Martempering

Limit distortion of long or complex parts.

Steel parts come in all shapes and sizes, and that means flexibility in heat treatment is critical. Because longer workpieces or those with more complex shapes are at higher risk of warping and distortion during heat treatment, Paulo’s martempering process is right for the job of eliminating that risk while achieving high hardness, resistance to cracking, increased impact strength and higher wear resistance in a steel part.

After heating, the pieces are quenched in our vertical salt baths. We set the temperature of the bath to just above the given material’s martensitic start point. Compared to austempering, where quenches run at higher temperatures, martempered parts are quenched at a cooler temperature (generally around 350 degrees, depending on the alloy). The parts are held in the quench at this temperature to cool only long enough —between five and ten minutes— for the core and surface temperatures to equalize.

The parts are then pulled from the quench and further cooled in still air at room temperature.

Quenching the part only long enough to stabilize surface and core temperatures and then cooling in still air promotes the formation of martensite, the hardest form a steel can take. Forming martensite via other heat treatment processes is possible, but parts encounter significantly more stress in those processes, heightening the risk of distortion.

High-quality, highly-hardenable steels or production parts with thick or dramatically variable cross sections respond best to martempering.

Paulo’s martempering process delivers:

  • Reduction of warping and distortion
  • Reduced risk of cracking
  • Higher hardness
  • Increased wear resistance
  • Higher impact strength

Martempering results in a hardness similar to that achieved via oil quenching. Because this hardness is often higher than specifications require, the part must be tempered. To soften a part down to specified hardness levels, it must be reheated to between 300 and 1,200 degrees. Tempering also increases a part’s ductility.

The amount of hardness removed from a part during tempering varies depending on the reheat temperature. For example, tools and dies that must remain very hard are tempered at lower temperatures. Parts like springs are tempered at higher temperatures because higher temperatures remove hardness but make parts more tough and ductile.

Other heat treatment processes, including austempering, do not require tempering because the hardness level of a part is achieved based on the temperature of the molten salt quench.

Key features

  • Paulo’s salt to salt martemper system at the 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