A study on age hardening in cast Fe-Mn-Al-Si-C alloys

Phase transformations in a group of cast and solution treated (at 1100° C) Fe-Mn-Al-Si-C alloys during isothermal ageing have been investigated as a function of (a) ageing temperature (500 to 800° C), (b) aluminium (5 to 10%) and carbon (0.27 to 0.9%) contents for fixed manganese ( 30%) and silicon ( 1.5%) levels. Irrespective of the ageing temperature and carbon content, 5% Al alloys do not undergo appreciable ageing. Ageing tendency increases with increase in aluminium and carbon contents. Hardening is caused by the precipitation of Al(Fe, Mn)C _x phase inside the austenite grain and Mn₁₂Si₇Al₅ phase at the grain boundaries. The sequence of precipitation of the phases depends on the ageing temperature and composition. Cold working by rolling, after homogenization at 1100° C, accelerates ageing.