超快冷处理低合金Q345B钢的折弯开裂失效分析与对策

Failure analysis and improvement of bending cracking of low alloy Q345B steel treated by ultra-fast cooling process

利用扫描电镜对超快冷工艺生产的Q345B钢弯曲失效开裂的断口形貌、显微组织和钢中的夹杂物进行了分析。结果表明,Q345B钢中存在超标的大尺寸夹杂物诱发了弯曲变形过程中裂纹的萌生,而超快冷工艺产生的网状渗碳体和粒状贝氏体硬相组织降低了Q345B钢的塑性和韧性,促进了裂纹的扩展。通过延长LF工序精炼时间和控制超快冷工艺冷却速度及提高终冷温度,使钢中夹杂物尺寸大大降低,显微组织转变为铁素体和珠光体组织,从而提高了Q345B抗弯曲性能。

Fracture morphology,microstructure and inclusions of bending cracking of Q345B steel treated by ultra-fast cooling process were systematically analyzed by scanning electron microscopy. The results show that a lot of large-size inclusions are observed in the Q345B steel which causes the crack initiation during bending deformation. However,the hard-phase microstructure including network cementite and granular bainite are produced during ultra-fast cooling process reduces the plasticity and toughness of the Q345B steel and promotes further the crack propagation. By extending refining time of LF process,controlling ultra-fast cooling rate and increasing the final cooling temperature,the inclusion size in the steel is greatly reduced,and the microstructure is transformed into ferrite and pearlite,thus the bending resistance of the Q345B steel is improved greatly.