分析型透射电子显微术在材料工业中的应用:双相不锈钢断裂韧性的研究(英文)

Application of analytical transmission electron microscopy in materials industries:fracture toughness of duplex stainless steel

不同的热加工工艺导致双相不锈钢2205(50/50铁素体/奥氏体)产生了不同的断裂韧性,尤其是断裂韧性降至不可接受的低值。本文通过分析透射电子显微镜研究其显微结构,对这种现象提供了解释。尤其是对断裂韧性的急剧变化提出了试验上的观察与分析,获得正确且有效的解决此类问题的方法。β-Cr2N相沿{110}α原子平面析出是导致断裂韧性降低,特别是在低温下的断裂韧性大幅降低的根本原因。因为在韧性至脆性转变温度时形变的机制为位错的移动性,而沿{110}α原子平面析出的β-Cr2N相阻碍了位错的运动,导致α铁素体的脆性,从而使材料整体脆化。材料经1200℃退火随即空气冷却到室温之后,断裂韧性恢复到正常值,是由β-Cr2N相的溶解所致。α-Fe(Cr)→α-Fe+α′-Cr相变(又常称为在475℃失稳分解)导致断裂韧性在低温与室温下都急剧下降是由富铬的铁素体α′-Cr固有的脆性所引起。将材料加热致800℃后随即急冷至室温后,断裂韧性恢复到正常值。这是由于材料经加热将α-Fe+α′-Cr相溶解并经急冷而避免了α-Fe(Cr)→α-Fe+α′-Cr相变的再发生。本研究中观察到的析出相的尺寸均为纳米量级,只有应用分析透射电子显微镜后才可得以同时获得其形态、化学成分以及晶体学的结果,从而解释断裂韧性变化的根本的原因,并找出解决问题的办法。

Different thermo-mechanical processes resulted in different fracture toughness in duplex stainless steel 2205.Investigation of microstructure of the material using analytical transmission electron microscopy provides the explanation of the differences,particularly the cause of low fracture toughness.The formation of β-Cr_2N along the {110}_α atomic planes was found to be attributed to the low fracture toughness,particularly at low temperature.This was explained in terms of deformation mechanism in the α-matrix at the ductile-to-brittle transition temperature,which is controlled by dislocation mobility.The recovery of the fracture toughness was obtained by the dissolution of β-Cr_2N during annealing at 1 200 ℃ followed by cooling in air.The phase transformation α-Fe（Cr）→α-Fe＋α＇-Cr（called spinodal decomposition at around 475 ℃）resulted in the degradation of fracture toughness both at room temperature and low temperature.The embrittlement of this type was removed by reheating to 800 ℃ and then cooling rapidly to room temperature,thus preventing the spinodal decomposition to occur.