Guide
How Should MIM Parts Be Heat Treated: Quench and Temper, Carburize or HIP?
MIM parts are heat treated with the same operations as their wrought counterparts, and the specification decision is whether hardness alone is needed or whether fatigue and impact justify adding hot isostatic pressing. The rules below follow MIMA guidance and the MPIF Standard 35-MIM condition names.
By Saola Manufacturing engineering team · Published · Updated
On this page
What does heat treatment add to a sintered MIM part?
A sintered MIM part has properties similar to annealed conventional metal, so hardness and strength beyond that come from heat treatment. MIMA states that MIM components use the same heat treatment operations as their wrought counterparts.
MIMA reports that parts commonly reach 96% to 99% of theoretical density in a controlled-atmosphere furnace, with properties similar to annealed parts made by conventional methods (MIMA, Process Overview). MIMA’s secondary-operations page adds that heat treatment can be included within the cooling cycle or done by a properly designed post-sintering cycle (MIMA, Secondary Operations), so a separate furnace step is not always needed. The Wikipedia article on the process makes the same point, that post-sintering heat treatments for MIM are the same as for other fabrication routes (Metal injection molding).
This guide is for an engineer specifying a hard or fatigue-loaded MIM part such as a pawl, a cam, a small gear or a lock part. It compares the four conditions you can ask for and decides when hot isostatic pressing (HIP) is worth adding. It gives no hardness values, no fatigue values and no prices, because the sources do not publish them.
Which condition fits: as sintered, quench and temper, carburize or HIP?
Choose by the load the part sees: as sintered or aged for corrosion and moderate strength, quench and temper for through hardness, carburizing for a wear face, and HIP only when fatigue or impact justifies an extra operation. Each option needs a named condition on the drawing.
The table separates the choices. The first four are conventional heat treatments and follow the logic of any steel part. The mix of alloy and treatment matters: a martensitic grade is hardened by its treatment, a precipitation-hardening grade is aged, and a low-alloy steel is either quenched and tempered or carburized for a hard skin. The alloy side of that choice is in the guide on which MIM material fits a corrosion, strength or wear requirement, and the condition names come from MPIF Standard 35-MIM, which has listed HIP’d and heat-treated entries since 2018.
Do not copy a wrought heat-treat note onto a MIM drawing without checking it. The note for a machined bar may assume a depth of case or a hardness that a sintered part reaches differently, and the wrought guides on effective case depth and 17-4 PH H900 versus H1150 are written for machined parts. Use them for the vocabulary, and take the values from the MIM standard.
| Option | Use when | What the sources say | What to put on the drawing |
|---|---|---|---|
| As sintered | The alloy’s sintered properties meet the requirement, as is common for a corrosion-driven stainless part | MIM properties are similar to annealed conventional metal | State “as sintered” so no one assumes a hardened part |
| Quench and temper | A low-alloy or martensitic grade must be hard or strong through the section | Same operations as wrought counterparts. MPIF 35-MIM lists quenched and tempered entries, such as 4140 added in 2016 and HIP’d 4605 added in 2018 | The condition name from the standard, the hardness range your design needs and where it is measured |
| Age (precipitation hardening) | 17-4 PH needs its strength condition | A mill datasheet describes a one-step treatment, in a temperature range of 900 to 1150 °F depending on the strength and toughness wanted. MPIF 35-MIM added H975 and H1025 entries in 2018 | The aged condition designation, not just “heat treated” |
| Carburize | A wear surface is needed on a tougher core | Carbon surface additions in an atmosphere with high carbon potential give a high surface hardness | Case depth, the hardness level at the surface, and how effective case depth is judged |
| HIP | Fatigue or impact life is the failure mode, or residual porosity is a concern | Eliminates non-surface-connected porosity and in most cases brings the part to 100% of theoretical density. MPIF 35-MIM lists HIP’d, quenched and tempered 4605 and a HIP’d, heat-treated 4-20 entry | State that HIP is required, its position in the sequence, and the final condition after it |
When does HIP pay for itself?
When fatigue or impact life is what limits the part and a sintered part at typical density leaves pores that could start a crack, HIP is the option to evaluate; for hardness alone the sources give no reason to add it. MIMA says HIP eliminates non-surface-connected porosity and, in most cases, takes the part to 100% of theoretical density.
