Optimization of two-step ADI heat treatment of Cu-Ni ductile iron by means of thermal analysis methods

Based on the results of dilatometric investigations, parameters of standard single-step and multi-step (or non-isothermal) ADI heat treatment were optimised. The optimisation was based on analysis of the heat treatment processes simulated under laboratory conditions and used correlation between volume changes accompanying the decomposition of an ausferritic structure at 400-650°C and the amount of α acicular ferrite and γ_s (C) high-carbon austenite, the proportions of which determine the mechanical properties of alloys.
Optimisation of the complex heat treatment of nodular cast iron predicts mechanical properties of ADI, impossible to obtain through the standard, single-step heat treatment.
The results of mechanical tests have not confirmed the expectations; very good mechanical properties R_m and A₅ obtained by multi-step and non-isothermal treatments, were also obtained by standard heat treatment with appropriately selected parameters.

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