Vacuum brazing is a special hard brazing process based on capillary action. For this, a suitable brazing material is melted and applied as a coating on the parts to be joined. The subsequent cooling creates a firmly bonded joint. The vacuum atmosphere prevents unwanted reactions with the environment, such as oxidation, and provides optimum brazing conditions.

 

The process starts with a thorough cleaning of the components, in order to remove grease, oxides, and other impurities. Next, the brazing material is applied in the form of a foil, wire, paste, or a galvanic coating. The components are then precisely fixed in place in the vacuum furnace in order to ensure exact positioning.

 

Once the target temperature has been reached, the brazing material is kept molten for a defined dwell time, ensuring the complete coating of the join surfaces. The controlled cooling keeps the material from warping and ensures a uniform microstructure. To ensure the highest quality standards, the process concludes with a check of the workpieces for strength, tightness, and dimensional accuracy.

The process offers numerous advantages, including high-strength and reproducible joints with flawless, corrosion-resistant surfaces. Since it does not require fluxes, the process does not produce any residues, thus eliminating the need for costly rework. Another benefit is the option to combine brazing and hardening in a single process step - thus providing an efficient solution that saves time and money.

 

The key advantages at a glance:

 

• High strength and corrosion resistance of the joint
• Clean surfaces free of oxides, as no flux residues are produced
• Combination of different materials, e. g. metal/ceramic combinations
• Even heat distribution thanks to the vacuum, minimising dimensional deviations
• Reduced need for rework, as the process does not create any oxidation layers
• Ideal for high-precision applications in the fields of aerospace and medical engineering

Its versatility has made vacuum brazing an established solution in numerous branches of industry. It very suitable for high alloy steels, super alloys, stainless steel, copper, titanium, and aluminium, as well as for demanding materials such as ceramics, carbides, CBN, and diamond. This compatibility across a wide range of materials makes the process particularly attractive for machine and tool making, where it is used, for instance, for joining carbide and steel.

 

The process also plays an essential role in aerospace, as it allows the production of extremely strong and temperature-resistant structural components. Its applications in the automotive industry include the production of hydraulic and cooling systems. Medical engineering benefits from the hygienic, gap-free joints that vacuum brazing makes possible, while it is used in vacuum and measurement technology for the production of high-precision components. Another important area of application is the manufacture of heat exchangers and heating elements, which require optimum heat transfer.

To achieve even better results, vacuum brazing can be further optimised with the help of a variety of special processes. One common method is vacuum hardening with subsequent tempering, which substantially increases the mechanical strength of the components. Similarly, surface hardening by nitriding contributes to boosting wear resistance, thus improving the durability of the components.

 

Another key aspect is stress-free annealing, which reduces internal stresses in the material and thus minimises the risk of warping or cracks. Moreover, the targeted use of capillary action can help achieve an even more precise coating of the joining surfaces, and this optimises the quality of the solder joint even further. These specialised processes make it possible to systematically adapt vacuum brazing to specific requirements and thus to ensure even higher performance and reliability.

 

Would you like to learn more about vacuum brazing? Contact our team of experts!

 

Our locations in Germany and Europe are shown here.

During laser hardening, the carbon-containing edge region of a component is heated to temperatures between 900 and 1,500°C by a high-intensity laser beam. This local introduction of heat causes the steel to become austenitised. While the laser beam moves, the surrounding material quickly cools the heated zone, causing the formation of martensite. This rapid self-quenching eliminates the need for additional quenching media. The process makes it possible to harden only specific functional surfaces in a targeted manner, while maintaining the ductility of the remaining component.

 

Laser hardening is an edge layer hardening process that leaves the chemical composition unchanged. Laser hardening is also a particularly good choice for large workpieces that need to be hardened only in certain areas.

 

By means of point-by-point or two-dimensional heating, laser beams can be used to heat the steel surface to its austenitising temperature. Heating with laser beams is very fast. This facilitates quenching, which takes place almost by itself, on account of the fast heat conduction.

