Stainless Steel 420

Your guide to 420 Stainless Steel Machining



A general purpose high carbon martensitic steel

Highest hardness amongst all stainless grades

Exceptional wear resistance

420 stainless is usually supplied hardened and tempered or annealed condition. It has the highest hardness amongst all the stainless grades with 12% chromium.

This guide will take you through the main attributes, common applications, notes for designers and suitable finishing and treatments, as well as UK stock sizes and property tables. Don't forget to bookmark the page so you can refer back later.

If you are interested in stainless 420 machined parts, please scroll to the bottom of the page for more information about our service and to request a quote.

420 Guide: Properties, Applications and Design Considerations


What is 420 Stainless Steel?
Stainless 420 is a general purpose high carbon martensitic steel. It is usually supplied hardened and tempered or annealed condition. Martensitic stainless steels are designed for high hardness and sometimes other properties are compromised on. 

420 has the highest hardness amongst all stainless grades with 12% chromium. The addition of sulphur to improve machinability does lower the corrosion resistance and weldability to below that of grade 410 (non-free machining equivalent).


420 Machinability

Stainless 420 machines best in the hardened and tempered condition R or condition S. It is similar to machining high carbon tool steels in that it gives tough, stringy chips. There is a free-machining type of 420 but this does come at the expense of other properties.


Similar or obsolete designation and trade names

You may also see stainless 420 referred to as:

  • 420C
  • British Standard Grades:
    • 420S37 (1.4021)
    • 420S45
    • 420S29
  • European Specifications:
    • 1.2083
    • 1.4034
  • Related Specifications:
    • 1.4021 (Bar)
    • 1.4020
    • 1.4034
    • 1.2083
    • UNS S42000
    • ASTM A276
    • BS EN 10088
    • AISI BS970
    • UNS X20Cr13
    • X30Cr13

Industry Examples: Medical | Food processing


Typical Components & Applications: Surgical and dental instruments | Cutting tools | Wear plates | Needle valves | Hand tools | Bushings | Pump parts | Valve parts | Shafts

Main Attributes:
  • Rust resistant
  • High hardness
  • Exceptional wear resistance
  • Good corrosion resistance achieved when hardened and surface ground or polished (to atmosphere, foods, fresh waters, mild acids)
  • Magnetic
  • Although it can be used in continuous service up to 650°C, this can result in a considerable drop in its core properties (hardness, tensile strength, corrosion resistance), therefore not recommended for use at working temperatures above 400°C

Finishing & Treatments:

Stainless 420 is usually supplied in a heat treated condition:

  • Annealing – annealed at temperatures between 840-900°C
  • Tempering – temper at temperatures between 145-205°C
  • Hardening – soak at 1010-1065°C
Can we meet your stainless steel 420 machining needs? Contact us now
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Further Reading & Resources

British Stainless Steel Association


420 Machining Stainless Steel Machined Parts


Penta Precision provides the following 420 machining services: 
  • CNC milling
  • CNC turning
  • Prototypes and batch runs
  • Insert installation
  • Part marking
  • Manual milling
  • Manual turning
  • Machining design advice
  • Design for manufacture service

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