Gloucester Heat Treatment Ltd

Heat Treatment Processes

We perform the following heat treatment processes and NADCAP Accredited Heat Treating:

• Annealing (cyclic, in air, atmosphere or salt bath)
• Austempering
• Carbon Restoration
• Carbonitriding
• Carburising or case hardening salt bath
• Castings
• Cyaniding
• Forgings
• Gaseous Nitriding
• Marageing
• Martempering
• Nitrocarburising
• Normalising
• Precipitation Hardening
• Shrink Fitting
• Solution Treatment
• Stabilising
• Stress Relieving
• Sulfinuzing (salt bath nitriding)
• Tempering
• Test Piece Manufacturing (full machining)
• Through Hardening

We offer consultancy & materials advice as well as full metallurgical services. We can perform full NDT, corrosion testing, weld testing and chemical analysis at our UKAS approved testing facilities. Our services are aerospace-approved.

Capacity

Our salt bath capacity is 28" x 28" diameter for annealing and stress healing, and 24" x 23" diameter for the following processes:

• Austempering / Marquenching
• Case Hardening / Carburising
• Hardening and Tempering
• Normalising
• Precipitation Hardening

Our sulfinuzing (salt bath nitriding) capacity is 23" x 23" diameter, and our gaseous nitriding capacity is 36" x 23" diameter.

The capacity for sub zero deep freeze is 36" x 23" x 23" high, and the capacity for normalising, annealing, stress relieving and precipitation hardening in air is 12ft x 6ft x 4ft-8" high.

Aluminium heat treatment capacity is 36" x 26" diameter for solution treatment and hot / cold water quench, and the artificial ageing / stress relieve / annealing capacity is 12ft x 6ft x 4ft-8" high.

Salt Bath

There are several advantages to Salt Bath Heat Treatment. As a liquid medium, salt provides support and prevents distortion of thin wall section components. Transfer of heat into components is fast and uniform. The salt protects components from decarburisation and oxidation during heating and the transfer to the quench.

The heat treater has flexibility with salt baths, as several quenching methods are available, including oil, polymer or water, or transfer to another salt bath for Austempering or Marquenching.

Since there is very tight control over case depths, shallow case depths can be easily achieved when case hardening or Carburising in salt baths. End only treatments that can eliminate the necessity for expensive plating or re-machining are another advantage of salt baths.

At present, we have fifteen salt bath furnaces with associated quench facilities.

Aluminium

There are several thermal treatments that strengthen aluminium and increase its hardness. 

Solution treatment increases ductility and allows cold working such as forming, bending or stretching of the alloy during the period before natural ageing begins to harden the alloy.

Artificial ageing is more efficient at strengthening and hardening than natural ageing.

Annealing allows extreme bending and forming by softening the alloy.

Stabilising or stress relieving, performed at a specific temperature suited to the alloy's mechanical properties, relieves residual internal stresses while leaving the mechanical properties of the alloy unchanged.

Nitriding

Nitriding results in a case depth enriched in nitrogen and produces superior surface hardness without quenching than conventional case hardening. It also eliminates most distortion.

Normally the steels selected for nitriding treatment have been heat treated and fully stabilised at a high temperature. During nitriding, nitrogen diffuses into the component's surface and combines with elements to perform nitrides. This produces a compound layer that is usually beneficial as it can increase corrosion resistance. Spalling, however, can affect compound layers thicker than 20 microns so these are often removed after the nitriding process. Modern processes can control the thickness of the compound layers.

Stress Relief

Forming, machining, cutting or fabricating parts by welding can result in high internal stresses. These stresses can be relieved without affecting the part's mechanical properties by heating it to a temperature that will result in thermal relaxation. The result is a part or assembly that is far more resistant to warp change dimensions during subsequent use or processing. Thermal stress relieving is suitable for several materials including aluminium, plastics, alloys and steels, subject to a maximum load size of 12 ft x 6 ft x 4 ft 8 inches high.

Inspection & Testing

We offer a complete range of non-destructive and destructive testing with full metallurgical laboratory facilities.

Our in-house testing includes Brinell, Vickers and Rockwell hardness testing as well as equotip portable hardness testing, with certificates of conformity and release issued by our fully trained staff.

In association with Southdown Materials Testing Limited, we offer UKAS approved testing to  include:

• Chemical Analysis
• Crack Detection
• Dye Penetrant
• Hardness Surveys
• Impact Testing
• Metallurgical Laboratory
• Photography
• Radiography
• Tensile Testing
• Ultrasonic Inspection
• Welding Services

Sulfinuzing

Sulfinuzing, a process developed more than fifty years ago, increases resistance to frictional wear, scuffing, fatigue and fretting of components made of many ferrous metals.

A low temperature salt bath treatment, Sulfinuz is normally operated in the range of 570 - 600C, dependent upon the material being treated. At these temperatures, treatment times vary from a few minutes to three hours. Components may be quenched into hot water or air cooled, according to the component geometry and material as well as the distortion factor.

Basically a salt bath nitriding process, Sulfinuzing has been proven over the decades to increase the performance and life of a wide variety of components such as pistons, valves, crank shafts and extrusion dies.