MIM Material Selection Guide for OEM Buyers and Engineers
How to choose the right MIM material family: stainless steels, low-alloy steels, soft-magnetic alloys, and specialty grades such as tungsten and titanium — with shrinkage, density and RFQ notes.
Material selection drives more outcomes in a metal injection molding program than almost any other choice. The grade defines corrosion behaviour, mechanical strength, magnetic response, achievable tolerances, finishing options, and cost. Choosing the right family early saves tooling iterations and prevents the most common RFQ mistakes we see at the drawing-review stage.
This guide walks through the material families SINTS runs most often for OEM programs, with the property and process notes our engineering team uses when reviewing customer drawings. It is written for sourcing teams, design engineers, and program managers who need to set a direction before going to RFQ.
Why material choice drives the whole program
In MIM, material choice sits upstream of geometry, tolerance and surface finish. The selected powder affects feedstock rheology (how the mix flows into the mold), debinding behavior, sintering shrinkage and the achievable density. Different families also need different sintering atmospheres: stainless can be sintered in vacuum or partial-pressure hydrogen, while soft-magnetic and tungsten grades often need hydrogen or argon to keep carbon and oxygen under control.
The practical effect is that a part designed for 316L may not simply be re-cut for 17-4PH or titanium. Shrinkage changes, tooling may need to be re-cut, and post-sinter operations (such as heat treatment or machining) shift. Deciding the material family early avoids multiple tooling iterations.
Start from the application, not the grade
Before comparing alloys, identify the dominant requirement. Five questions usually narrow the choice to a single family:
Corrosion or biocompatibility? → Stainless 316L or 17-4PH, possibly titanium.
Strength or hardness after heat treatment? → 17-4PH, low-alloy steels (4140, 4605, Fe-2Ni).
Magnetic response? → Fe-Ni 50%, Fe-3%Si, Fe-49Co-2V, or pure iron.
High mass in small volume or radiation shielding? → Tungsten heavy alloy (W-Ni-Fe, W-Ni-Cu).
Lightweight or bioinert? → Titanium (Ti-6Al-4V).
Once the family is fixed, the next step is grade selection within that family (for example, 316L vs 304L, H900 vs H1025 on 17-4PH). Most of the program decisions — sintering profile, finishing options, certificate type — follow from the family.
Stainless steels — the workhorse family
Austenitic and martensitic stainless steels account for the majority of MIM production. Both families sinter predictably, accept a wide range of finishing operations, and meet common industry certifications for medical, food and consumer programs.
SS 316L (UNS S31603)Austenitic stainless. Density 7.6–7.9 g/cm³ (96–99% of wrought). Excellent biocompatibility and corrosion resistance. Typical tensile 450–550 G. Used for medical, sensor housings, consumer hardware, locks.
SS 17-4PH (UNS S17400)Martensitic precipitation-hardenable stainless. Tensile 900–1,100 G after H900, ductility 6–12% elongation. Used for structural parts, locking hardware, valves and pump components.
SS 304L (UNS S30403)Austenitic stainless, lower nickel than 316L. Lower cost option where chloride exposure is mild. Less commonly requested than 316L for MIM programs.
SS 420 / 440CMartensitic stainless, hardenable to 50+ HRC. Used where wear resistance is required (cutting edges, valve seats). Sintering and post-process control must be tighter.
316L is the most versatile MIM stainless. It is the default choice when the part must survive corrosion, skin contact, food contact or sterilization. 17-4PH is the right answer when 316L is strong enough but the part still needs heat-treated strength. Mixing the two is a common mistake: specifying 17-4PH for corrosion reasons adds cost without benefit over 316L.
Stainless steel MIM parts combine corrosion performance with the shape complexity MIM is known for. 316L and 17-4PH cover the majority of structural and locking hardware programs.
Low-alloy and structural steels — cost-effective strength
Low-alloy steels are the most economical way to reach high tensile and hardness in a MIM part. They contain small additions of nickel, molybdenum or chromium to improve hardenability, and are usually heat-treated (quench and temper) after sintering.
Fe-2Ni (FL4605 / FN02)Iron with 2% nickel. Most common MIM low-alloy grade. Hardenable to 30–45 HRC. Used for gears, levers, lock components and structural hardware.
4140 (low-alloy Cr-Mo)Chromium-molybdenum steel. Excellent through-hardening. Used for tools, shafts and high-strength structural parts. Cost is moderate.
4605 (Fe-Ni-Mo)Similar to Fe-2Ni with molybdenum addition. Better through-thickness hardness. Used for safety-critical structural parts.
Carbon steel (Fe-C)Lowest-cost MIM grade. Used where appearance and corrosion are not critical. Surface protection or plating is usually required for outdoor use.
The trade-off with low-alloy steels is corrosion resistance. They will rust in humid or salt-exposed environments unless a plating, black oxide or similar finish is applied. For most indoor and protected applications this is fine; for outdoor or wet environments, a stainless grade is the safer specification.
Soft-magnetic alloys — for sensor and solenoid parts
When the MIM part must carry magnetic flux (sensor cores, solenoid plungers, flux guides, magnetic shielding), the grade choice is driven by magnetic properties rather than corrosion or strength.
Fe-Ni 50% (UNS K94840)Permalloy-type. High maximum permeability, low coercivity. Used for sensor yokes, flux guides and shielding where high sensitivity is needed.
Fe-3%Si (electrical steel)Lamination-grade silicon iron. High saturation induction. Used for motor and solenoid cores that operate at power frequencies.
Fe-49Co-2V (permendur-type)High saturation flux density (about 2.2 T). Used for high-power actuator cores and aerospace components. Cobalt makes it more expensive.
Pure Fe (low carbon)Cost-effective option for shielding and simple magnetic parts. Lower permeability than Fe-Ni but adequate for many shielding tasks.
