JIS SUS440C Stainless Steel: The Ultimate Guide to Hardness, Uses & More

If you need a stainless steel that’s extremely hard and wear-resistant—for knives, surgical tools, or industrial blades—JIS SUS440C stainless steel is the top choice. As a high-carbon martensitic steel, it delivers unmatched hardness (up to 60 HRC) after heat treatment, making it perfect for parts that need to stay sharp or resist wear. This guide covers everything you need to use it effectively.

1. Material Properties of JIS SUS440C Stainless Steel

JIS SUS440C stainless steel’s superpower is its hardness, driven by its unique material properties—especially its high carbon and chromium content. Let’s break it down:

Alloy Composition

The “C” in SUS440C stands for “high carbon”—the key to its exceptional hardness. Here’s the precise mix:

Mechanical & Physical Properties

After heat treatment (hardening + tempering), its properties are unmatched for wear-resistant parts:

A premium knife maker in Japan uses SUS440C for high-end chef’s knives. After heat treatment, its 59 HRC hardness keeps blades sharp through months of slicing meat and vegetables—something cheaper steels can’t match.

2. Applications of JIS SUS440C Stainless Steel

Thanks to its extreme hardness and mild corrosion resistance, JIS SUS440C stainless steel is used for precision tools and wear-resistant parts. Here are its top applications:

• Cutlery and Knives: High-end chef’s knives, hunting blades, and straight razors. A U.S. knife brand uses it for “lifetime” hunting knives—customers report blades stay sharp for years.
• Surgical Instruments: Scalpels, bone saws, and dental tools (not for long-term body contact). A medical supply firm in Germany uses it for surgical scalpels—its hardness ensures clean, precise cuts during operations.
• Industrial Tools: Blades for paper cutters, textile shears, and metal slitting machines. A factory in China uses SUS440C for paper cutter blades—they last 6 months before needing sharpening (vs. 1 month for SUS410).
• Aerospace Components: Bearings, valve seats, and small gears (handles high wear in engines). An aerospace supplier uses it for jet engine bearings—its 1900 MPa tensile strength resists extreme pressure.
• Automotive Parts: High-performance brake rotors and transmission gears (for racing cars). A racing team in Italy uses SUS440C for brake rotors—its wear resistance handles 200+ mph stops.
• Hardware: Precision bearings and lock pins (need to resist wear from friction). A lock manufacturer uses it for high-security lock pins—they don’t wear down, even with 10,000+ uses.

3. Manufacturing Processes for JIS SUS440C Stainless Steel

JIS SUS440C stainless steel requires careful processing—especially heat treatment—to unlock its hardness. Here are the key manufacturing processes:

1. Hot Rolling: Heated to 1050–1150°C and rolled into bars or coils (thick enough for tools). A steel mill in South Korea uses hot rolling for SUS440C bar stock—ensures uniform carbon distribution.
2. Annealing: Heated to 800–850°C and cooled slowly. Softens the steel for machining (critical—untreated SUS440C is too hard to cut). A knife maker anneals SUS440C blanks before drilling handle holes—prevents tool breakage.
3. Machining: Done with carbide tools (HSS tools wear out too fast). Use slow speeds and coolant to avoid overheating (high carbon causes brittleness). A surgical tool shop machines SUS440C scalpels—uses diamond-tipped tools for precision.
4. Heat Treatment: The most important step!
   • Hardening: Heated to 1010–1070°C, held for 30 minutes, then quenched in oil (rapid cooling forms martensite).
   • Tempering: Reheated to 150–200°C to reduce brittleness (keeps hardness at 58–60 HRC).
     A blade maker heat-treats SUS440C knives in a controlled oven—this is why their blades stay sharp so long.
5. Pickling: Treated with nitric acid to remove scale from heat treatment. Enhances corrosion resistance—critical for surgical tools.
6. Grinding/Sharpening: Finished with diamond grinders to create ultra-sharp edges. A dental tool maker grinds SUS440C into tiny drill bits—achieves edges thin enough for tooth cavities.

4. Corrosion Resistance of JIS SUS440C Stainless Steel

JIS SUS440C stainless steel has mild corrosion resistance—enough for dry tools but not harsh environments. Here’s what you need to know:

• Mild Atmospheric Resistance: Resists rust in dry air or indoor use. A chef’s SUS440C knife stayed rust-free for 2 years when cleaned and dried after use.
• Limited Pitting Resistance: Avoid saltwater, chlorinated water (e.g., pools), or acidic foods (e.g., citrus) for long periods. A test showed SUS440C rusted in seawater within 1 week—use SUS316 for marine parts.
• Intergranular Corrosion: Low risk if heat-treated properly (tempering prevents carbide buildup). A surgical tool maker tests SUS440C scalpels—no corrosion after 100+ autoclave sterilizations.
• Stress Corrosion Cracking: Prone to cracking if bent or stressed in moist environments. Never use SUS440C for parts that need to flex (e.g., springs)—stick to rigid tools.
• Surface Treatment for Protection: Passivation (nitric acid treatment) thickens the oxide layer. A knife brand passivates SUS440C blades—adds 6 months of rust protection.

