氧化铈对高强钢复合焊接焊缝组织与韧性的影响*

稀土是理想的变质和微合金化元素，采用Nd:YAG激光-MAG电弧复合焊接方法，以预置方式向高强钢复合焊接熔池过渡氧化铈，研究焊缝组织与低温(-40 ℃)冲击性能。结果表明：适量氧化铈能控制晶粒尺寸并细化焊缝组织，当添加量为0.3%时，焊缝晶粒得到明显细化，随着添加量的增加，晶粒尺寸和枝晶间距均增大，但氧化铈并不能改变焊缝组织相成分，仍以板条马氏体组织为主。氧化铈能够净化焊缝组织，变质夹杂物并起到异质形核作用，夹杂物主要由硅、铝、铁的氧化物或碳化物及少量含铈类氧化物和氧硫化物组成。低温冲击测试发现，焊缝及其热影响区冲击吸收能量随氧化铈添加量的增加而呈先增后降的变化趋势，当添加量为0.3%时，焊缝冲击吸收能量达到最大，而添加量为0.5%时，热影响区冲击吸收能量达到最大值，其断口处韧窝均多而深，以韧性断裂为主。

Effect of Cerium Oxide on Microstructure and Toughness of the Hybrid Welding Joints of High Strength Steels

Rare earth is an ideal modification and alloying element.Cerium oxide is transited into welding pool through preset method for Nd∶YAG laser-MAG arc hybrid welding.Then microstructure and low temperature (-40 ℃) impact properties of welded joints are studied.Results indicated that proper amount of cerium oxide can control the grain growth and refine the microstructure of weld;the grain refinement level is very obvious in the addition of 0.3％.Grain size and dendrites gap are increased with the increase of cerium oxide,but cerium oxide doesn't change its microstructure,they are still dominated by lath martensite.Cerium oxide can purify the weld,modify the inclusion effectively and play a heterogeneous nuclei role;inclusions of the weld zone are mainly cerium oxides and cerium oxysulfide.Through low temperature impact test,it was found that the impact energy of the weld and heat affect zone is first increased and then decreased with the increase of the amount of cerium oxide,the impact energy is the maximum in the addition of 0.3％ and 0.5％,there are many and deep dimples in the fracture,It is mainly ductile fracture for welded joint.