What is the highest temperature for sintering?

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Today’s powder metal market is dominated by the automotive industry, advancing from its early acceptance of bearings and suspension components into more demanding applications in the internal combustion engine and automatic transmissions. Lessons learned from the automotive sector, have transformed current and potential new users in the non-automotive and electric vehicle applications to look at PM for planetary gear set and gear reduction opportunities.

When most people think of powder metal, they think of pressed and sintered components. After compaction, a vital step in the PM process is sintering. The current norm for sintering is a temperature of 2050°F (1120°C) -- this has proven successful for most PM applications and has brought the industry to its currently highly regarded position of a cost-effective, mechanically proven metal forming technology.

In our opinion, the current sintering practice is good, but are there other sintering practices that can produce a better or perhaps best practice for the increasing demands being put on PM components? Ultra-high temperature sintering may be the solution.

The Automotive Industry: An Emerging Technology

With the ever-increasing “electrification” of transportation, many engineers are leaving the world of “good enough.” The increased torque of electric motors puts greater demands on components used in conjunction with these propulsion systems. Although the electrification of vehicles is inevitable, internal combustion engines will be a segway between the current market and full electrification. Internal combustion engines in this interim period will have increased demands for higher fuel efficiency, higher performance, and lighter weight (through the use of turbocharged combustion engines), thus placing even greater demands on existing sintered PM components.

This changing dynamics of the automotive industry will force a reevaluation of the role of sintering in powder metallurgy, specifically newer parts demanding higher tensile and fatigue strengths.

Sintering: Good, Better, & Best

This next leap in performance for powder metallurgy is not years away, but here today in the form of ultra-high temperature sintering (UHTS). UHTS opens the door to using non-traditional alloys to achieve greater mechanical properties.

Your design can achieve a combination of strength and ductility superior to current ferrous powder metallurgy material. Powder metallurgy now has the tools to take on applications previously thought unattainable with current PM.

That’s the short version (honestly!). Keep reading for a deeper dive into unique alloying additions, processing details, and the resulting mechanical property boosts UHTS delivers. 

Sintering: Where the Magic Happens

We’ve already established that over 95% of powder metal parts are created through the art of sintering. Sintering, and more importantly sintering temperature, is key to creating interparticle bonds, partially alloying any elemental additives, and subsequently creating the mechanical properties that you see with these components. 

The sintering temperature is a lot more than just a number. It’s a window of opportunity for part performance and customization. 

First, let’s define terms. As in most things, there is good, better, and best.

• Conventional Sintering: 2050°F (1120°C) in a nitrogen hydrogen atmosphere (good)

• High-temperature sintering: 2125-2300°F (1160-1260°C) (better)

• Ultra-high-temperature sintering: In excess of 2500°F (1370°C) (best)

  
  

Conventional Sintering in Powder Metallurgy (Good)

Proper sintering of the compacted powder metal parts requires the following steps:

• Delubrication

• Oxide reduction

• Formation of metallurgical bonds between pressed particles

• Complete or partial alloying

More than 80% of all structural powder metal components are sintered at 2050°F. These materials and processes have provided a low-cost metal-forming technology with adequate mechanical properties for a wide variety of powder metal parts in production today.  

Despite this universal acceptance, limitations exist for sintering in this temperature range:

• Incomplete homogenization of premixed alloying elements, even copper

• When sintering at conventional temperatures, there are limited premix additives available to increase mechanical properties

• Oxides of alloying elements that provide greater mechanical properties may not necessarily reduce at 2050°F

• Limitations of conventional PM 2050°F sintering for structural components are reduced impact toughness, along with limited alloy selections

High-Temperature Sintering (Better)

High-temperature sintering is considered between 2125° and 2300° F.

Sintering non-stainless, ferrous materials at higher temperatures improves the performance:

• Hig

  her

  Density

• Higher Tensile Strength

• Higher Fatigue performance

• Higher Modulus of elasticity

High-temperature sintering enables reduced time at temperature, thereby partially offsetting the increased cost associated with high-temperature sintering.

Despite the many benefits of high-temperature sintering, current market use for this technology is quite low. So, what’s the holdup?

• An assumed lack of dimensional precision

• Capital cost of equipment

• Cost (both fixed and maintenance) associated with the technology

Although these potential roadblocks exist, the advantage of using this better sintering, coupled with PMs shape and material efficiency, offers opportunities for existing and new PM parts designs with potentially lower costs.

Ultra-High-Temperature Sintering (in excess of 2500°F) (Best) 

Ultra-high-temperature sintering enhances the many advantages of high-temperature sintering, with expanded mechanical performance and alloying options. At these ultra-high temperatures, the potential exists to use more compressible premixed metal powders, yet still achieve complete homogenization within the final part.

The result? New levels of strength of up to and greater than 200,000 psi tensile strengths and elongations approaching 2% are possible even at densities below 7.2 g/cm³.

Also of note’ there’s greater pore rounding with UHTS. This seemingly small feature has been shown to further improve:

Contact us to discuss your requirements of Hot-Press Sintering. Our experienced sales team can help you identify the options that best suit your needs.

• Tensile strength

• Fatigue strength

• Impact strength

One other advantage of conventional sintering is the ability to sinter-harden the PM part during the sintering process. Sinter hardening is a process that effectively merges sintering and heat treating into one operation. With the advent of ultra-high temperature sintering and its unique alloying opportunities, sinter-hardening can be achieved even after sintering at this high temperature. This creates a unique opportunity to have the best of both worlds: high levels of performance with the added advantage of no secondary heat treatment (win-win). 

Aim for the Best with UHTS

To conclude, PM offers many advantages including little to no machining, material efficiency, and potentially low cost. The results of ultra-high-temperature sintering, specifically higher strength, higher modulus, and higher fatigue allow the designer to advance smaller, lighter-weight components for their high-demanding applications.

