Investigation of Surface Finish on Orthogonally Machined Heat-Treated Nodular Cast Iron

Abstract

This study investigated the influence of annealing heat treatment temperature on the surface roughness characteristics of orthogonally machined nodular cast iron (NCI). NCI, known for its excellent mechanical properties, is widely used in various industries. The surface finish of machined components impacts their performance and longevity. Annealing, a critical heat treatment process, was employed to modify the microstructure of NCI, enhancing its machinability. This research aimed to establish the relationship between annealing temperature and the resulting surface roughness after orthogonal machining. The methodology involved annealing NCI samples at different temperatures (750°C - 950°C), followed by orthogonal machining at different cutting speeds (340 rpm - 1400 rpm). Surface finish was quantified using average surface roughness. The hardness and microstructural changes were characterized using a Vickers hardness tester and metallographic techniques. The results showed that increasing annealing temperature improved the surface finish with an optimal surface roughness of 2.62 µm at 900°C. Cutting speed also significantly affected the surface roughness, with higher speeds resulting in smoother surfaces up to a certain threshold. However, excessive cutting speeds increased roughness due to thermal effects, tool wear, and machine vibration. The optimal combination of annealing temperature and cutting speed was identified as 900°C and 1150 rpm, respectively, yielding an average surface roughness value of 2.62 µm. The annealing heat treatment reduced the hardness and improved machinability. Optimizing the annealing process led to a significant improvement in the surface finish of orthogonally machined NCI components. This research provides valuable insights into the machinability of annealed NCI and offers practical guidelines for enhancing manufacturing processes, ultimately improving product quality and performance.