 

Caption: Process: Laser hardening

Laser hardening may serve as an alternative heat treatment process to inductive hardening or flame hardening. It is also ideal as a subsequent surface treatment for protecting component areas that are prone to sustaining wear and tear. The process can be effortlessly integrated into existing production processes, e.g. in conjunction with processing or production machines.

• Precise hardening: Local hardening of specific partial areas.
• Minimum warping: Low heat input reduces material deformation.
• High reproducibility: Exact control of the heat input.
• No quenching medium: Self-quenching makes additional processes unnecessary.

Laser hardening is used in various industries, including toolmaking, the automotive industry and agricultural technology. It is particularly suitable for components with complex geometries or heavily stressed components, such as camshafts, cutting tools or gear wheels.

 

Typical materials are:

• Tool steels (e.g. cold and hot worked steels)
• Quenched and tempered steels
• Sectional steels
• Stainless steels resistant to corrosion (containing 0.2% carbon or more)
• Cast iron

The PACD process relies on the diffusion of carbon atoms from a carrier gas into the surface layers of the treated component. The process is based on the application of a voltage that generates a plasma of ionised gas in a vacuum. The depth of the diffusion layer can be varied depending on process parameters (temperature, time, and gas composition). The detailed sequence of the process is as follows:

1. Preparation of the material: Cleaning the workpiece ensures that it is free of impurities that could compromise the PACD process.
2. Vacuum formation: The component enters into a vacuum chamber having a vacuum of 0.1 to 10 millibar. Otherwise, the ambient air would hinder the subsequent plasma formation.
3. Gas injection: A gas mixture containing typical carbon carrier gases such as methane or propane is fed into the vacuum chamber.
4. Generation of the plasma: High tension from 100 to 1,000 volts is applied between the vacuum chamber and the workpiece. This ionises the injected gas, thus providing the energy necessary for the diffusion of the carbon atoms. The resulting mixture of high-energy ions, electrons and neutral particles forms the plasma.
5. Carbon diffusion: The high-energy particles in the plasma remove material atoms from the surface of the workpiece. Simultaneously, they release carbon atoms in the gas, and these can now diffuse into the component surface in accordance with the concentration gradient. This typically happens at temperatures between 300 °C and 400 °C.
6. Cooling: After reaching the desired diffusion depth, the plasma is switched off and the workpiece is cooled in a controlled atmosphere in order to further optimise the mechanical properties and prevent oxidation.

As well as combining the advantages of other case hardening processes, PACD offers additional benefits:

 

• Improved surface properties: PACD delivers increased hardness, improved wear resistance and extended fatigue resistance.
• Retention of corrosion resistance: Since this process involves diffusion rather than coating, there is no risk of flaking.
• No increased brittleness: Since it takes place without carbide formation, compared with traditional carburising methods the diffusion results in reduced brittleness of the treated surface.
• Precise process control: The precise control of process parameters such as temperature, pressure and gas composition allows exceedingly uniform carbon distribution and results that can be reproduced at any time.
• Lower temperatures: The lower process temperatures are responsible for minimised grain growth and carbide formation, significantly reducing the risk of warping.
• Environmental performance: Through the use of an enclosed vacuum chamber, PACD generates lower emissions and less environmentally harmful by-products.
• Selective case hardening: Only the workpiece surface is treated, leaving deeper layers unaffected. Moreover, the targeted treatment of certain areas is ideal for workpieces with complex geometries.
• Combination with other processes: PACD can easily be combined with other manufacturing techniques in order to optimise different component properties.

The thickness of the PACD zone achieved lies between 20 to 40 micrometres, depending on the type of stainless steel and the process parameters. Because the carbon atoms are introduced directly into the material rather than being applied as an additional layer, the corrosion resistance of the surface is retained.

 

Exceptionally high degrees of hardness can be achieved on the surface. These vary depending on the stainless steel alloy. For example, a surface hardness of over 1,100 HV0.1 can be achieved for the AISI 316 grade of stainless steel.

