Analysis of a Progressive Failure of a Work Roll in Hot Strip Mill

In hot rolling mills, premature failure of rolls is a major concern as it adversely affects the mill operation as well as production. Analysis of failed roll materials and actual rolling conditions in service are therefore necessary to understand the roll failure mechanism and thereby improve the service life of rolls. The hot strip mill referred here consists of two stands in a roughing mill and seven stands in a finishing mill. Indefinite chilled double poured cast iron rolls are used in the finishing mill for rolling of the sheet in the last two stands. HSM produces coils in the thickness range of 2–25 mm. This present case describes one of the finishing stand work roll failures and analysis which was carried out using destructive as well as nondestructive testing techniques. The spalled roll showed fatigue arrest marks in a smooth continuous path along the circumferential direction. Characteristic features of the fracture surface were similar to those of surface-initiated spalling which is known as ribbon fatigue spalling. The fracture or spalled region was analyzed with Ultrasonic test to identify the origin of the crack. Past data and roll schedule were also studied for root cause.