Grade dossier
420 Stainless Steel
420 stainless steel is a heat-treatable martensitic chromium grade identified as UNS S42000. It is selected when a stainless component needs substantially more hardness and wear resistance than 410 can normally provide, while retaining moderate corrosion resistance after proper hardening, tempering and surface finishing. Common procurement routes include cutlery, surgical instruments, molds, dies, brake discs, press plates and other wear-resistant mechanical parts.
Identity before substitution
Define the 420 variant, carbon level and final heat-treatment condition
The commercial name “420” covers more than one closely related martensitic chemistry in international practice. UNS S42000 is the U.S. identity, while EN 1.4021 is a common European cross-reference and higher-carbon EN variants such as 1.4028, 1.4031 and 1.4034 are also sold within the 420 family. The purchase order should therefore state the exact standard, chemistry or grade designation, form, section size, annealed or hardened condition, hardness target, finish and MTC requirements.
420 stainless composition
ATI chemistry reference for UNS S42000 sheet and strip
420 chemistry is not one universal carbon target
ATI currently lists UNS S42000 with 12.0–14.0% chromium and a minimum 0.15% carbon, while EN 1.4021 / X20Cr13 uses a defined carbon range around 0.16–0.25%. Outokumpu also publishes several 420-family EN variants with progressively higher carbon and achievable hardness. Do not approve an EN/UNS substitution by the “420” name alone.
| C | 0.15% min |
|---|---|
| Cr | 12.0–14.0% |
| Mn | 1.00% max |
| Si | 1.00% max |
| Ni | 0.75% max |
| Mo | 0.50% max |
| P | 0.040% max |
| S | 0.030% max |
| Fe | Balance |
420 stainless properties
Heat treatment changes 420 from a machinable annealed bar to a high-hardness alloy
Carpenter typical · 25.4 mm round bar · annealed
| 0.2% yield strength | about 345 MPa |
|---|---|
| Tensile strength | about 655 MPa |
| Elongation | about 25% |
| Hardness | about 196 HB |
Carpenter typical · 1038°C oil quench + 204°C temper
| 0.2% yield strength | about 1482 MPa |
|---|---|
| Tensile strength | about 1724 MPa |
| Elongation | about 8% |
| Hardness | about 512 HB |
These are producer-published typical results for a specific 25.4 mm bar and heat-treatment route, not universal 420 acceptance values. ATI separately reports roughly 48 HRC for a 0.25%C 420 sheet sample hardened at 1038°C and tempered at 204°C. Final properties depend on carbon level, section size, austenitizing, quench, temper and the controlling product specification.
Selection boundary
Use 420 when hardness and wear resistance drive the decision
420 is a practical choice when the part can be heat treated after rough machining or forming and the design values hardness, edge retention or wear resistance. Its corrosion resistance is moderate rather than a substitute for 304/316, and welding becomes more difficult as carbon and hardenability increase.
Good reasons to evaluate 420
Cutting utensils, knife-related parts and surgical instruments requiring a hardened, polishable martensitic grade.
Molds, dies, press plates and other tooling where hardness and wear resistance are procurement drivers.
Brake discs, springs and mechanical parts operating in water, steam or other reviewed mild-corrosion environments.
Components that can be machined in the annealed state and then hardened and tempered to a defined final property target.
Stop and review before release
Severe chloride, reducing-acid, immersion or crevice service being treated as equivalent to an austenitic corrosion grade.
Welding-heavy fabrication: Carpenter notes that air-hardening 420 is seldom welded and requires preheat plus post-weld heat treatment when welding is unavoidable.
Orders that say only “420” without defining the carbon variant, EN/UNS designation, condition and final hardness requirement.
Tempering above about 427°C when maximum corrosion resistance is required; Carpenter specifically advises against this condition.
Fabrication route
Machine annealed stock, then harden and temper to the final requirement
Carpenter gives maximum-softness annealing at about 843–900°C followed by slow furnace cooling. Rough machining is normally easier before final hardening.
For hardening, producer guidance places 420 around 1010–1066°C before oil quenching; thin sections may use air cooling under appropriate procedures.
