The Effects of Alloying Elements, Cr, Si, and Transformation Temperature on the Microstructures and Tensile Properties of Hyper-Eutectoid Steels

The effects of alloying elements, especially Cr and Si, and transformation temperature on the microstructures and mechanical properties of hyper-eutectoid steels were investigated. Increases in Si and Cr changed the morphology of cementite in upper bainite, while the morphology of pearlite seemed to be unchanged by the amount of alloying elements, except for variation in interlamellar spacing. Increasing Si and Cr content also caused increases in tensile strength and a reduction of area of the steels containing pearlitic microstructure, while decreasing tensile strength and reduction of area in steels transformed into upper bainitic microstructure. The tensile strength of steels consisting of pearlite, upper bainite and a mixture of pearlite and upper bainite, can be expressed with the equation σ= (σ_po+k_p·λ_p^-1/2)·V_p+(σ_ubo+k_ub·λ_ub^-1/2)·V_ub. The values calculated using the above equation coincided well with the measured tensile strength of hyper-eutectoid steels containing Cr and Si.