AISI 420
AISI 420 Stainless Steel: A High Carbon Martensitic Alloy Hardenable by Heat Treatment
AISI 420 is one of the high carbon members of the martensitic stainless steel family and is essentially preferred in applications requiring hardness, cutting performance and wear resistance. The fact that the carbon ratio is also high, together with the chromium content that provides the stainless character, makes it possible to reach very high hardness levels by heat treatment. For this reason AISI 420 is preferred in many industries, from surgical blades to mould parts and from pump components to food processing equipment.
While this article explains the technical aspects of AISI 420 such as its chemical composition, mechanical behaviour, heat treatment properties and surface quality, it also details its classifications according to international standards such as ASTM and AMS. It has been written in a language suited to purchasing, so as to make supply decisions easier for industrial users.
AISI 420 Chemical Composition and Microstructural Properties
AISI 420 is a martensitic steel class that can have a carbon content starting at 0.15% and going up to 0.40%. Its chromium content, on the other hand, varies in the range of 12% to 14%. This composition makes it possible to obtain high hardness after heat treatment. As the carbon ratio increases, machinability decreases while cutting and wear resistance increase.
Its approximate chemical composition is as follows:
- Carbon (C): 0.15% – 0.40%
- Chromium (Cr): 12.0% – 14.0%
- Manganese (Mn): Maximum 1.0%
- Silicon (Si): Maximum 1.0%
- Phosphorus (P): Maximum 0.04%
- Sulphur (S): Maximum 0.03%
Thanks to the martensitic structure obtained after heat treatment, it is suitable for use in applications where both mechanical strength and edge retention are high.
AISI 420 Heat Treatment and Mechanical Properties
AISI 420 is a material that can be hardened by quenching and tempering. The hardening operation is generally applied at a temperature of 980–1035 °C and is then transformed into a martensitic structure by rapid cooling. Thanks to the high hardness obtained, it is preferred especially in cutting edge applications.
Its mechanical properties generally lie in the following range:
- Tensile Strength: 700 – 1400 MPa
- Yield Strength: 350 – 1000 MPa
- Hardness (HRC): 48 – 55 (in the hardened and tempered condition)
- Elongation: Approximately 10% – 20% (in the annealed condition)
- Density: 7.75 g/cm³
While this alloy has formability in the annealed condition, its performance in terms of hardness and wear resistance reaches its peak after quenching. However, this hardness limits properties such as weldability and ductility. For this reason it is recommended that re-annealing be carried out after the welding operation.
ASTM, AMS and Other Technical Standards
Since AISI 420 steel has a widespread area of use in many industries, it has been defined by various standards organisations such as ASTM, AMS, EN and DIN.
ASTM Standards:
- ASTM A276: Stainless steel bar and section products
- ASTM A240: Sheet, plate and strip products
- ASTM A582: For free-machining bars
- ASTM A314: Industrial bar products
- ASTM A895: For special applications requiring excellent surface quality
AMS Standards:
- AMS 5621: 420 steel in the annealed and machinable condition
- AMS 5506: Cold rolled sheet products
DIN/EN Equivalents:
- DIN 1.4021 / X20Cr13
- EN 10088-3
Compliance with these standards in the supply chain is of critical importance especially in sensitive applications such as the aerospace and medical sectors. .
AISI 420 Industrial Application Areas
AISI 420 stainless steel is used in many applications that require high hardness and where a medium level of corrosion resistance is sought. It has less corrosion resistance compared with austenitic steels, but the high strength provided by the martensitic structure makes it ideal for special applications.
- Cutting Tools and Surgical Equipment: AISI 420 is widely used especially in surgical blades, scissors, razor blades and industrial knives. Hardness and edge strength are the most important criteria in this field.
- Mould and Injection Equipment: The use of AISI 420 in plastic injection moulds is widespread because it provides both hardness and a polishable surface.
- Pump and Valve Components: The 420 series is a suitable choice for pump shafts, valve parts and turbine components operating in water and in mildly acidic or alkaline environments.
- Food and Agricultural Equipment: AISI 420 is preferred in machine parts that come into contact with food but do not require high chemical resistance. In these fields, designations such as “420 food grade stainless” guide the supply process.
Advantages and Disadvantages of AISI 420
Advantages:
- Very high hardness (up to 55 HRC) can be obtained by heat treatment.
- It offers good wear resistance.
- With its polishable surface quality it can also be used for decorative purposes.
- Its corrosion resistance is higher than that of low alloy carbon steels.
- Thanks to its compliance with standards it offers widespread availability in the supply chain.
Disadvantages:
- Its corrosion resistance is low compared with austenitic stainless steels.
- Low toughness and impact strength give rise to a risk of brittleness, especially in cold environments.
- Weldability is limited; preheating and annealing may be required.
- Even in the annealed condition its formability is limited.
Conclusion and Purchasing Perspective
AISI 420 stainless steel is a cost-effective solution that can be shaped by heat treatment in applications where cutting resistance and wear strength are required.
Compliance with the ASTM and AMS norms to be used in the supply process is of vital importance, especially for industrial quality assurance. When making a material selection, the corrosion character of the service environment and the form of mechanical loading should be taken into account.
In conclusion, AISI 420 is a versatile martensitic stainless steel grade that strikes a balance between surface quality, wear resistance and mechanical strength and can be used across a broad range of sectors.
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#AMS5620 Bars / forging (free mach)
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| Chemical Properties | Min. | Max. | Mechanical Properties | Value | |
|---|---|---|---|---|---|
| C | 0.16 | 0.25 | Tensile Strength (MPa) | 655 | |
| Mn | - | 1.00 | Proof Stress (MPa) | 345 | |
| Si | - | 1.00 | Elongation A50 mm | 25 | |
| P | - | 0.04 | Hardness Brinell | 196 Max HB | |
| S | - | 0.030 | Density | 7.80 g/cm3 | |
| Cr | 12 | 14 | Melting Point | 1454-1510 °C | |
| | | Modulus of Elasticity | 200 kN/mm² | ||
| | | Electrical Resistivity | 0.55 Ωmm²/m | ||
| | | Thermal Conductivity | 24.9 W/m.K | ||
| | | Thermal Expansion | 10.3 – 11.7 x 10-6/K |
We supply this material
We supply AISI 420 (1.4021) — to AMS 5621, AMS 5506 standards, in the dimensions and forms required. For stock availability and pricing:
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