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Stainless Steel 420 CNC Machining Material
Stainless Steel 420 is a high-carbon martensitic stainless steel capable of being hardened by heat treatment. Often referred to as "Cutlery Grade" stainless, it offers a higher carbon content than 410, delivering superior strength, hardness, and wear resistance. At JUCHENG, we frequently utilize 420 for applications that demand a combination of corrosion resistance and high hardness. It is particularly valued in the mold-making industry for creating polished mold cavities and cores, as well as in the medical sector for precision surgical instruments. We provide comprehensive machining services for 420, from soft machining to final grinding and polishing after hardening.
Stainless Steel 420

JUCHENG's 420 Machining Capabilities

To unlock the full potential of 420, specific processing steps are required. JUCHENG delivers:
  • Pre-Hardening Machining: We machine complex geometries while the material is in its annealed (soft) state to maximize efficiency and reduce tool wear.
  • Vacuum Heat Treatment: We offer heat treatment services to harden the machined parts to 50-52 HRC without causing surface oxidation or scaling.
  • Precision Grinding: After hardening, we use cylindrical and surface grinding to achieve micron-level tolerances on bearing surfaces or mold shut-off areas.
  • Mirror Polishing: 420 is excellent for polishing. Our finishing team can achieve an SPI A-2 or A-1 mirror finish, critical for optical mold inserts.
420 stainless steel mold insert

Advantages of CNC Machining 420

Advantage Detailed Description Key Benefit
Hardenability Can be heat treated to approximately 50-52 HRC. Provides excellent wear resistance and edge retention for cutting tools.
Good Polishability Its fine grain structure allows for a high-gloss finish. Essential for plastic injection molds to produce clear parts or prevent sticking.
Corrosion Resistance Resists atmosphere, fresh water, mild acids, and alkalis (when hardened and polished). Better than tool steel (like P20), reducing mold maintenance and rust issues.
Cost-Effectiveness More economical than 440C while offering sufficient hardness for most applications. A balanced choice for high-volume wear parts and mold bases.
Magnetic Ferromagnetic in all conditions. Suitable for parts requiring magnetic properties.

Technical Parameters & Material Standards

We machine 420 in specific states to match the production lifecycle:
Grade Category Condition  Characteristics & Ideal Uses
420 Annealed Soft State Characteristics: Delivered soft (approx. 95 HRB). Easy to mill, drill, and tap. Good toughness but low wear resistance.
Uses: Rough machining of mold cavities, structural brackets before hardening.
420 Hardened Quenched & Tempered Characteristics: High hardness (50-52 HRC). Maximum corrosion resistance is achieved in this state. Difficult to machine (requires ceramic tools or grinding).
Uses: Finished mold cores, surgical shears, valve needles, bushings.

CNC Machining Guidelines 420

  • Machining Strategy: Always aim to remove the bulk of material in the annealed state. Leave 0.2mm - 0.5mm stock for finishing after heat treatment.
  • Chip Control: In the annealed state, chips can be stringy and tough. We use chip breakers to prevent tool entanglement.
  • Coolant: Essential to prevent thermal shock and maintain surface finish.
  • Corrosion Note: 420 achieves its full corrosion resistance only after hardening and polishing. In the annealed state with a rough surface, it is susceptible to rust.

Application Scenarios

  • Mold Making: Plastic injection mold cavities, cores, inserts, and slides (replacing P20 for better rust protection).
  • Medical: Surgical instruments, dental tools, scalpels (where 440C hardness is not strictly required).
  • Industrial: Valve trims, needle valves, pump shafts, shear blades.
  • Automotive: Fasteners, shafts, and wear components.
  • Cutlery: Knife blades, scissors, and straight edges.

Physical Properties Table

Comparison: Annealed vs. Hardened:
Property SS 301 (Annealed) SS 301 (Full Hard) Unit
Density 7.75 7.75 g/cm³
Tensile Strength 655 1600 - 1750 MPa
Yield Strength 345 1350 - 1450 MPa
Elongation 25 < 5 %
Hardness ~ 95 HRB 50 - 52 HRC Rockwell
Corrosion Resistance Fair Good -
 
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    Shenzhen: Fourth Industrial Zone, Xisha Road, Shajing Street, Baoan District, Shenzhen.
    Dongguan: Building 5 and 4, No. 198, Chang'an Section, Guanchang Road, Chang'an Town, Dongguan.
     
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