Technology
REDUCTION OF GAS CONSUMPTION IN HARDENING TECHNOLOGY THROUGH THE USE OF INNOVATIVE GAS MEASUREMENT TECHNOLOGY
Nils Bernhagen, Bora Özkan, Alain Barillet and Professor Gerhard Wiegleb introduce the GreenFlow System from Ipsen and explain how it can perform high-quality surface treatments on steels
Hardening steel is a process for enhancing mechanical resistance by specifi cally altering and transforming the microstructure.
The most important alloying element added to iron to produce steel is carbon. The hardening process can be carried out very effi ciently and reproducibly by heat treatment in a defi ned reaction gas atmosphere, which makes it possible to specifi cally adjust the carbon content at the surface of the workpiece.
Atmosphere furnaces are therefore increasingly being used in hardening technology to ensure a controlled gas atmosphere for an optimal hardening process.
However, this also requires a gas supply system that can meet these high demands.
Introduction
During the hardening process, elemental carbon [C] is deposited and embedded in a thin layer of the workpiece through a defi ned surface reaction at T>750°C.
Carbon monoxide CO can be used, for example, to initiate this chemical reaction from the gas phase.
First, the CO is adsorbed on the surface and then decomposes into its elemental components.
CO→[C]+O2- (1)
This process can be optimised by measuring oxygen in situ [1,2]. The elemental oxygen O2-
then reacts immediately with another CO molecule to form CO2 (2) .
This process is described by the Boudouard equation (1): 2CO→[C]+CO2
This process can therefore be monitored and controlled by measuring CO2
. Furthermore, carbon monoxide can also react with hydrogen (H2 CO+2H2→[C]+H2 O (3)
This reaction pathway can therefore also be monitored using water vapour measurement.
The embedded carbon must have narrowly defi ned carbon content (C level) to achieve a high-quality surface fi nish.
A typical value for the edge carbon content is 0.7% C. However, in order to accelerate the carburisation process, which takes several hours, carburisation is carried out at C levels of approximately 1.1% C and only reduced to 0.7% C towards the end of the process for about one hour.
During this process, some of the initial excess carbon diffuses into the interior of the component, while another part is removed again by the gas. Precise and rapid control of the atmosphere in all process steps is therefore a basic prerequisite for the success of the process.
The GreenFlow system
The GreenFlow system [3] measures and regulates the gases present in equations 1-3. In particular, the required gas supply is reduced to a minimum.
Figure 1 shows a typical design of an industrial hardening furnace with a specifi ed gas atmosphere. The gas fl ow is adjusted so that there is an excess of process gas, even if this is not always needed.
Gas consumption is therefore very high, resulting in unnecessary operating costs.
)
to form water vapour and release elemental carbon. This reaction is described as heterogeneous water gas equilibrium:
Figure 1: Basic design of an atmospheric furnace with a specifi ed excess gas fl ow
The Ipsen GreenFlow system is an innovative solution that signifi cantly reduces process gas consumption and optimises furnace processes.
, which not only signifi cantly lowers operating costs but also makes a sustainable contribution to environmental protection (fewer CO2
emissions).
The following options are available for use in a gasifi cation system:
• Endogas2 • Nitrogen/methanol The endo gas is produced on site using a generator (EndoSave® from natural gas (CH4
) or propane (C3 conversion, air oxygen O2 CH4+2.5(0.2O2+0.8N2 )→CO+2H2 H8 ). For catalytic
is also added to a ratio of 1:2.5. +2N2
(4) Endogas produced from natural gas (CH4
composition at a dew point of 5°C: • 19.8 vol.% CO
• 0.26 vol.% CO2 • 38.3 vol.% H2 • 0.85 vol.% H2
) then has the following
This innovative system reduces the amount of gas required by up to 80%1
)
O
• Rest N2 After loading the system, the furnace atmosphere is analysed in detail.
10
IET - JANUARY / FEBRUARY 2026
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