Selection summary
Overview
420 denotes a higher-carbon martensitic stainless family capable of substantially greater hardness than 410 after quenching and tempering. Carbon limits and commercial variants differ, so an order must identify the exact UNS or product specification, required hardness, heat-treatment route, section size, finish, and corrosion expectations rather than relying on the name 420 alone.
This page separates standard-oriented limits from typical reference data. Purchase acceptance comes from the ordered specification and certified material test report.
Names and systems
Identity & standards
Similar designations across ASTM, EN, JIS, and other systems are not automatically interchangeable. Product form and ordered standard control chemistry, properties, dimensions, condition, and testing.
Reference chemistry
Composition
| Element | Reference range | Why it matters |
|---|---|---|
| Carbon | ≥ 0.15% | Hardness and wear response |
| Chromium | 12.0–14.0% | Corrosion resistance and hardenability |
| Manganese | ≤ 1.00% | Deoxidation and hardenability control |
Concise grade-family reference only. Confirm every element limit against the current standard for the exact product ordered.
Condition matters
Reference properties
Typical hardened-and-tempered capability; exact result depends on chemistry, section, and cycle
Do not mix annealed and hardened-and-tempered data
Typical room-temperature engineering reference
Environment first
Corrosion behavior
Provides moderate stainless corrosion resistance when correctly heat treated, polished, passivated, and maintained.
Higher carbon and carbide population reduce corrosion margin relative to lower-carbon or austenitic stainless grades, especially in chlorides and crevices.
Temperature, concentration, deposits, crevices, stress, surface finish, cleaning, and fabrication quality can change service performance.
Service limits
Temperature & service
Service temperature must remain compatible with the chosen tempering condition; overheating can soften the part or change toughness and corrosion behavior.
Delivery condition
Heat treatment & condition
420 is machined or formed in a softened condition, then austenitized, quenched, tempered, finished, and passivated to a qualified cycle.
Commercial 420 variants differ in carbon and hardness response; the exact UNS, section, austenitizing temperature, quench, temper, and final hardness must be controlled.
Process route
Fabrication
Machine in the annealed state where possible, then harden, temper, finish, and passivate under controlled procedures.
Welding is generally difficult because of cracking and hardness; alternative grades or a fully qualified thermal procedure may be preferable.
Magnetic response: Ferromagnetic.
Decision boundaries
Comparisons & substitution
410 normally offers greater toughness and easier fabrication at lower hardness; 420 is chosen when wear or edge retention justifies the higher-carbon route.
440C can attain greater hardness and carbide volume, while precipitation-hardening grades can provide high strength with different toughness, corrosion, and dimensional-control trade-offs.
Where it is used
Applications
Ordering scope
Product forms & standards
Bar and shapes ordered with the exact annealed or hardened-and-tempered condition, section, straightness, and test requirements.
Plate, sheet, strip, wire, forgings, or machined components under the form-specific standard with heat identity preserved through final treatment.
Decision support
Selection guidance
Choose this grade when
- High hardness, edge retention, or wear resistance is required with moderate corrosion performance.
- The exact chemistry and heat-treatment response can be qualified on the production section.
Review another grade when
- Weldability, high toughness, or aggressive chloride resistance is more important than hardness.
- The term 420 is being used without a defined UNS, carbon range, condition, or hardness target.
Before ordering
Procurement checklist
Name the governing product specification and edition, exact UNS designation, dimensions, tolerances, finish, and delivery or heat-treatment condition.
Require a traceable material test report and verify chemistry, mechanical tests, heat treatment, marking, and any supplementary examination against the purchase order.
State the service environment, design temperature, fabrication route, inspection plan, certification, packaging, and any regulatory or end-user approval before order release.
Traceable evidence