Design of air-cooled bainitic microalloyed steel for a heavy truck front axle beam

On the basis of the relationship between mechanical properties, chemical composition and cooling rates during the bainitic transformation, both composition design method and empirical formulas are proposed to develop an air-cooled bainitic microalloyed steel for the front axle beam in heavy trucks. Based on the given effective thickness, the desired mechanical properties and microstructure, and low cost, the type and content of alloying elements can be predicted by these formulas. Taking a 600-MPa yield strength class front axle beam as an example, the design process and associated calculations are discussed in detail. The experimental results show that the chemical composition of the designed steel with 0.20% C, 1.80% Mn, 1.0% Si, 0.10% V, 0.003% B and 0.03% P accords well with the design specification. Also, the mechanical properties (σy ≈ 630 MPa, σy/σt ≈ 0.64, δ ≈ 14%, ψ ≈ 43% and HRC ≈ 28) and the fatigue life (over 106 number of times) are in accordance with the design prediction.