410 vs 420 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
Engineers and procurement professionals frequently choose between AISI 410 and AISI 420 when specifying martensitic stainless steels for components that must balance cost, formability, strength, and moderate corrosion resistance. Typical decision contexts include selecting a grade for valve components, shafts, fasteners, or cutlery where trade-offs among wear resistance, hardenability, weldability, and finishing cost matter.
The principal technical distinction is that 420 is a higher-carbon variant compared with 410, which gives 420 substantially greater achievable hardness and wear resistance after hardening, while 410 retains relatively better ductility and toughness in many service conditions. Because both are martensitic stainless grades with similar chromium levels, they are often compared for applications that require a martensitic response (hardening + tempering) rather than the superior corrosion resistance of austenitic grades.
1. Standards and Designations
- Common standards and designations:
- AISI/SAE/UNS: 410 (UNS S41000), 420 (UNS S42000)
- ASTM/ASME: commonly referenced materials derived from AISI designations for bar, plate and forgings
- EN: X12Cr13 (comparable to 410); variants of 420 appear as X20Cr13 family members or other martensitic codes depending on carbon
- JIS/GB: comparable martensitic stainless equivalents exist in Japanese and Chinese standards (e.g., SUS410 family), but local standards use distinct numbering
- Classification: Both 410 and 420 are martensitic stainless steels (stainless, air-hardenable, heat-treatable). They are not tool steels or HSLA steels; they are stainless, heat-treatable alloys intended for moderate corrosion resistance and high hardness capability.
2. Chemical Composition and Alloying Strategy
The alloying strategy for both grades centers on chromium for corrosion resistance and carbon for hardenability and strength. 420 increases carbon relative to 410 to enable higher hardening response and wear resistance at the cost of ductility and weldability.
| Element | Typical range / notes — 410 | Typical range / notes — 420 |
|---|---|---|
| C (carbon) | Low–moderate (lower carbon than 420; designed for balance of ductility and hardenability) | Higher carbon (intentionally elevated to increase hardenability and hardened hardness) |
| Mn (manganese) | Small additions (deoxidation, limited solid solution strengthening) | Similar small additions |
| Si (silicon) | Small, for deoxidation; minor strengthening | Similar |
| P (phosphorus) | Controlled low levels (impurity control) | Controlled low levels |
| S (sulfur) | Controlled low (improves machinability in some grades when present) | Controlled low (may be present in machinable variants) |
| Cr (chromium) | ~12% (provides basic stainless/oxidation resistance and martensitic stainless characteristics) | ~12–14% (similar chromium level as 410) |
| Ni (nickel) | Typically low to none (keeps structure martensitic) | Typically low to none |
| Mo, V, Nb, Ti, B, N | Usually absent or in trace amounts; some commercial variants may include small alloying additions | Usually absent or trace; specialty 420 variants (e.g., 420HC) may have tailored C/S/P for machinability/hardness |
Notes: Exact percentages vary by standard and product form (bar, strip, sheet, forgings). The key alloying levers are chromium (for corrosion resistance) and carbon (for hardenability and maximum hardness after quench-temper).
How alloying affects properties: - Chromium creates a passive oxide film that gives stainless behavior at moderate concentrations (~11–14% in these martensitic grades). - Carbon increases martensite hardness and strength after quenching; higher carbon reduces toughness and weldability and promotes carbide formation during heat exposure or welding. - Low Ni and low alloy contents keep these steels magnetic and martensitic, permitting heat-treatment paths that austenitic grades cannot follow.
3. Microstructure and Heat Treatment Response
Microstructure: - In the annealed condition both grades are generally ferritic/pearlitic or partially austenitic depending on exact chemistry and thermal history. After austenitizing and quenching, both produce martensitic microstructures; retained austenite and carbide distribution depend on carbon and cooling rate. - 410: With lower carbon, martensite is less carbon-supersaturated and typically finer; carbides are present but less abundant than in 420. - 420: Higher carbon produces a harder martensite matrix and a greater volume fraction of chromium carbides (M23C6-type carbides) after certain thermal cycles.
Heat-treatment response: - Normalizing (air cooling from austenitizing): refines grain size and can homogenize microstructure; used more for dimensional stability and toughness improvement in 410. - Quench and temper: primary route to obtain a hardened, tempered martensitic structure in both grades. 420 attains higher hardness at equivalent temper temperatures because of higher carbon; but it also requires careful tempering to balance toughness and reduce brittleness. - Thermo-mechanical processing: forging and controlled rolling can refine austenitic grain size prior to quench and increase toughness in both grades; effects are more pronounced in 410 due to its lower hardenability.
Practical note: 420 is more sensitive to overheating and carbide precipitation during slow cool or weld thermal cycles; this can reduce local corrosion resistance and toughness.
4. Mechanical Properties
Mechanical properties are heat-treatment-dependent. Below is a comparative, application-ready summary for common conditions (annealed vs. quenched & tempered or hardened + tempered).
| Property | 410 (typical behavior) | 420 (typical behavior) |
|---|---|---|
| Tensile Strength | Moderate in annealed; increases with quench/temper but lower maximum than 420 at equivalent hardening | Lower in annealed but can reach higher ultimate tensile strength when hardened due to higher carbon |
| Yield Strength | Moderate; good balance between yield and ductility | Higher achievable yield when hardened; lower ductility at equivalent strength |
| Elongation (ductility) | Better ductility and elongation in annealed and tempered conditions | Reduced elongation after hardening; lower ductility than 410 at comparable strength |
| Impact Toughness | Generally better toughness (less embrittlement at moderate hardness levels) | Lower impact toughness in heavily hardened condition; more brittle tendency when pushed to high hardness |
| Hardness (maximum achievable) | Moderate max hardness after hardening (suitable for some wear) | Higher max hardness (greater wear resistance and edge retention), but sacrifices toughness |
Interpretation: 420 is the stronger, harder option after heat treatment; 410 is more forgiving — easier to obtain reasonable toughness and ductility while still providing modest hardened strength.
