镁处理对船体钢组织细化作用的高温原位分析

In-situ research on microstructure refining effect of Mg treatment for shipbuilding steel at high temperature

船体钢经镁处理后其焊接热影响区性能显著提升。为进一步弄清镁的作用机制,采用高温激光共聚焦显微镜原位观察传统船体钢和镁处理船体钢在升降温过程中显微组织的演变过程,并对不同保温时间下钢组织在连续冷却过程中的相变进行研究。通过对比发现,镁处理船体钢在升温过程中因微细夹杂物粒子的钉扎作用使得奥氏体晶粒尺寸并未发生粗化,并且在冷却过程中奥氏体晶粒内部出现大量夹杂物诱发的针状铁素体,使钢组织得到进一步细化,而夹杂物这种诱发晶内针状铁素体的能力则呈现出随保温时间延长而逐渐增强的规律。与此同时,夹杂物数量及分布情况的统计也为上述结果提供了有力佐证。

With Mg treatment process,the welded heat affected zone performance of shipbuilding steel is significantly improved.To further clarify the mechanism of action of Mg,the microstructure evolution of the traditional shipbuilding steel and Mg treated shipbuilding steel during the temperature rise and fall process was observed by high temperature laser confocal microscopy,and the phase transformation of the steel structure during continuous cooling with different holding time was also studied.By comparison,it is found that the austenite grain size was not coarsened due to the pinning action of the fine inclusion particles for Mg treatment during heating process,and a large amount of IAF(intragranular acicular ferrite)were induced by inclusions inside the austenite grains during the cooling process also.The both effects caused the steel structure to be further refined,and the inclusions,which induced the IAF,exhibit a law of increasing gradually with the prolongation of the holding time.At the same time,statistics on the number and distribution of inclusions also provide strong evidence for the above results.