Martensitic AISI 440B stainless steel (UNS S44003)

AISI 440B stainless steel (UNS S44003) is a high-carbon martensitic stainless steel with precisely controlled composition, achieving an ideal engineering balance between hardness, wear resistance, and moderate corrosion resistance. Its carbon content ranges from 0.75% to 0.95%, and after proper heat treatment, it can achieve a hardness of 56–58 HRC, offering higher edge retention than 440A while retaining better impact toughness than 440C. This makes 440B an ideal material choice for applications requiring both wear resistance and moderate corrosion resistance, such as industrial blades, bearing components, valve assemblies, food processing equipment, and medical devices. The material is available in bars, sheets, wire rods, and forgings, and is widely used across the global precision manufacturing industry.

Chemical Composition of SS 440B

The excellent performance of Martensitic 440B stems from the synergistic effect of its alloying elements: 16–18% chromium forms a dense passive film on the surface, providing reliable corrosion protection in fresh water, atmospheric environments, and weak organic media; 0.75–0.95% carbon combines with chromium to form chromium carbides, which transform into a hard martensitic matrix upon quenching; additionally, up to 0.75% molybdenum significantly improves resistance to pitting and crevice corrosion, offering an advantage over molybdenum-free martensitic steels, especially in chloride-containing environments.

Physical Properties of SS 440B

SS 440B Mechanical Properties

After oil quenching at 1010–1070°C and tempering at 150–200°C, 440B exhibits excellent wear resistance and compressive strength, making it suitable for components subjected to high contact stress.

Thermal Properties of Martensitic 440B

Heat Treatment & Hardening Cycle – SS 440B

Heat Treatment of Martensitic 440B

Annealing is typically performed. Soft annealing should be carried out at temperatures ranging from 780°C to 840°C, followed by cooling in air or in an oven. Stress relief annealing can be performed at 600°C to 650°C, followed by furnace cooling. For hardening (quenching), AISI 440B stainless steel can be heated within the temperature range of 1000°C to 1050°C, and cooling can be achieved by oil quenching, hot water bath, or air cooling.

Fabrication Properties of Martensitic 440B

Welding: Welding is generally not recommended. If welding is unavoidable, preheating to above 260°C is required, using austenitic stainless steel or nickel-based filler rods, followed by immediate post-weld heat treatment at 732–760°C.

Cold Forming of UNS S44003

Cold forming capability is limited. Hot forming (approximately 800–900°C) is recommended as an alternative to cold forming.

Typical Applications of 440B Steel

Suitable for applications requiring an excellent combination of wear resistance and moderate corrosion resistance, 440B is commonly used for:

• High-end cutlery and kitchen knives
• Surgical scalpels and dental instruments
• Rolling element bearings and bearing components
• Valve seats and needle valves
• Industrial blades and shear knives
• Razor blades and cutting tools
• Measuring instruments and gauges
• Marine hardware requiring high hardness

Available Forms & Size Range – SS 440B

If you need to ensure high hardness and corrosion resistance for industrial blades, bearing components, or precision mechanical parts under harsh environments, then 440B (UNS S44003) is your ideal choice. C&N offers a variety of high-quality 440B sheets, wire rods, pipe fittings, and forgings. Please contact us immediately if you have any requirements.

Frequently Asked Questions

Q: Can you cut 440B to a specific length?

Yes, we offer precision sawing and cutting services for 440B bars. We can cut to your exact requirements and, for hardened materials, utilise specialised abrasive cutting methods to prevent thermal alteration of the ends.

Q:What is the hardness of 440B in the annealed condition?

In the annealed condition, 440B stainless steel has a maximum hardness of 265 HB (Brinell), which is approximately equivalent to 26 HRC. This condition is optimal for heavy machining before final hardening.

Q:Is 440B suitable for welding?

Due to its high carbon content and air-hardening nature, which easily leads to cracking, welding is generally not recommended for 440B. However, if welding is absolutely necessary, the material must be preheated to 260°C, followed by post-weld annealing at 732–760°C for at least six hours, with the material then being cooled slowly in a furnace.

Q:What is the difference between 440B and 1.4112?

Although they are often considered equivalent, EN 1.4112 typically has a slightly higher chromium range (17–19% vs. 16–18%), a mandatory molybdenum content of 0.90–1.30%, and a small vanadium addition of 0.07–0.12%. These differences give 1.4112 marginally better edge retention and corrosion resistance than standard ASTM 440B.