SUS440 Stainless Steel: General-Purpose High-Carbon Martensitic Grade for Wear-Resistant Components

SUS440 is a general designation of high-carbon martensitic stainless steel in the Japanese standard (C=0.60%-1.20%, Cr=16.0%-18.0%), which is divided into SUS440A, SUS440B and SUS440C according to the carbon content. The general SUS440 grade has the common characteristics of high hardness, high wear resistance and moderate corrosion resistance, and is a general-purpose material for high-wear precision components.

Core Parameters

Chemical Composition (wt%): C=0.60-1.20, Si≤1.00, Mn≤1.00, P≤0.040, S≤0.030, Cr=16.00-18.00, Fe=Balance

Mechanical Properties (Quenched & Tempered): Tensile Strength ≥795-950MPa, Yield Strength ≥550-700MPa, Elongation ≥10-12%, Hardness 55-62HRC

Service Temperature: -20℃ to 250℃ (continuous service)

Equivalent Grades: EN 1.4104/1.4109/1.4125, UNS S44002/S44003/S44004, GB/T 9Cr18

Performance Advantages: High carbon content ensures excellent hardenability and wear resistance; good edge retention, suitable for cutting tools and precision components; good dimensional stability after heat treatment; moderate corrosion resistance in dry environments; magnetic; can be polished to a mirror finish.

Typical Applications: General-purpose cutting tools, bearing components, precision molds, valve seats and cores for high-pressure systems, measuring tools, textile machine parts, marine hardware, high-end hardware accessories.

Practical Q&A

Q1: What is the classification basis of SUS440 series (A/B/C)? A1: The core basis is carbon content: SUS440A (0.60-0.75%), SUS440B (0.75-0.95%), SUS440C (0.95-1.20%). With the increase of carbon content, the hardness and wear resistance of the material increase gradually, while the toughness decreases gradually.

Q2: What are the common heat treatment processes for SUS440? A2: The basic process is "quenching + low-temperature tempering": quench at 1010-1090℃, oil cool; temper at 150-220℃, air cool. For different sub-grades, adjust the temperature: SUS440A (quench 1010-1050℃, temper 180-220℃), SUS440C (quench 1050-1090℃, temper 150-200℃).

Q3: Is SUS440 suitable for making precision molds? A3: Yes. Its good dimensional stability after heat treatment (linear expansion coefficient 10.5×10⁻⁶/℃) and high hardness make it suitable for precision mold cores and cavities. For molds requiring ultra-high precision and wear resistance, SUS440C is preferred.

 

Q4: How to improve the corrosion resistance of SUS440? A4: After heat treatment, perform passivation treatment with 25-30% nitric acid solution (room temperature, 20-30 minutes) to thicken the surface oxide film; in harsh environments, apply anti-rust oil or ceramic coating for protection; avoid long-term contact with chloride ions and acidic media.

Q5: What are the precautions for machining SUS440? A5: Machining should be carried out in the annealed state (hardness ≤269HB) to reduce cutting resistance; use cemented carbide tools, and select appropriate cutting parameters (low cutting speed, large feed rate); sufficient coolant should be used during machining to avoid overheating and material hardening.