 

The positive properties and the relative environmental friendliness of the process make PACD relevant to a wide range of industries and areas of application:

 

• Industries: Automotive, aerospace, medical equipment, water systems, etc.
• Components: Pumps, transmissions, shafts, surgical instruments, cutting tools

The basic prerequisite for PACD case hardening is an understanding of physics, chemistry and material science which allows correct assessment of the interactions between material and process. The following challenges must be mastered:

 

• Correct process parameters: The proper temperature, treatment duration and gas composition, as well as appropriate pressure, are crucial to achieving all the desired properties on the workpiece surface.
• Different types of stainless steel: Different types of stainless steel respond differently to the PACD treatment. The respective process parameters must always be adapted to the specific alloy.
• Pre-treatment and post-treatment: Only experts can assess the impact of previously conducted pre-treatments on the PACD process, and the pre- and post-treatments which may be necessary to achieve the desired final result.
• Quality control: Stringent quality controls are essential for ensuring reproducible results and consistently high quality.

Chamber volume: 1.25 m3
Chamber dimensions: Diameter 800 mm, height 2,500 mm
Power supply: Voltage (100-1,000 V), current (10-300 A)
Temperature control: 300°C to 400°C

To ensure the success of the PACD treatment, we require information from you about the characteristics of the workpieces to be treated and about the desired properties to be achieved. Our customer service will be happy to provide you with the relevant form. The information required includes the following:

 

• Material: Which stainless steel alloy (e.g. AISI 304, AISI 316) is to be treated?
• Dimensions and geometry: What is the size and shape of the workpiece, and how many workpieces are to be hardened?
• Surface condition: Have certain pre-treatments (e.g. cleaning, blasting) been performed, or are they desired?
• Required properties: What specifications are to be achieved? (degree of hardness, wear resistance, fatigue life, etc.)
• Special requirements: Are there additional requirements, such as selective hardening of specific areas?

ALDOX offers exceptionally high corrosion resistance and gives your workpieces a refined surface ranging from anthracite to black. It is an environmentally friendly alternative to the usual corrosion protection processes such as nickel plating, chrome plating or salt bath nitriding.
 
We use ALDOX for components that need to satisfy the most demanding technical requirements - whether as a single part, in custom sizes or as batch production parts. We are happy to be at your disposal for a personal, no-obligation consultation that will help us meet your individual requirements in the best possible way.

Der Prozessablauf beim ALDOX-S-Verfahren ist nahezu identisch mit dem NIOX-Verfahren. Wir haben aber Parameter wie Temperatur, Gaszusammensetzung und Schichtaufbau angepasst, um im Salzsprühnebeltest ein optimales Ergebnis zu erzielen. So wird zum Beispiel nach dem Nitrieren die Temperatur auf Oxidiertemperatur abgesenkt.

Auf diese Weise entsteht an der Bauteiloberfläche eine 0,5 bis 2 μm dicke, dichte Oxidschicht aus Eisenoxid Fe3O4. Die Kombination aus der Nitrierschicht (Verbindungsschicht) und Oxidschicht bestimmt maßgeblich die Verbesserung der Korrosionsbeständigkeit.

Process flow ALDOX-S

ALDOX-P is distinguished from ALDOX-S by the addition of an intermediate treatment and another oxidation process. This results in the creation of a component surface with anoxide layer composed of iron oxide Fe3O4 that is 1 to 3 µm thick and offers excellent adhesion.The combination of the nitrided layer, acting as a compound layer, with this oxide layer leads to significantly improved corrosion resistance in the treated workpiece.

The optimized nitrocarburising is followed up with a post-oxidation of the workpieces . In this step, the compound layer produced in the preceding step is partially converted into an oxide layer by dwelling and cooling in an oxidising environment. The process concludes with another complete oxidation process (heating, oxidising, and cooling). This lends an additional oxide layer to the workpieces.

Process flow ALDOX-P

• Greater surface hardness
• Improved resistance to corrosion
• Increase in wear resistance
• Excellent friction and sliding properties
• High reproducibility
• Attractive dark grey to black colour
• Environmentally friendly method
• Only minimum increase in surface roughness
• Great dimensional stability
• Dimensional changes resulting from manufacturing can be factored in

The ALDOX processes allow for the treatment of a wide range of materials, including non-alloy and low-alloy steels, tool steels, cast materials and sintered iron. The treated workpieces are perfect for use in the automotive industry as well as in areas of mechanical and plant engineering.

