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Effect of silicon content on microstructures and mechanical properties of spheroidal graphite cast iron grade EN-GJS-400-18-LT

An investigation on speroidal cast iron grade EN-GJS-400-18-LT was performed on the shop floor in real conditions. The relationship between production parameters and realized mechanical properties was determined by examination of chemical compositions of the treated melts, inspection of microstructure in as-cast and heat treated conditions and finally by assessment of impact energy, hardness and tensile properties of heats. The presence of manganese and other pearlite forming elements, and low nodule count prevented the formation of as-cast fully ferritic matrix in the samples even with silicon content over 3.0 %. Increase in silicon content, in examined range from 2.0 % to 3.0 %, cause a mildly reduce of hardness and tensile strength in as-cast samples, yield strength stands unchanged, while elongations values progressively rose. The effect of silicon content variation on tensile strength and hardness in heat treated samples is quite opposite, which can be attributed to ferrite strengthening by silicon. Probability of attaining the specified values of impact toughness, tested at -20°C, was increased by ferritizing annealing treatment of the samples and limiting of final silicon content in the nodular cast iron below 2.5 %.

Speroidal cast iron; Silicon effect; Microstructure; Mechanical properties

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