HW3 corresponds to X45CrSi9-3 (Wnr. 1.4718), a chromium-silicon heat-resisting valve steel rather than a conventional cold- or hot-work tool steel. The "HW" catalog label groups it with hot-work-adjacent grades because of its elevated-temperature stability, but its real-world use is almost entirely in internal-combustion-engine exhaust and intake valves, valve seats, and valve guides — components that see sustained exposure to hot combustion gases rather than repeated die-cycling. The alloy's defining feature is a high silicon content, roughly 2.7-3.3%, combined with 8-10% chromium. Silicon at that level promotes a stable, adherent oxide scale that resists spalling under thermal cycling up to around 850°C, while the chromium delivers the martensitic hardenability and moderate corrosion resistance the grade needs in a combustion environment.

Because HW3 is a martensitic stainless-adjacent alloy rather than a high-carbide tool steel, it does not carry the wear resistance of D- or M-series grades — its value is heat and scaling resistance, not abrasion resistance. Bar stock is typically supplied in the annealed or normalized condition and machined into valve blanks before hardening and, often, nitriding of the stem and seat areas.

The old page listed this designation as "X45GrSi93" and "X45GrSi8" — a transcription error (Cr misread as Gr, hyphen dropped). The correct DIN/EN designation is X45CrSi9-3, confirmed against independent steel-standard references.

The old page's composition table was hidden in an HTML comment and listed W 8.5-10%, Cr 3.0-3.75%, and Si only 0.15-0.40% — figures that actually belong to a tungsten hot-work steel, not this Cr-Si valve steel. The table above reflects HW3's real chemistry (dominant silicon and chromium, no tungsten).

HW3's machinability is shaped by its unusually high silicon content rather than by carbide volume, since this grade carries essentially no free carbides in the annealed state. Silicon in the 2.7-3.3% range raises the abrasiveness of the matrix itself and increases work hardening tendency during cutting, which is a different wear mechanism than the carbide-driven abrasion seen in D2 or M2. In the annealed/normalized condition (roughly 250-300 HB), cutting forces run moderate to high for a steel of this hardness, and flank wear tends to progress steadily rather than through chipping.

Because the alloy work-hardens readily, maintaining a consistent feed and avoiding light, rubbing passes is more important than with a typical Cr-Mo tool steel — dwelling or skating across the surface accelerates work hardening and shortens insert life on the next pass. A sharp, positively-raked coated carbide edge with steady feed and adequate coolant gives the most consistent results. Most HW3 machining happens on bar stock before hardening and nitriding; the finished valve seat and stem surfaces are ground rather than turned.

Starting-point ranges for annealed/normalized HW3, set below general Cr-Mo hot-work grades to account for the work-hardening tendency driven by its high silicon content. Always verify with a test cut.

Turning

Parting / Grooving

Milling