What is the highest temperature for sintering?

Discovering the Highest Temperature for Sintering

High-temperature sintering typically ranges between 2100°F to 2500°F, with ultra-high-temperature sintering extending beyond 2500°F or 1370°C. This range is essential for achieving optimal mechanical properties in powder metal parts.

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Today’s powder metal market is dominated by the automotive industry, which has progressed from its early use of bearings and suspension components to more demanding applications in internal combustion engines and automatic transmissions. Lessons learned from the automotive sector have influenced non-automotive and electric vehicle applications to consider PM for planetary gear sets and gear reduction opportunities.

When most people think of powder metal, they envision pressed and sintered components. After compaction, sintering is a critical step in the PM process. The standard sintering temperature is 2050°F (1120°C), which has been effective for most PM applications and has established the industry as a cost-effective, mechanically reliable metal-forming technology.

But is there a superior sintering practice to meet the increasing demands on PM components? Ultra-high-temperature sintering may be the answer.

The Automotive Industry: An Emerging Technology

With the ongoing electrification of transportation, many engineers are moving beyond "good enough." The increased torque of electric motors puts greater demands on components used with these propulsion systems. Although vehicle electrification is inevitable, internal combustion engines will serve as a bridge between the current market and full electrification. During this period, these engines will need higher fuel efficiency, better performance, and lighter weight, adding further stress to existing sintered PM components.

This dynamic shift in the automotive industry will necessitate a reevaluation of the role of sintering in powder metallurgy, especially for newer parts requiring higher tensile and fatigue strengths.

Sintering: Good, Better, & Best

The next significant advancement in powder metallurgy is already here in the form of ultra-high-temperature sintering (UHTS), which provides the opportunity to use non-traditional alloys to achieve superior mechanical properties.

Your design can attain a combination of strength and ductility that surpasses current ferrous powder metallurgy materials. Powder metallurgy now offers the capability to tackle applications previously deemed unattainable with current PM.

This is just a brief overview. Keep reading to delve deeper into unique alloying additions, processing details, and the mechanical property enhancements that UHTS provides.

Sintering: Where the Magic Happens

We’ve established that over 95% of powder metal parts are produced through sintering. Sintering, particularly the sintering temperature, is crucial for creating interparticle bonds, partially alloying elemental additives, and establishing the mechanical properties of these components.

The sintering temperature is more than just a number; it represents a window of opportunity for part performance and customization.

Firstly, let's define the terms:

• 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: Above 2500°F (1370°C) (best)

Conventional Sintering in Powder Metallurgy (Good)

Proper sintering of compacted powder metal parts requires several steps:

• Delubrication
• Oxide reduction
• Formation of metallurgical bonds between pressed particles
• Complete or partial alloying

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

Despite this widespread use, limitations exist:

• Incomplete homogenization of premixed alloying elements, even copper
• Limited premix additives available to enhance mechanical properties
• Oxides of alloying elements that provide superior mechanical properties may not reduce at 2050°F
• Limited impact toughness and alloy selections at conventional PM 2050°F sintering

High-Temperature Sintering (Better)

High-temperature sintering, performed between 2125°F and 2300°F, significantly improves the performance of non-stainless, ferrous materials:

• Higher Density
• Higher Tensile Strength
• Higher Fatigue Performance
• Higher Modulus of Elasticity

High-temperature sintering reduces the time at temperature, partially offsetting the increased cost. Despite its advantages, the current market use is relatively low due to:

• Assumed lack of dimensional precision
• High capital cost of equipment
• High technology costs (both fixed and maintenance)

Despite these roadblocks, the advantages of better sintering, together with PM's shape and material efficiency, offer opportunities for new and existing PM part designs at potentially lower costs.

Ultra-High-Temperature Sintering (Best)

Ultra-high-temperature sintering enhances the numerous benefits of high-temperature sintering with expanded mechanical performance and alloying options. These ultra-high temperatures allow for the use of more compressible premixed metal powders while achieving complete homogenization within the final part.

