Marquench Hardening

ThermTech is proud to offer marquench hardening for gears. This process is usually used for higher alloy grades of steel or intricately machined components 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.

Capability & Process

ThermTech has two primary ways of performing marquench hardening operations for gears.

The first is an atmosphere furnace-to-salt operation in which parts are heated (austenitized) in a batch atmosphere furnace from 1500-1600°F, then automatically transferred to a 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 maximum weight of 7000 lbs.

The second marquench hardening method we employ is a salt-to-salt process in which 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 marquench hardening processes for many alloy grades, and not necessarily just higher alloy steels. Most commonly, the following marquench processes are performed:

  • Marquench Hardening 4340 steel
  • Marquench Hardening 4150 steel
  • Marquench Hardening 6150 steel

Please note that once the materials reach a certain thickness, equivalent core properties to oil or polymer quenching may no longer be achievable with marquench hardening as 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 or those made from high carbon and/or high alloy grades that are prone to cracking in other liquid quenchant process. If the parts in question have heavier sections that require core properties, oil or polymer quenching may be required to meet the specification. Please contact a technical representative at ThermTech and they will work to develop a process that will meet all part requirements with minimum distortion.

Contact a sales representative today to discuss the benefits of marquench hardening for your Gear parts products!