Quality assurance for process-relevant refractory materials
14.12.2022 | Salzgitter Flachstahl GmbH
To produce steel in an integrated steelworks such as that operated by Salzgitter Flachstahl, in addition to raw materials such as ore, coal and scrap, a large number of other process materials and products are also required. One essential type of material, without which the steel production process would not function, is refractories. These materials make an major contribution to the reliability and quality of the finished products.
In principle, refractory materials are used wherever processes take place at high temperatures. Refractory products are therefore defined as non-metallic, ceramic materials with a cone drop temperature of ≥ 1500 °C. In practice, however, all products suitable for use within a temperature range of between 600 °C – 2000 °C are generally referred to as refractories.
Forms of refractory materials
Various types of refractory products are used at Salzgitter Flachstahl, whereby each application makes different demands on the material. In principle a distinction is drawn between 4 types of product: Shaped products including converter and ladle bricks are materials that are delivered to the steelworks in their final form. Unshaped products include types of refractory concrete which are mixed with water or a binder and cast in situ. Examples include the lining of the blast furnace troughs and the tundish troughs featured in continuous casting. So-called key components include products that are more complex in shape than pre-formed products and are used at “key points” in the production process. Examples of these include slide gate plates at the converter which control tapping, or immersion spouts used in continuous casting which protect the liquid steel from oxidation and guide it from the tundish into the mold. The last product group is comprised of insulation materials. In contrast to the other product groups, these are not in direct contact with the liquid melt; they serve to protect the metallic exteriors of the plant modules against high temperatures.
Significance of refractory materials for product quality
Given that refractory materials are in direct contact with the items being produced, they have a direct or indirect influence over product quality. Another important aspect is the protection of plant modules against (premature) failure or damage to machinery. In view of these factors, quality assurance and the use of the “right” materials is eminently important.
The laboratory as the guardian of quality
The most important refractory products such as ladle bricks and blast furnace mixes, etc. are therefore typically quality-tested in the refractories laboratory. Each application has its own particular program of tests which includes the individual temperature, contact media and the properties to be tested. This database serves on the one hand to minimize risk and provide an analysis of possible damage, but also as a means by which to directly contact the supplier in case of fluctuations in quality.
Through intensive communication with the individual plant operations in which refractories are used, there is constant coordination of the testing methods in the laboratory and immediate feedback in the event of anomalies.
In addition to regular quality control, the refractories laboratory can also provide concrete information as to whether it would be advantageous or meaningful to use new materials available from the refractory supplier.
Another important task for the refractories laboratory is for example to play a role in the relining of major plant such as for example a blast furnace. The first task is to select suitable refractory materials. The materials selected are then checked on arrival and an acceptance conducted on the supplier’s premises. And of course the laboratory provides technical support for the relining itself.
The transformation to low-CO2 steel production also heralds a major new development in refractory technology. The change in the process of producing steel results in new challenges for the refractory material. In order here too to be able to make a well-founded choice of refractory material, the focus during procurement and testing will in particular be on adjusting the atmospheric conditions including the use of hydrogen.