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?

Heating directly in the workpiece by inductive hardening

The heating needed for inductive hardening takes place within the component itself. This makes it possible, for instance, to restrict the hardening specifically to the interior or the exterior surfaces of a component. This is accomplished through induction. For this, a copper coil is used to generate an alternating electromagnetic field. The electrical resistance in the component causes the development of heat, which can be used to reach the specific hardening temperature.  
 

Hardening procedure

Unlike other hardening processes, induction hardening takes place in sequences. This means that each segment of the area to be hardened can be heated in turn by repositioning the inductor and quenching the segment using a sprinkler.
 
Depending on the size of the component and inductor, the workpiece can also be gradually slid through the inductor. It may also be necessary to perform a rotary motion during this process (e.g. for shafts).
 
The stresses in the steel are subsequently relieved at low temperature or by tempering.

Brief heating and dwell times ensure very low oxidation. Formation of the desired microstructure requires that the dwell time and hardening temperature are set in the correct relationship. This relationship depends on the type of the material, and especially its carbon content. The typical temperatures lie between 800 °C and 950 °C
 

Discover some of the major advantages of inductive hardening:

• Locally limited hardening easily possible
• Quick processing time thanks to short process duration
• Slight warping and minimum scale formation
• Suitable for automation, and reproducible

Inductive hardening is ideally suited for components with complex geometries and tools that are exposed to extreme wear in certain places. For example, the blade of a pair of pliers is suitable for induction hardening. Further application examples include bolts, crankshafts, gear wheels, valve tappets, and rollers.

Quenched and tempered steels selected for inductive hardening must have a carbon content greater than 0.3 %.
 
Suitable materials include:

Material number	Short name	Steel grade	HRC
1.0503	C45	Quenched and tempered steel	48-58
1.7225	42CrMo4	Quenched and tempered steel	48-60
1.3503	100Cr6	Ball bearing steel	50-65
1.8159	50CrV4	Quenched and tempered steel	48-60
1.2826	60MnSiCr4	Collet steel	48-58

We are delighted that you wish to commission inductive hardening from us. To complete your order, the information required includes:

• Material designation
• Nominal value for the surface hardness
• Nominal value for the hardness depth
• Identification of drill holes near the surface
• Is tempering also required?

For further information required, please refer to the printed order form, which we will be happy to provide.

Refer to our location overview to learn at which Härtha locations we perform inductive hardening.

During carbonitriding, the steel component is heated in a gas mixture composed of 0.5% to 0.8% carbon and 0.2% to 0.4% nitrogen. This causes the carbon and nitrogen to diffuse into the steel surface. The component is afterwards quenched in water, oil, or a salt melt. The process concludes by tempering the component at 160 °C to 300 °C in order to reduce brittleness.

Compared to carburising, carbonitriding requires lower temperatures, between 820 °C and 900 °C, and is also generally shorter. These are ideal prerequisites for minimum warping. What is more, the nitrogen lowers the cooling rate that is critical for the formation of martensite, resulting in improved hardenability.

The hardness penetration depth depends on the general hardenability of the steel grade, the component geometry, the carbonitrided layer, the hardening temperature, and the cooling rate. The maximum hardness penetration that can be achieved with carbonitriding is 1.0 mm.

 

Steps of the carbonitriding process

 

Categorisation of carbonitriding heat treatment

Despite the name of the process, carbonitriding is not a nitriding process. Instead, carbonitriding is a hardening process. This is due to the low amount of nitrogen absorbed into the microstructure. The result is that no compound layer forms during heating. In fact, the hard edge layer forms during the quenching process.

 

The advantages at a glance

Carbonitriding offers many advantages for the treated components:

• The hardenability of alloy and non-alloy steels is increased by the enrichment with nitrogen and carbon.
• The edge layer becomes harder and more wear-resistant than that produced by case hardening.
• Only slight warping thanks to lower temperatures compared to case hardening.
• No cracks, thanks to milder quenching media.
• Improved emergency running properties and better friction wear resistance
• Greater tempering resistance as a function of the nitrogen diffused into the edge layer.
• Ideal for the series production of small components that require a clean environment.

Carbonitriding is used to increase the fatigue strength and wear resistance of various grades of steel. The process is of particular interest for components whose case hardening depth is intended to range between 0.1 mm and 1.00 mm. It is very suitable for mass production and for small workpieces.

Examples of components typically treated by carbonitriding include pistons, rollers, shafts, gear wheels, and levers for various types of drive mechanisms.

Carbonitriding is suitable exclusively for steels with a maximum carbon content of 0.25%. Primarily, these are non-alloy and low-alloy case-hardened steels, as well as sintered, construction, and machining steels.

