Carburising and Nitriding of Iron Alloys

Our civilisation is changing and developing, and with this, the expectations of the societies of different countries are changing. The social transformations over the centuries are so significant that, in sociological and economic sciences, the successive stages in the development of societies have been given names of their own, in the likeness of industrial revolutions. A material world capable of satisfying human needs cannot exist without the material and the process and equipment necessary for its technological production.

The importance of improving the functional properties of steel was understood in ancient Greece and intensively developed in the Middle Ages. The Industrial Revolution, which began with the English textile industry, only increased the importance of mining, steelmaking and metallurgy. The development of thermo-chemical treatment was closely related to the increase in knowledge about diffusion phenomena and research equipment for examining the structure of materials. In the twentieth century, carburising, nitriding and other diffusion treatments had wide industrial applications in the machinery, automotive, tool and aviation industries. Currently, PLC controllers control and monitor chemical treatment devices and the way they work. The development of computer computing techniques has accelerated the prediction and control of processes.

It is estimated that there are 200,000 carburising plants operating in the global industry, 75–80% of which are atmospheric plants and 15–20% of which are vacuum plants. A gradual process of replacing operationally worn atmospheric plants with vacuum plants is also being observed, which will increase the market share of low-pressure carburising technologies. This will force a gradual shift away from this technology, just as global trends are moving away from sources of fossil-based raw materials and energy (natural gas, oils). In the second half of the twentieth century, new designs of carburising equipment were developed that precisely implemented the process conditions more efficiently and more ecologically. For the optimisation of the carburising process, further work seems to be possible only by optimising numerical calculations, as is the case with low-pressure carburising technology, where an efficient and effective method of process utilisation is achieved by integrating the technology with computer-based optimisation and simulation systems. Currently, the challenge for carburising is producing short series and diverse products. This is an even greater challenge for device design than for the process.

The main flywheel of the quenching methods progress is the need to reduce or at least control quenching deformations and thus ensure the quality and reduce unnecessary costs during the production stage. The literature analysis shows that the further development of quenching methods will be closely linked to the applications of computational techniques, both in the area of designing optimal heat removal from the component, reducing quenching deformations and building equipment to conduct them. Additionally, civilisation’s growing concern for the ecological aspects of production may be a reason to move away from traditional oil quenching towards gas quenching, as long as there will be ready-made solutions for gas quenching with cooling intensities analogous to those of oil. In terms of improving the uniformity of hardened layers in surface hardening, devices for unit gas quenching are of interest to the industry. They are an interesting option for micro-factory, i.e. local factories, where a wide range of items is produced in the same factory for the local market.

Economic factors are probably the strongest motivator for technology development. Since production costs are influenced (leaving aside the cost of human labour) by run time and the amount of energy consumed, raw materials and consumables used, the need to reduce all these factors was clearly recognised at the dawn of the twenty-first century.

Computer-aided reproduction of thermo-chemical treatment processes and phenomena helps to predict the properties of materials with a considerable reduction in financial outlays and the time needed for further experiments and implementation. In the near future, there will be an increasing demand for effective, precise and easy-to-handle computational tools for predicting and designing thermal and thermo-chemical low-pressure treatments. Both conventional and numerical models, as well as those of the data mining type, are already widely applied in modelling such processes. The constant growth of the computational capacity of computers favours the development of numerical methods. It is expected that results will be obtained by numerical methods more quickly and more accurately. This process is favoured by the development of knowledge of low-pressure treatments, which enables the establishment of coefficients describing the process in individual devices with greater precision.

According to the Industrial Heating Equipment Association (IHEA), heat and thermo-chemical treatment accounts for 2–15% of total production costs.

The global directions for improving heat and thermo-chemical treatment processes and materials in 2000–2020 included a few crucial aspects.