Extreme value detection method for enlarging detection volume

The invention relates to the technical field of steel detection, in particular to an extreme value detection method for enlarging detection volume, which comprises the following steps: putting a plurality of steel products into an ultrasonic flaw detector for detection; detecting by using a first ultrasonic water immersion flaw detector; cutting the steel product without inclusions, taking sheets, and detecting by using a second ultrasonic water immersion flaw detector; detecting the steel product without inclusions by using an optical microscope; performing fitting on the maximum size of the inclusion by utilizing Gumbel function fitting to obtain a predicted maximum inclusion size; and calculating the number of the maximum inclusion length-width ratio meeting a threshold value, and performing comprehensive judgment according to the predicted maximum inclusion size and the number of the maximum inclusion length-width ratio to obtain a process evaluation result of the finished steel product. According to the