Solution annealing of steel
The aim of solution annealing is to dissolve formed precipitates!
https://youtu.be/PJ2FKTHAo5s
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 steel
The aim of diffusion annealing is to compensate for concentration differences!
https://youtu.be/PJ2FKTHAo5s
When steels with high alloy concentrations solidify, the alloying elements may not be distributed homogeneously in the microstructure or in the...
Recrystallization annealing of steel
The aim of recrystallisation annealing is to restore a deformed microstructure to improve its deformability!
https://youtu.be/PJ2FKTHAo5s
The microstructure of rolled, bent or deep-drawn workpieces is strongly deformed by the high forming forces. This...
Coarse-grain annealing of steel
The aim of coarse grain annealing is to improve machinability!
https://youtu.be/PJ2FKTHAo5s
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 of steel
The aim of soft annealing is to improve formability and machinability!
https://youtu.be/PJ2FKTHAo5s
Not every material has to be designed to withstand high mechanical forces. With a curved sheet metal with milled out slots,...
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!
https://youtu.be/7UcNNuqKA6U
Surface hardening like flame hardening, induction hardening, laser...
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)!
https://youtu.be/7UcNNuqKA6U
Laser-beam hardening (laser hardening) offers even shorter heating times of the...
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!
https://youtu.be/7UcNNuqKA6U
The flames during flame hardening generally lead to a...
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.
https://youtu.be/7UcNNuqKA6U
Introduction
A hard surface layer is essential to increase...
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 (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 (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...
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
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...
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...
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
The fatigue test provides information about the strength of a material under continuously changing stress (dynamic load).
https://www.youtube.com/watch?v=V2FItB2m4lk
Introduction
The intensity of the stress increases slowly but steadily in the tensile, compression and flexural...
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.
https://www.youtube.com/watch?v=pMUbK2DTJRs
Fatigue limit diagrams
Although the Wöhler curve is suitable for the evaluation...
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!
https://www.youtube.com/watch?v=blECIlqda2Y
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!
https://www.youtube.com/watch?v=B-caaAtTsDk
Test setup
In the bending flexural test, a specimen is loaded under uniaxial...
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...
Tensile test
The tensile test is used to determine the strength (yield point, ultimate tensile strength) and toughness (elongation at break) of a material!
https://www.youtube.com/watch?v=nOdcE2pJx2A
Setup
The tensile test is one of the most important testing...
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...
Case hardening (surface hardening)
With case hardening, low-carbon steels are first enriched with carbon in the surface layer (carburisation) and then quenched!
https://youtu.be/7UcNNuqKA6U
Case hardening
The toughness (ductility) of steels increases with decreasing carbon content, as then less...
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.
https://youtu.be/64qw1am8twE
Introduction
The heat treatments explained in the chapter on annealing processes...
Normalizing of steel (annealing)
The aim of normalizing is to achieve a uniform homogeneous microstructure with reproducible properties!
https://youtu.be/PJ2FKTHAo5s
As already explained in the chapter deformability of metals, fine roundish grains generally lead to better toughness and...
Overview of heat treatment of steel
Heat treatment processes are used to specifically influence the properties of the steel.
https://youtu.be/PJ2FKTHAo5s
The microstructure of a steel has a particular influence on its properties. However, the steel microstructure is not only...
Cast iron
https://youtu.be/lSfmU8cmzLE
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...
Summary of the phase transformations of steel
In this article, a summary is given about the phase transformations during solidification and cooling of steel.
https://youtu.be/b581J_SmCM4
Introduction
In the article Phase transformations in the solidified state the microstructural changes of steels during...
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).
https://youtu.be/b581J_SmCM4
The figure below shows steel part of the iron-carbon phase diagram of the...
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.
https://youtu.be/b581J_SmCM4
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...
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.
https://youtu.be/b581J_SmCM4
Introduction
As explained in the article Microstructure formation...
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.
https://youtu.be/b581J_SmCM4
Introduction
In principle, steels are binary systems consisting of the host element iron and the...
From steel to semi-finished products
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...
From crude steel to steel
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...
From pig iron to crude steel
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...
Direct reduced iron process
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...
Blast furnace process
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...
Ironworks
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...
Iron ore mining and dressing
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...
Alloys – limited solubility of components in solid state
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.
https://youtu.be/AcMwxu_-Jjs
Introduction
A complete solubility or complete insolubility...
