In this paper, microstructure observations and mechanical behaviour of fusion line and offsetting positions from fusion line by 1, 2 and 3 mm were analysed. For the welding of X80 pipeline steel plates, different magnitudes of heat inputs such as high heat input (HHI) 25 kJ/cm, medium heat input (MHI) 20 kJ/cm and low heat input (LHI) 15 kJ/cm were employed. Critical values of J‐integral (J_0.2) and crack tip opening displacement (CTOD_0.2) for predetermined regions in the X80 weldment were determined as per ASTM‐E1820a. M‐A constituents of different sizes such as small (1–2 μm), large >2 μm and slender (>4 μm) were observed in the microstructure of subzones of weldments for different heat inputs. Formation of granular bainite, M‐A constituents and inclusions of Ti, Si, Mo in the microstructure impaired fracture toughness property. In the X80 weldment, the fusion line (FL) for HHI was found weakest in terms of fracture resistance, which subsequently increases the risk of fracture.

中文翻译：

---

热输入量对X80管线钢焊件不同区域组织和断裂韧性的影响

在本文中，分析了熔合线的微观结构观察和力学行为以及与熔合线的偏移位置为1、2和3 mm。对于X80管线钢板的焊接，采用了不同的热输入量，例如高热输入（HHI）25 kJ / cm，中热输入（MHI）20 kJ / cm和低热输入（LHI）15 kJ / cm 。J积分的临界值（J _0.2）和裂纹尖端的开口位移（CTOD _0.2）对于X80焊件中的预定区域，按照ASTM-E1820a确定。在不同热量输入的焊件分区的微观结构中，观察到了大小不同的M‐A成分，例如小（1-2μm），大> 2μm和细长（> 4μm）。显微组织中粒状贝氏体，MA成分和Ti，Si，Mo夹杂物的形成破坏了断裂韧性。在X80焊件中，发现HHI的熔合线（FL）在抗断裂性方面最弱，从而增加了断裂的风险。