Читать книгу Welding Metallurgy - Sindo Kou - Страница 80

Weld thermal simulators, though very useful, have some limitations. First, extremely high cooling rates during electron and LBW cannot be reproduced, due to the limited cooling capacity of the simulators. Second, because of the surface heat losses, the temperature at the surface can be lower than that at the centerline of the specimen, especially if the peak temperature is high and the thermal conductivity of the specimen is low [66]. Third, the temperature gradient is much lower in the specimen than in the weld heat‐affected zone, for instance, 10 °C/mm, as opposed to 300 °C/mm near the fusion line of a stainless‐steel weld. This large difference in the temperature gradient tends to make the specimen microstructure differ from the real HAZ microstructure. For example, the grain size tends to be significantly larger in the specimen than in the heat‐affected zone, especially at high peak temperatures such as 1100 °C and above.