X120管线钢回火过程中断口分离问题研究

针对一种高强度X120管线钢高温回火条件下出现的夏比冲击试样断口分离现象。利用扫描电镜、透射电镜及冲击试验机等，从磷、硼、锰等元素的偏析，晶界处第二相如碳化物、合金析出物等的析出及长大角度进行讨论分析。研究结果表明：随回火温度升高，断口分离加剧，分离平均长度及数量增加。夏比冲击功降幅达60％；断口分离先于主断口形成，导致试验钢表面能增加，刚度、主断口裂纹形成功及裂纹扩展功下降；磷、硼、锰等元素在晶界偏聚引起的回火脆性导致分离裂纹产生，夹杂物对分离起促进作用，尺寸较大的第二相弱化了晶界强度。

RESEARCH ON FRACTURE-SEPARATION PROBLEM IN TEMPERING PROCESS OF X120 PIPE LINE STEEL

The scanning electron microscopy （SEM）, the transmission electron microscopy （TEM）, the Charpy impact test machine, ere were used to analyze the fracture-separation phenomenon of test specimens in high temperature tempering process of a high-strength X120 pipeline steel in view of alloy elements＇ segregation, such as phosphor, boron, manganese, second-phase＇ s precipitation and growth, such as carbide, precipitates. The results indicated that, as tempering temperature increased, fracture-separation intensified, average length and amount of separation increased, Charpy impact energy decreased by 60%. Fracture-separation appeared earlier than the main fracture, which led to increasing of surface energy, and decreasing of stiffness, forming energy and propagation energy of main fracture. The separated fracture was induced by temper brittleness which was caused by alloy elements segregation at grain boundaries. The separation was promoted by inclusions, and grain boundaries strength was weakened by second-phase with larger size.