304 vs 316L Stainless Steel in Powder Metallurgy: Which Grade Should You Choose?

Composition Overview

The two key differences are:

1. Molybdenum: 316L contains 2–3% Mo, which significantly improves resistance to chloride pitting and crevice corrosion
2. Carbon content: 316L has lower maximum carbon (the "L" designation), which reduces carbide precipitation during sintering and improves intergranular corrosion resistance

In PM processing, both differences matter. The molybdenum content of 316L is the primary reason it outperforms 304 in chloride-containing environments. The lower carbon of 316L also makes it more robust during the sintering cycle, where carbon management is important.

Corrosion Resistance

This is the most common reason to choose between the two grades.

304 stainless provides good general corrosion resistance in mildly corrosive environments:

• Atmospheric exposure (general industrial, outdoor)
• Fresh water
• Weak acids and weak alkalis
• Food-contact applications where chloride content is low

316L stainless adds molybdenum, which provides resistance to:

• Chloride-containing environments (seawater, saline solutions, chlorinated cleaning agents)
• Pitting and crevice corrosion in aggressive environments
• Acidic environments (dilute sulfuric acid, phosphoric acid)
• Stronger oxidizing and reducing acid combinations

The practical implication: if your part will be exposed to chlorides at any meaningful concentration—salt spray, marine environments, chlorinated wash water, body sweat in handheld devices—316L is the appropriate choice. 304 will eventually show pitting in chloride environments even if it passes initial corrosion testing.

For interior applications with no chloride exposure, 304 is often adequate and costs less.

Mechanical Properties in PM

Both grades are produced as sintered PM parts to MPIF standard grades. Typical as-sintered properties for comparison:

Properties are comparable. 316L is slightly softer and more ductile on average, which can be an advantage for parts that need to deform slightly under load or be press-fitted without cracking.

These values are representative and application-dependent. Final material properties should be specified from your supplier's material data sheet for the specific density and processing condition.

Neither grade is typically chosen for high mechanical load applications. If tensile strength above 300–400 MPa is needed, iron-based alloys with heat treatment are more appropriate. Stainless PM is selected primarily for corrosion resistance, hygiene, or appearance requirements.

PM Processing Differences

Both grades sinter well in hydrogen or vacuum atmospheres. The key processing consideration is:

Carbon control during sintering. At elevated sintering temperatures, carbon from furnace atmosphere or lubricants can diffuse into the part. In 304, this can form chromium carbides at grain boundaries (sensitization), reducing intergranular corrosion resistance. In 316L, the lower base carbon content and presence of molybdenum make sensitization less likely, but it is still a consideration in processing.

For parts with critical corrosion requirements, specifying 316L provides an additional margin against sensitization-related issues in production sintering.

Density. Both grades achieve similar densities under typical PM compaction pressures. There is no significant practical difference in compactability.

Sizing and secondary operations. Both grades can be sized, though the austenitic structure (non-magnetic, moderate work hardening) means sizing forces are higher than for iron-based grades. This should be factored into tooling design for tight-tolerance features.

Cost Comparison

316L consistently costs more than 304. The difference is primarily driven by:

• Higher nickel content (10–14% vs 8–12%)
• Molybdenum addition (2–3%)

In PM, the powder cost is typically 15–30% higher for 316L than 304 for comparable grade and particle size. This translates to a meaningful per-piece cost difference at volume, particularly for larger or heavier parts.

If your application genuinely does not require the chloride resistance of 316L, the extra cost is not justified. However, specifying 304 in a borderline chloride environment to save cost creates field failure risk. The material upgrade decision is worth making clearly, not defaulting to the cheaper grade without analysis.

Application Guide

Choose SS-304 when:

• The environment is non-chloride (fresh water, dry air, weak acid/base)
• The application is interior, sealed, or protected from atmospheric salts
• Cost is a constraint and the corrosion environment is well-characterized as mild
• The part will be further protected by coating, plating, or paint
• Food contact in low-chloride environments (consult applicable food-contact standards for the specific use)

Choose SS-316L when:

• Chloride exposure is likely or uncertain (marine, outdoor, coastal, medical wash cycles)
• The part contacts saline solutions, seawater, or chlorinated cleaning agents
• The application involves body fluids or sweat (wearable devices, medical)
• The environment involves acidic media beyond mild concentrations
• Long service life in aggressive environments is required and field replacement is expensive
• The application is in food processing where chlorinated CIP (clean-in-place) wash is used

Common PM Applications by Grade

Other Stainless Grades in PM

For completeness: PM is also used to produce 410 (martensitic, hardenable, magnetic) and 434 stainless steel. These have higher hardness and wear resistance but lower corrosion resistance than 304 or 316L. They are typically chosen for automotive and mechanical applications where wear resistance matters more than corrosion performance.

If your application requires hardness above 30 HRC or magnetic properties, 410 or 434 may be the right stainless grade—not 304 or 316L.

Summary Decision

If you are specifying a stainless PM part and are unsure which grade fits your application, contact our engineering team. We can help evaluate your environment and application conditions before you commit to a material specification.