Development of Nano-scale Precipitation Strengthened Hot-rolled 590MPa Grade Wheel Steel

摘要

In order to promote the production of lightweight automobiles and enhance the strength grade of the automobile wheel steel, a nano-scale precipitation strengthened hot-rolled 590MPa grade wheel steel was developed to replace the Q235 steel, which was originally use for the wheel. The new wheel steel type was based on a C-Mn steel composition, microalloyed with Nb, V and Ti, thus making full use of the strengthening from both grain refinement as well as nano-scale precipitation. The microstructure of the wheel steel was composed of fine-grained ferrite and pearlite and carbides distributed along the ferrite grain boundaries. The yield and tensile strengths of the strip were about 550 MPa and 620 MPa, respectively. The value of hole expansion rate was 90%. The strip has shown high low temperature impact toughness and cold formability. The strengthening mechanisms of the strip were mainly governed by grain refinement and nano-scale precipitation (Nb,V,Ti)C, and the amount of the contribution from precipitation strengthening alone was about 215 MPa. The finishing rolling start temperature was about 950℃ and the finish rolling temperature was between 790～830℃. Coiling temperature of 650℃ gave the best combination of mechanical properties.