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Gas Carburise

   Carburising is undertaken under a protective endothermic gas atmosphere in integral quench furnaces. Controlled levels of carbon are diffused into the steel surface at appropriate temperatures until the desired case depth is achieved. Carburizing followed by hardening produces a hard case with good wear and fatigue resistance and a softer, tough, core. Common alloy case hardening steels processed: EN36, En39B, 4317 (Hycase), 8620, Hollow Bar (20MnV6). Case depths frequently undertaken: 0.25 –3 mm. Surface hardnesses of 60HRC+ are achievable.


  Carbonitriding is a modification of the carburizing process. Nitrogen, formed by the dissociation of ammonia, is diffused into steel surfaces along with carbon. This has the effect of increasing the hardenability of the case of low carbon, mild steels and free cutting steels. Lower alloy case hardening steels such as 8620 or Hollow Bar may also be carbonitrided. Case depths frequently undertaken: 0.15-1 mm. Surface hardnesses of 60HRC+ are achievable.

Neutral harden

Constructional steels and spring steels are hardened by heating to elevated temperatures (austenitising) under a protective (endothermic) atmosphere and then oil quenched in integral quench furnaces. Parts are then tempered to achieve the specified hardness (mechanical properties).Common steels processed:1040/1045, 1340, 4140, 4340, 5140, EN25, EN26, 300M (S155), Arne/01/Silver steel, K245, CK1055, 9258, 5160, SUP9n.

Stress Relieve

Stress Relieving is undertaken to remove residual stresses generated by processes such as machining, forming, welding etc. These stresses may result in unwanted distortion after further processing. They may also have detrimental effects on fatigue life and stress corrosion. Whilst peak stresses can be relieved at 150-200°C after hardening, to remove all residual stresses, stress relieving is undertaken at temperatures 550-680ºC. Stress relieving at high temperatures may often be referred to as sub-critical annealing or process annealing.


Shot peening is a surface treatment where small spherical shot is impacted on a surface. This results in a residual compressive stress at and beneath the surface of a part. This process is highly beneficial in the prevention of fatigue cracking, fretting fatigue and stress corrosion cracking. VHT uses fully conditioned, hardened steel cut wire shot complying with the requirements of AMS2431. This shot is well suited to shot peening case hardened parts such as gears and other parts susceptible to fatigue failure.