关键词: Q890D钢, 中厚板, 调质, 硬度, 显微组织, 取向

Abstract: As a steel used in construction machinery, the uniformity of microstructure and properties along the thickness of Q890D steel medium-thick plate has an important influence on the safety and life of the steel during service. The microstructure and properties of 50 mm thick Q890D steel quenched and tempered plate from a domestic steel mill were analyzed along its thickness direction. The metallographic microstructure, microhardness, orientation distribution and defects at different positions along the thickness direction were analyzed. The results show that the 50 mm thick Q890D steel quenched and tempered plate has a significant thickness cross-section effect, showing high hardness at the surface and low hardness at the center, respectively, which is the comprehensive result by the difference of microstructure and orientation. After quenching and tempering, the surface of the steel is dominated by tempered lath martensite with high defect density, while the center is dominated by tempered lath martensite and a small amount of bainite with low defect density. In addition, the surface of the steel has a clear [001] preferred orientation, while the center of the plate shows a less obvious [101] preferred orientation. The thickness cross-section effect is related to the temperature gradient during the quenching and tempering process. Large cooling rate on the surface is easy to form martensite, while slow cooling rate in the center is easy to form bainite. The transformation constraint effect of martensite on the surface is obviously smaller than that in the center, so a differentiated preferred orientation is shown along the thickness direction.

Key words: Q890D steel, medium-thick plate, quenching and tempering, hardness, microstructure, orientation