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To get the best properties-a hard skin over a ductile / tough core reduces wear and increases strength. If you make that skin selective in terms of areas on a part even more options.

When metal cools from its manufacturing temperatures it locks in stresses from the differential cooling rates between surface and centre. It may also be rolled, forged or simply shrink from cooling after casting. Nor will the material be uniform because of the different thermal history across the section of the metal.

Machining may ease stress changes but it can distort parts.

The range of treatments (stress relieving, annealing and normalising) give improved dimensional and mechanical stability.

Effective case depth is defined by a cut-off point at a given hardness down the gradient into the core of the steel. The total case depth spans to where there is al least some rise above core readings and is therefore always greater. Achieving an effective case to an equivalent depth takes more power or time so ends up costing more.

Induction Hardening has a number of distinct advantages.

For a start a big gain is the fact that very localised areas can be hardened (like lasers that can paint by numbers to a degree).

Induction Hardening however requires steel alloys with a medium carbon content. (The steel can be specified and purchased accordingly or we can carburise the component and then induction heat).

Excellent control of heating and quenching processes is essential to prevent damage either by distortion or cracking.

We can harden one side and then straighten a component, because the hardened region increases in volume distortion always takes place with asymmetric hardening.

Surface hardening through induction heating delivers selective surface hardening precisely where it is needed. The types of components processed vary from gears to cams, shafts, dies etc.

With CNC controlled hardening equipment extremely accurate and reproducible heating cycles are maintained. Tempering usually follows.

Induction Annealing can be performed for a variety of reasons, such as reducing hardness, improving machinability, allowing more cold working or homogenising the material to get a desired macro-and micro-structure, specific mechanical properties, removing internal stresses, etc. Annealing thus covers a wide variety of treatments and can vary from a low temperature sub-critical anneal, to a complex full anneal cycle.

Full annealing produces a softer, ductile steel with lowered tensile and yield strengths so machining after heat treatment can give the desired end result. Each route is different so thought should be given to the purpose of the treatment before committing.

Materials treated may be Irons, Plain Carbon to Stainless, Duplex and High Alloy Steels such as tool steel.

Two or more parts can be joined by adding at the junction a lower melting point alloy, typically silver in ring form, in the presence of a flux to break down oxides and ensure wetting.

The joint will fill by capillary action with the correct design of heat profile and gap geometry and for joints about 0.1mms thick the resulting assembly can be as strong as the parent metal.

Benefits of using induction brazing include : Local heating of the joint area gives minimal heat-affected zone and distortion; Precise and uniform heating gives high quality repeatable strong and leak-proof joints; Common metals joined include steel, stainless steel, copper and brass.

Carburising involves the introduction and diffusion of carbon into the surface layers of the steel, after which the steel has a high carbon content at the surface.

On subsequent hardening of the component, this surface responds to give an exceptionally high level of hardness and wear resistance, whilst the low carbon core remains relatively unaffected and maintains its original toughness.

The depth of the hardened surface is measured by case depth defined as either (as mentioned above above) Effective Case Depth or Total Case Depth.

Carburising has an effective operating window. A very high threshold temperature before carbon absorption and diffusion will commence and a limit on the upper temperature range because of the risk of softening and sagging of the work piece. A narrow band of carbon concentration, too little and the diffusion into the steel stall, too much and it precipitates as iron carbides destroying the sought after mechanical properties.

The combination of carburising and hardening changes the microscopic structure and therefore size of the surface of the steel. In effect the surface grows which can lead to distortion particularly in deep case depths or when thin components are carburised

We accurately control the type and depth of case, using computer modelling and in process control techniques to account for the variation in processing different steel alloys or casts and so meet the most exacting specifications. Cases from just 0.25 on thin sections up to several mms are made.

Case hardening is used on low carbon steels where the choice of alloy determines the properties that can be achieved. This is necessary to gain a good hardness.Case hardening is applied to components that are very close to their finished shape. Carbon is diffused into the surface of the component in the CARBURISATION process. Either directly after carburisation or after cooling and re-heating the component is rapidly cooled in the quench process.The quench process transforms the crystal micro structure of the carbon rich surface – the case – to give a hard, wear resistant layer around the tougher, less brittle core.