All soft-magnetic MIM grades are sintered under controlled atmosphere (hydrogen or argon) and have a tight carbon ceiling, often below 0.02%, to keep coercivity low. If a part needs both structural strength and magnetic response, the design usually ends up using a stainless or low-alloy housing plus a separate Fe-Ni or Fe-Si magnetic insert.
Tungsten and titanium — specialty grades
Tungsten and titanium are run less often than stainless or low-alloy steels, but they are essential for several programs. Both need more careful process control.
Tungsten heavy alloy (W-Ni-Fe, W-Ni-Cu)Density 17.0–18.5 g/cm³, more than twice steel. Used for counterweights, balance weights, vibration masses and radiation shielding. Sintering at high temperature (1,400–1,500 °C) in hydrogen.
Titanium Ti-6Al-4V (UNS R56400)Density 4.4 g/cm³, biocompatible, high strength-to-weight. Used for medical implants, lightweight structural components and aerospace. Sintered under vacuum or high-purity argon.
Tungsten heavy alloy MIM parts reach densities above 17 g/cm³, enabling counterweight and shielding components that would be impractical to machine from solid bar.
Specialty grades cost more per kilogram and have longer cycle times, so the geometry must justify the material. A small detail part that does not need tungsten weight is usually a candidate for 17-4PH or 316L. Tungsten earns its place when the part needs shielding, balance, or vibration damping in a compact space.
Material property summary
The table below brings the most common MIM families together for at-a-glance comparison. All values are typical for sintered MIM parts after the indicated heat treatment, not wrought material.
Property values are typical ranges for SINTS production runs and depend on part geometry, sintering profile and heat treatment. SINTS confirms achievable properties during drawing review and reports actual test results on first article samples.
How material affects sintering, shrinkage and tolerances
Each material family has a characteristic sintering profile. Linear shrinkage from the as-molded green part to the sintered part runs 15–20% for most stainless and low-alloy steels. Tungsten shrinks less (around 12–16%) and titanium more (around 18–22%). Tooling is cut to compensate, but the shrink rate is influenced by geometry, so trial parts confirm the actual value.
As-sintered density follows the material: stainless grades reach 96–99% of wrought theoretical density; low-alloy steels reach 94–97%; tungsten heavy alloy reaches near-full density. Higher density gives better mechanical strength, better corrosion resistance and tighter tolerances.
The implication for tolerance is straightforward: harder-to-sinter materials and larger sections need slightly wider tolerance bands, and post-sinter machining is more often used. Discussing these details early with the supplier avoids surprises during sampling.
How to specify material in your RFQ
The clearest RFQ always names the material by UNS or AISI designation, the heat-treatment condition, and the property or certificate requirements. Vague specifications such as “stainless steel” or “magnetic grade” force the supplier to guess and slow the quotation.
Name the grade: Use UNS (S31603 for 316L, S17400 for 17-4PH, R56400 for Ti-6Al-4V) or AISI designation. Avoid trade names.
State the heat-treatment condition: Annealed, sintered only, solution-treated and aged, H900 / H1025 / H1100 for 17-4PH.
List required properties: Tensile strength, yield, elongation, hardness, density, magnetic permeability if relevant.
Specify finish and protection: As-sintered, tumbled, polished, passivated, plated, PVD-coated, etc.
Note certification needs: Material certificate (EN 10204 3.1), FAI report, dimensional report, RoHS or REACH statements if the end market needs them.
When SINTS helps you decide
The material choice almost always affects the part geometry, the sintering profile and the inspection plan. For OEM programs with first-time MIM use, the most valuable step is to send the drawing and a short application note before locking the spec. SINTS engineering reviews the drawing against the chosen family, confirms achievable tolerances and density, and proposes the most cost-effective combination of family, finish and inspection.
For programs where the material is already locked (because of regulatory, biocompatibility or end-use requirements), the review focuses on geometry and finish. Either way, the earlier the supplier is in the loop, the fewer iterations are needed on the way to stable production.
Need help choosing a material?
Send your drawing and a short application note. SINTS engineering reviews the part against the chosen family, confirms tolerances and density, and responds within 1 business day.
Practical answers for OEM sourcing and engineering teams.
What is the most common MIM material?
Austenitic stainless steel 316L is the workhorse grade, accounting for a large share of MIM production because of corrosion resistance, biocompatibility and stable sintering behaviour.
When should I choose 17-4PH instead of 316L?
Choose 17-4PH when the part needs higher strength, hardness, or heat-treated properties. 17-4PH is precipitation-hardenable to H900/H1025/H1100 conditions; 316L stays austenitic and softer.
Can MIM parts be soft magnetic?
Yes. Fe-Ni 50%, Fe-3%Si, Fe-49Co-2V (permendur-type) and pure iron are used for sensor cores, solenoid plungers and flux guides. Sintering is run under controlled atmosphere to keep carbon low.
What density does MIM 316L reach?
Sintered MIM 316L reaches 7.6 to 7.9 g/cm³, which is 96 to 99 percent of wrought 316L density. Residual porosity is closed and isolated, so corrosion behaviour tracks wrought material closely.
Can SINTS make tungsten or titanium MIM parts?
Yes. Tungsten heavy alloy (W-Ni-Fe) reaches 17.0 to 18.5 g/cm³ for shielding and counterweights. Titanium (Ti-6Al-4V) is run for biocompatible, lightweight parts; titanium sintering is more reactive and usually requires vacuum or high-purity argon.
How do I specify material in my RFQ?
State the grade by UNS or AISI designation, the required mechanical properties (tensile/yield/hardness), any heat-treatment condition (annealed, H900, etc.), surface finish and whether a material certificate is required.
