Annealing/Hardening

PVA-LWT offers the whole range of annealing techniques as well as hardening operations for some special air-hardening steels.

Hardening operations are used to install a defined hardness in the materials. With PVA-LWT heat-treatment technology we can harden the so-called air-hardening steels, which form a martensitic structure despite slow cooling conditions. A typical steel, which can be hardened with PVA equipment is the martensitic-ferritic steel X20Cr13.

The gear part, which is hardened by vacuum heat-treatment to a macro-hardness of HB 250 is made of X20Cr13. A speciality of this part is the combination of the heat-treatment with a brazing process to make the joint between the cap and the cylindric component. Therefore the brazing temperature has been adapted to the annealing temperature of the steel. After fast cooling under nitrogen atmosphere the brazed parts will finally be annealed at 550°C.

Further heat-treatments offered by PVA-LWT:

Diffusion annealing:
Is used to eliminate microstructure inhomogeneities and concentration differences in the parts. The annealing temperature should be very high and is in some cases immediately under solidus temperature. Diffusion annealing is sometimes used for stainless steel parts, which have been brazed with nickel-base alloys. Diffusion annealing leads to a diffusion of certain filler metal elements into the bulk material thus eliminating brittle phases in the brazing joint. The result of the heat-treatment is an enhancement of mechanical and corrosion resistance properties of the joints.

• Recrystallisation annealing:
  Is used to give a new orientation and relaxation to the deformed microstructure of a cold rolled material. Recrystallisation annealing is generally applied after metal forming processes to prevent the material from cracking due to the embrittlement of the part.
  
• Stress relieving:
  Is used to eliminate tensions in the material, which arise through unequal temperature input (e.g. during welding) and mechanical treatment. Stress relieving is usually applied for milled parts prior to a brazing process. Aim is to avoid distortion of the part during the brazing process. The soft annealing temperature typically is in the range of 650°C and 900°C.
  
• Degassing and cleaning:
  With this kind of heat-treatment materials and parts with surface contaminations can be treated, that cannot be removed in a liquid cleaning bath. During annealing at high temperatures and under high vacuum atmosphere the residues evaporate or will be reduced. The parts will be shiny and will show no more contamination. Degassing under high vacuum is used to remove gas, which is solved in the material. The degassing of hydrogen in stainless steels is an example.