High plasticity hot-forming steel with oxidation resistance for automobiles and hot-forming process

Abstract

Provided are a high-plasticity hot-forming steel with oxidation resistance for automobiles and a hot-forming process thereof, and the hot-forming steel has chemical compositions in mass percentages as follows: C: 0.18%-0.28%, Si: ≤0.20%, Mn: 1.20%-2.0%, P: 0.030%-0.080%, S≤0.004%, Als: 0.02%-0.06%, Nb: 0.02%-0.06%, Ti: 0.025%-0.045%, V: 0.05%-0.15%, Cr: 0.5%-2.50%, Mo: 0.10%-0.30%, B: 0.0015%-0.0035%, N≤0.005%, the balance Fe and inevitable impurities. The hot-forming steel provided in the present invention has high oxidation resistance, high plasticity. The steel does not need atmosphere protection during hot forming, and does not need shot blasting treatment after hot forming.

1 . A high-plasticity hot-forming steel with oxidation resistance for automobiles, wherein the hot-forming steel has chemical compositions in mass percentages as follows:
 C: 0.18%-0.28%, Si: ≤0.20%, Mn: 1.20%-2.0%, P: 0.030%-0.080%, S≤0.004%, Als: 0.02%-0.06%, Nb: 0.02%-0.06%, Ti: 0.025%-0.045%, V: 0.05%-0.15%, Cr: 0.5%-2.50%, Mo: 0.10%-0.30%, B: 0.0015%-0.0035%, N≤0.005%, the balance Fe and inevitable impurities.   
     
     
         2 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein a microstructure of the hot-forming steel includes a ferrite, a martensite and a retained austenite. 
     
     
         3 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 2 , wherein the ferrite has a volume fraction of 5%-12%, the martensite has a volume fraction of 78%-89%, and the retained austenite has a volume fraction of 6%-10%. 
     
     
         4 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein a tensile strength of the hot-forming steel is 1400 MPa-1700 MPa. 
     
     
         5 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein an oxidation resistance rate of the hot-forming steel is <0.1 g/(m 2 ·h). 
     
     
         6 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein a yield strength of the hot-forming steel is 900 MPa-1450 MPa. 
     
     
         7 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein an elongation of the hot-forming steel is ≥18.0%. 
     
     
         8 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein a surface of the hot-forming steel is not completely decarburized with a thickness of decarburized layer ≤15 μm. 
     
     
         9 . The high-plasticity hot-forming steel with oxidation resistance for automobiles according to  claim 1 , wherein the thickness of the hot-forming steel is 0.8 mm-12.0 mm; 
     
     
         10 . A hot-forming process of the high-plasticity hot-forming steel with oxidation resistance for automobiles, comprising following steps:
 (1) placing a hot-forming substrate containing the compositions according to  claim 1  into a heating furnace at a temperature of A C3 -A C3 +15° C. for heating and heat preservation for a period of 180 s-300 s; and   (2) taking the heated hot-forming steel out of the heating furnace for air cooling to a temperature of A r3  and staying for 5 s-8 s before being put into a hot-forming mold for deformation and cooling, at a cooling rate of ≥18° C./s, performing the pressure holding for 40 s-80 s after cooling to 180° C.-250° C., and taking out the formed parts for air cooling to room temperature after pressure holding to obtain the hot-forming steel.