新型耐热合金SP2215的热变形行为

Hot Deformation Behavior of New Heat-Resistant Alloy SP2215

摘要:

针对火力发电超超临界锅炉过热器/再热器管道用新型耐热合金SP2215，利用Gleeble 3500热模拟试验机对合金在1100~1250 ℃、0.01~10 s^–1、变形量为50%，变形条件下进行了一系列热压缩试验，研究了不同变形温度和变形速率对合金流变曲线、变形组织等的影响，并通过对流变曲线进行摩擦与温度双修正，建立了SP2215合金的热变形Arrhenius本构模型、Avrami动态再结晶模型与Yada动态再结晶平均晶粒尺寸模型，同时基于不同的流变失稳准则分别构建了合金的Prasad热加工图、Murty热加工图和Malas热加工图。结果表明，随着变形温度的升高，SP2215合金的加工硬化程度有所减小，更容易发生动态再结晶；随着应变速率的增加，合金的流变应力更高，加工硬化率更大，当变形速率为1 s^–1时合金的再结晶程度最低，当变形条件选择不佳时合金极易出现混晶现象，在实验条件下合金的最佳热变形窗口为1200~1250 ℃、5~10 s^–1。

Abstract:

A series of hot compression tests were conducted on the new heat-resistant alloy SP2215 for supercritical and ultra-supercritical power plant superheater/reheater tubes using a Gleeble 3500 thermal simulation testing machine at 1100–1250 ℃ and the deformation rate of 0.01–10 s^–1 with a deformation amount of 50%. The influence of deformation temperatures and deformation rates on the rheological curve and deformation structure of the alloy was investigated. Furthermore, by modifying the rheological curve based on friction and temperature effects, we established thermal deformation Arrhenius constitutive model, Avrami dynamic recrystallization model, and Yada dynamic recrystallization average grain size model for SP2215 alloy. Additionally, Prasad-Murty-Malas hot working maps were constructed for alloys based on various rheological instability criteria. The results indicate that as the deformation temperature increases, the degree of work hardening decreases while dynamic recrystallization becomes more obvious in SP2215 alloy. Moreover, higher strain rates result in increased flow stress and work hardening rate for this alloy. The recrystallization of the lowest degree occurs at a strain rate of 1 s^–1; however, without certain conditions, mixed crystal phenomenon may occur easily in this alloy. Under experimental conditions in this research, the optimal thermal deformation window for SP2215 alloy is the temperature of 1200–1250 ℃ and the strain rate of 5–10 s^–1.