Metallographic Analysis of DIN(DEUTSCHES INSTITUT FÜR NORMUNG e.V.) X5CrNi18-10 Steel
Metallographic analysis has been used in the study and evaluation of structural materials for many years. It is a powerful and cost-effective form of material characterization. In this paper, metallographic analysis is utilized to study and evaluate DIN(DEUTSCHES INSTITUT FÜR NORMUNG e.V.) X5CrNi18-10 steel.
DIN X5CrNi18-10 steel is an austenitic stainless steel which contains 18.50% chromium, 8.00% nickel, and 0.030% nitrogen. This steel is often used in the production of medical and food processing equipment, as well as chemical and petrochemical processing. The chemical composition of the steel was determined by optical emission spectrometry (OES).
For the metallographic analysis, a sample of this steel was heat treated at 1050 °C and quenched in oil. A metallographic cross section was prepared and polished using standard metallographic procedures. The cross section was then etched in an aqueous solution of 2.5% nitric acid and 2.5 % hydrofluoric acid for 10 seconds.
The metallographic cross section revealed a microstructure of nearly uniform ferrite and a few large ferrite-austenite grains. The grain size was determined to be about 26 μm. It was observed that the grain boundaries were well-defined and sharp. Martensite was also present in small amount, which indicates that the steel was able to reach its full hardness during the heat treatment process.
The polished cross section was then etched with a 10% solution of potassium permanganate (KMnO4). This revealed the presence of chromium carbides, which were distributed in a uniform manner throughout the microstructure. The carbides appeared as dark gray inclusions which were slightly larger than the surrounding ferrite grains. The chromium carbides were found to be well-distributed throughout the grains, indicating that the steel was properly heat treated.
Scanning electron microscope (SEM) images were also taken to further investigate the microstructure. This analysis showed that the chromium carbides were in contact with the austenite but not with the ferrite grains. This indicates that the chromium carbide precipitates within the ferrite-austenite boundaries were able to remain relatively stable even after the heat treatment.
Overall, the metallographic analysis of DIN X5CrNi18-10 steel revealed a uniform ferrite microstructure with well-defined grain boundaries and scattered chromium carbides. The grain size of the ferrite was determined to be about 26 μm, and the chromium carbide precipitates were found to be well distributed throughout the grains. The SEM images confirmed that the chromium carbides were in contact with the austenite grains but not with the ferrite grains. These observations suggest that the heat treatment was successful in achieving the desired microstructure.
