X80管线钢焊接粗晶区韧化因素的研究

采用热模拟技术研究了不同热循环对X80管线钢焊接粗晶区低温冲击韧度的影响.实验结果表明,随着冷却时间t8/5的增加,第二相粒子的数量减少且出现聚集现象,晶粒尺寸增加,但是当t8/5小于6.8s时,粒状贝氏体含量较高,板条束贝氏体细小且方向性较弱,试样的冲击韧性较高;而当t8/5超过6.8s后,粒状贝氏体含量逐渐下降,板条贝氏体逐渐粗大、平行,试样韧性又逐渐降低.M-A组元由于其含量低,尺寸小,对韧性的影响不显著.因此为提高焊接粗晶区的韧性,应采用小线能量和合适的预热温度来控制晶粒尺寸和组织形态.

Research on Influencing Factor of Impact Toughness in Coarse Grain Heat-affected Zone for X80 Pipeline Steel

Thermal simulating technology was used to simulate weld coarse grain heat-affected zone of pipeline steel X80 for the purpose of investigation on the influence of thermal cycle on low-temperature impact toughness. The experimental results showed that with the increase of t_(8/5), the crystal grains became coarser, small quantity of second phase particles precipitated and the phenomenon of aggregation occured. However, the impact toughness of specimens improved for the formation of a certain quantity of granular bainite and thin lath bainite when t_(8/5) was shorter than 6.8s. But if the t_(8/5) was longer than 6.8s, it would cause the lower percent of granular bainite, and the lath bainite would be coarser and tending parallel. The M-A constituent had little influence on toughness for its low percentage and small size. So it was concluded that lower heat input and suitable preheated temperature should be adopted to control grain size and microstructure morphology.