In iron ore sintering, the bed structure transformation is caused by coalescence process occurring at flame front which determines sinter micro-structure. This study aims at how this can be affected by realistic thermal conditions. Analogue iron ore sinter mixes were sintered in an Infrared furnace and the micro-structure was studied by measuring porosity, pore size and circle factor. Pore property analysis results showed that increasing maximum temperature, lengthening holding time and slowing heating rate have led to a reduced porosity and more round pore structure. The mechanism of coalescence and densification in iron ore sintering has been explored for the purpose of understanding and quantifying how sinter micro-structure develops and is affected by flame front speed in sintering. The theoretical calculations and experimental results indicated that thermal conditions does have a large impact on microstructure development. Finally, proposed was a reasonable diagram for micro-structure development in sinter under realistic thermal conditions. (C) 2017 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.