等温热处理对U-2Nb合金力学性能的影响研究

Effects of Isothermal Heat Treatment on Mechanical Properties of U-2Nb Alloy

摘要:

采用光学显微镜、扫描电镜、拉伸、压缩实验等分析测试方法,系统地研究了U-2Nb合金450℃~635℃的等温相变过程及其对应的力学性能变化,对结构与性能的关联做了分析总结。结果表明U-2Nb合金在550℃-635℃的等温热处理过程中存在两类特征鲜明的显微组织样貌,影响它们力学性能的主要因素是针状组织或者胞状组织的片层间距,受温度与时间的共同影响。片层间距主要取决于其形成温度,温度越高,片层间距越大,强度随之降低,塑性随之提升,等温时间与片层间距呈正相关。这一温区内获得的最好综合性能为延伸率22%,断面收缩率27.4%,抗拉强度875Mpa,屈服强度410Mpa。在450℃~500℃进行淬火并回火的样品主要形貌特征为针状马氏体与回火形成的团状组织共存状态,影响其力学性能的主要因素可能是针状马氏体的织构与回火生成的颗粒状组织的分布与大小,其整体强度高,均在1000Mpa以上,塑性差,延伸率与断面收缩率均在5%以内。等温温度对其强度的影响相对塑性更大,延长等温时间对其塑性有微弱改善。

Abstract:

The phase transformation process of U-2Nb alloy under isothermal condition and the mechanical properties corresponding to the morphological changes were studied within 450℃~635℃.By applying the Optical Microscope、Scanning Electron Microscope techniques, tensile and compression tests, the relationship between structure and performance was discussed. The results show that U-2Nb alloy has two distinct microstructure features during isothermal heat treatment from 550℃ to 635℃. The main factor affecting the strength and plasticity was the lamellar spacing of the dual-phase in the range of 550℃~635℃.The lamellar spacing was mainly determined by the formation temperature. The higher the temperature, the greater the lamellar spacing, and so, the lower the strength and the higher the plasticity. The isothermal time is positively correlated to the lamellar spacing. The best overall properties we obtained were elongation of 22%, reduction area of 27.4%, tensile strength of 875Mpa and yield strength of 410Mpa.The rest samples were quenched and annealed at 450℃~500℃.The main factors influencing the mechanical properties within this temperature range are speculated to be the texture of the acicular martensite and the distribution or size of the granular structure. All samples with quenching+annealing treatment show overall strength higher than 1000Mpa, but with low plasticity. Elongation and reduction of area were within 5%. The annealing temperature affect the strength much more than plasticity. The plasticity was improved slightly by extending the annealing time.