Forging Heat Treatment with Marquenching

ThermTech is proud to offer marquench hardening for forgings. Marquenching is usually used for higher alloy grades of steel that are prone to excessive distortion or cracking.

Instead of lower temperature oil or polymer, components are quenched in hot molten salt, which greatly reduces the risk of distortion and cracking while still providing an equivalent microstructure on many part types.

Due to core property requirements and the section sizes of most forgings, marquenching is not commonly used on forgings unless they are extremely prone to cracking.

Capability & Process

ThermTech has two primary ways of performing marquench hardening for forgings:

1.    Atmosphere Furnace-to-Salt: Parts are heated (austenitized) in a batch atmosphere furnace from 1500-1600°F. Then they are automatically transferred to the molten salt quench, which is set anywhere from 375°F to 500°F depending on steel grade. Parts are then tempered down to the specified hardness range. 

The maximum capacity for this operation is 36”W x 72”L x 48”H with a maximum weight of 7000 lbs.

2.    Salt-to-Salt: Parts are austenitized in a high-heat salt bath, then transferred into another lower temperature bath for the quench.

This process can be even more beneficial for products with distortion issues since parts spend less time at the high heat temperature.

The maximum dimensions for this process are 20”OD x 30”H.


ThermTech offers the marquenching for many alloy grades, and not necessarily just higher alloy steels. Most commonly, the following are performed:

  • Marquench 4340 steel forgings
  • Marquench 4140 steel forgings
  • Marquench 4150 steel forgings
  • Marquench 5160 steel forgings

Please note that once forgings reach a certain thickness, equivalent core properties to oil or polymer quenching may no longer be achievable with marquench hardening. This is because the thermal driving force (to provide adequate quench rates in the core of thicker parts) is less during the high heat salt quench used in marquenching.

The marquench process tends to be used most commonly for thin-walled materials. It is also commonly used for forgings made from high carbon and/or high alloy grades that are prone to cracking in any liquid quenchant process.

If the parts in question have heavier sections that require core properties, oil quench hardening or polymer quench hardening may be required to meet the specification. To develop a process that meets all part requirements with minimum distortion please contact ThermTech for assistance.

For components that are extremely prone to distortion or cracking, an austempering process may be the best option. Austempering is also ideal for producing superior ductility properties in parts of all geometries.

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