440C Stainless Steel – CNC Machining

440C stainless steel is selected for CNC machined components requiring very high hardness, wear resistance, and dimensional stability under load.

Its high-carbon martensitic structure significantly increases cutting forces and tool wear during machining.

At ShvaveyMetal, 440C stainless steel machining strategies are defined around material condition, tool selection, and controlled heat treatment sequencing.

440C stainless steel is a high-carbon martensitic chromium stainless steel capable of achieving extremely high hardness through heat treatment.

It offers superior wear resistance compared to 420 stainless steel, with reduced toughness and corrosion resistance relative to austenitic grades.

Mechanical Properties (Typical – Hardened & Tempered)

Property Typical Value Units
Density ~7.7 g/cm³
Yield Strength ~1,600 MPa
Ultimate Tensile Strength ~1,900 MPa
Elongation at Break ~5 %
Elastic Modulus ~200 GPa
Hardness ~58–60 HRC

Mechanical properties vary significantly depending on heat treatment parameters.

Thermal & Physical Properties

Property Typical Value Units
Thermal Conductivity ~24 W/m·K
Coefficient of Thermal Expansion ~10.2 µm/m·K
Melting Range ~1,425–1,530 °C

These properties influence heat flow and dimensional response during CNC machining.

Chemical Composition (Representative)

Element Typical Content (%)
Iron (Fe) Balance
Chromium (Cr) 16.0 – 18.0
Carbon (C) 0.95 – 1.20
Manganese (Mn) ≤ 1.0
Silicon (Si) ≤ 1.0
Molybdenum (Mo) ≤ 0.75

Composition ranges depend on material standards and supplier certification.

440C stainless steel machining behavior is strongly governed by hardness and microstructure.

Key machining characteristics include:

  • Extremely high cutting forces in hardened condition
  • Rapid tool wear and edge degradation
  • Short, brittle chip formation
  • Improved surface finish achievable after final heat treatment

Machining is typically performed in the annealed state, followed by hardening and tempering.

Benefit Description
Extreme Hardness Capability Suitable for severe wear applications
High Wear Resistance Maintains performance under sliding contact
Dimensional Stability Retains geometry after heat treatment
Edge Retention Suitable for cutting and bearing components
Magnetic Properties Applicable in magnetic assemblies

440C stainless steel is commonly used for CNC machined components such as:

  • Bearings and bearing races
  • Cutting tools and blades
  • Valve components and seats
  • Precision shafts and pins
  • High-wear mechanical components

Application suitability depends on hardness targets and operating environment.

Condition General Characteristics
Annealed Maximum machinability prior to hardening
Hardened Maximum hardness and wear resistance
Tempered Controlled balance between hardness and brittleness

Final properties are achieved through controlled heat treatment after machining.

When designing CNC machined parts from 440C stainless steel, consideration should be given to:

  • Machining in the annealed state wherever possible
  • Allowance for dimensional change during hardening
  • Conservative tooling strategies for hardened conditions
  • Clear definition of final hardness and surface finish requirements

Early coordination between design, machining, and heat treatment strategy is critical.

FAQ

What is the machinability of 440C stainless steel?

440C is machined in the annealed condition, where machinability is roughly 40–45% relative to B1112. Even annealed, its high carbon and chromium carbide content is abrasive and shortens tool life. Once hardened to 58–60 HRC it is generally no longer practical to machine conventionally, and finishing moves to grinding.

How should machining be sequenced around heat treatment for 440C?

Standard practice is to rough and semi-finish in the annealed condition, leaving stock for movement, then harden and temper, then finish-grind critical features to final tolerance. Because hardening produces dimensional change and distortion, allowing adequate finishing stock is essential for precision components.

What tooling is used for machining 440C stainless steel?

Carbide tooling with wear-resistant coatings is standard, chosen to withstand the abrasive carbides in the microstructure. Reduced cutting speeds compared with austenitic grades, rigid setups and consistent coolant help control heat and extend tool life. Tool wear should be monitored, since edge breakdown quickly degrades surface finish and dimensional accuracy.

What are machined 440C components used for?

440C is specified where hardness and wear resistance are critical alongside moderate corrosion resistance: bearing races and balls, valve seats and components, pump parts, nozzles, surgical and dental instruments, and wear surfaces in demanding mechanical assemblies.

Can 440C parts be supplied with surface coatings such as DLC?

Yes. Hardened 440C is a common substrate for DLC and similar coatings, which further reduce friction and improve wear performance. Coating requirements should be defined early, since surface finish and dimensional allowances before coating affect the final result and must be planned into the machining sequence.


Why Machine 440C Stainless Steel at ShvaveyMetal

ShvaveyMetal applies CNC machining workflows aligned with material condition, tooling limitations, and heat treatment requirements.

This approach ensures that CNC machined 440C stainless steel components meet defined dimensional, surface, and performance criteria across prototype and production programs.