Composition, microstructure and mechanical homogeneity evaluation of the Y-bearing 9Cr F/M steel fabricated by VIM & casting technique

Abstract

Casting is suggested to be a promising method to produce the low-cost ODS steel with large volume and high throughput. However, the ingot homogeneity of the cast ODS steel was rarely reported. Recently, our group prepared a castable ODS steel, which exhibited long creep life of 3800 h under 650 °C and 120 MPa. Thus the purpose of this work is presenting the homogeneity of the castable ODS steel. Theoretical addition of Y was 0.1 wt% thereby the steel was named as 9Cr-10Y. Nine samples were machined from the top, middle, bottom, left, center, right regions of this plate then subjected to homogeneity analysis. Y content, prior austenite grain size and second phase size of the nine specimens were 0.023-0.034 wt%, 9.27-0.94 μm and 294-314 nm, respectively. Low coefficient of variation (Cv) of 14.5% for Y content, 2.3% for prior austenite grain size and second phase size indicated that the homogeneous composition and microstructure were achieved in the 9Cr-10Y plate. Besides, hardness fluctuated within a small range and all the Cv values were in the range of 0.8%-4.3%, which demonstrated that the hardness distribution along RD, TD, and ND was homogeneous. Furthermore, the 9Cr-10Y plate exhibited high strength of 765 MPa and high elongation of 18.9% as well as low DBTT of -40 °C.