Abrasion-resistant (AR) plate is rated by Brinell hardness - AR400, AR450, AR500. The instinct is to spec the hardest plate available. The trade-off is toughness, weldability and forming ease.
AR400 (~360–440 BHN): the workhorse. Good toughness, weldable with standard procedures, formable in heavier sections. The right choice for ~80% of conveyor, dump body and hopper liner applications.
AR500 (~470–540 BHN): for severe abrasion against hard particles. Sacrifices toughness, requires preheat for welding, and is harder to form. Specify when service genuinely demands the harder face.