Study of the Influence of Quenching Cooling Medium and Tempering Temperature on the Microstructure and Mechanical Properties of DIN X20Cr13 Steel

Abstract

DIN X20Cr13 martensitic stainless steel tubes are widely used in oil and gas services because they combine mechanical strength, corrosion resistance, and microstructural stability. This study examines the effects of quenching media (still air and forced air, considering air and not merely a simple cooling medium) and tempering temperatures (600, 650, and 700 °C) on the mechanical behavior of this material. Tensile, impact, and Rockwell C hardness tests were carried out. Furthermore, the microstructures were characterized by x‑ray diffraction, optical microscopy, and scanning electron microscopy. The experimental data were analyzed using a full factorial design. The results indicated that forced‑air quenching favored the formation of a higher martensite fraction, which increased strength and produced a finer, more uniform structure. Tempering at 600 °C led to partial martensite breakdown and progressive carbide precipitation, causing hardness loss but improving toughness. Under the examined conditions, forced‑air quenching followed by tempering at 600 °C exhibited the highest yield strength of about 770-1020 MPa but the lowest impact toughness (≈ 7-20 J). In contrast, tempering at 650 °C provided the best strength–toughness balance for DIN X20Cr13 tubes in oil and gas service, achieving 734-835 MPa in yield strength and approximately 15-20 J in impact energy.