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1. Martensitic 420 Overview
Martensitic 420 stainless steel (UNS S42000) is a high‑carbon martensitic stainless steel with minimum 12% chromium. It can be significantly hardened by heat treatment and provides good ductility in the annealed condition and excellent corrosion resistance when polished, ground, or hardened. It offers the highest hardness (up to 50 HRC) among 12% chromium stainless grades.
Brinell range 223 – 277 or in the annealed condition with a maximum Brinell hardness of 241.Characterised by good corrosive resistance in mild atmospheric, domestic and industrial environments. It is resistant to ammonia, blood, carbonic acid, crude oil, detergent solutions, dilute nitric acid, fresh water, food acids, many petroleum products, steam and vinegar etc. coupled with good strength and reasonable impact properties in the as supplied hardened and tempered condition.420 due to its excellent hardenability is capable of being through hardened up to Rc52 or higher depending upon carbon content and section size. Small sections can be air cooled and larger sections oil quenched for maximum through hardness.
Pre hardened and tempered 420 will also respond readily to nitriding achieving a typical surface hardness of over Rc65. The nitriding process however reduces the corrosion resistance and is therefore not generally recommended except for critical applications where the benefit outweighs all other considerations.
Material magnetic in all conditions.
Key equivalent grades:
- EU: 1.4021, X20Cr13
- UK: 420S37
- Japan: SUS 420J1
- Standard: ASTM A276
2. Chemical Composition (wt%)
| Element | C | Cr | Mn | Si | P | S |
| Min | 0.15 | 12.0 | – | – | – | – |
| Max | – | 14.0 | 1.0 | 1.0 | 0.040 | 0.03 |
3. Mechanical Properties (from ASTM A276)
Annealed Condition
| Property | Value |
| Tensile Strength | 655 MPa |
| Yield Strength (0.2% proof) | 345 MPa |
| Elongation (50mm) | 25% |
| Brinell Hardness (HB) | max 241 |
Tempered Conditions
| Tempering Temp (°C) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Brinell Hardness (HB) | Charpy V Impact (J) |
| 204 | 1600 | 1360 | 12 | 444 | 20 |
| 316 | 1580 | 1365 | 14 | 444 | 19 |
| 427 | 1620 | 1420 | 10 | 461 | – |
| 538 | 1305 | 1095 | 15 | 375 | – |
| 593 | 1035 | 810 | 18 | 302 | 22 |
| 650 | 895 | 680 | 20 | 262 | 42 |
4. Physical Properties (Annealed)
| Property | Value |
| Density | 7800 kg/m³ |
| Elastic Modulus | 200 GPa |
| Thermal Expansion (0–100°C) | 10.3 ×10⁻⁶ m/m·°C |
| Thermal Conductivity | 24.9 W/m·K |
| Specific Heat (0–100°C) | 460 J/kg·K |
| Electrical Resistivity | 550 nΩ·m |
5. Heat Treatment
- Annealing: 840–900°C, slow furnace cool to 600°C, then air cool
- Process Anneal: 735–785°C, air cool
- Hardening: 980–1035°C, quenching in oil or air
- Tempering: 150–370°C for high hardness
| Elevated Temperature Properties | |||||||||||
| 420 displays good resistance to scaling in continuous service up to 650oC. Its use however at these higher working temperatures results in a substantial drop in tensile strength and hardness, plus a reduction in corrosion resistance.It is therefore not recommended for use at working temperatures above 400oC. | |||||||||||
| Low Temperature Properties | |||||||||||
| 420 is also not recommended for use at sub-zero temperatures due to a substantial drop in impact properties consistent with most steels other than the austenitic steel types. | |||||||||||
| Cold Bending | |||||||||||
| In the hardened and tempered as supplied condition will be more difficult due to the high yield strength which must be taken into account. | |||||||||||
| Hot Bending | |||||||||||
| In the hardened and tempered as supplied condition it is not recommended due to its affect on the mechanical properties within the heat affected zone. |
6. Welding
- Preheating: 150–320°C
- Postheating: 610–760°C
- Recommended filler: Grade 420 or Grade 309
| Machining | |||||||||||
| 420 machines best in the hardened and tempered as supplied condition R or condition S, and despite its relatively high carbon content is still regarded as having reasonable machinability with all operations such as drilling, turning etc. capable of being carried out as per machine manufacturers recommendations for suitable tool type, feeds and speeds. It does not work harden to the same extent as the 300 series austenitic stainless steels, but is more similar in this respect to the low alloy high tensile steels such as 4150 or 6150 etc. | |||||||||||
| Welding | |||||||||||
| 420 is not generally recommended for welding in either the annealed or hardened and tempered condition, due to its air hardening capability which can lead to the formation of brittle martensite, resulting in cold cracking due to contraction stresses within the weld and heat affected zone. The higher the carbon content the higher the hardening capability and the greater the risk of cracking.Pre heating and interpass temperature control during welding, plus very slow cooling and post-weld annealing is the best method to prevent cracking.The following welding procedure and post-weld heat treatment may be taken as a guide only if welding is necessary. |
| Welding Procedure | |||||||||||
| Welding electrodes or rods should be low hydrogen types 420 or *similar when strength is required or when post-weld hardening and tempering, otherwise an austenitic stainless electrode or rod such as 309 or *similar may be used to give a more ductile weld, when strength is not so critical and post-weld annealing is not possible or intended.Pre-heat at 200oC – 300oC and maintain a high heat input during welding. On completion of welding cool slowly as possible until hand warm and as required:Post-weld sub-critical anneal at 650oC – 750oC or full anneal and harden and temper as required. |
7. Corrosion Resistance
- Good resistance to fresh water, atmosphere, foods, alkalis, and mild acids
- Best performance in polished or hardened condition
- Lower corrosion resistance than 304, 316 austenitic grades and 430 ferritic alloys
8. Typical Applications
- Valve components, needle valves, flanges, pump parts
- Cutting tools, shear blades
- Surgical and medical instruments
- Cutlery and food‑processing equipment
- Mechanical parts requiring high hardness and wear resistance
9. Our Service
We supply Martensitic 420 stainless steel in forms including bars, plates, forgings, flanges, and fittings. We support:
- ASTM, EN, GB, and customer-specified standards
- Full material test reports (MTC)
- Custom machining, heat treatment, and surface finishing
- Stable quality and on-time delivery
Contact us for a quote now.