Temper to the required hardness/toughness balance. Carpenter recommends about 149–204°C when maximum hardness and corrosion resistance are the priority and cautions against tempering above about 427°C for maximum corrosion resistance.
If welding is unavoidable, Carpenter cites roughly 149–204°C preheat followed by a 732–788°C anneal for 6–8 hours and air cooling. Use a qualified WPS rather than a generic web procedure.
420 stainless supplier checklist
Use mill-source forms and real stock ranges without treating every 420 variant as identical
A 420 stainless supplier should identify the exact designation, form, standard, dimensions, annealed or heat-treated condition, surface finish, target hardness, quantity, traceability and MTC requirements. The ranges below are attributable producer or stockholder evidence, not a claim that this website holds live inventory.
Universal Stainless: plate, round bar, RCS billet, flat bar and ingot
Universal specs include AMS 5621 and ASTM A276 / A314 / A473
Outokumpu Dura 420/4021: hot-rolled coil and cold-rolled coil
Swiss Steel UK stock evidence: 1.4021 round bar about 8–115 mm diameter
MTC / heat-treatment release checkpoint
Verify heat number, UNS S42000 or exact EN grade, governing specification and edition, chemistry, product form and dimensions, delivered condition, hardness or strength results required by the order, surface condition and traceability. A practical MTC release line should identify the heat, grade/standard, chemistry, condition, mechanical or hardness result and any supplementary NDT. If 1.4028 or another higher-carbon 420-family grade is proposed, approve it as a documented substitution rather than treating it as chemistry-identical 1.4021.
Interactive selection check
Test 420 against the controlling procurement question
Procurement FAQ
Questions to close before ordering 420 stainless steel
What is 420 stainless steel?
420 is a heat-treatable martensitic chromium stainless steel identified as UNS S42000. Its higher carbon level compared with 410 supports higher achievable hardness and wear resistance after hardening and tempering.
What is the EN equivalent of 420 stainless steel?
EN 1.4021 / X20Cr13 is a common cross-reference for the lower-carbon 420 family, but 420 is also used commercially for higher-carbon EN variants such as 1.4028, 1.4031 and 1.4034. Do not substitute solely on the “420” name; compare the exact chemistry and product standard.
How hard can 420 stainless steel become?
Hardness depends strongly on carbon level and heat treatment. ATI reports about 48 HRC for a 0.25%C 420 sample hardened at 1038°C and tempered at 204°C, while Outokumpu lists roughly 44–50 HRC for Dura 420/4021 and higher ranges for higher-carbon 420 variants.
Is 420 stainless steel easy to weld?
No. Carpenter describes Type 420 as air-hardening and seldom welded. Where welding is unavoidable, preheat and post-weld heat treatment are normally required, with filler and procedure controlled by a qualified WPS.
What should a 420 RFQ include?
State UNS S42000 or the exact EN grade, governing standard and edition, product form, dimensions and tolerances, annealed or heat-treated condition, target hardness or strength, final heat-treatment responsibility, finish, quantity, service environment, MTC and any NDT or supplementary inspection.
Sources, scope and RFQ
Trace the 420 variant, heat treatment and actual supply evidence before release
UNS S42000 identity, current sheet/strip chemistry, density, heat-treatment sensitivity and producer-published typical heat-treated properties. ATI’s broader martensitic sheet data also provides annealing, hardening and corrosion-comparison guidance.
Typical 25.4 mm round-bar mechanical properties in annealed and hardened/tempered conditions, hardening and tempering guidance, machinability, weldability limitations, preheat and post-weld heat-treatment notes.
420 / S42000 family mapping across EN 1.4021, 1.4028, 1.4031 and 1.4034, typical carbon/chromium levels, achievable HRC ranges, hot- and cold-rolled coil forms, and applications including cutting utensils, surgical instruments, brake discs and wear-resistant parts.
Universal Stainless lists plate, round bar, RCS billet, flat bar and ingot for 420, with AMS 5621 and ASTM A276/A314/A473 among its produced specifications. Swiss Steel UK currently lists 1.4021 / 420 round bar around 8–115 mm diameter as a concrete stock-range reference.