Salt bath nitriding has long been a popular surface treatment process in the metalworking industry, primarily used to enhance wear resistance, corrosion protection, fatigue strength and a cosmetic black finish. The process typically involves immersing components in a molten salt bath containing a mixture of alkali cyanides, cyanites, carbonates, and other nitrogenous compounds. This treatment…
read moreThe achievable surface hardness mainly depends on the base material. Alloying elements such as chrome and aluminium lead to higher hardness. The Nitriding depth depends on customer requirements. Also the component’s condition at delivery, i.e. distortion, heat treatment status also affect the layer parameter to be achieved. Dimensional changes can further be positively influenced by…
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Carburising is accomplished by heating the metal in a carbon rich atmosphere above transformation temperature for a pre-determined time. Subsequent to carburising, parts are quenched to harden the surface carburising layer. The core remains unaffected. It is a widely used surface hardening process for low carbon steel. The industrial importance of carburising is expressed in its market share, as one third of all hardening heat treatment is covered by carburising and hardening.
Carburising and quench produce hard surfaces which are resistant to wear. Moreover, failure from impact loading is avoided due to a softer core. Unlike case hardening processes, this process is usually used for deep case depths.
Powdermet® NNS technology produces components with a high degree of complexity not possible via conventional means.
High-Velocity Oxygen Fuel (HVOF) coating is a thermal spray coating process used to improve or restore a component’s surface properties or dimensions, thus extending equipment life by significantly increasing erosion and wear resistance, and corrosion protection.
Molten or semi-molten materials are sprayed onto the surface by means of the high temperature, high-velocity gas stream, producing a dense spray coating which can be ground to a very high surface finish.
The utilization of the HVOF coating technique allows the application of coating materials such as metals, alloys, and ceramics to produce a coating of exceptional hardness, outstanding adhesion to the substrate material and providing substantial wear resistance and corrosion protection.
As the technology specialists in HVOF coating, Bodycote provides an array of spray coating materials to suit your specific needs. Backed by a customer-driven service, our facilities process a wide variety of component sizes to exacting standards with reliable, repeatable results.
HVOF coating:
Induction hardening is used to increase the mechanical properties of ferrous components in a specific area. Typical applications are powertrain, suspension, engine components and stampings. Induction hardening is excellent at repairing warranty claims / field failures. The primary benefits are improvements in strength, fatigue and wear resistance in a localised area without having to redesign the component.
Favoured for components that are subjected to heavy loading. Induction imparts a high surface hardness with a deep case capable of handling extremely high loads. Fatigue strength is increased by the development of a soft core surrounded by an extremely tough outer layer. These properties are desirable for parts that experience torsional loading and surfaces that experience impact forces. Induction processing is performed one part at a time allowing for very predictable dimensional movement from part to part.
Corr-I-Dur® is a proprietary Bodycote thermochemical treatment for simultaneous improvement of corrosion resistance and wear properties through generating an iron nitride-oxide compound layer.
Corr-I-Dur® is favoured for components that are subjected to a corrosive environment in combination with wear. A very successful alternative to hard chromium, electroless nickel and various galvanic coatings through simultaneous improvement of corrosion and wear behaviour; Corr-I-Dur® layers have a very good bonding to the substrate as they are produced in a diffusion process. In many cases parts can be machined with the final dimensions and customers can skip additional steps such as grinding after the Corr-I-Dur® treatment.
Bodycote offers a unique range of thermochemically formed ceramic coatings for the prevention of wear and corrosion in a wide variety of industrial applications and for every type of surface.
Bodycote’s K-Tech ceramic coatings range, have been uniquely developed for applications in specific industries. Several formulae cover a virtually limitless number of potential applications which can be applied to most ferrous and some non-ferrous metals.
Chromium oxide ceramic material thermochemically bonded to customer specified areas on a part, including external diameters, internal diameters and some out-of-sight holes and ports. Individual ceramic particles are sub-micron in size and consist of mixtures of selected ceramic materials bonded together and to the substrate.
Plasma spray is a thermal spray coating process used to produce a high quality coating by a combination of high temperature, high energy heat source, a relatively inert spraying medium, usually argon, and high particle velocities.
Plasma is the term used to describe gas which has been raised to such a high temperature that it ionizes and becomes electrically conductive.
The utilisation of plasma spray coating technology allows the spraying of almost any metallic or ceramic on to a large range of materials with exceptional bond strength, while minimising distortion of the substrate.
