サーモプロセス技術

Martempering Furnaces using Neutral Salts Electrically Heated

Marttempering furnace QS 20 with charging basket Martempering furnace QS 30 with charging aid

Martempering hardening in practice

QS 20 - QS 400 martempering furnaces are filled with neutral salt and offer remarkably rapid and intensive heat transmission to the workpiece while ensuring optimum temperature uniformity. Since the batch is heat treated with the exclusion of oxygen, scale and discoloration on the surface of the parts are reduced to a minimum. For working temperatures at between 180 °C and 500 °C these martempering furnaces are useful for quenching or cooling with minimal workpiece distortion, retempering, austempering for optimal toughness, recrystallization annealing after electrical discharge machining (EDM) and for blueing. The quenching or cooling process is applied in order to achieve an even temperature uniformity throughout the workpiece‘s entire cross-section before the formation of martensite and to avoid distortion and formation of cracks in complex mechanical components during the subsequent hardening process. Tempering in a martempering bath is the same as the tempering process in forced convection furnace and is used to reduce a previously hardened workpiece to a desired hardness, to increase toughness and reduce stress within the workpiece. Austempering is a good choice to achieve a high level of toughness and dimensional accuracy in oil hardened low-alloy steels. Workpieces subject to austempering have high tensile strength and good elasticity.

  • Tmax 550  °C
  • Very good temperature uniformity
  • Martemper bath temperature control
  • Over-temperature limiter with adjustable cutout temperature for thermal protection class 2 in accordance with EN 60519-2 as temperature limiter to protect the furnace and load
  • Heating with immersion heating elements
  • Rectangular crucible, integrated in the housing
  • Charging basket
  • Crucible made of 1.4828
  • Defined application within the constraints of the operating instructions
  • NTLog Basic for Nabertherm controller: recording of process data with USB-flash drive

Additional equipment

  • Charging aid with hand crank and cable winch, mounted on side of furnace
  • Process control and documentation via VCD software package for monitoring, documentation and control
Process Examples with Petrofer and Durferrit Salts

QS-baths (steel/Nitinol)
Hardening, isothermic treatment of steels up to 950 °C, stress relieving, annealing, bluing, bainitizationAS 135, AS 140, AS 220, AS 225, AS 200, AS 235, GS 230
Homogenization annealing, recrystallization annealing; warm-bath curing, tempering, banitizing, bluingAS 300
ModelTmaxInner dimensions in mmVolumeOuter dimensions in mmHeatingElectricalWeight
 °Cwdhin lWDHpower in kW1connection*in kg
QS 20550300210460206105809202.61-phase110
QS 30550300210580306105809203.21-phase140
QS 70550400300680707506809807.53-phase240
QS 200550540520880200900900120018.03-phase660
QS 40055073072098040011001100130024.03-phase1150
1Depending on furnace design connected load might be higher *Please see page 89 for more information about supply voltage