Unlike the classic hardening of, for example, quenched and tempered steels in oil or water, which creates martensite, the purpose of the process is to create the bainite to which the process owes its name. It develops from austenite under isothermal conditions or continuous cooling below the temperature necessary for pearlite formation.
 
Bainite is categorised as lower bainite or upper bainite, based on the temperature range of bainite formation. Upper bainite consists of a mixture of needle-shaped ferrite and films of carbides that are arranged in parallel. In the case of lower bainite, the carbides are formed at an angle of 60° to the ferrite, which is arranged in plates. Based on the transformation conditions, bainite is further sub-categorised as inverse, granular, or long needle bainite.
 
Bainitising process:

• The steel is heated to a temperature between 790 - 950 °C, leading to the formation of austenite in the microstructure. This process is referred to as austenitising.
• Next, the material to be hardened is quenched in a hot bath, e.g. in a salt melt. An isothermal transformation requires a constant temperature between 220 °C and 400 °C. The exact temperature depends on the alloy and the specific position of the bainite area in the time-temperature conversion diagram. It should be greater than the martensite start temperature.
• Until the austenite has been converted to bainite as completely as possible throughout the entire workpiece, the steel remains in the quenching bath. This may take minutes or hours, depending on the temperature, the steel composition, and the dimensions of the component.
• The process concludes with cooling to room temperature. Because of the low residual stresses in the resulting microstructure, there is no need for tempering.

Bainitising is used to specifically adjust specific properties of steels and cast iron, and it offers the following advantages:

 

• Increased strength and hardness at maximum toughness
• Minimum warping (especially in thin-walled workpieces)
• Greater fatigue strength (compared to quenching and tempering in oil)
• Reduced wear and greater resistance (e.g. also against hydrogen-induced embrittlement during a coating treatment)

 

Bainitising is suitable for a wide range of applications. It is particularly suitable for thin-walled components that are exposed to high loads and require minimum warping.
 
One field of application is the automotive industry , where bainitising is used, for example, for screws and fasteners or for sheet metal parts in such safety-critical elements as seatbelt systems or seat adjusters. These elements require maximum ductility and high load capacity before breakage is to be expected.
 
Other applications include nails, springs, crankshafts made of cast iron or, in general, all components made of metal sheets and strip coils with a small cross-section.
 
Steels with a medium or high carbon content and a hardness of 35 to 55 HRC, as well as ductile iron castings, are well suited for bainitising. Examples of suitable materials can be found in the material table.

Areas of application

Bainitising is a key process for the preparation of steel in a multitude of industries. These include:

• Wind turbines
• Semi-finished metal products
• Automotive industry
• Safety engineering
• Agricultural machinery

Our locations in Germany and Europe are shown here.

Continuous treatment system:

 

Heating capacity: 500 kg/h

Belt width: 900 mm

Heated length of the furnace: 5.4 m or 7.20 m

Suitable for bulk material with up to approx. 300 g per part

Length of the parts: <200 mm

We need the following information from you:

 

• Material designation
• Required hardness (HRC) and tolerance
• Maximum permissible warping
• Hardening temperature/material data sheets and empirical values

 

If a test area is stipulated, please send us a corresponding drawing, and add a note in your order.

Oxidising is a post-treatment which follows nitriding and applies an oxide layer to workpieces, thus creating a noticeable improvement in a wide variety of properties. The process is carried out by introducing oxygen at a temperature up to 570 °C. 
 
Nitriding and nitrocarburising create a thin compound layer of only a few micrometres on the workpiece. During oxidising, the free iron molecules as well as the iron nitrides in this compound layer react with the introduced oxygen to produce stable iron oxide, which then accumulates as a thin oxide layer of no more than 3 µm on the surface of the component. This layer is extremely resistant to chemicals and, together with the compound layer, it gives the workpiece high corrosion resistance and other important properties. 
 
