The Structural Analysis of Martensite Lath Structures in High-Temperature Strength Material by AFM

Sample: 12Cr steel (grain size 30 μm)
Lath width: 0.26 μm to 0.42 μm

Tempered high-Cr steel has high strength at high temperatures due to its martensite lath structure. The smallest of the martensite structures is the lath structure, a shape that has a significant effect on the strengthening mechanism. One value that represents the size of the lath structure is the lath width.

TEMs are commonly used to observe the lath structure and measure the lath widths. However, by corroding the carbides deposited at the lath boundaries using galvanic action, the lath widths can be easily measured by AFM.
Fig. 1 is an example of lath structure observation and lath width measurement using an AFM for three-dimensional observation and cross-sectional profiling. The lath width was 0.26 μm to 0.42 μm.

Sample: 12Cr steel (grain size 200 μm) Lath width: 0.55 μm to 0.76 μm

Fig. 2 shows clearly how the lath width becomes larger in response to an increase in the grain size. The lath width was 0.55 μm to 0.76 μm.

Ryuji Sugiura, Toshimitsu Yokobori, Shinjyu Takamori, Masaaki Tabuchi, Akio Fuji, Mitsuo Yoda, Kenichi Kobayashi, Takeo Yokobori: Journal of the Japan Institute of Metals and Materials, 2006, 70(5): 452-460