Alloys – complete insolubility of components in solid state
If the components of an alloy are completely insoluble in each other in the solid state, then a mixture of pure crystals is formed.
https://youtu.be/6NFBEoPMMv0
Introduction
If the two components of a binary alloy...
Alloys – complete solubility of components in solid state (solid solution)
If the components of an alloy are completely soluble in each other in the solid state, then solid solutions form.
https://youtu.be/N-RQntCjTZk
Introduction
If the two components of an alloy (binary system) are completely soluble...
Typs of alloys
Depending on the extent to which the two components are soluble in each other in the solid state, different types of alloys result.
https://youtu.be/Ig7UV8yTlOs
Introduction
In many technical fields, high demands are placed on...
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.
https://youtu.be/7xPfW2hYt8w
Introduction
As explained in the article on solidification conditions, the...
Schmid’s law
External normal stresses induce shear stresses inside a material, which become maximum at an angle of 45°.
https://youtu.be/AaHxsDl2ZWg
Shear force
If a material is stressed under tension, it will eventually deform if the tensile...
Microstructure formation
The solidification of a melt starts from nuclei, resulting in the typical polycrystal microstructure.
https://youtu.be/7xPfW2hYt8w
Polycrystal
A metallic material generally does not have a uniform lattice orientation (see crystallographic defects). Exceptions to this are...
Crystal growth
In polygonal crystal growth, the heat of solidification is transferred through the crystal and in dendritic crystal growth through the melt.
https://youtu.be/LOmCxNNbDN4
Introduction
In the article homogeneous nucleation or heterogeneous nucleation, the formation of...
Heterogeneous nucleation
In heterogeneous nucleation, nuclei that do not consist of the same substance as the melt trigger solidification.
https://youtu.be/CtKK6Vznd4Y
Introduction
The nucleation considered in the article homogeneous nucleation referred to the own particles in the...
Homogeneous nucleation
In homogeneous nucleation, nuclei consisting of the same substance as the melt trigger solidification.
https://youtu.be/uyYxyTKEIzg
Gibbs energy
In order to understand the processes of nucleation, an energetic analysis is indispensable. In this context the...
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...
Heat of solidification
During solidification, heat is released, which is called heat of crystallization or heat of solidification. It counteracts the external cooling.
https://youtu.be/7xPfW2hYt8w
Introduction
The hand warmer described in the article solidification conditions shows another phenomenon...
Conditions for solidification
Two conditions must be met for solidification: The melt must be supercooled and nuclei must be present in the melt.
https://youtu.be/7xPfW2hYt8w
Introduction
The origin for the formation of a microstructure is usually the...
Deformation process in single crystals
Deformation in single crystals is divided into four stages: elastic, easy glide (single slip), multiple glide and recovery.
https://youtu.be/meUF-9i-4Qw
Introduction
Even if single crystals are used far less than polycrystals, one can understand very well the processes...
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.
https://youtu.be/xaNPAMxLXdE
Introduction
If a material on the atomic level is...
Deformation process in real crystal structures
Dislocations provide low-stress deformation due to the gradual sliding of atomic blocks.
https://youtu.be/54H5HQlMEio
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 ductility
Each type of lattice structure has a different number of slip systems (possibilities of sliding) and is therefore differently deformable.
https://www.youtube.com/watch?v=AT7D8Ab93BE
Slip system
As explained in the article on Fundamentals of Deformation, a plastic deformation processes in...
Crystallographic defects
Crystallographic defects are deviations from an ideal microscopic lattice structure of metals such as vacancies or dislocations.
https://www.youtube.com/watch?v=EoCtPYHaRAE
Introduction
The previous article dealt with a uniform and error-free structure of the metals. However, such...
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.
https://youtu.be/gjdb9QfRg0I
Definition of the packing density
The packing density is the ratio of...
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.
https://www.youtube.com/watch?v=AT7D8Ab93BE
Introduction
The relatively good deformability of metals (also referred to as...
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).
https://youtu.be/FD0-mMozSxk
Introduction
The article on lattice structure of metals explains why the atoms in a metal...
Lattice structure of metals
The lattice structure is the periodic structure of metals. The lattice structure is characterized by the unit cell.
https://youtu.be/FD0-mMozSxk
Introduction
Metals play an important role in mechanical engineering. Compared to other materials, they can...