线能量对大电流MAG焊缝组织和性能的影响

Effects of Heat Input on the Microstructure and Property of the High Current MAG Welding Seam

在15kJ/cm和28kJ/cm两种焊接线能量下,对大电流MAG焊接头进行了室温弯曲试验。后者接头弯曲180°合格,前者弯曲15°脆断。分析了焊缝金属化学成分、显微和断口组织,结果表明:小线能量焊接时,溶池停留时间短,脱氧反应不充分,焊缝金属中的碳、硅、钛偏多,形成脆而粗大的贝氏体组织,降低了接头的塑性;另外,小线能量时溶池冷却速度快,夹杂物来不及上浮而滞留在焊缝金属中,易形成裂源,导致脆性断裂。大线能量有利于夹杂物逸出,溶池脱氧充分,降低了焊缝金属中的碳、硅、钛含量,得到细小的针状铁素体,提高了塑性。

Side bend test was carried out at room temperature on the high current MAG welding joints under 15kJ/cm and 28kJ/cm heat input respectively.The experimental results showed that the joints with 28kJ/cm heat input bended with 180° were acceptable,but those with 15kJ/cm failed at a bending angle less than 15°.OM,SEM,EDAX and chemical composition analyses showed that small heat input led to shorter weld pool time,the oxiddation reaction could not complete fully,which resulted in overmuch C,Si and Ti in weldmetal,and brittle and massive bainitic microstructure was formed.All these reduced the joint toughness.In addition,small heat input led to welding pool cooled more quickly,which made the multi-kind oxides escape from the solidifying weldmetal difficultly and inclusions formed.Inclusions reduced the actual sectional area and stress concentration tended to occur there,resulting in crack initiation during the side bend test,which led to brittle fracture finally.With increasing heat input,the C,Si and Ti were lowered and the microstructure was fined in the weldmetal,inclusions also reduced,so that the joint toughness was improved.