As the technology specialists in plasma spray, Bodycote provides an array of thermal spray coating materials to suit your specific needs. Backed by a customer-driven service, our facilities process a wide variety of component sizes to exacting standards with reliable, repeatable results.
The great advantage of the plasma spray coating technique is its ability to spray a wide range of materials, from metals to refractory ceramics, on both small and large components offering:
LPC is an advanced technology that offers the design engineer an alternative to atmosphere carburising for improved case depth uniformity, dimensional control, part cleanliness, and process flexibility.
LPC is a method of pure carburisation combined with pure diffusion and is used to obtain a hardened surface and tough core, giving increased wear resistance and fatigue life, with minimal risk of treatment distortion.
The process gives high hardness below the surface compared to conventional carburising treatments, and allows precise control of case depth, microstructure and hardness, even for complex shapes and blind holes.
The process doesn’t create inter-granular oxidation on the surface of steels due to lack of oxygen in the atmosphere and eliminates the post grinding operations for parts that require higher surface quality and hardness.
LPC is a clean process carried out under vacuum, and has signifcantly lower environmental impact than atmospheric heat treatment technologies.
Boriding is a thermochemical surface hardening method which can be applied to a wide range of ferrous, non-ferrous and cermet materials. The process entails diffusion of boron atoms into the lattice of the parent metal and a hard interstitial boron compound is formed at the surface. The surface boride may be in the form of either a single phase or a double phase boride layer.
Boriding provides a uniform hardness layer from the surface on to the entire depth of the diffused layer. The hardness achieved is many times higher than any other surface hardening process. The combination of high hardness and low coefficient of friction enhance wear, abrasion and surface fatigue properties. Other benefits associated with boriding are retention of hardness at elevated temperature, corrosion resistance in acidic environment, reduction in use of lubricants and a reduced tendency to cold weld.
Carbonitriding is an austenitic (above A3) case hardening process similar to carburising, with the addition of nitrogen (via NH3 gas), used to increase wear resistance and surface hardness through the creation of a hardened surface layer.
Carbonitriding is applied primarily to produce a hard and wear resistant case. The diffusion of both carbon and nitrogen increases the hardenability of plain carbon and low alloy steels, and creates a harder case than carburising. The carbonitriding process is particularly suited for clean mass production of small components. Due to the lower temperature required for the carbonitriding, compared to carburising, distortion is reduced. Mild quenching speed reduces the risk of quench cracking.
Plasma nitriding (Ion nitriding) is a plasma supported thermochemical case hardening process used to increase wear resistance, surface hardness and fatigue by generation of a hard layer including compressive stresses.
The advantages of gaseous nitriding processes can be surpassed by plasma nitriding. Particularly when applied to higher alloyed steels, plasma nitriding imparts a high surface hardness which promotes high resistance to wear, scuffing, galling and seizure. Fatigue strength is increased mainly by the development of surface compressive stresses. Plasma nitriding is a smart choice whenever parts are required to have both nitrided and soft areas. The possibility of generating a compound layer free diffusion layer is often used in plasma nitriding prior to PVD or CVD coating. Tailor made layers and hardness profiles can be achieved.
Gas nitriding is a thermochemical case hardening process used to increase wear resistance, surface hardness and fatigue life by dissolution of nitrogen and hard nitride precipitations.
Favoured for components that are subjected to heavy loading, nitriding imparts a high surface hardness which promotes high resistance to wear, scuffing, galling and seizure. Fatigue strength is increased mainly by the development of surface compressive stresses. The wide range of possible temperatures and case depths, which allow adjustment of different properties of the treated parts, give gas nitriding a broad field of applications.
Bodycote’s proprietary process of this low temperature surface treatment, called Lindure®, involves the addition of oxygen. As a result, there are significant improvements of fatigue properties, adhesive wear resistance and anti-seize properties.
The primary objective of ferritic nitrocarburising treatment is to improve the anti-scuffing characteristics of components. The compound layer exhibits significant improvement in adhesive wear resistance. With the introduction of nitrogen in the diffused zone fatigue properties are enhanced. An added benefit of the process is minimal distortion due to short process cycle within the ferrite phase.
Also named martensitic or quench hardening, neutral hardening is a heat treatment used to achieve high hardness/strength on steel. It consists of austenitising, quenching and tempering, in order to retain a tempered martensite or bainite structure.
