Casting Glossary

Air quenching and tempering	Annealing	Austenite	Bainite
Bainitise	Blasting	Carbide	Cementite
Chrome plating	Corundum blasting	Ductility	Eutectoid
Ferrite	Galvanising	Glass bead blasing	Graphite
Hardness	Hardening	Heavy-duty castings	Heat-treatable cast steel
Heat resistant cast steel	Lamellar graphite cast iron	Magnetic particle testing	Martensite
Ni-Resist/austenitic cast iron ..	Non-destructive material testing	Oil quenching and tempering	Perlite
Pickling	Polishing	Radiographic testing	Soft annealing
Solidity	Solution annealing	Spherulitic graphite cast iron	Stress relief annealing
Tempering	Ultrasonic testing (UT)	Vacuum hardening	Water quenching and tempering
Zinc plating

Air quenching and tempering Air quenching and tempering refers to the process of annealing and thus of hardening and tempering of a casting, where the process of quenching takes place in the air. In general we also talk about air hardening Annealing Annealing is a technical term in foundry techniques and it refers to heat treatment of cast products with the goal to achieve higher toughness of a material. The process of annealing consists of two procedures: hardening and tempering. Hardening is done with iron alloys with steel and quenching and tempering is done through heating and cooling to ambient temperature. According to the variety of the agents which are used for quenching we differentiate between water quenching, air quenching and oil quenching. In the case of steel through hardening martensite is created, which is transferred through a tempering procedure to carbide with a fine dispersion within the material. Austenite Austenite is the name for mixed crystals of iron alloys with a face-centred cubic structure. It is often found in high-alloy steels, which have alloy elements with the same crystal structure. Austenite has low hardening values, it is not ferromagnetic and has poor machining characteristics. The solidity of austenitic structures can be improved by cold moulding. In unalloyed or low-alloyed steels austenite completely transforms during the cooling process at a temperature of 723 degrees Celsius in perlite. At the cooling process of steel we can create austenitic structures by adding so called austenite agents. Classic austenite agents are the elements cobalt, carbon, nickel, manganese and nitrogen. Austenite is a pre-phase of heat after-treatment, mostly of hardening. The expression austenite is also often used for other face-centred cubic mixed iron crystals. Bainite Bainite refers to an intermediate stage of iron and carbon alloys. We can describe the structure of bainite as needle like and chemically it consists of a mixture of carbides and ferrite. Bainite forms itself when during a heat treatment of a cast a certain cooling process is followed. Here one has to especially pay attention that neither martensite nor perlite form itself. If the formation of bainite occurs in the upper temperature range and thus just below ferrite formation, we refer to it as upper bainite. In adherence to this bainite which forms itself in the lower temperature range and about martensite formation, is called lower bainite. Both lower and upper bainite have different characteristics and they mostly influence the grade of toughness of steel. Upper bainite shows higher impact energy values. Also the transition temperature is higher. Lower bainite has lower values on the high-level, but also lower transition temperatures. Therefore it is mostly suitable for use at lower ambient temperatures. Bainitise With bainitise we mean the production of a bainitised structure via heat treatment of a casting. Another expression for this is austempering. Blasting Blasting is the abrasive treatment of the surface of a cast part with the aid of the so called blasting agent. The most well-known agent is sand. According to their working area or desired effect also other granulate agents are used. Examples of blasting agents in metal treatment are Corundum and glass. In most cases the process is used for surface cleaning and thus for the removal of coatings, colours or impurities as are rust or scale. Through blasting we can reach also hardly accessible areas or we can treat complex surfaces in shorter time and with less material used. Carbide Generally, carbides are metal-carbon compounds with the chemical formula MxCy. The most renowned is cementite Fe3C, also known as iron carbide. Carbide can develop during the solidification of all alloys of iron and carbon, which depends on the cooling speed or chemical composition of the material. Pockets of carbide have a high influence on the mechanic characteristics of a material: they impair the toughness and treatment capability of the material. Cementite Cementite is the chemical compound of iron carbide Fe3C, made of iron and carbon. It occurs in steel and white iron cast as a meta-stabile phase, it is brittle and not easily to be formed, but it has a high resistance to wear. The meta-stability of the phase shows itself at slow cooling or at long annealing times: in this case cementite decomposes into iron and graphite. Chrome plating Chrome-plating is a galvanic procedure, where iron and steel casting parts are coated with a protective chrome layer. The used electrolytes are aqueous solutions on the basis of chromic acid. In order to increase the effectiveness acids are added as catalysts. Chromium is a very hard, brittle and silver-shining metal, which never oxidises neither on air not in water. Therefore it is perfectly suitable surface finishing for corrosion protection. Corundum blasting Corundum blasting is an abrasive surface treatment with corundum as a blasting agent. Corundum is a highly sharp-edged granulate. Blasting with corundum therefore creates very rough surfaces. Corundum blasting