Our Heat Treatment Services

Carburising is the first stage of the case hardening process in which carbon is added into the surface of the material to change the composition. After this step the material can be quenched in a variety of mediums (depending on steel grade) to create a hard outer surface that is wear resistant. As the carbon is only added to the surface, the core will usually remain soft and ductile, however with some materials it will still be tough and durable, without being brittle. This treatment is applied to mild steels or low carbon steels typically after machining. Mild steels will remain very soft in the core, allowing for more movement and flexibility. The cores of low carbon steels with more complex compositions (such as EN36) will toughen up as a by-product of the case hardening process due to the incorporated elements. The combination of EN36 and Case Hardening is a popular way to produce gears due to the resulting high impact resistance and durability to prevent gear teeth shearing off. After quenching parts can be tempered to reduce the hardness to the customers required specifications. An object usually undergoes the case hardening process once it has been formed into its final shape, but the process can also be used to enhance the hardening element of bars to be used in pattern welding and similar processes.

The Harden and Temper (through hardening) process is conducted by heating a metal (usually steel or cast iron) above the upper critical temperature and then rapidly cooling (quenching) it to make the metal harder. Depending on the alloy and other considerations (such as concern for maximum hardness vs. cracking and distortion), quenching may be done in air or a variety of liquids, such as oil, water, or an aqueous polymer. After this quenching a portion of austenite (a high-temperature phase of iron, dependent on alloy composition) will transform to martensite, a hard, brittle crystalline structure. The quenched hardness of a metal depends on its chemical composition and quenching method. Cooling speeds, from fastest to slowest, are fresh water, polymer (i.e. Silicon), oil, and then in air. However, quenching a certain steel too fast can result in cracking, which is why high-tensile steels such as EN24 should be quenched in oil. However, most non-ferrous metals, like alloys of copper, aluminium, or nickel, and some high alloy steels such as austenitic stainless steel (304, 316), produce an opposite effect when they are quenched: they soften. Austenitic stainless steels must be quenched to become fully corrosion resistant, as they work-harden significantly. After the quenching, tempering is performed. Tempering is performed by heating the metal up in an air bath, holding at a certain temperature for a length of time determined by the size of the part, then allowing to cool in air. This process reduces the hardness and stabilises the material, allowing us to reduce the hardness to the customers tolerance range. Temperatures for this step range from 120 to 700 °C, with higher heats reducing the hardness of the material more than lower ones. Other methods of tempering consist of quenching to a specific temperature, which is above the martensite start temperature, and then holding it there until pure bainite can form or internal stresses can be relieved. These include austempering and martempering.

Tufftride Q (also known as Nitro-Carburizing) and the variation QPQ (Quench Polish Quench) is a heat treatment process that enhances wear, fatigue and corrosion properties of any ferrous material. It has relative minimal distortion compared to other heat treatment hardening processes due to the low process temperatures of no more than 580°C. During the Tufftride process a nitrocarburized layer is formed due to immersion in a salt bath. This consists of the outer compound layer (ε-iron nitride) and the diffusion layer beneath. The formation, microstructure and properties of the compound layer are determined by the base material. Benefits of low temperature nitro-carburising: - High Corrosion Resistance - Increased fatigue strength - Low co-efficient of friction - High wear resistance The process was originally created for treating crankshafts; however, many other applications benefit from its characteristics, including automotive, aero, marine and industrial. Due to the advantages of the process, more expensive materials can be replaced with low-cost alternatives.

Blackodising, also known as chemical blacking, black oxide coating, and oil blacking, produces a black cosmetic metal finish that also improves storage life and corrosion resistance. The process is conducted using a sequence of various liquid baths, including degreasers, acid and alkaline tanks. As this is processed in a solution an even, all-over coating is obtained. The finish is produced chemically on steel by the conversion of the surface to FE3 04. There is no change dimensionally, making it ideal for the machine tool, armament and instrument trades. Immersion in a high alkaline bath eliminates the problems of hydrogen embrittlement (via Hydrochloric acid) common to electro plating and phosphating processes, which makes an additional stress relieving process unnecessary. Research from the automobile industry indicated that this process was preferable to phosphate conversion coating, giving up to ten times the anti-scuffing life before breakdown is observed. This has also been confirmed by the aircraft industry where the process has been approved for many years on gears and other bearing surfaces.

Induction hardening is used for the surface hardening of medium/high carbon steel alloys which require high wear resistance, such as springs, shafts, gears, and other alloy components. Heat is produced within the surface layer of an object using a non-contact heating process based on the principles of Electromagnetic Induction. The parts to be heat treated are placed inside a water-cooled copper coil and then heated above their transformation temperature by applying an alternating current to the coil. The alternating current in the coil induces an alternating magnetic field within the workpiece, which if made from steel, causes the outer surface of the part to heat to a temperature above the transformation range. Parts are held at that temperature until the appropriate depth of hardening has been achieved, and then quenched in an oil, water or polymer base, depending upon the steel type and hardness desired. By quenching the heated layer, the surface layer is transformed to form a martensitic structure leaving the core component unaffected by the treatment. This process is most widely used when durability, fatigue life and wear resistance are desired, however only locally, allowing for the rest of the part to be untreated.

CBS provides small scale shot blasting services on site for various purposes including manufacturing, restoration, and part maintenance. We do have relationships with companies who process larger parts or offer equivalent services such as acid dipping, if required by our customers. We can also fulfil requests for other surface finishes, such as anodising, and wet spraying through our friends over at Racepaint UK in Eastwood. Due to the number of processes we do and projects we have been involved in over the years, our highly trained and dedicated team are always available to give expert advice on a wide variety of topics, such as engineering, welding (including aluminium), heat treatment, surface finishing, chemical blacking, shot blasting, and powder coating. From alloy wheels to garden furniture, cycle frames to large fabrications we have the capacity and ability to produce a stunning finish on a wide range of objects. CBS Engineering and Heat Treatment are also very dedicated and sympathetic in our approach to the refurbishment of cars and motorcycles, so you are in safe hands.