700MPa Grade Steel for Heavy-duty Truck Development and Carriage Lightweight Design

摘要

In order to realize the weight reduction of the carriage of heavy-duty truck, the 700 MPa hot-rolled high-strength C-Mn steel plate was successfully developed on 1750 mm hot-strip mills to replace the Q345 steel plate which was originally used for carriage. The microstructure of the plate was composed of fine-grained ferrite, carbides distributed along the ferrite grain boundaries, a little pearlite with 40～50 nm lamellar spacing and a mount of bainite. The yield and tensile strengths of the plate were about 680 MPa and 740 MPa, respectively. The value of n, r_m and hole expansion rate (λ) were 0.12, 0.8 and 60%, respectively. The plate has great low temperature impact toughness and weldability. The strengthening mechanisms of the plate were mainly governed by fine-grained strengthening and (Ti,Nb)C nano-precipitates strengthening. If the carriage of heavy-duty truck was constructed by new plate, the weight could reduce 20% due to the thickness reduction. For further reduction of the weight of the carriage, the optimization design was carried out by finite element method. Then, the weight of the carriage could be reduced 12%.