MIM 316L

MIM 316L stainless steel (austenitic grade, food grade) is used in applications requiring extremely high corrosion resistance. Other qualities include excellent elongation and ductility, and non-magnetic properties. Parts made from this material are commonly used in the food, marine and medical industries.

MIM-316L is the most widely used MIM steel because of its high strength and corrosion resistance, making it safe for food and drinking water storage. These characteristics are very important for metals in contact with acids, which are very suitable for food-grade applications, and are mostly used in the manufacture of parts for food, drinking water, and seawater purification

equipment.

In comparison to heat-treatable stainless steels such as 17-4 PH, 420, and 440C, stainless steel 316L has lesser strength and hardness but higher corrosion resistance, ductility, and superior polishing qualities. Applications requiring an appealing surface quality, such consumer wristwatch products, are a good fit for MIM 316L. Additionally, it is appropriate for uses like dentistry and medical devices that have exceptional corrosion resistance. Stainless steel 316L’s high sintered density reduces surface porosity to prevent the buildup of impurities and meet high hygiene standards.

 

Composition of Chemicals

Here is the typical chemical composition table for sintered stainless steel 316. The specific values may vary slightly depending on the sintering process and application requirements:

Element Content (%)
Iron (Fe) Balance
Chromium (Cr) 16.0 – 18.0
Nickel (Ni) 10.0 – 14.0
Molybdenum (Mo) 2.0 – 3.0
Carbon (C) ≤ 0.08
Silicon (Si) ≤ 1.00
Manganese (Mn) ≤ 2.00
Sulfur (S) ≤ 0.03
Phosphorus (P) ≤ 0.045

Explanation

  • Chromium (Cr) and Nickel (Ni): Provide excellent corrosion and high-temperature resistance.
  • Molybdenum (Mo): Enhances pitting and crevice corrosion resistance, especially in chloride-rich environments.
  • Carbon (C): Controlling carbon content helps maintain corrosion resistance while adding some hardness.

This composition makes sintered stainless steel 316 highly resistant to corrosion, with excellent mechanical strength and toughness, suitable for various industrial environments.

 

Common Mechanical Characteristics

Here are the typical mechanical properties of stainless steel 316. Specific values may vary depending on heat treatment and manufacturing processes:

Property Value
Tensile Strength ≥ 485 MPa
Yield Strength ≥ 170 MPa
Elongation ≥ 40%
Hardness ≤ 217 HB (Brinell) or ≤ 95 HRB (Rockwell)
Elastic Modulus 193 GPa
Density 7.98 g/cm³

These mechanical properties make stainless steel 316 ideal for environments that require high strength, corrosion resistance, and toughness, such as medical devices, chemical equipment, food processing equipment, and marine applications.

Feedstock for MIM 316

JHMIM uses MIM 316L feedstock with a catalytic debinding mechanism based on nitric acid. Precision structure integrated manufacturing is made possible by our expert MIM experience. Our production advantages include high batch production, high automation, and broad material adaptation.

Mobile phone parts, wearable smart terminals, automobile parts, medical equipment, and aerospace parts are all made with MIM 316L. High strength and toughness are necessary for all of these components.

Different MIM 316L feedstocks with particular application needs can be used by JHMIM. The stainless steel 316L kinds include the following:

1. Standard 316L Stainless Steel

  • This is the basic low-carbon version of 316, with a maximum carbon content of 0.03%. It has excellent corrosion resistance, particularly in chloride environments, and is commonly used in marine, chemical, and food processing industries.
  • Applications: Medical implants, marine fittings, chemical equipment, and food-grade equipment.

2. 316LVM (Vacuum Melted) Stainless Steel

  • This type undergoes a vacuum melting process to enhance purity and reduce impurities like sulfur and phosphorous. The vacuum melting results in a very clean metal with improved biocompatibility, making it ideal for medical and dental implants.
  • Applications: Medical devices, surgical instruments, orthopedic implants, and dental applications.

3. 316L Powder for Metal Injection Molding (MIM)

  • 316L is also available as a powder form specifically for metal injection molding (MIM) processes. This powder allows for the production of small, intricate parts with excellent mechanical properties and corrosion resistance.
  • Applications: Precision parts in medical devices, automotive components, and consumer electronics.

4. 316L Stainless Steel for Additive Manufacturing (AM)

  • This version of 316L is available in powder form optimized for additive manufacturing (3D printing). It offers similar corrosion resistance and strength properties, with the added benefit of being easily customizable into complex shapes.
  • Applications: Prototyping, aerospace components, dental and medical implants, and customized industrial parts.

5. 316L Dual-Certified Stainless Steel (316/316L)

  • Dual-certified 316/316L stainless steel meets the specifications for both 316 and 316L grades. It has the low-carbon content of 316L, enhancing weldability, but also meets the mechanical property requirements of 316.
  • Applications: Pressure vessels, structural components, and welded parts where high corrosion resistance and strength are required.

