About the difference between quenching and tempering and normalizing and tempering

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Quenching and tempering is a comprehensive heat treatment process of quenching and high-temperature tempering. I looked at some grades and found that A182.F22.CL2 materials must be quenched and tempered. Then I checked the ASTM A182 standard, which stipulates the heat treatment method for related materials of the A182 grade. There is this paragraph in it.: When agreed to by the purchaser, liquid quenching followed by tempering shall be permitted provided the temperatures in Table 1 for each grade are utilized. It should be said that under normal circumstances, it is normalizing + tempering. With the buyer's consent, quenching and tempering can be carried out. I would like to ask under what circumstances the material needs to be quenched and tempered. I also know that the function of quenching and tempering is to make the material obtain better comprehensive mechanical properties of strength, plasticity and toughness. Is this to prevent stress cracking corrosion?