Abstract: The influence of silicon content on microstructure and mechanical properties of heat-resistant nodular cast iron at room temperature and high temperature was studied by means of optical microscope, scanning electron microscope and electronic universal tensile testing machine. The test results show that with the increase of silicon content, the roundness of graphite gradually decreases. When the silicon content(mass fraction, similarly hereinafter) reaches 3.8%, fragmented graphite begins to appear in the matrix, and the spheroidization grade is grade 3. As the silicon content increases from 2.8% to 4.8%, the pearlite content decreases from 51.06% to 8.65%. With the increase of silicon content, the room temperature tensile strength first increases and then decreases, and the elongation decreases gradually. When the silicon content is 3.8%, the tensile strength is 726 MPa and the elongation is 1.6%. With the increase of silicon content, the high temperature tensile strength gradually increases and the elongation decreases gradually. When the silicon content is 4.8%, the tensile strength is 532 MPa and the elongation is 6%. A large number of cleavage planes and river patterns appear in the tensile fracture at room temperature, and the form is brittle fracture. Dimples and tear edges appear in the high temperature tensile fracture, and the tensile fracture form is ductile-brittle mixed fracture.

Key words: heat-resistant nodular cast iron, microstructure, room-temperature properties, high-temperature properties, fracture morphology