Comparative analyses of the mechanical and microstructural properties of screws manufactured by cutting, extrusion and deep rolling techniques

Abstract

This article evaluates the influence of different fabrication techniques, extrusion (ET), cutting (CT), and deep rolling techniques (DRT) on the microstructural and mechanical behavior of medium carbon steel screws for fastening applications. It involves mechanical, microstructural, and compositional analyses of an identical medium-carbon steel composed of chromium (Cr), vanadium (V), niobium (Nb), silicon (Si), manganese (Mn), and carbon (C). It also considers the effects of fabrication method on the fatigue performance, hardness, and fracture characteristics of the screws. The analytical studies considered constitutive equations; whereas, the numerical approaches used finite element analyses (FEA) to corroborate the fatigue stress distributions in the threads of the screws manufactured by ET, CT and DRT. The results showed that the microstructures had area fractions of ∼0.03, ∼0.20 and ∼0.23 for DRT, CT, and ET, respectively, owing to the respective phase structures high in carbon in the steels. The DRT significantly reduced martensite area fraction and refined grain structure, leading to improved ductility and fatigue performance. Mechanical testing showed that DRT screws had the highest fatigue limit (109 MPa), while CT screws had the greatest surface hardness (∼467 HV). The FEA showed a DRT sample with improved fracture toughness (∼300 MPa√mm) and a slower rate of crack growth. The stress distributions and crack growth under loading in the FEA analyses corroborate the experimental trends. The results suggest that the DRT is particularly beneficial for screw components subjected to cyclic stresses and fatigue-critical applications.