In our material table you can see an excerpt of suitable materials.

Would you like us to perform carbonitriding for you? To complete your order, we need the following information:

• Type of material
• Desired case hardening depth
• Target edge hardness
• Where relevant, the insulation requirements 

We will firstly advise you whether the desired hardness values can be realised for your type of material. Afterwards, you will receive our ordering form including all other necessary information.

Refer to our location overview to learn which Härtha locations offer carbonitriding.

Edge layer hardening designates the partial hardening of metal components in their edge layer. The process is synonymous with surface hardening. The surface is heated to its austenitising temperature and then quenched. The core remains largely unaffected by this procedure.

The process creates various layers with different properties in the workpiece – the tough primary material in the core, and the hardened surface with significantly greater wear resistance. This combination of properties is ideal for components subjected to great mechanical strain, such as gear wheels and presses.

Edge layer hardening involves hardening by austenitising followed by a subsequent formation of martensite, i.e. a change of the microstructure. In contrast, nitriding does not result in a change of the microstructure, but in a chemical change in the edge layer.

 

Technical details

Only quenched and tempered steel with a carbon content of at least 0.45% is well suited for edge layer hardening, as this process involves no external supply of carbon. As a general rule, the hardenability of steels depends on their carbon content. This content can be increased by carburising.

The appropriate temperature for edge layer hardening depends on the material. It is 50 to 100 °C higher than the hardening temperature of the respective steel grade. The material is heated by induction, laser beam, electron beam, or flame.

To reduce stresses and brittleness, hardening can be followed up with annealing or tempering. These steps make it possible to regulate individual parameters for the workpiece.

Steels subjected to edge layer hardening provide a number of attractive benefits:
 

• Their general durability and fatigue strength increase, because the component becomes more resistant to wear.
• Residual compressive stresses and tensions increase the vibration resistance of the component surface.
• The rigidity and resilience of the use surfaces are improved by the increased surface hardness (which is important, for instance, for the rolling surfaces of gear wheels).
• In addition, subsequent grinding can provide even greater precision and higher surface quality.

Edge layer hardening process without changing the chemical composition

 

Induction hardening/inductive hardening

The basic principle behind induction heating is the heating of the workpiece surface using alternating magnetic fields. The hardening takes place during the subsequent quenching process. Inductive hardening is an excellent option for the mass production of components, because it is ideally suited for automation and high throughput.

 

Process: Inductive hardening

 

Edge layer hardening is a standard process at Härtha. What sets our process apart is the inductive hardening. We will be happy to advise you on hardening processes that fulfil your specific requirements.

 

Laser and electron beam hardening

Electron beam and laser beam hardening are particularly well suited for small workpiecesthat require only shallow hardening depths.

Both laser beams and electron beams can be used to heat the steel surface until it reaches its austenitising temperature - by means of point-by-point or plane heating. Heating with laser beams or electron beams is very fast. The rapid speed facilitates quenching, which takes place almost by itself through the slow heat conduction.

 

Caption: Process: Laser hardening

 

Process: Electron beam hardening

 

Thermochemical diffusion treatment with change of chemical composition

• Case hardening

Hardening of the edge layer by carburising using carbon and subsequent hardening and tempering

 

• Nitriding

Hardening of the edge layer with nitrogen feed

 

• Carbonitriding

Hardening of the edge layer with carbon and nitrogen supply, and subsequent hardening and tempering

 

• Low pressure carburising (LPC)

Hardening of the edge layer in a vacuum furnace with hydrocarbon

For case hardening, carburising is of key importance, i.e. the enrichment of the component’s edge layer with carbon. A high-carbon environment is essential for this process. During carburising, the carbon content at the edge continues to drop relative to the core.

 

Structure and functional principle of case hardening in a gaseous atmosphere

 

Learn more detail about the individual process steps from carburising to tempering:

 

Carburising

The prerequisite for carburising is a suitable medium capable of diffusing carbon into the component. This medium can be solid, liquid, or gaseous – such as carburising powder, a salt melt, or a mixture of gas containing methane.

Case-hardened steels are particularly well suited for carburising. The component in its austenitic state is heated to temperatures between 880 °C and 950 °C. At temperatures above 950 °C, the process is referred to as high-temperature carburising.

 

 

This process primarily involves the enrichment of the component’s edge layer with carbon, which further diffuses towards the core as the process proceeds. However, the core usually retains its original carbon content as per the carbon content of the steel grade used. The standard carburising depth varies between 0.1 and 2.5 mm.

 

Steps of the case-hardening process

 

Hardening

Carburising can be followed by a slow quenching of the component, with subsequent hardening . Another alternative is direct hardening. During this process, the temperature of the workpiece after carburising is lowered to the hardening temperature for the edge layer, and rapidly quenched afterwards.