6. 316L High Mo (High Molybdenum) Stainless Steel

  • Some 316L alloys have a higher molybdenum content, typically in the range of 2.5-3%, which provides even greater corrosion resistance, particularly against pitting and crevice corrosion in aggressive environments.
  • Applications: Offshore and marine applications, chemical processing, and environments with high chloride exposure.

7. 316L High Precision Stainless Steel

  • This type of 316L is produced to meet specific dimensional and surface finish requirements for highly sensitive applications. It undergoes precise machining and finishing to achieve these specifications.
  • Applications: Watch parts, fine jewelry, and precision medical components.

Types of Alloys in 316L

Alloy master and pre-alloy

Both pre-alloy and master alloy powders can be applied to stainless steel in metal injection molding. Atomized powders that are precisely the same chemical composition as the finished 316L are used in the pre-alloy process. The master alloy approach, on the other hand, uses carbonyl iron powder mixed with enriched alloy powder to produce 316L composition following final sintering. The use of master alloy technology offers considerable cost savings when fine particle size (16 μm) is needed.

Specifications such as chemical composition, tap density, and particle size distribution are known for pre-alloyed MIM 316L powders. Stainless steel 316L’s chemical makeup, particularly about carbon levels, frequently deviates from international standards.

Therefore, tailored chemistry with minimal element variation is needed to produce the final composition after sintering. Additionally, distinct application features are produced by the relatively wide Ni range of 10% to 14%: high nickel levels will decrease the magnetic susceptibility of the final sintered components, while low nickel levels will yield high sintered density through liquid phase sintering.

Sintering Parameter for 316L

The sintering process parameter affects the primary characteristics of stainless steel 316L. The microstructure and sintering density have the biggest effects on the mechanical characteristics. The sintering process will be hampered by residual carbon from incomplete debinding, volatile components will evaporate during high-temperature vacuum sintering, and the cooling rate will regulate the hard and brittle sigma phase.

One feature of high temperature sintering is that the final sintered qualities are dependent on both controllable and uncontrollable conditions. The primary variables for MIM 316L are the injection molding parameters of temperature, pressure, and sintering conditions, which include debinding, sintering atmosphere, and temperature.

To avoid distortion, the debound and sintered components are supported by ceramic Al2O3/SiC plates. These ceramic plates are far more stable during high-temperature sintering (1350°C) than metallic supports. About 1Pa of absolute pressure is used for the vacuum sintering process. Stainless steel is sinterable using either liquid-phase sintering (LPS) or super-solidus liquid-phase sintering (SLPS). According to thermodynamic calculations, the majority of sintering occurs in the solid state because liquid only begins to form at temperatures above 1390°C.

Common Properties of Sintering

The extreme characteristics of stainless steel can vary significantly, and the chemical specification (UNS SD31603) is quite broad. According to its classification, 316L is a completely austenitic alloy. However, this is dependent on the absolute levels of Cr, Ni, Mo, and the Cr/Ni ratio; the final microstructure still contains the delta ferritic phase.

In medical applications, metal components must be non-magnetic and free of residual delta ferrite, particularly when they are near powerful magnets (such as MRI scanners). After sintering, a Ni concentration of 10–14% will guarantee a fully austenitic microstructure and encourage austenite production.

Typical performance characteristics for different types of MIM 316L powders:

Performance Index Standard 316L Powder High-Density 316L Powder High-Purity 316L Powder Fast Sintering 316L Powder
Particle Size Distribution (D50) 5-15 µm 5-15 µm 5-15 µm 5-20 µm
Apparent Density (g/cm³) 3.5-4.2 4.0-4.4 3.8-4.2 3.6-4.3
Sintered Density (g/cm³) 7.85-7.98 7.95-8.00 7.90-7.98 7.85-7.95
Tensile Strength (MPa) ≥ 485 ≥ 500 ≥ 485 ≥ 480
Yield Strength (MPa) ≥ 170 ≥ 180 ≥ 170 ≥ 170
Elongation (%) ≥ 40 ≥ 40 ≥ 40 ≥ 35
Hardness (HB) ≤ 217 ≤ 220 ≤ 217 ≤ 215
Oxygen Content (ppm) ≤ 600 ≤ 500 ≤ 400 ≤ 700
Carbon Content (%) ≤ 0.03 ≤ 0.03 ≤ 0.03 ≤ 0.04
Nitrogen Content (ppm) ≤ 500 ≤ 500 ≤ 300 ≤ 600

The Density

In contrast to its theoretical density of 8.0g/cm3, SS 316L may reach an average sintered density of 7.81g/cm3, or 97.6%. Due to the fact that internal gas pressure does not impede pore shrinking, vacuum sintering achieves a comparatively high density. The experimental density decreases by 0.1% in a reductive hydrogen environment.

Strength in tensile

Sintered stainless steel 316L has a tensile strength of up to 587.0 MPa. The tensile strength of prealloyed feedstock is clearly higher than that of master alloy, nevertheless. The carbon residue from carbonyl iron powder or the contamination from element (Si, C, H, and N) diffusion are the primary causes of this discrepancy.

