Formation of Multiphase Microstructure in Steel 35CrMnSi by Intercritical Annealing – Quenching – Partitioning Heat Treatment

Low-alloy steel 35CrMnSi (0.37% C, 1.18% Cr, 0.85% Mn, 1.24% Si) is studied after an annealing – quenching – partitioning heat treatment. The steel with an initially martensitic structure is subjected to 15-min austenitizing in the intercritical temperature range of 790 – 810°C, quenching to a temperature below Ms (240°C), 100-sec holding at this temperature for redistributing the carbon between the phases, and water cooling. The mechanical properties of the steel are determined in tensile tests and the microstructure is studied by light and scanning electron microscopy. Fracture surfaces are investigated. A mode of annealing – quenching – partitioning heat treatment is suggested for creating an optimum microstructure raising the elongation without worsening the high strength properties of the steel.