利用使低温（－１９６℃）冲击裂纹停止在试样中和中止拉伸变形的准动态方法和变形－断裂进行时观察表面组织的动态方法，研究经α＋γ相区处理的Ｎｉ９钢的显微组织在低温冲击和拉伸变形时的行为．结果表明：当样品中热稳定的沉淀奥氏体（γ＇）较多（≈１０ｖ．－％）时，在冲击断裂影响区（ＩＦＥＺ）内，γ＇转变为α＇（马氏体）并形成密度较大的空洞，良好的低温韧性（≈２００Ｊ）是相变增韧机制作用的结果；当γ＇相很少时，ＩＦＥＺ内形成密度很高且扩展受阻的微裂纹，良好的低温韧性是微裂纹增韧机制作用的结果．在低温冲击值较低时，ＩＦＥＺ中只有稀疏的长裂纹．在裂尖前的拉伸变形使α＇板条堆转动，板条界趋于与裂尖前进方向垂直，利于裂尖钝化和冲击韧性．表明高韧性材料的组织具有抵抗动载荷的自调节功能．
The behaviour of α+γ region treated microstructure of Ni9 steel during-196℃ cryogenic impact and tensile deformation has been studied by using both a quasi-dynamic method in which the low temperature(-196℃) impact cracks stopped in the specimen and the tensile deformation halted,and a dynamic method to observe the surface structure under deformation to fracture.The results show that if more(about 10 v.-%) thermally stable γ'-phase occurred in specimens,the excellent cryogenic toughness is resulted in γ'to α'transformation and very dense cavities formed in the impact fracture effected zone(IFEZ);in case of littl γ'-phase,high cryogenic toughness is caused by the high density of hindered tiny cracks in IFEZ:while no γ'-phase,the cryogenic toughness may be poor owing to some sparse and longer cracks only.The tensile deformation ahead of the crack tip makes the lathy packet turn toward the direction being beneficial to crack tip passivation and to toughness.It is shown that the structure of materials with high toughness can adjust oneself to resist the impact load.
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| [8] | OokaT,MimuraH,YanoS,SuginoK,ToizumT．JJpnInstMetals,1966 |
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