Microstructure Characterization and Mechanical Properties of Al Alloyed 9Cr ODS Steels with Different Al Contents

• Published in: Steel research international Vol. 90; no. 7
• Main Authors: Xu, Shuai, Zhou, Zhangjian, Jia, Haodong, Yao, Zhongwen
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2019
• Subjects: Chromium; Dislocation density; Dispersion hardening alloys; Dispersion hardening steels; Duplex stainless steels; Ferrites; Iron; Martensite; Mechanical properties; Microstructure; ODS steels; oxide nanoparticles; phase diagram; Phase diagrams; Solid solutions; Substitutional solid solutions; tensile strength
• ISSN: 1611-3683; 1869-344X
• DOI: 10.1002/srin.201800594

The microstructural evolution of different Al contained (0.4, 2.5, and 4.5 wt%) Fe–9wt%Cr ODS steels (hereinafter referred to as 0.4Al‐ODS, 2.5Al‐ODS, and 4.5Al‐ODS) is investigated using XRD and TEM. The XRD analysis shows that the addition of Al into the Fe–9wt%Cr ODS steels leads to the formation of substitutional solid solutions, and the interplanar spacing increases with the increase of Al content. According to TEM bright field image observation, the 0.4Al‐ODS steel shows ferrite/martensite duplex microstructure, while 2.5Al‐ODS and 4.5Al‐ODS steels show a single‐phase of ferrite, which is in agreement with the thermodynamic phase diagram calculation. The dispersed particles is mainly Y–Al–O oxide according to EDS analysis, and the Y/Al ratio of most of dispersed particles is less than 1 in all Al alloyed ODS steels. The dislocation density of the three steels is calculated by the residual strain of XRD. The results show that, compared to 2.5Al‐ODS and 4.5Al‐ODS steels, the 0.4Al‐ODS steel contains more dislocations. The strengthening mechanism analysis shows that the modified theoretical hardening models fit well with experimental data of yield strength for 2.5Al‐ODS and 4.5Al‐ODS steels. The 0.4Al‐ODS steel shows ferrite/martensitic duplex steel microstructure, and 2.5Al‐ODS and 4.5Al‐ODS steels are ferrite single‐phase steels. The composition of dispersed particles in all ODS steels is mainly Y–Al–O and the Y/Al ratio of most particles is less than 1. The calculation of theoretical hardening models fit well with experimental data of yield strength for 2.5Al‐ODS and 4.5Al‐ODS steels if the gain boundary strengthening is not considered.