420 Stainless Steel – CNC Machining

420 stainless steel is selected for CNC machined components where high hardness, wear resistance, and edge retention are required.

Its martensitic structure and heat-treatable nature directly influence cutting forces, tool wear, and achievable surface finish.

At ShvaveyMetal, 420 stainless steel machining strategies are defined around material condition, heat treatment state, and controlled cutting parameters.

420 stainless steel is a martensitic chromium stainless steel capable of achieving high hardness through heat treatment.

It offers higher strength and wear resistance than austenitic grades such as 304, with reduced corrosion resistance.

Mechanical Properties (Typical – Hardened & Tempered)

Property Typical Value Units
Density ~7.7 g/cm³
Yield Strength ~700 MPa
Ultimate Tensile Strength ~900 MPa
Elongation at Break ~10 %
Elastic Modulus ~200 GPa
Hardness ~48–52 HRC

Mechanical properties vary significantly with heat treatment condition.

Thermal & Physical Properties

Property Typical Value Units
Thermal Conductivity ~24 W/m·K
Coefficient of Thermal Expansion ~10.3 µm/m·K
Melting Range ~1,450–1,515 °C

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

Chemical Composition (Representative)

Element Typical Content (%)
Iron (Fe) Balance
Chromium (Cr) 12.0 – 14.0
Carbon (C) 0.15 – 0.40
Manganese (Mn) ≤ 1.0
Silicon (Si) ≤ 1.0
Nickel (Ni) ≤ 0.75

Composition ranges depend on material standards and supplier certification.

420 stainless steel machining behavior is strongly dependent on hardness and heat treatment state.

Key machining characteristics include:

  • Significantly increased cutting forces in hardened condition
  • Accelerated tool wear compared to austenitic stainless steels
  • Short, brittle chip formation
  • Improved surface finish potential after final heat treatment

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

Benefit Description
High Hardness Capability Suitable for wear-critical components
Wear Resistance Performs well in sliding or cutting applications
Dimensional Stability Maintains geometry after heat treatment
Magnetic Properties Suitable for magnetic assemblies
Strength Potential Achieves high mechanical strength when hardened

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

  • Cutting tools and blades
  • Shafts, pins, and wear components
  • Valves and mechanical seals
  • Medical and surgical instruments
  • High-strength mechanical parts

Application suitability depends on hardness requirements and corrosion exposure.

Condition General Characteristics
Annealed Maximum machinability prior to hardening
Hardened Maximum hardness and wear resistance
Tempered Balanced hardness and toughness

Final properties are achieved through controlled heat treatment after machining.

When designing CNC machined parts from 420 stainless steel, consideration should be given to:

  • Machining prior to final hardening where possible
  • Allowance for dimensional change during heat treatment
  • Tooling selection suitable for high-hardness steels
  • Clear definition of final hardness and surface requirements

Early alignment between machining and heat treatment strategy is essential.

FAQ

What is 420 stainless steel?

420 is a martensitic stainless steel with around 12 to 14% chromium and sufficient carbon to be hardened by heat treatment. It combines moderate corrosion resistance with good hardness and excellent polishability, and is supplied annealed for machining before being hardened to the required condition.

How is 420 stainless steel machined?

420 is machined in the annealed condition, where it cuts reasonably well with carbide tooling. As a martensitic grade it becomes progressively harder to cut once heat treated, so the machining sequence is normally planned around hardening. Rigid setups and controlled parameters are important for maintaining surface quality and dimensional accuracy.

What are machined 420 stainless steel parts used for?

Typical applications include moulds and tooling, shafts, valve components, wear parts, surgical and dental instruments, and cutlery-type components. It is chosen where moderate corrosion resistance combined with good hardness and excellent polishability is required.

Does 420 stainless steel distort during heat treatment?

Yes, like other martensitic stainless steels, 420 moves dimensionally during quenching and tempering. Precision components are therefore rough-machined with finishing stock left on, then hardened, then finish-machined or ground to final dimensions. Planning for this movement is the key to holding tight tolerances reliably.

What hardness can 420 stainless steel reach?

Depending on carbon content and heat treatment, 420 typically reaches around 48 to 52 HRC after quenching and tempering. Tempering temperature governs the balance between hardness and toughness, so the required condition should be stated on the drawing to allow the process to be planned and verified.


Why Machine 420 Stainless Steel at ShvaveyMetal

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

This approach ensures that CNC machined 420 stainless steel components meet defined dimensional, surface, and performance criteria across prototype and production programs.