| Abstract Scope |
P91 steel, also known as creep strength-enhanced ferritic heat-resistant steel, has been extensively employed in thermal power generation applications, where welding is necessitated in the manufacturing process. Delta-ferrite is often retained in the heat-affected zone adjacent to the weld fusion line, which plays a role in the mechanical properties of final product. In the present work, phase transformation and microstructural evolution behaviors of the coarse grained heat-affected zone have been systematically studied by a high-temperature confocal scanning laser microscope (CSLM). In situ CSLM observation shows that delta-ferrite to austenite to martensite transition commences at 1468.6 K and 578.7 K, respectively. On cooling, austenite initiates from the triple point of the delta-ferrite grain boundaries with a trihedral shape, while not all of the delta-ferrite transforms back to austenite, 2~5 pct is retained. Subsequently, the rapid growth of martensite lath is almost instantaneous, with an average rate of 1051.16 μm/s. |