NANO-SIZED CARBIDE PRECIPITATES IN HIGH-STRENGTH LOW-ALLOY STEELS

摘要

In the present work, the nano-sized carbide precipitates in three high-strength low-alloy (HSLA) steels with different rolling thicknesses (12 and 25 mm) and chemical composition (Ti and Nb-Ti steels) were obtained by using nondestructive electrolysis extraction technology and their precipitation behaviors were discussed. The results show that a large number of M_3C precipitates, which are needle- and flat-shaped, and MC precipitates, which are quadrilateral, exist in the HSLA steel. The average sizes of M_3C precipitates are smaller than those of MC precipitates. The average size of M_3C and MC precipitates rises with the increase of rolling thickness, while their mass fractions remain stable. Besides, the average sizes of M_3C and MC precipitates in the surface decrease by 25% as compared to those in the center. Furthermore, after adding a small amount of Nb element, a (Ti, Nb)C complex carbide is formed, which substantially increases the mass fraction and average size of MC precipitates.