Study the impact of post treatment on pack borided AISI 1040 steel

Present study systematically investigated the effects of different post-treatment methods air cooling, austempering and cryogenic treatment on the microstructure and mechanical properties of pack-borided AISI 1040 issteel. A Taguchi L9 (3³) orthogonal array was employed, considering boriding temperature (850, 925, and 1000°C), holding time (3, 6 and 9 h) and post-treatment type as process parameters. The results demonstrate that cryogenic treatment post-boriding yielded a superior combination of properties, achieving a maximum surface hardness of 1683Hv0.1 and an ultimate tensile strength of 817 MPa which represents an increase of over 100% compared to the lowest strength values observed in austempered samples (55.6% contribution). Analysis of Variance (ANOVA) identified that the post-treatment method had the most significant effect on the tensile strength (71.7% contribution) while the boriding temperature had the most significant effect on the surface hardness. Microstructural analysis via Scanning Electron Microscopy (SEM) revealed that the development of a saw-tooth morphology conformed the formation of iron boride and needle like structure revealed the formation of martensite in Cryo-treated samples. Stress–strain diagram showed that transition from ductile to brittle fracture behaviour. These findings provide a definitive guideline for selecting post-boriding treatments to tailor the performance of components for specific applications, balancing hardness and strength.