The reasoning has three links. MIMA gives 96% to 99% of theoretical density for a sintered part, so some porosity remains. MIMA says HIP removes non-surface-connected porosity. And MIMA and MPIF both say that removing the porosity improves the material’s mechanical properties (MPIF, Isostatic Pressing), without naming fatigue. The step from there to fatigue life is engineering reasoning, not a statement from these sources: internal pores are places where a fatigue crack can start, so removing them is expected to help a cyclically loaded or impact-loaded part. No source behind this guide gives a fatigue life or a cost for HIP’d MIM, so treat the decision as an engineering judgment to confirm with data on your part.
Two limits keep the claim honest. HIP does not close pores that open to the surface, so a part with a surface-connected pore is not fully sealed by it. And HIP is an additional operation, so ask for the quote with and without it, and ask the supplier for fatigue or impact data on the HIP’d condition, or plan a test on your own part. The property tables in MPIF Standard 35-MIM list HIP’d entries separately from sintered ones, which is a place to see what the standard attributes to the condition.
How does heat treatment interact with distortion and machining?
Heat treatment after sintering can move a part, so features that must be tight are best finished after it, with allowance left on them. MIMA lists machining and coining among the operations that can follow sintering.
This is the same logic as for any heat-treated part: the thermal step changes the shape and the hardness, so a tolerance that must hold goes on a feature that is finished afterward. The guide on heat treatment distortion allowance covers how to leave stock on machined parts, and decarburization explains a surface effect that matters to hardness. Both are written for machined parts, so take the principle and ask the MIM supplier for the numbers.
MIMA also notes that all common machining operations can be applied to MIM components (MIMA, Secondary Operations). A threaded or toleranced feature can therefore be added after the last thermal step, in the hardened material, which is harder to cut than the sintered state. That is an inference from the order of operations, not a figure from the source, and the supplier will know what their alloy allows.
What should the drawing and RFQ say about heat treatment and HIP?
Name the condition from the standard, state the hardness range and where it is measured, say whether HIP is required and where it sits in the sequence, and list which features are finished afterward. A note that says only “heat treat” is not a specification.
- The material designation and the standard with its edition year, and the condition name as the standard writes it.
- The hardness requirement, the location and the test method, because a surface reading and a core reading are different requirements.
- Case depth, if carburized, and how effective case depth is judged.
- Whether HIP is required, and the condition after HIP.
- Which features are machined after the thermal steps, and the stock left on them.
- The records to be delivered, such as the heat-treatment record and the hardness results, tied to the certificate type you want.
Add the annual volume and the failure mode, such as fatigue at a stated load or wear on a named face. They tell the supplier whether HIP and carburizing are justified, and they make the quotes comparable.
Who performs heat treatment and HIP in a managed MIM program?
In a managed program the MIM work goes through a partner plant, and heat treatment and HIP are arranged through that plant, not run by Saola. The quote states the production site and the country of origin.
The MIM and powder metal capability page describes how the program is organized. Faces and threads that must be machined after the thermal steps are finished by CNC, and CNC turning and CNC milling are the machined side. Ask for the heat-treatment route in the quote, so that it is a stated step and not an assumption.
Frequently asked
Can MIM stainless be heat treated like wrought stainless?
MIMA says MIM components use the same heat treatment operations as their wrought counterparts (MIMA, Secondary Operations). The values you get are the ones listed for the MIM entry in the standard, not the wrought datasheet.
What density does HIP reach?
MIMA says that in most cases HIP brings the part to 100% of theoretical density, by eliminating non-surface-connected porosity (MIMA).
Does HIP close pores that open to the surface?
The MIMA description is of non-surface-connected porosity, so assume it does not. Ask the supplier how surface-connected porosity is handled if it matters to your part.
Where do I find the hardness a condition reaches?
In the property tables of MPIF Standard 35-MIM or ASTM B883, which are sold. This guide gives no values.
How much does HIP cost?
The sources give no figure. Ask for the quote with and without HIP and compare it with the benefit you need in fatigue or impact life.
Sources
- MIMA, Secondary Operations with MIM, Metal Injection Molding Association, accessed October 2026
- MIMA, Process Overview: MIM, 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
- MPIF, Isostatic Pressing, Metal Powder Industries Federation, accessed October 2026
- Metal injection molding, Wikipedia, accessed October 2026