Intrinsic Mechanisms of Ductile-brittle Transition for F460 Steel Welding Coarse Grained Heat Affected Zones with Different Heat Inputs

• Main Authors: LI Jing, CAO Rui, MAO Gao-jun, LIU Dong-sheng, CHEN Jian-hong
• Format: Article
• Language: zho
• Published: Journal of Materials Engineering 2016-08-01
• Series: Journal of Materials Engineering
• Subjects: F460 steel; welding coarse grain heat affected zone; ductile-brittle transition; critical event; cleavage fracture stress
• Online Access: http://jme.biam.ac.cn/CN/10.11868/j.issn.1001-4381.2016.08.012

Coarse grain heat affected zone (HAZ) of F460 steel was simulated by a Gleeble 3800 thermo-mechanical simulator. The microstructure, critical event of the HAZ formed at various heat inputs (<i>E</i>) were characterized and determined by optical microscopy (OM) and scanning electronic microscopy (SEM), and cleavage fracture stress <i>&#963;</i>_f was also calculated by ABAQUS software. Based on above systematic analysis, the intrinsic mechanism of ductile-brittle transition for F460 steel heat affected zones with different heat inputs were revealed. The results indicate that:with the improvement of heat input, the microstructures in sequence are a minority of lath martensite and massive fine lath bainite, more lath bainite with less granular bainite, more granular bainite with less lath bainite, bulky of granular bainite; and the maximum size of the original austenite grain and bainite packet becomes bigger with the improvement of heat input. The size of bainite packet is critical event of the cleavage fracture for coarse grain heat affected zone specimens with various heat inputs by comparing the relationships among residual crack length, original austenite grain size and bainite packet size. With the decreasing of the bainitic packet, the ductile to brittle transition temperature decreases. In addition, cleavage fracture stress <i>&#963;</i>_f is also calculated by ABAQUS software, <i>&#963;</i>_f gradually decreases with the increase of the heat input, which can explain the intrinsic mechanism of ductile to brittle transition temperature <i>T</i>_k with the change of the heat input.