S355J2W钢及焊接接头低温性能研究
发布时间：2019-05-28 20:44
【摘要】：S355J2W耐候钢主要用于高速列车转向架的制造,转向架是保证列车运行稳定性及安全性的关键部件。然而,S355J2W钢在低温下会发生韧脆转变,使材料突然发生脆性断裂。转向架各部位的连接主要通过焊接,焊接缺陷及组织的不均匀性等因素均会增大焊接接头的低温敏感性,从而使接头发生低温脆断的可能性增大。因此,有必要对S355J2W钢焊接接头的低温性能进行研究。本文以S355J2W钢MAG焊接接头为研究对象,通过在不同的温度下进行拉伸试验、冲击试验及断裂韧性试验,研究强度、塑性及韧性等指标随温度的变化规律,并深入探究了接头各区的韧脆转变行为;通过断口金相观察讨论了接头各区解理断裂的临界事件,通过EBSD分析了母材和焊缝晶粒取向及裂纹扩展路径;通过TEM对比分析了常温及低温下断口附近的微观组织及位错形貌;采用有限元分析方法结合断口细观参数测量,计算了接头各区的解理断裂应力,并深入分析了微观组织对低温韧性的影响。低温力学性能及韧性试验结果表明,随着温度降低,接头各区的强度增大而塑性、韧性降低,母材具有最好的低温韧性和最低的韧脆转变温度,而焊缝低温韧性最差,韧脆转变温度最高,为焊接接头最薄弱环节。低温下,接头各区的微观断裂机制逐渐由韧性断裂向脆性断裂转变。母材在-80～-115℃解理断裂的临界事件为晶粒尺寸的微裂纹穿过晶界扩展,在-196℃临界事件转变为微裂纹的形核,焊缝和热影响区微观组织的不均匀性造成解理断裂临界事件的差异性。母材中大角度晶界的比例较高,可有效阻碍裂纹扩展而使低温韧性提升,焊缝中先共析铁素体及侧板条铁素体内部的小角度晶界对裂纹扩展阻碍作用较小,而针状铁素体区域高比例的大角度晶界有利于提升低温韧性。母材在常温下较大的塑性变形引起位错增值,在-196℃下具有较低的位错密度,Nb2C析出相对位错的钉扎作用显著。母材解理起裂源位于晶界,焊缝解理起裂源多为夹杂相诱发形成,热影响区存在晶界和夹杂相两种形核机制。母材细小的微观组织使特征微裂纹长度较小,从而具有较大的解理断裂应力,宏观上表现为较好的低温韧性;焊缝和热影响区的中粗大的组织显著降低了解理断裂应力,从而具有较差的低温韧性,组织的不均匀性造成了解理断裂应力较大的离散性。
[Abstract]:S355J2W weather-resistant steel is mainly used in the manufacture of high-speed train bogie, which is the key component to ensure the stability and safety of train operation. However, the ductile-brittle transformation of S355J2W steel will occur at low temperature, which will cause brittle fracture of the material. The connection of each part of the bogie mainly through welding, welding defects and microstructure inhomogeneity and other factors will increase the low temperature sensitivity of the welded joint, thus increasing the possibility of low temperature brittle fracture of the joint. Therefore, it is necessary to study the low temperature properties of S355J2W steel welded joints. In this paper, the tensile test, impact test and fracture toughness test of MAG welded joint of S355J2W steel are carried out at different temperatures, and the variation of strength, plasticity and toughness with temperature is studied. The ductile-brittle transition behavior of the joint was deeply investigated. The critical events of cleavage fracture in each area of the joint were discussed by means of fracture metallographic observation, the grain orientation and crack propagation path of base metal and weld were analyzed by EBSD, and the microstructure and dislocation morphology near fracture surface at room temperature and low temperature were compared and analyzed by TEM. The cleavage fracture stress in each area of the joint is calculated by finite element analysis method combined with the measurement of fracture meso-parameters, and the effect of microstructure on low temperature toughness is deeply analyzed. The results of low temperature mechanical properties and toughness tests show that with the decrease of temperature, the strength and toughness of the joints increase and the toughness decreases. The base metal has the best low temperature toughness and the lowest ductile brittle transition temperature, while the low temperature toughness of the weld is the worst. The ductile-brittle transition temperature is the highest, which is the weakest link of welded joint. At low temperature, the microscopic fracture mechanism of the joint gradually changes from ductile fracture to brittle fracture. The critical event of cleavage fracture of base metal at-80 鈮，
本文编号：2487350
[Abstract]:S355J2W weather-resistant steel is mainly used in the manufacture of high-speed train bogie, which is the key component to ensure the stability and safety of train operation. However, the ductile-brittle transformation of S355J2W steel will occur at low temperature, which will cause brittle fracture of the material. The connection of each part of the bogie mainly through welding, welding defects and microstructure inhomogeneity and other factors will increase the low temperature sensitivity of the welded joint, thus increasing the possibility of low temperature brittle fracture of the joint. Therefore, it is necessary to study the low temperature properties of S355J2W steel welded joints. In this paper, the tensile test, impact test and fracture toughness test of MAG welded joint of S355J2W steel are carried out at different temperatures, and the variation of strength, plasticity and toughness with temperature is studied. The ductile-brittle transition behavior of the joint was deeply investigated. The critical events of cleavage fracture in each area of the joint were discussed by means of fracture metallographic observation, the grain orientation and crack propagation path of base metal and weld were analyzed by EBSD, and the microstructure and dislocation morphology near fracture surface at room temperature and low temperature were compared and analyzed by TEM. The cleavage fracture stress in each area of the joint is calculated by finite element analysis method combined with the measurement of fracture meso-parameters, and the effect of microstructure on low temperature toughness is deeply analyzed. The results of low temperature mechanical properties and toughness tests show that with the decrease of temperature, the strength and toughness of the joints increase and the toughness decreases. The base metal has the best low temperature toughness and the lowest ductile brittle transition temperature, while the low temperature toughness of the weld is the worst. The ductile-brittle transition temperature is the highest, which is the weakest link of welded joint. At low temperature, the microscopic fracture mechanism of the joint gradually changes from ductile fracture to brittle fracture. The critical event of cleavage fracture of base metal at-80 鈮，
本文编号：2487350
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