Optimization of EDM parameters for heat-treated Hadfield steel considering microstructural and crystallographic changes
REVIEWS ON ADVANCED MATERIALS SCIENCE, cilt.65, sa.1, ss.1-18, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 65 Sayı: 1
- Basım Tarihi: 2026
- Doi Numarası: 10.1515/rams-2025-0292
- Dergi Adı: REVIEWS ON ADVANCED MATERIALS SCIENCE
- Derginin Tarandığı İndeksler: Academic Search Ultimate (EBSCO), Scopus, Science Citation Index Expanded (SCI-EXPANDED), Compendex, INSPEC, Directory of Open Access Journals
- Sayfa Sayıları: ss.1-18
- Gazi Üniversitesi Adresli: Evet
Özet
Heat treatment procedures applied or designed to improve the machinability performance of Hadfield steels are very important. Therefore, this study consists of two main stages. In the first stage of the investigation, cast Hadfield steel was austenitised at 1,050 °C for holding times of 1 h and 5 h, followed by rapid quenching to retain the austenitic matrix. The effects of different austenitisation durations on microstructural evolution, crystallographic transformations, and the machinability characteristics of the alloy were systematically evaluated. In the second stage, the machinability characteristics of the materials were investigated using plunge electrical discharge machining (EDM), which is classified as a non-conventional machining process suitable for difficult-to-machine alloys. The experimental design incorporated three principal machining parameters: discharge current, pulse-on time, and reference voltage. For this purpose, three discharge current levels (4.5, 9, and 18 A), three pulse-on durations (50, 100, and 200 µs), and three reference voltage values (40, 45, and 50 V) were employed. According to the experimental results obtained, the most ideal processing parameter was determined by the Taguchi-based Gray Relational Analysis method, which is widely used in multiple output results. The results indicated that the optimal machining condition for the H1 sample was obtained at 4.5 A discharge current, 200 µs pulse-on time and 40 V reference voltage (A1B1C3D1). XRD analyses revealed the formation of ε and α′ martensite phases on the EDM-processed surfaces, indicating deformation-induced phase transformations during machining. Dislocation density values calculated using the Williamson–Hall method were determined as 6.76 × 1015 m−2 for the H1 sample and 10.18 × 1015 m−2 for the H5 sample. Microstructural observations also revealed the presence of recast layers, heat-affected zones and deformation twins caused by intense thermal cycles during EDM processing. The findings demonstrate that EDM-induced thermal effects significantly influence the microstructural evolution and machining performance of Hadfield steel, and that the Taguchi–GRA approach provides an effective method for multi-response optimization of EDM parameters.