There are several benefits of neutral hardening, depending on the steel type:
Tool steels: the desired properties of high hardness, wear resistance, heat resistance and machinability can only be given by hardening.
Martensitic stainless steels: these steels only get their maximum corrosion resistance by hardening.
For all steel types: during the shaping of the parts, (takes place before the heat treatment), the material is relatively soft and therefore easy to machine.
Quenching technique (limited to certain high strength alloy steels) that reduces the residual internal stresses and distortion resulting from non-uniform transformation and thermal shock typical of conventional oil quenching.
Reduction in residual stress and distortion as compared to conventional oil quenching of selected high strength steels. May permit heat treatment of near net shape parts and minimise required machining/grinding of components after heat treatment.
Austempering is used to increase strength, toughness, and reduce distortion. Parts are heated to the hardening temperature, then cooled rapidly enough to a temperature above the martensite start (Ms) temperature and held for a time sufficient to produce the desired bainite microstructure.
Austempering is a hardening process for metals which yields desirable mechanical properties including:
The purpose of Martempering/Marquenching is to delay the cooling for a length of time to equalise the temperature throughout the piece. This will minimise distortion, cracking and residual stress.
Reduced cracking due to thermal stress. Reduced residual stress in the quenched part section for parts with varying geometry, size, or weight.
The controlled hardening in restraining dies, of close tolerance components, such as gears, bearing races etc. Ensures good dimensional control and uniform hardening.
Sometimes, due to misuse of language, double hardening means long duration of austenitisation or long carburising time, followed by a soft hardening or a slow cooling outside the heating chamber (like an annealing step) and re-austenitisation followed by a hardening step (quench).
Double hardening also involves hardening a carburised part twice whereby the first hardening is carried out from the hardening temperature of the core part, and the second from the hardening temperature of the case (see DIN 17014).
Tempering is a low temperature (below A1) heat treatment process normally performed after neutral hardening, double hardening, atmospheric carburising, carbonitriding or induction hardening in order to reach a desired hardness/toughness ratio.
The maximum hardness of a steel grade, which is obtained by hardening, gives the material a low toughness. Tempering reduces the hardness in the material and increases the toughness. Through tempering you can adapt materials properties (hardness/toughness ratio) to a specified application.
There are a number of wrought and cast aluminium alloys that can be strengthened by solution treating and aging to a variety of different tempers.
The mechanical properties of heat treatable alloy components can be optimised by the selection of an appropriate solution and age process sequence. For certain alloys, corrosion resistance can, for example, be improved at the expense of strength and vice versa.
Depending on the alloy and cross section at the time of solution treatment, various cooling methods can potentially be utilised to reduce distortion.
Solution treatment is the heating of an alloy to a suitable temperature, holding it at that temperature long enough to cause one or more constituents to enter into a solid solution and then cooling it rapidly enough to hold these constituents in solution. Subsequent precipitation heat treatments allow controlled release of these constituents either naturally (at room temperature) or artificially (at higher temperatures).
There are a multitude of cast and wrought nickel-based alloys that can have various desirable characteristics enhanced by either solution treating or by solution treating and precipitation age hardening. Characteristics such as room temperature and/or elevated temperature mechanical strength, corrosion resistance and oxidation resistance are typically enhanced by such heat treatments.
Precipitation heat treatments strengthen materials by allowing the controlled release of constituents to form precipitate clusters which significantly enhance the strength of the component.
There are a multitude of cast and wrought stainless steel alloys that can have various desirable characteristics enhanced by either solution treating or by solution treating and precipitation age hardening. Characteristics such as room temperature and/or elevated temperature mechanical strength and corrosion resistance are typically enhanced by such heat treatments.
Typically, in steels, annealing is used to reduce hardness, increase ductility and help eliminate internal stresses.
Annealing will restore ductility following cold working and hence allow additional processing without cracking. Annealing may also be used to release mechanical stresses induced by grinding, machining etc. hence preventing distortion during subsequent higher temperature heat treatment operations. In some cases, annealing is used to improve electrical properties.
Recrystallisation is a process accomplished by heating whereby deformed grains are replaced by a new set of grains that nucleate and grow until the original grains have been entirely consumed.
Recyrstallisation annealing is an annealing process applied to cold-worked metal to obtain nucleation and growth of new grains without phase change. This heat treatment removes the results of the heavy plastic deformation of highly shaped cold formed parts. The annealing is effective when applied to hardened or cold-worked steels, which recrystallise the structure to form new ferrite grains.
