Abstract
High-chromium ferritic stainless steels strengthened by Laves phase precipitates were developed for a high-temperature application in steam power plants. The impact of tungsten content on the precipitation of the intermetallic Laves phase during the newly developed thermomechanical process route was investigated. Due to rapid thermomechanically induced precipitation, a considerable reduction in processing time in comparison to the conventional solely thermal two-step processing of high chromium ferritic steels was achieved. Nevertheless, comparable mechanical properties at room temperature, i.e., the ultimate tensile strength of 712 MPa and the yield strength of 434 MPa, were obtained. The microstructure was analyzed by scanning electron microscopy (SEM) in combination with digital particle analysis, to estimate the particle size and the phase fraction of the Laves phase. The mean particle size of 52 nm and the volume fraction of 4.11% were achieved. Due to the tungsten content, an increase in the volume fraction and particle size was observed, giving rise to the higher strengthening effect.
Highlights
The alloy concept of fully ferritic stainless steels strengthened by the Laves phase focuses on high creep strength and steam oxidation resistance
The chemical composition of the experimental melting was developed by systematically varying the concentration of the mean alloying, Laves phase-forming elements
The aim of the design was to maximize the volume of the Laves phase at the operating temperature (650 ◦ C)
Summary
The goal of this project was to achieve a stable ferritic, heat-resistant microstructure by combining solid solution and Laves phase precipitation strengthening
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