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通过调整焊接热输入研究了Q460低合金高强钢CO2气体保护药芯焊接接头的组织及其对不同温度下动态断裂韧性(JId)的影响规律,探究了影响接头动态断裂行为的机理.结果表明,低热焊接输入的接头熔合区(FZ)柱状晶界面处存在仿晶界型铁素体;随热输入增加,FZ柱状晶形态特征逐渐减弱、仿晶界铁素体消失,FZ以针状铁素体组织为主,且随热输入的增加针状铁素体平均尺寸增大.在室温至-70℃范围内,中等热输入的焊接接头均表现出优异的动态断裂韧性,而低热输入的接头动态断裂韧性值最低.随温度由室温降低至-70℃,Q460钢焊接接头动态断裂机制发生了由延性断裂逐渐向解理脆性断裂的转变.低热输入焊接接头FZ柱状晶界面具有平面生长特征的仿晶界铁素体,易诱发低温下裂纹沿晶快速扩展.研究发现,在低温动态断裂过程中,细小针状铁素体组织由于可有效地阻碍裂纹扩展,成为其维持高动态断裂韧性的要因.
The influence of weld heat flux on the dynamic fracture toughness (JId) of Q460 low alloyed high strength steel CO2 gas shielded arc welded joint was studied by adjusting the welding heat input, and the mechanism affecting the dynamic fracture behavior of joint was investigated. With the increase of heat input, the morphological characteristics of FZ columnar crystals gradually weakened, the ferrite on the grain boundaries disappeared, and the FZ was transformed into acicular ferrite Body tissue and the average size of acicular ferrite increased with the increase of heat input.The welded joint with medium heat input showed excellent dynamic fracture toughness at room temperature to -70 ℃, The dynamic fracture toughness value is the lowest.With the temperature decreasing from room temperature to -70 ℃, the dynamic fracture mechanism of Q460 steel welded joint changes from ductile fracture to cleavage brittle fracture.The FZ columnar grain interface of low heat input welded joint has the characteristics of planar growth The intergranular ferrite can easily induce the rapid propagation of cracks along the crystal at low temperature.It is found that the fine acicular ferrite can effectively prevent the crack propagation during the dynamic fracture at low temperature Show, as its main reason for maintaining high dynamic fracture toughness.