Abstract
Ultra‐low carbons steels (ULCS) also known as interstitial free steels are widely used especially for automobile plates because of their excellent deep‐draw ability and low deformation resistance has been studied. The influence of alloy elements and nitriding on fatigue properties of ultra‐low carbon steel have been investigated using four types of specimens with same chemical composition (mass %) i.e. un‐nitrided specimens and nitrided specimens. For un‐nitrided specimens, fatigue strength at 1×107 cycles of material added with Niobium element is greater compared to the material added with titanium element, due to the effect of niobium on the grain refinement as Nb has an outstanding status retarding recrystallization during austenite processing via thermomechanical rolling [Niobium information, 17/98, CBMM/NPC, 1998]. The fatigue strength of nitrided specimens is generally higher than that of un‐nitrided specimens which is related to the hardness distribution of the specimens, the maximum hardness is recorded at the surface and decreased gradually toward the center of the specimen. Accordingly, the fatigue limit and strength of the nitrided specimens are determined by internal properties of the materials due to the influence of nitriding processes to the hardness properties at the surface as well as internal layer.