Effect of Heat Treatment on Microstructure and Mechanical Properties of a 12 wt.% Cr Cold Work Tool Steel
摘要
The X200Cr12 steel, widely used for cold working tools such as cutting blades, dies, and punches, is subjected to severe mechanical conditions including repeated impact loads, abrasive wear, and high compressive stresses, which often lead to premature damage such as chipping and edge flaking. Its initial microstructure, composed of hard and insoluble eutectic carbides of type M7C3 dispersed in a ferritic matrix, gives it excellent formability properties. Although heat treatments, such as quenching and tempering, help to develop the desired mechanical properties, the alloy remains constrained by the presence of retained austenite, which simultaneously reduces hardness and toughness. The mechanical and microstructural properties were evaluated using methods such as hardness testing, optical microscopy, scanning electron microscopy, and X-ray diffraction (XRD). This study aims to understand the impact of heat treatments, particularly double tempering, on the evolution of retained austenite and the microstructural transformations of this steel. The samples were austenitized at temperatures ranging from 940 to 980 °C, followed by oil quenching, and then subjected to tempering cycles between 300 and 450 °C. XRD analysis was used to monitor the evolution of retained austenite at different stages of the heat treatment. Tempering at 400 °C led to the most pronounced microstructural transformations and mechanical enhancements, making it the most effective among all the studied tempering temperatures. A significant reduction in retained austenite was observed in the double-tempered samples, leading to a more stable microstructure and a notable improvement in mechanical properties.