SUS440 Stainless Steel

SUS440 is a high-carbon martensitic stainless steel family (440A/B/C) with 16-18% Cr, offering exceptional hardness, wear resistance, and corrosion resistance. Carbon content increases from A (0.60-0.75%) to C (0.95-1.20%), boosting hardness. It's the top choice for high-performance cutting tools and precision components needing extreme edge retention.

Chemical Composition (wt%): C (A:0.60-0.75; B:0.75-0.95; C:0.95-1.20), Si≤1.00, Mn≤1.00, P≤0.040, S≤0.030, Cr=16.00-18.00, Mo (C:0.40-0.60), Fe=Balance

Mechanical Properties (Quenched&Tempered): Tensile≥795MPa (all), Hardness (A:56-58HRC; B:57-59HRC; C:58-60HRC), Elongation≥8%

Performance Advantages: Extreme hardness/wear resistance; good corrosion resistance (better than 420); heat-treatable; Mo in 440C enhances pitting resistance.

Equivalent Grades: 440A: EN 1.4125; 440B: EN 1.4126; 440C: ASTM 440C, EN 1.4127, UNS S44004

Applications: 440A: Razor blades, valves; 440B: Bearings, industrial cutters; 440C: High-end knives, surgical scalpels, mold cores.

FAQ

1. Q: What differentiates SUS440A, B, and C? A: The primary difference is carbon content, increasing from A to C. 440A (0.60-0.75% C) is the most ductile, suitable for razor blades needing sharpness and some flexibility. 440B (0.75-0.95% C) balances hardness and toughness, ideal for bearings. 440C (0.95-1.20% C) adds molybdenum, offering the highest hardness (58-60HRC) and pitting resistance, perfect for high-end knives. As carbon rises, hardness increases but ductility decreases-choosing the right grade depends on wear vs. toughness needs.

2. Q: Why is SUS440C used for high-end knives? A: SUS440C's properties align with premium knife requirements. Its high carbon content enables 58-60HRC hardness, ensuring exceptional edge retention-critical for hunting or chef's knives. Molybdenum enhances corrosion resistance, preventing rust from food acids. It polishes to a sleek finish, appealing to consumers. While harder to sharpen than 420, its edge lasts far longer, justifying the effort. Unlike carbon tool steels, it resists rust, making it low-maintenance for everyday use.

3. Q: Can SUS440 be used in marine environments? A: SUS440C (with Mo) has limited marine use, others not recommended. 440C's molybdenum improves pitting resistance in saltwater, but it's not as durable as SUS316. It works for small, non-critical marine parts (e.g., small boat fittings) but not for submerged components or long-term exposure. Salt spray can still cause pitting over time. For marine applications, SUS316 (austenitic, high Mo) is superior, offering long-term corrosion resistance. SUS440 is better for dry or mild coastal tools, not permanent marine structures.

4. Q: How to machine SUS440 effectively? A: Machine SUS440 in the annealed state (soft, ≤241HB) for best results. Use high-speed steel (HSS) or carbide tools-carbide is preferred for hardening grades like 440C. Use slow cutting speeds (10-20 m/min) and high feed rates to avoid work hardening, which can damage tools. Coolant is essential to prevent overheating and tool wear. After machining, heat treat to achieve desired hardness. Avoid machining after heat treatment, as its high hardness (up to 60HRC) makes it extremely difficult to cut without specialized tools.

5. Q: What's the maximum operating temperature for SUS440? A: SUS440 performs well up to 315°C continuously. Above this, it loses hardness and strength-tempering occurs, softening the steel. For short-term use, it can withstand up to 425°C but may not retain properties. Its high carbon content makes it prone to oxidation at high temperatures, forming scale. Unlike heat-resistant grades like SUH409, it's not suitable for exhausts or furnaces. It's designed for room-temperature or low-heat applications like cutting tools, bearings, or precision parts where high-temperature exposure is minimal.