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Abstract
In this experiment, the microstructure and toughness of the heat-affected zone of samples under different t8/5 times were monitored. According to the results, 100% bainite transformation took place in the heat-affected zone under a rapid cooling rate. The bainite content decreased, and the ferrite content increased with prolonged t8/5. The impact toughness of the heat-affected area was shown to vary with its microstructure. The tests demonstrated that the normalised zone showed good weldability with a fine microstructure, and the impact toughness was optimised when t8/5 of the over-heated and partial transition zones was between 10 and 15 seconds. Cooling cracks could be prevented by preheating at a temperature of 50°C, and was shown using the oblique Y test. This study supports the high weldability of SA738Gr.B steel.