Heat
treatment

Heat treatment

Heat treatment is a complex process, used to impart particular mechanical, chemical or physical properties by changing their structure. All types of heat treatment consists of three states: heating, tempering and cooling. At every stage, properties of alloys in solid state change. Particular types of heat treatment have different temperatures and sometimes different times considering time which is needed for subsequent processes. These two factors determine properties obtained by treated material. Metal heat treatment is first and foremost quenching, tempering and annealing. We, Sacher Company, having modern furnaces and our own quenching station, offer all these services and a wide range of more complex techniques of heat treatment.

Quenching

This  type of steel heat treatment and other metal alloys allows to obtain elements of increased hardness but at the same  time of increased brittleness,  which makes them more  subject to cracking. Such treatment is performed  at different temperatures, depending on steel grade. The process consists in heating steel elements and keeping them at particular temperature and then cooling.  Depending on what we want to achieve, we select cooling time and environment in which the whole process will be carried out: oil, water, air or  salts.  It is important to reduce stresses and strains which occur during the change of  structure of processed material- the best effects are achieved if we apply  quenching with isothermal process.

Vacuum hardening

This advanced  type of  metal heat treatment is conducted at high temperatures. It consists of austenitization at temperature of  800-1200 °C and then quick cooling and tempering in order to maintain the structure of martensite or bainite. This treatment allows to obtain exceptionally high steel hardness and strength. 

Carburizing

This kind of heat treatment, also referred to as case hardening, is used to increase material hardness and its abrasion resistance, maintaining softness and core ductility. Such effect may be obtained by carburizing  the near-surface layers of steel  with coal. We need to remember that this type of heat treatment is used only  with steels of carbon content up to 25%. When carburizing, steel is heated to temperature of  850-900 °C.

Carburizing time lasts  from 3 to 20 hours, depending on thickness of  surface layer in which changes are about to occur, being the result of  carburizing. Subsequently, treated elements are subject to quenching and tempering.

Piro-carb carburizing

Sacher Company, having technologically advanced furnaces, is able to offer also modern technology of Piro-carb vaccum hardening. It does not cause oxidations or  material deformations and leaves clean surface o workpieces. It is faster than conventional carburizing and due to energy consumption reduction is more environmentally friendly.

Annealing

Annealing is used to reduce hardness and stresses generated as a result of  mechanical processing or heat treatment. Its distinctive feature is longer duration and very high temperature as compared to other types of heat treatment.

We distinguish two types of annealing:

  • Soft annealing is performed to reduce the hardness of  steel elements, which require mechanical processing. The elements are heated  below the transformation temperature and kept for 5-10 hours and then slowly cooled.

  • Stress relief  annealing is applied to remove or  reduces stresses generated during welding,  hammering, cold forging and  thick workpiece machining. Steel is  heated to temperature above  quenching temperature, kept for 4-6 hours and then slowly cooled.

Vacuum tempering

Tempering is a process which is necessary after each steel quenching. It allows  to remove stressed generated during  heat treatment or chemical heat treatment and to achieve desired hardness of workpieces. Vacuum tempering consists in repeated heating  and then cooling down steel material. It does not cause oxidation of workpieces.

Depending on temperature, we can distinguish the following:

  • Snap tempering used to remove quench stresses. It takes place without changing the steel hardness achieved during quenching.

  • Medium tempering used in spring tempering. The effects of tempering are changes in crystalline steel structure, which results in brittleness reduction at the same time maintaining hardness and elasticity.

  • High tempering used to increase steel resistance to dynamic load with high amplitude.

Plasma nitriding

This metal heat treatment consists in nitrogen saturation of  surface layers, which increases their abrasion resistance and fatigue strength and also corrosion resistance. It  is performed in vacuum. As heating and cooling down processes are slow, plasma nitriding considerably limits the occurrence of  deformations and stresses. Subsequently, surface grinding or other  mechanical processing is not required  and  this type of treatment is  possible to apply in case of steel types which are difficult to quench.

Active  screen plasma nitriding( ASPN) provides uniform formation of  nitrides reflecting the shape of  workpieces without creating “ white”layer. This effect is obtained by plasma glowing, which activates nitrogen on the mesh and on nitrided workpiece, which guarantees that there will be no damage or charring effect caused by too excessive plasma  dischargers on the workpiece.

Tool steels, steels to be carburized, high-chromium and stainless steels are subject to nitriding.  effective layers reach 0,5 mm and achieve hardness range between 700 to  1300 HV.

Vacuum soldering

It is a process of  connecting metals  in vacuum furnaces using soldering materials.

It is characterized by high purity, lack of overheating and stresses and  very high  strength of  soldering connection. Within once cycle, we can connect soldering and  quenching.

Cleaning and degreasing

Cleaning and degreasing are essential before  each heat and chemical treatment  and soldering. Clean-Tec technology implemented by Sacher Company provides high standard of surface preparation before technological process. Used chemical agents are neutral as regards the environment and  people. Cleaning temperature is  40°C.