If post-oxidation is planned, it forms the final step of the process, immediately after nitriding. The surface must not be processed further after oxidising, as this would remove the protective layer. The formation of a compound layer during nitriding is a prerequisite for successful, long-lasting oxidation. This is because the hardened compound layer consists mainly of iron nitride, while the underlying diffusion layer contains ferrite, to which the oxide layer adheres much less strongly.

Since oxidising is a post-treatment of nitrided workpieces, all metals that can be nitrided are suitable for this process. In principle, these include all common cast and sintered materials, as well as non-alloy, low-alloy, and high-alloy steels.

 

Oxidising is a good alternative to burnishing, and can also be applied to materials that are not suitable for burnishing. Compared with burnishing, the protection against corrosion achieved by oxidising is considerably more effective. Studies have shown that it is comparable to the corrosion protection provided by a hard chrome coating with a thickness of 10 μm.

In addition to improving its mechanical properties, the process also enhances the component surface visually by giving it a colour that ranges between grey and black. The exact shade of the surface depends on the grade of the steel.

Oxidising is especially recommended for nitrided parts made of low-alloy materials where the requirements call for high resistance to wear and corrosion. These components include hydraulic cylinders, transmission spindles, and other moving and friction-loaded components.

 

As a post-treatment, oxidising offers a wide range of advantages. Especially when combined with nitriding, these have a positive effect on the practical use of the components:

• high level of corrosion protection
• excellent resistance to wear
• improved operating characteristics
• enhanced sliding performance
• visual enhancement thanks to black colouring

 

 

You will find Härtha in Germany, Italy, and the Netherlands. Refer to our interactive location overview to learn which other processes besides oxidising we offer at locations near you.

 

As a rule, only materials that can be hardened are suitable for quenching and tempering. The development of the desired martensite or bainite microstructure requires the carbon content to be at least 0.2%. Suitability for quenching and tempering is furthermore influenced by the grain size. Generally, the material used is heat-treatable steel with a carbon content between 0.35% and 0.6%. However, non-ferrous metals such as titanium alloys are also suitable for the process. Other steels are better suited for edge layer hardening.

Quenching and tempering is performed in three steps: heating to the austenitising temperature/ hardening, quenching, and tempering..

 

INFO: What is the difference between hardening and quenching and tempering?
Hardening and quenching and tempering differ in their objectives and in the last step of the respective procedure. While hardening focuses on creating a wear-resistant surface, the process of quenching and tempering aims to achieve great strength/toughness.
This difference in properties is achieved by applying significantly higher tempering temperatures during quenching and tempering. The tempering temperature during hardening is between 200 °C and 400 °C, while it ranges between 550 °C and 700 °C during quenching and tempering.

Hardening

During hardening, the component is heated at a rate of over 4 K/min until the temperature reaches at least the austenitising temperature of the material. The appropriate rate of heating is essential because raising the temperature too quickly increases the risk of cracks and warping.
 

Quenching

Hardening is followed by the quenching process. During this step, the heater material is cooled down quickly in a suitable quenching medium. Commonly used media are water, air, and oil. The quenching medium, the temperature, and the speed determine the target microstructure of the material, and its properties.

The maximum rate of cooling using mineral oil is 150-200 °C/s. The speed can be three times as high during the cooling using water.

For sub-eutectoid steels, the quenching temperature range is 30 °C to 50 °C above the AC3 temperature specified in the iron-carbon chart. For hypereutectoid steels, the temperature prior to quenching should be just above the AC1 given in the iron-carbon chart.

The thickness of the component (s) determines the dwell time (tH) in the quenching medium. The following formula helps estimate the dwell time:

If the carbon is in a dissolved state in the austenite, then the austenitising temperature can be increased to dissolve the carbides completely. This leads to the formation of martensite and embrittlement, which can be treated by subsequent tempering. On the other hand, a temperature below the austenitising temperature may result in soft ferrite nuclei in the martensite. This occurrence is referred to as soft spot formation.
 