It is clear that tensile strength is greatly impacted by various powder types and sintering settings, while ultimate hardness is barely affected. The optical micrographs in the following images are in both etched and polished states. There is reduced porosity and a lower sintering temperature since the master alloy clearly has finer grain size than the pre-alloy.

Dependent on

C/B
Small additions of B and Cu will improve the mechanical characteristics, raise the final sintering density, and improve densification.

Zinc is a stabilizing metal that can increase oxidation resistance at high temperatures in ferritic stainless steels. Its effect on crystal grain refinement will raise suspicions about the refinement of the grains in MIM 316L and can prevent the production of silicon oxide. The excessive growth of Si oxide at the grain boundary during MIM 316L sintering will prevent densification, which will result in a deterioration of the material’s hardness and mechanical qualities. The finely distributed silicon oxide will serve as the pinning agent when the Zr additive is added. This will improve the 316L parts’ microstructure and stop crystal grains from growing too much.

Overall, the addition of Zr will help refine the powder’s structure and prevent Si oxide from forming on its surface. Lastly, enhance the mechanical qualities and sintering characteristics of MIM 316L sintering.

The Delta Ferrite

Tensile ductility and axial fatigue strength will decline in the MIM 316L process as delta ferrite content rises. To counteract these effects, delta ferrite will also promote densification. Delta ferrite content decreases with carbon content and increases with sintering temperature (over 1300°C). In stainless steel, the austenite phase is stabilized due to the carbon element.

Environment for Sintering

MIM 316L is often sinterable in vacuum, H2, and N2.

The atmosphere of H2

The best option for low carbon stainless steel is an H2 environment, according to early 316L sintering experience. Because silicone and chromium oxides are stable even at high temperatures, this will guarantee their reduction. Furthermore, sintered 316L components in a vacuum atmosphere and those in an H2 atmosphere are of the same quality. The microstructure of the phase distribution of 316L with a low Ni concentration (10.4%) is shown in the accompanying image. It is composed of an island of delta ferrite and an austenitic matrix (red arrows).

Following sintering of 316L components with a high Ni content (13.5%) in a vacuum atmosphere and H2, the microstructures have a completely austenitic appearance, as seen in the following image. But because there are so many visible pores, the theoretical density value of 95% is low.

N2 Ambience

Nitrogen absorption from sintering in N2 lowers density and increases yield strength. The most strength is achieved after sintering by the fine powder with the largest surface area, which also loses some of its ductility.

Only austenite is apparent in the microstructure of 316L components sintered in an atmosphere containing N2, even for 316L with low Ni (10.4%), which readily forms a delta ferrite phase during sintering. Kindly review the 316L (Low Ni) micrograph in the N2 sintering environment.

The highest hardness value is obtained through sintering in a N2 environment; as metal powder particle size reduces, hardness increases. In addition, nitrogen sintering increases stress by over 100 MPa in comparison to hydrogen sintering. The sintering atmosphere has a major impact on the elongation results: on average, H2 sintering achieves 70% elongation, whereas vacuum results in 43% and N2 results in 33%. The fact that N2 and vacuum have lower carbon contents than H2 indicates that carbon, not hydrogen, is the main reductant for surface oxygen.

In conclusion

In a severe chloride environment, stainless steel 316L offers superior resistance to corrosion and abrasion. Without a question, MIM 316L offers the ideal ratio of efficiency to cost.

 

Chemical Content

316L C Si S P Mn Cr Ni Mo N
w.t/% 0.03 0.75 0.03 0.045 2 16-18 10-14 2-3 0.1
316L Finished product density Injection density Hardness Hardness after heat treatment Tensile strength yield strength
7.88-7.90 5.40-5.50 ≥HV130 / ≥514Mpa ≥180Mpa
304 C Si S P Mn Cr Ni Fe
w.t/% ≤0.03 ≤1.00 ≤0.03 ≤0.03 ≤2.0 18.0-20.0 8.0-11.0 Bal
420 C Si S P Mn Cr Ni
w.t/% 0.16-0.25 ≤1.00 ≤0.03 ≤0.04 ≤1.0 12.0-14.0 ≤0.75
420 Finished product density Injection density Hardness Hardness after heat treatment Tensile strength yield strength
7.25-7.3 4.66-4.70 ≥320 ≥460 ≥1600Mpa ≥1300Mpa
17-4PH C Si S P Mn Cr Ni Nb+Ta
w.t/% ≤0.07 ≤1.00 ≤0.03 ≤0.04 ≤1.0 15.5-17.5 3.0-5.0 0.15-0.45
17-4PH Finished product density Injection density Hardness Hardness after heat treatment Tensile strength yield strength
7.56-7.60 5.38-5.50 HV260-340 ≥550 ≥950Mpa ≥660Mpa
440C C Si S P Mn Cr Ni
w.t/% 0.95-1.20 ≤1.00 ≤0.03 ≤0.035 ≤1.0 16.0-18.0 ≤0.60
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