The solid-state phase transformation in the coarse-grained heat-affected zone of P91 steel under simulated welding thermal cycle has been investigated in situ by confocal scanning laser microscope. It is found that γ-austenite initiates from the triple point of δ-ferrite grain boundaries (GBs), then at ordinary δ-GBs, and eventually from grain interiors. Upon further cooling, martensite laths are observed to nucleate and growth instantaneously, with the growth rate being estimated ranging from 175 to 454 μm/s.

中文翻译：

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P91耐热钢粗粒热影响区模拟焊接过程中相变的原位观察

在下模拟焊接热循环P91钢的粗粒热影响区的固态相变已经研究原位通过共焦激光扫描显微镜。发现γ-奥氏体从δ-铁素体晶界（GBs）的三点开始，然后在普通的δ-GBs处开始，最终从晶粒内部开始。进一步冷却之后，马氏体板条被观察到核和生长瞬间，与正被估计的生长速度范围为175至454  μ米/秒。