High-tech research exploring steel’s innermost core

March 03, 2026 | Reading time: 8 minutes

Uncovering the secrets of steel on a daily basis: in Salzgitter and Duisburg, the experts at Salzgitter Mannesmann Forschung GmbH (SZMF) analyze the microstructure of the material.

If you want to improve a material, you need to understand its inner workings. Not many people are involved quite so deeply and intensely with steel as the experts of the metallography department at Salzgitter AG. Their work is crucial – for not all steels are created equal. “Alloying, forming, and heat treatment always alter the microstructure of a material and therefore inevitably define its properties,” as Markus Krieger, Head of Material Characterization at SZMF outlines. That is why it is essential to decipher this microstructure. The patterns and colors that become visible when magnified by a factor of thousands under the optical microscope reveal to his colleagues just what makes a special steel tick.

[Translate to Englisch:] Bild von Markus Krieger — Markus Krieger, Head of Materials Characterization at SZMF

Even steel requires a little finesse

The required preparatory work is conducted by experts such as Timo Barthelmes, a metallographer at SZMF in Salzgitter. He prepares steel samples cast in synthetic resin. He is tasked with preparing the sample surface for the optical microscope so that it reflects light in an optimal manner. To accomplish this, he grinds and polishes the cut edges that are embedded in the synthetic resin. While this may sound simple, however, it is actually incredibly complex. Whether working lengthwise parallel to the line of the grain, crosswise in relation to a weld seam, or along a component defect, Barthelmes must know exactly how to prepare the sample. “Even the best microscopic analysis is worthless if preparation errors – such as scratches, deformations, or contamination – distort the true structure,” explains Barthelmes.

[Translate to Englisch:] Bild von Timo Barthelmes — Timo Barthelmes, SZMF employee in Salzgitter, prepares steel samples for the automatic preparation machine.

Expert staff active in the field of metallography and materials testing use extremely fine sandpaper with a grit size of up to 2,400. By comparison, DIY enthusiasts tend to use sandpaper that is around twenty times coarser for finishing wooden furniture. And if Barthelmes and his team ever required even greater precision, they work with automatic preparation machines.

After polishing the samples, the SZMF teams are able to detect non-metallic inclusions measuring just a few micrometers in size. These include oxygen- and sulfur-containing reaction products, oxides, and sulfides resulting from steel production. And they play a crucial role: how resistant a steel reacts under stress depends on their type, quantity, size, and distribution in the steel.

Uncovering the microstructure of steel

[Translate to Englisch:] Bild einer Topografie von Stahl im Rasterelektronenmikroskop — Not a coral reef – but zinc dendrites: these are skeletal crystals on a galvanized steel surface.

However, the metallography experts typically delve even deeper into the nature of the material: to do this, they etch the sample after polishing. This reveals the structure, or microstructure, of the steel.

Based on the microstructure they are able to draw conclusions concerning the alloy – that is, the chemical composition – of the steel. They uncover cracks and inclusions or fine precipitates that increase strength. This process can be used to determine the purity and strength of the steel, but also how well the steel can be formed. Generally speaking, the components of the microstructure determine the properties of the steel.

Scanning electron microscopes are also used in Salzgitter and Duisburg, enabling magnifications at a scale of more than 100,000:1, thereby capturing the topography of the sample surface. This dispels the commonly held notion that steel is smooth. The images reveal peaks, troughs, and proliferating structures. Thanks to their depth of field, such images are well suited for examining fracture surfaces. And when the SZMF experts are keen to analyze steels on an atomic level, they collaborate with universities and Max Planck Institutes.

How knowledge flows into new steels

When developing new steels with specific properties, experts consider how to coordinate alloying elements, deformation, and heat treatment. In order to accomplish this, they use computer-aided simulation models and material databases. The next step involves laboratory experiments and trials in a production environment. “We model the majority of steel manufacturing processes and the most important customer processing steps, both by conducting physical experiments on a laboratory scale and digitally,” explains Benedikt Ritterbach, Managing Director of SZMF.

AI: a new driving force in steel development

For some time now, the SZMF has also been focusing on digitalization and artificial intelligence, with plans to automate a number of future studies. A prime example of this is the "Gefüge-Genie" [English: Microstructure Genius] software, which has been developed in-house and is capable of analyzing microstructures using machine learning.

AI is viewed as a tool to support employees in carrying out routine tasks. This is because, moving forward, complicated samples in particular will continue to require manual human input and natural intelligence.

What holds steel together

The textured surface of steel is referred to as its microstructure. It consists of multiple individual areas, known as grains. Fine gaps can be observed in these grains, which experts refer to as pores. Foreign bodies or impurities are called inclusions. When experts talk about phases, they are referring to areas with similar composition. These are often only a few nanometers to micrometers in size. Because the etching agent – for example, nitric acid diluted with alcohol – attacks the phases and grains of the material to varying degrees, they appear under an optical microscope in different colors and shades.

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