Limiting distortion of long or complex parts.
Reducing Risk in Hardening Complex Parts
Paulo’s martempering (also sometimes known as stepped quenching, interrupted quenching, or marquenching) process eliminates the risk of distortion while achieving high hardness, resistance to cracking, increased impact strength, and higher wear resistance in steel parts.
How Martempering Works
After heating, pieces are quenched in our vertical salt baths where the temperature of the bath is set 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°F, 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 using other heat treatment processes is possible, but parts encounter significantly more stress in those processes, which heightens the risk of distortion.
High-quality, highly-hardenable steels or production parts with thick or dramatically variable cross sections respond best to martempering. Parts that are well suited for martempering include bearings, gears, tooling, dies, and shafts where tolerances are a chief concern.
Martempering helps de-risk the heat treatment process, and its accuracy is enhanced by Paulo’s automated furnace controls. Martempering yields the following benefits:
- Reduction of warping and distortion
- Reduced risk of cracking
- Higher hardness
- Increased wear resistance
- Higher impact strength
Achieving In-Spec Hardness With Martempering
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 to specified hardness levels, it must be reheated to between 300°F and 1,200°F. 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 typically require tempering because the hardness level of a part is achieved based on the temperature of the molten salt quench.
- 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°F and a quenching range of 300°F to 900°F.
- Computer-controlled loading, processing and tracking systems are used at all Paulo facilities.
Advance Your Processing, Advance Your Results
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