What is sintered stainless steel?

16 Dec.,2024

 

Sintered Stainless Steel Parts | PSM Industries

The stainless steel sintering process typically follows these steps:

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Blending
The sintering process begins by blending the necessary powdered metals into a uniform mixture. Typically, the initial material is an iron-based powder mix, which is combined with different alloying elements depending on the property requirements of the finished product. Blending also involves the addition of a solid lubricant, which serves to reduce friction between the surface of the compaction tool and the powder mass.

Compacting
During the compaction phase, a predetermined amount of the powder mixture is fed into the die cavity before it is compacted with a force up to 45 tons per sq inch. The resulting material has an approximate density of 85% to 95%. After compaction, the &#;green&#; part has the desired shape, but not the final dimensions. Because of this, allowances are made to accommodate the shrinkage that occurs during the sintering stage.

Sintering
The last step is sintering. This stage involves placing the &#;green&#; part into a furnace at a temperature just below the metal&#;s melting point. Stainless steel parts are typically exposed to temperatures up to ° F. During sintering, the powdered particles fuse together and form a molecular bond, enhancing the part&#;s mechanical properties.

What is Sintered Metal?

When you start investigating how powdered metal parts are made, learning about sintered metal is essential. Many of the things we love most about powder metallurgy can be traced back to the sintering process.

What is sintered metal? Fortunately, while the fine details are quite complex, the basics are easy to understand. Keep reading to not only better understand sintered parts, but also how the powder metal process can create high-strength parts that are viable in many more applications than you realize.

What Is a Sintered Metal Part?

To make small metal parts, you&#;ve got to poke them, prod them, and (usually) put some heat to them. Metal is stubborn, and sintering helps make sure the powder behaves after your part is formed.

The sintering process in powder metallurgy (PM) involves heating a compacted powder to fuse the particles, which leads to a harder, stronger part. While the compaction process does a lot of the work, the physical pressure produced in the press isn&#;t enough to create a final, work-ready component. Sintering is what comes after -- the final major step to produce a powder metal part you can rely on.

Before & During the Powder Metal Sintering Process

To get a clearer idea of how sintering fits into PM, let&#;s start at the beginning of the powder metal process:

1. Choosing a Powder Composition

After talking with you about your performance requirements, your manufacturer will pick a powder composition that will yield the right results.

The powder mix will include the basic stuff you need, such as iron, nickel, molybdenum and or copper. It will also include other substances like lubricants to improve the flow of the powder into the die. Lubricants are removed by evaporation and heat as a leadup to sintering in a single-furnace process.

2. Compaction

After the powder is poured into the die, it&#;s pressed with a whole lot of force to interlock the powder. The pressure creates connections strong enough to be called &#;green strength.&#; A green part won&#;t exactly crumble in your hands, but it still needs to be finished by sintering to achieve optimal strength and hardness.

3. Sintering

Sintering is done by putting your parts through a rather toasty furnace. The goal is to control the temperature so it reaches just below the melting point of your parts&#; primary metal &#; but not quite. The sintering process causes the metal particles to bond together so you get a part that does what you need it to do.

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Sintering Vs. Melting

It&#;s easy to assume they're very similar, but there are distinct differences between sintering and melting.

Melting actually gets the metal hot enough that it changes from solid to liquid. Sintering is different because the heating process is highly controlled. You get the enhanced properties you need without having to melt the metal. One of the great things about sintering is that you can easily make parts out of metals with high melting points.

Sintering can accomplish a lot when done right, including:

  • Eliminating the lubricants in the compacted powder
  • Reducing the amount of oxygen on the powder&#;s surface
  • Developing sintered necks between the particles, reducing pores and increasing strength
  • Partially or fully diffusing other elements in the mix, such as nickel, copper, and graphite 

The last two points are of key importance to the customer. These steps are what produce better properties for your part.

High-Temperature Sintering

Conventional sintering and high-temperature sintering are different shades of the same color.

In our eyes, for sintering to be considered high-temperature, it needs to happen at around 100-250 °F hotter (in the case of iron-heavy materials) than the standard sintering temp for a particular metal. For iron-heavy metals, the typical temperature is °F. High-temp sintering is more expensive than conventional sintering because you&#;re paying for extra &#;oomph&#; from the manufacturer&#;s equipment.

However, the extra cost can produce powdered metal material properties not available in any other way. One study showed that high-temp sintered parts improved in the following ways:

  • Increases in tensile strength of 30%
  • Bending fatigue strength increases of 15%
  • Increases in impact energy of 50%

It&#;s only one study, but the results were impressive nonetheless and we&#;ve seen similar results in our building. There are a few potential drawbacks to consider, though:

  • High-temperature sintering furnaces are much more expensive than conventional furnaces -- a cost that is passed on to the customer.
  • Parts that are sintered at high temps can shrink more than expected -- your manufacturer needs to plan accordingly.


Other Advances in Powder Metallurgy

Today, a select few powder metallurgy suppliers are going beyond the temperatures normally considered to be high-temperature sintering. What we now call ultra-high-temperature sintering further improves the properties of sintered metal by ramping the heat up to - °F.

To learn more about sintering, or how your project could combine the net shaping ability of PM with the strengthening ability of sintering to improve part performance, ask an engineer below. Or, to keep learning on your own, check out the related resources underneath.

Related Resources

 

(Editor's note: This article was originally published in September and was recently updated.)

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