Austempering

Achieve superior toughness (while minimizing distortion).

When workpieces require added hardness, higher impact and fatigue strength, increased ductility, resistance to embrittlement higher wear resistance, Paulo’s state-of-the-art austempering process ensures your parts are finished to specification with minimal distortion.

In austempering, pieces are first heated in continuous belt furnaces or salt baths to temperatures as high as 1,650 degrees Fahrenheit, depending on the material. The carbon atoms that add hardness to a part cannot dissolve into it unless a part is austenitized, causing a transformation of the part’s crystal structure.

After heating, parts are quenched in a bath of molten salt. While this temperature varies depending on the part’s makeup and its desired finished hardness, it is generally done at around 600 degrees. This delivers added strength and ductility to the part.

The part is held at this temperature until bainite forms. Bainite refers to the microstructure that is created by the austempering process. Austempering can take as little as ten minutes or as long as an hour and a half depending on how a part’s makeup affects bainite formation.

The quench-and-hold at higher temperatures for the hardening in austempering greatly minimizes the risk that parts will distort compared to quenching in oil. That’s because cooling parts at elevated temperatures rather than at lower temperatures significantly slows cooling. Slower cooling means parts encounter less stress due to thermal expansion and contraction and less stress from transformation.

The process concludes by final cooling of the part in open air at room temperature.

Final tempering of austempered parts is not required because the part’s desired hardness can be achieved via the temperature of the salt bath quench that follows heating. Other forms of heat treatment, including martempering, do require tempering because parts emerge from quenches harder than needed and must be softened to meet specification.

Paulo’s austempering process delivers:

  • Greater ductility
  • Uniform hardness
  • Higher impact and fatigue strengths
  • Wear resistance
  • Resistance to hydrogen embrittlement

Pieces treated by austempering are ideal for use as components of systems under frequent stress, such as springs, clips and seat belt loops in cars or lawn mower blades.

Austempering delivers the highest ductility available for steels in the mid- to upper-40s on the HRC hardness scale. Steels with medium amounts of carbon and higher alloy levels, including thicker parts made of steels like 4140, 4150, 5160 and 6150 and thinner parts made of steels from between 1050 and 1095, usually respond best to austempering.

Our multi-furnace capabilities offer both continuous belt and vertical bath setups to accommodate a broad range of parts and volumes. Because our facilities have redundant capabilities and capacity, we’ll meet any order on deadline, no matter what.

Key features:

  • The continuous mesh belt austemper in our Murfreesboro Division can is capable of treating 3,000 pounds of parts per hour with maximum temperature of 1,650 degrees Fahrenheit. Murfreesboro salt quench bath temperature range of 585 to 680 degrees.
  • The salt bath and salt quench in our Kansas City Division has dimensions of 16” x 32” x 58” with maximum temperature of 1,650 degrees and a quenching range of 300 to 900 degrees.
  • Computer-controlled loading, processing and tracking systems are used at all Paulo facilities.
  • Our equipment includes automatic carbon control.

Locations offering this service:

Heat treating 101: An Introduction to Heat Treating Procedures