410 vs 420 Stainless Steel in Powder Metallurgy

When an application requires both corrosion resistance and high hardness, the two stainless steel PM grades most commonly evaluated are 410 and 420. Both are martensitic stainless steels - hardenable by heat treatment - unlike the austenitic grades (304, 316L) which cannot be hardened to high levels. The choice between 410 and 420 comes down primarily to carbon content, and the consequences of that difference in hardness and corrosion resistance.

Composition

The single most important difference: carbon content. 420 has significantly more carbon than 410. In martensitic stainless, carbon is the primary hardening element. More carbon ->higher achievable hardness after quench. But more carbon also reduces chromium available for corrosion protection (carbon ties up chromium in carbides) and reduces toughness.

Hardness and Wear Resistance

As-sintered (annealed condition):

• SS-410: Typically 20 - 0 HRC as-sintered depending on density and sintering atmosphere
• SS-420: Typically 25 - 5 HRC as-sintered

After heat treatment (quench and temper):

• SS-410-HT: Maximum hardness approximately 38 - 4 HRC (application and temper dependent)
• SS-420-HT: Maximum hardness approximately 48 - 5 HRC (application and temper dependent)

These are illustrative ranges. Actual hardness depends on sintering density, carbon control during sintering, quench rate, and temper temperature.

420 achieves significantly higher hardness than 410 after heat treatment. For applications where surface hardness is the primary requirement - wear surfaces, knife edges, cutting inserts, pump wear components - 420 is the correct grade.

Corrosion Resistance

Higher carbon in 420 reduces corrosion resistance relative to 410:

• More carbon means more chromium carbides form during sintering and heat treatment
• Chromium locked in carbides is not available to form the protective passive oxide layer
• 420 has lower effective chromium in solid solution than 410, resulting in less corrosion resistance

Practical comparison in PM:

For chloride-containing or aggressive corrosion environments, neither 410 nor 420 is the right choice - use 316L or 304 PM instead. The martensitic grades are selected for hardness and wear resistance, not for corrosion performance in aggressive media.

For applications where mild corrosion resistance is needed alongside hardness - pump shafts in clean water, valve components in mild environments, general-purpose structural parts - 410 is the better corrosion choice. If maximum hardness is more important than corrosion resistance, 420 is appropriate.

Toughness

Higher carbon in 420 also reduces impact toughness. Heat-treated 420 is harder but more brittle than heat-treated 410.

For applications with:

• Impact or shock loading
• Vibration with stress concentrations
• Thin cross-sections under dynamic load

410 is preferable to 420. The lower hardness is offset by better toughness and less risk of brittle fracture.

For wear applications with moderate load and no significant impact - sliding contact, abrasion resistance - 420 can tolerate the reduced toughness and the hardness advantage is useful.

Magnetic Properties

Both 410 and 420 are magnetic in both annealed and hardened conditions. This is a defining characteristic of martensitic stainless steels vs. austenitic (304, 316L which are non-magnetic).

For applications where magnetic properties are a functional requirement - magnetic sensors, brake rotors for magnetic actuation, components in magnetic assemblies - both 410 and 420 are suitable, and both offer better magnetic response than austenitic stainless.

PM Processing Considerations

Both grades sinter well, but with some important process requirements:

Carbon control. Carbon in PM stainless parts can be gained or lost during sintering depending on furnace atmosphere. Precise atmosphere control is required to reach the specified carbon range at the end of the sintering cycle. This is more critical for 420 (where carbon content spans a wider range) than for 410 (where maximum carbon is lower and the target is simply "not too high").

Sintering atmosphere. Both grades are sintered in vacuum or high-purity hydrogen. Nitrogen must be avoided or carefully controlled - nitrogen can form chromium nitrides that degrade corrosion resistance in the same way carbides do.

Heat treatment. Austenitizing temperature for 410 is typically 980 - 010 deg C; for 420 it is 980 - 050 deg C. Both are oil or air quenched, then tempered. The tempering temperature significantly affects final hardness - lower temper temperature ->higher hardness but lower toughness. Specifying both hardness range and impact/toughness requirement helps the supplier set the correct temper.

Grinding after sintering. Heat-treated 420 at 50+ HRC is hard to machine but can be precision ground. Many PM 420 applications require grinding of wear surfaces after heat treatment to achieve surface finish and dimensional accuracy.

Typical Applications by Grade

SS-410 Applications

• Valve components in mild fluid environments (discs, seats, spools)
• Pump shaft sleeves and wear rings where moderate hardness and corrosion resistance both matter
• Structural fasteners and hardware where strength and mild corrosion resistance are both needed
• General-purpose PM structural parts where some hardness is useful but 420 hardness is excessive
• Components in mildly corrosive environments where neither 304/316L nor tool steel is appropriate

SS-420 Applications

• Cutting and shearing components (blade holders, cutting edges, knife carriers)
• Pump wear parts under abrasive flow conditions
• High-hardness valve seats in abrasive or erosive media
• Gear teeth in abrasive lubrication environments
• Mold and die components that require corrosion resistance as well as hardness
• Components that alternate between wet and dry exposure with wear requirement

Summary Decision

If you are specifying a martensitic stainless PM part and are unsure whether 410 or 420 is appropriate, contact our engineering team. We can evaluate the wear, load, and corrosion conditions and recommend the correct grade and heat treatment.