Evaluation of microstructures and mechanical properties of chromized steels with different carbon contents

Chromization process is a method for developing a surface coating providing hardness, wear and corrosion resistance. Three carbon steels, AISI 1020, 1045 and 1095 with 0.20, 0.45 and 1.0 wt.% carbon contents, respectively, were chromized with pack cementation process at 950 °C for 1, 4 and 9 h. The primary phase on the chromized surface is (Cr,Fe)2N1−x and the rest is (Cr,Fe)23C6 phase. The thickness of the chromized layer obeys the parabolic rate law: X=K√t and increases with chromization time and carbon contents in the matrix. The parabolic rate constants K are evaluated to be 4.04, 7.25 and 8.43 μm/√h for AISI 1020, 1045 and 1095, respectively. The nanohardness of the chromized layer is 18 GPa, which is attributed to the (Cr,Fe)2N1−x phase on the surface. Values of lower and upper critical loads of the chromized AISI 1020 steel decrease with increasing chromization time, whereas the increasing critical loads with chromizing time are observed on the chromized AISI 1045 and 1095 steels. High critical loads and sufficient adhesion properties are achieved due to the thicker (Cr,Fe)2N1−x phase on the chromized surface.