Producing As-Cast Ferritic Nodular Iron for Safety Applications

摘要

Although Si has a strong ferrite promoting effect that results on increases of impact energy it provokes ferrite embrittlement at low temperatures. Also increases of nodule numbers have a double effect, as it has a ferrite promoting effect due to the reduction of the distance for C diffusion and it results in reduction of the energy to fracture on the ductile region as the number of potential crack nucleation sites is increased (nodule/matrix interface). Considering these aspects the present study attempts to characterize the role of different levels of Si, in stream inoculation with FeSi and trace levels of Cu and Mn on impact properties of as-cast Ferritic Nodular Iron designed for safety applications where a minimum energy of 12J must be reached on Charpy impact test at―40℃ using U-notched 10x10x55 mm test pieces. The design of the experiments and the results analysis were done using Taguchi techniques. Two series of experiments were carried out and the effects on microstructure and static and dynamic mechanical properties were analyzed. The results presented reveal the strong influence of Si and in stream inoculation on materials properties. The Si content that optimized its effect was nearby 2.4%. In stream inoculation resulted in increase of the energy at low temperatures. The best results in the work frame with energies above 12J at ―40℃ were obtained with a Si content of 2.4%, in stream inoculation (≥0.1% FeSi) and low traces of pearlite promoting elements (≤ 0.13% Mn and ≤ 0.04% Cu).