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)Cx 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. © 1990 Chapman and Hall Ltd.