Marquench / Salt Hardening

ThermTech is proud to offer marquench hardening for steel investment castings.  This process 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 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 three primary ways of performing marquench hardening operations for investment castings.

The first is an atmosphere furnace-to-salt operation in which parts are austenitized in a batch atmosphere furnace from 1500-1600°F, then automatically transferred to the molten salt quench which is set anywhere from 375°F to 500°F (depending on requirements).  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 7000lbs per batch.

The second marquench hardening method we employ is a manual salt-to-salt process in which parts are austenitized in a high-heat salt bath, then manually 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 due to salt’s superior thermal conductivity.  The maximum dimensions for this process are 20”OD x 30”H.

The third marquench hardening method we employ is an automated salt line in which parts are austenitized in a high-heat salt bath, then automatically transferred into another lower temperature bath for the quench.  This process is perfect for parts with larger run quantities due to the labor cost savings associated with automation.  Our automated salt line is rated for 1500lbs per hour and has a working load size of 12”LR x 24”FB 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 52100 Steel

  • Marquench Hardening 4340 Steel

  • Marquench Hardening 4150 Steel

  • Marquench Hardening 4140 Steel

Please note that once castings 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 of a salt quench is less than that of an oil or a polymer quench.  

The marquench process tends to be used most commonly for thin-walled castings or those made from high carbon and/or high alloy grades that are prone to cracking in any liquid quenchant process.  Parts with heavier sections with core property requirements are typically best processed by oil or polymer quenching.  Please contact a technical representative at ThermTech and they will work to develop a process that will meet all part requirements with minimum distortion.

For components that are extremely prone to distortion or cracking, an austempering process may be the best option.  In addition to further reducing risk of distortion and cracking, austempering produces a bainitic microstructure that has superior ductility versus martensitic microstructures of equivalent hardness.

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