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Solution annealing of steel

The aim of solution annealing is to dissolve formed precipitates! During welding or hot forming, microstructural changes occur in the steel due to the influence of heat and uncontrolled cooling. This is...
Diffusion annealing of a high-alloy steel

Diffusion annealing of steel

The aim of diffusion annealing is to compensate for concentration differences! When steels with high alloy concentrations solidify, the alloying elements may not be distributed homogeneously in the microstructure or in the...
Recrystallization annealing of a rolled sheet

Recrystallization annealing of steel

The aim of recrystallisation annealing is to restore a deformed microstructure to improve its deformability! The microstructure of rolled, bent or deep-drawn workpieces is strongly deformed by the high forming forces. This...
Coarse grain annealing of a free cutting steel

Coarse-grain annealing of steel

The aim of coarse grain annealing is to improve machinability! In general a coarse-grained steel microstructure is undesirable due to the relatively low toughness and strength values. The only advantage of a...
Soft annealing

Soft annealing of steel

The aim of soft annealing is to improve formability and machinability! Not every material has to be designed to withstand high mechanical forces. With a curved sheet metal with milled out slots,...
Nitriding of a nitriding steel

Nitriding of steel (surface hardening)

Nitriding is not based on the formation of martensite but on the formation of hard and wear-resistant nitrides on the surface of the workpiece! Surface hardening like flame hardening, induction hardening, laser...
Laser hardening

Laser hardening of steel (surface hardening)

With laser hardening, the surface is heated by a laser beam and quenched by heat dissipation in the workpiece (self quenching)! Laser-beam hardening (laser hardening) offers even shorter heating times of the...
Induction hardening

Induction hardening of steel (surface hardening)

With induction hardening, the workpiece is heated by induced eddy currents. The hardening depth is controlled by the frequency of the alternating current! The flames during flame hardening generally lead to a...
Flame hardening of a surface

Flame hardening of steel (surface hardening)

Surface hardening is used to produce a hard and wear-resistant surface layer on steel workpieces, while the toughness in the core is largely retained. Introduction A hard surface layer is essential to increase...
Measuring tool for eddy current testing

Eddy current testing (ECT)

Eddy current testing is used to non-destructively inspect components for surface defects such as cracks. With eddy current testing, electrically conductive materials can be examined for pores, inclusions and cracks in the...
Magnetic particle inspection (magnetic field flow method)

Magnetic particle inspection (MPI)

With magnetic particle inspection (MPI), surface defects such as cracks of ferromagnetic components are made visible. Introduction Like the dye penetrant inspection, magnetic particle inspection is also a method for examining surface defects...
Dye penetrant inspection

Dye penetrant inspection (DPI)

With Dye penetrant inspection, cracks on the surface of components can be made visible in a non-destructive manner. The dye penetrant inspection (or liquid penetrate inspection) can be used to visualize surface...
Principle of ultrasonic testing

Ultrasonic testing (UT)

Ultrasonic testing uses sound waves to non-destructively inspect a component for flaws. Introduction Ultrasonic testing is a non-destructive testing technique because the workpieces or components to be tested are not damaged during the...
Cupping test

Cupping test

In the cupping test according to Erichsen, the deep drawing behavior of a metal sheet is examined. Sheets for deep-drawing applications must have very good cold formability, i.e. they must be able...
Schematic setup for stress-relaxation test

Stress-relaxation test

The relaxation strength indicates for a certain temperature to which value the stress falls at a given strain after a certain time! In the creep rupture test, material samples are subjected to...
Zeitstandschaubild

Stress rupture test (creep rupture test)

The creep rupture test (stress rupture test) is used to measure the strength of materials that are subjected to constant stress at elevated temperatures. Creep If components are subjected to a constant tensile...
Fatigue test setup

Fatigue test

The fatigue test provides information about the strength of a material under continuously changing stress (dynamic load). Introduction The intensity of the stress increases slowly but steadily in the tensile, compression and flexural...
Fatigue endurance diagram acording to Haigh

Fatigue limit diagram according to Haigh and Smith

Fatigue limit diagrams according to Haigh or Smith show the maximum yieldable stress amplitude as a function of the mean stress. Fatigue limit diagrams Although the Wöhler curve is suitable for the evaluation...
Test setup for Charpy impact test

Charpy impact test

The Charpy impact test (Charpy V-notch test) is used to measure the toughness of materials under impact load at different temperatures! Introduction The elongation at break and reduction in area obtained by the...