The result? New strength levels up to or exceeding 200,000 psi tensile strengths and elongations nearing 2% are achievable, even at densities below 7.2 g/cm³.

Additionally, greater pore rounding with UHTS further improves:

• Tensile strength
• Fatigue strength
• Impact strength

One notable advantage of conventional sintering is the ability to sinter-harden PM parts during the sintering process. Sinter hardening merges sintering and heat treating into one operation. With the advent of UHTS and its unique alloying opportunities, sinter-hardening is achievable even after sintering at high temperatures, creating an opportunity for high performance without the need for secondary heat treatment—a win-win scenario.

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Aim for the Best with UHTS

In conclusion, PM offers numerous advantages, including minimal machining, material efficiency, and potential cost savings. Ultra-high-temperature sintering results, specifically higher strength, higher modulus, and higher fatigue performance, allow designers to create smaller, lighter components for high-demand applications.

Editor's note: This blog was originally published on 06/25/2021 and was updated on 1/30/2023.

Beginner's Look at High-Temperature Sintered Parts

Sintered parts begin as powder compacts, also known as “green” parts. Heating them in a furnace—a process known as sintering—bonds the powder grains together, creating hard components ready for use.

Sintering of iron-based PM parts is usually done at around 2020-2100°F. When performed at higher temperatures, the process is termed “high-temperature sintering.” This process modifies part properties and can greatly enhance performance. Anyone specifying or purchasing sintered metal parts should know the differences and understand how this process can benefit both cost and performance.

What Is High-Temperature Sintering Vs. Conventional Sintering?

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

Metallurgists perform sintering in a controlled atmosphere to remove surface oxides, allowing diffusion bonding to take place, and to exclude oxygen, preventing further oxidation. High-temperature sintering furnaces run 100 to 250 degrees hotter than those used for standard sintering. This difference significantly impacts component properties, operating costs, and furnace construction.

Defining 'High-Temperature'

Not all high temperatures are the same. Definitions for “high-temperature sintering” vary among OEM customers.

For example, in stainless steel terms, 2100°F is considered high-temperature. For structural powder metal parts, 2100°F is high-temperature, while for stainless steel PM parts, 2350°F is accurate. For other materials:

• Aluminum: 1350°F
• Copper: 1900°F
• Iron: 2150°F
• Tungsten: 3200°F

Benefits of Higher-Temperature Sintering

Higher sintering temperatures enhance diffusion bonding and make pores more rounded, improving mechanical properties. In one study, high-temperature sintering increased:

• Tensile strength by 30%
• Bending fatigue strength by 15%
• Impact energy by 50%

Your specifications might be a few hundred degrees short of achieving optimal performance. Understanding part performance is crucial, and your PM parts maker can provide higher sintering temperatures for better performance.

Drawbacks Vs. Conventional Sintering

Improvements in sintered metal part strength come at a cost. High-temperature sintering can cause components to shrink, which can be managed during the design of compaction tools. Additionally, high-temperature sintering is more costly due to expensive equipment and lower productivity.

However, stronger sintered metal parts enable the use of less expensive powder materials, potentially reducing costs. Designing smaller parts can also save material and reduce expenses.

Applications for Metal Parts Sintered at High Temperatures

The best candidates for high-temperature sintering are components subject to high tensile and fatigue loads, such as those in appliances, firearms, and especially the automotive sector. Improved properties open new applications for sintered metal, including brackets and hooks.

The More Expensive Process May Be Cheaper

Most powder metal parts are sintered at around 2050°F, but some applications benefit from high-temperature sintering. While more expensive, this process can result in lower-cost parts with intelligent design and the guidance of a high-temp sintering expert. Assessing the value of sintering involves considering atmospheric conditions as well as temperature. For more technical factors, consult a PM parts supplier.

Next up: Ultra-High-Temperature Sintering

Ultra-high-temperature sintering (UHTS) involves sintering ferrous powder at temperatures approaching 2500°F. UHTS enhances the benefits of regular high-temperature sintering. To learn more about sintering, ask an expert engineer directly.

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