420 Stainless Steel (UNS S42000)
Martensitic · ASTM A240/A240M, A276 · Density 7.75 g/cm³
Type 420 (UNS S42000) is a 13% chromium martensitic stainless steel with at least 0.15% carbon. Supplied annealed for machining and forming, it is then hardened and tempered to 48–52 HRC, which makes it the standard grade for knife blades, surgical instruments, plastic mold tooling and valve trim.
Chemical Composition (wt%)
| C | Mn | Si | Cr | P | S |
|---|---|---|---|---|---|
| ≥0.15 | ≤1.00 | ≤1.00 | 12.0–14.0 | ≤0.040 | ≤0.030 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A240/A240M, A276.
Mechanical Properties
| Condition (as supplied) | Annealed |
|---|---|
| Hardness (annealed) | ≤223 HBW |
| Hardness (hardened + tempered) | 48–52 HRC (typ.) |
| Tensile (hardened, typ.) | ≈1600–1800 MPa |
Room-temperature minimum values are summarized for annealed flat product under ASTM A240/A240M, A276 unless a condition is named in the property label; product form and thickness can change the requirement.
Physical Properties & Structure
| Density | 7.75 g/cm³ |
|---|---|
| Magnetic response | Magnetic in annealed and hardened conditions. |
| Microstructure | Martensitic |
Corrosion Resistance & Limits
- Corrosion resistance depends on chromium, carbon, heat-treatment condition and surface finish and is generally below common 304-type austenitic stainless steel.
- Avoid assuming hardness implies corrosion resistance. Chlorides, tempering condition, retained scale and grinding contamination must be evaluated for the part.
Fabrication & Heat Treatment
| Welding | Welding requires grade- and section-specific preheat, filler and post-weld heat treatment to control hard cracking and restore properties. |
|---|---|
| Forming | Carry out substantial forming in the annealed condition and allow for reduced ductility as carbon and target hardness increase. |
| Machining | Machine in the annealed or softened condition where possible; hardened material needs appropriate tooling, speeds and allowance for final grinding. |
| Heat treatment | Final properties depend on a specified austenitize, quench and temper route. Temperature, hold time, section size and required hardness belong on the order. |
Equivalent Grades
The closest international equivalents of 420 Stainless Steel are 1.4021 / 1.4028 (X20Cr13 / X30Cr13) in the EN system, SUS420J1 / SUS420J2 in the JIS system, 20Cr13 / 30Cr13 in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S42000 |
| EN | 1.4021 / 1.4028 (X20Cr13 / X30Cr13) |
| JIS | SUS420J1 / SUS420J2 |
| GB | 20Cr13 / 30Cr13 |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 420 stainless steel: Bar, Sheet / Plate, Coil / Strip.
| Conditions | Annealed; hardening by 980–1035 °C oil quench + temper |
|---|---|
| Bar diameter | 6–300 mm |
| Sheet / plate thickness | 2–60 mm |
Common surface and delivery options: No.1, 2B, BA or mechanically polished finish when supported by the product route; Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Knife blades and cutting tools
- Surgical and dental instruments
- Plastic injection mold bases
- Pump shafts and valve trim
- Scissors and hand tools
Frequently Asked Questions
What is the difference between 420J1 and 420J2?
Carbon content: J1 runs roughly 0.16–0.25% C, J2 0.26–0.40% C (JIS designations). More carbon means higher attainable hardness — J2 reaches about 52 HRC versus 50 for J1 — at some cost in toughness and corrosion resistance. Budget knives typically use J2.
Is 420 stainless steel rust proof?
Only in the hardened and polished condition. Corrosion resistance of martensitic grades depends on carbon being dissolved during hardening; annealed or coarsely ground 420 stains noticeably faster. Even hardened, it suits kitchen and clinical environments rather than marine exposure.
420 vs 440C — which knife steel should I choose?
440C carries about 1% carbon and 17% chromium, reaching 58–60 HRC with better edge retention and slightly better corrosion resistance, at higher price and lower toughness. 420 is easier to sharpen, tougher and cheaper — fine for utility knives, surgical tools and molds.
420 Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301309S316Ti347904L409L4394414442507303317L254 SMO440C17-4 PH2304
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