Slaves to the Metal Horde by Stephen Marlowe

Johnny Hope knew the robot armies had been created to serve Man. But war and a plague had destroyed civilization, leaving humans as --

Johnny Hope backed off warily, retreating toward the sun-dried creek bed, a jagged brown scar across the parched grassland. He carried no weapon and as the others closed in about him in a tightening semi-circle his eyes darted furtively in all directions. But all the faces were stamped, as from a mold, with uncompromising hostility.