镍基690合金的晶粒控制及其对力学性能的影响

Grain control of Ni-based alloy 690 and its effect on mechanical properties

针对不同C含量的690合金,分别研究了C含量对合金晶粒长大行为及退火孪晶的影响。结果表明:在0. 011%~0. 028%的范围内,C含量变化显著影响690合金晶粒长大过程,其平均晶粒尺寸随着C含量升高而逐渐减小,尤其是C含量在0. 020%~0. 028%区间时,C含量的晶粒细化效果更为显著。合金组织中∑3n(n=1、2、3)晶界体积分数基本均随C含量升高而呈先升后降趋势;0. 020%左右C含量合金具有更高的∑9和∑27晶界体积分数分布。在此基础上选择C含量为0. 02%的合金进一步探讨了固溶温度变化引起的合金晶粒尺寸与力学性能之间的定量关系发现:690合金晶粒细化对强度的影响规律遵循位错塞积模型的Hall-Petch关系,且通过拟合发现抗拉强度强化系数kT值(18. 95 MPa·mm1/2)小于屈服强度强化系数ky值(23. 67 MPa·mm1/2),晶粒细化对屈服强度的强化效果比抗拉强度更高。溶质元素变化通过固溶强化引起的强化增量为243 MPa,而晶粒细化引起的强化增量在157~7 MPa之间,690合金强化机制主要为固溶强化机制。

The effects of C content on grain growth and annealing twins of alloy 690 with different C contents were studied. The results show that within the range of 0. 011%-0. 028%,the change of C content significantly affects the grain growth process of the alloy 690,and its average grain size gradually decrease with the increase of C content. Especially when C content is between 0. 020% and 0. 028%,the grain refinement effect of C content is more significant. The grain boundary volume fraction of ∑3n( n = 1,2,3) increases first and then decreases with the increase of C content in the alloy structure. The content of C in the alloy of about 0. 020% has a higher distribution of the grain boundary volume fraction of ∑9 and ∑27. On this basis,the alloy containing 0. 02% C is selected to explore the quantitative relationship between the grain sizes and mechanical properties of the alloy caused by the change of solid solution treatment temperature was further discussed. The influence of grain refinement on the mechanical strength of alloy 690 follows the Hall-Petch relationship of the dislocation pile-up model. Moreover,it is found by fitting that the kT value of the strengthening coefficient of tensile strength( 18. 95 MPa·mm1/2) is smaller than the ky value of the strengthening coefficient of yield strength( 23. 67 MPa·mm1/2),and the grain refinement has a higher strengthening effect on the yield strength than the tensile strength. The strength increment of solute elements caused by solid solution strengthening is 243 MPa,while that caused by grain refinement is 157-7 MPa. The main strengthening mechanism of alloy 690 is solid solution strengthening mechanism.