Tempering

Tempering is used to remove the so-called glass hardness after the quenching step. The process can take place in different tempering stages. The first one is best performed immediately after quenching. The tempering temperature during this step is approx. 150 °C.

The needle martensite or the tetragonal martensite microstructure resulting from the hardening process is now transformed into a cubic martensite microstructure, with the precipitation of fine to ultra-fine carbides. The volume of the material decreases, and the grain lattice relaxes.

This prevents dislocations from sliding at high loads, and crack formation resulting from this. The secondary hardness maximum resulting from balancing hardness and toughness is attained.

Additional tempering stages can be carried out at temperatures between 200 °C and 350 °C to increase the hardness of the workpiece even further. When applied to high-alloy steels, a tempering stage above 500 °C can convert the iron carbide to more stable special carbides.

The diagram shows the material properties that can be achieved by tempering in the respective material.
 

The advantages at a glance

The quenching and tempering of materials offers the following essential advantages:

• Balance of high strength and high toughness
• High resistance to plastic deformation (thanks to high strength)
• Considerably lower risk of cracking and breakage (thanks to high toughness)

The objective of quenching and tempering is to achieve the best possible relationship between high strength and toughness. This is of particular importance for components that are subjected to particularly high loads and must possess the corresponding resistance. Examples include:

• Crankshafts
• Forged parts
• Machine parts
• Fixture parts
• Components for agricultural technology

 

 

Certain alloying elements can increase the steel’s suitability for quenching and tempering, as well as its strength. One of the most widely used heat-treatable steels is 42CrMo4, a chromium-molybdenum alloy steel.

An overview of other suitable materials can be found in the material table.

 

Would you like to commission quenching and tempering from us? We look forward to working with you and need the following information:

 

• Material designation
• Desired target hardness and properties
• Planned subsequent processing steps

 

 

Quenching and tempering is standard good practice at Härtha. Refer to our location overview for more information.

 

For PVD coating, high-purity, solid metals are used as layer materials. Depending on the desired properties of the coating, these metals may be, for example, titanium, aluminium, or chromium, as well as zirconium and silicon. This material is referred to as the target.

The composition, thickness and properties of the coating can be controlled by the selection of the target, the process parameters, and the deposition conditions. This allows regulation of such factors as the structure and hardness of the workpiece, and also its thermal resistance.

The desired coating thickness furthermore depends on the size and purpose of the workpiece. In principle, the coating can be up to 10 μm thick. For micro tools, on the other hand, the coating thickness is usually less than 1 μm.

There are different PVD coating methods, and these can also be combined. Those most commonly used are:

• Arc-PVD: During arc evaporation, an arc is created between an electrode and the coating material in order to detach particles from the target.
• Sputtering: The target is bombarded with magnetically deflected ions or electrons
• Laser: Laser beams are fired at the material in order to initiate evaporation.

At Härtha, we offer sputtering and arc coating. In principle, the different techniques all follow the same sequence of steps.

Evaporation

During evaporation deposition, the target is heated so much that the atoms on the surface are released as gas, and thus become available for the next step. Different techniques can be used to accomplish this. At Härtha, we use the arc technique.

To ensure controlled conditions and prevent interaction with air molecules, evaporation takes place in a vacuum.

Reaction

To deposit the evaporated material onto the workpiece surface, a reactive gas is now supplied, and this combines with the metal vapours. The choice of gas has an important influence on the properties of the coating. Generally, the gas of choice is either a gas containing carbon or nitrogen. These gases deliver strong adhesion, and form nitride and oxide compounds that protect against rust and corrosion.

In order to prevent unwanted chemical reactions, this step takes place in a chemically non-reactive atmosphere. This can be achieved by using an inert gas such as argon. To ensure that the coating thickness is uniform across the entire workpiece, the workpiece is rotated about multiple axes during this step.

Deposition

 
In the final step, the evaporated atoms of the target condense on the workpiece surface, forming a thin film coating.

Wear-protection coatings at a glance

PVD coatings are suitable to function as wear-protection coatings. Frequently used basic types include titanium nitride, titanium carbonitride, and titanium aluminium nitride.

