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Ultrasound can induce water solution quickly cracking hydroxyl and hydrogen atoms, and can cause chain reactions. But in the water system hydroxyl radicals’life is only about 10-9S. How to accurately detect ultrasound hydroxyl radicals is very important. Ultrasound is used in depolarization, enhancing the electric analysis current, and electrode pretreatment in metal corrosion aspects. But reports using in ultrasound applies, metal corrosion, corrosion inhibitor and effects to corrosion rate are rare. So, researching its reaction system of ultrasonic mechanism and its effects is the starting point.The influences of ultrasound time, temperature, ultrasound frequency and vibrating ultrasound on testing hydroxyl free radicals have been investigated. Moreover, the corrosion behaviors of Q235 and N80 steel under the condition of ultrasonic cavitation have been studied by means of weight lose, polarization curve and scanning electron microscopy （SEM）.First, the results indicate that at 25℃the amount of hydroxyl free radicals increases under the condition of ultrasound, but when the ultrasound time reaches 1 hour, the amount reaches the maximum 0.1875mM; with the rise of temperature, the amount of hydroxyl free radicals increases especially between 20 to 30℃, and up to 50℃, the amount is stability. Moreover, with the increase of ultrasound frequency, the amount of hydroxyl free radicals also rises, and vibratory ultrasound takes a good performance on formation of hydroxyl free radicals.Next, ultrasound reduces corrosion of Q235 steel. At low temperature, ultrasound modifies hexamethylenamine’s corrosion inhibition, with the increase of temperature, ultrasonic cavitation has less effect. SEM and polarization curves support the same result. For N80 steel, ultrasound increases corrosion, but takes advantages on hexamethylenamine’s corrosion inhibition; by means of SEM and polarization curves the results indicate that corrosion pits become worse, and ultrasound promotes corrosion of N80 steel.
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