Guide
Which MIM Material Fits: 316L, 17-4 PH, 4605 Low-Alloy or 420?
A MIM material is a metal alloy powder, mixed with binder, molded and sintered, and named on the drawing by a designation such as MIM-316L, MIM-17-4 PH, MIM-4605 or MIM-420. The choice is mostly a trade between corrosion resistance, strength and hardenability.
By Saola Manufacturing engineering team · Published · Updated
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Which MIM alloys are the standard choices for stainless and steel parts?
MIMA says nearly half of the commercial activity in metal injection molding is in stainless steels, and that the most popular alloys are MIM-17-4 PH and MIM-316L. Low-alloy steel 4605 and the 420 stainless series sit on the same materials list.
The grades in this guide’s title are also named in the ASTM specification for MIM materials: ASTM B883-24 lists MIM-316L, MIM-17-4 PH, MIM-420, MIM-4605 and several other grades, among them MIM-440, MIM-430L, MIM-2200, MIM-2700, MIM-4140 and MIM-Cu. The MIMA list also notes that the designation 4650 was replaced by 4605, so an older drawing that says 4650 is asking for the grade now called 4605. Confirm that with the supplier instead of assuming it.
A MIM alloy is not simply the wrought grade of the same name. MIMA describes MIM parts as reaching typically 96% to 99% of theoretical density, with properties similar to annealed parts made by conventional metalworking, and the property values you can design to are the ones tabulated for the MIM entry in a MIM standard, in a stated condition. This guide is for an engineer choosing among four common options for a corrosion, strength or wear requirement. It stays qualitative on purpose, because the property tables sit inside the paid standards.
How do you match a MIM alloy to the requirement?
Start from the failure you are trying to prevent: pick 316L when corrosion drives the design, 17-4 PH when strength matters and corrosion is moderate, and 4605 or 420 when a heat-treated hard surface is the goal. Treat the table as a shortlist to check against the standard, not as a final choice.
Every cell in the table comes from a source in the sources list, apart from the one point marked as inference, and none gives a property number. The standards that carry numbers are sold: MPIF Standard 35-MIM is a 2025 edition that makes all prior editions obsolete, and ASTM B883-24 holds its composition limits in a table that is not public. That is why the table says what to confirm, not what the strength is.
The comparison between the two stainless choices is the one that comes up most. 316L is an austenitic grade and gives the better general corrosion position, but it does not offer the strength route that 17-4 PH does. 17-4 PH is martensitic in the annealed condition and is strengthened by a low-temperature treatment that precipitates a copper-containing phase (ATI 17-4 datasheet), which is why its strength depends on the condition you call out. If both corrosion and strength matter, ask the supplier for the MPIF 35-MIM corrosion data for 17-4 PH and for test coupons in your environment before you commit. The wrought-material view of the same trade is in the guides on 316 versus 316L and 17-4 PH H900 versus H1150, but copy no property value from a wrought datasheet onto a MIM drawing.
| Main requirement | Start with | What the sources say | What to confirm with the supplier |
|---|---|---|---|
| Corrosion resistance, general | MIM-316L | MIMA lists it among the most popular MIM alloys. A stainless industry body notes that 316 types are widely used in marine service but are susceptible to crevice and pitting corrosion in seawater, and recommends low-carbon 316L for welded structures. Austenitic stainless is usually non-magnetic. | The actual environment (chlorides, crevices), whether the part is welded, and the property values in the standard for the condition you buy |
| Strength with moderate corrosion resistance | MIM-17-4 PH | A mill datasheet describes 17-4 as a precipitation-hardening stainless used where high strength and a moderate level of corrosion resistance are needed. MPIF 35-MIM added H975 and H1025 conditions in 2018 and 17-4 PH corrosion data in 2025. | The aged condition to put on the drawing, and whether the MIM corrosion data in the standard matches your environment |
| Hardened wear surface, no corrosion duty | MIM-4605 | A low-alloy steel on the MIMA and ASTM B883 lists. MIMA says MIM parts use the same heat treatments as wrought counterparts, including carburizing for surface hardness. MPIF 35-MIM added 4605 HIP’d, quenched and tempered in 2018. | The heat-treatment condition, the finish that protects it from rust (inference: low-alloy steel is not stainless), and any case-depth requirement |
| Hardness with some corrosion resistance | MIM-420 | Martensitic stainless grades are hardenable by heat treating. MIM-420 was added to MPIF Standard 35 with property values in the 2007 edition, and ASTM B883-24 lists it. | The tempered condition, and test evidence for corrosion in your environment; do not assume 316L-level performance |
When does 4605 or 420 beat a stainless choice?
