Effects of N and B on continuous cooling transformation diagrams of Mo-V-Ti micro-alloyed steels

• Published in: Phase transitions Vol. 85; no. 5; pp. 419 - 426
• Main Authors: Yuhui, Wang, Bo, Liao, Ligang, Liu, Xianfeng, Li, Hang, Su, Caifu, Yang, Qingfeng, Wang
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 01.05.2012; Taylor & Francis Ltd
• Subjects: acicular ferrite; Bainite; Boron; CCT curves; Cooling; Cooling effects; Cooling rate; Diagrams; Ferrite; High strength low alloy steels; Metallography; micro-alloyed steels; microstructure; Molybdenum; Nitrogen; pearlite; polygonal ferrite; Steel alloys; Transformations
• ISSN: 0141-1594; 1029-0338
• DOI: 10.1080/01411594.2011.611401

Effects of the single addition of nitrogen (N) and boron (B) and the combined addition of N and B on continuous cooling transformation (CCT) diagrams and properties of the three Mo-V-Ti micro-alloyed steels were investigated by means of a combined method of dilatometry and metallography. Microstructures observed in continuous cooled specimens were composed of pearlite (P), quasi-polygonal ferrite (QPF), granular bainite (GB), acicular ferrite (AF), lath-like bainite (LB) and martensite (M) depending on the cooling rates and transformation temperatures. Single addition of 12 ppm B effectively reduced the formation of QPF and broadened the cooling rate region for LB and M. Added N makes the action of B invalid and the QPF region was prominently broadened, and even though the cooling rate is higher than 50°C s −1 , it cannot obtain full bainite.