Evolution of Morphology, Size and Distribution of MnS Inclusions in Hot Forging Steel by Heat Treatment

摘要

The morphology, size and distribution evolutions of MnS inclusions in hot forging steel during heat treatment were investigated by in-situ observation under confocal scanning laser microscope (CSLM for short) and iso-thermal treatment in electric resistance furnace, respectively. The variation of single large-sized slender MnS at the elevated temperatures was in-situ observed by CSLM. This slender MnS was found to first change into a string of pearls in small size and then dissolved, difffused and coarsened during the rise of temperatures. Iso-thermal treatment shows that ovulation of large-sized MnS inclusions was remarkable with the sample held at 1573K for a half hour. And the Ostwald ripening occurs when the soaking time elongated to three hours. The present study proved that heat treatment is an effective way to modify morphology, size and distribution of MnS inclusions, especially for large-sized slender ones, which are the main cause of poor transverse toughness and stress corrosion cracking of medium plates.