<p>This study investigates the industrial application of Fe-0.15C kiln steel in production line of cement manufacturing industries. The two different grades of kiln steel Fe-0.15 and Fe-0.21 named A and B respectively were examined. The detailed microstructural investigation was performed with the help of optical microscopy, electron backscattered diffraction (EBSD) and field emission scanning electron microscopy (FE-SEM). The phase diagram for A and B was plotted by the Thermo-Calc software. Two methods had been used that can estimate material fracture allowable; (1) facture toughness determination (FTD) and (2) fatigue crack growth rate (FCG) that can generate the whole regions of da/dN curve. The impact of heat treatment for tailoring microstructure was studied, and the research revealed significant improvements in hardness by 129.18%, tensile strength by 303.72%, fracture toughness improvement improves fatigue cycle by 656.55%, and fatigue threshold was improved by 47.12%. The maximum fracture toughness was 613.50&#xa0;KJ/m² after modifications in initial samples compared to minimum of 395.23&#xa0;KJ/m². The present phase’s ferrite, cementite and graphite, along with the pearlite colonies in the microstructure governed the improved properties of kiln steel. Considering all these factors, the crack propagation mechanism for kiln steel was proposed in this study.</p>