If you just want hardness on the skin locally we can either: Carburize all the part, leave soft then induction harden the area OR 'Stop-off' the areas needed soft during the carburising then drop quench to harden the needed areas. The risks of distortion between the two are different.

Increasing the hardness level of a steel by heat treatment normally involves heating to an elevated temperature and quenching into a suitable medium. The quenching medium and the hardness attainable depends primarily on the type of steel in the skin being treated. The steel may be an alloy that can be hardened directly or it may require the addition of carbon to the surface.

We offer treatments to suit a wide variety of material types, shapes and sizes. Furnace types used vary but they allow Inductoheat to cater for materials from plain carbon, low alloy, high alloy, tool and die steels, grey and nodular irons, and even aluminium alloys. Hardening causes changes in structure that can induce stresses and cause damage if the component is not prepared and treated correctly.

Nitriding is the process whereby nitrogen is diffused into the surface layers of a suitably steel alloy (EN19, EN24, EN40B & EN41 are good choices) to produce a hard surface with good resistance to seizure and galling. Because the treatment temperature is relatively low and quenching is not involved, nitriding offers an exceedingly low level of distortion.

Nitriding produces a thinner case depth than carburising typically from 0.15-1.0 mm but EN41 will nitride to a hardness of around 70 Rockwell C

We aim to give a product with the minimum or no brittle white layer that is associated with nitriding, even with deeper case depths.

Selective Hardening: Specific features can be masked prior to processing to prevent the absorption of nitrogen during processing.

Normalizing homogenises the structure and modifies the grain size of the material. It is recommended after forging, hot rolling, flame cutting, etc.

The treatment in itself enhances the properties of the material, but is also advantageous in preparing material for subsequent heat treatment processes. The process is sometimes confused with some of the annealing processes and it does have some similarities because normalizing involves heating to the austenitizing temperature of the steel (or iron). However normalizing is generally considered to include a faster cooling rate that is undertaken in air rather than a controlled atmosphere.

Normalizing can also offer improvements in mechanical properties (UTS, YS, reduction of area, and impact strength), to levels higher than which are achievable with annealing. Stress relieving is generally recommended as an aid to dimensional and stress stability as part of overall manufacturing the process after casting, cold working, heavy machining or fabrication.

Although stress relieving is commonly included in the manufacture of components which require no further treatment after machining, it is also of advantage for many components which are to be subjected to other forms of heat treatment at later stages of manufacture. For example it is invariably included after heavy (rough) machining, and before final machining of rolls and shafts for flame and induction hardening, in order to eliminate the distortion which would occur from the relief of residual stresses during heating for surface hardening, helping to minimize the final level of distortion.

When solution/precipitation/aging grades of alloys are manufactured any working (e.g. rolling) or time (aging) hardens the material, this reduces formability and machinability of the metal.

Solution treating restores the processibility of the material and is it is followed by precipitation hardening or controlled aging which develops the final resilience, uniformity and strength required of the finished product.

After solution treating the strength giving alloying elements are truly dissolved in the parent metal (a solid solution). With precipitation treatment the elements are brought out of solution to form particular microscopic structures within the metal that increase properties such as hardness & tensile strength in the final product.

Sub Zero treatments are used to complete the hardening process in particular grades of steel.

The component is cooled to less than -70C which increases the conversion rate of the microstructure of the steel to the hard phase known as martensite. Additionally it is used to convert metastable regions to the hard form to prevent reversion to softer weakened structures at operating temperatures.

As hardened components are rarely suitable for immediate service due to the high degree of brittleness and residual stress associated with hardening treatments Tempering is necessary.

Tempering moderates the hard and brittle structure, delivers an increase in toughness, shock resistance and ductility coupled with a controlled reduction in hardness. Tempering is always recommended to be carried out after case hardening. It offers real benefits in promoting dimensional stability, reducing brittleness, and the prospects of cracking in grinding.

Even low temperature tempering, which only reduces the surface hardness by one to two points on the Rockwell C scale offers real benefits.

Some steels demand repeated tempering in a tightly controlled regime to generate the required properties to meet design requirements and ensure suitability for purpose in the end use.