420MPa级海洋工程用钢大线能量焊接接头显微组织及力学性能研究

Study on microstructure and mechanical properties of large heat-input welded joints for 420MPa marine engineering steels

采用厚度规格为50 mm的EH420海洋工程用钢板为母材,以200 kJ/cm的焊接线能量进行双丝埋弧焊焊接试验。通过光学显微镜,扫描电镜,电子探针等先进的表征设备分析焊接接头附近不同区域的力学性能及显微组织变化及对焊接热影响区力学性能的影响。研究发现:焊缝金属的化学成分对冲击韧性影响较大,可适当降低熔覆金属的含碳量及碳当量,保证焊接接头强韧匹配;200 kJ/cm下焊接接头附近FL+2 mm位置冲击韧性显著下降,较大的原奥氏体晶粒尺寸对冲击韧性不利;Al-Mn-S的复合氧化夹杂物可造成局部应力集中,成为裂纹的起裂源,不利于冲击韧性的提高。

The EH420 offshore engineering steel plate with the thickness specification of 50 mm was used as the base material,and the welding test of double wire submerged arc welding was carried out with the heat-input of 200 kJ/cm.Optical microscope,scanning electron microscope,electron probe and other advanced characterization equipment were used to analyze the mechanical properties and microstructure changes of different areas near the welding joint and the influence on the mechanical properties of the welding heat affected zone;It is found that the chemical composition of the weld metal has a great influence on the impact toughness,so the carbon content and carbon equivalent of the cladding metal can be appropriately reduced to ensure the strength and toughness match of the welded joint;The impact toughness at the position FL+2 mm near the welded joint decreases significantly at 200 kJ/cm,and the larger original austenite grain size is not favorable to the impact toughness;Al-Mn-S complex oxide inclusions can cause local stress concentration and develop into the source of crack initiation,which is not conducive to the improvement of impact toughness.