Hard Nanostructured PVD Coatings on Cemented Carbide Cutting Tools for Sustainable Dry High-Speed Milling of Hardened Injection Mould Steels (P20, H13, D2): A Critical Review of Tribological Behaviour, Surface Integrity, Corrosion Resistance, and a R

Cutting-fluid elimination in the finish milling of hardened injection mould steels represents one of the most commercially and environmentally urgent challenges in contemporary precision manufacturing. This review paper presents a unified critical synthesis that simultaneously addresses tribological wear mechanisms, surface integrity outcomes, electrochemical corrosion behaviour, and life-cycle environmental impacts of hard nanostructured physical vapour deposition (PVD) coatings on cemented carbide (WC-Co) end mills across all three industrially dominant mould-steel grades—P20 (32–40 HRC), H13 (44–52 HRC), and D2 (58–62 HRC)—under dry high-speed milling conditions. Drawing on a corpus of 105 primary publications and review articles spanning 2003–2025, we demonstrate that coating architecture, rather than bulk chemical composition alone, is the decisive factor governing tribological stability, and that the AlCrN family—particularly when deposited by high-power impulse magnetron sputtering (HiPIMS)—delivers the most consistent balance of low coefficient of friction (CoF 0.35–0.42 at 500 °C), compressive subsurface residual stress (−600 to −900 MPa in H13 and D2), high oxidation resistance (stable to 1050 °C), and corrosion protection (barrier resistance >10 MΩ·cm2 in 3.5 wt% NaCl). Drawing on evidence consolidated from multiple independent experimental studies, the review highlights the V2O5 tribochemical mechanism as a practically critical constraint on AlCrN performance in H13—A mechanism that prior reviews have acknowledged only in passing. Crucially, this review is the first to quantify the consequent inversion of coating performance rankings (AlCrN vs. TiAlSiN) as a function of cutting speed and workpiece grade in a cross-grade format, providing actionable selection boundaries for each mould-steel grade. A six-theme structured research roadmap is proposed, encompassing vanadium-tolerant graded coating design, toughness engineering in nanocomposites, AI-driven digital-twin process monitoring, standardised surface-integrity reporting, comprehensive life-cycle assessment of HiPIMS and nanocomposite coatings, and finite-element simulation of industrial mould-cavity geometries. These contributions collectively define an actionable path toward certified green precision manufacturing of injection mould cavities.