A572 Gr.50厚板对接焊缝断裂性能研究

FRACTURE PROPERTIES OF BUTT WELD OF A572 Gr.50 THICK STEEL PLATES

A572 Gr.50厚板常用于锅炉钢结构大板梁的加工制作,其对接焊缝易存在焊接裂纹缺陷。为评定含缺陷的锅炉钢结构大板梁的安全性,通过焊接接头模拟制作实际大板梁下翼缘的A572 Gr.50厚板对接焊缝,分别对其母材、焊缝金属及热影响区材料进行了系列单轴静力拉伸试验、冲击韧性试验和直三点弯曲断裂韧度试验,并结合有限元分析对A572 Gr.50厚板对接焊缝存在裂纹缺陷时的断裂性能进行了研究。研究结果表明:厚板对接焊缝母材、焊缝和热影响区材料基本力学性能均能满足规范要求,均具有良好的塑性变形能力;随温度的降低,母材、热影响区及焊缝处的夏比冲击功减少,但均具有良好的冲击韧性;比较而言,母材的抗低温冷脆性能最好,焊缝最差;母材、焊缝和热影响区3个区域中焊缝的断裂韧度最差;厚板对接焊缝接头的焊缝区是大板梁焊接缺陷安全性评估的重点控制区域;基于断裂力学,可以运用有限元软件方便的对带裂缝的工作状态下工作的钢结构构件的断裂性能进行分析,保证其安全性。

A572 Gr.50 thick plates are commonly used in large-scale plate girder fabrication. The welding cracks are likely contained in the butt weld of A572 Gr.50 thick plates. To evaluate the safety of welding defects of the in-service large-scale plate girders in boiler steel structures, A572 Gr.50 thick plate butt-welded joints were fabricated to reflect the similar material properties of the butt-welded lower flange plate of large-scale plate girders. Uniaxial tensile tests, Charpy V-notch tests and three-point bending tests were conducted for the base metal, heat-affected zone and the butt weld of this simulated welding joint respectively. Combined with the finite element analysis, the fracture properties of A572 Gr.50 thick plate butt-welded joints were investigated. Results indicated that materials from base metal, butt weld and heat-affected zone showed good mechanical properties, satisfying the relevant specification requirements, and possessed good capability of plastic deformation. Charpy impact energy reduced with the decrease in temperature. In addition, the base metal, weld and heat affected zone had good impact toughness. With respect to the low-temperature brittleness, the brittle resistant ability of the base metal was the best while that of weld was the worst. Compared with base metal and heat-affected zone steel, fracture toughness of molten zone was still the worse. To summarize, more attention should be paid to the butt weld zone of the thick-plate welding joints for their safety assessment. Finite element software packages can be used to analyze the fracture properties of steel structural members with cracks under working conditions to ensure structural safety.