How to Read MPIF Material Grades for Powder Metallurgy Parts

# How to Read MPIF Material Grades for Powder Metallurgy Parts

If you are reading a PM part drawing for the first time, you may see a material callout like `FC-0208-70` or `FN-0405-115HT` and have no clear sense of what it means. These designations follow a coding system defined in MPIF Standard 35 - the primary material standard for structural PM parts in North America. Once you understand the structure, these codes carry a lot of useful information in a compact form.

This guide explains how to decode MPIF grade designations, what each element means, and how to use the standard as a practical reference when specifying or reviewing PM drawings.

What MPIF Standard 35 Is

MPIF Standard 35 - Materials Standards for PM Structural Parts - is published by the Metal Powder Industries Federation. It defines:

• Compositional ranges for a set of standard PM alloy families
• Minimum mechanical property requirements (tensile strength, yield strength, elongation, hardness)
• Density ranges associated with each property class
• Test methods and sampling procedures

It is not a compulsory standard in the same way some ISO or ASTM standards are - you can specify a PM part outside Standard 35 - but it is the common reference for North American PM, and most PM suppliers quote to it by default. ISO 5755 is the international equivalent with similar structure.

Grade Designation Structure

MPIF grade codes follow a systematic pattern:

``` [Material code] - [Nominal composition] - [Minimum strength or hardness] ```

Example: FC-0208-70

That one code tells you: this is a sintered iron part with approximately 2% copper and 0.8% carbon, and it must meet a minimum UTS of 70 ksi. If you know the alloy system, you can also infer density range, hardness, and heat treatability.

Material Family Prefix Codes

The first one or two letters identify the alloy family:

Knowing the prefix immediately tells you the base system, which determines corrosion behavior, magnetic response, and heat treatability.

Composition Digits

The four digits after the hyphen encode the nominal alloying element contents.

For iron-based grades, the convention is:

``` FC - [Cu%×10 / 2 digits] [C%×10 / 2 digits] ```

Wait - it is simpler than that formula implies. Look at it directly:

• FC-0208: 02 = ~2% copper, 08 = ~0.8% carbon
• FC-0205: 02 = ~2% copper, 05 = ~0.5% carbon
• FC-0808: 08 = ~8% copper, 08 = ~0.8% carbon
• FN-0205: 02 = ~2% nickel, 05 = ~0.5% carbon
• FN-0405: 04 = ~4% nickel, 05 = ~0.5% carbon

The digits represent nominal percentages scaled by 100. `02` means ~2%, `08` means ~0.8% (i.e., the digit pair `08` in the carbon position is 0.8 because carbon is typically well below 1%).

For stainless grades:

• SS-316L-15: Stainless 316L, minimum tensile 15 ksi (used in low-density, highly porous PM; for structural parts the number is higher)
• SS-410-55: 410 stainless PM, minimum tensile 55 ksi

Minimum Strength / Property Class Suffix

The number at the end of the grade code is the minimum ultimate tensile strength in thousands of psi (ksi):

A higher suffix means higher minimum strength, which corresponds to higher density and/or heat treatment. The same alloy composition can appear with multiple suffixes - FC-0208-55, FC-0208-70, FC-0208-90 - representing different density ranges or processing conditions.

The "HT" Suffix

`HT` after the number indicates the property class requires heat treatment:

• FC-0208-90: FC-0208 at the 90 ksi property level, achieved by pressing and sintering to appropriate density - no heat treatment
• FC-0208-90HT: FC-0208, heat treated (typically quench and temper), achieving 90 ksi

In practice, the HT suffix marks a significant difference. Heat-treated PM grades achieve higher strength and hardness at a given density than as-sintered equivalents. Hardness values for heat-treated grades are typically in the 30-50+ HRC range depending on alloy and temper, versus 10-25 HRB for as-sintered equivalents.

If your drawing calls out an HT grade, the supplier must apply a specific heat treatment cycle and verify hardness - it is not optional.

Practical Examples

FC-0208-70: Iron with ~2% copper and ~0.8% carbon, as-sintered, minimum UTS 70 ksi (483 MPa). Typical density 6.6-6.9 g/cm³. Common structural gear and hub grade. Moderate strength, good dimensional stability, cost-effective.

FN-0405-115HT: Iron with ~4% nickel and ~0.5% carbon, heat treated, minimum UTS 115 ksi (793 MPa). High-strength grade for demanding structural applications - automotive connecting rods, high-load gears, cam followers. Requires quench and temper.

SS-316L-25: 316L stainless PM, minimum UTS 25 ksi (172 MPa), low-density grade used for self-lubricating or porous filter applications. For structural stainless parts, the suffix is higher (SS-316L-55 or similar).

CT-1000-14: Copper-tin (bronze) PM, 10% tin (the first two digits in some CT grades represent tin%), minimum tensile 14 ksi. This is a bearing-grade bronze PM - low strength, high oil retention, used for self-lubricating bushings.

Where Standard 35 Falls Short

MPIF Standard 35 covers the most widely used PM grades, but it does not cover everything:

• Proprietary and diffusion-alloyed grades (Distaloy series, Ancorsteel series, Höganäs grades) have specific compositions and properties that may not map exactly to a Standard 35 designation. Suppliers using these grades will provide their own data sheets.
• High-performance PM grades for automotive structural parts (connecting rods, transmission components) are often specified to proprietary OEM or Tier 1 material standards rather than MPIF.
• Custom alloys developed for specific applications may not fit the standard coding system.
• Density-only specification is not part of the grade code - if you need to ensure a minimum density separate from the property class, that must be called out separately on the drawing.

How to Use This on a Drawing

When specifying or reviewing a PM material callout:

1. Identify the alloy family from the prefix - it tells you corrosion behavior, magnetic response, and whether heat treatment is possible.
2. Read the composition digits - they tell you what alloying elements are present and at what level.
3. Check the property suffix - it defines the minimum mechanical property floor. Higher suffix = higher density or processing requirement.
4. Look for HT - if present, heat treatment is required and must be specified in the process.
5. Cross-reference MPIF Standard 35 for the full property table at the specified grade, including density range, yield strength, elongation, and hardness.

If your drawing specifies only a material designation without minimum mechanical property requirements, your supplier will produce to the minimum of that class. If you need properties above the class minimum, you need to specify a higher class - or add a separate property requirement on the drawing.

Contact our engineering team if you need help interpreting a material callout or selecting the right MPIF grade for your application.