An overview of coating systems and their properties can be found in our table.

PVD coatings are used across a multitude of industries and for a wide variety of components:

• Cutting tools
• Forming and shaping tools
• Plastic moulds
• Industrial components
• Automotive components
• Jewellery and watches
• Medical engineering
• Decorative and sporting applications
• Aluminium die casting

PVD coating is a surface treatment. To prevent changes to the microstructure and hardness, and to ensure dimensional stability, the material must be subjected to a heat treatment appropriate to the coating.

 

Since PVD coatings can be applied below 500 °C, the process is highly suitable for high-speed steels, hot worked steels, and some cold worked steels.

 

Even steels tempered at very low temperatures are generally suitable for coating – with special coating systems for low-temperature processes (between 250 °C and 450 °C).

The key advantages of PVD coatings at a glance:

• Great dimensional stability thanks to low coating thickness
• High adhesive strength
• Increase in wear resistance and hardness
• Reduced friction, thanks to smooth surfaces
• Coating temperature up to 450 °C
• Any type of layer structure (mono-layer, multi-layer)
• Visual refinement

At Härtha, we offer you the PVD coating and DLC coating processes. We coat workpieces of different sizes, from the micro range to a diameter of 500 mm. In addition to standardised coatings, we also develop tailor-made solutions that will fit your specific application.

We inspect all PVD coatings visually. If you require an in-depth test, we can recommend non-destructive testing methods.

Before we can quote you an offer for PVD coating or find a different coating solution for you, we need you to provide us with the following information first:

• Purpose of application
• Material designation
• Thermal pre-treatments
• Desired coating thickness in µm

Find a location near you. Our location overview shows you which Härtha locations offer PVD coating and which other metalworking processes we provide.

 

With increasingly tight tolerance ranges, rectification of steel is becoming increasingly important. It is comparable to bending. Rectification cannot be used to restore the initial state of the workpiece. Various procedures are available.

 

There are now electromechanical and hydraulically powered rectification benches that operate under computer control. This is particularly advantageous for series production. At Härtha, we use a manual straightening press .

 

Requirements

The objective behind steel rectification is to ensure compliance with a specified tolerance range for warping. Before, during, and after rectification, the component geometry and the deviations are measured manually or using an NC system. If the shape deviation of series production parts is always the same, a fixed deformation can be set without the need for measurements.
 

 

Circular rectification

Circular rectification refers to various methods for rectifying round components. Deviations are measured by means of sensors during rotation. It is important that these sensors make contact with the component throughout the measurement. Circular rectification is differentiated into rolling rectification and bending rectification.

Rolling rectification

Rolling rectification is most commonly used early in the manufacturing process of components, for example for blanks after forging. It is intended to achieve flatness in the material and reduce tensions. This type of circular rectification usually impacts the entire component.

Bending rectification

Bending rectification is intended to eliminate existing deviations by means of a targeted correction. This requires measurement of the component’s geometry and of concentricity deviations. Only then can the workpiece be correctly positioned in the rectification press. Next, the bending stroke is performed by the press. This can be done manually or using an NC system.

High-frequency hammering

High-frequency hammering is suitable, for example, for welds or for increasing the service life of components. This rectification method makes it possible to treat deformations and residual stresses in specific areas of the component. Particularly high dimensional stability can be achieved.

Moulding rectification

Moulding rectification is suitable for components that are not rotationally symmetrical, such as aluminium castings. This requires that the measuring device is calibrated to a target value. Rectification is performed by bending.
 
INFO: Rectification of pipes
The production of pipes often brings about straightness deviations which need to be rectified. In the past, the straightness of pipes was determined subjectively by visual judgement. Today, pipes often need to meet highly specific requirements. For example, a 1-metre pipe must have a straightness deviation no greater than 0.2 mm. The permissible deviations increase accordingly with the length of the pipes. These stringent requirements require the use of state-of-the-art rectification machines.