Normalising aims to give the steel a uniform and fine-grained structure. The process is used to obtain a predictable microstructure and an assurance of the steel’s mechanical properties.
After forging, hot rolling or casting a steel’s microstructure is often unhomogeneous consisting of large grains, and unwanted structural components such as bainite and carbides. Such a microstructure has a negative impact on the steel’s mechanical properties as well as on the machinability. Through normalising, the steel can obtain a more fine-grained homogeneous structure with predictable properties and machinability.
Sub-critical annealing (or sub-critical treatment) is annealing carried out slightly below the eutectoid temperature (Ac1 point = eutectoid transformation (723°C for carbon-steels)). Sub-critical annealing does not involve the formation of austenite, while intercritical annealing involves the formation of ferrite and austenite (< 0.8%C carbon-steels).
The aim of the soft annealing process is to form an even distribution of spheroidal carbides in the steel, which will make the material softer and tougher. Normally, increasing the size of the spheroids will increase the steel’s machinability.
Soft annealing is a high temperature heat treatment process performed around A1. As the name suggests the aim of the process is to make a material as soft as possible. After soft annealing the material will have a soft and easy to machine structure.
Steels with higher carbon content, and most high-alloy steels, which are allowed to air cool after hot working, such as forging or hot rolling, are usually hard to machine. Soft annealing reduces the hardness and makes the material easier to machine. Soft annealing of low carbon steels < 0,35% C will normally result in a structure too soft and sticky for cutting operations.
The risk of hardening cracks during re-hardening of quenched and tempered steel can be reduced by soft annealing prior to the hardening and tempering process.
Bodycote’s Implantec process can be used to improve the friction coefficient, adhesive wear and surface hardness of polymers and metals by bombarding surfaces with a high energy ion beam.
Ion implantation has a number of benefits, including:
The process is carried out locally and on pieces that are already fully machined, and can be applied to metals, polymers or elastomers.
Stress relieving is carried out on metal products in order to minimise residual stresses in the structure thereby reducing the risk of dimensional changes during further manufacturing or final use of the component.
Machining, and cutting, as well as plastic deformation, will cause a build up of stresses in a material. These stresses could cause unwanted dimension changes if released uncontrolled, for example during a subsequent heat treatment. To minimise stresses after machining and the risk for dimension changes the component can be stress relieved.
Stress relieving is normally done after rough machining, but before final finishing such as polishing or grinding.
Parts that have tight dimensional tolerances, and are going to be further processed, for example by nitrocarburising, must be stress relieved.
Welded structures can be made tension free by stress relieving.
Hydrogen brazing is a braze process that uses the cleaning (reducing) properties of high purity hydrogen to improve the flow characteristics of the braze alloy. The hydrogen atmosphere reduces surface oxides on the parent material, enabling the braze alloy to flow (wet) more effectively to create a high integrity braze joint.
HIP diffusion bonding is used to create a usually solid state bond between two or more materials (either solid or powder) in contact with each other without adhesive, allowing for higher service temperatures and a stronger metallurgical bond.
HIP diffusion bonding allows dissimilar materials to be bonded together without the temperature limitations of adhesives. It forms a metallurgical bond with diffusion occurring on an atomic level. It allows premium materials to be bonded to more economical substrates selectively only where the premium material properties are needed, greatly extending lifetimes of critical components in corrosive and/or erosive environments and in elevated temperature applications.
Electron beam welding (EBW) is a specialist metal joining technique used to create high integrity joints with minimal distortion.
Induction brazing is when two or more materials are joined together by a filler metal that has a lower melting point than the base materials using induction heating. In induction heating, usually ferrous materials are heated rapidly from the electromagnetic field that is created by the alternating current from an induction coil.
Furnace brazing is a semi-automated process by which metal components are joined using a dissimilar lower filler metal. Furnace brazing allows design and manufacturing engineers to join simple or complex designs of one joint or multi-joint assemblies.
One of the most common forms of furnace brazing is accomplished in a vacuum furnace and referred to as vacuum brazing. Parts to be joined are cleaned, brazing filler metal applied to the surfaces to be joined, then placed into the furnace. The entire assembly is brought to brazing temperature, after the furnace has been evacuated of air, to eliminate any oxidation or contamination occurring as the braze filler metal melts and flows into the joints.