Editor's note: This blog was originally published on 06/25/2021 and was updated on 1/30/2024.

Sintered parts start out as powder compacts, sometimes referred to as “green” parts. Heating these in a furnace -- a process known as sintering -- bonds the powder grains together, to create hard components ready for use.

Sintering of iron based PM parts is usually done at around 2020-2100°F. When done at higher temperatures, the process is called “high-temperature sintering.” High-temperature sintering changes part properties and can have amazing performance implications. Anyone specifying or purchasing sintered metal parts should know the differences and understand how this process can benefit both price and performance.

Below are the differences between regular and high-temperature sintering. We'll also address the benefits and drawbacks of the high-temp sintering and wrap up by describing some applications that can benefit from this advanced process.

What Is High-Temperature Sintering Vs. Conventional Sintering?

Sintering is a process of diffusion bonding. Below a material’s melting point, adjacent grains of metal begin to share molecules. This forms “necks” between the grains that lock them into a rigid structure.

Metallurgists carry out sintering in a controlled atmosphere. This has two functions:

1. Removes surface oxides so diffusion bonding can take place

2. Excludes oxygen from the furnace, preventing further oxidation

A high-temperature sintering furnace typically runs 100 to 250 degrees hotter than one used for regular sintering. The difference may seem small, but it has fascinating implications for component properties, operating costs, and furnace construction.

(DYK? Two distinct options called sinter bonding and sinter brazing are great for optimizing your project’s cost efficiency, strength, and more.)

Defining ‘High-Temperature’

Not all high temperatures are created equal.

OEM customers come to powder metal parts manufacturers with all sorts of definitions for “high-temperature sintering.” In a way, the definition depends on your perspective.

For example, in terms of stainless we’ve heard 2100° called “high-temp.” Technically, that’s (barely) correct because conventional sintering is performed at 2050°.

We prefer to think of “high-temperature” for structural powder metal parts as 2100°. For stainless steel PM parts, we consider 2350° an accurate description.

If you’re sintering these materials instead, here’s what we consider high-temperature:

• Aluminum: 1350°

• Copper: 1900°

• Iron: 2150°

• Tungsten: 3200°

So, it very much depends on the material you use.

Benefits of Higher-Temperature Sintering

A higher sintering temperature increases diffusion bonding and causes the remaining pores to become more round, improving the resulting mechanical properties. The necks between the grains grow larger, and the pores between grains shrink and become like tiny soccer balls. This shrinkage of pores leads to significant improvements in strength.

In one study, researchers were able to increase a component’s:

• Tensile strength by 30%

• Bending fatigue strength by 15%

• Impact energy (a measure of toughness) by 50%

You may not realize it, but your specs may be a few hundred degrees short of where you should be performance-wise. It’s important the customer understands what the part has to do to get the performance you’re looking for. That’s where your PM parts maker should come in. Parts manufacturers with top-end capabilities may seem pricier, but they’ll also give you higher sintering temperatures for optimal performance.

Drawbacks Vs. Conventional Sintering

Improvements in sintered metal part strength come at a cost. (Isn’t there always a caveat?)

The components themselves actually shrink in size by the time it’s ready to be shipped. This can be addressed by your metal parts manufacturer during design of the compaction tools. Sometimes manufacturers limit maximum temperature to better control the part size.

Perhaps of greater relevance to buyers and end users, high-temperature sintering is more costly. That doesn’t necessarily mean parts produced through this process will be more expensive.

A paper presented at the International Conference on Powder Metallurgy & Particulate Materials (PM²TEC) addressed this apparent contradiction. Furnaces for high-temperature sintering are far more expensive than those for regular temperature work. In addition, productivity tends to be lower.

On top of that, as you get above the 2150° range, sintering belt life goes down dramatically. Fortunately, a few smart-thinking parts manufacturers have devised setups that avoid some belt-life issues.

Still, the supplier’s high production and equipment costs inevitably limits your own costs-effectiveness -- unless you take this opportunity to benefit from improved part properties.

Since sintered metal makes stronger parts, it's possible to switch to less expensive powder materials. In some cases -- and it is very application-specific -- this can actually result in less expensive sintered parts. Another way you can leverage these improved properties is to design smaller parts that require less material -- and therefore less investment.

Applications for Metal Parts Sintered at High Temperatures

The best candidates for high-temp sintering are projects where the component in question is subject to high tensile, and possibly fatigue, loads. These include components in appliances and firearms, but especially those in the automotive sector. With weight being an overarching concern in modern vehicles, any opportunity to reduce part size is a potential contribution toward fuel economy goals.

Improved properties open up new applications for sintered metal, too. More specifically, increased impact strength means sintered metal can be considered where wrought iron and steel are currently king. Brackets and hooks are examples -- we’d love to hear your other ideas, too.

The More Expensive Process May Be … Cheaper?

The majority of powder metal parts are sintered at around 2050°F, but some specific applications can benefit from moving to high-temperature sintering. The process is more expensive, yet can lead to lower-cost parts with smart design and the guiding hand of a high-temp sintering expert.

Assessing the value of sintering isn’t always all about temperature. Factors like atmospheric conditions also matter. If you need to know more about these more technical factors, it may be best to get in touch with a PM parts supplier.

Next up: Ultra-High-Temperature Sintering

Through unique, recent advances in powder metallurgy, you can take your component yet another step further -- through a process we call ultra-high-temperature sintering.

Ultra-high-temp sintering (UHTS) is defined as sintering ferrous powder at temperatures approaching 2500° F.  The benefits of regular high-temperature sintering are augmented with UHTS.

If you have a question about any level of sintering, ask an expert engineer directly. It's as simple as clicking below:

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