304L Stainless Steel Powder for MIM

Overview of 304L Powder for MIM

304L is an austenitic stainless steel containing chromium, nickel and low carbon content. The ‘L’ denotes lower carbon to avoid carbide precipitation during welding. 304L offers excellent corrosion resistance comparable to 316L but at a lower cost.

Key characteristics that make 304L suitable for MIM include:

• Excellent corrosion resistance in a range of environments
• Good ductility, toughness and mechanical properties
• High sintered density achievable
• Excellent moldability due to spherical powder shaping
• Cost-effective compared to 316L powder
• Readily available in a variety of powder specifications

This article provides a detailed overview of properties, processing, sintering, applications, and other specifics of 304L powder when used in metal injection molding.

Typical Composition of 304L Powder for MIM

The composition of 304L powder for MIM is:

Nickel enhances corrosion resistance while chromium provides oxidation resistance. Low carbon minimizes carbide precipitation during sintering.

Properties of 304L Powder for MIM

304L powder exhibits the following properties:

These properties make 304L suitable for producing high-performance MIM parts needing corrosion resistance.

304L Powder Specifications for MIM

304L powder for MIM has the following specifications:

• Particle Size – Typically 10-20 microns with narrow distribution. Critical for high sintered density.
• Flow Rate – Minimum flow rate of 25 s/50 g. Ensures smooth injection molding without blockages.
• Morphology – Predominantly spherical powder for excellent moldability and density.
• Oxygen Content – Low oxygen levels (<2000 ppm) to minimize oxidation.
• Apparent Density – Higher apparent density improves powder loading during molding.
• Tap Density – Higher tap density above 4 g/cm3 desired for good compaction.

Processing of 304L Powder in MIM

304L powder undergoes the following processing steps during MIM:

1. Mixing – The powder is mixed with a suitable binder, lubricants, plasticizers to form the feedstock.

2. Granulation – The feedstock is granulated into spherical pellets to improve flow into the injection barrel.

3. Injection Molding – The feedstock pellets are molded into complex net-shape parts using injection molding.

4. Debinding – The binder is removed from the molded parts through solvent and/or thermal debinding processes.

5. Sintering – The debound parts (brown parts) are sintered at 1300-1400°C in hydrogen to produce dense components.

Sintering Response of 304L Powder

• 304L powder can achieve >95% theoretical density upon sintering with minimal distortion.
• Excellent sinterability owing to fine spherical powder, good surface cleanliness and purity.
• Low carbon minimizes precipitation of chromium carbides during sintering.
• Controlled temperature and atmosphere is needed to achieve high densification and properties.
• Post-sinter heat treatment can enhance properties further.

Applications of Sintered 304L Parts from MIM

MIM using 304L powder is ideal for:

• Surgical instruments like scalpel blades, clamps, retractors, forceps.
• Dental and orthodontic components like implants, braces.
• Watch components like fingers, gears, springs.
• Electrical contacts and connectors.
• Catheters, cannulae and micro fluidic devices for medical.
• Corrosion resistant fittings, fasteners and other hardware.
• Decorative and costume jewelry.

Benefits of Using 304L Powder for MIM

Benefits include:

• Excellent corrosion resistance comparable to cast or wrought 304L stainless steel.
• High dimensional accuracy and superb surface finish of MIM parts.
• Complex geometries possible only through MIM.
• Near full density and good mechanical properties.
• Scalable process capable of economical medium and high volume production.
• Lower component weight and material utilization compared to machining.

Global Suppliers of 304L Powder for MIM

Some leading global suppliers of gas-atomized 304L stainless steel powder tailored for MIM include:

• Sandvik Osprey (UK)
• Carpenter Powder Products (USA)
• AMETEK (US)
• Rio Tinto Metal Powders (Canada)
• Höganäs (Sweden)
• Guangdong Huijin Powder Material (China)

These companies offer various grades of 304L powder meeting the stringent requirements of MIM.

304L Powder Prices for MIM Industry

The ultrafine spherical gas-atomized powders used in MIM are costlier than standard grades. Smaller quantity purchases can be 50% higher priced.

Storage and Handling of 304L Powder

304L powder should be stored in sealed containers under controlled humidity and inert gas purging to prevent:

• Oxidation/reaction with environment
• Moisture absorption leading to poor sintering
• Safety precautions from supplier SDS should be followed

Careful powder handling techniques should be used during MIM processing.

Quality Control Testing for 304L Powder

Important tests include:

• Particle size distribution (laser diffraction)
• Morphology (SEM)
• Flow rate (Hall flowmeter)
• Apparent density
• Tap density
• Chemical composition

Proper testing ensures powder meets the critical requirements for high quality MIM feedstock.

Comparison of 304L and 316L for MIM

304L and 316L powders are compared for MIM use:

• 304L offers better value with lower cost.
• 316L provides higher corrosion resistance in harsh environments.
• Both offer excellent sinterability.
• 304L has slightly better tensile strength whereas 316L offers higher yield strength.
• 304L suffices for most applications whereas 316L is preferred for more demanding conditions.

FAQs

Q: What is the typical 304L powder size used for MIM feedstock?

A: 10-20 microns with narrow particle size distribution is typically used for optimal powder loading, moldability and sintered density.

Q: How much does high purity 304L powder for MIM cost?

A: High purity spherical gas atomized 304L powder costs $25-50 per kg based on order volume. Small quantities are significantly costlier.

Q: What sintered density can be achieved with 304L MIM parts?

A: With optimized processing, sintered density above 95% theoretical density (approx. 7.6-7.8 g/cm3) can be achieved for 304L MIM parts.

Q: Is any post-sinter heat treatment used for 304L parts from MIM?

A: Yes, solution annealing followed by air cooling can be performed on sintered 304L MIM parts for enhancing mechanical properties.

Q: Where can I purchase 304L powder suitable for medical MIM applications?

A: 304L powder meeting stringent specifications for medical sector can be purchased from leading suppliers including Sandvik Osprey, Carpenter Powder Products, AMETEK, Rio Tinto Metal Powders.