Bending flexural test

In a bending flexural test, a standardized specimen is bent under uniaxial bending stress until plastic deformation or fracture occurs! Test setup In the bending flexural test, a specimen is loaded under uniaxial...
Setup for compression test

Compression test

In the compression test, a standardized specimen is loaded under compressive stress until it breaks or until a first crack appears. The testing of materials under compressive stress is carried out in...
Brittle fracture and ductile fracture

Tensile test

The tensile test is used to determine the strength (yield point, ultimate tensile strength) and toughness (elongation at break) of a material! Setup The tensile test is one of the most important testing...
Types of loads

Destructive material testing & non-destructive testing (NDT)

In destructive materials testing, the material is damaged; in non-destructive materials testing, the workpiece is left undamaged. Materials such as steels generally have to withstand a wide variety of loads. The different...
Carburizing of a case-hardening steel

Case hardening (surface hardening)

With case hardening, low-carbon steels are first enriched with carbon in the surface layer (carburisation) and then quenched! Case hardening The toughness (ductility) of steels increases with decreasing carbon content, as then less...
Temperature curve during quenching and tempering

Quenching and tempering of steel

The aim of quenching and tempering is to achieve a hard and wear-resistant surface or to increase the strength of a workpiece. Introduction The heat treatments explained in the chapter on annealing processes...
Normalization of a heterogeneous microstructure

Normalizing of steel (annealing)

The aim of normalizing is to achieve a uniform homogeneous microstructure with reproducible properties! As already explained in the chapter deformability of metals, fine roundish grains generally lead to better toughness and...
Temperature ranges of the heat treatment processes

Overview of heat treatment of steel

Heat treatment processes are used to specifically influence the properties of the steel. The microstructure of a steel has a particular influence on its properties. However, the steel microstructure is not only...
Micrograph of hypoeutectic cast iron with a carbon content of 3.85 %.

Cast iron

Introduction Up to now, the iron-carbon phase diagram has only been considered up to a carbon content of 2.06 %. If this carbon content is exceeded, further phase transformations occur. Basically, this...
Overview of the microstructure formation of steels

Summary of the phase transformations of steel

In this article, a summary is given about the phase transformations during solidification and cooling of steel. Introduction In the article Phase transformations in the solidified state the microstructural changes of steels during...
Comparison of the iron-carbon phase diagram with the phase diagram of a crystal mixture

Comparison of phase transformations in steels

Phase transformations in steels can be compared to those of solid solutions (completely soluble) and crystal mixtures (completely insoluble). The figure below shows steel part of the iron-carbon phase diagram of the...
Determination of the microstructure fractions of a hypoeutectoid steel

Determination of microstructure and phase fractions in steels

For steels, the microstructure and phase fractions in the iron-carbon diagram can be determined using the lever rule. Introduction For many applications it is important to know exactly what microstructure or phase fractions...

Influence of carbon on hardness and strength of steels

With increasing carbon, the hardness and strength of unalloyed steels increases. Above a content of 0.8% C, the strength decreases. As the carbon content increases, the proportion of cementite in the steel...
Micrograph of eutectoid steel with a carbon content of 0.8 % (C80)

Phase transformations of steels in solidified state (metastable system)

Depending on the carbon content, further phase transformations take place in the steel in the solidified state. The cooled microstructure consists of pearlite and ferrite. Introduction As explained in the article Microstructure formation...
Transformation lines in the iron-carbon phase diagram (steel part)

Microstructure formation of steels during solidification

Steels solidify as solid solutions. The face-centered cubic lattice structure with the embedded carbon atom is called austenite. Introduction In principle, steels are binary systems consisting of the host element iron and the...
Continuous casting of steel

From steel to semi-finished products

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Semi-finished products are mainly produced by (discontinuous) ingot casting or by continuous casting. Ingot casting With ingot casting, the molten steel from the steelworks solidifies in moulds to form conical blocks, each with...
Electro-slag remelting process (ESR)

From crude steel to steel

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In order to meet today's requirements for steels, crude steel must be further treated by various processes after it has been refined. Introduction In the early days of steel production, the crude steel...
Ladle transfer car

From pig iron to crude steel

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After the pig iron has been tapped, it must be desulfurized and oxidized with oxygen (refining) to obtain crude steel. Introduction Due to its high carbon content and relatively high concentrations of phosphorus...
Shaft furnace for the direct reduced iron process

Direct reduced iron process

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The direct reduced iron process (DRI) is becoming more and more important in the climate change debate about producing steel with as little CO2 as possible. Direct reduced iron (DRI) process In addition...
Zonen im Hochofen

Blast furnace process

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In the blast furnace, the iron ore reacts with the carbon contained in the coke to form grey or white pig iron. Combustion process The iron in the processed ores must be dissolved...
Construction of a blast furnace

Ironworks

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Steel is produced from iron ore in the ironworks. The ironworks includes charging, coking plant, Cowper stove and the blast furnace. Charging After the ground ores have been processed in forms of sinter...
Schematic overview of an ironworks

Iron ore mining and dressing

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After the iron ore has been mined, it has to be processed for use in the blast furnace in order to optimize the chemical processes. Introduction Iron is one of the most important...
Phase diagram and microstructure diagram of an alloy system with limited solubility of the components

Alloys – limited solubility of components in solid state

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In general, the components of alloys are soluble in each other only to a limited extent. In this case, a mixture of solid solutions is formed. Introduction A complete solubility or complete insolubility...
Phase diagram and microstructure diagram of an alloy system with complete

