Comparative Overview: Three Types of Stainless Steel Powder
| Feature | Atomized Spherical Powder | Ultrafine Powder | General (Water-Atomized) Powder |
|---|
| Primary Process | Gas Atomization (or VIGA, EIGA) | Specialized Gas Atomization (with fine classification) or Chemical
Processes | Water Atomization |
| Particle Shape | Spherical | Spherical or Sub-Spherical | Irregular, Jagged |
| Particle Size | 15-150 µm (process-dependent) | Typically < 10 µm (Nanopowders are < 1 µm) | 5-250 µm (process-dependent) |
| Flowability | Excellent | Very Poor (cohesive) | Fair to Good (mechanical interlock) |
| Packing Density | Very High | Low | Moderate |
| Oxygen Content | Low | Can be High (due to high surface area) | High |
| Cost | High | Very High | Lowest |
| Primary Applications | Additive Manufacturing, MIM, HIP | Specialty MIM, Conductive Inks, Catalysts, Sintering Aids | Press & Sinter (P/M), Welding Electrodes, Surface Coating |
1. Atomized Spherical Stainless Steel Powder
This is the high-performance, premium-grade powder used in advanced
manufacturing.
Production Method:
Primarily Gas Atomization. Molten stainless steel is disintegrated
by a high-velocity stream of inert gas (Argon or Nitrogen), forming
spherical droplets that solidify as they fall.
Key Characteristics:
- Morphology: Perfectly spherical, smooth surface. This is its defining feature.
- Size Range: Tightly controlled distributions. Common for Laser Powder Bed
Fusion (3D printing) is 15-45 µm or 20-53 µm. For MIM, it's finer,
typically 5-25 µm.
- Flowability: Excellent, crucial for automated layering in 3D printers and
uniform mold filling in MIM.
- Purity: Very low oxygen content due to the inert gas atmosphere.
Why Sphericity is Critical:
- For AM: Ensures a smooth, consistent powder bed for reliable laser melting
and high-density parts.
- For MIM: Allows for high powder loading in the binder, leading to less
shrinkage and better final properties.
Common Grades:
316L, 304L, 17-4PH, 316, 420.
Applications:
- Metal Additive Manufacturing (3D Printing)
- Metal Injection Molding (MIM)
- Hot Isostatic Pressing (HIP)
- Coating via Plasma Spray
2. Ultrafine Stainless Steel Powder
This refers to powders with particle sizes typically in the
sub-micron to ~10 micron range. They are characterized by their
extremely high surface area.
Production Method:
- Specialized Gas Atomization: Standard gas atomization followed by advanced air classification
to separate the finest fraction.
- Chemical Methods: Such as reduction of oxide powders or electrolysis.
Key Characteristics:
- Morphology: Can be spherical but often less perfect than standard gas-atomized
powder. Nanopowders are often agglomerated.
- Size Range: Generally < 10 µm. True nano-powders are < 1 µm (1000 nm).
- Flowability: Very Poor. These powders are highly cohesive and behave more like
a fluid or paste due to strong interparticle forces (Van der Waals
forces). They do not flow freely.
- Reactivity: Very high surface area makes them highly reactive (pyrophoric in
some cases) and susceptible to rapid oxidation. Handling requires
inert atmospheres.
Primary Applications (Niche & High-Value):
- Specialty MIM: For producing micro-MIM parts with ultra-fine
features.
- Sintering Activator: Added to coarser powders to enhance sintering
kinetics and allow for lower sintering temperatures.
- Conductive Inks and Pastes: For printed electronics.
- Catalysts: In chemical processing.
- Energetic Materials: As a fuel component in pyrotechnics and
propellants.
3. General Stainless Steel Powder (Water-Atomized)
This is the most common and economical type of stainless steel
powder, representing the bulk of the powder metallurgy (P/M)
industry's consumption.
Production Method:
Water Atomization. Molten steel is broken up by high-pressure water
jets.
Key Characteristics:
- Morphology: Irregular, jagged, and raspberry-like. This shape is a direct
result of rapid quenching by water.
- Size Range: Broad distribution, from a few microns up to 250 µm.
- Flowability: Fair to good. The irregular particles mechanically interlock,
which is beneficial for achieving "green strength" in compacted
parts before sintering.
- Oxygen Content: Higher than gas-atomized powder due to oxidation during water
atomization.
Why Irregular Shape is an Advantage for its Applications:
- For Press-and-Sinter: The jagged particles cold-weld together under high pressure,
forming a strong "green" part that can be handled before it goes
into the sintering furnace.
Common Grades:
304L, 316L, 430, 409, 17-4PH.
Applications:
- Traditional Press-and-Sinter (P/M) Parts: Such as automotive
components (sensor rings, exhaust flanges), appliance parts, and
industrial machinery parts.
- Welding Electrodes & Flux-Cored Wire.
- Metal Additives for Coatings.
- Porous Filters (the irregular shape creates interconnected pores).
Summary and Selection Guide
- Choose Atomized Spherical Powder when your process demands
excellent flowability and high packing density. This is essential
for Additive Manufacturing and MIM to produce high-integrity,
complex parts.
- Choose Ultrafine Powder for highly specialized applications where
extreme surface area or very fine features are required, such as in
micro-MIM, catalysis, or as a functional filler. Cost and handling
difficulty are significant factors.
- Choose General Water-Atomized Powder for cost-effective,
high-volume manufacturing of structural components via
Press-and-Sinter, or for applications like welding and coatings
where particle shape is less critical than cost.
