 4), the cooling speed is ≥30° C./s.