Comparison of 440A, 440B and 440C Stainless Steel: High-Carbon Martensitic Gradient Grade

440A, 440B and 440C are gradient grades in the 440 series, with the core difference being carbon content. With the increase of carbon content (440A: 0.60-0.75%, 440B: 0.75-0.95%, 440C: 0.95-1.20%), their hardness and wear resistance gradually increase, while toughness gradually decreases. This gradient makes them suitable for different wear resistance and toughness balance requirements.

Core Parameter Comparison

Parameter	440A Stainless Steel	440B Stainless Steel	440C Stainless Steel
Chemical Composition (wt%)	C=0.60-0.75, Cr=16.00-18.00, Fe=Balance	C=0.75-0.95, Cr=16.00-18.00, Fe=Balance	C=0.95-1.20, Cr=16.00-18.00, Fe=Balance
Mechanical Properties (Quenched & Tempered)	Tensile Strength ≥795MPa, Yield Strength ≥550MPa, Elongation ≥12%, Hardness 55-57HRC	Tensile Strength ≥860MPa, Yield Strength ≥620MPa, Elongation ≥12%, Hardness 57-59HRC	Tensile Strength ≥950MPa, Yield Strength ≥700MPa, Elongation ≥10%, Hardness 60-62HRC
Service Temperature	-20℃ to 250℃	-20℃ to 250℃	-20℃ to 250℃
Equivalent Grades	SUS440A (JIS), EN 1.4104, UNS S44002	SUS440B (JIS), EN 1.4109, UNS S44003	SUS440C (JIS), EN 1.4125, UNS S44004

Key Performance Differences: 1. Hardness gradient: 440A (55-57HRC) < 440B (57-59HRC) < 440C (60-62HRC); 440C's hardness is the highest, close to tool steel. 2. Wear resistance gradient: In standard abrasive wear tests, wear loss 440A > 440B > 440C; 440C's wear resistance is 1.5-2 times that of 440A. 3. Toughness gradient: Impact toughness 440A (≥20J) > 440B (≥18J) > 440C (≥15J); 440C is prone to brittle fracture. 4. Machinability: 440A is the easiest to machine, 440C is the most difficult, requiring special tools and processes. 5. Cost: 440C is 15-20% more expensive than 440A, 8-12% more expensive than 440B.

Applicable Scenario Distinction: 440A is suitable for components requiring balanced hardness, toughness and wear resistance, such as household high-grade kitchen knives, scissors, low-speed bearing rings, and general precision molds. 440B is suitable for components requiring high wear resistance and moderate toughness, such as hunting knives, medium-speed bearing balls, high-pressure valve cores, and high-wear plastic mold cores. 440C is suitable for components requiring ultra-high wear resistance and low impact load, such as professional chef's knives, surgical scalpels, high-speed bearing raceways, ultra-precision molds, and measuring tools (micrometers).

Practical Q&A

Q1: Why is 440C the preferred material for high-end professional knives? A1: Its ultra-high hardness (60-62HRC) ensures excellent edge retention, which can maintain sharpness after cutting hard materials for a long time; mirror-polished surface is easy to clean; it is the gold standard for high-end knives.

Q2: What is the selection principle of 440A/B/C for bearing components? A2: Choose 440A for low-speed, low-load bearings (such as textile machine bearings); choose 440B for medium-speed, medium-load bearings (such as general mechanical bearings); choose 440C for high-speed, high-load bearings (such as precision machine tool bearings).

Q3: How to avoid temper brittleness during heat treatment of 440 series? A3: Strictly control the tempering temperature, avoid 300-450℃; the optimal tempering temperature for 440A is 180-220℃, 440B is 180-220℃, 440C is 150-200℃; cool in air quickly after tempering.

Q4: What is the corrosion resistance of 440 series? A4: Similar, all have moderate corrosion resistance in dry environments; 440C's slightly higher carbon content makes its corrosion resistance slightly worse; all are prone to rust in humid or chloride-containing environments, requiring passivation treatment.

Q5: How to balance cost and performance when selecting 440A/B/C? A5: Choose 440A if budget is limited and balanced performance is required; choose 440B if high wear resistance is needed and cost is moderate; choose 440C if ultra-high wear resistance is the core requirement and cost is not a concern.