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Difference Between Martempering and Austempering Steel

April 22nd, 2021

Various heat treatment processes are used to achieve the optimal hardness, strength levels and other features for particular applications. Your industrial manufacturing components may require either martempering or austempering to create dependable products for your customers. Explore the differences between these two processes to see how Specialty Steel Treating can help you improve your manufacturing efficiency.

Both processes use quenching and tempering. Quenching is the process of cooling the product down at varying speeds. Most steel products are quenched in oil, water or air. Tempering is the process of actually applying heat to the material in order to improve its hardness and other features.

The Martempering Process

Also known as marquenching or interrupted quenching, this process uses several steps to create a distinct heat treatment process. It starts by heating the product to a temperature above the upper critical point. This process is usually achieved with a salt or oil bath.

Afterward, it’s quenched to reduce the temperature to a point between 150 and 300 degrees Celsius. This point is above the martensite start point. It’s held at this point until the entire workpiece reaches a uniform temperature. This uniformity is critical to martempering. It allows the austenite to transform to martensite without the formation of ferrite, bainite or pearlite. The workpiece is finally cooled, typically with air.

Advantages of This Process

The Martemper process creates a uniform temperature throughout the material before it’s quenched. This uniformity removes residual stresses that are typically retained with common quenching and tempering processes.

Workpieces that are martempered also allow for a greater control of decarburizing and carburizing. Fire hazards and pollution are avoided by using nitrate-nitrite salts as a bath rather than oil. Here are some common grades of steel that work well with the martempering process:

  • 1090
  • 4130
  • 300M
  • SAE 1141
  • 410 stainless

Disadvantages of This Process

There are, of course, some drawbacks to choosing martempering. First, this process requires higher levels of heat in the initial phase. This can increase the cost or power output required to achieve a martempered product.

Second, this quenching and tempering process cannot be used on a large workpiece, as there is a limit to the size of a piece that can reach a uniform temperature throughout. Finally, this heat process isn’t applicable to all types of steel.

The Austempering Process

Use austempering to achieve a bainite structure in your workpiece for a tough, ductile material. Austempered products are heated at an even higher level than martempered ones, typically between 840 and 950 degrees Celsius.

This not only produces a uniform interior and exterior temperature, but allows the bainite microstructure to form throughout the product. It can be used with ductile iron or steel workpieces. The cooling process is quite rapid, and the entire process doesn’t require final tempering.

Advantages of Austempering

Compared to martempering and other tempering forms, austempering creates less cracking and distortion. It’s also usually a more energy-efficient and rapid process. Products that are austempered offer improved ductility, toughness and impact resistance when compared to conventionally treated products.

Austempered ductile iron is used in a range of industrial applications. It offers increased mechanical resistance in order to create dependable industrial components. When you work with a qualified team with precision heat treatment capabilities, you won’t have to worry about the uniform quality of the workpiece.

Limitations of This Process

Austempering requires the transformation to bainite, but needs to avoid pearlite transformation. This requires a rapid, consistent cooling method. In most cases, this means that austempered materials can’t be more than 1/2 inch thick. This process isn’t suitable for every material or workpiece, and requires even higher heating capacities than martempering.

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