水电工程1000 MPa等级超高强钢埋弧自动焊接头显微组织及力学性能研究

Microstructure and mechanical properties of 1000 MPa grade ultrahigh-strength steel submerged arc welding joints in hydropower engineering

为研究水电工程1000 MPa等级超高强钢埋弧焊焊接接头的显微组织及力学性能特征,通过扫描电子显微镜表征了焊接接头不同区域的显微组织,通过拉伸试验、冲击试验和弯曲试验测定了焊接接头的力学性能。研究结果表明:打底焊道和填充焊道焊缝金属由柱状晶、树枝晶以及等轴晶组成,组织多为针状铁素体和少量粒状贝氏体;热影响区形成了多个典型区域,靠近熔合线沿厚度方向上分别出现了临界粗晶区和粗晶区;远离焊缝出现了细晶区和临界区,组织多为粒状贝氏体、M-A组元和板条马氏体;盖面焊道焊缝金属为典型的柱状晶,组织主要为针状铁素体;热影响区包含了粗晶区、细晶区、临界区和亚临界区,由于没有后续焊道,未形成临界粗晶区,组织主要为板条马氏体、粒状贝氏体及M-A组元;焊接接头的平均抗拉强度达到980 MPa等级,在焊缝区和热影响区–40℃低温冲击吸收能量分别为118.7、149.3J(T/4部位)和67.0、154.0J(T/2部位),横向侧弯未出现裂纹。

To investigate the microstructural and mechanical properties of 1000 MPa grade ultra-high strength steel submerged arc welding welded joints for hydroelectric engineering,the microstructure of different regions of the welded joint was characterized using scanning electron microscopy(SEM).Mechanical properties of the welded joint were determined through tensile testing,impact testing,and bending testing.The results reveals that,the weld metal of the root pass and fill passes is composed of columnar,dendritic,and equiaxed grains,with a microstructure dominated by acicular ferrite and a small amount of granular bainite.The heat-affected zone(HAZ)exhibits multiple typical regions,including a critical coarse grain zone and a coarse grain zone near the fusion line along the thickness direction.Away from the weld,fine grain zones and critical zones are observed,with a microstructure primarily consisting of granular bainite,M-A constituents,and lath martensite.The weld metal of the cap pass exhibits typical columnar grains with a microstructure primarily composed of acicular ferrite.The HAZ of the cap pass includes coarse grain,fine grain,critical,and subcritical zones.Due to the absence of subsequent welding passes,no critical coarse grain zone is formed,and the microstructure is primarily composed of lath martensite,granular bainite,and M-A constituents.The average tensile strength of the welded joint reaches 980 MPa grade,the low-temperature impact absorption energy of the weld zone and the HAZ at–40℃is 118.7 J and 149.3 J(at T/4),67.0 J and 154.0 J(at T/2),respectively.No cracks appear in the lateral bending.