Honda Motor Co Ltd's new "N-Box" light car features an increased usage ratio of high-tensile steel plates to reduce the mass of the body frame by about 15%.
In the case of the body frame of the previous model, the usage ratio of high-tensile steel plates with a tensile strength of 440MPa or higher is 60.3% (mass ratio), which can be broken down to 440MPa- (9.7%), 590MPa- (35.2%), 780MPa- (4.9%) and 980MPa-class (10.5%) steel plates. So, 590MPa-class plates are mainly used, and the ratio of 780MPa-class and higher-tensile-strength plates is only 15.4%.
On the other hand, in the case of the body frame of the new model, the usage ratio of 440MPa-class and higher-tensile-strength steel plates was increased to 64.8%, which can be broken down to 440MPa- (11.1%), 590MPa- (7.0%), 780MPa- (19.1%), 980MPa- (15.9%) and 1.2GPa-class (11.7%) steel plates.
Compared with the previous model, the usage ratio of 590MPa-class and lower-tensile-strength steel plates was decreased from 44.9% to 18.1%, and the usage ratio of 780MPa-class and higher-tensile-strength steel plates was drastically increased from 15.4% to 46.7%. Also, a 1.2GPa-class plate was employed for the outer panel of the center pillar, eliminating the reinforcement material inside it.
Because of the increase in the usage ratio of 780MPa-class and higher-tensile-strength steel plates, it became possible to reduce the weight of the body frame by about 15%.
Suzuki Motor Corp's "Wagon R" light car also uses a 1.2GPa-class high-tensile steel plate as a reinforcement material for its center pillar. Daihatsu Motor Co Ltd's "Mira e:S" uses 1.2GPa-class plates for its front side member, etc. In this away, 1.2GPa-class plates are being increasingly employed even for light cars.