5. Weldability
Weldability considerations hinge on carbon content and hardenability. Both grades are martensitic stainless steels and present weld challenges compared with low-carbon steels or austenitic stainlesss.
Useful indices (qualitative interpretation): - Carbon Equivalent (IIW): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (important for steel weld cracking susceptibility): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - 420 has a higher carbon term in both indices, increasing hardenability and the risk of cold cracking and HAZ martensite formation. Preheat and interpass temperature control plus post-weld tempering or PWHT reduce hydrogen embrittlement risk. - 410, with lower carbon, is easier to weld but still requires attention to hydrogen control and preheat when welds penetrate heavily cold-worked sections or thick sections. - Use of matching filler metals, low-hydrogen processes, preheating, and post-weld tempering helps both grades; 420 generally demands more stringent controls and higher post-weld heat treatment to restore toughness.
6. Corrosion and Surface Protection
- Both 410 and 420 are martensitic stainless steels: they provide corrosion resistance superior to plain carbon steel in dry atmospheres and mild environments but inferior to austenitic grades (304/316) in chloride or acidic exposures.
- Chromium content is the primary contributor to corrosion resistance in both grades; since both have similar chromium, base corrosion resistance is comparable in many conditions.
- Higher carbon in 420 can encourage chromium carbide precipitation at grain boundaries during slow cooling or welding. This localized depletion of chromium may reduce resistance to intergranular corrosion.
- PREN (not commonly used for martensitic grades) formula (for guidance only in some stainless families): $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index is principally applicable to duplex and austenitic stainlesses; it is of limited use for martensitic grades because Mo and N are typically low or absent.
Surface protection options for both grades when corrosion resistance needs augmentation: - Galvanizing (for 410 in some forms) — but galvanizing stainlesss is uncommon and may be unnecessary for typical service. - Painting, polymer coatings, or plated coatings (nickel/Chrome) — widely used for components where corrosion or appearance matters. - Passivation treatments and careful control of heat treatment/weld cycles to avoid sensitization.
7. Fabrication, Machinability, and Formability
- Machining: Both should be machined in the soft/annealed condition for best tool life. 420’s higher carbon and potential higher hardness in some product conditions require care; machinable variants (e.g., 420 with controlled sulphur) improve chip formation.
- Forming and bending: 410, with lower carbon and higher ductility in the annealed state, is easier to cold-form and bend. 420 needs more aggressive forming parameters or must be formed in annealed condition, and springback can be higher after tempering.
- Grinding, polishing, and finishing: 420 is preferred for applications requiring edge retention and a polished cutting edge (cutlery, blades) because it responds well to hardening and polishing; 410 takes polish and finishes adequately but with lower hardness achievable.
8. Typical Applications
| 410 — Typical uses | 420 — Typical uses |
|---|---|
| Fasteners, bolts, shafts, valve components, pump parts where moderate corrosion resistance and toughness are required | Cutlery, surgical instruments, razors, bearings, wear parts, valve seats where higher hardness and edge retention are needed |
| Structural components in power-generation, petrochemical non-severe environments | Tools and components requiring higher surface hardness or wear resistance after hardening |
| General-purpose martensitic stainless where welding/fabrication ease matters | Components prioritizing wear resistance and high hardness; selected for finishing/polishing |
Selection rationale: - Choose 410 if the application values ductility, ease of welding/fabrication, and moderate corrosion resistance at lower cost. - Choose 420 if the application requires higher hardened hardness and wear resistance (edges, seals, wear faces) and the design can tolerate reduced toughness and more stringent welding/heat-treatment controls.
9. Cost and Availability
- Cost: 410 is generally less expensive than 420 in many product forms because of lower carbon content and broader commodity use; 420 variants (especially high-carbon or “HC” grades) can cost more due to processing for enhanced hardness and specific finishing.
- Availability: Both grades are widely available in common forms (bar, plate, strip, forgings), though specialty variants of 420 (e.g., 420HC, 420J2) are often marketed for cutlery and surgical uses. Lead times are typically short for standard mill products; specify the exact variant (annealed, hardenable, sulphurized for machinability) early in procurement to avoid substitutions.
10. Summary and Recommendation
| Attribute | 410 | 420 |
|---|---|---|
| Weldability | Better (lower carbon) | More challenging (higher carbon) |
| Strength–Toughness trade-off | Balanced toughness with moderate strength | Higher achievable strength/hardness but lower toughness |
| Cost | Generally lower | Generally higher for high-carbon/high-hardness variants |
Conclusions: - Choose 410 if you need a martensitic stainless with relatively better ductility and toughness, easier fabrication and welding, and moderate corrosion resistance — for example, shafts, valves, fasteners, and components where weldability and toughness are priorities. - Choose 420 if you need higher hardened hardness and wear resistance (cutting edges, seals, wear faces, precision blades), and the design allows for stricter welding controls and post-weld heat treatment to mitigate brittleness and corrosion risks.
Final practical advice: specify the exact product condition and post-fabrication heat-treatment plan in procurement documents (e.g., “420, quenched and tempered to X HRC with final temper at Y°C” or “410, normalized for improved toughness”), and require chemical and mechanical certification to ensure the selected grade meets the intended balance of hardness, toughness, and corrosion performance.