Pro tip: Oil SUS440C tools after use (especially knives) to block moisture—this extends their rust-free life.

5. Welding JIS SUS440C Stainless Steel

JIS SUS440C stainless steel has poor weldability—its high carbon content causes brittleness and cracking. Here’s what you need to know (if you must weld it):

• Welding Processes: Only TIG (Tungsten Inert Gas) is feasible—low heat input minimizes brittleness. MIG or arc welding will almost always cause cracks. A aerospace welder uses TIG for small SUS440C bearing parts—works only for thin sections (≤2mm).
• Welding Rods: Use high-carbon martensitic fillers like AWS ER440C. Avoid austenitic fillers (e.g., ER308)—they’ll soften the weld and reduce wear resistance.
• Preheating: Heat parts to 300–400°C before welding. This reduces stress and slows cooling (prevents excess martensite). A tool maker preheats SUS440C brackets—cuts cracking risk by 50%.
• Post-Weld Heat Treatment: Mandatory! Temper at 150–200°C after welding to soften brittle martensite. Without this, the weld will crack within days. A factory tempers welded SUS440C gears—restores 80% of the base metal’s strength.
• Welding Safety: Wear a heat-resistant jacket and helmet—SUS440C produces intense sparks, and high carbon can release toxic fumes.
• Better Alternative: Avoid welding SUS440C if possible. Instead, machine parts from a single piece or use mechanical fasteners (e.g., screws) for assembly.

6. Standards and Specifications for JIS SUS440C Stainless Steel

To ensure quality (critical for hard tools), JIS SUS440C stainless steel follows strict global standards. Here’s what you need to know:

• JIS G4303: The Japanese Industrial Standard for cold-rolled stainless steel (covers SUS440C’s carbon content: 0.95–1.20%).
• ASTM A240: The U.S. standard (ASTM A240 Type 440C is equivalent)—you can use them interchangeably.
• EN 10088: The European standard (EN 10088-2 X105CrMo17 is the equivalent grade).
• ISO Standards: ISO 15510 specifies its chemical composition (including molybdenum: 0.40–0.60%) and mechanical properties.
• Material Certification: Ask for a Mill Test Certificate (MTC) to verify carbon and chromium content. A knife brand requires MTCs—ensures blades reach 58+ HRC after heat treatment.
• Quality Control: Manufacturers test for hardness (Rockwell C scale) and corrosion resistance (salt spray tests). A supplier rejects batches with hardness below 58 HRC—they won’t be wear-resistant enough.

7. Comparison with Other Materials

How does JIS SUS440C stainless steel stack up against other hard or corrosion-resistant materials? Here’s a clear breakdown:

For extreme hardness and wear resistance (knives, surgical tools, industrial blades), SUS440C is unbeatable—it’s harder than any common stainless steel and more corrosion-resistant than carbon steel.

Yigu Technology’s Perspective on JIS SUS440C Stainless Steel

At Yigu Technology, JIS SUS440C is our top pick for clients needing ultra-hard, wear-resistant parts—like premium knife makers or surgical tool manufacturers. Its high carbon content delivers the hardness they need, while chromium adds just enough corrosion resistance for dry use. We help clients optimize heat treatment (hardening + tempering) to hit 58–60 HRC, and advise against welding unless absolutely necessary. While it’s not for forming or harsh environments, SUS440C solves the “lifetime sharpness” problem for 80% of our precision-tool clients.

FAQ About JIS SUS440C Stainless Steel

1. How hard is JIS SUS440C?
   Extremely hard—58–60 HRC on the Rockwell scale. To put it in perspective: SUS304 is ~20 HRC (soft enough to bend), while SUS440C is as hard as a industrial drill bit.
2. Can JIS SUS440C be bent or formed?
   No—its low elongation (≥5%) means it will crack if bent sharply. It’s designed for rigid parts (knife blades, scalpels), not for forming into curves or shapes.
3. Does JIS SUS440C rust?
   It can rust in moist/salty environments (e.g., seawater, citrus juice). But if cleaned, dried, and oiled regularly (for tools/knives), it stays rust-free for years—much better than carbon steel.