Technologia procesów termicznych

Martempering Furnaces using Neutral Salts Electrically Heated

Martempering furnace QS 30 with charging aid

Martempering hardening in practice

Double martempering bath

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. For working temperatures at between 180 °C and 500 °C these martempering furnaces are ideal 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 valuable 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 500  °C
  • Optimal 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
  • Charging basket
  • 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 mounted on side of furnace
  • Process control and documentation via VCD software package for monitoring, documentation and control
ModelTmaxInner dimensions in mmVolumeOuter dimensions in mmHeatingElectricalWeight
 °Cwdhin lWDHpower in kW1connection*in kg
QS 20500300210460206105809202.61-phase110
QS 30500300210580306105809203.21-phase140
QS 70500400300680707506809807.53-phase240
QS 200500540520880200900900120018.03-phase660
QS 40050073072098040011001100130024.03-phase1150
1Depending on furnace design connected load might be higher *Please see page 81 for more information about supply voltage
Information about salts by Petrofer and Durferrit and their application

SaltApplicationWorking temperatureComment
  in °C 
AS 135/140Martempering hardening, tempering, austempering180 - 500Not for use with workpieces which are heated up to above 950 °C and salts which contain more than 13 % KCN
AS 220/225Tempering, austempering250 - 500 
AS 200/235Tempering, austempering280 - 500Nitrite-free in the as-received condition
AS 200/235Tempering340 - 500