is mostly suitable for the removal of layers of rust, varnishes and scale from metallic surfaces. The process has also proven as pre-treatment for later powder coating or varnishing of metallic casts Ductility The ductility of a material refers to its capability to withstand plastic strain without the occurrence of cracks. Eutectoid With eutectoid one solid phase converts in two solid phases, which compounds are present in the final product as dispersed fine alloys. A known example for an eutectoid phase conversion is the conversion from austenite to perlite. Ferrite Ferrite as a micro-constituent is found in ferritic steels and in ferritic cast iron. It is extremely soft, it has a low thermal expansion, is easily corrosive and easily malleable. A ferritic structure consists of mixed iron crystals, is monophased, polyhedral and without twin-characteristics. Galvanising Galvanising means the coating of metals such as iron or steel with stainless plating of a "more precious" metal via electrolysis. The casting, which needs to be coated, is inserted into a brine solution of the coating metal as the negative cathode – this is the galvanic bath. The anode is insoluble or made of the same material as the coating metal. The electrolysis procedure and thus the coating is performed under direct current. Galvanic procedures are: • Chromium plating • Zinc plating • Copper plating • Nickel plating • Tin plating • Silver-plating • Gold plating Glass bead blasting Glass bead blasting refers to a especially mild procedure for the treatment of metallic surfaces. Through blasting with glass pearls the surface is by far less rough as with the blasting agents sand or corundum. With glass bead blasting we remove colourations or residues from tools, we polish surfaces and we condense and make a matt-finish shine. Also this method is used for the production of plastic formations with the goals to increase the hardness and fatigue strength of a casting. Graphite Graphite is the chemical element carbon, abbreviated as C, in its pure form. It forms grey-black crystals with a metallic shine. The crystal system is mostly hexagonal. Sometimes it is also known as black lead. Hardness The hardness of a material defines its resistance towards a mechanic or dynamic penetration of a figure with great hardness. Besides hardness typical features of a material are its solidity, ductility, stiffness and toughness. Hardening Hardening is a casting technique where we deliberately change the mechanic characteristics of a cast material with the aid of heat treatment. Normally, the goal is to increase the mechanic resistance of a casting. At hardening we distinguish between transformation hardening, e.g. through quenching and age hardening. For hardening of steel and iron alloys the process of quench hardening is used. If after hardening the process of tempering is carried out, we talk of annealing. Heavy-duty castings Heavy-duty castings, also known as cast iron or white cast iron, is outstanding for high stresses. The reason for this exceptional hardness is a high share of carbon and the inclusion of carbon as carbide within the iron-carbon alloy. From here comes the white fracture which also gives wear castings the name white cast iron. At highly alloyed cast irons carbides of chromium, molybdenum, vanadium or niobium develop according to the selected alloy element. Chromium carbides have the highest wear resistance. The alloys contain shares of carbon between 2 to 3.8 per cent and of chromium from 10 to 30 per cent. Here we are also talking about chromium cast iron. Heat-treatable cast steel Cast steel for heat treatment counts among low-alloyed materials, which consist besides of carbon also of further alloy elements at a concentration of not more than five mass per cent for one element. These alloy supplements, which are often chromium, manganese, molybdenum, nickel and vanadium, are contributing to the breaking and fatigue stress of steel and ensure the complete hardening of casts with greater wall thickness. Cast steels for heat treatment are within the founding procedure in general brittle, coarse-grained and inhomogeneous and therefore they must go through heat treatment, also known as annealing. Here parameters are formed via a two-phase after treatment according to mechanic requirements for the later cast piece. Heat resistant cast steel Castings from heat resistant cast steel can be used at working temperatures over 600 degrees Celsius. Some materials can even reach operating temperatures of up to 1200 degrees Celsius. This heat resistance is achieved mostly with a high share of chromium within an iron-carbon alloy. Therefore heat resistant cast steel is "high-alloyed". Lamellar graphite cast iron Cast iron with lamellar-graphite, also known as grey iron, is an iron-carbon alloy with good characteristics for use and treatment. The material predominantly has high pressure resistance, extremely good dampening characteristics, resistance to wear and good resistance to corrosion. The reason for these exceptional physical features is the arrangement of the graphite in the casting material. In grey iron it is present in flakes, which form a three-dimensional complex structure. Lamellar-graphite cast iron is mostly used for contoured and thin-walled casts. And for casts with a complicated form. As grey iron is absolutely the best at profitability, it is clear that this cast material is used mostly. The standardised term for flake-graphite cast iron is EN-GJL. Magnetic particle testing Magnetic particle testing, short MT-testing, is a procedure of non-destructive quality control of ferro-magnetic materials as iron. With it we wish to find cracks or imperfections on or near the surface of castings. We refer to it also as magnetic crack inspection. For