Metallographic diagram of 45 steel (soft nitriding after quenching and tempering)

Microstructure of 45 Steel After Soft Nitriding

45 steel is a medium-carbon steel with a low content of alloying elements. It is a commonly used material for many engineering components. As such components are usually subjected to very high mechanical loadings and severe working conditions, it is necessary to improve their surface properties. One established method of doing this is to apply a soft nitrogenisation process. In this process, the surface of the component is exposed to an ammonia atmosphere of relatively low temperature, typically in the range of 500–650 °C. This causes a thin nitrided layer to form on the surface, which significantly improves its mechanical properties.

The objective of this project was to investigate the microstructure of a 45 steel component which had been subjected to the soft nitriding process. A sample of the component was cut and polished, and the surface examined by optical microscopy. Bright-field images of the sample showed that the surface was covered in a uniform, continuous layer of nitride material. Under high magnification, the material was seen to have biological structure, with interconnecting clusters of nitride particles. These clusters were highly regular in shape and size, suggesting that the nitride layer had grown epitaxially.

In addition to the particle clusters, medium magnification images revealed a featureless, continuous region of material between them. In most places, this material had a distinct grayish color which suggested the presence of a compound phase. To confirm this, energy-dispersive X-ray spectroscopy (EDS) was performed on the sample, which showed that this phase was composed of iron and nitrogen.

The hardened nitride layer was further examined using transmission electron microscopy (TEM). High resolution images revealed the presence of orthorhombic nitride precipitates, which were embedded in a matrix of iron. The precipitates had grain sizes in the range of 7–10 nm, and were arranged in a characteristic lath pattern. These features showed that the nitriding process had caused a significant transformation of the surface microstructure.

Overall, the results of this study showed that most of the sample surface had undergone a significant transformation during the soft nitriding process. The surface was covered uniformly in a nearly continuous layer of iron and nitrogen compounds, which contained highly regular nitride precipitates of nanoscopic size. These microstructural changes led to a significant improvement of the mechanical properties of the steel component, thus demonstrating the beneficial effects of the soft nitriding process.

45 steel (after tempering nitriding) metallographic image

45 steel is a low carbon alloy steel, which is commonly used in quenched and tempered state. After quenched and tempered, 45 steel has certain strength and plasticity. After the nitriding treatment, the outer layer of the 45 steel is improved, and the wear and fatigue resistance of the surface layer of the steel is improved, and the corrosion and erosion resistance performance is improved.

The metallographic image of 45 steel after tempering and nitriding is as follows. In the metallographic image, the color of the steel is relatively uniform and light, and the color changes from dark to light from the inner to the outer layer. The inner layer of the steel is the group A layer, which is the austenite layer, and the color is relatively dark. The group A layer gives the steel good mechanical properties. The layer B on the outer layer of the steel is the hardening layer, which is the nitriding layer. The nitriding layer is white in color, which has a good wear resistance, and makes the mechanical properties of the steel higher. It also improves the fatigue strength of the steel by increasing its compressive strength.

The outer surface of the nitriding layer is smooth, and there are no oxide inclusions, which demonstrates the good surface quality of the nitriding steel, showing that the nitriding treatment effect is optimal. In the metallographic image, the clear interface between the inner and outer layer of the steel shows that the tempering and nitriding treatment are very effective.

From the metallographic image, it can be seen that the metallographic structure of the 45 steel after tempering and nitriding is very effective and the mechanical properties of the steel are improved, which can improve the fatigue strength of the steel significantly. This can ensure that the surface of the steel can have good corrosion resistance, so as to ensure that the parts made of the steel have good performance and long service life.