The objective behind case hardening is to create a surface of great strength and hardness. However, it is intended that retains its toughness. The target hardness of the edge layer depends primarily on the amount of carbon that can be enriched. This in turn depends on the basic hardenability of the selected grade of steel.

However, the quenching medium plays an important role as well. Suitable mediums include a salt melt, water, and oil, as well as helium and nitrogen. The next step in the process is tempering.

 

Tempering

Tempering is the final step in the entire process. This step is required for relieving the stresses produced in the edge layer during carburising and hardening. This step increases ductility. The tempering temperatures used during case hardening generally range between 160 °C and 400 °C.

 

The advantages at a glance

Case hardening is beneficial to the treated workpiece in a variety of ways. The most essential benefits are:

• A hard edge layer resistant to wear combined with a core of great toughness can be ensured.
• Specific properties such as individual hardness depth can be adjusted flexibly.
• Bending fatigue resistance and fatigue strength are increased.
• The use of a masking compound allows easy partial hardening of selected areas.

 

 

Alternative methods

Apart from case hardening, there are other suitable alternative hardening processes, depending on the intended application or the material.

These include inductive hardening, which is a particularly good choice for hardening single parts. In contrast, case hardening makes it possible to treat many components simultaneously.

Another option is carbonitriding, a variation of case hardening. This process uses nitrogen in addition to carbon in order to harden the edge layer.

Case hardening makes it possible to combine reliable bending fatigue resistance and a high degree of wear resistance with great fatigue strength. These characteristics make case hardening ideal for workpieces that are subjected to great dynamic stresses and that interact significantly with other parts. This is the case, for instance, with gear wheels or other components used in engines.

Because the objective of case hardening is to increase the carbon concentration in the edge layer of the workpiece, steels with a relatively low carbon content and that interact significantly with other parts are particularly suitable. This applies especially to non-alloy or low-alloy steels with a carbon content less than 0.25%, and to high-quality construction steels and case-hardened steels with a low carbon content.
 
An extract of typical materials for case hardening can be found below in the material table.

What depths can be attained with case hardening?

The typical hardness depths achieved with case hardening vary between approx. 0.1 mm and 2.5 mm.
 

How long does case hardening take?

The duration of the individual case-hardening processes, i.e. carburising, quenching, and tempering, may vary depending on the type of material and the desired case hardening depth. The carbon diffusion alone during carburising takes several hours. Ask us about the specific conditions for your particular application.

Would you like us to case-harden your material? For this the information required includes:

• Material designation
• Desired case hardening depth (CHD)
• Desired edge hardness
• If applicable, a workpiece drawing identifying the location not intended to be hardened

You will find all necessary information in the ordering document, which our customer service will be happy to provide.

You will find our process locations here.

Low pressure carburising (LPC) is an alternative to case hardening under protective gas. The steel is heated in a carburising atmosphere to a temperature between 900 °C and 1,000 °C. This leads to an enrichment of the edge layer with carbon. This enrichment increases the hardness of the component surface, while keeping the core malleable. This is usually followed by processes for hardening and tempering.

The combination of the acetylene carrier gas and the vacuum furnace makes low pressure carburising emission-free in terms of CO2, and thus counts as environmentally friendly.

 

The advantages at a glance

• Uniform case hardening depths even on components with complex geometries, holes, and blind holes
• No intergranular oxidation layer thanks to dry quenching
• As the component surface is exceptionally clean, there is usually no need for subsequent grinding
• Increased hardness under the surface and faster than alternative carburising methods
• Enhanced fatigue properties
• Little warping
• Environmentally friendly (no CO2 emission)
• The hardness and case hardening depth can be regulated with precision

Low pressure carburising is of particular interest for components where an exceedingly uniform surface is of great importance. Because this process ensures an exceptionally uniform carburising layer, it is the preferred option for oil pump gears and transmission gearing. However, it is also used for nozzles, injection valves, and axles.

 

Below is a brief overview of some types of material that are particularly well suited for low pressure carburising.

Maximum batch size:

900 mm x 600 mm x 800 mm

Maximum batch weight:

600 kg

Operating temperature:

500 – 1,250 degrees

Initial cooling pressure:

1 - 20 bar

Nitrogen or helium

If you would like us to perform low pressure carburising (LPC) for you, the information which we require includes:

• Material designation
• Case hardening depth
• Nominal values for edge hardness

For all other information which we require, please refer to the ordering form, which we will be happy to provide upon request.

Härtha operates with various locations across Europe. Refer to our location overview to learn which processes we offer at which location.