Digression on the subject of heat treatment.

It all depends on the right heat.

Depending on individual requirements, various heat treatment processes are used. These ensure that the properties of the material, such as strength, ductility, durability, change in order to obtain the desired properties. Depending on the target definition, different heating rates, holding times, holding temperatures and cooling conditions are used to achieve the desired structural changes in the material by rearranging particles (atoms, molecules).

Heat treatments in a vacuum or under shielding gases produce first-class, durable and high-quality workpieces with clean and bright surfaces that meet high quality standards.

QUENCHING AND TEMPERING

Quenching and tempering is a combined heat treatment process consisting of hardening and subsequent tempering. In this process, the hardness and tensile strength of the hardened steel decrease. At the same time, the ductility and toughness of the material increase. This process is particularly suitable for components that are subjected to high stresses / are subject to high dynamic loads and require high toughness, such as in mechanical engineering and apparatus construction.

Advantages

High toughness and tensile strength at the same time
Optimum notched impact strength
Good flexural fatigue strength
Avoidance of warpage or cracking (due to controlled tempering temperature)

ANNEALING

Annealing processes aim to change the existing microstructure and make the material easier to form or tougher / more machinable due to a better microstructure. All annealing processes include at least the three stations: Heating, maintaining temperature and cooling. The heating and cooling temperatures or rates vary depending on the material and the desired purpose. For high and more complex material requirements, it may be necessary to divide the three phases into further ones. Based on our expertise and know-how, we know which process is best suited for which objective.

Advantages

Reduction of working and processing stress
Improvement of mechanical and magnetic properties
Easier machining
Creation of an optimal microstructure for cold forming
Restoration of toughness
Increase in corrosion resistance
Optimum dimensional and shape stability
Bright components due to clean process

Typical annealing processes –

1. NORMALIZING

The aim of normalizing is to restore a fine-grained or uniform microstructure after a pretreatment such as welding, casting, hardening or forming. Depending on the carbon content of the steel, the annealing temperature here is approx. 800 °C to 950 °C.

2. SOFT ANNEALING

Soft annealing is used to soften steels so that they can be better machined. Temperatures here are just below the transformation line at 723 °C followed by slow cooling. This produces spherical pearlite in the material, a softer microstructure which allows optimum processing in non-cutting forming and in machining.

3. STRESS RELIEF HEAT TREATMENT

Stress relief heat treatment relieves residual stresses caused by mechanical deformation or machining of the material/workpiece (e.g. cold forming, microstructural transformation, uneven cooling or machining). To ensure that the other properties of the steel, such as strength, are retained, stress relief heat treatment is carried out in a temperature range between 500 and 650° C. The steel is cooled slowly to ensure that the material/workpiece is not stressed. Cooling is carried out slowly so that no new stresses are created.

4. SOLUTION ANNEALING (RECRYSTALLIZATION ANNEALING)

Solution annealing is usually applied to austenitic steels. (1,020 °C -1,080 °C). Materials harden by cold working, such as bending. At the same time, the toughness of the material decreases. Recrystallization annealing reverses the strain hardening and makes the microstructure softer and more malleable. At temperatures just above the recrystallization temperature, the growth of new grains is stimulated. Lattice defects that have arisen during cold forming are reduced. The material regains the structure and properties it had before cold forming.

5. DIFFUSION ANNEALING

Diffusion annealing is a long annealing process (up to 50 hours) at high temperatures between 1,050 °C and 1,250 °C. The aim is to eliminate or reduce concentration differences (e.g. crystal segregation) in the workpiece or structural heterogeneities. The aim is to eliminate or reduce concentration differences (e.g. crystal segregation) in the workpiece or structural heterogeneities. The high temperatures make the steel microstructure permeable to such an extent that segregations formed during cooling dissolve again by diffusion, resulting in a uniformly mixed microstructure.

6. MAGNETIC FINAL ANNEALING

During the manufacture of soft magnetic components, machining and forming operations cause damage to the magnetic properties, which often makes safe use in magnetic systems impossible. In order to optimize the magnetic properties, we use magnetic final annealing. The aim here is to obtain a uniform atomic lattice with the lowest possible distortions and to achieve a homogeneous magnetic state in the material. The annealing is carried out in a vacuum or under protective and reaction gases. Special charging processes can be used to prevent „sticking“ and „bending“ of stampings to the greatest possible extent, which further increases the quality and results of the final annealing process. To be on the safe side, the components should be checked for their magnetic properties and prove these with the Hc value test with Koerzimat 1.095 e.g. from Institut Dr. Förster. If required, a universal hardness test can also be carried out.

HEAT TREATMENT OF NON-FERROUS METALS

For the heat treatment of non-ferrous metals, such as copper and aluminum alloys, various annealing processes are used, depending on the component and application.

Advantages

Improvement of mechanical machinability
High-temperature brazing makes it possible to join copper alloys with stainless steels in a high-strength manner, thus continuing to ensure thermal/electrical conductivity as well as the necessary strength in the wear/contact area.

Typical annealing processes for NON-FERROUS METALS

1. ALUMINUM ALLOYS

The lightweight aluminum is gaining ground as a material and, thanks to its very good technical properties, it is no longer possible to imagine aircraft or vehicle construction without it. Aluminum components are characterized by high strength and low density. This makes it possible to achieve enormous energy and cost savings. Special heat treatment processes have a positive effect on the mechanical machinability of aluminum alloys. Deep-drawn aluminum components can also be stress-relief annealed to ensure further formability.

2. COPPER ALLOYS

Copper is characterized by excellent corrosion resistance and very high conductivity for heat and electricity. It has medium strength and can be readily formed. However, the properties of pure copper are not sufficient for many industrial applications. However, they can be significantly optimized by combining them with other elements. In most cases, only a small amount of „adding“ is necessary to change the strength or machinability, for example. With these various alloys, depending on the requirements, the following, for example, can be achieved

MATERIALS

COPPER AND SILVER ALLOYED COPPER

PROCESS

STRESS RELIEF HEAT TREATMENT

SOFT ANNEALING

TEMPERATURE

MATERIALS

BRASS (CuZn)

PROCESS

STRESS RELIEF HEAT TREATMENT

SOFT ANNEALING

HOMOGENIZING

TEMPERATURE

MATERIALS

BRONZE (CuSn), WROUGHT MATERIAL

PROCESS

Artificial aging is often used for components which have the desired dimensional stability after the processing stage (e.g. machining), but where component distortion due to the natural aging process can only be tolerated to a very limited extent.

Advantages

Acceleration of microstructural and property changes for the purpose of dimensional stabilization in the use of tightly toleranced components
Prevention of component distortion or other age-related processes

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