the procedure itself the casting, or a part of it at big parts, is magnetised and iron powder is applied over the inspected surface. Because of magnetic effects the powder accumulates at the imperfection and identifies the error. Considering, if we want to inspect longitudinal or lateral cracks, we use different methods of magnetising: • Current carrying the aim is to identify longitudinal cracks • Field carrying the aim is to identify lateral cracks • Combined crack detection, when we suspect cracks without primary directions. In order to make imperfections visible at magnetic powder testing, we work with fluorescent testing agents Martensite Martensite is a brittle and fine-pinned structure in steel. Great breaking stress and hardness are typical for it, but it does not have any fracture strain. We form martensite with quenching of austenite. The cooling happens very fast, so carbon does not diffuse from the grid and a tetragonal spatially centred structure develops. At tempering with temperatures of up to 720 degrees Celsius and with a long annealing time martensite transforms into ferrite with enclosed cementite in spherical form. Ni-Resist / austenitic cast iron (EN-GJLA/EN-GJSA) Ni-Resist, also called austenitic cast iron, is a high-alloyed material with an austenitic structure. The material contains nickel, manganese and partly copper and chromium, whereas copper and chromium are used for stabilising the austenitic structure at room temperature. Carbon is contained either in the form of flake-graphite or spheroidal graphite. Here the cast iron type with spheroidal graphite shows better mechanical values. The high share of nickel with a value of more than 20 per cent is responsible for the high resistance towards corrosion and it improves the tensile strength and the expansion characteristics of the material. Construction parts made of Ni-Resist are used when characteristics as scaling and erosion resistance, resistance against sea water and alkaline media or a not-magnetisable material are needed. Some types of the materials are registered for construction parts for punch-out machines according to EU-directive 97/23/EC. Further information can be obtained from the norm DIN EN 13835. Non-destructive material testing A non-destructive material testing refers to a quality control of a material without destructing or damaging it. According to this we make advantage of only physical effects. A well-known example for a non-destructive material testing is the Archimedean suppression method for calculating the thickness of a vessel. For the control of castings we at Esterer use the following procedures: • Radiographic testing (RT) • Ultrasonic testing (UT) • Magnetic powder testing (MT) • Penetration testing (PT) The abbreviations are made according to the standard ISO 9712. Oil quenching and tempering Oil quenching and tempering means a special process of annealing, where the hardening or quenching is performed in oil. Perlite Perlite is the name of the crystalline mixture of ferrite and iron carbide Fe3C, also known as cementite. It is a flake-like structure constituent of steel. Flake-like means in this case, that cementite is enclosed in ferrite in the form of flakes. This is why we also talk about striped perlite. Through hardening we can gain a spherical form of cementite. Thus, grainy perlite develops. The crystalline mixture perlite is an eutektoide, which transforms itself at a temperature of over 726 degrees Celsius completely into austenite. Pickling We use pickling during the after-treatment of castings in order to clean, roughen or colour the surface. The method works either chemically or electro-chemically (galvanising), with the aid of chemically reactive fluids, of the so called pickle. The main aim of pickling is to remove rust, descale or remove residues from brazing. Polishing [Translate to Englisch:] Unter Polieren versteht man ein Verfahren zur Bearbeitung von Gussteilen, durch das außerordentlich glatte Oberfläche erzeugt werden können. Dies wird zum einen durch den Abtrag kleinster Werkstoffmengen und das Auffüllen von Vertiefungen erreicht. Zum anderen werden mittels Polieren Erhebungen und Spitzen verformt und geebnet. Metallische Oberflächen werden zumeist mit Maschinen mit rotierenden Polierscheiben bearbeitet. Für diese Polierscheiben werden Materialien wie Filz, Stoff oder Leder und als Poliermittel Öle und Fette, gemischt mit Aluminiumoxid, Chromtrioxid oder Tonerde, verwandt. Radiographic testing At radiographic testing, in short RT-test, we test materials via Y-ray and gamma radiation. With this non-destructive material testing we search for imperfections and we use it for investigating pores, segregation and cracks in the inner part of casts. Mainly it is used for quality control for security-relevant castings and welding seams. Mainly it is used for quality control for security-relevant castings and welding seams. The principle of this method is based on the fact, that different material thickness leaves different levels of darker colouring on the radiographic image. The thicker is the material, the brighter is the projected image. With the aid of contrasts, which are used for the radiation of castings on a roentgen film, we can not only see the differences in the material thickness but also faults in the solidity of the material. Soft annealing Stress-relief annealing is a procedure of heat treatment of metals where a change in the structure of the material occurs. The goal is to have better machining or forming characteristics of the metal in its cold state. For this purpose the material is heated up to annealing and this is done for such a long time till all defects and dislocations are corrected and stress is relieved. At slow cooling of the material the process of