Q460鋼焊接接頭組織及動態(tài)斷裂行為的研究

Q460鋼焊接接頭組織及動態(tài)斷裂行為的研究STUDY ON MICROSTRUCTURE AND DYNAMIC FRACTURE BEHAVIOR OF Q460 STEEL WELDING JOINTS

通過調(diào)整焊接熱輸入研究了 Q460 低合金高強鋼 CO2 氣體保護藥芯焊接接頭的組織及其對不同溫度下動態(tài)斷裂韌性(JId)的影響規(guī)律, 探究了影響接頭動態(tài)斷裂行為的機理. 結(jié)果表明, 低熱焊接輸入的接頭熔合區(qū)(FZ)柱狀晶界面處存在仿晶界型鐵素體; 隨熱輸入增加, FZ 柱狀晶形態(tài)特征逐漸減弱、仿晶界鐵素體消失, FZ 以針狀鐵素體組織為主, 且隨熱輸入的增加針狀鐵素體平均尺寸增大. 在室溫至-70 ℃范圍內(nèi), 中等熱輸入的焊接接頭均表現(xiàn)出優(yōu)異的動態(tài)斷裂韌性, 而低熱輸入的接頭動態(tài)斷裂韌性值最低. 隨溫度由室溫降低至-70 ℃, Q460 鋼焊接接頭動態(tài)斷裂機制發(fā)生了由延性斷裂逐漸向解理脆性斷裂的轉(zhuǎn)變. 低熱輸入焊接接頭 FZ 柱狀晶界面具有平面生長特征的仿晶界鐵素體, 易誘發(fā)低溫下裂紋沿晶快速擴展. 研究發(fā)現(xiàn)細小針狀鐵素體組織, 在低溫動態(tài)斷裂過程中, 由于可有效地阻礙裂紋擴展, 成為其維持高動態(tài)斷裂韌性的要因。

Effects of welding heat input on the microstructure and dynamic fracture toughness (JId) of the CO2 shielded arc welded joints of Q460 high strength low alloy steel were investigated. The mechanism of effects on the dynamic facture behavior of the welded joint was also discussed. The results showed that there existed the allotriomorphic ferrite at the columnar interface in the fusion zone of welded joint under the condition of low heat input. The morphological characteristics of columnar crystal in the fusion zone gradually decreased and the allotriomorphic ferrite disappeared as the heat input increased. The fusion zone was mainly composed of acicular ferrite, and its average size increased with increasing heat input. The welded joint exhibited the optimal dynamic fracture toughness under the condition of medium heat input while it showed the lowest value under low heat input within the temperature range of -70 ℃ to room temperature. When the temperature decreased from room temperature to -70 ℃, the dynamic fracture mechanism of Q460 welded joint changed from ductile fracture to brittle cleavage fracture. Under the condition of low heat input, the allotriomorphic ferrite characterized by the planar growth at the columnar interface in the fusion zone of welded joint can lead to the rapid intergranular crack propagation at low temperature. The fine acicular ferrite in the fusion zone of the welding joint obtained at medium heat input which can hinder the crack propagation during the dynamic fracture at low temperature to the greatest extent is the reason why the welded joint exhibits high dynamic fracture toughness.

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