Transformation Mechanism and Precipitation Behavior of Nanoscale Cementite in Carbon Steels during Ultrafast Cooling

• Published in: Steel research international 2022-08, Vol.93 (8), p.n/a
• Main Authors: Wang, Bin, Zhang, Xile, Jia, Tao, Wang, Bingxing, Li, Yanmei, Tian, Yong, Wang, Zhaodong, Wang, Guodong
• Format: Article
• Language: English
• Subjects: Carbon; Carbon steels; Cementite; Cooling; degenerate pearlite; Ferrite; Heat treating; Hot rolling; nanoscale cementite; Pearlite; precipitation behavior; Transformation temperature; ultrafast cooling
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.202100686

The precipitation behavior and transformation mechanism of cementite in low‐ and medium‐carbon steels (0.04–0.5% C) after hot rolling are studied using ultrafast cooling (UFC) technology. The results show that the carbon concentration and stop‐cooling temperature are the primary factors influencing the precipitation behavior of nanoscale cementite. It is found that 1) the pearlite grows discontinuously, and the nanoscale cementite is dispersed and precipitated in the 0.17% C and 0.33% C steels cooled by UFC from 953 to 873 K without the addition of microalloys, and 2) the yield strength increases gradually with decreasing UFC stop temperature. The discontinuous growth state of cementite is attained when ferrite and pearlite formation occurs alternately and competitively on the α/γ interface forefront. The growth length of ferrite when v α is equal to v p decreases significantly with the increase in carbon concentration. Moreover, the difference between the ferrite growth length and pearlite lamellar spacing decreases with the decreasing transformation temperature. The moderate carbon concentration and lower stop‐cooling temperature are more conducive to breaking up the continuity of the pearlite growth. This study of the transformation behavior of degenerate pearlite under continuous cooling conditions is more instructive for actual production. The precipitation behavior and transformation mechanism of cementite in hot‐rolled carbon steels are studied using ultrafast cooling technology. The discontinuous growth state of cementite is attained when ferrite and pearlite formation occurrs alternately and competitively on the interface forefront. The moderate carbon concentration and lower stop‐cooling temperature are more conducive to breaking up the continuity of pearlite growth.