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440 Stainless Steel

440 Stainless Steel (UNS S44000) is a high-carbon, martensitic stainless steel known for its high strength, excellent wear resistance, and the highest hardness among stainless steels. It is widely used in demanding applications like knife blades, surgical instruments, and ball bearings. The 440 series includes grades 440A, 440B, and 440C, with 440C offering the highest carbon content and maximum hardness, making it ideal for parts that need superior strength and moderate corrosion resistance.

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Chemical Composition of 440 Stainless Steel

Element	440A (%)	440B (%)	440C (%)
Carbon (C)	0.60-0.75	0.95-1.20	1.20
Chromium (Cr)	16.0-18.0	16.0-18.0	16.0-18.0
Manganese (Mn)	≤ 1.00	≤ 1.00	≤ 1.00
Silicon (Si)	≤ 1.00	≤ 1.00	≤ 1.00
Phosphorus (P)	≤ 0.04	≤ 0.04	≤ 0.04
Sulfur (S)	≤ 0.03	≤ 0.03	≤ 0.03
Molybdenum (Mo)	0.50 max	0.50 max	0.50 max
Iron (Fe)	Balance	Balance	Balance

Technical Specifications of 440 Stainless Steel

Physical Properties

Property	Metric	Imperial
Density	7.65 g/cm³	0.280 lb/in³
Elastic Modulus	200 GPa	29 x 10⁶ psi
Thermal Conductivity (at 100°C)	24.2 W/m·K	14 BTU/hr·ft·°F
Coefficient of Thermal Expansion	10.1 µm/m°C	5.6 x 10⁻⁶ in/in°F
Specific Heat	460 J/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	600 nΩ·m	23.68 µΩ·in
Melting Point	1370 – 1480°C	2500 – 2700°F

Mechanical Properties

Tempering Temperature (°C)	Tensile Strength (MPa)	Yield Strength (MPa)	Elongation (%)	Hardness (HRC)	Charpy Impact (J)
Annealed	760	448	14	269 HB	–
Tempered (204°C)	2030	1900	4	59	9
Tempered (316°C)	1860	1740	4	56	9
Tempered (593°C)	1035	810	18	302	20
Tempered (650°C)	895	680	20	262	42

Thermal Properties

Property	Metric	Imperial
Thermal Conductivity (at 100°C)	24.2 W/m·K	14 BTU/hr·ft·°F
Coefficient of Thermal Expansion	10.1 µm/m°C	5.6 x 10⁻⁶ in/in°F
Melting Point	1370 – 1480°C	2500 – 2700°F

Electrical Properties

Property	Metric	Imperial
Electrical Resistivity	600 nΩ·m	23.68 µΩ·in

Product Specifications by Solitaire Steel & Engineering LLP

Product Type	Standards	Sizes	Types	Applications
Sheets & Plates	ASTM A240	Thickness: 1.5mm – 50mm	Hot Rolled, Cold Rolled	Cutlery, surgical tools, wear parts
Pipes & Tubes	ASTM A268, A249	Diameter: 6mm – 1200mm	Seamless, Welded	Precision instruments, valve components
Bars	ASTM A276	Diameter: up to 100mm	Round, Square, Hex	Bearings, bushings, fasteners
Angles, Channels, Beams	ASTM A484	Custom sizes available	L-Angles, U-Channels, I-Beams	Structural and load-bearing components
Fittings	ASTM A403	Size: 1/2″ – 72″	Buttweld, Socket Weld	Industrial, marine applications

Processing and Fabrication Properties of 440 Stainless Steel

Forming: Limited ductility; best suited for moderate cold forming operations.
Welding: Not typically recommended due to air hardening; if welding is necessary, preheating to 250°C is advised with post-weld heat treatment.
Heat Treatment:
- Annealing: Heat to 850-900°C, followed by slow furnace cooling.
- Hardening: Heat to 1010-1065°C, then air or oil quench. Oil quenching is suggested for heavy sections.
- Tempering: For maximum hardness, temper at 150-370°C. Avoid tempering between 425-565°C to maintain impact and corrosion resistance.
Heat Resistance: Performs well up to 650°C but should not be used above tempering temperature to avoid softening.
Machinability: Easily machinable in annealed condition but challenging when hardened.

Applications of 440 Stainless Steel

Due to its high hardness, corrosion resistance, and strength, 440 Stainless Steel is used in:

Cutlery: Ideal for knife blades and cutting tools.
Bearings and Valves: Suitable for components requiring wear resistance.
Medical Instruments: Used in surgical tools, dental instruments, and other medical devices.
Industrial Tools: Commonly found in shear blades, dies, and chisels.
Automotive: Valves, bushings, and other wear-resistant parts.