The engineer first carried out the chemical analysis of the roll body, W (Mg)>0.056%. It is reasonable to say that the spheroidizing of the Mg content roll should be good, but the spheroidization and non-spheroidization phenomenon occur. At that time, the export task was tight, and at the same time, the cause of the spheroidalization was not found, and the problem was serious. Metallographic examination of the tensile test bars showed that the spheroidization of graphite was directly related to the nickel content (when nickel was used at the time), when W (Ni) was 1.2% to 1.6%, the graphite had blossomed. The tensile strength is 310-316N/mm; when W (Ni) is 2.0%-2.3%, the graphite has a sheet tensile strength of only 257N/mm (national standard >300N/mm2). When the chrome-molybdenum ductile iron 690mmX1800mm rough-rolling roll of the same day was not examined, the graphite was spheroidized and the tensile strength was >360 N/mm.
According to the analysis, it is considered that the reason for the spheroidization of the batch of rolls is caused by the addition of waste nickel, that is, the waste nickel contains anti-spheroidizing elements, resulting in poor spheroidization and a decrease in tensile strength. In order to verify whether this judgment is correct or not, the use of pure nickel results in a good spheroidization of the rolls. After the Ni-containing ductile iron rolls were changed to pure nickel, no such spheroidized rolls were found to be scrapped.
