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Stainless Steel 440C CNC Machining Material
Stainless Steel 440C is a high-carbon martensitic stainless steel designed to provide the highest strength, hardness, and wear resistance of all standard stainless alloys. Capable of attaining a hardness of up to 60 HRC after heat treatment, it essentially functions as a corrosion-resistant tool steel. At JUCHENG, we have specialized protocols for machining 440C. We typically machine parts in the annealed condition and then perform heat treatment and precision grinding to achieve final tolerances, delivering components that offer exceptional edge retention and durability for the bearing, cutlery, and mold industries.
Stainless Steel 440C

JUCHENG's 440C Machining Capabilities

Handling materials that can become as hard as 440C requires a mix of machining and finishing strategies:
  • Hard Turning & Milling: We utilize rigid CBN and ceramic tooling to machine 440C even in its hardened state for final finishing passes.
  • Precision Grinding: To achieve the tightest tolerances on hardened 440C shafts or bearing races, we offer cylindrical and surface grinding services.
  • Heat Treatment: We provide vacuum heat treatment services to harden 440C without surface scaling, ensuring the part reaches its maximum potential hardness.
  • Surface Finishing: Due to its high hardness, 440C polishes exceptionally well. We can achieve mirror-like finishes for mold inserts and cosmetic wear parts.
440C stainless steel bearing race

Advantages of CNC Machining 440C

Advantage Detailed Description Key Benefit
Highest Hardness Can be heat treated to ~58-60 Rockwell C, the highest of any standard stainless series. Resists deformation and indentations under extreme point loads.
Superior Wear Resistance The hard carbide structure resists abrasion and sliding wear. Ideal for bearings, bushings, and valve seats that operate in continuous friction.
Excellent Edge Retention Maintains a sharp cutting edge longer than 304 or 17-4 PH. The standard material for high-quality surgical instruments and knife blades.
Moderate Corrosion Resistance Resists fresh water, steam, crude oil, and gasoline (best when fully hardened and polished). Better than tool steel, allowing use in mildly corrosive environments without rusting.
Magnetic Ferromagnetic in all conditions. Suitable for parts requiring magnetic interaction or sorting.

Technical Parameters & Material Standards

We process 440C in two distinct stages:
Grade Category Condition  Characteristics & Ideal Uses
Annealed 440C Soft State Characteristics: Delivered in a soft, machinable state (approx. 20-25 HRC). Microstructure consists of primary carbides in a ferrite matrix.
Uses: General machining of complex geometries before hardening.
Hardened 440C Heat Treated & Tempered Characteristics: Maximum hardness (58-60 HRC). Corrosion resistance is maximized in this state. Difficult to machine (requires grinding or hard turning).
Uses: Finished bearings, nozzles, pump parts, surgical tools.

CNC Machining Guidelines 440C

  • Machine in Annealed State: We perform the bulk of material removal while the material is soft to reduce cost and time.
  • Grinding Allowance: We leave a small amount of stock material on critical dimensions to account for slight distortion during heat treatment, which is then removed by precision grinding.
  • Coolant: Essential. 440C chips can be hot and abrasive. Good lubrication ensures surface finish quality.
  • Corrosion Note: Unlike 304/316, 440C must be hardened and polished to achieve its full corrosion resistance. It is not recommended for saltwater use (pitting may occur).

Application Scenarios

  • Rolling Element Bearings: Ball bearings, races, and rollers requiring high fatigue life.
  • Medical: Surgical scalpels, dental instruments, cutting tools.
  • Fluid Power: Valve seats, high-wear pump components, nozzles.
  • Mold Making: Plastic injection mold inserts requiring high polish and wear resistance.
  • Cutlery: High-end knife blades and shears.

Physical Properties Table

Comparison: 440C (Hardened) vs 304 (Standard):
Property SS 440C (Hardened) SS 304 (Annealed) Unit
Density 7.80 8.00 g/cm³
Tensile Strength 1900 - 2000 515 MPa
Yield Strength 1800 - 1900 205 MPa
Corrosion Resistance Moderate 10 %
Hardness 58 - 60 HRC Excellent Rockwell C
Magnetic Yes NO -
 
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