HNV3 — Werkstoffnummer 1.4718, DIN/EN X45CrSi9-3, also known by its JIS designation SUH1 — is a martensitic chromium-silicon heat-resisting steel developed for engine exhaust valves. Its chemistry runs roughly 8-10% chromium and 2.7-3.3% silicon, a combination chosen specifically for valve service: the silicon addition raises resistance to hot-gas oxidation and scaling far beyond what chromium alone would provide, while the chromium keeps enough corrosion resistance for the combustion environment. Unlike the nitrogen-strengthened austenitic valve steels (such as EV8/1.4871) used for the most severe high-temperature exhaust duty, HNV3 is a quench-and-temper hardenable martensitic grade, giving it higher as-supplied strength and a more conventional machining response.

HNV3 bar and forging stock is typically supplied quenched and tempered, with tensile strength in the 900-1100 N/mm² range, a 0.2% proof strength around 700 N/mm², and hardness of roughly 266-325 HB in that condition (or about 300 HB when supplied annealed for machining). FM Carbide customers working with HNV3 are usually producing exhaust valve blanks, valve seats and guides, or other engine hardware that needs to hold strength and resist scaling at sustained elevated temperature without the cost of a fully austenitic valve alloy.

Per EN 10090 for valve steel 1.4718. Quenched & tempered mechanical properties: tensile strength 900-1100 N/mm², 0.2% proof strength ≈700 N/mm², hardness 266-325 HB; annealed condition ≈300 HB max. Density 7.7 g/cm³.

HNV3 is generally machined in its softer, annealed condition (around 300 HB or below) before the final quench-and-temper hardening cycle that brings a finished valve up to service strength. Even in that pre-hardened state, the 2.7-3.3% silicon content behaves like a hard, abrasive constituent distributed through the matrix, so tool wear on this grade leans toward abrasive flank wear rather than the adhesive, work-hardening behavior seen on austenitic stainless. Cutting forces run higher than on a plain carbon or low-alloy steel of similar hardness, and heat generation at the tool tip is elevated by the alloy's chromium-silicon chemistry.

Rigid setups and a wear-resistant carbide grade matter more here than exotic geometry: abrasive silicide particles chew away at the cutting edge over the length of a cut, so coating hardness and edge toughness both need to be adequate for sustained material removal. Positive rake geometries reduce cutting forces and help manage heat, and coolant helps control both tool temperature and built-up edge tendency at lower speeds. Because HNV3 is quenched and tempered to its final properties after most machining is complete, roughing and semi-finishing should be done in the softer condition whenever the process allows, leaving only light finishing cuts for any post-hardening operations.

Values assume the annealed/pre-hardened condition, a well-matched insert grade, rigid tool and workpiece clamping, and good-quality raw material. Reduce speeds after quench and temper hardening.

Turning

Parting / Grooving

Milling