recrystallization begins, new cores form and crystals grow. Metals which undergo the process of stress relief annealing lose hardness and can then be milled easier and without cracks, stretched to wires or punched. Solidity The solidity of a material is defined with its resistance towards separation and deformation Solution annealing Solution annealing is an annealing treatment with the aim to reintegrate into the solution compounds of the structure of a casting which were initially eliminated. The process of solution annealing takes places at temperatures above the solution threshold of the dissolving phase. Through a subsequent quenching we achieve that the treated structure endures also at ambient temperature. Solution annealing can be used at all alloys which have the capability of elimination and hardening. Spherulitic graphite cast iron (EN-GJS) Spherulitic graphite cast iron, also known as nodular cast iron, is an iron-carbon-alloy with a high carbon share of up to four per cent. Accordingly, the structure of graphite has a big influence on the mechanic characteristics of the material. It has a spherical form and due to this it is highly resistant to breaking, it is low in notch sensitivity and it has a high ductility. The last feature gives it also extremely high values at fracture strains. The standardised naming of spherulitic graphite cast iron is EN-GJS. Stress relief annealing According to its name, stress relief annealing is an after-treatment procedure of casts with the aim to reduce inner stress within the castings through annealing and slow cooling-down. The heating of the material, resp. annealing, takes place – at least with steel – at a temperature between 550 and 650 degrees Celsius and is therefore under the range of austenite formation. During the subsequent slowly performed cooling process we temporarily reduce the yield strength and the maximum breaking stress. The material begins to flow plastically. The inner tensions reduce up the range of the yield strength. Without this process the inner tensions would be released during further treatment of the part and they would lead to defaults and thus to geometric deviations. Tensions within a cast can develop during founding or welding due to uneven cooling or through strong mechanic treatment Tempering Tempering is a process of heat treatment which follows hardening. The aim is to influence the mechanical characteristics of a cast to the desired level. The modification in this case occurs in the whole casting part, thus from the surface to the centre. If the tempering process is done directly after hardening, we call it annealing. A central procedure with tempering is the heating up of the product to the so called tempering temperature and the subsequent cooling to room temperature. The tempering temperature level is defined by the desired hardness and the material variety. The length of the process depends on the diameter and the size of the parts and on the quantity. Through the process of tempering we can increase the ductility of a cast up to the desired level and with a decrease in hardness. When tempering a steel cast part oxidation occurs and thus the surface receives a special colouring. These so called tempering colours are characteristic for a desired tempering temperature. Ultrasonic testing (UT) Ultra-sonic testing, in short UT-testing according to EN 12680-1,-2,-3, is a non-interfering control method where via ultrasound imperfections in materials can be found. The procedure is suitable for all sound conductive materials and thus for metals. It investigates internal and external imperfections and it measures layer thickness. The physical basis for ultrasonic testing is the varied propagation of sound waves according to its medium. On the transfer from one to another material the changed wave impedance leads to the fact that sound waves are spreading at a different speed, or they change directions or they are partially reflected. The reflected share of the waves is the greater the higher the difference between the wave impedance between the two materials is. Such a border surface where the audio impulse is reflected can be a crack or cavity in a material. Through special measuring methods after a transmission of an impulse a signal image is created which enables to define the position and the size of the imperfection within the material. In general we divide between two measuring processes: reflective wave procedure, also impulse-echo procedure and the through-sonic procedure. Vacuum hardening The procedure of vacuum hardening refers to heat treatment of castings under vacuum. It is used mostly when high reproduction, metallic blank surface and low distortion of casts are needed. Vacuum hardening is predominantly suitable for after-treatment of high-quality individual casting parts and its characteristics are high profitability and environmental friendliness. Water quenching and tempering Water quenching is a treatment of hardening and tempering, named annealing, where the hardening of the casting happens through quenching in water. Zinc plating At zinc-plating iron and steel are coated with zinc, mostly in order to protect it from corrosion. According to the selected procedure we distinguish between: • Zinc spraying Liquefied zinc is applied with an airbrush on compressed air. • Hot-dip zinc coating The parts which need to be zinc-coated are dipped into liquid zinc in order to create an alloyed layer. • Galvanic zinc-plating The zinc coating is applied with an aqueous electrolyte with direct current onto the protecting part. • Application of zinc powder Suitable parts are coated with zinc powder through diffusion or plating. This procedure also includes the application of protective layers of coatings which are pigmented with zinc powder.