When the job is wear or surface hardness and corrosion is handled by a coating or a benign environment, a heat-treatable low-alloy steel such as 4605 is the usual candidate. Grade 420 is the stainless route when some corrosion resistance must come with hardness, and both depend on a heat-treatment condition that has to be on the drawing.
MIMA says that MIM components use the same heat treatment operations as their wrought counterparts, and that a high surface hardness is attained by carbon surface additions in an atmosphere with a high carbon potential (MIMA, Secondary Operations). That is the case for a latch pawl, a pivot or a gear tooth: a hard surface that resists wear on a steel that can take it. A martensitic stainless such as 420 gives a hardenable material that is also a stainless, with the corrosion caveat in the table. Which heat-treatment route fits a given part is its own decision, and the MPIF entry for HIP’d, quenched and tempered 4605, added in the 2018 edition, shows that the standard treats a densified condition as a separate entry.
The cost of the low-alloy route is a finish for corrosion protection, which is outside the alloy. The cost of 420 is a corrosion position you must prove for your environment. Neither cost appears in a catalog line, so name them in the RFQ.
What belongs in the material note on the drawing and RFQ?
The designation (for example MIM-17-4 PH), the standard and its edition year, the heat-treatment or aging condition, and the environment the part sees. Then ask the supplier to name the certificate type they will provide and the tests behind it.
A workable material note names one standard and does not mix them. Which standard to cite, and how the three common ones differ, is a separate decision; here the rule is only that the designation, the standard, its year and the condition travel together. Add one line that states the service environment, for example a chloride exposure, a cleaning chemical or a wear contact, because it tells the supplier which row of the table you are in.
Ask three further things. First, which tests the standard calls for and which are run on your lot. ASTM B883-24 says the materials shall be subjected to tensile and unnotched Charpy impact tests, but the page does not say how often, so ask. Second, what certificate comes with the shipment: see the guides on EN 10204 3.1 versus 2.2 certificates and certificate of conformance requirements. Third, whether the quoted density and condition match the property data in the standard you cite.
How does alloy choice affect finishing and machining after sintering?
The alloy sets what comes next. MIMA states that all common machining operations can be applied to MIM components, so a threaded or toleranced feature can be added after sintering, and the finish has to suit the alloy: a stainless part may be passivated, and a low-alloy steel part needs a protective finish.
Saola places MIM work through a partner plant it manages, and faces and threads that need machined tolerances are finished by CNC, so the alloy decision and the finishing decision are made on the same drawing. The MIM grades listed on the capability page are 304, 316L, 17-4PH and 4605; a part drawn in 420 needs its material source confirmed in the written quote before it is priced. The MIM and powder metal capability page describes the program, and CNC turning covers the machined side. For the finishing choices on stainless, the guides on passivation and plating defects apply to the surface, and sintered porosity adds a caveat that the wrought-part guides do not cover.
Whichever alloy you pick, one rule holds: state the condition after the last thermal step, and say which operations follow it. A feature machined after heat treatment is machined in a harder material than one machined before, and the supplier needs to know which you mean.
Frequently asked
What is the most common MIM stainless steel?
MIMA names MIM-17-4 PH and MIM-316L as the most popular alloys, and says nearly half of MIM commercial activity is in stainless steels (MIMA, Materials Range).
Is MIM 17-4 PH the same as wrought 17-4?
It is the same alloy family and the same heat-treatment idea, but the properties you can design to are the values in the MIM standard for the condition you specify, not the wrought datasheet.
Is 4605 the same as 4650?
The MIMA materials list says 4650 was replaced by 4605. Confirm the equivalence with the supplier on any older drawing before you reorder.
Where do I find the strength values?
In the MIM standard for the grade and condition, such as MPIF Standard 35-MIM or ASTM B883. Both are sold, so this guide gives no values.
Is 316L the right choice for any corrosion duty?
No. A stainless industry body notes that 316 types have limited corrosion resistance in seawater and are susceptible to crevice and pitting attack, so match the grade to the environment and ask for test evidence.
Sources
- MIMA, Materials Range, Metal Injection Molding Association, accessed October 2026
- MPIF Standard 35-MIM, 2025 edition, Metal Injection Molding Association, accessed October 2026
- MPIF Standard 35-MIM, Summary of Major Changes, Metal Powder Industries Federation, file dated April 2025
- ASTM B883-24, Standard Specification for Metal Injection Molded (MIM) Materials, ASTM International store page, last updated February 2024
- ATI 17-4 Technical Data Sheet, ATI, version 1 dated August 2016
- Selection of 316, 304 and 303 types of stainless steels for seawater applications, British Stainless Steel Association, accessed October 2026
- Stainless steel, Wikipedia, accessed October 2026
- MIMA, Secondary Operations with MIM, Metal Injection Molding Association, accessed October 2026
- MIMA, Process Overview: MIM, Metal Injection Molding Association, accessed October 2026