Alloys – complete insolubility of components in solid state

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If the components of an alloy are completely insoluble in each other in the solid state, then a mixture of pure crystals is formed. Introduction If the two components of a binary alloy...
Reading the phase diagram of an alloy system with complete solubility of the components (solid solution)

Alloys – complete solubility of components in solid state (solid solution)

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If the components of an alloy are completely soluble in each other in the solid state, then solid solutions form. Introduction If the two components of an alloy (binary system) are completely soluble...
Classification of alloys

Typs of alloys

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Depending on the extent to which the two components are soluble in each other in the solid state, different types of alloys result. Introduction In many technical fields, high demands are placed on...
Heterogeneous and homogeneous nucleation

Types of nuclei

Solidification can be triggered either by nuclei consisting of the same substance as the melt or by nuclei consisting of a different substance. Introduction As explained in the article on solidification conditions, the...
Slip plane and slip direction

Schmid’s law

External normal stresses induce shear stresses inside a material, which become maximum at an angle of 45°. Shear force If a material is stressed under tension, it will eventually deform if the tensile...
Microstructure of polycrystalline iron

Microstructure formation

The solidification of a melt starts from nuclei, resulting in the typical polycrystal microstructure. Polycrystal A metallic material generally does not have a uniform lattice orientation (see crystallographic defects). Exceptions to this are...
Dendritic crystal growth (nucleus growth)

Crystal growth

In polygonal crystal growth, the heat of solidification is transferred through the crystal and in dendritic crystal growth through the melt. Introduction In the article homogeneous nucleation or heterogeneous nucleation, the formation of...
Water droplet on a tablecloth

Heterogeneous nucleation

In heterogeneous nucleation, nuclei that do not consist of the same substance as the melt trigger solidification. Introduction The nucleation considered in the article homogeneous nucleation referred to the own particles in the...
Critical nucleus radius and activation energy for nucleation

Homogeneous nucleation

In homogeneous nucleation, nuclei consisting of the same substance as the melt trigger solidification. Gibbs energy In order to understand the processes of nucleation, an energetic analysis is indispensable. In this context the...
Golf clubs as application of an amorphous metal (metallic glass)

Amorphous metals

In amorphous metals, supercooling is so strong that nucleation is suppressed and crystalline structures do not form. In the article on types of nuclei it was explained that with stronger cooling and thus...
Cooling curve of a pure substance

Heat of solidification

During solidification, heat is released, which is called heat of crystallization or heat of solidification. It counteracts the external cooling. Introduction The hand warmer described in the article solidification conditions shows another phenomenon...
Conditions for solidification

Conditions for solidification

Two conditions must be met for solidification: The melt must be supercooled and nuclei must be present in the melt. Introduction The origin for the formation of a microstructure is usually the...
Stress-strain curve of a single crystal

Deformation process in single crystals

Deformation in single crystals is divided into four stages: elastic, easy glide (single slip), multiple glide and recovery. Introduction Even if single crystals are used far less than polycrystals, one can understand very well the processes...
Lattice orientation for single and multiple gliding

Deformation of ideal crystal structures (single crystal)

During the deformation of single crystals, slip steps preferably form at 45° to the tensile axis, since the shear stresses are at a maximum. Introduction If a material on the atomic level is...
Illustration of an edge dislocation

Deformation process in real crystal structures

Dislocations provide low-stress deformation due to the gradual sliding of atomic blocks. Introduction To initiate a deformation process, a certain critical resolved shear stress (CRSS) is required at the atomic level. As described in...
Influence of the lattice structure on the ductility

Influence of the lattice structure on ductility

Each type of lattice structure has a different number of slip systems (possibilities of sliding) and is therefore differently deformable. Slip system As explained in the article on Fundamentals of Deformation, a plastic deformation processes in...
Real crystal with crystallographic defects

Crystallographic defects

Crystallographic defects are deviations from an ideal microscopic lattice structure of metals such as vacancies or dislocations. Introduction The previous article dealt with a uniform and error-free structure of the metals. However, such...
Derivation of the packing density of the face-centered cubic lattice structure (fcc)

Derivation of the packing density

The packing density is the ratio of the atomic volume within a unit cell to the volume of the unit cell. Definition of the packing density The packing density is the ratio of...
Slip planes and slip steps

Fundamentals of deformation

Deformation of metals is based on the shifting or sliding of atomic blocks. A distinction is made between elastic and plastic deformation. Introduction The relatively good deformability of metals (also referred to as...
Important lattice structures of metals

Important types of lattice structures

Important lattice structures are the face-centered cubic (fcc), the body-centered cubic (bcc), and the hexagonal closest packed (hcp). Introduction The article on lattice structure of metals explains why the atoms in a metal...
Acting forces on the metal ions

Lattice structure of metals

The lattice structure is the periodic structure of metals. The lattice structure is characterized by the unit cell. Introduction Metals play an important role in mechanical engineering. Compared to other materials, they can...