High-speed turning of AISI 304 stainless steel is limited by rapid tool wear driven by thermal accumulation and tribological instability. This study compares five cooling/lubrication strategies (dry, flood cooling, MQL, internally cooled tools—ICT, and ICT + MQL) under a fixed severe cutting regime (Vc = 400 m/min, f = 0.1 mm/rev, ap = 0.2 mm) and develops a low-complexity tool end-of-life predictor using cutting power as the sole monitoring signal. Dry machining produced the highest cutting forces 26.7 N), whereas lubricated/cooled conditions showed statistically similar force levels (≈11 6 – 118 N). Cutting force and derived power increased monotonically with wear, supporting power as an indirect tool-state indicator. A binary XGBoost classifier trained on statistical and trend descriptors of one-second power windows achieved accuracies of 96.5% (training), 95.9% (test), and 93.3% (validation) with AUC–ROC values of 0.988, 0.993, and 0.959, respectively, despite moderate class imbalance (≈85 % healthy/15% worn). SHAP analysis identified average power and distributional descriptors (skewness and amplitude ratios) as dominant predictors, providing interpretable links between signal statistics and wear progression. The results demonstrate that reliable end-of-life detection can be achieved using a single energetic signal across heterogeneous cooling environments, supporting scalable monitoring compatible with low-fluid and closed-loop cooling strategies.

Residual stress limits dimensional accuracy and service performance in the Laser-based Directed Energy Deposition (DED-LB) of 316L stainless steel. Process-integrated mitigation was demonstrated using off-axis (oblique-incidence) laser delivery. A 20 mm-thick multilayer build was characterized by neutron diffraction, neutron tomography, electron backscatter diffraction (EBSD), and Vickers macrohardness mapping. Residual stresses were confined to ±100 MPa, with interior tension and surface-adjacent compression; neutron tomography measured ∼0.001% porosity for pores ≥50 μm. Hardness of 150–230 HV20 colocated with compressive zones, and EBSD showed elongated columnar grains with position-dependent texture. The reduced stress state is attributed to the enlarged projected footprint and lower peak irradiance of off-axis delivery, which spread heat laterally, reduce the thermal gradient (G) and cooling rate (T˙), and favor conduction-mode melting. These results establish off-axis DED-LB as a route to in situ residual-stress control and microstructural tailoring while maintaining negligible resolved porosity in additively manufactured 316L components. The bulk, through-thickness maps and datasets provide component-scale validation to calibrate models and support process qualification.

Post-build tempering response was investigated for AISI Type 431 martensitic stainless steel produced via laser-based Directed Energy Deposition (DED-LB) at 350-650 °C. Phase evolution and stored strain were quantified using electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) with Rietveld refinement, then correlated with hardness and build-oriented tensile properties. A wrought AISI Type 431 hardened-and-tempered bar served as a benchmark reference. The as-deposited DED-LB microstructure comprised highly strained lath martensite containing δ-ferrite pockets, retained austenite, and Si-Mn-rich oxide inclusions inherited from the water-atomized feedstock, resulting in inherently brittle mechanical behavior. A low-temperature austenite reversion window was identified, with austenite peaking at approximately 6.7% following tempering at 350 °C and preferentially nucleating at δ-ferrite/martensite interfaces. This condition produced a substantial ductility increase, with elongation rising from 1.2% in the as-deposited state to 10.2% while sustaining tensile strength above 1180 MPa. Tempering at 450 °C induced secondary hardening, achieving a peak hardness of 606 HV5, accompanied by reduced elongation as austenite content declined. Above 550 °C, austenite decreased below 1%, transitioning toward a predominantly tempered martensitic microstructure and wrought-like ductility. The ductility evolution across the tempering series is governed by matrix recovery rather than inclusion content. The austenitization-free, single-step tempering route provides a systematic and industry-relevant thermal processing strategy for tailoring strength–ductility trade-offs and mitigating build-induced residual strain sensitivity in additively manufactured martensitic stainless steels. Graphical Abstract