As you know, when producing balls, two methods of casting and forging are used. In the casting method, there are no problems such as porosity, shrinkage due to freezing, and its strength and toughness are high. However, there is no weight limit in the casting method and it is possible to produce different alloys. According to the images published by you, there are reasons such as the temperature of the forging, the distance between the forging rollers and the resulting pressure. Also, creating grooves in the surface of forged rollers can damage the surface of the balls.