 

Rectification can be applied wherever warping occurs on steel parts – whether during thermal or mechanical metalworking. Warping can also occur during the use of workpieces. Rectification is suitable for all types of steel - from non-alloy construction steel to quenched and tempered special steel.

 

 

Depending on the procedure, rectification offers the following advantages:

 

• Great dimensional stability
• Optimum flatness
• Suitable for different component geometries
• Suitable for different types of steel

 

 

Would you like to commission our services for rectifying your workpieces made of steel, stainless steel or aluminium? Then we will first need the following information about your workpiece:

 

• Material designation
• Hardness
• Heat treatments
• Weight and quantity
• Dimensions

 

 

Refer to our location overview to find the Härtha location closest to you, and to learn which processes we offer besides the rectification of steel.

 

 

A deep cryogenic treatment makes sense only for materials containing residual austenite at room temperature. Although primarily applied on high-alloy ledeburitic tool steels, it is also used for eutectoid tool steels. In the case of non-alloy and low-alloy steels, residual austenite forms only when the carbon content is at least 0.5%.

 

A deep cryogenic treatment is usually applied after hardening. However, because of the high risk of cracking during the cryogenic treatment, this now increasingly takes place after the first tempering treatment. The objective of this process is to eliminate dispersed η-carbide particles. However, this effect has not been proven conclusively.

 

It depends on the material whether the residual austenite content should be stabilised by repeated tempering or by deep cryogenic treatment.

 

 

Steels Subjected to deep cryogenic treatment are also hardened, and they achieve dimensional stability. This is achieved by cooling to a temperature between -90 °C and -196 °C. At these temperatures, the residual austenite in the material is converted to martensite.

 

Unless the residual austenite content is reduced, it may cause changes in the microstructure and volume of the component during subsequent use. The reason for this is the soft residual austenite, which becomes converted to the harder martensite over a number of weeks. The deep cryogenic treatment of steel prevents this slow gradual change in dimensional stability. This is especially important for precision components and high-precision tools.

 

INFO: Cryogenic methods
The development of various methods has made it possible to achieve ever lower temperatures during deep cryogenic treatments. Air is cooled down as low as -60 °C in deep-freeze chests or cabinets. Temperatures can be lowered far below -60 °C by means of mixtures of alcohol, dry ice, and liquefied gas. Finally, the use of liquid nitrogen and liquid helium allows cryogenic treatment down to -196 °C and -269 °C respectively.

 

 

What happens during deep cryogenic treatment?

In deep cryogenic treatment, the cooling process after hardening is extended, in order to accelerate the rate of conversion from austenite to martensite. For this purpose, the component is generally cooled to -90 °C. To achieve an even higher conversion rate, the material can also be cooled over an extended period to as low as –196 °C. This step is followed by at least one tempering cycle.

 

This procedure transforms the previously heterogeneous microstructure into a homogeneous lattice structure. This reduces residual stresses in the microstructure. Finally, hardness and wear resistance are increased because of the higher martensite content.

 

 

 

Cryogenic treatment is primarily intended to prevent slow gradual changes in dimensional stability and offers the following advantages:

 

• Consolidation of dimensional stability
• Reduction of residual stresses
• Reduced wear thanks to increased wear resistance
• Suitable for automation, and reproducible
• Ideal for precision tools

 

 

Basic requirements for deep cryogenic treatment are a carbon content of at least 0.5 % and a sufficient content of alloying elements with a martensite finish temperature (Mf) below 30 °C. All steels that meet these requirements are suitable for cryogenic treatment. Examples are:

 

• Ledeburitic chromium steels (e.g. 1.2080, 1.2379, 1.2436)
• High-speed steels
• Eutectoid tool steels (e.g. 1.2842)

 

 

Our deep cryogenic equipment has the following dimensions:
1,150 x 750 x 600 mm/500 kg

 

 

Refer to our interactive location overview to learn which Härtha locations offer deep cryogenic treatment of steel.

 

 

Would you like to subject your components to hardening and deep cryogenic treatment at our company? We will gladly provide you with a proposal. Please tell us the material designation, dimensions, weight, and quantity of workpieces to be treated.